ISSN 1224-6808

Transcription

ISSN 1224-6808

ISSN 1224-6808
CONTENTS
Stefania TESCARI, Georg UMGIESSER, Christian FERRARIN, Adrian STĂNICĂ, Current circulation and
sediment transport in the coastal zone in front of the Danube Delta...............................................................................................5
Mariline DIARA, Jean Paul BARUSSEAU, Late Holocene evolution of the Salum-Gambia Double Delta (Senegal)......17
Laura JUGARU, Mireille PROVANSAL, Nicolae PANIN, Philippe DUSSOUILLEZ, Apports des Systemes
d’Information Géographiques à la perception des changements morphodynamiques (1970-2000) dans le Delta
du Danube. Le cas du bras de Saint-George............................................................................................................................................29
Adrian TEACĂ, Tatiana BEGUN, Marian-Traian GOMOIU, Recent data on benthic populations from hard
bottom mussel community in the Romanian Black Sea coastal zone.............................................................................................43
Adrian TEACĂ, Tatiana BEGUN, Marian -Traian GOMOIU, Gabriela-Mihaela PARASCHIV, The present state
of the epibiontic populations to the biocenosis of stone mussels in the shallow water off the Romanian Black
Sea coast...........................................................................................................................................................................................................53
Tatiana BEGUN, Adrian TEACĂ, Marian -Traian GOMOIU, Gabriela-Mihaela PARASCHIV, Present state of the
sandy invertebrate populations in the Mamaia and Mangalia sector of the Romanian Black Sea coast............................67
Mihaela Carmen MELINTE, Cretaceous-Cenozoic paleobiogeography of the Southern Romanian Black Sea
onshore and offshore areas.........................................................................................................................................................................79
Radu OLTEANU, Dan C. JIPA, Dacian basin environmental evolution during Upper Neogene within the
Paratethys domain.........................................................................................................................................................................................91
Vlad RĂDULESCU, Florian RĂDULESCU, Ioan STAN, Geoelectrical measurements applied to the assessment
of groundwater quality.............................................................................................................................................................................. 107
Florian PĂUN, Mirel Ciprian PĂUN, MS Excel built-in program for flow and channel profile determination................. 111
Book Review.................................................................................................................................................................................................. 117
CURRENT CIRCULATION AND SEDIMENT TRANSPORT
IN THE COASTAL ZONE IN FRONT OF THE
DANUBE DELTA
Stefania TESCARI(1), Georg UMGIESSER(2), Christian FERRARIN(2), Adrian STĂNICĂ(3)
(1) University of Padova, Department of Physics, Italy
(2) ISMAR-CNR, Institute of Marine Science, Venice, Italy
(3) GEOECOMAR, Institute of Marine Geology and Geo-Ecology, Bucharest, Romania
Corresponding author: [email protected]
Abstract. The objective of this study is to simulate, through an interaction of two mathematical models, the current circulation and sediment transport in
the Northern part of the Romanian coastal area. The area of study has a length of about 34 km, North – South oriented, between the Sulina and Sf. Gheorghe branches of the Danube River, extending for about 30 km offshore. First a 3-dimensional hydrodynamic model of 5500 triangular elements is used to
simulate the current circulation pattern at different depths in the proximity of the coastal area. Closer to the coast, the resolution of the element is about
200 m. Parameters used as data input were the bathymetry map of the studied zone interpolated with the grid, the wind stress calculated from real values
using the formula of Smith and Banke and the liquid discharge of the Danube River. The sediment transport model, that aims to simulate the sediment
dynamics, is coupled with the hydrodynamic one and forced by solid discharge and sea bed sediment characteristics. Three ideal situations considering
the most frequent wind regimes have been carried out to better understand the general pattern of the circulation. The anti-cyclonal current described in
literature could be simulated and analysed with particular meteorological conditions. Subsequently, real data measured in 2002 have been used to force a
one year simulation. The results show the presence of seasonal differences in the erosion and deposition dynamics mainly due to different wind regimes.
Key words: Danube Delta coast, modelling, sediment transport, coastal dynamics
INTRODUCTION
ear shape mainly due to the cut-off of many of its meanders
The Danube is the second longest river in Europe, with
a length of 2857 km. Its source is in the mountains of the
Black Forest in Germany. Its drainage basin covers an area of
817000 km2 (Panin and Jipa, 2002).
made during the last century, that shortened it by 15% .
The Southern branch is Sf. Gheorghe, with the 28% of the
total discharge. 5 km before the mouth of the river it splits
into two smaller branches that make up the Sf. Gheorghe
It finally flows into the North-Western area of the Black
Sea through three principal mouths: Chilia, Sulina and Sf.
Gheorghe (Fig. 1).
Delta.
Chilia is the Northern branch of the Danube. It has a
length of 117 km mapping out the border between Romania
and Ukraine. It carries half of the total Danube discharge in
the Black Sea through 45 smaller branches, from which the
biggest arms are Oceacov and Stambulu Vechi.
from which 165 km are Romanian territory.
Sulina is the central branch and it accounts for 22% of
the total discharge (Panin, non published data). It has a lin-
The Danube Delta covers an area of 5800 km2 (90% in Romania, and 10% in Ukraine) with a coastal length of 240 km,
The attention is focused on the coastal area between the
two Southern branches: Sulina and Sf. Gheorghe. It is 34 km
long and mainly North-South oriented.
It is probably the most important natural reservoir in
South Eastern Europe.
GEO-ECO-MARINA 12/2006
Coastal Zones and Deltas
S. Tescari, G. Umgiesser, C. Ferrarin, A. Stănică - Current circulation and sediment transport in the coastal zone in front of the Danube Delta
The interest in this area is related to the coastal dynamics. During the last century the human influence modified it
relevantly, causing a strong erosional rate.
For example the construction of the two Iron Gates dams
along the river, in 1970 and 1985, caused a sharp decrease in
the sediment load carried by the Danube, that is, 35 to 50% of
its previous discharge (Panin, 1997). Another important effect
was caused by the construction of the Sulina jetties, which
began in the second half of the XIXth Century to reach now
a length of 8 km (Stanica, 2004). This work caused a strong
impact in the current circulation and therefore in the sediment dynamics, accounting for the increase of the erosional
phenomenon in the Danube Delta coastal zone.
The objective of this study is to simulate, through two
coupled mathematical models, the current circulation and
the sediment transport in the coastal zone between the
branches of Sulina and Sf. Gheorghe. The study is divided into
two parts: one of ideal simulations with constant wind and
discharge in order to better understand the effect of different
wind directions and meteorological conditions on erosion or
deposition; the second one simulates the annual water and
sediment dynamics, through four simulations in order to
investigate the seasonal differences, related to the seasonal
meteorological conditions.
This work should be considered as the beginning of a
collaborative project between Romania and Italy, aiming to
implement and better calibrate the model, and to increase
the quantity of the measured data used both as input and as
comparison with the simulated results.
MODELS
A 3-dimensional hydrodynamic model (SHYFEM) together with a sediment transport model (SEDTRANS05) were used
in this study. SHYFEM uses the hydrodynamic equations to
simulate the values of the barotropic transport and of the
water level at each point of the grid. The sediment transport
module gives the erosional or depositional rate in each element of the grid and the sediment concentration flowing in
and out from the water column.
Shyfem
SHYFEM (Shallow Water Hydrodynamic Finite Element
Model) is a 3-dimensional hydrodynamic model developed
at CNR-ISMAR of Venice (Umgiesser et al., 2004a,b; Umgiesser
2004; Ferrarin and Umgiesser, 2005; Scroccaro et al. , 2003, 2004)
which solves the hydrodynamic Shallow Water equations.
For the spatial discretization, it uses the finite element
method for the horizontal plane, and for the vertical one, a
Fig. 1 Danube Delta map, division into the three main branches (figure from Google Earth modified by Elias Tahchi)
system of layers that divide the water column. The finite element method offers the advantage of a bigger flexibility allowing for change in the shape and the size of the elements
in different places of the grid. This advantage makes the
model very suitable for areas with a complex geometry and
bathymetry.

∂Vi
∂Vi
Adv iy =  −Ui
− Vi
∂x
∂y

The stress terms in every layer are described as:
 ∂u 
τix = νρ0 

 ∂z i
For the temporal discretization it uses an algorithm with
a semi-implicit time resolution, which has the advantage of
both explicit and implicit methods.
The equations used by the model are the hydrodynamic
equations in the Shallow Water approximation, derived from
the momentum and mass conservation equations, simplified
with the incompressibility condition and the hydrostatic approximation.
Relations between water level ζ , and velocity u and v (in
the x and y directions, respectively) are presented as:
 ∂ 2u ∂ 2u 
du
1 ∂p 1 ∂τ x
− fv = −
+
+ AH  2 + 2 
 ∂x
dt
ρ0 ∂x ρ0 ∂z
∂y 

Dividing the water column into L layers i (with i=1,...,L),
where 1 is the superficial layer and L the bottom one, which
have constant thickness except for the superficial one (with a
variation due to the water level ζ), the transport U and V are
defined as:
Vi =
udz
∫
hi
The bottom stress terms are calculated as:
τbottom
= cB ρ0UL UL2 + VL2 / hL2
x
τbottom
= cB ρ0VL UL2 + VL2 / hL2
y
where cB is the bottom drag coefficient, UL and VL the two
components of the bottom velocity.
where C is the Chezy coefficient which varies with the depth
as:
where τ is the stress, g the gravity acceleration, H=h+ζ the water column total depth, h the undisturbed depth and ζ the
water level, t the time, f the Coriolis parameter, ρ0 the reference water density, p the pressure and AH horizontal eddy
viscosity.
hi
where ν is the kinematic viscosity.
cB = g / C 2
∂ς ∂Hu ∂Hv
+
+
=0
∂t
∂x
∂y
∫
 ∂v 
τiy = νρ0 

 ∂z i
The drag coefficient of the water is calculated with the
Chezy equation:
 ∂ 2v ∂ 2v 
dv
1 ∂p 1 ∂τy
+ fu = −
+
+ AH  2 + 2 
 ∂x
dt
ρ0 ∂y ρ0 ∂z
∂y 

Ui =
vdz
where the integrals are calculated for each layer, between the
lower and upper interface, and hi is the thickness of the layer i.
C = ks H
∂ U ∂ U
∂Ui
1 ∂pi 1 i −1 i
− fVi = Adv ix − hi
+
τ x − τ x + AH  2i + 2i
 ∂x
∂t
ρ0 ∂x ρ0
∂y




 ∂ 2V ∂ 2V
∂Vi
1 ∂pi 1 i −1 i
− fUi = Adv iy − hi
+
τy − τy + AH  2i + 2i
 ∂x
∂t
ρ0 ∂y ρ0
∂y




(
(
)
)
where the advective terms are:

∂Ui
∂Ui 
Adv ix =  −Ui
− Vi
 / hi
∂x
∂y 

2
1
6
where ks is the Strickler coefficient.
The drag coefficients relative to the water surface are calculated with the following formula:
τsurf
= ρaCDuw (uw2 + v w2 )
x
τsurf
= ρaCDv w (uw2 + v w2 )
y
where ρa is the air density, CD the drag coefficient, uw and vw
the wind velocity in the x and y directions, respectively.
The drag coefficients for the shear stress induced by the
wind are parameterized by Smith and Banke (1975) as:
(
)
(
)
CDx = 0.066 uw + 0.63 ⋅ 10−3
Integrating vertically, the first equations become:
2

 / hi

CDy = 0.066 v w + 0.63 ⋅ 10−3
Sedtrans05
SEDTRANS05 is a numeric zero-dimensional model for
the study of the bottom boundary layer dynamics and the
sediment transport in continental shelf and in coastal environments.
This is the last version of the Sedtrans model, originally
developed at the logical Survey of Canada-Atlantic (GSCA) in
the ‘1980s. It is used to simulate the transport rate of sedi-
ments under the effect of current or combined current and
waves.
The sediment dynamics is studied with a transport and
diffusive module. The bottom sediments are studied with a
direct advective scheme.
The sediment is composed of different grain size classes
considered independently. Erosion and deposition processes
mainly occur in the bottom boundary layer, which is formed
between the water column and the sea bed. To calculate the
bottom shear stress and the velocity profile, the program
uses the bottom boundary layer theory (Grant and Madsen,
1986).
In order to calculate the bedload transport of noncohesive sediments, it applies the algorithms of Yalin
(1963) and Van Rijn (1993), whereas for the total transport
(bedload+suspended) it uses the methods of Engelund and
Hansen (1967) and Bagnold (1963).
The bottom level and sediment distribution due to erosion and deposition are updated at each time step.
The bottom is schematized through different layers, out
of which only the superficial one is active.
Friction factor and bed shear stress
In order to predict the bottom shear stress and the velocity profile in the bottom boundary layer, the continental
shelf bottom boundary layer theory formulated by Grant and
Madsen (1986) is used.
To calculate the total bed roughness z0, both grain roughness, bed form (ripple) and bedload roughness due to the
sediment transport are considered.
Bedload transport
To predict the bedload transport of non-cohesive sediments there are five algorithms which can be used. The Van
Rijn (1993) formula is applied in this study.
If the bottom stress is not high enough, the sediments
stay in their inertial position.
The critical shear stress for motion initiation is:
where ρs is the sediment density, D the average sieve diameter and θcr the dimensionless critical Shields parameter calculated with the Yalin method (Li et al., 2001).
In the Van Rijn (1993) method, as in the previous Bagnold
approach, the bedload transport consists of jumps of the particles under the effect of hydrodynamic and gravity force.
The instantaneous bedload is defined as the product between the saltation height and the bed concentration, and is
calculated as:
q = ηi α(s − 1)
g
0 .5
1 .5
D
D*−0.3 τ2m.1
τm =
τcs − τcr
τcr
with τcs the instantaneous skin friction current shear stress,
and τcr the critical shear stress for the sediment motion initiation.
D* is the dimensionless grain size calculated as:
 g (s − 1) 
D* = 

2
 ν

1
3
D
SUSPENDED SEDIMENT TRANSPORT
When the sediment velocity in the bottom layer is comparable with the settling velocity a part of the sediments can
be resuspended.
Once the sediments are in the water column, these can
be transported and diffused by the current, as long as the
force upwards is higher than the gravity force.
The critical shear stress for initiation of the suspended
transport is calculated with the Van Rijn (1993) method:
1 < D* < 10 →
D* > 10 →
*
ucrs
4
=
ws
D*
*
ucrs
= 0 .4
ws
where u*crs is the shear velocity, ws the settling velocity calculated with the Soulsby’s formula (1997):
ws =
(
ν
10.362 + 1.049D*3
D 
)
0 .5

− 10.36 

The critical shear stress is calculated using the following
formula:
*
τcrs = ρ(ucrs
)2
Advection and diffusion equations
τcr = θcr (ρs − ρ)gD
0 .5
where s is the ratio between the sediment and water density, ηi is the availability relative to the fraction i of bottom
sediment, α is a constant equal to 0.053, and τm the shear
stress parameter calculated as:
When the bottom shear stress is higher than the suspended critical shear stress, the particles enter in the water
column and move under the current effect.
The concentration C of the suspended sediment is described by the 3-dimensional equation of advection and diffusion:
 ∂ 2C ∂ 2C 
∂C ∂uC ∂vC ∂wC
∂C
∂ 2C
+
+
+
− ws
= νH  2 + 2  + νV 2 + E
 ∂x
∂t
∂x
∂y
∂z
∂z
∂y 
∂z

where νH and νV are the horizontal and vertical turbulent diffusion coefficient, respectively, while ws is the settling velocity and E is the external source term.
Using this equation, the mass of sediment which can be
advected with the current, settled due to gravity and diffused
by turbulence, is conserved.
Its vertical boundary conditions are:
∂C 

 −νV
 + w sCtop = 0
∂z z =0

Morphodynamics
Modifications in the bed elevation are obtained as the
sum over the different sediment fraction of the net exchange
due to suspended and bedload transport.
The net sediment exchange due to bedload is calculated
using the sediment continuity equation:
∂C 

+ w sCbot = ED
 + νV

∂z z = bottom

b
∂h
1  ∂q xb ∂qy

=
+
∂t 1 + ε  ∂x
∂y
where the first equation refers to the top of the surface layer,
and the second to the bottom layer. ED is the net sediment
flux between the bottom and the water column, thus equal
to the difference between resuspension and deposition of
each grain size material.
The term ED ( >0 if there is erosion) is calculated explicitly in case of erosion, implicitly in case of deposition, thus
avoiding the possibility to obtain a negative concentration if
the deposition rate is bigger than the quantity of sediments
existing in the water column.
Sediment exchange with the bed
The net flux between the accumulated and resuspended
sediments (ED) is calculated as the difference between the
equilibrium concentration and the concentration present in
the lower layer of the water column:
ED = w s (Ceq − C )
where Ceq is the average sediment concentration of equilibrium in the lower layer, calculated from the equilibrium concentration Ceq close to the bed and assuming a logarithmic
velocity and concentration profile of the suspended sediment. C is the suspended sediment concentration present in
the lower level for the considered sediment class.
This equation shows that when the sediment concentration close to the bed is smaller than the equilibrium value,
the net flux of particles is from the bed to the water column
(ED>0, erosion). On the contrary, if the concentration exceeds
the equilibrium value the flux is in the opposite direction
(ED<0, deposition).
The sediment concentration at the reference height (bed
roughness z0) is calculated following the Smith and McLean
(1977) formula adapted for a different material.
Ceq =
ηi γ 0Cb τ*
(1 + τ* )
with Cb the volume concentration of the sediment bed and
τ* =
( τcws + τcr )
τcr
is the normalized excess of shear stress, τcws the skin-friction
combined with the shear stress, τcr is the critical shear stress
for the initiation of the motion and γ0 the empirical sediment
resuspension coefficient (Li and Amos, 2001).




where h is the variation of the bed elevation, ε the sediment
porosity and q xb and qyb are the volumetric transport rate in
the x and y directions.
The change in the bed elevation due to resuspension and
redistribution of the suspended sediment is calculated as:
ρs (1− ε )
∂h
= −ED
∂t
with ρs the sediment density.
INPUT DATA
Grid
To apply the mathematical model it is necessary to create
a numerical grid first.
The first step is the digitalization of a map; in this study
the bathymetric map from 2002 is used.
The basin extends about 34 km to the North-South direction between Sulina and Sf. Gheorghe arms of the Danube. In
the East-West direction, it covers an area between the shoreline and an offshore distance of approximately 30 km, reaching a depth of 40 m in the Southern zone.
The basin is then divided into 5493 triangular elements
that vary in shape and dimension in order to have different
resolutions in different zones. In this case, for example, in
the area near the shoreline, the resolution is of about 200 m,
while at the other basin border, in deep water, it is of about 2
km. There are 3022 vortexes of elements (nodes).
Once the grid is regular enough, the bathymetry is inserted.
Elements on the final grid are differentiated by the grain
size of the bottom sediment. That is made by dividing the
basin into three different zones: one constituted only of fine
sand (200 µm), one made of 65% silt (20 µm) and of 35% clay
(4µm), and the last one constituted of these three grain size
classes in equal proportions.
The water column is divided into 15 layers. In the first 10
m, each layer is 1 m thick. At higher depths the thickness increases, reaching 13 m in the deepest layer.
Table 2 Average frequency values of the wind in 2002 in the main
directions (%)
Discharge
The discharge data used in this study are measured by
the National Institute of Hydrology and Meteorology of Bucharest and have monthly frequency (one data each month).
The average liquid discharge from the Sulina mouth (22%
of the total water mass carried by the Danube) has a value of
1390 m3/s, which corresponds to 6318 m3/s by the whole river (199 km3/year). The only branch of the Chilia Distributary
considered in this study is the Southern one called Stambulu
Vechi, accounting for 60% of Chilia`s discharge (30% of the
entire river discharge). This is the only one able to influence
the studied zone, since the Sulina jetties stop all the sediments transported from the North close to the shoreline.
Solid discharge
N
19.0
The solid discharge distribution for the three branches is
similar to the liquid one (22% through Sulina, 28% through Sf.
Gheorghe and 50% through Chilia).
The solid discharge is divided into three grain size classes:
fine sand (200 µm), silt (20 µm) and clay (4 µm).
Most of the sediments transported by the Danube are
silty. Sand and clay have more or less the same percentage
(6%-8%). The data are shown in Table 1.
Table 1 Percent composition of the sediments discharged by the
three Danube branches divided by the grain size (Ungureanu et
al., 2005; Olariu et al., 2005), and total average solid discharge
(kg/s) from the values measured in 2002
Branch
Sulina
Sf. Gheorghe
Stambulu Vechi
Fine sand
8%
8%
6%
Silt
86%
86%
86%
Clay
6%
6%
8%
Discharge
340 (kg/s)
433 (kg/s)
464 (kg/s)
Wind
The wind data used in this study are measured in the meteorological station at Sulina by the Regional Meteorological Centre of Drobogea (Ministerul Mediului si Gospodaririi
Apelor, Administratia Nationala de Meteorologie), and has a
frequency of four values per day (one every 6 hours).
The wind data are inserted into the model as stress values, calculated using the Smith and Banke formula.
Analyzing the wind data measured in 2002, the three
predominant wind directions of wind are North, South and
North-East (percentages are shown in Table 2).
10
E
10.3
SE
7.1
S
14.4
SW
12.9
W
7.4
NW
12.3
Still
0.9
A different analysis is made on the wind velocity. For 0.9%
of the year 2002, the wind was considered still. The highest
percentage (49.7%) was measured for wind velocities between 1 and 5 m/s, the second most frequent wind velocities
(33.9%) are between 5 and 10 m/s; velocities between 10 and
15 m/s were present 9.3% of the year, and higher than 15 m/s
in 6.2% of the time. The wind velocities are strongly related
to the wind directions. The average velocities in the different
directions are shown in Table 3.
The quantity of sediments that flow into the Black Sea carried by the Danube during 2002 had an average value of 1689
kg/s, which corresponds to an annual total of about 63 million
tons. Out of these, 340 kg/s were carried by the Sulina branch.
As input into the model, the solid discharge is expressed
as average concentration. The average concentration in 2002
was about 331 g/m3.
NE
15.7
Table 3 Average wind velocities (m/s) in 2002 in the main
directions
N
7.3
NE
8.4
E
6.7
SE
4.9
S
6.6
SW
5.8
W
4.5
NW
5.5
RESULTS
General setup of simulations
The study is divided into two parts: the first consists of
ideal simulations using as input data average values of discharge and of wind speed, separately studying the different
wind directions. The second simulates the sediment dynamics
and the annual circulation, using as inputs the data measured
in 2002, with particular attention to the seasonal differences.
In both groups of simulations the vertical viscosity coefficient is set at the reference value of 10-3m2/s. The time step
is 300 secs throughout the entire simulation. The data output
is daily.
The first group of simulations lasts for one month. The current circulation becomes stationary after 2 days of simulation,
while the erosional and depositional phenomena increase
with time. The attention is focused on the moment when an
erosional or depositional rate higher than 0.5 cm begins to
occur and on the situations simulated after one month.
In the second part of the study the circulation varies
strongly, with, mainly, the wind speed and direction. The interest is thus focused on current characteristics in moments
when there were considerable changes in the bottom elevation. An extra analysis is based on the final maps of erosion
and deposition resulting from the singular seasonal simulations, in order to compare them with the seasonal meteorological characteristics.
The data inputs for the model simulations are the Danube discharge and the wind stress. Constant average values
are used in the first part, while variable data are used in the
second part.
Idealized simulations
This part of the study can be divided into two further
parts.
The first studies the current circulation, using only the 3dimensional hydrodynamic model. The output is represented
by circulation maps at different depth levels.
The second part regards mainly the sediment transport.
In this case both models are used (the hydrodynamic model
is used, nevertheless, in 2-dimensional mode). The barotropic
circulation simulated by the 2-dimensional hydrodynamic
model is similar to the one obtained by the average circulation at all levels.
The ideal simulations have a constant value of solid and
liquid discharges, equal to the average values measured for
2002. These values are shown in Table 4.
Table 4 Liquid discharge (m3/s) and concentrations (g/m3) in the
different branches of the Danube river
Branch
Stambulu Vechi
Sulina
Sf. Gheorghe
Liquid
discharge
1890
1386
1764
Concentration
Sand
13.17
17.57
17.57
Silt
188.85
188.85
188.85
Clay
17.75
13.17
13.17
The model allows us to calculate the average current in
all the layers. This barotropic current (Fig. 2) seems similar to
the one simulated by the 2-dimensional model. It presents
an anti-cyclonal current which occupies the Northern area
(about 6.6 km) of the coast and a parallel current along the
coast in the Southern zone.
The sediment dynamics is simulated under this wind condition.
Most of the sediments discharged through the Sulina
mouth settle close to the jetties, at few kilometres from the
coast, due to an evident reduction of the current velocity. The
remaining is divided into two parts: one carried by the anticyclonal current, is moved towards the Northern coast, while
the second one, carried by the current parallel to the coast,
flows towards the Sf. Gheorghe mouth.
For the assessment of the deposition pattern the simulation has to run for at least 8 days, and after a month it reaches
a value of the order of 1 cm. In the immediate proximity of the
coast (except for the Northern area) the current speed is too
high to allow deposition.
With a wind speed of 13 m/s, the sediments released
from the Sulina mouth can be carried closer to the coast, and
the deposition is relevant after 3 days of simulation. After a
month, the deposition reaches the value of about 3 cm.
The wind stress is constant for each time step, equal to
the average value of the 2002 measured data in the first simulation. Other ideal simulations are made with constant values
of wind, increasing gradually to 15 m/s. The simulations are
made in the three main wind directions: North, South and
North-East.
North
The simulation is done with a constant Northern wind
with a speed of 7.3 m/s.
Once arriving at a stationary state in the first (superficial)
layer, the current flows Southwards, parallel to the shoreline
along the entire coast. Close to the Sulina jetties, a divergence point from which the water flows in various directions
is obvious.
At a depth of one meter the current begins to change
its shape, revealing the presence of an anticyclonal current,
forming an eddy whose diameter is directly proportional to
the water depth. This eddy has a diameter of several kilometres, starting near the end of the jetties and extending towards the coast.
In the Southern area there are no differences in the current direction at different depths.
As expected, the current velocity decreases inversely proportional with the water depth, due to the bottom friction
increasing influence.
Fig. 2 Barotropic current circulation in the ideal case of constant
wind from North with a speed of 7.3 m/s
11
Deposition was the only phenomenon resulting from this
simulation. In order to understand the critical wind speed
value that generates erosion, other simulations with higher
wind speed values are made. Erosion starts, only in the Southern zone, when the wind speed approaches 13 m/s, and in
this case it is higher than 0.5 cm after only one day of simulation. After one month of simulation it reaches an average
value of 2 cm, with peaks of 10 cm.
South
The simulation is done with a constant wind from the
South with a speed of 6.6 m/s.
The current in the Southern zone flows Northwards, parallel to the coast, for all the considered water depth levels. Its
speed decreases with increased depth. When arriving close
to the Sulina jetties, the water turns Eastwards, toward the
open sea.
At the surface and in the first layer a small cyclonal eddy
is formed, due to the wind effect and to the coastal morphology. This eddy disappears in the deeper levels.
It is anyway present in the average barotropic circulation,
even if it does not significantly influence the coastal dynamics.
The Northward oriented current carries all the sediments
discharged from the Sulina mouth out of the study zone
Northwards. Also, the sediments from Sf. Gheorghe mouth
are carried by a Northward current and deposited along the
coastal area, without reaching the Northern part, due to the
slow current speed.
The highest deposition is in front of the Sf. Gheorghe
mouth and it has a value of 3 cm.
The study of the erosional threshold is particularly interesting. Increasing the wind speed, the erosion begins at
13 m/s. After a month of simulation it has a slightly smaller
value than in the previous case (an average of about 2 cm
with peaks of 10 cm).
With this wind speed value, the current velocity in the vicinity of the coast is very high, being thus able to carry the
eroded sediments to the Northern zone, where the current
slows down to a value of about 15 cm/s. Here this allows the
sediment deposition that, after a month, increases the bottom elevation by 1 cm.
This phenomenon is more obvious when the wind has a
velocity of 15 m/s. In this case the sediments eroded from the
Southern zone are carried close to the jetties allowing an increase of the bottom elevation of about 4 cm.
It must be noted that this is the only case in which the settled sediments are mainly sandy, due to the bottom sediment
characteristics near the shoreline.
The erosional process is evident from the first day of simulation. For the deposition the model must run with an aver12
age wind speed for at least 6 days, and for 1 day only with a
higher value of wind speed.
North-East
The simulation is done with the North Eastern wind with
a speed of 8.4 m/s.
The same situation occurs as in the case of Northern wind:
an anticyclonal current appears from the 2mnd layer on in the
Sulina zone. The diameter of the eddy increases with depth,
but in this case it is smaller and further from the shoreline.
In the barotropic circulation, obtained by averaging the
levels, the eddy has small dimensions and is far from the
shoreline.
In fact, in the Northern area the current flows Westwards,
parallel to the jetties, and then parallel to the coast, Southwards
for the entire studied area. The current speed in the Northern
coast is higher than the one obtained with the Northern wind
simulation, due to the absence of the anticyclonal current and
to a higher value of the average wind speed.
In this case the sediments discharged by the Sulina mouth
are carried by the current parallel to the jetties.
The deposition zone is similar to the one obtained in the
case with Northern wind, but moved Northwards, adjacent to
the jetties for the first kilometres.
Compared to the simulation performed for Northern
winds, even the values are similar, with an increase of the
bottom elevation of about 1 cm after a month of simulation.
There are differences, though, as the deposition rate amounts
to 0.5 cm after 11 days.
The sediments not carried towards the Northern coast are
transported Southwards, to the Sf. Gheorghe mouth. Nevertheless these never touch the shoreline due to the high current speed.
Gradually increasing the wind speed, it is possible to notice the erosional phenomenon in the Southern part of the
coast when the wind speed approaches 15 m/s. In this case,
erosion becomes relevant after only one day of simulation
and reaches a value of about 2 cm after a month. Compared
to the previous simulations, it has the same average erosion
value but with much lower peak values.
The deposition rate in the Northern area is higher, directly
proportional with the wind speed. The deposition reaches a
value of 6 cm after one month.
SIMULATIONS OF 2002
In this part of the study the wind stress input is once for
every 6 hours, using the measured data of 2002. The average annual wind speed is of 6.5 m/s. The wind speed highest
value (29 m/s) is reached by the end of winter. The longest
storm period (about 4 days) was at the beginning of December, with an average wind velocity of 21.8 m/s.
The discharge input consists of the monthly values measured in 2002.
The highest value is reached in December, with a value of
1790 m3/s through the Sulina branch. The lowest discharge is
in January, with a value of 935 m3/s.
For the solid discharge also the highest value is in December (1290 kg/s) which strongly differs from all the others (except for December and November, the monthly discharges of
other months do not exceed 500 kg/s). The smallest value is
in January with a solid discharge of 20 kg/s.
General features
After the entire simulation, the meteorological conditions
during relevant changes in the sea bottom were analysed.
It was thus possible to identify the general features that
allow deposition or erosion of the bottom sediment.
The deposition in the Northern area was present in different situations: average value of wind speed mainly from
North and North-East for a period of at least 2 or 3 days; high
values of wind from South; sharp decrease in the wind speed,
and therefore in the current velocity, after a period of storm,
or equivalently a fast change in the wind direction, which
causes a decrease in the current velocity.
The erosional process is mainly due to winds from North
and North-East with speeds higher than 13 m/s. The longer
the period with winds stronger than 13 m/s, the higher is the
erosion rate.
Table 6 The main seasonal variation of wind characteristics
Season
Max Vel
Aver Vel
Winter
Spring
Summer
Autumn
29 m/s
18 m/s
17 m/s
26 m/s
6.6 m/s
5.5 m/s
5.9 m/s
8.0 m/s
Vel >
13m/s
10.3%
3.9%
6.9%
19.1%
Main dir
SW, S
N, NE
NE, N
N
The highest wind speed value in 2002 is 29 m/s, registered during winter. This value does not strongly influence
the coastal dynamics because it is isolated. The storm during
which that value was measured lasted for only one day.
During winter the average wind velocity, as the frequency
of wind speed higher than 13 m/s, is the second highest. Nevertheless, the erosional rate (about 9 cm decrease in bottom
elevation), found after the simulation of the entire season
(Fig. 3), is only the third in comparison with the other seasons. This is due to two factors: first, the high wind values are
generally isolated, so they are not able to strongly increase
the current velocity. Second, the most frequent wind direction is South-West, and from this direction the current speed
is slower than the one caused by a wind from either North or
South, and the erosional threshold is higher.
The deposition rate is the lowest found in all seasons, and
it is situated very far from the coast. This is mainly due to the
very low value of solid discharge present in this season, and
If a high wind event is isolated, i.e. the strong wind lasts
for only a few hours, the current does not have the time to
increase and erosion cannot develop. Otherwise, if strong
winds last longer, erosion can occur from the first day.
Seasonal differences
In order to investigate the seasonal differences in coastal
dynamics, it is useful to analyse the differences in the meteorological conditions for the various seasons. In Table 5 the
average seasonal solid and liquid discharge values through
the Sulina branch are shown. In Table 6, the wind is described
through some characteristic values such as the highest velocity, average velocity and main directions, measured in each
season. As pointed out in the ideal study, the erosion process
is greatly influenced by winds stronger than 13 m/s. For this
reason the percentage of wind higher than this value is computed for each season.
Table 5 The main seasonal variation of discharge characteristics
Season
Winter
Spring
Summer
Autumn
Liquid discharge
1190 m3/s
1470 m3/s
1280 m3/s
1603 m3/s
Solid discharge
700 kg/s
890 kg/s
450 kg/s
2070 kg/s
Fig. 3 Final map of bottom elevation after the winter simulation
13
to the small quantity of eroded sediments available for the
current to be carried towards the Northern area.
In spring, the modelling shows the best conditions for
a high deposition rate. In fact the wind speed, mainly coming from North and North-East, has small values and the frequency of winds faster than 13 m/s is lower than 4%. There
are many periods during which the wind continuously blows
from the same directions for more days so it is possible that
the sediments are carried to the Northern coast, by the anticyclonal current when the wind is from North, and by the current parallel to the jetties when the wind is from North-East,
as it is shown in the ideal simulations.
The simulation of this season is shown in Fig. 4. The deposition rate close to the coast is higher than in all the other
seasons, as it reaches the value of about 4 cm. Erosion in the
Southern area has a lower value than in all the other seasons,
equal to about 5 cm.
In summer, the wind has the 2nd lowest speed, and this
produces the 2nd biggest deposition rate (about 3 cm) close
to the Northern coast. This was mainly due to the fast decrease
in the wind speed after storms (in several cases decreases from
more than 15 m/s directly to less than 5 m/s). Many of the sediments suspended during the storm, settled quickly when the
current velocity decreased, and this happened mainly in the
Northern area due to the presence of the jetties that stopped
the water flow. Results are shown in Fig. 5.
Fig. 4 Final map of bottom elevation after the spring simulation
When the wind speed is higher, the main directions of
wind are from North-East and North. This causes a strong erosion along the Southern coast (about 12 cm after the entire
season).
The highest wind speed values in 2002 are in autumn, and
the percentage of time during which it was higher than 13 m/s
is close to 20%. This is why during autumn the results showed
the highest erosion rate. During the first part of the season, the
Southern coast was in erosion, whereas the Northern one was
in deposition, mainly due to the sediments deposited when
the current velocity decreased sharply after a storm.
At the beginning of December the most relevant event
of the entire year happened. A storm more than 4 days long
affected the zone. The average value of wind speed was 21
m/s, in a range between 18 and 26 m/s, mainly coming from
North and North-East.
This caused a current speed higher than 70 cm/s in the
Southern coast and of about 30 cm/s in the Northern area
protected by the jetties.
In only 4 days the coastal dynamics relevantly changed,
as shown in Fig. 6. The deposition zone in the Northern coast
disappeared and switched to erosion (10 cm). In the Southern
area the higher erosion rate made the bottom decrease by
more than 30 cm only during this storm.
The highest deposition rate in December is of 5 cm, positioned far from the coast.
14
Fig. 5 Final map of bottom elevation after the summer simulation
DISCUSSION AND CONCLUSION
Ideal simulations comparison
Analysing the current circulation, the anticyclonal current, described in literature, was identified under the effect of
particular meteorological conditions.
With an average North Eastern wind, the eddy is far from
the coast and its diameter has only a few kilometres. With an
average Northern wind, the eddy is well defined and its diameter is a little smaller than the length of the jetties. The eddy
arrives to its highest dimensions during North Western winds,
when its diameter is as long as the jetties and the only current
present near the Northern coast is the anticyclonal one.
The bottom sediments characteristics show that the simulated deposition zone situated at several kilometres from
the jetties as well as from the coast is mainly composed of
silt. This is the main material discharged by the Sulina mouth,
being thus in agreement with the simulated data.
It was possible, through the ideal simulations, to identify
three different ways of deposition in the Northern area, depending on the wind direction.
With a Northern wind, the sediments discharged by the
Sulina mouth are carried by the anticyclonal current. The high
current speed at the river mouth allows the transport of the
sediments towards a circular area, few kilometres off the jetties and from the coast, where the current speed decreases
and the sediments settle. This deposition area increases in
width until it reaches the coast.
With a North-Eastern wind, the sediments are carried by
a current parallel to the jetties. The deposition zone has a
shape similar to the previous one but moved Northward, in
contact with the jetties in the first kilometres.
The third way of deposition is during Southern winds
stronger than 13 m/s. In this case the deposited sediments
are those eroded along the Southern coast and carried by
the current toward the Northern area to the jetties, where the
current quickly decreases. These sediments are mainly sandy,
different from the other case, when they are mainly silty.
The threshold wind speed necessary to generate erosion was also identified. When the wind blows from North or
South, the wind speed has to be higher than 13 m/s, while
when the wind blows from North-East the speed must exceed 15 m/s.
Annual simulations comparison
The wind is the main factor that influences the coastal
dynamics. Except for autumn (8.0 m/s), the average values of
wind speed in the other seasons are quite close (winter 6.6
m/s, summer 5.9 m/s and spring 5.5 m/s). It is important to
analyse the different wind directions and the period during
which the wind is higher than 13 m/s.
Fig. 6 Maps of the bottom elevation before (top) and after
(bottom) the storm of the beginning of December 2002
During winter, the second highest value of average wind
speed was recorded, but the direction, mainly from SouthWest, causes only the third highest value of erosion.
15
During the same season, the very low discharge also
caused the lowest deposition rate.
During spring, the average wind is from North and NorthEast. That causes the highest deposition rate close to the
coast in the Northern area, mainly due to the transport of the
sediments discharged by Sulina through the anticyclonal current and the current parallel to the jetties.
The highest erosion rate is in autumn, strongly increased by
the tempest in the beginning of December, as well as the highest rate of deposition far from the coast in the Northern area.
The year’s simulation presents a high rate of erosion all
along the coast. In the Southern part it is due to the sum of
the erosional rates computed for all the seasons, while in the
Northern coastal area it is due mainly to the storm from the
beginning of December 2002, which induced an erosional
rate higher than the sum of the deposition rates computed
for all the other three seasons.
From the measured data (presented in Fig. 7) the Northern area is the only one with a tendency of deposition in the
first 2 km. Moving southwards, after a stable zone (about 1.5
km), there is an area of about 2 km influenced by an erosional
rate between 3 and 4 m/yr (Stanica, in press).
The Southern area, up to 6 km from the Sf. Gheorghe
mouth, follows a tendency of erosion ranging between 5 and
7 m/yr of coastline retreat. The highest erosion rate was 23 m
in one year (between1997 and 1998).
The area near the Sf. Gheorghe mouth is generally stable.
The tendency shown in this study is qualitatively in agreement with the simulated results. Thus, the Northern part is
generally in deposition until the storm of December 2002.
The Southern coast is mainly under the effect of erosion.
Fig. 7 Coastal dynamics from measured data
A stable zone means that the shoreline changes from
deposition to erosion in different years. In 2002 the simulated
data show a total tendency of erosion.
It must be noticed that the results cannot be quantitatively compared with the measured ones, because the model
outputs differences in the bottom elevation, leaving the position of the shoreline unchanged. However, the measured
data gives the movements of the shoreline.
REFERENCES
Bagnold, R. A., 1963 - The sea. Vol. 3. Hill, M.N. Ed., Ch. Mechanics of marine sedimentation., pp. 265-305.
tie. Ph. D. thesis Faculty of Geology and Geophysics, University of
Bucharest.
Engelund, F., Hansen, E., 1967 - A monograph on sediment transport in
alluvial stream. Teknisk Vorlag, Copenhagen, Denmark.
Stanica, A., Panin, N., (in press) 2006 - Present evolution and future predictions for the black sea coastal zone between the Sulina and Sf.
Gheorghe Danube river mouths (Danube Delta). A theoretical view
of sustainable shoreline management issues. Geomorphology.
Ferrarin, C., Umgiesser, G., 2005 - Hydrodynamic modelling of a coastal
lagoon: the Cabras lagoon in Sardinia, Italy. Ecological modelling
188, 340-357.
Grant, W. D., Madsen, O. S., 1986 - The continental shelf bottom boundary layer. Annual review of fluid mechanics 18, 265-305.
Panin, N., 1997 - On the geomorphologic and the geologic evolution of
the river Danube – Black Sea interaction zone. GEO-ECO-MARINA
2, 31-40.
Umgiesser, G., 2004 - SHYFEM finite element model for coastal sea-user
manual- version 4.85. Pp. 42.
Umgiesser, G., Amos, L., Coraci, E., Cucco, A., Ferrarin, C., Canu, D. M., Scroccaro, I., Solidoro, C., Zampato, L., 2004a - An open source model for
the Venice lagoon and other shallow water bodies. Cambridge
University Press.
Panin, N., Jipa, D., 2002 - River Danube and Black Sea geosystem. Birth
and development. CIESM Workshop Series 175, 63-68.
Umgiesser, G., Canu, D. M., Cucco, A., Solidoro, C., 2004b - A finite element
model for the Venice lagoon. Development, set up, calibration and
validation. Journal of marine systems 51, 123-145.
Scroccaro, I., Matarrese, R., Umgiesser, G., 2004 - Application of a finite element model to the Taranto sea. Chemistry and ecology 20, supplement 1, 205-224.
Van Rijn, L. C., 1993 - Priciples of sediment transport in rivers, estuaries
and coastal sea. Aqua publications Amsterdam, Netherlands
Stanica, A., 2004 - Evolutia geodinamica a litoralului romanesc al Marii
Negre din sectorul Sulina- Sf. Gheorghe si posibilitati de predic-
16
Yalin, M. S., 1963 - An expression for bedload transportation. In: Journal
of hydraulics and division. Vol. ASCE 89 (HJ3). Pp. 221-250
Late Holocene Evolution of the Salum-Gambia
Double Delta (Senegal)
Mariline DIARA(1), Jean Paul BARUSSEAU(2)
(1) Department of Geology – Cheikh Anta Diop University – Dakar (Senegal) – e-mail : [email protected]
(2) LEGEM –Via Domitia University – Perpignan (France) – e-mail : [email protected]
Abstract. The post-glacial transgression up to the present sea level, which occurred about 5500 years B.P., deeply modified the coastal zone morphology,
especially in the river mouth region, where, in a few millennia, the geographical pattern changed from an open bay to a delta environment. The Salum
islands case illustrates this evolution. Sediments deposits and anthropic shell-middens, built in a time interval starting 6000 years B.P. up to now, based on
radiocarbon dating, provide a chronological framework of the delta evolution. At first, the open post-transgression bay was subject to filling-up. A major
second stage, occurring not later than 2550 years B.P., is characterized by the formation of beach barriers. The third stage is the completion of the filling-up
behind the beach barriers. The whole construction is under the distinct influences first, of the Sahelian and the Salum River sediment fluxes in the Northern
part of the delta and then, the Gambia River sediment input in the Southern part. Detailed analyses of the sediment testify to this double origin of the
various morphosedimentary exhibited units: tidal flats and beach barriers. Grain-size analysis, SEM examination and heavy mineral assemblages revealed
sand as the dominant component in the Northern part. It originated from atmospheric and fluvial conditions favouring the coarse component input. To the
South, a clay dominant influx, controlled by the Gambia River discharge, is responsible for back-barrier mud-flats, accumulated in relation to the reduction
or the absence of the tide-dominated fluvial processes in the Salum River. Hence, the Diomboss arm does not form one of the delta distributaries between
the Northern and the Southern part as previously considered but a residual space of the former mid-Holocene bay, separating the real Salum River delta to
the North and the pre-Gambian delta to the South. All morphological units described in the delta are established at a level located within the present tidal
range. There is no need to refer to sea level variations to explain the geomorphologic pattern. The sedimentological input and forcing seem to be the major
agents of sedimentary unit distribution.
Key words: delta – eustatic stability – beach barriers – tidal flats - Holocene – West Africa
Introduction
The delta areas are part of terrestrial environments that
– apart from volcanic phenomena - have undergone the most
important transformations in recent millennia, and in particular
since the post glacial sea attained its current level. This event occurred between 6000 and 5000 years B.P, and for the few millennia that followed, the sea level has varied only slightly, whereas
the coastal area has undergone considerable changes.
The most obvious cause of these changes in deltas is the
volume of sediment fluxes redistributed by fluvio-marine dynamics, as illustrated by the morphologic and stratigraphic
classification of the deltas (Galloway, 1975). The possible variations of the sea level and local or regional lithospheric upwelling or subsidence phenomena have also played a role.
In a simplified context where one of the factors can be
considered as a constant, the comparison of the respective
effects of the other two must be facilitated. Consequently,
the share of the incidence of the hydrosedimentary factors
and that of the purely eustatic component can be estimated,
provided that the tectonic effects are negligible on the scale
of the time considered. This comparison is difficult in large
deltas such as those of the Rhone, the Po or the Mississippi,
which are well known for the subsidence processes that occur there to variable degrees. It may be simpler to assess in
small arrangements, such as a site on the West-African coast
in Senegal, on the Petite Côte to the South of Cape Verde
(Dakar): the Salum “delta,” selected for this study. Small delta
environments are not extensively studied and are even less
known; they provide an opportunity to diversify knowledge
on this type of environments.
Description of the site under study
The Salum delta, that now covers an area of 2250 km²,
opens up at about 150 km to the South of Dakar, in a Miocene geological setting known as the “Continental Termi-
17
M. Diara, J.P. Barusseau - Late Holocene Evolution of the Salum-Gambia Double Delta (Senegal)
nal” which has undergone a profound ferrallitic pedogenesis
(Lappartient, 1985). The sector is part of the West-African passive margin, where indications of crust mobility in the Senegalo-Mauritanian basin are limited to a certain subsidence
in the Senegal River delta area (Monteillet, 1986). A general
lithospheric stability prevails elsewhere (Einsele et al., 1974)
as attested, for instance, by observations at Cap des Biches
(Diouf et al., 1995). The Eemian is encountered there at a low
altitude (~1 m) above mean sea level, showing that this stability is observed at a time scale that most certainly includes
the Holocene.
The climate of the region is Sudanese, characterised by
two alternating, contrasting seasons. Considerably different
modalities are nonetheless encountered in Senegalese territory (Ausseil-Badie and Monteillet, 1985). In the North of the
country, the Senegal River flows in an arid to semi-arid Sahelian region; conversely, among the “Rivers of the South,” the
Gambia flows in a tropical area (Diop, 1990). The Salum Delta
is situated at the edge of these two areas and consequently
enjoys a specific bipolar climate (Diara, 1999). The Salum
River (Fig. 1) is actually a ria now fed only feebly by a limited
river flow for two to three months during the rainy season,
from July to September. Its hydrodynamics are governed essentially by the penetration of the tidal wave and the strong
evaporation regime which develops in the vast system of
interdistributaries (known as ‘bolons’) and mangroves of the
delta (Barusseau et al., 1985). Conversely, the Gambia River,
which opens in the immediate South of the delta, is fed continuously with fresh water, albeit subject to wide fluctuations
(Marius, 1985; Diop, 1990; Dacosta, 1993). The delta spreads
out between the Salum and the Gambia rivers, and is cut by
two unequal arms. The Bandiala to the South is a long, narrow
and quite shallow bolon, unlike the vast Diomboss, which
seems to form a border between the most extensive semidelta in the North and the Betanti Islands in the South (Fig. 1).
In the Diomboss, the greater depths (25 m) and the width
(2 to 5 km) do not seem compatible with a normal fluvio-deltaic process.
Fig. 1 Location of the studied area
18
In relation to Galloway’s classification (1975), the Salum
delta displays an organisation strongly dominated by fluviatile fluxes and tide. The latter is microtidal in the North (Diaw,
1993) and macrotidal in the South (Barusseau et al., 1988; Diara, 1999). According to these characteristics, it is of a mixed
type, neither clearly lobate like the delta of the Senegal, nor
cuspate, like the delta of the Rhone. The influence of the swell
is marked by a long, Senegalese type of spit, the Sangomar
Spit, similar to the Langue de Barbarie that diverts the Senegal River when it reaches sea and shifts its mouth several
tens of kilometres to the South. In two cases, however, natural (Salum) or anthropogenic (Senegal River) processes have
recently created intermediate openings that tend to stay, unlike similar events in the recent past (Cuq et Diaw, 1985; Ba
et al., 1993; Diaw, 1997; Thomas and Diaw, 1997; Ba and Diouf,
1998). In the Salum, the spit was broken in February 1987, and
the breach has widened constantly in the years that follow to
reach more than 4 km. The process is indicative in particular
of a sedimentary dearth responsible for erosion phenomena
that are widespread in all of the Petite Côte, between the Cap
Verde and the Gambia (Barusseau, 1980).
These particular features have long attracted the attention
of researchers from various fields such as morphology (Michel,
1973; Sall, 1983; Diop, 1990), hydrology (Barusseau et al, 1985;
Saos and Pages, 1985), pedology (Kalck, 1978; Marius, 1985),
sedimentology and micropaleontology (Ausseil-Badie et al.,
1991; Barusseau et al., 1985, 1995) who have noted wide differences in the distribution of beach ridges, mud tidal flats
and sand flats (locally known as “tanne” units) – the three main
morphosedimentary units encountered between the Northern and Southern parts of the delta (Diara, 1999). Another
particular feature of the Salum delta is the existence of a large
number of anthropogenic shell middens. They attest to the
presence of Neolithic cultures since at least 1940 B.P. (Faboura
mound, to the North of delta, Descamps et al., 1977; Thilmans
et Descamps, 1982). They were erected near gathering areas of
the main mollusc, exploited for its meat, Anadara senilis, along
sand-mud or sand-silt areas, often in a sheltered and internal
position, as can still be seen today (Descamps, 1989). The different mounds are located on the edge of reliefs that surround
the delta plain, as well as inside the plain along active bolons
or old distributaries that have now disappeared. They mark the
different stages of the sedimentary filling of the delta plain and
their chronological positioning consequently provides reference points of this history.
These works have made it possible to sketch an explanation of how the estuary functioned, as well as an initial framework for these formations (Ausseil-Badie et al., 1991). Fig. 2
summarises the steps, from the open bay stage at the beginning of the filling between 6000 and 3500 B.P. (Fig. 2A), until the current stage marked by the deposit, in two episodes
(2000-1500 years B.P., then 1000-600 years B.P.) of mud and
sand-flats (Figs. 2C and 2D), behind vast beach ridges formed
between 3150 and 2550 years B.P., with an apparently different polarity in the North and in the South (Fig. 2B).
Questions nonetheless remain unsolved and pertain
more particularly to two clearly distinct issues. The first concerns the relative importance of factors that determine the
nature and abundance of deposits as well as the articulation
of its constituent units. The second has to do with the origin
of the median Diomboss (Fig. 1) and to the origin of the differences between the two parts of the delta that it separates.
The purpose of this article is to present the state-of-the-art
about these two issues.
Methodology
The delta plain consists of deposits organised into distinct
geomorphic and sedimentologic units, which were studied
by Diara (1999). The indication of the role of possible fluctuations of the sea level in the formation and architecture of
these units implies that their altimetric position is determined
in relation to the sea level, in light of the tidal and/or marine
variations (storm surges) that affect it. The methods used fall
under topography. In each point study, a reference level was
defined in relation to the level of the highest watermarks on
the shore or the banks. All the stratigraphic limits marked in
the cross-sections and boreholes have thus been connected
to this reference level. Nevertheless, with no zero adjustment,
and taking the tidal range into account, the precision of these
evaluations is subject to an error of up to ±0.50 m. Some verification with a total station has shown that the altitude of the
units varies in particular from North to South, depending on
a likewise variable tidal range.
To understand the formation of the delta and its evolution through time, surface and subsurface samples were
taken down to – 6.80 m on the ridges and – 5.20 m in the
tidal flats – positions measured in relation to the reference
level determined in the field. Their analysis in the laboratory
has made it possible to define their grain-size and SEM grain
surface characteristics, to study their heavy minerals, and to
determine their clayey minerals with X rays. Some additional
radiocarbon dating was performed on shells.
A total of 53 stations to the North of Diomboss and 39 to
the South have been described and studied. They are more
concentrated around the beach ridges, entailing a less homogeneous distribution to the North than to the South of
Diomboss, because they are located to the West of the delta
plain in the North, whereas they are vaster and regularly distributed in the South.
Results
Their main sedimentological and morphological characteristics are described below, underlying the differences between the Northern and Southern parts on either side of the
Diomboss.
The three types of morphosedimentary units of
the delta
The sediments are organised into morphosedimentary
units, which show clear differences between the Northern
and Southern parts in terms of their distribution and mutual
– in particular stratigraphic – relations.
19
Fig. 2 The four major stages of the delta construction according to Ausseil-Badie et al.(1991). Explanations in text
20
Three types of units were considered (Fig. 3):
Fig. 3 The main geomorphic and sedimentary units in the delta. Dotted areas: beach barriers; white surfaces: tidal flats (mud flats and the so-called “tannes”= sand-flats are not distinguished). The grey surfaces correspond to the geological substratum outcrops (= “Continental terminal”)
21
•
•
•
The morphology of the beach ridges is very different depending on the sector studied. In the Northernmost part,
the ridges are flat and dismantled, at a low altitude that
does not exceed 1 m. In descending towards the South,
they gradually become more imposing and form long,
wide, voluminous and high barriers, at an altitude that
at time reaches 10 m. Fine, at times cross-bedded laminations show on the fresh sections of the ridges in the
South but, generally, because of the very homogeneous
deposits, both in the North and in the South, stratigraphic
correlations cannot be established.
The mud tidal-flats are actually complex units, rarely totally
composed of mud, but most often of mixed sand-clay, and
at times sand-silt sediments: they correspond to the slikke of
the mud-flats. They are located at the base of the ridges or
at the edge of the third units, the “tannes,” and do not exceed
some twenty metres in thickness above the Continental Terminal (Marius, 1985). On the high parts of the mud tidal-flats
develops the mangrove, thick and often inextricable in the
South, poor and sparse, in riparian position in the North. The
mud tidal-flats in the North are characterised by abundant
sand interlayers from the ridges that are dismantled, striped
and swept by the wind. The boreholes in the mud tidal-flats
in the North are rapidly stopped by sandy beds and exceptionally exceed 1.50 m under the surface, whereas a depth of
6 m is attained more easily in the South. The mud tidal-flats
of the South are more developed and more clayey; although
they too often show alternating beds of very fine sand and
of clay, they show a less developed pedogenesis.
The “tannes” form very flat areas, most often emerged
during spring tides and the rainy season; they correspond
to bare or herbaceous schorre, except where geochemical processes occur because long periods of desiccation
alternate with short periods of flooding. From the South
to the North, the evolution of the “tannes” is accompa-
nied by an increasingly more intense pedological transformation due to oxidation phenomena whereby pyrite
is transformed into jarosite, and Rhizophora roots are fossilised into iron pipes (Vieillefon, 1974). The “tannes” are
much extended in the extreme North, and have evolved
into hyper-salted and acid soils.
Location of the mud tidal-flats in relation to sea
level
The highest level (in altitude) of the mud tidal flats is always situated at the high tide limit and varies from North to
South. The high tide accompanying the gradual increase in
the tidal range in this direction rises from 0.50 m in the North
to 2.5 m in the South.
Sand fraction grain-size
An often abundant sand fraction is found in the ridge, mud
tidal flat and “tanne” sediments. It must therefore be examined.
The sand barrier sediments of the three units are fine to very
fine (Figs. 4 and 5). The Northern sand barriers have a grain-size
modal value essentially between 160 and 250 μm, generally
higher than that observed in the Southern sand barriers. The
same difference is noted between the sands of the Northern
and of the Southern mud flats, even if the grain-size modes of
the quartz component are finer than those of the barriers. It
is worth noting, in fact that the sands of the mud flats often
have bi-modal grain-size curves. This is due to two particular
features. The texture of the pelitic fraction of the muds is in fact
favourable to the development of an endofauna that produces
a coarse bioclastic component. Furthermore, prismatic or saccharoid gypsum stemming from the authigenic processes is
often encountered. Shell debris like gypsum crystals appear
only after the sediment has been deposited, in the final development phase of mud tidal flats. Consequently, unlike the
quartz framework population, this post-depositional formation provides no argument on the deposition process.
Fig. 4 Grain-size mode distribution in sand-barrier sediments
(x-coordinate in microns; y-coordinate in %).
Fig. 5 Grain-size mode distribution in mud-flat and “tanne”
sediments (x-coordinate in microns; y-coordinate in %).
The textural grain-size duality observed is also underscored by the distribution of the asymmetry indices which
reveal significant differences between samples from the
delta to the North and to the South of the Diomboss. Sandbarrier sediments in the North show a preponderant asymmetry towards the coarse tail of the grain-size distribution,
while those of the South clearly show an asymmetry towards the fine end. In mud flats, this opposition is reversed,
with an asymmetry towards the fine in Northern sand barriers, whilst the majority of those in the South have an asymmetry towards the coarse end of the distribution (Fig. 6 and
Fig. 7).
22
Fig. 6 Asymmetry index distribution in sand-barrier sediments
(y-coordinate in %).
Nature and quantitative distribution of pelites
Pelites are not a dominant category in the Salum delta,
even in the mud tidal flats, as we have seen. They are present
in higher proportion in the mud tidal flats of the South than
in those of the North; the opposite is true in the “tannes” (Table 1).
Table 1 Pelitic index in mud-flats and “tanne” sediments
(number of samples in parentheses)
Content of pelites in
mud flat sediments
Content of pelites in
“tanne” sediments
Northern part
36.5±14.12 (18)
Southern part
45.8±27.15 (39)
18.6±18.60 (63)
7.4±10.01 ( 9)
The clayey paragenesis is highly constant, as already
recognised by Kalck (1978). It is represented by two species,
kaolinite and smectite, which constitute more than 80% of
the clayey fraction under 2 μm, whereas illite, more subsidiary, represents only 5 to 20%. Kaolinite constitutes more than
50% of the clayey assemblage of the sediments. According to
Kalck (1978), kaolinite is inherited from the alteration of the
Continental Terminal; illite comes from the same source. According to this author, smectite (of the ferriferous beidellite
variety) is always symptomatic of a marine flux.
This situation must be compared with a certain abundance of pelites at the outlet of the Gambia, in the inner-shelf
zone (Barusseau, 1983), over an area of more than 20 km², at
times exceeding 25% of the total sediment. The Gambia actually has real floods and a solid flow rate of 660000 tons/year
at 530 km from the mouth (Lerique, 1975). This river therefore
has the necessary capacities to bring fine elements in suspension. At the outlet of the Salum, on the other hand, this proportion is lower, about 5 % over a reduced area.
SEM examination of the quartz fraction
A SEM surface analysis of the quartz grains has shown
that, all the grains in the delta have marks indicating that
they passed in a coastal area, at times in high energy sectors. The grains are often very clean and show marks of current shock. However, a clear distinction appears among all
Fig. 7 Asymmetry index distribution in mud-flat and “tanne” sediments (y-coordinate in %).
the sand barrier, mud flat and “tanne” sediments: the quartz
grains of the Northern clearly demonstrate a prevailing wind
component with a high percentage of round and mat grains,
traces of wind-derived scratch, sharp edge fractures and, at
times, even flat surfaces reminiscent of dreikanters. Grains
are also often found with traces of shocks on silica coatings
typical of desert areas. The SEM examination of these grains
shows a provenance from a desert environment and, very
frequently, indications of wind transport. In the Southern
units, on the other hand, the wind-derived component is always feebly represented and grain shapes are largely dominated by rougher forms; among which exoscopy has shown
numerous alterations manifested by, e.g. rounded edges
and blunted peaks. This set of characteristics, together with
the frequency of non-worn grains (15 to 50%) attests to a
consequent fluvial flux and suggests that the Southern delta was fed from sources nearby. Only the Gambia – because
of its proximity and water discharge – can be considered as
a valid source for this type of sediments.
Quantitative and qualitative analysis of heavy
minerals
The same opposition is established when the distribution
of heavy minerals is considered. The weighted percentage
of heavy minerals is three times higher in the Southern than
in the Northern beach barriers: the average in the South is
0.70%, but only 0.21% in the North. When notable percentages are on occasion recorded in the North (Niodior: 0.42
% and Fandong: 1.42), it is because the light fraction is winnowed, thereby implying residual enrichment.
The dominant mineralogical species in the delta are zircon, tourmaline, rutile, highly resistant minerals; then come
metamorphic minerals: staurotide, andalousite and disthene.
Garnet, sphene, and muscovite, chemically or mechanically
more fragile, are in low quantity. The distribution of these
mineral species shows two tendencies: the Southern barriers are richer in rutile, whereas the Northern beach barriers
are richer in muscovite. All the other heavy minerals show a
homogeneous distribution between North and South of the
delta.
23
Dating
Several new dates have been obtained on samples of
shell remains (Anadara senilis, Dosinia isocardia and Gryphea
gasar) taken from beach barrier sediments (4), “tanne” sediments (2) and tidal flats (4). The results are given in Table 2.
These dates supplement, but do not challenge the
scheme of relations between the different units and the chronology of the steps shown by Ausseil-Badie et al. (1991) as
presented above (Fig. 2).
Table 2 14C dates on shell remains from various morphosedimetary units of the Salum delta
Morphological unit
Beach barrier
Beach barrier
Beach barrier
Beach barrier
Tidal flat (slikke))
Tidal flat (slikke)
Tidal flat (slikke)
Tidal flat (slikke)
Tidal flat (schorre)
Tidal flat (schorre)
Location
Falia
Dionewar
Dionewar
Niodior
Niodior
Niodior
Niodior
Djiffère
Diogane
Diogane
Depth (m)
0.80
2.10
2.50
0.70
0.10
0.47
0.63
0.25
0.10
0.35
Interpretation - DISCUSSION
Relative weight of eustatic and sedimentary
forcing factors
The sequence of deposits formed during the filling of the
primitive estuary bay of Salum represents a dynamic system,
where the evolution in time and space is regulated by a balance between three allocyclic factors (Vail et al., 1977): variation in sea level (i.e. the change in the volume of the world’s
ocean water), isovolume deformation of the solid substrate
(i.e. variation of its geometry), and sedimentary fluxes that
modify the form of the substrate locally through the addition
of new material.
The problem in the Salum delta is actually limited to establishing the share between the relative weights of two factors only: eustatism and sedimentary forcing, for the sector
belongs to the West African passive margin, where a general
lithospheric stability prevails (Diouf et al., 1995).
It can point out first that the sedimentary reservoir was
considerable throughout the period. There were voluminous
ergs to the North of the Salum-Gambia region from the previous glacial phase (“Ogolian”; Michel, 1977). In the South,
the entire first half of the Holocene was marked by a hot and
humid climate, favourable to abundant fluviatile sediment
fluxes.
The question arises as to possible positive and/or negative variations in the sea level during the entire interval of
the construction of the delta plain. Such variations have frequently been cited in the region to explain the arrangement
of the deposits (Faure and Elouard, 1967). The observations
reported here seem to suggest that no considerable variation
in sea level is either necessary or demonstrable. The argument is provided by the altitude of the mud tidal flats.
24
Species
Dosinia isocardia
Anadara senilis
Anadara senilis
Anadara senilis
Gryphea gasar
Gryphea gasar
Anadara senilis
Gryphea gasar
Gryphea gasar
Gryphea gasar
14C Date (years B.P.)
3670±100
2370±50
2780±60
570±40
170±50
390±70
530±70
1180±80
580±60
400±60
This unit is established according to the tide, and its highest level is always at the limit of mean high tide (De Vries
Klein, 1985).
The considerable variation of the tidal range in the delta,
although progressive from North to South, is not linear. On
the coastal sector from the North of Salum to Guinea-Bissau,
the spring tidal range rises from 1.10 m in Djiffère to 1.60 m
in Banjul (Gambia) and to more than 4 m in Guinea-Bissau.
This rise in the tidal range essentially explains the variations
observed in the delta. It is not sufficient, however, and the
abruptly tapered end of the funnel-shaped morphology of
the Bandalia helps explaining a strong, hypersynchronous
characteristic in the bolons of the South, whereas the maintained width beyond the neck of the distributary explains a
synchronous behaviour in the internal reach (Diara, 1999). A
local amplification of the tidal range results (up to 2.50 m) and
the variation in altitude of the mud tidal flats corresponds to
this exaggeration, and not to eustatic variations in the sea
level. So there seems to be an adjustment in the organisation
of the mud tidal flats of the entire delta depending only on
present conditions.
The delta construction: a two-fold process
This dual formation is expressed by the origin of the sediments at the interface of two climate zones: Sahelian and
tropical. The origin may be defined from the distribution of
morphosedimentary units, the results of the grain-size, SEM
surface aspects and mineralogical analysis of the sand fraction and the distribution of pelites.
Two types of sedimentary units in the Salum delta have
a clearly antagonistic distribution between North and South:
the sand barriers and the “tanne” sediments. The sand barriers are long, numerous, but not very high in the North. They
have undergone multiple modifications connected to the
movement of channels and the arms of the Salum (Ausseil
et al., 1991). They are more massive and not much affected by
the variations of the delta process in the South. The extension
of the “tanne” sediments is nowhere in the world as important as in Northern part of the Salum delta. It is, however, very
limited in the South of the Diomboss.
The sedimentological study of the constituents of the
different units also leads to underscore wide differences between the two parts of the delta on either side of the Diomboss. The central role of a terrigenous quartz population was
noted, as it is still present and coarser to the North than to the
South of the Diomboss, even if it is at times masked by circumstantial components (bioclastic, authigenic). The causes
of this grain-size duality are to be found in the two possible
sources of the terrigenous sand material.
To the North and to the North-East of the delta extend the
Ogolian ergs of the Ferlo (Michel, 1973; Barbey, 1982); then,
further North, the Mauritanian desert. These two areas are
reservoirs of sediment easily blown away by the wind – and
the North and North-West winds are frequent in this region,
where vegetation is very sparse when not totally absent, or by
streaming during rain periods, or by the North-South coastal
drift (Gac et al., 1992). They can also transport coarser sediments (Kocurek and Lancaster, 1999). Consequently, sandy
material from the North can be thought to have their source
in the North.
The second potential source is in the South with the powerful hydrological system of the Gambia, the existence of
which at the Southern edge of the delta cannot be ignored.
Draining a catchment area where the tropical hydrolysis systems are highly active, it plays a role in both the coarse input
and the arrival of fine materials.
The SEM examination provides convergent arguments.
The quartz grains show surface states that justify distinguishing them according to their belonging to two different provinces separated by the Diomboss sound.
To the North, the sediment has the same origin as the
coarse component. This predominantly wind-originated sand
with obvious marine reworking has constituted the Northern
delta in part during climatic periods of the late Holocene interval.
In the South, the sediments show quartz grains of essentially fluvio-marine origin with a secondary wind component.
The distance of the Salum from this part and the proximity of
the Gambia justify identifying the latter as the vector of the
dominant fluvial-marked component.
Based on the above, the quartz grains finally show that
they belong to two different provinces separated by the Diomboss sound, a hydraulic border that prevents grains with
fluviatile marks from crossing from the South to the North.
The wind component, on the other hand, crosses this space
and its presence is recognized in the sediments of the South,
albeit not as abundant as in the North.
The North-South duality thus underscored is confirmed
by more discrete signals such as the assemblage of heavy
minerals and the distribution of the pelites. In the case of
Salum, two distinctive heavy minerals are present: muscovite in the North and rutile in the South. They are available
not only because they exist in the sources, but also because
of different processes that occur after they are mobilised: a
pedogenetic alteration in the source massifs and geological formations, weathering or fracturing during the different
transport phases in a fluvial or marine environment, involving
their mechanical and chemical resistance, early post-depositional diagenesis (Morton and Hallsworth, 1999).
The fragility of the muscovite, crystallised into flakes, excludes transport in an energetic hydrodynamic environment. Its
relative abundance in the North could suggest relatively nearby
sources, transport in a calm environment and, consequently, reduced shocks. The Salum corresponds to a low energy outflow.
It would have conveyed the muscovite from the sedimentary
layers of the Meso-Cenozoic basin up to its deposit in the delta.
On the contrary, the rutile is a mineral both mechanically and
chemically resistant. Although generally small in size, it is a
highly dense mineral (4.2 to 5.5). Its more frequent presence in
the South may therefore adapt to the conditions of a sedimentary history that adds transport phases and alteration phases.
Other mineralogical species are relatively less represented, because they have not resisted as well. The high density of the rutile moreover entails that it can be transported only by energy
outflows. Its rounded form does not, in fact, make it particularly
buoyant. It is therefore necessary to acknowledge a sufficient
flux to understand how it got established in the South. There
too, the Gambia, the floods of which produce high flow rates,
must be the essential agent of this transport.
The muscovite and the rutile therefore help identify a
Northern mineralogical province (the Meso-Cenozoic sedimentary basin), the sediments of which are conveyed by the
Salum, and a province originating in the South-East, the folded range of the Mauritanides, one of the culminating points
of which is the Fouta Djalon, the source of the Gambia.
The different relative abundance of the heavy mineral
fraction in the North and the South also confirms this distinction. Whereas in the Northern part, the material is fed by the
reworking of the sedimentary strata where the heavy residue
has already extensively diminished and is being transported
and deposited under not very energetic agents, the direct
flux from the crystalline massifs by a powerful river is easier
to understand in the South.
The distribution of pelites provides a second discrete yet
significant signal. The pelitic assemblage is homogenised by
a dynamic, geochemical mixing; it is not discriminating. The
same cannot be said when its relative abundance is consid-
25
ered; we have seen that mud flats are incomparably more
abundant in the Southern half than in the Northern part.
The fine materials are generally dispersed in the sea by a
turbid plume. Their evolution then depends on the proximity of the deposit zones characterised first and foremost by
hydrodynamic calm. Two preferential sites generally have
such potential: the depths of the inner shelf below the storm
wave-base and the sheltered areas of the coast. This pattern
is encountered near large estuaries, such as the Gironde and
the Marennes-Oléron Basin (Lesueur et al.1994; Barusseau.
1973) or, closer to Senegal, in the mud tidal flats of Guinea
(Rüe, 1988) and Guinea-Bissau (PNUE, 1985).
It is also found off the Gambia, in the sheltered environments of the nearby continental shelf (Domain. 1977; Ba-
russeau, 1983) and in the entire delta, in all the parts of the
former estuary bay, as it was protected by the sand barrier
structures erected from 4000 B.P.
Furthermore, the fact that the mud tidal flats to the North
of the Gambia are dated 6000 B.P. at 10 m of depth (Kalck,
1978) show that the delta bedrock was established there from
the beginning of the sedimentary filling under the influence
of fluxes from this river, at the Southern edge of the area. The
North of the delta, being far from the source, receives less fine
sediments.
Finally, the relative abundance of muds, highly imbalanced between the North, rather poor in pelites, and the
better provided South, attests to a separation between the
Northern and the Southern part of the delta (Fig. 8).
Fig. 8 The distinct origin of the Northern and Southern parts of the delta.
Conclusion
At the end of a discussion that takes into account the results obtained on the arenic and pelitic fractions of the sediments, on the exoscopic characteristics of the quartz grains
and on the formation of the heavy fraction, a double origin of
the sedimentary flux emerges clearly, identifying two provinces of origin, two modes of flux and two parts of the delta:
•
26
a Northern part, characterised by a quartz flux, chiefly windtransported, reworking slightly the deposits of a highly
altered sedimentary basin. The fluvial hydrodynamics are
discrete and subordinated to the coastal transfers by waves
and tidal currents in the reverse estuary part of the Salum;
•
a Southern part under the influence of the wide catchment area of the Gambia, and the mineralogical province
of the Mauritanides that it drains. The fluvial hydrodynamics produce a recognizable imprint, even if the last
marine characteristics attenuate it somewhat.
The Salum delta must therefore be reduced in the Northern part; whereas the Southern part represents the pre-Gambian delta.
Between the two, the Diomboss, originally considered as
one of the distributaries of a large delta of the Salum, actually represents only a remnant of the original estuary bay that
existed when the sea reached its current level.
There are no indications that justify retaining the idea
of extensive changes of the eustatic position of this level in
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Apports des Systemes d’Information
Géographiques à la perception des changements
morphodynamiques (1970-2000) dans le delta du
Danube. Le cas du bras de Saint-George
GIS USE FOR ASSESSING MORPHODYNAMICAL CHANGES IN THE DANUBE
DELTA. CASE STUDY: St. GEORGE DISTRIBUTARY (1970-2000)
Laura JUGARU (1,2), Mireille PROVANSAL (2), Nicolae PANIN (1), Philippe DUSSOUILLEZ (2)
(1) INCD GEOECOMAR, Rue Dimitrie Onciul, No 23-25, 024053, Bucarest, Roumanie, [email protected], [email protected], [email protected]
(2) UMR 6635, CEREGE-CNRS, Europôle Méditerranéen de l’Arbois, 13545, BP 80, Aix-en-Provence, Cedex 04, [email protected], [email protected]
Abstract. The paper describes the evolution of one distributary of the Danube Delta (the St. George distributary) over the last 30 years by use of topographic maps as well as aerial and satellite images transformed and georeferrenced in a geographic information system (GIS). By analysing a multitude of
parameters the authors intend to assess the changes in channel and meanders morphology induced by human intervention in the drainage basin of the
Danube River and in its delta in the early 80s. The anthropogenic changes (damming of the river, cut-offs of the distributary meanders within the delta
area) have significantly altered the hydraulic and sediment dynamics in the distributary resulting in diminished migration of meander belts, occurence of
longitudinal sand bars, bathymetric changes. The natural channels of meanders and the newly cut channels evolve differently, fundamentally changing
the sediment transport processes.
Key words: GIS, St. George distributary, meander belt, cut-offs, channel evolution
Introduction
Ce papier présente une première analyse de l’évolution
du bras de Saint George au cours des 30 dernières années,
à partir du traitement de cartes topographiques et d’images
satellitaires par les logiciels Mapinfo et ERMapper.
Le traitement d’image et les SIG permettent la reconstitution de l’évolution récente des milieux fluviaux en vue d’une
analyse des réponses du système aux différents forçages (naturels et anthropiques). L’analyse des modifications morphologiques des systèmes fluviaux à partir de cartes anciennes,
photographies aériennes et images satellitaires est fréquemment utilisée (Huckleberry, 1994 ; Large et Petts, 1996 ; Rinaldi et Simon, 1998 ; Leys et Werritty, 1999 ; Biedenharn et al.,
2000 ; Winterbottom, 2000 ; Lach et Wizga, 2002 ; Pisut, 2002;
Citterio et Piégay, 2000 ; Dzana, 2000 ; Warner, 2000).
De nombreuses recherches ont été réalisées sur la mobilité des méandres à partir des années 1970. Les impacts mor-
phologiques des aménagements fluviaux ont été aussi analysés. Les dynamiques ont été étudiées à différentes échelles, à
partir des processus caractérisant l’érosion des rives (Hooke,
1979 ; Knighton, 1973 ; Thorne et Tovey, 1981), le transport
sédimentaire et le dépôt dans les sinuosités (Bridge, 1984,
Dietrich et al, 1984) et les changements dans la configuration
des écoulements (Hickin, 1978).
Les impacts morphologiques et sédimentaires en relation
avec les aménagements hydro-électriques ont été analysés
sur des organismes de tailles très différentes (Arno - Fleuve
Jaune, Timar – Tisza, Winkley - Mississippi). La réduction de
la charge sédimentaire par les barrages est variable selon les
fleuves. Elle est estimée à 30% sur le Mississippi, 95% sur le
Nil et l’Ebre (Milliman & Meade, 1983 ; Shahin, 1985, J. Guillén
& A. Palanques, 1992). Les conséquences sont en général une
augmentation de l’activité érosive dans le chenal, liée au déficit de charge sédimentaire.
29
L. Jugaru, M. Provansal, N. Panin, P. Dussouillez - Apports des Systemes d’Information Géographiques à la perception des changements morphodynamiques dans le Delta du Danube
L’endiguement et les recoupements des méandres,
destinés à améliorer les conditions de la navigation et à
permettre une évacuation plus rapide des eaux de crue,
entraînent des modifications significatives sur les profils en
long (Emerson J.W., 1971 ; Keller E.A.., 1975). Les études sur
les rectifications des méandres montrent qu’ils ont un effet
sur le régime hydrologique, mais aussi sur la morphométrie
des bras recoupés qui se colmatent progressivement, alors
que les bras de recoupement s’approfondissent (Ichim, Radoane, 1986).
Sur les cours d’eau à méandres, la constructions de barrages, les endiguements (protection contre les débordements) et les recoupements destinés à améliorer les conditions de la navigation et à permettre une évacuation plus
rapide des eaux de crue ont entraîné des modifications significatives sur les profils en long (Emerson J.W., 1971 ; Keller E.A., 1975).
La zone d’étude : présentation générale Le bras de Saint George est le plus méridional du delta du
Danube. Il débute à 108 km de la mer par une diffluence du
bras médian (bras de Tulcea). Sa largeur est variable (150 à 550
m), sa profondeur est comprise entre 3 et 27 m sous le niveau
d’étiage local (Bondar, 2004). Très méandriforme, ce bras est
actuellement le plus actif du delta du Danube, par son activité
morpho-dynamique (mobilité des méandres), par l’évolution
rapide de son embouchure (progradation d’un lobe deltaïque
et mobilité de l’île-barrière de Sakhaline (Panin, 2003). Actuellement le bras véhicule environ 21-22% du débit liquide et
20% du débit solide du Danube à l’entrée dans son delta.
La morphologie du bras permet d’identifier 3 secteurs différents, d’amont en aval (fig. 1):
• un secteur presque rectiligne, peu sinueux, à partir de la
diffluence jusqu’au PK 90, contraint par l’affleurement de
l’orogène nord-dobrogéen et un système de failles en rive
droite (« fractures de Saint George », Panin 2003) ;
• un secteur de méandres libres dans la plaine fluviale (6
méandres entre les PK 90 et PK 22) ;
• un secteur peu sinueux, qui recoupe les cordons littoraux
historiques progradants entre le PK 22 et l’embouchure.
Les méandres du bras de Saint George n’ont pas été
beaucoup étudiés ; des études ont été faites par Panin et
Popa (1994) sur l’impact des constructions des barrages des
Portes de Fer I et II sur le bras de Saint George. Une étude
systématique sur les impacts morphologiques induits par
les aménagements hydro-électriques et le recoupement des
méandres dans le delta n’a pas été réalisée. C’est l’objet de
cet article.
Trois types d’aménagements ont modifié les conditions
de fonctionnement du bras :
Deux objectifs ont été fixés à ce travail :
analyser et quantifier l’évolution dynamique d’un chenal
à méandre soumis à des variations d’apports liquides et
solides ;
analyser l’impact spécifique lié aux travaux de recoupements des méandres.
Depuis 30 à 40 ans, l’aménagement hydro-électrique du
bassin-versant (en particulier la construction des barrages
hydro-électriques des Portes de Fer I et II entre 1971 et 1984)
a modifié les flux solides entrants à l’amont du delta, provoquant une diminution des apports sédimentaires d’environ
25 – 30% (Panin et al., 1979-1994; Popa, 1994).
•
•
Fig. 1 Le Delta du Danube, secteur d’étude: le bras de Saint George
30
Dans les années 1984-1988, six méandres libres du bras
de Saint George ont été recoupés afin d’améliorer la navigation et d’augmenter les débits liquides du bras; la longueur
du bras a été ainsi diminuée de 32 km. Les chenaux de recoupement étaient initialement profonds de 7-8 m, avec une
largeur de 75-100 m. Ces travaux ont induit un changement
de répartition des débits liquides et solides du bras de Saint
George, qui capte partiellement les eaux des deux autres bras
du delta. La figure 2 montre que ces travaux jouent un rôle
déterminant sur le débit du bras de Saint-George.
La construction d’un éperon à la première diffluence
deltaïque (bras de Tulcea/bras de Sulina et de Saint-George)
dans les années 1970-1980, destiné à dévier le flux liquide
vers le bras de Sulina pendant les périodes de basses eaux, a
réduit l’alimentation du bras de Saint-George (A. Popa, 1993).
Le bras de Sulina captait 41% du flux en 1928-1929, 45% en
1958-1960 et 54% en 1990-1994.
Ces trois types d’aménagements modifient les conditions
hydrologiques et sédimentaires du bras de Saint George, sou-
mis successivement à une réduction des apports solides, puis
à une augmentation des apports liquides.
La figure 2 résume ces transformations, qui se surimposent à la variabilité naturelle des flux, saisonnière et pluriannuelle. La période 1971-1984, séparant la construction des
deux barrages, est caractérisée par deux crues importantes,
alors que la turbidité diminue. La période de rectification des
méandres (1984-1988) coïncide avec deux périodes d’afflux
sédimentaires importants (400 kg/s), associés à des débits
liquides annuels “moyens” (1300 m3/s). Les années suivantes
correspondent à une augmentation progressive des débits
liquides moyens annuels (jusqu’à 1900 m3/s), alors que les
concentrations de MES continuent leur diminution tendancielle (150 à 250 kg/s). L’année 1990 enregistre les débits liquides et solides les plus bas depuis 40 ans (A. Popa, 1994).
Ces modifications du rapport débit liquide/débit solide
accroissent de fait la capacité globale d’érosion du bras de
Saint George.
Fig. 2 Evolution des débits liquides et solides sur 37 ans sur le bras de Saint George
31
L’étude hydrologique réalisée par GeoEcoMar en 19891994 dans le secteur des méandres recoupés, confirme que
les chenaux de recoupements évacuent une partie croissante
des débits liquides et solides, « court-circuitant » ainsi les
méandres du chenal naturel (fig. 3). Le recoupement des petits méandres aval (méandres 2, 3, 5, 6 et 7) dérive 12 à 20%
des débits liquides et 11 à 22% des débits solides ; celui du
grand méandre amont (1) dérive 45,6% des eaux et 37,5%
des sédiments. On peut donc s’attendre à ce que ce dernier
joue un rôle majeur. Par ailleurs, l’effet des recoupements est
sensible dès la première année (1990) et s’amplifie très rapidement dans les années suivantes.
Méthodologie du travail
La démarche passe par les étapes suivantes :
(1) recherche de la documentation cartographique et photographique. Nous avons sélectionné 4 dates significatives
permettant de fournir une situation initiale « naturelle »,
puis d’encadrer les aménagements (1970, 1980, 1990,
2000):
• 1970-1972 : carte topographique au 1 :50 000 en projection Gauss Krüger (6 feuilles) (réalisées par la Direction Topographique Militaire);
• 1980 : carte topographique au 1 :25 000 en projection
Gauss Krüger (13 feuilles), (réalisées par la Direction
Topographique Militaire);
• 1980 : photographies aériennes au 1 :25 000 (réalisées
par la Direction Topographique Militaire);
•
•
1990 : image satellitaire Landsat 5 TM (résolution de
28 m/pixel) et Spot (résolution 10 m/pixel) ;
2000 : image satellitaire Landsat 7 ETM (panchromatique – canal 8, résolution 15 m/pixel).
(2) calage, géo-référencement et rectification sous MapInfo
et ERMapper des cartes topographiques et des photos.
Les résolutions choisies sur les cartes (4 m pour 19711972 ; 2 m pour 1980) sont meilleures que de celles des
images satellitaires (28, 10, 15 m).
(3) vectorisation des berges et réalisation de transects transversaux pour mesurer la largeur du chenal pour chaque
période, afin de localiser et quantifier les modifications
des surfaces mouillées et du périmètre du chenal (déplacement latéral, augmentation, rétrécissement).
Le secteur intermédiaire, correspondant aux méandres
recoupés, a été analysé particulièrement. Les caractéristiques
morphologiques de chaque méandre ont été calculées (longueur et largeur du chenal, longueurs d’onde et amplitudes
des méandres, indice de sinuosité (Is= λ/L, où λ = longueur
d’onde, L= longueur du thalweg entre deux inflexions de
même sens).
Les données exploitées dans le SIG sont affectées d’une
marge d’erreur qui doit être prise en compte. Ces incertitudes
tiennent à plusieurs facteurs (Raccasi et al., sous presse) :
• Les différentes résolutions spatiales des capteurs : la comparaison des images Spot (10 m/pixel) et Landsat 7 (28
m/pixel), acquises à des dates très proches (20.10.1989 et
Fig 3 Evolution des débits liquides et solides (%) dans les chenaux de recoupement du bras de Saint George, 1989-1994 (d’après A. Popa, 1993)
32
•
•
20.08.1989), montre après vectorisation une différence en
surface de la zone mouillée du chenal de 0.5 km2. L’erreur
liée à la résolution de l’image est de 4.7% de la surface
mouillée totale pour l’image Spot, de 12.3% pour l’image
Landsat 7.
La variation de la hauteur d’eau dans le chenal (liée aux
variations du débit) perturbe la comparaison entre les
différents documents. Elle donne en effet une image différente de la largeur du chenal, de la hauteur des berges
émergées et de l’extension des marges forestières. La
différence entre les surfaces mouillées des deux images
satellites s’explique également par la différence de débit
entre les 2 dates de prise de vue (1651 m3/s pour Spot et
1404 m3/s pour Landsat 7).
La diversité du matériel cartographique utilisé (images
satellites, cartes, photographies aériennes) : les cartes décrivent par principe une situation proche de l’étiage, alors
que les photographies et les images satellites correspondent à une visualisation instantanée dans des contextes
hydrologiques très variables.
Résultats
Globalement la largeur du bras n’a pas beaucoup varié
entre 1970 – 2000 (fig. 4). Dans le secteur amont, on observe
un faible élargissement (largeur moyenne 250 m en 1970,
260 m en 2000). Le secteur aval apparaît stable, à l’exception
de l’embouchure, où le rétrécissement (de 1570 à 380 m) est
lié à la progradation du lobe au-delà de la zone étudiée (laquelle passe ainsi d’un état « embouchure » à un état « che-
nal »). Le secteur des méandres est le plus mobile, caractérisé
par de fortes réductions/augmentations localisées, sensibles
en 1990 et 2000.
Cette disparité d’évolution souligne le rôle des recoupements artificiels des méandres et justifie une analyse par
secteurs.
(1) Le secteur peu sinueux à partir de la diffluence (entre
PK 108 - PK 90)
C’est la partie la plus stable du bras de Saint George. La
figure 5 montre cependant une tendance à l’élargissement.
Autour d’une moyenne de 35.60 m (soit 1,18 m/an), les valeurs extrêmes oscillent entre + 53 m (1,76 m/an, soit 20,15%
de la valeur initiale) et -70,5 m (soit 2,35 m/an, 22,65% de la
largeur initiale).
Le segment comprend deux principaux secteurs d’élargissement du chenal : entre les PK 102-101, où apparaît en 1980
une île qui s’accroît rapidement (fig. 6), puis entre les PK 94
et 91. Ils sont compris entre trois secteurs de rétrécissement,
dont le plus important est situé au PK 99 (-70,5 m soit 2,35
m/an, 22,65% de la largeur initiale). Au PK 90, situé à l’amont
du chenal de recoupement de Mahmudia, le chenal s’élargit
jusqu’en 1980, puis se rétrécit.
(2) Le secteur des 6 méandres libres dans la plaine fluviale
(entre Pk 90 et Pk 22)
Globalement, l’évolution de la largeur du chenal est très
disparate, entre les moyennes de +55 m (+1,81 m/an) et -
Fig. 4 Evolution de la largeur du chenal 1970-2000 (l’ordonnée zéro représente les valeurs 1970)
33
Fig. 5 Evolution de la largeur du chenal 1970-2000 entre les PK 108-90 (l’ordonnée zéro représente les valeurs 1970)
Fig. 6 Evolution d’une île à l’intérieur du chenal naturel entre1970-2000
34
107,1 m (- 3,57 m /an). Les valeurs extrêmes oscillent entre
+ 80,9 m (2,69 m/an, 45,45% de la valeur initiale) et -292,6 m
(14,63 m/an, 52,32% de la valeur initiale), cette dernière étant
acquise en seulement 20 ans (fig.7).
On peut opposer la partie amont (PK 90 à 50), caractérisée par une tendance dominante à la réduction, à la partie
aval qui a tendance à s’élargir. Ces déformations sont le plus
souvent acquises dès 1980. La figure 7 montre l’organisation
générale du secteur en 3 unités (méandre naturel-chenal de
recoupement) : le grand méandre de Murighiol à l’amont (1),
puis deux unités de petits méandres (2-3 et 5-6) séparé par le
méandre 4 qui n’est pas rectifié et enfin un dernier méandre
aval (7). Nous analyserons ces unités successivement.
Le secteur entre PK 84- 64 correspond au méandre de
Murighiol (1), qui est le plus grand et le plus complexe des
méandres du bras de Saint George (fig. 8). L’évolution est
dominée par la tendance au rétrécissement de la largeur du
chenal (-114,4 m en moyenne soit 3,8 m/an). Cette tendance
est la plus nette en amont du secteur, avec un maximum au
PK 74 (-292,6 m, 14,63 m/an, 47,6% de la valeur initiale), où
une île s’est développée en rive gauche. Elle est importante
entre 1990 et 2000.
La figure 8 permet de visualiser en plan l’évolution 19702000. Sur le premier tiers du méandre (PK 84 à 78), l’apex des
sinuosités conserve encore une certaine mobilité : au PK 81 la
rive convexe prograde, mais l’extrados reste stable (d’où une
réduction de 122 m la largeur du chenal) ; au PK 78 (à placer
sur la figure) le méandre se déforme en translation latérale et
le chenal s’élargit de 61 m. Vers l’aval, le colmatage devient
prédominant : quasi fermeture du chenal artificiel de Garla
Filatului (PK 74) et développement d’une île qui réduit de
Fig. 8 Evolution de la largeur du chenal 1970-2000 entre les PK 84-64 (méandre Murighiol) (l’ordonnée zéro représente les valeurs 1970)
35
192 m la largeur du chenal principal. Une île apparaît en 1990
au PK 65, qui double de surface entre 1990 et 2000.
réduction de la sinuosité (expansion et extension latérale dé-
Le secteur entre les Pk 59 et 49 est représenté par les deux
méandres de Dunavat de Sus et Dunavat de Jos (2) et (3).
recoupement (Dunavat de Sus et Dunavat de Jos) déforme le
La largeur du chenal s’est réduite sur l’ensemble du secteur, en particulier dans les apex des méandres (PK 57,5, 54
et 52), avec un maximum de -162,3 m au PK 54. L’érosion des
apex et la sédimentation sur les extrados aboutissent à une
Le secteur de correspondant au méandre (4) (fig. 10), en-
croissantes, Hooke, 1977). La connexion avec les chenaux de
bras dans la direction d’écoulement au PK 54.
tre les PK 49 et 44, est le seul qui n’a pas été rectifié à cause de
sa sinuosité peu élevée (Is=1.3). Stable à l’amont, il s’élargit de
1.84 m/an (16,56 % de la largeur initiale) à l’aval du PK 47.
Fig. 9 Evolution des
méandres Dunavat de Sus
et Dunavat de Jos entre
1970-2000
Fig. 10 Evolution de la
largeur du chenal 19702000 entre les PK 49-44,
méandre (4), (l’ordonnée
zéro représente les valeurs
1970)
36
Dans les méandres (5) et (6), recoupés par les chenaux
Dranov et Erenciuc (fig.11), le chenal est moins mobile (variations de largeur +/- 50 m, 17-18% de la largeur de 1970),
bien que les apex des méandres soient encore capables de
se déformer. Dans le détail, on observe une évolution en opposition de phase entre l’amont et l’aval : à l’amont (PK 41
et 34) le chenal ’élargit entre 1970 et 1980 (43 m et 65 m),
puis se rétrécit entre 1980 et 2000 (20 et 37 m) ; à l’aval (PK
29) la largeur diminue entre 1970-1980 (51 m), puis s’élargit
de 43 m.
(3) Le secteur peu sinueux, qui recoupe les cordons littoraux historiques progradants entre le PK 22 et l’embouchure.
Le méandre d’Ivancea (PK 22 à 16) est le dernier méandre,
situé à 19 km de l’embouchure. Il correspond à l’entrée du chenal dans le système des cordons littoraux sableux hérités qui le
limite vers le nord. Bien que recoupé par un chenal artificiel (chenal Ivancea), il est encore affecté par une mobilité latérale (extension des apex, PK 18,5 et 16). Son évolution est marqué par
une diminution de 10.4 m entre les années 1970-1980, puis une
augmentation de la largeur de 39.3 m entre 1980-1990 (après les
rectifications du méandre) et 5,8 m entre 1990-2000, fig.12.
Fig. 12 Evolution de la largeur du chenal 1970-2000 entre les PK 22-16
37
A l’aval de ce méandre, la morphologie apparente du bras
est très stable dans le temps et espace, ses variations de largeur ne dépassant pas +/-20 m. Son tracé est rectiligne, sans
doute contraint par la présence des cordons sableux de la
plaine maritime.
À partir du PK 5 la largeur du chenal a une évolution particulière. À l’embouchure le développement très rapide d’un
lobe deltaïque au cours du dernier siècle a influencé la mor-
phologie du chenal. La rive gauche reste stable, des modifications de la ligne de côte sont dues aux différents niveaux
énergétiques de la mer. La rive droite évolue en progradation
jusqu’à 1897 quand l’île de Sakhalin apparaît. À partir de cette
date la rive droite commence à reculer (fig.13, Giosan et al,
2003). Le recul du cordon littoral en formation Sakhalin vers
le continent fait que la rive droite du chenal du bras de Saint
George devient de plus en plus stable.
Fig. 13 Evolution du bras de Saint George à l’embouchure (Giosan et al, 2003). © Landsat 2000
38
Bilan de l’évolution morphologique
du bras de Saint-George, 1970-2000
(1) Variations de l’amplitude, de la longueur d’onde et de
la sinuosité des méandres (fig. 14). L’indice de sinuosité (L/λ,
L= longueur du thalweg entre deux inflexions de même sens,
λ= longueur d’onde) est élevé (entre 1.2 et 5.9), confirmant la
forte sinuosité du bras. Entre 1970 et 2000, il varie peu : stable
pour le premier et le dernier méandre, légèrement inférieur (0,1) pour les méandres 2 et 3, supérieur (+0,1) pour les méandres 4, 5 et 6.
L’amplitude des méandres va de 1030 m à 5510 m. Les
méandres 2, 3, 4, 5 sont peu déformés (±30 m), alors que
l’amplitude des méandres 1 et 6 diminue (– 70 m) ; seul le
méandre 7 est stable. La longueur d’onde de la plupart des
méandres est en diminution (-30 m pour 1, 3, 4, 5 ; -70 m pour
2 et 6), à l’exception du méandre 7 (+10 m).
Sur la base de la classification élaborée par Hooke (1977),
qui repose sur le mouvement des points d’inflexion et des
apex (i .e. les variations de l’amplitude et de la longueur d’onde), les méandres du bras de Saint George se caractérisent
par une extension et une expansion décroissantes. La mutation est la plus rapide sur les méandres 2 et 5, situés à l’amont
des deux systèmes doubles, recoupés respectivement par
les canaux de Dunavat de Sus et de Dranov. Le grand méandre de Murighiol présente la même tendance, mais sa taille
amortit l’amplitude des déformations. Seul le méandre aval
(7) présente une expansion croissante. La translation perpendiculaire sur l’axe du chenal est très faible en amont (PK 78,
Murighiol), plus importante à l’aval (méandres 3, 5, 6, 7). Sur
le méandre 7, elle est associée à une translation dans le sens
du courrant dans le chenal.
(2) Périmètre et superficie (fig. 15).
La longueur du périmètre s’accroît de 4 km en 30 ans,
soit de 2%. La surface mouillée reste quasi stable (diminution de 0,4 km2, soit 1,3%). Leurs valeurs augmentent entre
1970-1980, puis diminuent à partir de 1980. Les îles fluviales
apparaissent, puis croissent à partir des années 1980 (198090 - 0,19 km2 ; 1990-2000 - 0, 33 km2).
Fig. 14 Longueur d’onde, amplitude et sinuosité des méandres
du bras de Saint George
Fig. 15 Evolution du périmètre et de la superficie du chenal entre 1970-2000
39
Interprétation
Trois différents forçages décalés dans le temps entrent
en interaction : la construction des barrages hydro-électriques des Portes de Fer (1971-1984) réduit la charge solide ;
le recoupement artificiel des méandres en 1984-1988 ont
des effets contradictoires sur les débits liquides et les transformations de la diffluence amont du delta (Bras de Tulcea/
bras de Saint George et Sulina) dans les années 1980 qui ont
eu comme effet des modifications des distributions des débits liquides et solides entre les trois bras du Danube après
les rectifications des méandres du bras de Saint George. Ces
forçages ont un impact global sur la dynamique hydro-sédimentaire du bras de Saint-George, mais le recoupement des
méandres induit également des effets localisés sur les méandres et aux points de recoupement canaux-méandres.
Dès 1975 les barrages provoquent une réduction du
flux solide (fig. 2). A l’aval, le ralentissement du colmatage
de l’embouchure ainsi que l’amorce du recul du cordon de
Sakhaline confirme la précocité de cet impact. Le système
fluvial s’ajuste à ces changements : il se recharge en sédiments en érodant le chenal. Cette réponse est visible sur
la plupart des secteurs après 1980. Cette évolution morphologique se traduit, selon les cas, par une réduction de
la largeur moyenne du chenal (vraisemblablement corrélée
à une incision du fond) ou un élargissement (érosion des
berges en réponse au colmatage du fond du chenal). Ces
comportements contradictoires se succèdent sur le linéaire
: l’élargissement/colmatage est dominant à l’amont du bras,
dans la première partie du secteur 4, puis dans les méandres
5 et 6, alors que l’incision verticale caractérise le méandre de
Murighiol et l’aval du secteur 4. On peut faire l’hypothèse
d’un transit en relais de la charge de fond déstockée par
l’érosion du chenal, puis piégée dans les secteurs fluviaux
plus sinueux ou moins profonds. La mobilité des méandres
est réduite.
A partir de 1984, le recoupement des méandres provoque un accroissement du débit liquide moyen annuel qui
augmente la puissance fluviale et doit logiquement aboutir à une accentuation de l’évolution précédente. L’analyse
montre cependant que ce n’est pas toujours le cas : on peut
séparer les impacts globaux et locaux.
Globalement, la longueur d’onde et la sinuosité du système semblent se « figer », à l’exception de son extrémité
aval (méandre 7). La tendance générale est une réduction
de la longueur d’onde et de l’amplitude des méandres recoupés, traduisant une expansion-extension décroissante,
significative d’une perte d’énergie. La réduction des largeurs
(= incision), dominante dans les méandres amont (1, 2 et
3), contraste avec l’élargissement du chenal (= colmatage)
à partir du méandre 4 (fig. 7) : on peut faire l’hypothèse que
la charge de fond déstockée à l’amont est en cours de transit dans les méandres aval. Il est enfin difficile d’expliquer le
maintien d’une bonne mobilité dans le méandre recoupé 7,
à l’aval.
40
Dans le détail, les évolutions doivent être interprétées
en fonction des contextes locaux : amont/aval des canaux
de recoupement, méandres court-circuités. A l’amont du
système (PK 108-90, fig. 5), le chenal s’élargit progressivement entre 1970 et 2000 (à l’exception du PK 99) et une île
se développe à partir de 1990 : l’érosion des berges est donc
bien une réponse au colmatage du chenal. A partir du PK
91, très proche de l’entrée du canal de recoupement de Mahmudia, la réduction de la largeur du chenal pourrait correspondre à une incision par érosion régressive, induite par
l’accélération des vitesses du flux.
Dans le méandre recoupé de Murighiol, l’évolution morphologique traduit une réduction de l’énergie, de l’amont
(mobilité des apex, translation latérale au PK 78, forte réduction de largeur entre 1990 et 2000) vers l’aval (largeur stable,
apparition d’îles), qui s’explique par la captation d’une part
importante du débit liquide par le canal de recoupement.
Dans les méandres 5, 6 et 7, les variations alternativement positives/négatives de la largeur pourraient traduire
le transit de la charge de fond et le ré-ajustement du lit qui
l’accompagne. La translation des extrados démontre que
ces méandres bien qu’ils aient été recoupés, disposent encore d’une dynamique naturelle. Mais la vitesse d’extension
des apex s’est encore réduite depuis 1980. Enfin, dans les
zones de recoupement canaux-méandres, le chenal naturel
est déformé dans la direction de l’écoulement, témoignant
de l’énergie importante du flux liquide au débouché des canaux artificiels.
Ces observations sont conformes à celles de Ionita et
Radoane (1986). Mais elles ne recoupent pas systématiquement les données bibliographiques sur la dynamique des
méandres recoupés. Laczay (1977) confirme la variation rapide de la largeur des fleuves hongrois, alors que Matthes
(1947) montre la stabilité des méandres du Mississippi. Sur
la Wales, Thorne et Lewin (1979) démontrent que les recoupements favorisent le colmatage, la réduction de la mobilité
des méandres et l’élargissement dans les secteurs chenal
recoupé-méandre. Mais Mosley (1975) décrit une augmentation de la sinuosité du fleuve Bollin (Cheshire) après recoupement, comme Brice (1977) pour le Sacramento, où
l’augmentation de la sinuosité s’accompagne d’une réduction de la largeur du chenal. Enfin, pour Hickin (1983), les
coupures n’introduisent que des perturbations passagères
du système fluvial.
D’autres chercheurs ont fait des remarques sur l’incidence des rectifications avant et après (Lathrap, 1968), ou sur les
évolutions à long temps (300 ans sur le fleuve Klaralven par
Sundborg, 1956).
Les mutations du Danube apparaissent donc originales,
par la rapidité et l’ampleur des réponses morphologiques.
Ces particularités peuvent s’expliquer par la granulométrie
très fine des sédiments, à dominante limono-argileuses, y
compris sur les berges et les apex des méandres, qui est caractéristique du delta d’un très long fleuve médio-européen.
Elle confère une grande mobilité à la charge sédimentaire,
qui permet une réponse rapide du système fluvial au double
forçage des barrages et des recoupements de méandres.
Conclusion
Sur le bras méandriforme de Saint George, la réduction
des débits solides provoquée par les barrages, puis l’augmentation du débit liquide après le recoupement artificiel des
méandres, déterminent une augmentation globale progres-
sive de l’énergie fluviale. Ces forçages donnent naissance à un
mécanisme d’ajustement, qui tend vers un nouvel équilibre.
En diminuant la distance entre deux points d’un méandre, les
canaux de recoupement augmentent la puissance spécifique
à leur débouché, mais la réduisent sur le méandre recoupé. La
traduction morphologique (réduction de la longueur d’onde
et de l’amplitude des méandres, changement de la sinuosité
et de la largeur du chenal, colmatage ou incision) est variable
d’un point à un autre en fonction du contexte dynamique et
de la succession d’amont vers l’aval.
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RECENT DATA ON BENTHIC POPULATIONS FROM
HARD BOTTOM MUSSEL COMMUNITY IN THE
ROMANIAN BLACK SEA COASTAL ZONE
Adrian TEACĂ, Tatiana BEGUN, Marian -Traian GOMOIU
National Institute of Geology and Geoecology (GeoEcoMar), Constanta Branch,
304 Mamaia Blvd., 900581 Constanta, Romania
Tel/Fax: +40-241-69.03.66
Abstract. On the basis of the analysis of 27 samples collected by diving in 9 stations along the South Sector of the Romanian Black Sea coast, the authors
present the qualitative and quantitative state of the benthic community of the hard bottom mussels in the shallow waters. The study, carried out in mid
and upper-infralittoral in August 2001, reveals the occurrence of 68 species and 11 supraspecific taxa, with an average density of 750,000 indvs.m-2 and a
biomass of 16,500 g.m-2: Numerical dominants are represented by worms (~ 460,000 indvs.m-2) and crustaceans (~ 270,000 indvs.m-2), and the weight
dominants by mollusks – Mytilus galloprovincialis over 95% (~ 16,300 g.m-2) and crustaceans (~ 137 g.m-2). The general ecological state of the hard bottom mussel benthic community of the Romanian Black Sea coast in August 2001 can be considered satisfactory in comparison with the 1980s.
Keywords: hard substrate with mussel community, Black Sea, Romanian coast, macro- and meio-benthos
INTRODUCTION
The benthos researches of the Romanian Black Sea coast
have generally been focused on the sandy bottoms. There
are few studies that considered the holistic analysis of epibiont organisms due to numerous difficulties in collecting the
quantitative samples. The classic equipment for benthos
samplings is efficient only on sedimentary bottoms and only
a few dredges can collect samples from the hard bottom. In
addition to the researchers getting underwater with the help
of the self-contained diving suit, more detailed studies of the
stony areas of the benthos could be conducted through directly observing and collecting quantitative samples.
The first quantitative studies on the rocky bottoms associations of the Romanian Black Sea coast were published
more than 30 years ago (Băcescu et al., 1963, 1971; Gomoiu
et al., 1974, 1978; Ţigănuş, 1979). Until today, information has
actually remained limited, even though some studies of the
epibiont organisms, especially referring to fouling, have been
published.
Compared to the sandy bottoms, the rocky natural ones
occupy far less surface (0.3% of the total surface of the Romanian coast). These may be found only South of Constanta,
being represented by a discontinuous band of submerged
rocky platforms, interrupted by sandy beaches.
The shortage of rocky bottom was compensated for by
the construction of protective coastal dams in the ’70s-’80s,
which could be likened to artificial reefs (Gomoiu, 1986,1997).
The ecological implications of these water structures have
been both positive and negative, even if the shore protective
role, for which they were built, proved to be minor and sometimes adverse. The benthic communities grown on the artificial rocky bottoms, similar to the natural stony ones, have
a great importance in the ecology of this sector in spite of
the limited expansion of the habitat. This is partly due to their
qualitative and quantitative abundance and partly to the result of their coenotic structure (Gomoiu et al., 1981; Gomoiu,
1986).
The most important function of the associated fauna is
to be a vast natural water filter. In most cases, the sessile
organisms (mainly in terms of stability and abundance, in
the hard bottom biocenosis) are very efficient filtering species, and this has major consequences on the surrounding
environment.
43
A. Teacă, T. Begun, M.T. Gomoiu - Recent data on benthic populations from hard bottom Mussel Community in the Romanian Black Sea coastal zone
The nature of the substratum encourages the settlement
and domination of microbenthic sessile and vagile species,
the majority being mass species with a large density per unit
area, which indicates the maturity of an epibiont system. The
macrobenthic dominant species in this biocenosis, such as
Mytilus, Mytilaster and Balanus, act as a secondary bottom
with many gaps and anfractuosities, forming an array of niches and microhabitats.
The rocky bottom tends to be very complex both as a
result of its shallow depth and because of the pronounced
hydrodynamism, which leads to a resedimentation of suspended and organic matter.
MATERIAL AND METHODS
In order to analyze the benthic fauna related to the biocenosis of stone mussels from shallow waters, 27 quantitative
samples were taken by free diving during August 2001, from
9 stations along the Romanian Black Sea coast between Midia
Cape Dam and the coastal sector 2 Mai – Vama Veche:
• Station 1 – (CM) Midia Cape sea wall,
• Station 2 – (MC) The sea wall in line with “Casino” Mamaia
Hotel Complex,
• Station 3 – (PM) Pescarie Mamaia sea wall,
• Station 4 – (TC) Tataia beach (Constanta) sea wall,
• Station 5 – (MD) “Modern” beach (Constanta) sea wall,
• Station 6 – (AG) Agigea sea wall,
• Station 7 – (EN) Eforie Nord sea wall,
• Station 8 – (2M) the sea wall near the 2 Mai fishery,
• Station 9 – (MV) natural rocky bottoms from 2 Mai - Vama
Veche, in the neighborhood of the meteorological station.
Three samples were taken from each station at three different depths (0, 1m, 2m) by scraping out the epibiosis from an
area of 400 cm2 with the help of a 20 cm long knife. The knife
blade served jointly as a measuring reference for scraping a 20
x 20 cm square. The scrape areas were chosen at random. The
scraped biological samples were stored in a classic net (only
permeable to water); its hatch would close through a binder in
order to prevent the loss of the samples in the water.
The samples’ fixation was carried out differentially. The
larger organisms (mostly bivalves) were preserved in 5 - 6
% neutralized formaldehyde in sea water; vagile micro- and
macrobenthic fauna after being separated, were preserved in
80 % alcohol.
The taxonomic identification was performed in its totality
for the higher taxa and partially for genera and species.
Analytic ecological indexes and current indexes of biodiversity were used for the statistical processing of the results
obtained from the triage.
RESULTS AND DISCUSSIONS
General situation. Benthic communities of the
shallow waters in 2001
In terms of space, the rocky bottom of the Romanian littoral belongs to the medio- and infralittoral (upper and inferior), which is populated by a single authentic biocenosis
Mytilus galloprovincialis or the stone mussels biocenosis,
with a series of varieties depending on the depth.
After analyzing the samples, several aspects of quantitative and qualitative parameters were clarified concerning
the benthic fauna of shallow waters stone mussels. 18 supraspecific taxonomic groups were identified comprising 79
taxa. Among them, 15 (75%) are common to all 9 sampling
stations. The other 3 groups (25%) Spongia, Tanaidacea and
Tunicata are dominant in other well-defined locations in the
Southern part of the littoral. Excluding the organisms identified at the group level (Nemertini, Nematoda, Oligochaeta,
Harpacticoida, Insecta) and other species from the rest of the
groups (Turbellaria, Nemertini, Polychaeta, Halacarida, larvae), there were 68 taxa identified as species/genera.
The analysis of populations’ structure by supra-specific
taxonomic groups indicates that the qualitative differences
among the three depth levels (0, 1, 2m) are much reduced;
even if the biological diversity is slightly richer at the depth
of 2m, it does not differ basically from 0m and 1m, the most
dominant forms remaining the same (Table 1).
Table 1 Populations’ structure by supra-specific taxonomic groups
Taxa group
Spongia
Coelenterata
Turbellaria
Nemertini
Nematoda
Polychaeta
Oligochaeta
Mollusca
Halacarida
0
2
3+
2+
+
16+
+
3
1+
Depth (m)
1
1
2
3+
2+
+
18+
+
5
1+
Taxa group
2
2
2
3+
2+
+
20+
+
5
1+
Cirripedia
Ostracoda
Copepoda
Amphipoda
Isopoda
Tanaidacea
Decapoda
Insecta
Tunicata
0
1
5
+
10
4
2
2
+
-
Depth (m)
1
1
5
+
12
4
2
4
+
1
2
1
5
+
14
4
2
6
+
1
Note: The figures represent the number of taxa identified; + shows that some taxonomic group is present in the samples; shows absence of any taxonomic group in samples
44
The real diversity according to the number of species
shows a slight boost in the Southern locations, especially
for the benthic macrofauna (~ 45 species) compared to the
approximately 30 species from other locations. This development of specific biodiversity in the Southern littoral is justified by the stability of physical and chemical properties of
the water and the high heterogeneity of habitats (artificial
rocky bottom, natural rocky bottom, extensive algae fields,
coarse-grained sandy bottoms mixed with debris and sandy
enclaves among the rocky bottom) etc. (Fig. 1).
Depending on quantity, the numerical density and the biomass of the main epibiont invertebrate groups (Spongia, Coelenterata, Vermes, Mollusca, Crustacea, Halacarida, Insecta, Tunicata) fluctuated significantly in the analyzed coastal area. The
average density calculated at depths for each station is about
750,000 indvs.m-2 with an average biomass of approximately
16,500 g.m-2. In each of the dominant cases according to density
values, there were worms (~460,000 indvs.m-2) and crustaceans
(~270,000 indvs.m-2), followed by mollusks (5,500 indvs.m-2),
Halacarida (5,000 indvs.m-2), insects (3,000 indvs.m-2), Coelenterates (180 indvs.m-2), sponges and tunicates (Fig. 2).
Fig. 1 Variation of macro – and meiobenthic number of species
in the biocenosis of the stone mussels from the shallow waters of
the coast between Midia Cape – Navodari and Vama Veche, 2001
Fig. 2 Variation of average density (DAVG) and biomass (BAVG) of
the main groups of epibiontic organisms depending on the depth
of the Romanian littoral in 2001
The previous statistics are completely different from those
showing the average biomass values where mollusks are the
dominant species (~ 16,300 g.m-2), followed by crustaceans
(137 g.m-2), Coelenterates and sponges (26 g.m-2), and worms
(13 g.m-2). Halacarida, insects and tunicates make up an insignificant biomass of below 1 g.m-2.
along the Southern littoral (stations Agigea, 2 Mai, Vama
Veche). The factors influencing this increase are the cumulative particular biotic and abiotic conditions at the Southern
end of the Romanian coast, where some meio- and macrobenthic communities exhibit a greater variety of species
and higher quantitative parameters per unit area (Fig. 3).
Regarding density values, 10 taxa are dominant, making
up 96.6 % of the whole, of which only two, Nematoda and
Harpacticoida form 92.32 % of the total average densities.
The dominant taxa with average density values are: Nematoda, Harpacticoida, Cirripedia (Balanus improvisus), Halacarida (Rhombognathus sp.), Polydora ciliata, Mytilus galloprovincialis, Grubea clavata, Echinogammarus olivii, larvae of
Chironomida and ostracod - Xestoleberis decipiens. Biomasses
are dominant in the ratio of 95.85% of just a single species
– Mytillus galloprovincialis, followed by 9 macrobenthic species:
Mytilaster lineatus, Balanus improvisus, Actinia equina, Rhithropanopeus harrisi, Idotea baltica, Sphaeroma pulchellum, Echinogammarus olivii, Melita palmata and Platynereis dumerilii
(APPENDIX I).
A slight decrease in the average biomass of the sessile
macrofauna was observed in the more Southern locations.
This is essentially due to the nature of substratum (natural
calcareous), bottom relief (Sarmatian calcareous shelf ), and
the main orientation with regard to the direction of the prevailing winds coming from the Eastern and North-Eastern
regions, directly influencing aspect to the optimal areas for
sessile malacofauna growth. As a result, due to a lack of suitable areas (stones, grottos, niches, safe areas) for the growth
of sessile species which are weight dominant, of polistratification of bivalves’ colonies, as well as the substratum fragility
(Sarmatian limestone), the biomass average values are lower
than those for the artificial rocky bottom of safe areas. This is
valid only for the shallow waters near the coast (Fig. 4). With
the exception of mollusks, crustaceans represent the weight
dominant group, with 78% of the total biomass being zoobenthos (Fig. 5).
With an eye on the variation of average density and biomass of vagile meio- and macrofauna from one station to
the other, show that the number and weight values increase
45
Fig. 3 Variation of average density (DAVG) of the macro – and
meiobenthic epibiontic organisms in the shallow waters of the
Romanian Black Sea coast, 2001
Fig. 4 Variation of average biomass (BAVG) of the macro – and
meiobenthic epibiontic organisms in the shallow waters of the
Romanian Black Sea coast, 2001
Fig. 5 Average biomass (BAVG) of the main groups of epibiontic organisms (excepting mollusks) in the Romanian Black Sea coast, 2001
Fig. 6 Average density (DAVG) of the main groups of epibiontic organisms in the Romanian Black Sea coast, 2001
The average density variation of the main groups of organisms shows three numerical heights in the different stations (Casino Pescarie Mamaia, Agigea and 2 Mai). Thus, the
total average density for all stations, concerning the meioand macrobenthic worms, is 61% of the total density of zoobenthos (Fig. 6). Among these, Nematoda and Polychaeta
are the most abundant with an average percentage of 92.5%
for all stations, and Turbellariata, Nemertina and Oligochaeta
with just 7.5% of the total density of zoobenthos. There are
6 species of Polichaeta that are constantly dominant for all
three depths: Polydora ciliata, Grubea clavata, Sphaerosyllis
bulbosa, Fabricia sabella, Platynereis dumerilii and Neanthes
succinea, where basically, the first 4 are small-sized species
with a high ecological plasticity index. Turbellaria has a clear
demarcation in the distribution of its three dominant species,
where Leptoplana tremellaris and Stylochus tauricus are the
most common species in the rocky infralittoral. Convoluta
convoluta shows a high affinity only for natural rocky bottom
in the Southern point of the littoral.
heights, more or less broad, at Casino Mamaia, Agigea and
2 Mai-Vama Veche, in all stations having an average of 37%
of the total zoobenthos density (Fig. 6). Cirripeda, Ostracoda,
and Amphipoda have almost identical values for all stations
(≥10 000 ind.m-2) with a growing development towards the
southern littoral (Fig. 7).
The average density variation of the main groups of
meio- and macrobenthic crustaceans shows three numerical
46
The largest fluctuations are registered for macrobenthic
crustaceans such as Isopoda, Decapoda and Tanaidaceea due
to the pronounced algal blooming phenomenon from 2001.
After an analysis of the populations’ structure in supra-specific taxonomic groups, we witness that the numerical and
weight variables of the epibiont fauna have been seriously
influenced by this phenomenon.
Thus, it was evident that there was migration of macrobenthic forms (Decapoda, Isopoda, Amphipoda) from the
deeper levels towards the sub-superficial level, where the
oxic conditions allow their survival. At more than 2 meters
depth, the epibiont system would be seriously affected by
the algal blooming causing a mass mortality of mollusks and
other sessile species. A drastic decrease was noted in the
number of worms from the structure of the epibiont system.
crustaceans; the vagile and sessile macrofauna (Cirripedia,
Amphipoda, Isopoda, Tanaidacea and Decapoda), represented mainly by 12 taxa: Balanus improvisus, Echinogammarus
olivii, Microdeutopus gryllotalpa, Idotea baltica, Corophium
bonelli, Sphaeroma pulchellum, Stenothoe monoculoides, Hyale perieri, Naesa bidentata, Melita palmata, Jaera nordmanni
and Amphithoe vaillanti, forms only 8%.
the main groups of epibiontic organisms in the Romanian Black
Sea coast, 2001
The juveniles were practically absent. The multi-specific algal
blooming phenomenon due to the effect of the heat and
predominance of North and North-East marine circulation
caused an increase in the water temperature up to 26-28°C
and a salinity of less than 10 ‰.
All these conditions influenced an expansive development of diatoms such as: Leptocylindrus danicus, Cerataulina
pelagica and the dinoflagellate Prorocentrum minimum, the
latter being known for the huge algal blooming followed by
mass mortalities of organisms in the period between 19701980 and beginning of the 1990s. During this period, decreases of O2 were recorded in the littoral waters up to 4.96
cm3 l-1 and even 2.61 cm3 l-1; as a result of this phenomenon
the saturability decreased to 47.5%, which resulted in a mass
mortality of benthic-nektonic and benthic organisms.
The surprisingly low values of the Decapoda in certain
locations (e.g. Agigea), where they should have been present
in considerable densities, are a consequence of the predominance of the crabs Rhithropanopeus harrisi and Pilumnus
hirtellus in the north and in some southern stations. Among
these, Rhithropanopeus harrisi has simply invaded the epibiont communities without any restriction in the last 10 years.
Nevertheless, it does not mean that there is a qualitative decline of reptant decapodes on the Romanian seashore; proof
of this is the signalization of some rare listed species such as
Pisidia longicornis, which was found in large numbers at Agigea, and Eriphia verrucosa, found at 2 Mai – Vama Veche.
The biomasses generally follow the same tendencies
only for the meiobenthic forms; the biomass mainly consists
of worms (1.96 g.m-2), followed by crustaceans – juveniles of
amphipods, copepods and ostracods (1.62 g.m-2). As for macrobenthic forms, the majority of biomass invariably consists
of mollusks (over 16,000 g.m-2) and crustaceans (approximately 135.7 g.m-2).
The meiobenthic forms, represented by copepods (Harpacticoida) and ostracods (mainly Xestoleberis decipiens and
X. aurantia acutipenis), form 92% of the total abundance of
The general variation in zoobenthos density shows a
positive linear function along with the depth increase (R2=
0.6937). However, the existence of an increased correlation
between the ecological indexes of associated zoobenthos
and the increase of depth, due to the relative proximity of
vertical collection points (0, 1m, 2m) cannot be confirmed.
In general the upper zones (mediolittoral, superior infralittoral) are characterized by a relative qualitative homogeneity
of faunistic composition due to the proximity to the water
surface and the assembly of abiotic factors, which equally affect this shallow-water zone by selecting populations with a
more or less uniform distribution. However, even in this case
we may observe the existence of increased linear correlations
for certain groups, mostly reflecting a natural reality, which
can be justified ecologically.
Thereby, two of the four major groups (Mollusca, Varia)
record a diminution in the number of populations as depth
increases, and Crustacea and Vermes exhibit a conspicuous
increase. There is an explanation in the case of the mollusks,
where larvae of mussels and Mytilaster may find available surfaces for settlement and avoid the competitive interactions
with the adult forms from the upper zone of 0m, where free
surfaces, which are suitable for being populated by bivalves’
larvae, have been cleared due to periodically pronounced
hydrodynamism. Thus, we are witnessing a massive colonization of the wave breaking and run-up band with small-sized
forms, mainly less than 20mm; recordings also show increased
mass density in the superior zones compared to the sub-superficial. These colonies become more stable temporally and
spatially with the depth increase, and are able to resist certain
bad weather conditions and translocations, with a smaller
number of individuals per unit area but with a far bigger size.
This spatial endurance and dominance is preserved up to a
critical depth when the populations become more sporadic,
frequently clogged up because other factors encourage certain epibiont associations to establish themselves, and the
means through which they are realized.
The increase in the number of individuals per unit area
is compensated by the multilayered structure of the mussel colonies. This strategy, which solves the lack of available
areas, is practically absent in the 0m upper zone. There are
some exceptions depending on the orientation of areas with
the prevailing currents (exposed areas – protected areas). The
main factor that prevents mussels from forming beds is hydrodynamism and emersion for a long time permitting the
establishment of bivalves for no more than two layers. This
condition and all the hydrometeorological and hydrodynam-
47
ic activity, specific to shallow waters, result in an eloquent selection of associated fauna.
Varia, which is composed of Spongia, Coelenterata, Halacarida, Insecta and Tunicata, records an insignificant reduction in the number of populations with a more marked difference in depth, yet for the species associated with the algae
fields and those favoring highly saturated oxic conditions.
Thus, the abundance of coelenterates (especially Actinia equina) and tunicates (Botryllus schlosseri) will decline with depth
because they prefer shallow waters and optimal oxic conditions. As for halacarids (Rhombognathus sp.) and insects,
their preference is for thickets of algal macrophyte (especially
for the genera Ceramium and Cladophora), which obviously
record the highest densities in well-lighted shallow waters.
The above theories are valid only for the artificial hard
substratum represented by the hydrotechnical coastal protection structures. The situation differs somewhat for the natural substratum due to the interference of other factors that
regulate the distribution of these respective groups.
The numerical increase of the crustaceans and worms is
due to the accentuated diversity of habitats and the abundance of trophic resources in particular for detritivorous
forms (these represent the majority for the qualitative composition of the two groups).
By analyzing the frequency of taxa in the shallow-water
biocenosis of Mytillus galloprovincialis, it was discovered that
the following species were recorded in the summer season
of 2001:
• 13 euconstant species (F – 75.1-100%): Nematoda, Grubea clavata, Platynereis dumerilii, Polydora ciliata, Sphaerosyllis bulbosa, Mytilus galloprovincialis, Rhombognathus
sp., Balanus improvisus, Harpacticoida, Echinogammarus
olivii, Melita palmata, Idotea baltica, Sphaeroma pulchellum (APPENDIX I).
• 14 constant species (F – 50.1-75%): Actinia equina, Leptoplana tremellaris, Nemertini varia, Neanthes succinea,
Nerine cirratulus, Spio filicornis, Oligochaeta, Xestoleberis
decipiens, Amphithoe vaillanti, Hyale perieri, Microdeutopus gryllotalpa, Jaera nordmanni, Rhithropanopeus harrisi,
Insecta (APPENDIX I).
• 20 accessory species (F – 25.1-50.0%);
• 32 accidental species (F-1.0-25%).
With reference to the euconstant and constant species, it
was observed that there are 12 species of crustaceans (44.4%)
and 11 species of worms (40.7%), which are dominant on locations and depth. The mollusks (1 sp.) and varia (Coelenterata, Halacarida, Insecta – 3 sp.) are qualitatively more homogenous.
Thus, the qualitative diversity of the shallow-water epibiont populations is dominated by the crustaceans and worms
that include over 20 euconstant species forming a mature
epibiont system. Taking weight into consideration, the epibiont associations have always been dominated by the big48
sized sessile malacological fauna, represented by Mytilus galloprovincialis and Mytilaster lineatus. The function of mollusks
in the shallow-water upper zone consists in the complication
of primary substratum and the creation of microhabitats for
the vagile forms (meio-, macrobenthic) among the byssus filaments, which retain most of the water-mass-driven organic
and mineral suspensions.
The random spreading characteristic of benthic organisms and the abundance-related variations of quantitative
values are more representative in the southern locations (Agigea, 2 Mai, Vama Veche). The richness of associated populations here is dependent on the heterogeneity of substratum
conditions and the multitude of biotopes compared to a
more homogenous substratum and a qualitatively depleted
fauna in the northern locations (Mamaia, Constanta). Yet, the
abundance of the northern sectors’ populations records high
values of average densities due to the meiobenthic faunistic
sector, compensating for the small macrobenthic component
present within these locations.
CONCLUSIONS
The results of the ecological analysis of the shallow-water
epibiont populations (0-2m), of the littoral sector between
Midia Cape and 2 Mai – Vama Veche, in 2001, enabled us to
highlight the following general conclusions:
The qualitative structure of shallow-water hard-substratum associated meio- and macrofauna is formed of 18 major
taxonomic groups with a total number of 79 taxa, and the total number of identified species/genera-level taxa is 68.
The average abundance of the populations developed on
the analyzed artificial substrata varies around 750,000 indvs.
m-2 with a total average biomass of 16,500 g.m-2. The numerical dominants are represented by worms (~ 460,000 indvs.
m-2) and crustaceans (~ 270,000 indvs.m-2), and the weight
variables are dominated by mollusks (~ 16,300 g.m-2) and
crustaceans (~ 137 g.m-2).
The most important role in establishing the density
dominants is played by Nematoda and Copepoda in a ratio of
92.32% of the total average densities.
The biomasses are dominated in a ratio of 95.48% by
Mytilus galloprovincialis species followed by 2 macro-zoobenthic species, Mytilaster lineatus and Balanus improvisus.
The qualitative analysis on the euconstant (13 sp.) and
constant species (14 sp.) indicates that the location and
depth dominants are taken by crustaceans (12 sp.) (44.4%)
and worms (11 sp.) (40.7%).
The analysis of populations’ structure on supra-specific
taxonomic groups shows that the qualitative differences
among the three levels of depth (0, 1, 2m) are very reduced,
and the biodiversity, slightly higher at the depth of 2 m, does
not basically differ from 0m and 1m, while keeping the same
main forms.
APPENDIX I
General characteristics of the benthic populations recorded AT the Romanian littoral, 2001
No.
Taxa
F%
DAVG
1
Dysidea fragilis
3.7
2
Halichondria panicea
3
Eudendrium ramosum
4
Actinia equina
70.4
5
Convoluta convoluta
22.2
6
Leptoplana tremellaris
7
Stylochus tauricus
8
Turbellaria varia
9
Nematoda
10
Emplectonema gracile
14.8
23.7
11
Tetrastemma sp.
48.1
12
Nemertini varia
59.3
13
Grubea clavata
14
Grubea limbata
15
Grubea tenuicirrata
29.6
16
Fabricia sabella
48.1
17
Harmothoe reticulata
25.9
38.9
18
Hediste diversicolor
3.7
0.9
19
Perinereis cultrifera
14.8
20
Phylodoce tuberculata
11.1
21
Platynereis dumerilii
22
23
DECO
DD%
WD
RkD
BAVG
BECO
DB%
WB
RkB
0.9
25.0
0.000
0.02
75
2.31
62.50
0.014
0.23
39
7.4
1.9
25.0
0.000
0.04
72
4.63
62.50
0.028
0.46
24
25.9
13.9
53.6
0.002
0.22
57
1.11
4.29
0.007
0.42
25
171.3
243.4
0.023
1.27
32
17.74
25.21
0.108
2.75
4
610.2
2745.8
0.082
1.35
29
0.06
0.27
0.000
0.09
52
74.1
1375.0
1856.3
0.185
3.70
14
1.65
2.23
0.010
0.86
16
44.4
115.8
260.6
0.016
0.83
41
0.17
0.39
0.001
0.22
40
48.1
145.4
301.9
0.020
0.97
38
0.01
0.01
0.000
0.04
64
100.0 442481.5 442481.5
59.37
77.05
1
0.75
0.75
0.005
0.68
20
160.0
0.003
0.22
58
0.47
3.20
0.003
0.21
41
250.0
519.2
0.034
1.27
33
0.75
1.56
0.005
0.47
23
204.6
345.3
0.027
1.28
31
0.41
0.69
0.002
0.38
30
92.6
2732.8
2951.4
0.367
5.83
7
0.27
0.30
0.002
0.39
28
33.3
213.9
641.7
0.029
0.98
37
0.06
0.19
0.000
0.11
50
125.9
425.0
0.017
0.71
46
0.04
0.13
0.000
0.08
53
1250.0
2596.2
0.168
2.84
20
0.10
0.21
0.001
0.17
44
150.0
0.005
0.37
52
0.02
0.09
0.000
0.06
57
25.0
0.0001
0.02
76
0.06
1.75
0.000
0.04
67
6.5
43.8
0.001
0.11
64
0.03
0.22
0.000
0.05
60
6.5
58.3
0.001
0.10
68
0.02
0.20
0.000
0.04
66
81.5
484.3
594.3
0.065
2.30
23
4.12
5.05
0.025
1.43
10
Polydora ciliata
96.3
4492.6
4665.3
0.603
7.62
5
0.76
0.79
0.005
0.67
21
Pygospio elegans
14.8
5.6
37.5
0.001
0.11
67
0.00
0.00
0.000
0.01
78
24
Neanthes succinea
59.3
403.7
681.3
0.054
1.79
28
2.06
3.47
0.012
0.86
17
25
Nerilla antennata
25.9
34.3
132.1
0.005
0.35
53
0.02
0.08
0.000
0.06
58
26
Nerine cirratulus
51.9
102.8
198.2
0.014
0.85
40
0.02
0.04
0.000
0.08
54
27
Notomastus lineatus
3.7
3.7
100.0
0.0005
0.04
73
0.01
0.21
0.000
0.01
73
28
Scolelepis ciliata
48.1
158.3
328.8
0.021
1.01
36
0.05
0.10
0.000
0.12
49
29
Sphaerosyllis bulbosa
81.5
1165.7
1430.7
0.156
3.57
15
0.93
1.14
0.006
0.68
19
30
Sphaerosyllis hystrix
14.8
23.0
155.0
0.003
0.21
59
0.02
0.12
0.000
0.04
65
31
Spio filicornis
51.9
209.3
403.6
0.028
1.21
34
0.06
0.12
0.000
0.14
47
32
Syllis prolifera
14.8
34.3
231.3
0.005
0.26
55
0.03
0.19
0.000
0.05
61
33
Polychaeta larvae
3.7
138.9
3750.0
0.019
0.26
54
0.01
0.15
0.000
0.01
75
34
Polychaeta varia
14.8
8.3
56.3
0.001
0.13
63
0.01
0.03
0.000
0.02
71
35
Oligochaeta
70.4
1057.4
1502.6
0.142
3.16
18
0.21
0.30
0.001
0.30
36
36
Middendorfia caprearum
29.6
446.3
1506.3
0.060
1.33
30
2.39
8.06
0.014
0.65
22
37
Tergipes tergipes
7.4
7.4
100.0
0.001
0.09
70
0.001
0.02
0.000
0.01
77
38
Cyclope donovani
3.7
0.6
15.0
0.0001
0.02
77
0.27
7.42
0.002
0.08
55
39
Mytilaster lineatus
40
Mytilus galloprovincialis
41
42
43
Balanus improvisus
33.3
888.0
2663.9
0.119
1.99
27
504.78
1514.4
3.059
10.10
2
100.0
4143.2
4143.2
0.556
7.46
6
15817.6
15818
95.85
97.91
1
Rhombognathus sp.
96.3
4906.5
5095.2
0.658
7.96
4
0.05
0.05
0.000
0.17
45
Hallacarida varia
33.3
303.7
911.1
0.041
1.17
35
0.003
0.01
0.000
0.02
70
100.0
7091.7
7091.7
0.952
9.75
3
71.01
71.01
0.430
6.56
3
49
No.
Taxa
F%
DAVG
DECO
DD%
WD
RkD
BAVG
BECO
DB%
WB
RkB
44
Cyprideis littoralis
22.2
72.2
325.0
0.010
0.46
51
0.005
0.02
0.000
0.03
69
45
Cytherois valkanovi
11.1
18.5
166.7
0.002
0.17
60
0.001
0.01
0.000
0.01
76
46
Paradoxostoma
intermedium
22.2
273.1
1229.2
0.037
0.90
39
0.02
0.08
0.000
0.05
62
47
Xestoleberis aurantia
acutipenis
40.7
2202.8
5406.8
0.296
3.47
16
0.14
0.35
0.001
0.19
42
48
Xestoleberis decipiens
55.6
3376.9
6078.3
0.453
5.02
10
0.22
0.40
0.001
0.27
37
49
Harpacticoida
100.0 245555.6 245555.6
32.95
57.40
2
1.23
1.23
0.007
0.86
15
50
Amphitoe vaillanti
70.4
505.6
718.4
0.068
2.18
25
2.02
2.87
0.012
0.93
13
51
Apherusa bispinosa
18.5
241.7
1305.0
0.032
0.77
45
0.24
1.31
0.001
0.16
46
52
Caprella acanthifera
7.4
12.0
162.5
0.002
0.11
65
0.02
0.29
0.000
0.03
68
53
Corophium bonelli
37.0
1373.1
3707.5
0.184
2.61
22
0.55
1.48
0.003
0.35
35
54
Erichthonius difformis
3.7
18.5
500.0
0.002
0.10
69
0.02
0.45
0.000
0.02
72
55
Gammarus aequicauda
40.7
125.0
306.7
0.017
0.83
43
0.62
1.53
0.004
0.39
27
56
Echinogammarus olivii
88.9
2563.9
2884.4
0.344
5.53
8
7.35
8.27
0.045
1.99
8
57
Hyale pontica
22.2
158.9
715.0
0.021
0.69
47
0.40
1.79
0.002
0.23
38
58
Hyale perieri
74.1
1075.7
1452.2
0.144
3.27
17
2.34
3.16
0.014
1.03
11
59
Jassa ocia
14.8
160.2
1081.3
0.021
0.56
48
0.14
0.97
0.001
0.11
51
60
Melita palmata
85.2
673.1
790.2
0.090
2.77
21
4.04
4.74
0.024
1.44
9
61
Microdeutopus gryllotalpa
74.1
1728.3
2333.3
0.232
4.14
12
1.36
1.83
0.008
0.78
18
62
Nototropis guttatus
7.4
51.9
700.0
0.007
0.23
56
0.09
1.26
0.001
0.06
56
63
Stenothoe monoculoides
48.1
1261.1
2619.2
0.169
2.85
19
0.55
1.14
0.003
0.40
26
64
Amphipoda juv.
3.7
48.1
1300.0
0.006
0.15
61
0.002
0.05
0.000
0.01
79
65
Jaera nordmanni
51.9
670.3
1292.7
0.090
2.16
26
0.48
0.92
0.003
0.39
29
66
Idotea baltica
96.3
1501.4
1559.2
0.201
4.40
11
9.01
9.35
0.055
2.29
6
67
Naesa bidentata
40.7
915.7
2247.7
0.123
2.24
24
3.07
7.53
0.019
0.87
14
68
Sphaeroma pulchellum
96.3
1269.5
1318.3
0.170
4.05
13
8.29
8.61
0.050
2.20
7
69
Leptochelia savignyi
22.2
73.1
329.2
0.010
0.47
50
0.22
0.99
0.001
0.17
43
70
Tanais cavolini
22.2
230.6
1037.5
0.031
0.83
42
0.92
4.15
0.006
0.35
34
71
Palaemon elegans
18.5
4.8
26.0
0.001
0.11
66
1.25
6.76
0.008
0.37
31
72
Eriphia verrucosa
3.7
0.0
1.0
0.000
0.00
78
0.69
18.58
0.004
0.12
48
73
Pachygrapsus marmoratus
22.2
2.0
9.2
0.0003
0.08
71
1.02
4.58
0.006
0.37
32
74
Pilumnus hirtellus
33.3
4.4
13.2
0.001
0.14
62
5.11
15.34
0.031
1.02
12
75
Pisidia longicornis
3.7
1.3
35.0
0.0002
0.03
74
0.01
0.17
0.000
0.01
74
76
Rhithropanopeus
harrisi
70.4
29.6
42.1
0.004
0.53
49
14.81
21.05
0.090
2.51
5
77
Larvae megalope
33.3
150.9
452.8
0.020
0.82
44
0.02
0.05
0.000
0.06
59
78
Chironomida larvae
74.1
3021.3
4078.8
0.405
5.48
9
0.30
0.41
0.002
0.37
33
79
Botryllus shlosseri
3.7
0.0
1.0
0.000
0.004
79
0.09
2.50
0.001
0.05
63
Taxa
Vermes
Mollusca
5485
Crustacea
273442
Varia
8419
10433
1.13
Total
745250.3
100
50
Numerical abundance
DAVG
DECO
DD%
457904
469829
Weight
BAVG
61.44
8428
0.74
294793
36.69
13.19
BECO
DB%
24.00
0.08
16325
17347
98.93
137.27
202.33
0.83
26.24
157.46
0.16
16501.7
100
REFERENCES
Băcescu, M., Dumitrescu, E., Marcus, A., Paladian, G., Mayer, R., 1963 – Donnees quantitatives sur la faune petricole de la Mer Noire a Agigea
(secteur roumain) dans les conditions speciales de l’annee 1961,
Trav. Mus. Hist. Nat. “Gr. Antipa”, Bucureşti, 4: 131-155
Băcescu, M., Müller, G.I., Gomoiu, M.-T., 1971 – Cercetări de ecologie
bentală în Marea Neagră (analiza cantitativă, calitativă şi comparată a faunei bentale pontice), Ecologie marină, Ed. Acad., Bucureşti, 4: 357
Gomoiu, M.-T., Ţigănuş, V., 1974 – Contributions to the knowledge of the
fouling on the Romanian maritime ships, Cercetări marine, IRCM
Constanţa, 7: 83-112
Gomoiu, M.-T., Ţigănuş, V., Bondar, C., 1978 – Date privind formarea foulingului în apele de larg ale Mării Negre, Al VIII-lea Simpoz. Biodeter. Climat., Braşov: 375-380
Gomoiu, M.-T., Ţigănuş, V., 1981 – Structure qualitative et quantitative
des salissures formees dans les eaux du large de la Mer Noire,
Rapp. Comm. Int. Mer Medit., CIESM., Monaco, 27, 2: 185-184
Gomoiu, M.-T., 1986 – Donnees preliminaires sur la structure et le role
d’une communaute epibionte formee sur le substrat artificiel,
Rapp. Comm. Int. Mer Medit., CIESM., Monaco, 30,2: 17
Gomoiu, M.-T., 1986 – Importanţa construirii de recifi artificiali pentru
dezvoltarea mariculturii în zone deschise ale Mării Negre, Probleme de maricultură, IRCM Constanţa: 163-174
Gomoiu, M.-T., 1997 – Recifi artificiali la litoralul românesc. An. Univ.
„Ovidius” Constanţa, Seria Biologie-Ecologie, I (1): 159-174
Ţigănuş, V., 1979 – Observations sur la structure qualitative et quantitative de la biocenose des moules de rocher du littoral roumain
de la Mer Noire, Rapp. Comm. Int. Mer Medit., CIESM., Monaco,
25(26):159–160
51
THE PRESENT STATE OF THE EPIBIONTIC POPULATIONS
TO THE BIOCENOSIS OF STONE MUSSELS IN THE
SHALLOW WATER OFF THE ROMANIAN
BLACK SEA COAST
Adrian TEACĂ (1), Tatiana BEGUN (1), Marian -Traian GOMOIU (1), Gabriela-Mihaela PARASCHIV(2)
(1) National Institute of Geology and Geo-ecology – GeoEcoMar, Constanta Branch, 304 Mamaia Blvd, 8700 Constanta, Romania
(2) Department of Natural Sciences, The Ovidius University of Constanţa, Constanţa, 8700, Romania
Abstract. This paper presents observations and ecological analyses of benthic community of the hard bottom mussels in the shallow waters. This study is
based on the analysis of 21 quantitative biological samples collected by diving at 7 stations in two zones along the Romanian Black Sea Coast – Mamaia and
Mangalia in 2003. The study attempts to pinpoint some aspects related to defining and adopting the term of “littoral cell” and to highlight the possible differences between the epibiontic communities developing on the inside and the outside of these coastal artificial structures. These hydrotechnic structures
create a specific eco-climate inside the semi-closed aquatic area limited by the protective dams that influence the number and spatial distribution of the
epibiontic organisms. The study reveals the occurrence of 76 species of benthic organisms belonging to 13 supraspecific taxa, with an average density of
2 122 523 indvs.m-2 and a biomass of 19 437,2 g.m-2. Numerically, the dominant species are the crustaceans (~539 224 indvs.m-2) and worms (~416 972
indvs.m-2) and the weight dominants are molluscs – Mytilus galloprovincialis over 96 % and crustaceans (~136 g.m-2).
Keywords. Black Sea, macro-, meiobenthic communities of the hard bottom, qualitative, quantitative, littoral cell
INTRODUCTION
Aquatic ecosystems and their biotic and abiotic components in general, but above all marine coastal zones, have
been and continue to be both of great scientific interest
and also of considerable practical interest. The inherent difficulties in the analysis of the hard bottom have limited the
studies of the associated fauna because they are restricted
to a very narrow strip in the south of the Romanian littoral
and also because of the difficulties in collecting quantitative
samples. The first quantitative and qualitative research of the
microbenthic and macrobenthic component associated with
the natural hard bottom was started by the scientific group
led by the great oceanologist M. Băcescu, resulting in a series
of valuable papers (Băcescu et al., 1963, 1971). The research
of the rocky fauna proper, in a holistic approach to the study
of the substrata communities including the associated meioand macrofauna both qualitatively and quantitatively, began
at the same time as the Romanian littoral was transformed
by works; these brought about serious changes in the structure of the benthic communities, which are still affected at
present. The coastal protection dams, like artificial reefs, have
partially compensated for the lack of hard bottom along the
Romanian littoral, giving rise after a short time to an epibiontic sessile and vagile fauna very diverse and numerically
abundant (Gomoiu, 1986, 1997).
The installation of these hydrotechnical structures in the
littoral waters favoured the creation of some more or less
closed areas, called littoral cells, where the hydrologic processes and the dynamic of the benthic population present
certain differences in comparison with open areas. Consequently, “littoral cells” are coastal marine sectors bordered by
permeable or impermeable protective dams, usually built at a
right angle to the shore and having variable terminal shapes
in T, Y, L, etc. The majority of these structures delimit a semiclosed aquatorium communicating with the sea through
one of the sides or through a narrow canal (e.g. harbour enclosures). The initial aim of these coastal enclosures was to
protect the beaches against erosion and to reduce or break
the kinetic energy of the waves. It was later shown that these
hydrotechnical structures had and still have both positive
53
A. Teacă, T. Begun, M.T. Gomoiu, G.M. Paraschiv - The present state of the epibiontic populations to the biocenosis of stone mussels in the shallow water off the Romanian Black Sea coast
and negative ecological implications, and their initial role of
coastal protection proved to be insignificant or even sometimes adverse. The closed-in aquatorium has a specific “calm
waters” characteristic/encloses a unique “calm-water” area
where the eco-climate is different from that of the open sea,
and the hydrologic and geo-ecological processes are greatly
influenced by this relative isolation.
At the moment, there is little information regarding
the dynamic of the ecological variations of the epibionthic
populations in the cell, in comparison with those in the open
marine sectors. Because of the deficient exchange of water
mass from inside the aquatorium with the open sea,/the water mass inside the aquatorium is not influenced by the open
sea, these sectors experience important fluctuations in the
physical and chemical parameters of the water. During the
summer season, these aquatoria can become ecologically
high-risk areas because of the explosive growth of some algal, bacterial or fungi populations sometimes followed by the
mass mortality of the benthic and nektonic populations.
MATERIAL AND METHODS
The analysis of the structure of the associations of epibiontic organisms in the two littoral cells is based on 21 quantitative biologic samples collected by diving at 7 stations (5
stations in the Mamaia cell and 2 in the Mangalia cell) in the
summer and autumn 2003:
• Station 1 – the Midia Cape (CM) protective dam,
• Station 2 – the open sea dam in front of the hotel complex «Casino» Mamaia (external area) (DLC-ex),
•
Station 3 - the open sea dam in front of the hotel complex «Casino» Mamaia (internal area) (DLC-pt),
• Station 4 – protective dam in front of Pescărie Mamaia
(exposed area) (PM-ex),
• Station 5 – protective dam in front of Pescărie Mamaia
(protected area) (PM-pt),
• Station 6 – the Mangalia protective dam, in front of “Mangalia” hotel (external area) (MM-ex),
• Station 7 – the Mangalia protective dam, in front of
“President” hotel and very close to the Mangalia Harbour
(internal area) (MP-pt).
They comprise the protected internal and unprotected
external areas of the coastal protective dams. A sample was
collected from each station at a depth of 3 m, by scraping the
epibiosis over a 400 cm2 surface (20 x 20 cm) using a knife
with a 20 cm long blade. The blade was also used to measure
the scraping area, i.e. a square with 20 x 20 cm side/sq.cm. The
scraping areas were chosen randomly. The biological material
scraped was deposited in a classic mesh (permeable only to
water) the end of which was fastened by a string to prevent
loss of the material in the water. The sampled material was
preserved in formaldehyde neutralized (5 – 6 %) in seawater.
•
54
The samples were then processed in the following ways:
Washing samples using 3 sieves of 1 mm, 0,5 mm and
0,125 mm to separate macro- and meiofauna;
•
•
•
Identifying the species using either a magnifying glass
or a microscope, and, at the same time, counting the
number of individuals in each identified species;
For the macrobenthic forms, the biomass was determined
by weighing the organisms using an electronic scales, and
for the meiobenthic forms, their weight was determined
using standard weight tables;
Computer processing of the data for ecological parameters.
In order to statistically process the results obtained following separation, the analytical ecological indicators and
diversity indicators were used.
RESULTS AND DISCUSSIONS
General biological description of communities
from the littoral cells
The biological description of the areas investigated is
based on the results of laboratory analyses of samples, both
from the hard and the mobile bottom, as well as in situ observations.
The results of taxonomic determinations and the statistical analysis of the biotic component within the cells, when
compared to the data found in specialized literature, indicated that the associated biota is in a relatively good condition,
in comparison with that of previous years.
Direct observations in the areas of interest indicate the existence of a greater diversity of biotopes formed as a result of
hydrotechnical constructions (dams) and of specific hydrological conditions favouring the migration of pelagic forms (fish
– grey mullet, anchovy, atherine) and planktonic forms (coelenterates) in search of food in the shallow waters of the cells.
Planktonic forms include juvenile and adult jelly fish such
as Aurelia aurita and Rhizostoma pulmo, mainly during the
second half of July and the ctenophore – Mnemiopsis leydii in
its adult stage, with much lower densities but with a constant
presence in all studied locations. The North-Atlantic ctenofor
Beroe ovata was found at the end of the summer season, once
the water started cooling, in adult populations. Its density
however was lower in comparison with previous years, when
the species was found in the middle of the summer season, in
numbers comparable to those of Mnemiopsis. This situation
probably shows that a population balance was reached between these two alien species with different feeding regimes
– filtration (Mnemiopsis) and predator (Beroe).
It must be noted that Hyppocampides (sea horses) are
present at Pescărie Dam (Mamaia), Casino (Mamaia) and
Mangalia but reach impressive densities at the Casino. In
both these stations we discovered during the second collecting period, an area of approx. 30x30 cm, populated by small
seagrass (Zostera sp.), on a sandy-silty texture substratum in
the proximity of the dam. Numerous galleries and organisms
of Upogebia pusilla were also found on the sedimentary bottoms surrounding the inner dam.
As for plankton life forms, around September, it must be
emphasized that virtually every adult specimen of Rhizostoma pulmo was located near mackerel juvenils (Trachurus
mediterraneus ponticus), numbering between 3 and 15.
The re-apparition of the perennial brown alga Cystoseira
barbata in the southern extremity of the littoral is of a great
importance for the littoral hard bottom biocenosis. This situation has resulted in the diversification of habitats and favours
the apparition of species closely related to this very endangered species, which has a very sparse distribution.
Hydrological conditions underwent considerable variations during the two sampling periods – the first half of June
and the second half of July respectively. In July the hydrological conditions were typical, as far as temperature and salinity
were concerned, of the early spring cold water period with
temperatures as low as 11°C (ex. Midia Cape Dam). This phenomenon was due to a large extent to the dominance partly
of southerly winds and partly of winds blowing from a northern direction parallel to the shore combined with a noticeable upwelling of coastal waters. These conditions persisted
for approximately two weeks and also influenced the biotic
component of benthic biocenosis, favouring species that prefer low temperature waters. Thus, hard surfaces were almost
completely covered by algal macrophytes such as Ceramium
sp. (ex. Midia Cape). This is a rather typical situation, generally
characteristic of the periods from April to May and October
– November.
Warm water forms (Enteromorpha, Ulva, Cladophora) established in June were mainly removed by the more or less
marked wave activity present at the end of June and the beginning of July, also related to their inability to withstand low
temperatures, and they accumulated in deposits at the bottom of the sea in small semi-closed gulfs (in beds of up to
0.5m) or were stranded in impressive numbers on the shore
(ex. Cape Midia). Algae stranded on the shore or in shallow
(0.5m) waters harbour a vagile fauna exclusively dominated
by isopods (Idotea baltica, Sphaeroma pulchellum) and amphipods (Melita palmata etc.).
Algal deposits accumulated on the sedimentary bottoms
at depths exceeding 1.5m constitute excellent feeding and
living areas for a series of vertebrate and invertebrate organisms, such as Syngnathides, which “give birth” to their young
and feed in these thickets (firsthand observation in situ),
whereas hyppocampides and shoals of grey mullet feed at
the boundary between these accumulations and the mobile
sediments.
In the other sectors macrophites developed jointly,
although rhodophites were being gradually replaced by
clorophites (Enteromorpha, Cladophora) where there was
a gradual warming of the water column (approx. 18°C), but
with a sudden cooling near the bottom (at 0.5m – 1m) reaching temperatures as low as 10 - 11°C. The most significant example of vagile macrofauna shows that adult isopods (Idotea
baltica, Sphaeroma pulchellum, S. serratum) reappear when
the water gets colder.
The vagile macrofauna of the sandy bottom is dominated
in all locations, apart from Midia Cape, by mysidae, amphipods, shrimp (Crangon crangon), diogenic crabs (Diogenes
pugilator), the sand crab (Liocarcinus holsatus). As far as molluscs are concerned, Corbula mediterranea, Mya arenaria, Cyclope neritea are the dominant species.
The observations made in the last month of sampling
(September), showed the general tendency of the majority
of macrobenthic forms (misids, shrimp, hermits crabs, crabs,
etc.) to retreat towards the deep. At the edge of the Pescărie
dam, at 4-5 m deep, an interesting condensability or grouping
phenomenon was noticed in an impressive number of misids
belonging to the species Mesopodopsis slaberi and Paramysis
kroyeri concentrated in a water column of 3 x 3 m.
Characteristics of the benthic populations associated with the shallow hard bottom in the Mamaia and Mangalia littoral cells
Following the analysis of the biological material sampled,
95 types of benthic organisms associated with the hard bottoms were identified, belonging to 13 taxonomic supra-specific groups. Excluding the organisms identified at group level
(Foraminifera, Nematoda, Oligochaeta, Harpacticoida, Insecta) and the varia inside the groups (Hydrozoa, Turbellaria,
Nemertini, Polychaeta, Bryozoa, Halacarida, Larvae), the total
number of taxa identified according to species/type is 76. Out
of a total of 95 identified taxa, 57 (60%) are to be found in
both analyzed locations. The number of taxa found only in
the Mamaia cell was 20 (21%) and 18 (19%), respectively in
the Mangalia cell. Of these, worms are the most numerous as
species in the Mamaia area (10 taxa) in comparison with the
Mangalia area where only 4 species of polychaeta were found
out of a total of 18 taxa identified in this cell alone. In the case
of crustaceans, the situation is reversed, so that in Mamaia
the total number of species identified in this area alone is 7,
compared with 9 in Mangalia (Fig.1).
The ratio between the macrobenthic taxa identified in
both locations and of those taxa peculiar to only one location is quite balanced. Only 54% (41) of the identified taxa
are common to both locations. Thus, with regard to the macrobenthic associated with the shallow hard bottom, the mixture of conditions in each cell encourages the growth of certain taxa with specific preferences for that biotope (APPENDIX
I, Fig. 2). The differences regarding the presence or absence of
taxa in a cell were generally noted in the case of polychaeta
and superior crustaceans, because of their specific demands
in relation to the biotope.
The lowest specificity is noticed in the associated meiofauna, where 83% (15 taxa) of taxa are common for both locations, and the contribution of the characteristic forms is negligible (APPENDIX II, Fig. 3).
55
hard rock) that provides shelter for an amazingly abundant
microcosm. The interrelations established between various
cocenotes are vital for the maintenance of a dynamic equilibrium inside the system.
The real seasonal diversity, according to the number of
identified species, is higher in the Mangalia cell. This can be
explained by the same level of physical and chemical parameters of the water, vital for the selection of a population with
a low ecologic plasticity and a high heterogeneity of habitats
(artificial hard bottom, natural hard bottom, vast algal fields,
bottom of rough ground sand mixed with biogenic sediment,
enclaves of sand in the hard bottom) (Fig. 4).
Fig. 1 The percentage of specific and common macrobenthic and
meiobenthic taxa identified in Mamaia and Mangalia cells
Fig. 2 The percentage of specific and common macrobenthic taxa
identified in Mamaia and Mangalia cells
Fig. 3 The percentage of specific and common meiobenthic taxa
identified in Mamaia and Mangalia cells
These percentage estimations show the capacity of the
epibiontic system to form and of the associated fauna to
constantly evolve, with respect to the diversification of the
association and the reconfiguration of the habitat in relation with the abiotic conditions in the specific aquatorium.
A high percentage of macrobenthic in association ensure an
extraordinary complication of the primary biotope (denuded
56
The seasonal changes in the structure of the qualitative
composition of the benthos in the Mamaia and Mangalia cells
are not significant. They have to be considered not changes,
but a result of the random distribution of some benthic species, of the heterogeneity of the bottom and of some inherent limits of the sampling.
The most significant taxa occuring in the highest density and frequency parameters : harpactycides, nematodes,
veliger larval forms Mytilus galloprovincialis, Microdeutopus
gryllotalpa, Polydora ciliata, Balanus improvisus, Melita palmata, Rhombognathus sp., nectocheta larvae, Polydora antennata; and a series of species with reduced frequency, but with
numerous populations in certain periods or locations, such
as: turbelariates Stylochus tauricus and Leptoplana tremellaris, polychaeta Neanthes succinea, Fabricia sabella, Nerilla
antennata, Platynereis dumerilii, Sphaerosyllis bulbosa, chitons
Middendorfia caprearum, leading bivalve in the biocenosis of
the shallow hard bottom Mytilus galloprovincialis, the ostracodes represented especially by Xestoleberis decipiens and X.
aurantia acutipenis, the amphipodes Sthenothoe monoculoides, Amphithoe vaillanti, Jassa ocia, Erichthonius difformis, the
isopode Idotea baltica, the crustacean cypris larvae and chironomide larvae. Of these, the nematodes and harpactycides
lead in numbers, in 90 % of the total mean densities.
The biomasses are dominated in over 99,09 % cases by
only one species, a large form of bivalve Mytilus galloprovincialis. With the exception of bivalves, the following species
are predominant: cirripedia Balanus improvisus, the decapodes Pilumnus hirtellus and Rhithropanopeus harrisii tridentatus, the amphipodes Melita palmata, Microdeutopus gryllotalpa, Amphithoe vaillanti, polychaeta Neanthes succinea,
the coelenterate Actinia equina and the turbelariate Stylochus
tauricus.
The ecological parameters typical of the benthic populations indicate a homogenous distribution in the area in terms
of both species and abundance of density and biomass. The
most important major groups of benthic invertebrates, numerically dominant are the crustaceans – 54 % of the total
mean density of the associated fauna, and – 69 %, respectively, of the total mean biomass, and the worms – 38 % of
the total mean density and 19 % of the total mean biomass
(Fig. 5).
Fig. 4 Seasonal variation of the total number of epibiontic species identified along the Romanian littoral in 2003
Fig. 5 Variation of average density (DAVG) and biomass (BAVG) of the main groups of epibiontic organisms
in the Mamaia and Mangalia littoral cells
The scale of the density variations in the Mamaia cell is
between 866 922 indvs.m-2 and 3 853 500 indvs.m-2, and the
biomasses between 15 937 g.m-2 and 27 927 g.m-2. In the
Mangalia cell, they are between 1 417 923 indvs.m-2 and 3
070 000indvs.m-2 with biomasses of 14 090 g.m-2 and 20 602
g.m-2. In general, the mass values of the epibiontic organisms
are almost equal or slightly higher in the interior regions of
the Mamaia and Mangalia cells, compared to the external
regions. There are no great differences in the biotic composition of the two locations, from a quantitative point of view.
The difference in the structure of the epibiosis appears when
the macro- and meiobenthic fauna segment in each cell is
analysed. Namely, some quantitative differences between littoral cells exist but only in the case of macro-fauna. This can
be easily explained by the nature, conditions and variations
of biotopes (natural rocky, sand enclaves, algae fields, etc.) of
the Southern sector, in comparison with the Northern one,
which sustains a more qualitatively diversified epibiosis, with
a greater number of macrobenthic organisms. In the Northern sector, i.e. the Mamaia cell, the reduced density of macrobenthic organisms is compensated for by the abundance
of the meiofauna with affinity for both the hard and the mobile-sandy bottom dominating the distribution in the shallow areas in the Northern sector (Fig. 6, 7). The ratio between
the macro- and meiofauna associated for the Mamaia cell is
1 : 9.35 and for the Mangalia cell is 1 : 5.01. The bigger difference in the Mamaia cell is due to the eutrophic character of
the aquatorium; this situation permits the development of a
very abundant meiobenthic segment, constantly enriched by
organisms migrating from the sandy bottom.
57
the macrobental epibiontic organisms in the Mamaia and Mangalia littoral cells
the meiobental epibiontic organisms in the Mamaia and Mangalia littoral cells
Fig. 8 Diagram of the weight of the main macrobental epibiontic
groups in the Mamaia and Mangalia littoral cells, 2003
Fig. 9 Diagram of the weight of the main meiobental epibiontic
groups in the Mamaia and Mangalia littoral cells, 2003
The comparative analysis of the epibiontic macro- and
meiofauna by taxonomic groups shows that the main groups
that create the difference between cells are the Crustacean
and Varia in the case of the macrofauna and the Foraminifera, Molluscs and Varia in the case of the meiofauna (Fig. 8,
9). Out of a total of 26 superior macrobenthic crustacean
species, only 12 are common to both locations. Thus, in the
Mamaia cells 6 species were identified that are not found in
the Southern area, such as: Gammarus olivii, Sphaeroma pulchellum, Paramysis kroyeri, Palaemon adspersus, Palaemon elegans, Athanas nitescens. This does not suggest the absence
of those species in the epibiotic structure of the Mangalia
cell, and is due to some typical limitations of the sampling
method (the swimming decapods that represent half of the
missing species, because of their active locomotion capabilities, swim away when the biological material is scraped and
cannot be captured later). Based on direct visual observations
made during diving, Palaemon elegans and Athanas nitescens
are common species for the biocenosis of the rock mussels
in the shallow areas along the littoral. For the Mangalia cell,
the number of crustacean species identified in this location
alone is 8, as follows: Apherusa bispinosa, Hyale pontica, Jassa
ocia, Erichthonius difformis, Caprella acanthifera ferox, Naesa
bidentata, Cumella limicola, Siriella jaltensis jaltensis. Most of
these species present a degree of specificity with regard to
the environment conditions (except for Apherusa bispinosa,
Hyale pontica and Cumella limicola), being found only in the
Southern regions. Nevertheless, some of them, such as Jassa
ocia and Naesa bidentata, can be found in some Northern locations as well, but in smaller numbers.
58
The orientation of the substrata in the direction of/relative to the water masses represents an important ecological
factor in selecting and determining the settlement of the
epibiontic associations. The calcareous or sessiles species are
the dominant fauna segment; they can withstand dislocation
caused by the high hydrodynamics of shallow waters. Of the
two mollusc species dominating the epibiontic system, Mytilaster lineatus and Mytilus galloprovincialis, only the young of
the mussel and the adult specimens of Mytilaster accompanied by/and Balanus improvisus shape the epibiontic system
in the shallow area of 0 – 1m. Of these, Mytilaster lineatus is
the dominant species of the system, because of the robust
shape of its valves and its protruding/bulky carcass that
“breaks” the waves. In the direction of the water masses, the
molluscs never form more than 1-2 superposed levels, which
prevents the settlement and diversification of the vagile fauna segment; they form a tube using the detritus as a building
material or the detritus feeding. The detritus which abounds
at the bottom of a coastal protection dam, is mainly made
up of the pseudofecales of molluscs from upper levels and
is virtually inexistent in the 0m horizon, being permanently
washed away by water. The few vagile forms associated with/
found in the shallow areas are therefore either passive or active filtrating species.
The quantitative analysis of the macro- and meiobenthic
segments related to the orientation of the substrata, i.e. the
internal protected and the external unprotected areas of the
cell, shows certain quantitative and qualitative differences.
Generally speaking, the epibiontic communities on the internal side of the protective dams are more abundant and complex than those on the external side. There are nonetheless
cases when the quantitative and qualitative differences are
greatly reduced, where there is more communication with the
open sea or a large shallow area surrounding the cell. Shallow depths/areas, especially inside the cell – as in the case
of the Mamaia cell – favour the movement of the associated
fauna on the mobile seabed in periods of high hydrodynamism or when there is strong upwelling, supplementing both
qualitatively and quantitatively the epibiontic system on the
hard bottom. In this situation, the external area sometimes
seems more diversified than the internal one, as in the case
of the macrofauna in the Mamaia cell (Fig. 10). Among the
sandy macrobenthic invertebrates identified in the epibiosis
of the Mamaia cell in the external area, and not present in
the samples collected in the internal protected areas, were
the polychaeta with a number of 4 species typically sandy
worms: Laonice cirrata, Namanereis pontica, Pygospio elegans,
Fig. 10 Diagram representation of the macrobental populations
in the protected and exposed areas of Mamaia cell, in 2003
Spio filicornis. Certainly, in the case of annelids, which prefer
a mobile substratum, their presence in the epibiontic system
is due to the clogging of the epibiosis with sedimentary material in sufficient quantities for these species to be able to
perform vital activities. It must be stressed that the presence
of sandy species is characteristic for depths under 1.5 – 2 m
(generally) on the external unprotected areas of protective
dams, because the sedimentary material that usually clogs
the entire side of the dam (vertically) is easily removed from
the shallow area. The epibiosis in this area is therefore completely free of mineral or organic suspensions and does not
encourage the development of a species needing a mobile
substratum.
Consequently, the differences in number and weght are
very slight in the Mamaia cell, because of its vast area. The
epibiontic associations are nevertheless slightly more abundant in the internal area compared to the external area where
they are subject to the moving action of the water masses
(Fig. 11).
Because of the limited surface area and semi-closed character of the Mangalia cell, the differences in the numeric abundance of each fauna segment or in relation to the orientation
of the substrata seem greater. In any case, the epibiontic associations on the internal side of the dam are qualitatively and
quantitatively more abundant. The structure of the bottom
around the cell (natural hard calcareous bottom) eliminates
the possibility of the epibiontic system being “contaminated”
with sandy forms. Thus, most of the identified species are typical of rocky surfaces and some have a very strong stenobiotic
character, e.g. Siriella jaltensis jaltensis. Still, in the areas where
communication with the open sea is limited, the protected
nature of this aquatorium tends to trap excess organic material. This leads to the clogging of the epibiontic system and
encourages the evolution of opportunistic species with high
Fig. 11 Diagram representation of the meiobental populations in
the protected and exposed areas of Mamaia cell, in 2003
59
resistance to this type of biotopes. Such species include the
tubular and detritofagous species (ex. Polydora ciliata, Capitella capitata, oligochetes) (Fig. 12, 13).
The structure of the benthic fauna associated with rocky
bottoms (artificial-natural) in the two locations was analysed
and compared with the information regarding the epibiontic
populations of the last 2-3 decades; no significant qualitative
variations in the dominant species in the epibiontic system
was evident. The most significant differences were noted
between the observations made in the 1960s (Băcescu et
al., 1963; Băcescu et al., 1971), 1970s (Ţigănuş, 1979), 1980s
(Gomoiu, 1981, `86, `89) and 1990s (Ţigănuş, 1992 in Petranu,
1997; Gomoiu, 1992) concerning the qualitative structure of
upper crustacean macrofauna (swimming and crawling decapods). Yet, the most significant differences were probably
in the quantitative parameters for both the meio- and the
macrobenthic epibiontic forms. Thus, the mean densities of
shallow water sessile and vagile epibiontic populations at the
end of the 1970s and 1980s-1990s, a period considered to be
of the greatest ecological instability for coastal ecosystems in
the North-West of the Black Sea were between 163 352 indvs.
m-2 on the hydrotechnic constructions in Mamaia (Gomoiu,
1989) and 255 697 indvs.m-2 in the Agigea area (Ţigănuş,
1979). Compared with the data of 2003, when the total mean
density of the zoobenthos associated with the hard bottom
was 2122,52x103 indvs.m-2 these mean values are at least 10
times lower. These numeric differences are due to the extremely abundant meiobenthic segment in the epibiontic
associations, like the nematodes and the harpactides, forming densities generally higher than 600 000 – 800 000 indvs.
m-2. The values of the mean abundances obtained in 2003 are
only comparable with those noted in 1961 in Agigea (Băcescu
et al., 1963) and with those in the structure of the fouling on
ships’ keels where similar values of 500 000 – 1 500 000 in-
Fig. 12 Diagram representation of the macrobental populations
in the protected and exposed areas of Mangalia cell, in 2003
60
dvs.m-2 were noted for the vagile meiobenthic forms such as
nematodes and copepods (Gomoiu, Ţigănuş, 1974, 1976).
Consequently, the number of epibiontic organisms on
both artificial hydrotechnic structures and on natural hard
bottom has greatly increased in recent decades compared to
the ecological crisis in the 1980s-1990s (Fig. 14). The increase
in populations was noticed in all the major invertebrate
groups in association of rocky mussels.
The least significant variations were noted for the mean biomasses : 20540,11 g.m-2 in the Mamaia cell and 16679,76 g.m2 in the Mangalia cell, together with the malacological component compared to values mentioned in scientific papers.
Excluding the molluscs, the mean values for the other epibiontic groups present certain small differences between the two
locations. Thus, the mean values registered in Mamaia in 2003
and 1988-1989 were 198,46 g.m-2 and 171,75 g.m-2 respectively, and quantitative differences were only noted in the groups
of worms and crustaceans. For the Mangalia cell, the mean biomass is similar to that in the Mamaia cell, namely 197,80 g.m-2.
Generally, these mean values are greatly affected by the numeric abundance of cirripedia obscuring the contribution of
other zoobenthic groups without calcareous structures to the
total biomass per surface unit. The contribution of cirripedia in
terms of biomass compared to the rest of the crustacean species was 62,92 g.m-2 in 2003 and 226,678 g.m-2 in 1977. This was
approximately 45 % of the total crustacean biomass in 2003
(total crustacean biomass 143,43 g.m-2) and 89 % in 1977 (total
crustacean biomass 253,466 g.m-2) (Fig. 15).
The most important crustacean species (except the cirripedia) causing higher mean values per surface unit are the
decapods represented by Pilumnus hirtellus, Rhithropanopeus
harrisi tridentatus and the amphipods Melita palmata, Microdeutopus gryllotalpa, Amphithoe vaillanti.
Fig. 13 Diagram representation of the meiobental populations in
the protected and exposed areas of Mangalia cell, in 2003
The greatest quantitative changes in the shallow water
epibiontic associations were noted for worms, molluscs and
crustaceans. The 1980s-1990s represent the most unbalanced period in the coastal aquatic ecosystems, with serious
negative consequences in the structure of the epibiosis due
to exclusive dominance of the meiobenthic worms (Nematoda) and of the opportunistic annelids (polichaeta species:
Polydora ciliata, Capitella capitata and oligochaeta species)
with high ecological plasticity, capable of enduring the eutrophication of the marine environment during that period.
Crustacean and mollusc populations diminished dramatically
in terms of abundance and number of species (Fig. 16). Still,
both before and after the changes caused by eutrophication,
the numerically dominant groups/species among the crustaceans have been and still are: Harpacticoida, Microdeutopus
gryllotalpa, Balanus improvisus, Melita palmata.
recently, the situation of the benthos associated with the
hard bottom is between the normal limits of evolution for
the epibiontic communities, especially through the quantitative and qualitative enrichment of the vagile segment which
exhibiting the eco-functional maturity of any natural aquatic
system (Fig. 16).
Surprisingly, the total number of crustacean species identified in 2003 in the Mamaia and Mangaia cells is, in terms
of quality, at least 10 taxa higher than in the period of reference around 1977 (as shown by the analysis of the epibiosis
in the Agigea area). Thus, 20 taxa and 18 crustacean species
were identified in 1977 in the epibiotic associations. The total
number of species identified in 2003 is 32 and 33 taxa, respectively. There is an evident contrast between this qualitative
abundance and the state of the crustacean epibiontic populations in the 1960s on the natural rocky bottom of Agigea.
The same situation is found in the case of worms (Turbellaria, Nemertini, Nematoda, Annelida) where the total number
of taxa identified in 2003 is 39 and 34 species, respectively.
Thus, the yearly comparative analysis shows a deep imbalance in the population equilibrium of the benthic invertebrates, characterized at the end of the 1980s by the exclusive dominance of worms in contrast to other groups. More
Fig. 14 Variation of the average density of the main groups of
epibiontic invertebrates in the 1977 – 2003 interval along the
Romanian Black Sea littoral
The holistic comparative analysis of the shallow water
epibiontic associations for each littoral cell has brought to
light important aspects of the distribution and abundance
of the epibiontic system. This encourages the study of the
evolution of littoral biocenosis relative to changes in the Romanian coastal area. The rich biodiversity in the researched
locations can be compared (in the case of some extraspecific
groups) with the situation of the benthic populations in the
period of ecological stability in the 1960s-1970s.
CONCLUSIONS
The results of the ecological comparative study of the
epibiontic shallow benthic populations of the Mamaia and
Mangalia littoral cells in 2003 lead to the following conclusions:
• the qualitative structure of the associated meio- and
macrofauna in the two locations is represented by 95
types of benthic organisms belonging to 13 taxonomic
extraspecific groups, and the total number of taxa identified according to species/type level is 76;
• as regards quality, in 2003, the total number of crustacean
species observed in Mamaia and Mangalia cells was at
least 10 taxa higher than in the reference period in 1977,
when only 18 species were identified; in 2003, the total
number of species identified was 32;
• the quantitative analysis of the macro- and meiobental
segment relative to the sub-layer orientation, namely the
internal – protected – area and the external – unprotect-
Fig. 15 Variation of the average biomass of the main groups of
epibiontic invertebrates in the 1977 – 2003 interval along the
Romanian Black Sea littoral
61
Fig. 16 The percentage weight of the epibiontic organisms populations in the associations of the shallow hard bottom along the Romanian Black
Sea littoral in the 1977 – 2003 time interval
•
•
62
ed – area records some differences in both quality and
quantity. They are generally more abundant and more
complex on the internal side of the protective dams than
on the external side that is subject to the disturbing and
continuous action of the water mass;
due to the large surface area, the numeric and weight differences are very reduced for the Mamaia cell; the qualitative
uniformity of the epibiontic associations noted in the interior/exterior of the Mamaia cell is due to the large surface area
and extensive communication with the open sea, considerably reducing more significant qualitative differences;
the reduced surface and semi-enclosed nature of the
Mangalia cell, have resulted in greater differences in numerical abundance of each fauna segment according to
•
the sub-layer orientation; in all cases, the epibiontic associations on the internal side of the protection dam are
more abundant both in quality and quantity;
comparing the structure of the benthic fauna associated to/on the rocky floors (artificial-natural) of the two
locations examined with information about epibiontic
populations in the last two-three decades no important
variation is evident in the quality of the dominant species
in the epibiontic system. The most important differences recorded were quantitative parameters, for both the
epibiontic meio- and macrobenthos; the average values
of the epibiontic populations’ abundance in 2003 show
they were at least 10 times higher than those obtained in
the years `60-70.
APPENDIX I
General characteristics of the macrobenthic populations recorded in 2003 in the Mamaia and Mangalia area of interest
No. Taxa
Mamaia cell
F%
DAVG
DD%
RkD
Mangalia cell
BAVG
DB%
RkB
F%
DAVG
DD%
RkD
BAVG
DB%
RkB
1
Halichondria panicea
50.00
41.67
0.01
44
37.50
0.22
5
2
Hydrozoa
16.67
33.33
0.01
48
0.27
0.00
44
3
Actinia equina
60.00
150.00
0.07
27
4.01
0.02
9
66.67
45.83
0.01
38
6.14
0.04
13
4
Leptoplana tremellaris
60.00
4026.33
1.99
11
1.11
0.01
17
83.33
954.17
0.26
23
0.40
0.00
31
5
Stylochus tauricus
80.00
10452.27
5.16
8
2.95
0.01
10
66.67
363.17
0.10
28
0.59
0.00
28
6
Emplectonema gracile
6.67
1.67
0.00
57
0.01
0.00
53
66.67
45.83
0.01
39
0.82
0.00
21
7
Tetrastemma sp.
80.00
323.33
0.16
21
0.61
0.00
20
100.00
247.17
0.07
27
0.65
0.00
19
8
Nemertini varia
66.67
278.33
0.14
23
0.55
0.00
24
33.33
16.67
0.00
49
0.03
0.00
50
9
Brania clavata
60.00
1250.00
0.62
13
0.38
0.00
26
100.00
1845.83
0.51
17
0.53
0.00
22
10
Capitomastus minimus
33.33
541.67
0.15
30
0.32
0.00
40
11
Eteone picta
26.67
13.33
0.01
48
0.04
0.00
39
50.00
45.83
0.01
43
0.15
0.00
41
12
Eulalia limbata
26.67
46.67
0.02
40
0.04
0.00
40
16.67
4.17
0.00
56
0.00
0.00
57
13
Fabricia sabella
100.00
5262.50
1.45
13
0.31
0.00
33
14
Grubea limbata
20.00
111.67
0.06
39
0.03
0.00
44
16.67
16.67
0.00
51
0.01
0.00
56
15
Grubea tenuicirrata
40.00
133.33
0.07
30
0.04
0.00
34
33.33
20.83
0.01
46
0.01
0.00
53
16
Harmothoe imbricata
66.67
35.00
0.02
38
0.61
0.00
21
50.00
33.33
0.01
45
0.73
0.00
29
17
Harmothoe reticulata
80.00
125.00
0.06
26
1.51
0.01
14
83.33
33.33
0.01
41
0.77
0.00
20
18
Janua pagenstecheri
19
Laonice cirrata
20
Namanereis pontica
21
Neanthes succinea
22
Nereis pelagica
23
Nereis rava
24
66.67
3192.67
0.88
16
0.54
0.00
30
6.67
1.67
0.00
58
0.00
0.00
58
13.33
58.33
0.03
44
0.04
0.00
45
100.00
14778.33
7.29
6
26.52
0.13
5
100.00
6377.50
1.76
10
14.23
0.09
7
16.67
16.67
0.00
52
0.17
0.00
45
100.00
628.67
0.31
14
1.65
0.01
12
66.67
70.83
0.02
35
0.27
0.00
39
Nerilla antennata
13.33
1493.33
0.74
22
0.15
0.00
33
25
Nerine cirratulus
20.00
878.33
0.43
24
0.18
0.00
31
16.67
4.17
0.00
57
0.00
0.00
58
26
Nerine tridentata
13.33
3.33
0.00
53
0.00
0.00
57
27
Perinereis cultrifera
73.33
378.33
0.19
20
1.72
0.01
13
83.33
166.67
0.05
32
0.88
0.01
18
28
Pholoe synophthalmica
6.67
5.00
0.00
54
0.00
0.00
55
29
Phylodoce lineata
16.67
4.17
0.00
58
0.01
0.00
52
30
Platynereis dumerilii
60.00
941.87
0.46
16
1.61
0.01
16
100.00
390.00
0.11
26
3.42
0.02
14
31
Polydora antennata
86.67
18796.67
9.27
4
0.44
0.00
23
83.33
5629.17
1.55
14
0.50
0.00
25
32
Polynoe scolopendrina
33.33
78.33
0.04
35
0.05
0.00
35
16.67
12.50
0.00
55
0.01
0.00
54
33
Poydora ciliata
93.33
42601.00
21.02
1
1.21
0.01
15
100.00
5548.33
1.53
12
0.42
0.00
26
34
Prionospio cirrifera
6.67
3.33
0.00
55
0.02
0.00
48
35
Pygospio elegans
6.67
3.33
0.00
56
0.00
0.00
59
36
Sphaerosyllis bulbosa
86.67
5495.80
2.71
9
0.68
0.00
19
100.00
995.00
0.27
20
0.19
0.00
38
37
Spio filicornis
6.67
60.00
0.03
47
0.02
0.00
50
38
Syllis gracilis
6.67
640.00
0.32
32
0.06
0.00
46
50.00
58.33
0.02
40
0.02
0.00
49
39
Oligochaeta
46.67
129.87
0.06
29
0.03
0.00
38
83.33
1816.67
0.50
18
0.36
0.00
34
40
Doridela obscura
13.33
15.00
0.01
50
0.11
0.00
36
41
Tergipes tergipes
13.33
48.00
0.02
45
0.01
0.00
51
42
Middendorfia
caprearum
100.00
6395.00
1.76
9
10.40
0.06
9
63
Mamaia cell
No. Taxa
F%
DD%
RkD
Mangalia cell
BAVG
DB%
RkB
F%
DAVG
DD%
RkD
BAVG
DB%
RkB
43
Setia valvatoides
16.67
25.00
0.01
50
0.05
0.00
51
44
Mytilaster lineatus
100.00
2975.07
1.47
10
566.61
2.76
2
100.00
1462.00
0.40
19
273.87
1.64
2
45
Mytilus galloprovincialis
100.00
8721.80
4.30
7 19767.62
96.29
1
100.00
5726.33
1.58
11 16191.50
97.11
1
46
Bowerbankia gracilis
47
Bryozoa varia
48
49
6.67
9066.67
4.47
15
0.00
0.00
56
73.33
33.33
0.02
37
0.03
0.00
32
50.00
50.00
0.01
42
0.05
0.00
46
Balanus improvisus
100.00
35129.33
17.33
2
71.59
0.35
3
100.00
16559.00
4.56
7
41.23
0.25
3
Amphithoe vaillanti
100.00
483.00
0.24
17
1.83
0.01
11
100.00
17174.17
4.73
6
8.44
0.05
10
50
Apherusa bispinosa
66.67
675.00
0.19
25
0.44
0.00
35
51
Caprella acanthifera
ferox
66.67
245.83
0.07
31
0.30
0.00
37
52
Corophium bonelli
40.00
193.33
0.10
28
0.03
0.00
41
100.00
2704.17
0.74
15
0.28
0.00
36
53
Dexamine spinosa
33.33
140.00
0.07
31
0.12
0.00
30
66.67
141.67
0.04
33
0.09
0.00
42
54
Erichthonius difformis
83.33
14939.17
4.11
8
3.10
0.02
15
55
Gammarus olivii
40.00
64.33
0.03
36
0.26
0.00
28
56
Hyale perieri
20.00
57.33
0.03
41
0.06
0.00
37
16.67
16.67
0.00
53
0.01
0.00
55
57
Hyale pontica
100.00
590.83
0.16
24
0.51
0.00
24
58
Jassa ocia
100.00
62400.83
17.18
2
6.45
0.04
11
59
Melita palmata
100.00
15854.33
7.82
5
17.10
0.08
6
100.00
34780.00
9.58
5
20.17
0.12
4
60
Microdeutopus
gryllotalpa
100.00
22479.13
11.09
3
7.51
0.04
8
100.00
84070.83
23.15
1
11.20
0.07
8
61
Nototropis guttatus
20.00
8.33
0.00
51
0.02
0.00
47
66.67
283.33
0.08
29
0.50
0.00
32
62
46.67
66.67
0.03
33
0.00
0.00
49
100.00
35570.83
9.80
4
0.41
0.00
27
63
Naesa bidentata
100.00
940.83
0.26
21
2.43
0.01
17
64
Sphaeroma pulchellum
13.33
82.60
0.04
42
1.19
0.01
27
65
Idotea baltica basteri
66.67
1925.00
0.95
12
0.34
0.00
25
50.00
83.33
0.02
37
0.03
0.00
48
66
Cumella limicola
83.33
1120.83
0.31
22
0.64
0.00
23
67
Paramysis kroyeri
6.67
1.67
0.00
59
0.01
0.00
52
68
Siriella jaltensis
jaltensis
16.67
16.67
0.00
54
0.13
0.00
47
69
Palaemon adspersus
13.33
6.67
0.00
52
0.06
0.00
42
70
Palaemon elegans
40.00
15.00
0.01
46
0.18
0.00
29
71
Athanas nitescens
46.67
65.00
0.03
34
0.83
0.00
22
72
Pisidia longicornis
46.67
370.33
0.18
25
1.37
0.01
18
33.33
20.83
0.01
47
0.14
0.00
43
73
Pilumnus hirtellus
100.00
463.33
0.23
18
35.04
0.17
4
66.67
70.83
0.02
36
22.18
0.13
6
74
Rhithropanopeus
harrisi tridentatus
86.67
421.13
0.21
19
11.72
0.06
7
66.67
83.33
0.02
34
3.85
0.02
16
75
Larvae megalope
20.00
48.33
0.02
43
0.04
0.00
43
Chironomida
6.67
46.67
0.02
49
0.00
0.00
54
100.00
43150.00
11.88
3
4.59
0.03
12
Mamaia cell
No. Taxa
64
DAVG
DAVG
Vermes
103772.47
Mollusca
Crustacea
Varia
Total
DD%
Mangalia cell
BAVG
DB%
DAVG
42.29
0.21
11759.87
5.80
20334.35
99.05
77874.87
38.42
149.31
0.73
9296.67
4.59
4.05
0.02
43320.83
11.93
202703.87
100
20530.00
100
363132.00
100
33713.83
DD%
51.19
BAVG
DB%
9.28
26.34
0.16
13608.33
3.75
16475.82
98.82
272489.00
75.04
122.54
0.73
48.55
0.29
16673.24
100
APPENDIX II
General characteristics of the meioobenthic populations recorded in 2003 in the Mamaia and Mangalia area of interest
Mamaia cell
No. Taxa
1
Foraminifera
2
Turbellaria varia
3
Nematoda
4
5
6
Spionidae larve
7
Syllidae juv.
8
Polychaeta varia
9
Veliconcha Mytilus
10
F%
DAVG
73.33
2703.33
DD%
RkD
Mangalia cell
BAVG
DB%
0.14
7
0.12
RkB
F%
1.20
4
DAVG
33.33
DD%
354.17
RkD
BAVG
DB%
0.02
13
0.02
RkB
0.24
13
20.00
563.33
0.03
11
0.06
0.56
8
50.00
1133.33
0.06
12
0.12
1.86
10
100.00
705187.13
37.20
2
1.06
10.45
3
100.00
632882.33
34.79
2
1.00
15.32
1
Nereidae larve
13.33
576.67
0.03
12
0.02
0.23
10
Polydora sp. - juvenili
13.33
83.33
0.00
14
0.01
0.07
13
33.33
83.33
0.00
16
0.01
0.11
14
6.67
86.67
0.00
16
0.01
0.05
15
20.00
2213.33
0.12
8
0.05
0.52
9
33.33
4800.00
0.26
10
0.10
1.47
11
66.67
21461.93
1.13
4
0.08
0.78
7
100.00
34941.67
1.92
6
0.17
2.57
7
66.67
147733.33
7.79
3
7.30
72.25
1
33.33
6866.67
0.38
9
1.52
23.24
6
Rhombognathus sp.
60.00
12837.47
0.68
5
0.09
0.87
6
100.00
64053.00
3.52
5
0.55
8.48
5
11
Halacarida varia
13.33
1849.00
0.10
10
0.02
0.15
11
100.00
12082.83
0.66
8
0.09
1.31
9
12
Cyprideis littoralis
6.67
26.67
0.00
17
0.00
0.00
17
16.67
533.33
0.03
15
0.00
0.05
16
13
Paradoxostoma
intermedium
6.67
960.00
0.05
13
0.01
0.06
14
66.67
19096.67
1.05
7
0.24
3.72
8
14
6.67
106.67
0.01
15
0.00
0.01
16
100.00
93634.17
5.15
4
0.96
14.65
2
15
Xestoleberis acutipenis
13.33
2026.67
0.11
9
0.01
0.13
12
100.00
97334.17
5.35
3
0.84
12.82
4
16
Loxochoncha pontica
33.33
305.00
0.02
14
0.00
0.06
15
17
Harpacticoida
100.00
977576.33
51.56
1
1.08
10.71
2
100.00
846966.67
46.56
1
0.88
13.43
3
18
Larvae cypris
33.33
19876.80
1.05
6
0.20
1.97
5
16.67
4200.00
0.23
11
0.04
0.64
12
DAVG
DAVG
Mamaia cell
No. Taxa
DD%
Mangalia cell
BAVG
DB%
DD%
BAVG
DB%
Foraminifera
2703.33
0.14
0.12
1.20
354.17
0.02
0.02
0.24
Vermes
730172.40
38.51
1.28
12.66
673840.67
37.04
1.39
21.34
Mollusca
147733.33
7.79
7.30
72.25
6866.67
0.38
1.52
23.24
Crustacea
1000573.13
52.78
1.30
12.87
1062070.00
58.38
2.96
45.37
Varia
14686.47
0.77
0.10
1.02
4.18
0.64
9.80
76135.83
REFERENCES
Băcescu, M., Dumitrescu, E., Marcus, A., Paladian, G., Mayer, R., 1963 – Donnees quantitatives sur la faune petricole de la Mer Noire a Agigea
(secteur roumain) dans les conditions speciales de l’annee 1961,
Trav. Mus. Hist. Nat. “Gr. Antipa”, Bucureşti, 4: 131-155
Băcescu, M., Müller, G.I., Gomoiu, M.-T., 1971 – Cercetări de ecologie bentală
în Marea Neagră (analiza cantitativă, calitativă şi comparată a faunei
bentale pontice), Ecologie marină, Ed. Acad., Bucureşti, 4: 357
Gomoiu, M.-T., Ţigănuş, V., 1974 – Contributions to the knowledge of the
fouling on the Romanian maritime ships, Cercetări marine, IRCM
Constanţa, 7: 83-112
Gomoiu, M.-T., Ţigănuş, V., 1976 – Cercetări privind compoziţia foulingului de pe navele maritime româneşti, Al VI-lea Simpoz. Biodeter.
Climat., Constanţa, 1: 84-91
Gomoiu, M.-T., Ţigănuş, V., Bondar, C., 1978 – Date privind formarea foulingului în apele de larg ale Mării Negre, Al VIII-lea Simpoz. Biodeter. Climat., Braşov: 375-380
Gomoiu, M.-T., Ţigănuş, V., 1981 – Structure qualitative et quantitative
des salissures formees dans les eaux du large de la Mer Noire,
Rapp. Comm. Int. Mer Medit., CIESM., Monaco, 27, 2: 185-184
Gomoiu, M.-T., 1986 – Donnees preliminaires sur la structure et le role
d’une communaute epibionte formee sur le substrat artificiel,
Rapp. Comm. Int. Mer Medit., CIESM., Monaco, 30,2: 17
Gomoiu, M-T., 1989 – Potential role and ecological effects of artificial
reefs constructed on the coastal sandy bottoms of the Black Sea
(Romania), Trav. Mus. Hist. Nat. “Gr. Antipa”, Bucureşti, 30: 291306
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Gomoiu, M.-T., 1997 – Recifi artificiali la litoralul românesc. An. Univ.
„Ovidius” Constanţa, Seria Biologie-Ecologie, I (1): 159-174
Ţigănuş, V., 1979 – Observations sur la structure qualitative et quanti-
Petranu, A., (compiler), 1997 – Black Sea Biological Biodiversity – Romania. Black Sea Env. Series, 4, United Nations Publ. New York: 314
de la Mer Noire, Rapp. Comm. Int. Mer Medit., CIESM., Monaco,
66
tative de la biocenose des moules de rocher du littoral roumain
25(26):159–160
PRESENT STATE OF THE SANDY INVERTEBRATE
POPULATIONS IN THE MAMAIA AND MANGALIA
SECTOR OF THE ROMANIAN BLACK SEA COAST
Tatiana BEGUN (1), Adrian TEACĂ (1), Marian -Traian GOMOIU (1), Gabriela-Mihaela PARASCHIV (2)
(1) National Institute of Geology and Geo-ecology – GeoEcoMar, Constanta Branch, 304 Mamaia Blvd,
900581 Constanta, Romania
(2) Department of Natural Sciences, The Ovidius University of Constanţa, Constanţa, 900581, Romania
Abstract. This paper presents the quantitative and qualitative distribution of sandy invertebrate populations of coastal littoral cells bordered by protective
dams in Mamaia and Mangalia, in the summer and autumn of 2003. Overall, 60 taxa were found belonging to the 15 major taxa, with an average density
of 722,012 indvs.m-2, and a biomass of 192.25 g.m-2. The comparative analysis of sandy invertebrate populations in the tow areas under observation have
generally revealed differences of quantitative nature, both the macrobenthal and meiobenthal organisms in the Mamaia cell being approximately 2 times
more numerous than in the Mangalia cell, because of the spatial limitations of the mobile sediments in the Mangalia cell, a situation that does not allow for
the evolution of the typical psammic associations. The most abundant organisms were the meiobenthal populations, with Nematoda and Copepoda group
reaching the highest density in the summer 2003 in comparison with the 1970s.
Key words: Black Sea, littoral cell, sandy invertebrate populations, qualitative, quantitative
Introduction
The systematic concern for the research of the littoral
ecosystems in the shallow waters of the Romanian coastal
areas has a history of over a century. Now, there are several
observations and data concerning the situation of sandy
invertebrate populations along Romanian littoral, many of
which having been published in the series: ”Marine Ecology”
printed in the Romanian Academy Editions (Editura Academiei Române), in the periodicals “Marine Research” (“Cercetări
marine – Recherches marines”), etc. Nevertheless, there still is
a lack of information concerning detailed research on certain
sectors. On the other hand, some of these studies, although
of a real value, were conducted over 30 years before, when
major changes of the marine environment had occurred due
to the increasing pollution and eutrophy, changes that have
had a profound impact on all biotic and abiotic components
of the marine ecosystem.
This study presents the changes observed in the quantitative and qualitative structure of the sandy invertebrate populations of the littoral areas of Mangalia and Mamaia, as well
as the current status of the sandy invertebrate populations
in the “littoral cells” – coastal marine sectors bordered by permeable or impermeable protection dams, usually built perpendicularly to the shore, having variable terminal forms of T,
Y, L etc. In those sectors, water communicates with the open
sea only on one side (the exposed area), and this results in
the creation of a sheltered area, that protects beaches against
erosion and where the kinetic energy of the waves is lost or
reduced to a minimum. The coastal littoral cells have a special
character of “still waters”, inside them occurring ecologic conditions that are different from those outside them, due to the
relative isolation provided by the protection dams.
At the moment, little is known about the differences between the biotic composition in the cell interior and that in
the open sea sectors. Certainly, these semi-enclosed sectors
become, during summer, areas of ecologic risk, as a consequence of an explosive development of algae, bacteria or
fungi populations that may be followed, in some cases, by
mass mortality of benthal and nektonic organisms.
The areas undergoing research belong to the superior
infra-littoral layer, represented by the fine sand biocenosis
Corbula mediterranea – the only biocenosis that is typically
67
T. Begun, A. Teacă, M.T. Gomoiu, G.M. Paraschiv - Present state of the sandy invertebrate populations in the Mamaia and Mangalia sector of the Romanian Black Sea coast
psammobiontic, and that has an important presence along
the Black Sea and Azov seacoasts. Also, according to Bacescu
et al. (1971) this biocenosis is one of the most important biocenoses of the Black Sea, since it is the feeding area of several
fish species of economic value, as well as of their offspring.
Material and methods
The study is based on the analysis of 21 quantitative and
10 qualitative samples, collected in summer and autumn
2003, at 7 stations on the Romanian Black Sea coast (5 stations in Mamaia cell and 2 in Mangalia cell).
Quantitative sampling was done by Van Veen grab covering
an area of 200 cm2, and the qualitative sampling by a dredge
(“Băcescu dredge” – having the net mesh size Φ 1 mm).
The samples have been conserved with buffered formaldehyde 5 % and stained by Congo Red Laboratory processing:
• Washing samples through 3 sieves of 1 mm, 0.25 mm and
0.125 mm to separate macro- and meiofauna;
• Identification of the species by binocular microscope;
• Counting all species / individuals;
• Larger size forms were weighed (wet weight, including
shells, intervalvar water etc.);
• Meiobenthos biomasses were estimated using standard
weight tables;
• Computer processing of the data for ecological parameters were performed.
In order to statistically process the results obtained following separation, the analytical ecologic indicators and diversity indicators were used.
Results and Discussions
The results of researches carried out in summer and autumn 2003 at Mamaia and Mangalia shallow water zones
proved the presence in the biocenosis of the mobile sediments of 60 taxa, of which 50 have been identified accord-
ing to their species. Of the total taxa identified, foraminifers
represent 12 % of species, worms – 45 %, mollusks – 7 %,
crustaceans– 33 % and the other groups– 3 %. The average
density recorded in the sandy invertebrate populations in the
researched areas has been of 722,011.90 indvs.m-2, and the
biomass of 192.25 g.m-2.
The most important role in obtaining the density and
frequency of occurrence dominants is that of meiobenthal
forms: nematodes, copepods, polychaetes Nerine cirratulus
and Polydora antennata, turbellariates and the foraminifer
Amonia beccari. Of these, the nematodes and the copepods
represent 94 % of the total average density.
In the case of the biomasses, the macrobenthal populations account for 90 % of the total, represented by the bivalve
mollusks Mya arenaria, Corbula mediterranea, Cardium edule,
by the amphipod Ampelisca diadema etc.
After having conducted a comparative study of the sandy
invertebrate populations of both the Northern Romanian
shore (Mamaia) and the Southern area thereof (Mangalia) it
was noted that the diversity of macrobental populations, although richer in Mamaia (34 taxa) is not different from that in
Mangalia (30 taxa), where the fauna in the sandy areas is more
like that of the submerged beaches to the North of Constanta
than the fauna of the neighboring areas. Of the total taxa (40)
identified in both areas - 24 (60 %) are common, 10 taxons
(25 %) were present only in Mamaia and 6 taxa (15 %) only
in Mangalia (APPENDIX I, Fig. 1). The differences concerning
absence or presence of taxa in an area were noted in cases of
polychaetes and crustaceans.
Yet the diversity of the meiobenthal populations is higher
in Mangalia (18 taxa) than in Mamaia area (11 taxa), where
poorer ecological conditions favour the development of some
species with low ecologic plasticity (ostracods, some polychaetes) (APPENDIX II). Of the total identified taxa (20) only 8 taxa
(42 %) are common to both areas, 9 taxa (47 %) were present
only in Mangalia and 2 (11 %) only in Mamaia (Fig. 1).
Fig. 1 The percentage of specific and common macrobenthal and meiobenthal taxa in the studied areas, i.e., Mamaia and Mangalia in 2003
68
By analyzing the values of average density and biomass
of the macrobenthal populations that are cohabitating in the
two sectors of Romanian sea coast, it was noted that fauna in
the Mamaia cell (29,013 indvs.m-2, that is 235.13 g.m-2) has 1.4
times higher density and 3.2 greater biomass than in Mangalia
(20,300 indvs.m-2 that is 73.37 g.m-2) (Fig. 2). This has also been
noticed in the case of meiobenthal populations, which, in the
Mamaia area, have a density 1.8 times higher and an average
biomass 1.9 times greater than in Mangalia area (Fig. 3).
The reduced contribution of the macro - and meiobenthal
fauna segment in Mangalia sector to the formation of populations of average numeric and weight variables greater than
those in the Mamaia sector is due to the spatial limitation of
the mobile sediments, which does not allow the evolution of
typical psammic associations.
The sediments that aggregate in sufficient quantities to allow for the support of sandy invertebrate populations are only
achieved in the cell interior, sheltered by protection dams. Due
to the bordering of the sedimentary bottoms by the natural
one, the possibilities of fauna inflows from other regions are
limited, and the quality was only improved where the species
existed on the hard bottom (e.g.: polychaetes Brania clavata,
Eteone picta, etc., amphipods Amphithoe vaillanti, Hyale perieri,
Hyale pontica, cumaceans Cumella limicola etc). The reduction of the communities associated with the sandy bottom
is achieved also through the important aggregation of algae
that are wiped away from the hard bottom. This happens in the
circumstances of the summer stillness, which favours the occurrence of the hypoxia in these areas through the consumption of O2 in the shallow water column and subsequently by
the decomposition of excess organic material, a process also
related to high levels of O2 consumption. Because of the reduced surface and stillness of the water mass in summer, the
pseudo-faeces of the mollusks also contribute to a high extent
to the overloading of sediments with organic material (and
mineral, too). Generally, at the foundation of any coastal pro-
Fig. 2 The average density and biomass of the macrobenthal psammobiontic populations in Mamaia and Mangalia cells in 2003
tection dam, especially on the inside, the fauna associated with
mobile sediments is extremely poor in quality and in points of
abundance, because of the pseudo-faeces rain favouring the
decomposition processes using up the O2 in the sediment column. Direct observations in free diving have shown that the
sub-superficial layer of sediments was fully oxidized, and that
it was producing a strong smell of sulphurous hydrogen. Thus,
limitation of the hydrologic exchange in these semi-closed
cells represents a decisive factor in electing some populations
that are scarce in points of species count and abundance per
surface unit, when compared to Mamaia cell, where extended
exchange provides for a water mass circuit even in stillness periods, and the renewal of populations affected by mass mortality is more rapidly achieved.
The participation of macrobenthal populations, of the main
organisms groups in the psammic biotopes in the areas analyzed is presented in figure 4, and the domination of Vermes
group are obvious. Of these worms, in the Mamaia cell, a major
weight in points of number and an almost constant presence is
that of polychaetes that are exclusively psammic, Nerine cirratulus (9,460 indvs.m-2) and Polydora antennata (6,217 indvs.m-2)
followed by oligochaetes, with 2,467 indvs.m-2. In the Mangalia cell, apart from the species mentioned, a significant abundance has been recorded also in the polychaetes Sphaerosyllis
bulbosa (1,267 indvs.m-2) and Spio filicornis (1,100 indvs.m-2). As
compared to the years 1960 – 1970, the polychaete Spio filicornis, a species that is largely present in the infra-littoral with fine
sands, has reduced its densities in the areas analyzed.
The mollusks are the most representative element in the
sand area, defining the type of biocenosis. In the Mamaia cell,
the mollusk populations are represented by Corbula mediterranea, Mya arenaria and Cardium edule that have recorded
abundance and biomasses higher than those in the Mangalia
cell. Corbula, the most common species in the fine sand area,
has been thoroughly watched in its biocenosis by Băcescu et al.
(1965, 1967) and Gomoiu (1965, 1966, 1968a, 1968b, 1969).
Fig. 3 The average density and biomass of the meiorobenthal
psammobiontic populations in Mamaia and Mangalia cells in 2003
69
Fig. 4 Participation of the macrobenthal populations in the main groups of organisms to the psammic biotopes of Mamaia and Mangalia cells, 2003
Today, the populations of this species have undergone
important changes in structure. Thus, the leading species, of
the biocenosis, less tolerant to environmental changes has
reduced populations from 246,000 indvs.m-2 in the 1960s
(Bacescu et al. 1971) to 3,700 indvs.m-2 at the beginning of the
1990s (Petranu, 1997). At the moment, the densities of this
species in the upper infra-littoral area of Mamaia, on the isobaths of 1.5 m, have increased to approximately 7,350 indvs.
m-2, the most abundant species in the macrobental populations. It is worth mentioning that in the Mangalia cell Corbula
mediterranea has not been found in any of the samples analyzed, but its absence in the samples does not mean that it is
missing in the sandy areas in the Southern littoral.
In the sands of the Romanian shore, but especially in
Northern areas, Mya arenaria is an element quite frequent (it
is found in over 50 % of the stations analyzed). Sometimes
Mya arenaria remains the leading species in the biocenosis of
fine sands, replacing Corbula (in the Mangalia cell).
Almost all systematic groups represent the crustaceans in
the analyzed areas. Of the macrobenthal forms, the amphipods and cumaceans have recorded in the Mamaia cell densities almost twice as high as in the Mangalia cell. The amphipods populations are dominant in both areas by the species
having a large ecological plasticity, Ampelisca diadema, but
the important contribution of the populations of rocky – phitophagous species Amphithoe vaillanti, Echinogammarus olivii, Hyale perieri, H. pontica etc. should be noted.
Isopods, tanaids and decapods have a heterogeneous
spreading in the areas analyzed. Significant abundance has
been recorded in the populations of isopods represented by
Idotea baltica and Sphaeroma pulchelum and the tanaids in
the Mangalia cell, and the decapods analyzed from the quantitative samples in the Mamaia cell.
Among the meiobenthal forms, the worms represented
by Nematodes were dominant, 90 % of the total density in
both littoral cells. The meiobenthal crustaceans in the copepods group exhibited large densities in the Mamaia cell, 1.7
times higher than in the Mangalia cell, and the ostracods
were only identified in Mangalia.
70
As in our quantitative samples the epifauna organisms
have usually been missing, since they can only happen to
be taken by our semi-quantitative dredgers, a series of semiquantitative dredges were conducted, that revealed that the
epifauna is made of Mysida, as a dominant group, and of Amphipoda, Cumacea and Decapoda.
The dispersion of mysida populations is, in most cases,
an aggregate one, and their density in the biocenoses analysed is generally low, not reaching the high values indicated
in the specialized literature, namely thousands of items per
m2. This is supported also by the fact that mysida are species
intolerant to pollution, and in the last two decades a series of
changes in these aquatic ecosystems, following increase of
the anthropogenic pressure, has certainly affected the mysida populations, taking into account their low number in the
samples analysed.
Among the mysida populations of Mesopodopsis slabberi
average densities were recorded of 36 indvs.m-2, and Paramysis kroyeri of 118 indvs.m-2 in both areas analysed. The Mediterranean species slightly eurihalyne and psammic species
Gastrosaccus sanctus together with Siriella jaltensis jaltensis
– stenobiotic, rocky substratum, exceptionally phototropic
and an excellent predator have been found only in the south
of the Romanian Black Sea coast, (Mangalia cell) having average densities of 9 indvs.m-2.
The decapods species found in the qualitative samples
were the shrimp Crangon crangon, hermit crab Diogenes pugilator and the sand crab Liocarcinus holsatus.
The analysis of the quantitative and qualitative distribution of the macro - and meiobenthal fauna segment in the protected area of the Mamaia and Mangalia cells reveals mostly
quantitative differences. Thus, in the case of macrobenthal
populations in the Mamaia cell as well as in the Mangalia cell
in their protected areas, protected by dams, densities twice
as high as in the exposed areas were recorded. (Fig. 5, 6).
Fig. 5 Diagram representation of the macrobenthic populations
in the protected and exposed areas of Mamaia cell, in 2003
Fig. 6 Diagram representation of the macrobenthic populations
in the protected and exposed areas of Mangalia cell, in 2003
Fig. 7 Diagram representation of the meiobenthic populations in
the protected and exposed areas of Mamaia cell, in 2003
Fig. 8 Diagram representation of the meiobenthic populations in
the protected and exposed areas of Mangalia cell, in 2003
The differences are accounted for by the polychaetes
populations Polydora antennata, Nerine cirratulus as well as
by the oligochaetes, preferring the protected areas of the littoral cells, where densities 7 times higher were recorded, as a
consequence of the presence of a rich organic material found
as detritus preventing the inter-specific competition and allowing for the quantitative count development thereof.
Specific abundance was recorded among the meiobenthal
populations in the protected area of Mamaia cell, with densities exceeding 1,000,000 indvs.m-2, as compared to Mangalia
cell, where in both exterior and interior sides, the quantitative
variables are similar (~ 450,000 indvs.m-2) (Fig. 7, 8).
By comparing the structure of the sandy invertebrate
populations in the two locations analysed with the data
published by Băcescu et al. (1969) an increase is noted in the
average density of the psammobiontic organisms in 2003,
5.8 times in Mamaia and 4 times in Mangalia. This increase
is generated by the meiobenthal populations (worms of the
groups Nematoda, Turbellaria and Polychaeta, crustaceans of
the group Harpacticoida and Ostracoda) and affects the macrobental ones (Fig. 9).
71
But the average biomass of the benthal organisms in the
Mamaia area was twice as high in 2003 (239.3 g.m-2) as in 1968
(104.3 g.m-2), and in the Mangalia area, it was 5 times lower
in 2003 (74.8 g.m-2) than in 1968 (367.4 g.m-2) (Fig. 10). This
increase and decrease of the average biomass is achieved
based on the psammobiontic mollusk which, in the Mamaia
area (2003) has witnessed a recovery in number, especially,
populations of Corbula mediterranea. In the Mangalia area,
the populations of mollusks were represented by juvenile
stages of Mya arenaria and Cardium edule and this lead to the
achievement of a lower average biomass, compared to 19601970, when the biocenosis of gross sands in the Southern littoral was dominated by Corbula mediterranea. Due to its high
Fig. 9 Variation of average density of sandy invertebrate populations in Mamaia and Mangalia areas in the 1968 – 2003 interval
abundance, this small-scale species is the main element in
points of weight in the structure of psammic shallow water
populations of the Romanian shores.
A problem that is worth mentioning is the ratio between
macrobenthos and meiobenthos, that has lately changed compared to the years of reference (1960 –1970) (Table 1). The value
of the ratio macrobenthos – meiobenthos indicates the numeric
abundance of the meiobenthal populations in the period analysed, more resistant to external perturbations – permanent instability and high fluctuations of the defining ecological factors,
compared to the macrobenthal populations, that have better
used the new biotopic conditions of the aquatorium.
After analyzing the current status of the major groups of
macrobenthos and meiobenthos in the two areas under study,
compared with the status existing in 1960 – 1970, it is evident that the populations of macrobenthal and meiobenthal
psammobiotic organisms in the Mamaia area have recorded
quantitative changes, that are usually characterized by increases in the benthos abundance, both in points of number
and weight. The most important changes concerning the
quantitative weight in the analysed areas were recorded in
the groups of worms, crustaceans, and foraminifers, which
reached significant abundances in 2003 (Fig. 11).
In the Mangalia area, apart from the reduction of the taxa
count, there was a sharp decrease in the numeric abundance
of mollusks’ populations, from 40,120 indvs.m-² between
1960-1970, to only 1,075 indvs.m-² in 2003. But the macrobenthic crustaceans represented by amphipods, isopods, tanaids
and decapods have doubled their densities (Fig. 12).
Together with the reduction of populations in species
characteristic of the fine sands biocenosis with Corbula mediterranea, some opportunistic species have proliferated, benefiting from the increase of organic substance in the marine
environment, and also the competition has decreased in the
dominant species, the polychaetes Polydora antennata, Nerine cirratulus, the bivalves Mya arenaria and Scapharca inaequivalvis (Gomoiu, 1981, 1984a).
Fig. 10 Variation of average biomass of sandy invertebrate populations in the Mamaia and Mangalia areas in the 1968 – 2003
time interval
Table 1 The ratio of the average density and biomass of the macrobenthos and meiobenthos
DAVG
BAVG
D
Mangalia AVG
BAVG
Mamaia
72
1968
2003
Macrofauna : Meiofauna Macrofauna : Meiofauna
1 : 13
1 : 27
405 : 1
61 : 1
1:1
1 : 22
371 : 1
36 : 1
In order to maintain the essential ecological processes,
of the life support system, and of the biodiversity in the marine and coastal areas, an integrated management thereof is
required. This concept guarantees the sustainable development of marine and coastal areas, as well as reduction of their
vulnerability to the natural pressures and especially to the
anthropogenic ones.
Conclusions
The results of the ecological research on the sandy invertebrate populations in the upper infra-littoral in the Mamaia and
Mangalia cells in 2003 have revealed the following conclusions:
• The coastal marine ecosystems are directly or indirectly targeted by the most powerful ecological pressures exerted
by multiple human activities of the littoral areas, in the sea
as well as in the hydrographical areas of the rivers flowing
into the Black Sea, one of the two main coastal ecosystems
•
•
•
Fig. 11 Diagram of the quantitative and qualitative changes of
the main groups of organisms in the macrobenthos and meiobenthos in Mamaia areas in the 1968 – 2003 time interval
Fig. 12 Diagram of the quantitative and qualitative changes of
the main groups of organisms in the macrobenthos and meiobenthos in Mangalia areas in the 1968 – 2003 time interval
– the one of the sandy grounds with Corbula – Mya, has
recorded important ecological changes in the last decade,
and sediment associations have occurred that make use of
the organic material that is “captive” in the sediments;
The comparative analysis of the sandy invertebrate populations in the two areas under observation have generally
revealed differences of quantitative nature, both the macrobenthal and meiobenthal organisms in the Mamaia cell
being approximately twice as many as in the Mangalia
cell, because of the spatial limitations of the sandy bottoms in the Mangalia cell, a situation that does not allow
for the evolution of the typical psammic associations;
Following the comparative study between the protected
and exposed areas of the Mamaia and Mangalia cells, it
was noted that in the protected areas of the littoral cells,
densities recorded are approximately twice as high as in
the exposed ones, as a consequence of the presence of
a rich organic material in the form of detritus, preventing inter-specific competition and allowing the numeric
quantitative development thereof;
By comparing the structure of the sandy invertebrate
populations in the two localities analysed with the data
published by Băcescu et al. (1969), an increase was noted
in the average density of the psammobiontic organisms
in 2003, 5.8 times in Mamaia and 4 times in Mangalia;
the increase is marked in the meiobenthal populations
(worms in the Nematoda, Turbellaria and Polychaeta
groups, crustaceans in the Harpacticoida and Ostracoda
groups) to the disadvantage of the macrobenthal ones;
As for the average biomass, an increase approximately
double was noted in the Mamaia area of the psammobiontic mollusk populations which, in 2003 record a numeric recovery, namely through the populations of Corbula
mediterranea, and in Mangalia area the mollusk populations were represented by juvenile stages of Mya arenaria
and Cardium edule, a fact that has lead to obtaining an
average biomass lower than in the 1960-1970 interval,
when the biocenosis of the gross sands in the southern
littoral had been dominated by Corbula mediterranea;
The value of the ratio macrobenthos – meiobenthos in
the recent period has changed radically compared to
the reference years (1960 –1970), which indicates the numeric abundance of the meiobenthal populations in the
analysed period. These populations have proved a higher
resistance to external disturbances – permanent instability and high fluctuations of the defining ecological factors,
than the macrobenthal ones, and they make better use of
the new biotope conditions of the aquatorium.
•
•
73
74
13.33
100.00
6.67
6.67
33.33
33.33
13.33
20.00
20.00
66.67
86.67
Capitomastus minimus
Eteone picta
Eulalia limbata
Grubea tenuicirrata
Laonice cirrata
Magelona papilicornis
Neanthes succinea
Nereis rava
2
3
4
5
6
7
8
9
10 Nerine cirratulus
11 Nerilla antennata
12 Perinereis cultrifera
13 Platynereis dumerilii
14 Polydora antennata
15 Polydora ciliata
16 Prionospio ciliata
17 Pygospio elegans
18 Sphaerosyllis bulbosa
19 Spio filicornis
20 Oligochaeta
7350.00
25.33
41.10
2
8
36.35
16.27
15.46
6.92
0.21
0.14
0.01
0.01
0.08
0.01
2.64
0.01
0.01
0.80
0.04
0.14
0.03
0.00
0.00
0.00
0.00
0.01
32.10
15.19
4.26
3.02
0.54
0.48
1.03
0.60
9.39
0.23
0.31
8.97
0.75
2.17
0.42
0.08
0.05
0.02
0.25
0.33
WB
RkB
2
3
8
10
18
19
14
17
5
27
25
6
16
11
20
32
33
34
26
22
8.33
25.00
16.67
50.00
8.33
33.33
DAVG
75.00
50.00
425.00
16.67
83.33 3383.33
100.00 1100.00
66.67 1266.67
16.67
50.00 9441.67
16.67
83.33 2891.67
16.67
33.33
16.67
50.00
16.67
33.33
F%
66.67
6.25
0.49
0.32
0.03
0.03
0.19
0.03
6.21
0.02
0.03
1.89
0.10
0.33
0.06
0.00
0.00
0.00
0.00
0.01
DB%
23 Corbula mediterranea
1.17
3
5
15
9
18
11
4
23
33
1
25
12
28
32
31
30
10
14
BAVG
50.00
21
340.00
RkD
33.33
27.14
15.70
1.73
4.31
1.11
2.84
26.73
0.83
0.28
57.10
0.68
1.96
0.39
0.28
0.28
0.28
3.62
1.73
WD
22 Cardium edule
8.50
3.70
0.15
0.93
0.09
0.24
21.43
0.10
0.01
32.61
0.03
0.11
0.02
0.01
0.01
0.01
0.22
0.15
DD%
16.67
2466.67
1073.33
43.33
270.00
26.67
70.00
6216.67
30.00
3.33
9460.00
10.00
33.33
6.67
3.33
3.33
3.33
63.33
43.33
DAVG
Mamaia cell
Midendorphia
caprearum
33.33
6.67
6.67
6.67
6.67
60.00
20.00
Brania clavata
1
F%
Taxa
No.
2.09
0.08
16.67
5.42
6.24
0.25
46.51
0.37
14.24
0.04
0.12
0.08
0.25
0.04
0.16
DD%
10.23
1.17
37.27
23.28
20.40
2.03
48.22
2.48
34.45
0.83
2.03
1.17
3.51
0.83
2.34
WD
RkD
7
24
2
4
5
21
1
17
3
26
20
23
14
25
19
Mangalia cell
19.12
0.05
0.68
0.33
0.71
0.35
8.26
0.05
0.58
0.08
0.25
0.01
0.00
0.00
0.01
BAVG
26.05
0.07
0.92
0.45
0.96
0.48
11.26
0.06
0.79
0.11
0.34
0.01
0.00
0.00
0.01
DB%
36.09
1.08
8.77
6.71
8.01
2.82
23.73
1.01
8.10
1.38
3.37
0.34
0.37
0.14
0.67
WB
General characteristics of the macrobenthic populations recorded in 2003 in the Mamaia and Mangalia sector
2
19
6
10
8
13
3
20
7
16
12
26
25
30
22
RkB
APPENDIX I
6.67
13.33
13.33
28 Hyale perieri
29 Hyale pontica
30 Melita palmata
Taxa
Vermes
Mollusca
Crustacea
Varia
Total
0.14
0.14
4.97
26.55
68.34
DD%
29013.33 100
40.00
1443.33
7703.33
19826.67
DAVG
40.00
0.96
0.78
Mamaia
22
24
235.13
1.03
10.05
214.29
9.76
BAVG
1.03
4.67
100
0.44
4.27
91.14
4.15
DB%
0.44
1.98
0.03
1.71
5.14
1.67
12
7
13
33.33
50.00
6.67
0.05
0.07
15
83.33
50.00
50.00
66.67
16.67
16.67
50.00
33.33
50.00
66.67
40 Chironomida
13.33
7
1.01
9
30
23
28
24
31
21
29
4
1
F%
13.33
12.25
0.05
3.19
0.09
0.32
0.15
0.31
0.08
0.36
0.09
11.58
52.44
RkB
39 Diogenes pugilator
1.61
0.12
0.51
0.00
0.00
0.00
0.01
0.00
0.01
0.00
1.68
68.76
WB
50.00
466.67
21
1.20
0.00
0.01
0.00
0.02
0.00
0.02
0.00
3.94
161.67
DB%
93.33
0.96
16
20
13
27
26
29
19
34
6
17
BAVG
38 Iphinoe maeotica
0.05
1.66
RkD
16.67
13.33
0.14
1.04
1.92
0.55
0.55
0.39
1.07
0.28
14.91
1.36
WD
37 Cumella limicola
20.00
35 Sphaeroma pulchaelum
40.00
0.08
0.14
0.02
0.02
0.02
0.06
0.01
2.78
0.05
DD%
16.67
20.00
34 Idotea baltica basteri
23.33
40.00
6.67
6.67
6.67
16.67
3.33
806.67
13.33
DAVG
Mamaia cell
36 Tanais cavolini
13.33
33
32 Nototropis guttatus
26.67
20.00
27 Echinogammarus olivii
Microdeutopus gryllotalpa
6.67
26 Amphithoe vaillanti
31
80.00
25 Ampelisca diadema
F%
40.00
Taxa
24 Mya arenaria
No.
0.57
3.74
5.30
90.39
D%
0.57
0.82
0.04
0.04
0.25
0.66
0.33
0.12
0.41
0.04
0.04
0.21
0.12
0.66
3.12
DD%
20300.0 100
116.67
758.33
1075.00
18350.0
DAVG
116.67
166.67
8.33
8.33
50.00
133.33
66.67
25.00
83.33
8.33
8.33
41.67
25.00
133.33
633.33
DAVG
RkD
11
9
30
29
16
8
13
18
12
28
27
15
22
10
6
Mangalia
5.36
6.41
0.83
0.83
2.87
7.40
4.05
2.48
5.23
0.83
0.83
3.20
2.03
5.73
14.42
WD
3.01
5.39
53.67
11.30
BAVG
3.01
0.03
0.00
0.00
0.45
4.00
0.00
0.07
0.02
0.01
0.00
0.03
0.02
0.76
34.50
BAVG
73.37
Mangalia cell
100
4.10
7.35
73.14
15.40
D%
4.10
0.03
0.00
0.00
0.61
5.45
0.01
0.09
0.03
0.01
0.00
0.05
0.03
1.03
47.02
DB%
14.32
1.31
0.17
0.28
4.52
21.31
0.52
2.10
1.32
0.41
0.26
1.51
1.01
7.19
55.99
WB
9
1
5
18
29
27
11
4
23
14
17
24
28
15
21
RkB
75
76
Ammonia tepida
Ammonia pelucida
Elphidium incertum
Elphidium macellum
Cribroelphidium poeyanum
Quinqueloculina aspera
Turbellaria
Nematoda
Nerinidae larvae
Polydora larv. Juv
Spionidae larvae
Syllydae juv.
Polychaeta varia
Halacarida
Copepoda
Xestoleberis acutipenis
Loxoconcha pontica
Paradoxostoma intermedium
Taxa
Foraminifera
Vermes
Crustacea
Varia
Total
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
100.00
53.33
26.67
40.00
100.00
100.00
13.33
13.33
13.33
33.33
93.33
Ammonia beccarii
1
4896.67
796010.00
63473.33
727640.00
DAVG
63473.33
813.33
1366.67
2706.67
717326.67
5426.67
33.33
43.33
33.33
350.00
4436.67
100
7.97
91.41
0.62
DD%
7.97
0.10
0.17
0.34
90.12
0.68
0.00
0.01
0.00
0.04
0.56
8.26
0.24
0.27
0.24
1.21
7.21
28.24
2.33
2.14
3.69
94.93
WD
RkD
2
6
7
5
1
3
11
9
10
8
4
3.86
1.27
1.66
0.93
BAVG
1.27
0.03
0.05
0.11
0.22
1.25
0.02
0.02
0.02
0.07
0.81
BAVG
100
32.89
43.03
24.07
DB%
32.89
0.84
1.42
2.81
5.62
32.34
0.39
0.51
0.39
1.84
20.95
DB%
57.35
6.71
6.15
10.59
23.72
56.87
2.28
2.60
2.28
7.84
44.22
WB
RkB
16.67
33.33
16.67
66.67
83.33
2425.00
33.33
25.00
33.33
375.00
1816.67
DAVG
83.33
16.67
16.67
50.00
50.00
33.33
66.67
66.67
33.33
83.33
1 100.00
7
8
5
708.33
444183.33
216.67
39150.00
402533.33
2283.33
DAVG
100.00
133.33
275.00
37933.33
216.67
16.67
200.00
616.67
866.67
483.33
4 100.00 397925.00
2 100.00
11
9
10
6
3
F%
DD%
Mangalia
DAVG
F%
Taxa
No.
Mamaia
100
0.05
8.81
90.62
0.51
DD%
0.16
0.02
0.03
0.06
8.54
0.05
0.00
0.05
0.14
0.20
0.11
89.59
0.55
0.01
0.01
0.01
0.08
0.41
DD%
7.39
0.35
0.43
0.35
2.37
5.84
3.26
1.23
1.00
2.27
29.22
2.02
0.25
0.87
2.63
3.12
1.90
94.65
WD
RkD
5
12
13
9
2
10
18
14
7
6
11
1
3
17
15
16
8
4
2.02
0.02
0.84
0.89
0.28
BAVG
0.05
0.01
0.01
0.02
0.76
0.02
0.01
0.01
0.02
0.03
0.02
0.10
0.69
0.00
0.00
0.02
0.02
0.24
BAVG
100
0.75
41.53
43.92
13.79
DB%
2.28
0.32
0.43
0.89
37.61
0.75
0.50
0.40
1.22
1.72
0.96
4.81
34.32
0.07
0.06
0.74
0.84
12.08
DB%
12.34
4.63
3.78
8.59
61.33
7.92
2.87
2.57
7.82
9.27
5.65
21.93
58.59
1.11
1.36
3.52
7.47
31.73
WB
General characteristics of the meiobenthic populations recorded in 2003 in the Mamaia and Mangalia sector
3
5
12
13
7
1
8
15
16
9
6
11
4
2
18
17
14
10
RkB
APPENDIX II
References
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litoralul romanesc al Marii Negre. Cercetari marine – Recherches
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Petranu, A., (compiler), 1997 – Black Sea Biological Biodiversity – Romania. Black Sea Env. Series, 4, United Nations Publ. New York: 314
77
CRETACEOUS-CENOZOIC PALEOBIOGEOGRAPHY OF
THE SOUTHERN ROMANIAN BLACK SEA ONSHORE
AND OFFSHORE AREAS
Mihaela Carmen MELINTE
National Institute of Marine Geology and Geoecology (GeoEcoMar Bucharest),
23-25 Dimitrie Onciul St, 024053, Bucharest, Romania
Abstract. Investigations carried out on 22 drillings on the Southern onshore area of the Romanian Black Sea and on one drilling from the Southern
offshore area of the Romanian Black Sea are presented here. The lithological/sedimentological investigations and the micropalaeontological (calcareous
nannoplankton) quantitative and qualitative analyses revealed several depositional sequences. The oldest identified sedimentary cycle is latest Jurassic
(Tithonian) - Early Cretaceous (Berriasian - Valanginian) in age and composed of marine shallow water carbonates. The next cycle, in stratigraphic order, is
Barremian - Early Aptian in age, composed of marine shallow water carbonates. A fluvial-lacustrine formation, Middle - Late Aptian in age, was observed
only in the drillings from onshore area. The youngest Cretaceous cycle (Santonian – Maastrichtian) is mainly composed of chalks, with intercalations of
glauconitic sands towards the base. In the chalk offshore deposits of the Black Sea, a continuous sedimentation took place within the Cretaceous/Tertiary
boundary interval. The Paleogene deposits (Middle – Late Eocene) are characterized by the presence of marlstones and claystones. These are overlain by
Oligocene black shales, rich in organic matter and fish remains. Miocene, Pliocene and Pleistocene deposits were sedimented in a brackish environment,
but several marine influxes probably occured (based on the nannofloras encountered) within the Middle Miocene, latest Miocene-earliest Pliocene and Late
Pleistocene. The Cretaceous-Eocene nannofloras are dominated by warm water taxa (Tethyan nannofloras). The occurrence of the Cretaceous calcareous
nannoplankton confined to high latitudes (Boreal taxa) within the Late Valanginian, the Barremian - Aptian boundary interval and the latest Maastrichtian,
indicate cooler water surfaces. A more significant cooling could be assumed in the Early Oligocene, occuring at the same time with the separation of the
Paratethys Realm, and with the appearance of endemic nannofloras in the Black Sea offshore area.
Key words: Cretaceous - Paleogene - Neogene, litho- and biostratigraphy, nannofloras, NW Black Sea
INTRODUCTION
sediments cropping out in the Southern Dobrogea were pub-
The area on which this study is focused comprises both
the onshore and the offshore zone of the Southern Romanian
Black Sea region (Figure1). This area belongs, in terms of tectonic evolution, to the Eastern extension of the Moesian Platform (the Dobrogea sector - including both the Central and
the Southern Dobrogea, according to Săndulescu, 1984). The
analyzed onshore wells are placed in Southern Dobrogea, a
subsided block, which is separated from the uplifted block
of the Central Dobrogea by the Capidava - Ovidiu Fault (Dinu
et al., 2002).
Pioneer investigations of this region have started as early
as the second half of the XIXth century and the beginning of
the XXth century (Reuss, 1865; Peters, 1867; Anastasiu, 1898;
Simionescu, 1906 and Macovei, 1911). Detailed studies of the
lithology and palaeobiology of the Cretaceous - Cenozoic
lished, in the second half of the last century, by Chiriac (1968),
Tătărâm et al. (1977), Neagu et al. (1977), Neagu (1986, 1987),
Bărbulescu & Neagu (1988), Ion et al. (1998) and Avram et al.,
1988 (among others).
If there is a remarkable amount of data available for the
surface stratigraphy of Southern Dobrogea, the data concerning the subsurface of Southern Dobrogea are scarce.
One of the first published studies on this topic is by Băncilă
(1973). In the ’80s, the drilling of 22 wells, in the Southern Dobrogea area, revitalized the investigation of the subsurface
of the Southern Romanian Black Sea onshore. Stratigraphical
investigations of these drillings generated new data on Cretaceous subsurface deposits of this region (Avram et al., 1993;
Ion et al., 1998).
79
M.C. Melinte - Cretaceous-Cenozoic Paleobiogeography of the Southern Romanian Black Sea Onshore and Offshore Areas
This study aims to provide a reconstruction of the depositional history of the Southern Romanian Black Sea area,
based on the detailed lithological and palaeontological analyses of 22 onshore drillings. Investigations of the Cretaceous
- Cenozoic sequences, of one well (Tandala), drilled offshore
in the Southern Romanian Black Sea territory (Fig. 1), were
also completed.
MATERIALANDMETHODS
Detailed investigations were completed of 22 drillings
onshore in the Southern Romanian Black Sea and of one drilling offshore in the Southern Romanian Black Sea (Fig. 1).
Lithological and sedimentological analyses, as well as
preliminary micropalaeontological data were previously published by teams of scientists, including the author of this paper (Avram et al. 1993; Ion et al., 1998; Popescu et al., 1998).
Apart from a new interpretation of the data acquired,
detailed calcareous nannoplankton studies, on the Black Sea
onshore and offshore drillings, were also carried out. Both
qualitative and quantitative analyses were done. On each
smear-slide, 300 specimens were counted, the investigation
being completed to 200 fields of view. The diversity was estimated as the number of the total taxa in each sample, while
the abundance was considered as the number of nannofossils in one field of view. The nannofloral taxonomy follows
Perch-Nielsen (1985a, 1985 b).
RESULTS
Early Cretaceous
The oldest deposits traversed by the studied onshore
drillings belong to the Cernavodă Formation and yielded
two main facies: a North-Western facies, mainly composed of
evaporitic rocks, variegated clays, marls and sandstones (the
Amara Member, 150-180 m thick) and a South-Eastern one,
mainly made by calcarenites and calcilutites (the Alimanu
Member, 150-180 m thick) – figure 2.
The two units described above are Early Berriasian - Late
Valanginian, as proved by the identified calcareous nannofloral assemblages. The successive first occurrences (FO) of
the nannofossils Cretarhabdus angustiforatus (Black) Bukry
and Calcicalathina oblongata (Worsley) Thierstein led to the
identification of the NK1, NK2 and NK3 Calcareous Nannoplankton Zones of Bralower et al. (1989). The deepest Berriasian deposits were recorded at 397 m (drilling 19), while
the uppermost Berriasian sediments were identified at 55
m (drilling 8).
The quantitative studies focused on four taxonomical
groups : (1) Watznaueria barnesae, an extreme cosmopolitan
species, resistant to diagenesis; (2) the Tethyan Nannoconus
species, oligotrophic taxa, indicating warm surface waters
(Melinte and Mutterlose, 2001); (3) Tethyan taxa, especially
confined to low to middle latitudes (other then Nannoconus),
including Polycostella senaria Thierstein, Diazomatolithus leh-
Fig.1 Studied drillings in the Southern part of the Romanian Black Sea onshore and offshore (modified after Avram et al., 1993; Ion et al., 1998)
80
Fig. 2 Composite lithology and biostratigraphy of the studied drillings from the Southern Romanian Black Sea onshore
81
manii Noël and Conusphaera mexicana Trejo; (4) Boreal taxa
(sensu Mutterlose, 1992) including Micrantholithus speetonensis Perch-Nielsen, Sollasites horticus (Stradner) Čepek and Hay,
S. lowiei (Bukry) Rood et al., and Crucibiscutum salebrosum
(Black) Jakubowski, nannofossils which indicate relatively
cool water surfaces.
Similar to other Romanian sections (e.g. the Carpathian
Domain - Melinte and Mutterlose, 2001), the Berriasian of
the Black Sea onshore is characterized by nannofloral assemblages dominated by Watznaueria barnesae (Black) Perch
- Nielsen (yielding an abundance of 20-30%) and Nannoconus
spp. (with an equivalent abundance of 20-30%) – Figure 2.
The cosmopolitan species are, within most of the Berriasian,
more abundant than the Tethyan ones (Nannoconus spp., Polycostella senaria, Diazomatolithus lehmanii and Conusphaera
mexicana). The Late Berriasian - Early Valanginian nannofloras
(lower part of the NK2 Calcareous Nannoplankton Zone) are
dominated by the Tethyan taxa (the abundance of Nannoconus is almost 50%). In the Late Valanginian, there was a shift
in the abundance of nannoconids. The event is synchronous
with the appearance of the Boreal taxa, which represent up
to 12% from the assemblages. High fertility proxies, as Biscutum constans (Gorka) Black, Diazomatolithus lehmanii and
Zeugrhabdothus erectus (Deflandre) Reinhardt, increase in
abundance (amounting jointly to 15%) within the Late Valanginian.
In the investigated offshore drilling (Tandala), the oldest recorded deposits are latest Jurassic - earliest Cretaceous
(Tithonian - Valanginian) in age and 120 m thick. In terms of
lithology, these sediments are similar to the Lower Cretaceous
South - Eastern facies of the studied onshore drillings – i.e. calcarenites and calcilutites with frequent dasycladacean algae
belonging to the Alimanu Member (Cernavoda Formation).
The latest Jurassic (Tithonian) age was assigned based on foraminiferal assemblages containing Topalodiscorbis sp. and
mililoids (Neagu in Avram et al., 1993) and also based on the
presence of the Crassicolaria Calpionellid Zone. The BerriasianValanginian age is argued by the foraminiferal assemblages
with Pseudocyclammina litus and Trocholina alpina – Neagu in
Avram et al., 1993 and also by the identification of the NK1 and
NK2 Calcareous Nannoplankton Zones (Fig. 3).
The qualitative investigations of earliest Cretaceous nannofloras revealed similar trends to those recorded onshore of
the Black Sea in the calcareous nannoplankton fluctuations;
high abundance of the Tethyan species (including Nannoconus) within the Berriasian and Early Valanginian, and their significant decrease, within the Late Valanginian, together with
the occurrence of Boreal taxa and increase of Watznaueria
barnesae.
The next lithological unit (in the stratigraphical succession) traversed by the studied onshore drillings is the Ramadan Formation (90-100 m thick), which displayed two main
facies (Fig. 2). There occur red clays, sandstones and locally,
calcarenites in the Western part of the surveyed area; and ree82
fal limestones and calcarenites rich in orbitolinids and miliolids in its Eastern part. Comparing with the subjacent Lower
Berriasian - Upper Valanginian calcarenites of the Cernavoda
Formation, mainly containing dasycladacean algae, the most
abundant microfossil of the Ramadan Formation are the
arenaceous foraminifers, as well as the miliolids and orbitolinids (Neagu, 1986; Avram et al., 1993). The deepest recorded
level of the Ramadan Formation is 220 m (Well 24), while the
topmost is 48 m deep (Well 11).
The identified nannofloras indicate, for the Ramadan
Formation, a Late Barremian - earliest Aptian age, based on
the successive FOs of the nannofossils Vagalapilla matalosa
(Stover) Thierstein, Hayesites irregularis (Thierstein) Covington & Wise and Braarudosphaera hockwoldensis Black. The
latest bio-event approximates, in the Tethyan Realm (including the nowadays Romanian territory), the Barremian-Aptian
boundary interval (Barragan and Melinte, 2006).
The quantitative nannofloral studies focused on four
taxonomical groups : (1) Watznaueria barnesae, an eurytopic
cosmopolitan and ecologically robust form, one of the first
species to settle in new biotopes; (2) Nannoconus spp., taxa
which are believed to be restricted to lower photic zone and
controlled by fluctuations of nutricline depth (Erba,1994).
High abundance of Nannoconus indicates deep chlorophyll
maximum zone (DCM), with increased productivity of the lower photic zone and high surface water temperatures (Melinte
and Mutterlose, 2001; Bersezio et al., 2002); (3) Tethyan taxa
(other than nannoconids), which are also especially confined
to low to middle latitudes, including Assipetra terebrodentarius (Applegate et al. in Covington and Wise) Rutledge and
Bergen in Bergen, Hayesites irregularis, Conusphaera mexicana, and C. rothii (Thierstein) Jakubowski, (4) Boreal taxa (sensu
Mutterlose, 1992) including Sollasites horticus, Crucibiscutum
salebrosum, Zeugrhabdotus sysiphus (Gartner) Crux and Vagalapilla matalosa, species indicating relatively cool water
surfaces.
The Late Barremian nannofossil assemblages (upper part
of NC5 Calcareous Nannoplankton Zone of Roth’s Zonation,
1978) are dominated by the Tethyan taxa, which make up, together with Nannoconus spp. almost 70% of total nannofloras
– Figure 2. Within the latest Barremian (around the boundary between the NC5/NC6 Calcareous Nannofossils Zones of
Roth, 1978) there was a significant shift in the Tethyan taxa
(from 70% up to 45%). This bioevent is coincident with an
increased abundance of cosmopolitan nannofossil Watznaueria barnesae and of Boreal taxa. The shift in the Tethyan
calcareous nannoplankton is even more pronounced within
the earliest Aptian (lower part of the NC6 Calcareous Nannoplankton Zone). That is an interval in which they represent
only 25% of nannofloras – Figure 2.
In the Tandala Well, reefal limestones and calcarenites
(80 m thick), rich in orbitolinids and miliolids were identified.
The Hauterivian – Aptian age of the above-described succession was formerly confirmed based on the presence of
Fig.3 Lithostratigraphy of the Cretaceous-Cenozoic deposits traversed by the Tandala Well (Southern Romanian Black Sea offshore)
83
foraminiferal assemblages (Neotrocholina paucigranulata,
Gavelinella barremiana, Epistomina carpenteri Assemblage
– according to Neagu in Avram et al., 1993). Based on calcareous nannoplankton investigations, these deposits are Late
Hauterivian - earliest Aptian in age (an interval covered by
the NC5 and NC6 Calcareous Nannoplankton Zones of Roth,
1978). The nannofloral quantitative analyses of the offshore
sediments revealed a trend similar to the one in the onshore
deposits. The Hauterivian - Barremian nannofloras are dominated by Tethyan taxa. The Boreal nannofossils occurred
within the latest Barremian and the warm water nannofossils (including the nannoconids) decreased significantly
within the earliest Aptian.
The Ramadan Formation is unconformably overlain, in
the Southern offshore of the Black Sea, by the Gherghina
Formation, which is mainly constituted by sands with thin
coal lenses and kaolinitic clays. The Gherghina Formation
(50-60 m thick) was encountered in the onshore drillings 10,
11, 13, and 15, the deepest level where it was recorded being 182 m (Well 13), while its uppermost level is 50 m deep
(Well 11). This lithological unit is Middle - Late Aptian in age,
based on the identification of charophyte assemblages, containing among other taxa, Atopochara trivolvis trivolvis Pech,
A. trivolvis tricheta (Pech) Grambast, Clavator harrisi Peck,
Nodosoclavatus adnatus Martin-Closas & Grambast-Fessart,
Pseudoglobator paucibracteatus Martin-Closas & GrambastFessart and Perimneste horrida Grabast (Iva, 1990).
Late Cretaceous
The Upper Cretaceous deposits were identified in the
onshore area of the Black Sea in the wells 6, 7, 8, 9, 10 and
12 (Fig. 1). The oldest Upper Cretaceous lithostratigraphical
unit discovered (in drillings 8 and 10) is the Murfatlar Formation, made up of grey-whitish argillaceous chalks, with
reddish mottled clays in the lower part, overlain by yellowish clays and whitish, massive chalky limestones towards
the top (Ion et al., 1998). The Murfatlar Formation is 30-40 m
thick, with its deepest level situated at 113 m (in Well 9),
while its topmost level is placed 12 m deep (in Well 10). The
calcareous nannoplankton assemblages, characteristic of
CC18, CC19 and CC20 Calcareous Nannoplankton Zones (of
the Sissingh’s Zonation, 1977) argue for a Santonian – early
Late Campanian age (Fig. 2).
The next stratigraphical unit is the Nazarcea Formation
(found in the drillings 6, 7, 8, 9 and 12). Its deepest level is
113 m (in drilling 9) while its uppermost level is 10 m deep
(Well 8). The Nazarcea Formation (from 20 to 45 m thick) is
composed of reddish marls, gray-yellowish marls and clays,
as well as kaolinitic clays. The Nazarcea Formation was assigned to the Early Maastrichtian, based on its charophyte
content (according to Iva in Ion et al., 1998).
The youngest Upper Cretaceous unit found in the studied drillings of the Black Sea onshore is the Nisipari Formation, which was encountered in the drillings 8, 9 and 10. It
is 10-25 m thick. The deepest level where it was identified
84
is 68 m (in the drilling 9) while the topmost is 3 m (in the
drilling 10). The Nisipari Formation is made by chalky marls
and clays, overlain by glauconitic sands, and whitish massive chalky limestones. The age of this formation, i.e. latest
Campanian - Late Maastrichtian is proved by the identification of the CC22-CC26 Calcareous Nannoplankton Zones of
the Sissingh’s Zonation (1977) – Figure 2. This formation was
attributed the same age based on planktonic and benthic
foraminifers (Ion et al., 1998).
It must be noted that the youngest deposits traversed by
the 22 investigated wells, in the onshore area of the Black
Sea, are Neogene in age, and were not subject of this study.
The quantitative Late Cretaceous nannofloral analyses
focused on four taxonomical groups: (1) Watznaueria barnesae, an eurytopic cosmopolitan and ecologically robust
form; (2) Micula spp., the dominant genus in the Upper Cretaceous nannofloral assemblages. The genus Micula is mainly represented by Micula decussata Vekshina (80%). Within
the Upper Maastrichtian deposits, Micula murus (Martini)
Bukry and M. prinsii Perch-Nielsen also frequently occur. The
species of this genus are mostly confined to low to middle
latitudes, indicating also an oligotrophic environment; (3)
Prediscosphaera spp., another prevailing component of the
recorded calcareous nannoplankton is mainly represented
by the species P. cretacea (Arkhangelsky) Gartner. P. stoveri
(Perch-Nielsen) Shafik & Stradner was considered along
with the Boreal taxa; (4) the Boreal taxa are represented
by Nephrolithus frequens Górka, Cribrosphaerella daniae
Perch-Nielsen, Kamptnerius magnificus Deflandre and Prediscosphaera stoveri – nannofosils mostly confined to high
latitudes and particularly cool surface waters (Worsley and
Martini, 1970).
The Santonian (the lower part of the Murfatlar Formation) is dominated by Watznaueria barnesae and Micula
spp., which jointly amount to more than 50% of nannofloras. In the latest Santonian, there is an increase in the
abundance of Micula spp (up to 35%), synchronously with
the shift in abundance of Watznaueria barnesae. This trend
continues into the upper part of the Murfatlar Formation
(Early Campanian in age). There is a significant change in
the nannofloral composition within the Late Campanian earliest Maastrichtian (the Nazarcea Formation), when the
abundance of W. barnesae reaches a peak of 40% - Figure 2.
Concurrently, the abundance of genera Micula and Prediscosphaera sharply decreases. A significant fluctuation in the
abundance of the calcareous nannofloras took place within
the Late Maastrichtian (CC24, CC25 and CC26 Calcareous
Nannoplankton Zones). It was then that the assemblages
were, once again, clearly dominated by the genera Micula
and Prediscosphaera, jointly amounting to more than 50%
of the nannofloras. The latest Maastrichtian (upper part of
the Nisipari Formation) is characterized by an increase in
Boreal taxa (up to 15%), along with a decrease in Micula
spp. and Prediscosphaera spp., and mostly constant values
of Watznaueria barnesae (around 30%).
The Upper Cretaceous deposits identified in the Black
Sea offshore area (within the Tandala Well) consist of chalky
marlstones and claystones, as well as white chalky limestones, yielding a remarkable high calcareous nannoplankton content. More than 80 nannofloral taxa were recorded,
with an average abundance of 25 taxa/field of view. The
calcareous nannoplankton analyzes led to the identification
of the CC20, CC21, CC22, CC23, CC24, CC25 and CC26 Calcareous Nannoplankton Zones, spanning over the late Early
Campanian - latest Maastrichtian interval – Figure 3. The
whole Upper Cretaceous succession identified in the Tandala Well is 95 m thick. The Campanian calcareous nannofloras are dominated by Tethyan taxa - Ceratolithoides aculeus
(Stradner) Prins & Sissingh in Sissingh, Quadrum sissinghi
Perch-Nielsen and Quadrum trifidum (Stradner in Stradner
& Papp) Hattner & Wise, which together with the Micula
and Prediscosphaera genera amount to over 60% of nannofloras. The Early Maastrichtian calcareous nannoplankton
assemblages mainly consist of cosmopolitan taxa, while in
the latest Maastrichtian, the Boreal nannofossils represent a
significant component of the nannofloras (almost 20%).
The calcareous nannoplankton investigations yielded a
continuous sedimentation, in the chalk deposits of the Tandala Well, within the Cretaceous/Tertiary boundary interval.
This finding is supported by the identification of the nannofloral mass extinction within the upper part of the chalky
limestones. Over 95% of the Cretaceous calcareous nannoplankton have disappeared: that bioevent was previously
recorded not only in other Romanian sections across the K/T
Boundary (Melinte, 1999), but also in other continuous K/T
successions of the Tethyan Realm (e.g. Spain – Lamolda et
al., 2005; Italy – Monechi & Thierstein, 1985; Tunisia - Gardin,
2002).
The occurrence of the nannofossil Biantolithus sparsus Bramlette & Martini, together with a recorded acme of
Markalius inversus (Deflandre in Deflandre & Fert) Bramlette
& Martini, led to the identification of the NP1 Calcareous
Nannoplankton Zone of the Martini’s Zonation (1971) - earliest Paleocene (Early Danian) in age.
Paleogene
The Paleogene deposits were encountered only in the
Black Sea offshore area, in the Tandala Well.
The earliest Paleocene (Early Danian) is characterized by
chalky limestone deposits, as previously described. These
deposits are overlain by calcareous claystones and marlstones, interbedded with thin (cm) calcarenites (Fig. 3). The
presence of the NP15, NP16, NP17, NP18, NP19, NP20 and
NP21 Calcareous Nannoplankton Zones of Martini’s Zonation (1971) suggest continuous sedimentation within the
Middle - Late Eocene interval (corresponding to the Lutetian, Bartonian and Priabonian stages). The total thickness
of the Eocene deposits is 365 m.
The quantitative calcareous nannoplankton analyzes focus on four taxonomical groups : (1) Sphenolithus spp., taxa
confined to warm well oxygenated surface waters and open
marine environments (Aubry, 1992); (2) Discoaster spp.,
nannofossils mostly confined to warm water surfaces and
open-marine settings; (3) Zygrhablithus bijugatus Deflandre,
Lanternitus minutus Stradner, Orthozygus aureus (Stradner)
Bramlette & Wilcoxon and Isthmolithus recurvus Deflandre, holococcoliths abundant in near-shore environments
(Krhovsky et al., 1992); (4) Dictyococcites bisectus (Hay, Mohler & Wade) Bukry & Percival and Cyclicargolithus floridanus
(Roth & Hay) Bukry, cosmopolitan taxa, which proliferate remarkably under stable marine conditions, tolerating slight
salinity fluctuations.
The Middle Eocene nannofloras are generally dominated by warm water taxa (the genera Sphenolithus and Discoaster), which jointly amount to 40% of nannofloras. Both
the euthrophic nannofossils Dictyococcites bisectus and Cyclicargolithus floridanus represent up to 35%. Meanwhile,
the abundance of the holococcoliths decreases to 10%.
The Late Eocene nannofloral abundance, recorded in
the Tandala Well, is similar to that identified within the Middle Eocene deposits traversed by this drilling. A significant
shift of Tethyan taxa (Spehenolithus and Discoaster) to 10%
took place within the latest Eocene (Late Priabonian). The
holococcoliths become significantly abundant (up to 30%),
while the D. bisectus and C. floridanus jointly amount to 50%
of nannofloras.
The youngest Paleogene sediments recorded in the Tandala Well are bituminous clays (160 m thick), with numerous
fish remains (mainly scales). Such deposits are described in
the Carpathian Domain as “dysodilic shales”. Two distinct
laminitic limestones (the oldest one, at the lower part of the
bituminous clays, is 40 cm thick and the youngest, 30 cm
thick, towards the middle part), were identified.
According to nannofloral content, the bituminous clays
were assigned to the NP21 (pars), NP22, NP23, NP24, NP25,
NN1 and NN2 Calcareous Nannoplankton Zones Martini’s
Zonation (1970), spanning the Oligocene -earliest Miocene
interval (the Rupelian, Chattian, Aquitanian and Early Burdigalian stages).
The quantitative nannofloral studies focused on four
taxonomical groups : (1) Sphenolithus spp., taxa confined to
warm well oxygenated surface waters and to open marine
environments; (2) Helicosphaera spp., nannofossils mostly
related to warm surface waters and near-shore environments (Krhovský et al., 1992); (3) Dictyococcites bisectus and
Zygrhablithus bijugatus, cosmopolitan species, frequent in
near-shore environments (Krhovský et al., 1992), that bloom
whenever the nutrient input increases (Melinte, 2005); (4)
Pontosphaera spp., euthrophic taxa (Aubry, 1992) which
proliferated under stable marine conditions and tolerated
only slight salinity fluctuations.
85
The Eocene/Oligocene boundary interval exhibited a
significant decline in the abundance of warm water nannofossils (species of Sphenolithus and Discoaster) which resulted in their disappearance. The Early Rupelian nannofloras
are characterized by the dominance of cosmopolitan taxa,
such as Dictycoccites bisectus, Zygrablithus bijugatus and Cyclicargolithus floridanus.
There was an occurrence of endemic nannofossils (restricted to the Paratethys Realm), such as Transversopontis fibula Gheta, T. latus Müller and Reticulofenestra ornata
Müller, within the Rupelian deposits of the Tandala Well.
The endemic nannofossils have a remarkable abundance
amounting to over 80% of all recorded nannofloras within
the oldest level of the laminitic limestone (placed at the
lower part of the bituminous clays of the Tandala Well).
The warm water taxa (Sphenolithus spp.) reoccur in the
Late Oligocene (within the Chattian stage – NP24 Nannoplankton Zone), where they represent up to 35% of
nannofloras. In the upper Chattian (NP25 Calcareous Nannoplankton Zone), the total abundance of Sphenolithus significantly drops to 5%, to later increase to over 20% within
the Oligocene/Miocene boundary interval (NN1 Nannofossil Zone). Helicosphaera spp. varies from 5 to 35% of calcareous nannoplankton assemblages in the Oligocene deposits
traversed by the Tandala Well, with the maximum evidenced
in the uppermost Chattian (NP25 Calcareous Nannoplankton Zone), and the minimum in the Rupelian, (NP23b Calcareous Nannoplankton Zone). Dictyococcites bisectus and
Zygrhablithus bijugatus are also abundant in Oligocene nannofloras of the Tandala Well. The abundance of these species strongly fluctuates, from 35% (in the lower Rupelian –
NP23 Calcareous Nannoplankton Zone) to 70% in the Lower
Chattian (NP24 Calcareous Nannoplankton Zone), with the
maximum recorded within the youngest laminitic limestone
level. The lowest abundance of the genus Pontosphaera
(5%) was also observed in the Lower Oligocene deposits
(belonging to the NP23 Calcareous Nannoplankton Zone),
while its highest percentage (30%) was recorded in the Upper Oligocene sediments (assigned to the NP25 Calcareous
Nannoplankton Zone).
Neogene
The oldest Neogene deposits, traversed by the Tandala
Well, are bituminous clays (Aquitanian - Early Burdigalian
in age), lithologically similar to the Oligocene deposits. The
earliest Miocene (Early Aquitanian) calcareous nannoplankton assemblages are characterized by strong reworkings,
from Cretaceous, Eocene and Oligocene. Only 20% of the total nannofloras characterizing the NN1 Calcareous Nannofloral Zone of Martini’s Scheme (1971), are in situ, the most
common taxa being Helicosphaera scissura, H. mediterranea,
Coronocyclus nitescens, Cyclicargolithus floridanus, Sphenolithus moriformis, Triquetrorhabdulus carinatus, Coccolithus
miopelagicus and small reticulofenestrids.
86
The 410 m thick overlaying sequence, composed of
detrital sediments, was attributed to the Middle Miocene
(Lower Sarmatian), based on the identification of the NN7
and NN8 Calcareous Nannoplankton Zones (Mărunţeanu in
Popescu et al., 1998).
The youngest deposits encountered within the Tandala
Well, Late Miocene-Pliocene and Pleistocene-Holocene in
age, are, lithologically speaking, characterized by the presence of silty clays, with frequent layers of thin calcareous
sandstones. Within the Pleistocene, oolitic sandstones were
deposited – Figure 3.
The entire previously described sequence yielded
macrofaunas (mainly mollusks – Papaianopol in Popescu
et al., 1998), as well as microfaunas (ostracods – Olteanu
in Popescu et al., 1998). These lines of evidence suggest
the presence of the Upper Miocene (Pontian, 560 m thick),
Pliocene (Kimmerian and Kuyialnikian stages, jointly,
380 m thick) and Pleistocene-Holocene (with a thickness
of 213 m).
The identification of the NN11b, NN12, NN13, NN19
and NN20 Calcareous Nannofossil Zones (reported by
Mărunţeanu in Popescu et al., 1998) points to marine influxes
during the latest Pontian (Late Bosphorian), Early Pliocene
(Early Kimmerian), Late Pliocene (Early Kuialnikian), Early
Pleistocene and Holocene.
DISCUSSION
The results obtained so far suggest a very complex depositional history and paleobiogeography of the Southern
Romanian Black Sea onshore and offshore areas, during the
Cretaceous-Cenozoic times.
It was assumed that a wide carbonate platform has been
active in the Eastern part of the Moesian Platform (including the present onshore and offshore areas of the Black Sea
Southern Area) since Late Jurassic (Avram et al., 1996; Georgescu, 1997; Ion et al., 2001). The data presented herein confirms a shallow marine carbonate sedimentation spanning
over the latest Jurassic (Tithonian) – earliest Cretaceous
(Berriasian – Valanginian – early Hauterivian) interval.
The deposition of the Cernavoda Formation indicates a
coastal marine environment in the Eastern part of Southern
Dobrogea (the Alimanu Member) and mixed marginal marine and brackish water in its Western part (the sedimentation of the Amara Member). Oligotrophic conditions were
established on the water surface during the latest Tithonian
– Berriasian – early Valanginian interval, as indicated by the
high percentage of Nannoconus species, among the nannofloral assemblages. Since this genus seemed to proliferate,
during the Early Cretaceous, in the photic zone of the Tethys
Ocean (Erba, 1994; Bersezio et al., 2002), a high temperature
of surface waters, associated with a low fertility of the planktonic organisms, would have existed. The presence of Boreal nannofossils (normally confined to cold water and high
latitudes) could be indicative of a Late Valanginian sea-level
rise in the investigated area. Also, the Boreal taxa appear together with a significant increase in Biscutum constans and
Zygodiscus erectus (both indicating high fertility conditions
at surface waters and upwelling of cooler waters). These biostratigraphical patterns reflect surface water oligotrophic
(and stable) conditions within the Tithonian-Early Valanginian interval and eutrophic (and more unstable) ones, during
the Late Valanginian interval.
The next sedimentary cycle, observed in the investigated drillings from the Romanian Black Sea onshore and
offshore areas, is represented by Upper Barremian - Lower
Aptian sediments of the Ramadan Formation, deposited in
a marginal marine setting. In the Eastern part of the investigated area (SE part of Southern Dobrogea and Southern Romanian Black Sea offshore area), the Late Barremian - Early
Aptian deposits are reefal limestones and calcarenites with
orbitolinids, a sedimentation typical of the Urgonian Facies
of the Tethys Realm. The Late Barremian surface waters
are characterized by high temperature and low fertility, as
proved by the remarkable abundance of the Tethyan genus
Nannoconus. Pronounced shifts of low latitude nannofossils
(e.g. Nannoconus spp., Conusphaera spp. and Assipetra spp.)
were recorded in two distinct intervals (the latest Barremian
and the earliest Aptian). These bioevents, synchronous with
a significant increase in high latitude taxa in the nannofloral
associations, could be indicative of cooler periods, leading
to an instability in the Tethyan ecosystems, and to the occurrence of new, mostly cosmopolitan species.
During the same interval (Late Barremian - Early Aptian), the NW part of the investigated area was occupied by
coastal marine sediments – mainly variegated (red, green
and gray) clays and sandstones, interbedded with thin conglomerates, indicating a detrital littoral facies.
The next depositional sequence (Middle - Late Aptian),
observed in the onshore drillings only, is the Gherghina Formation, accumulated under fluviatile-lacustrine conditions
(as proved by its charophyte content). The multicoloured
clays of the Gherghina Formation contain a high percentage of kaolinite, among other clay minerals. Its source area
(still preserved in North-Dobrogea), is a pre-Cenomanian
lateritic weathering crust (Rădan, 1989).
The next sedimentary cycle is Late Cretaceous in age
(chalks covering the Santonian pro parte - Maastrichtian interval in the onshore drillings and the Campanian - earliest
Paleocene interval in the offshore drilling). The chalk deposition indicates an offshore sedimentation.
Furthermore, the marine Albian, Cenomanian and Turonian deposits, exposed in outcrops in Southern Dobrogea,
were not identified in the studied drillings.
The NE end of the investigated onshore area accumulated, during the Late Campanian - earliest Maastrichtian interval, continental-lacustrine deposits (mainly variegated clays
with charophytes – Ion et al., 1998). Presumably, during that
time, the Nazarcea-Nisipari area of Southern Dobrogea was
an emerged land.
Both in the Southern Romanian Black Sea offshore sector,
as well as in the central and SE part of Southern Dobrogea,
the Santonian – Late Campanian interval is characterized
by abundance and diversity of well preserved calcareous
nannoplankton. Within the above-mentioned interval, a
high abundance of Micula taxa is related to the oligotrophic
water surface conditions, exhibiting a stable and warm marine environment. The peak of abundance and diversity of
Tethyan taxa (including Micula spp., Quadrum trifidum, Q.
sissinghi and Ceratolithoides aculeus) occured within the latest Campanian, which could be regarded as the warmest
Upper Cretaceous interval in the investigated area.
Notably, the Late Cretaceous climate seems to have
been equally warm in both hemispheres, with very low latitudinal gradients (Barron, 1983). But, based on identified
calcareous nannoplankton associations from the Southern
Romanian Black Sea onshore and offshore areas, two significant cooler phases were identified in the Upper Cretaceous:
the oldest within the Early Maastrichtian and the youngest
within the latest Maastrichtian. This assumption is made on
the dramatic changes of recorded nannofloras: the shift of
Tethyan taxa, occuring with assemblages of the taxa normally confined to high latitudes (Boreal species). These
facts led to the conclusion that the end of the Cretaceous
was already an instable time-span, characterized by rapid
changes in marine ecosystems, increasingly eutrophic conditions and particularly cool surface waters.
The Cretaceous sedimentation ends (in the area covered
by the onshore drillings) in the latest Maastrichtian. In the
Tandala offshore drilling, an apparent continuity was recorded, within the Cretaceous/Tertiary boundary interval,
based on micropalaeontological evidences. These are the
mass extinctions of Cretaceous foraminifers and nannofloras (Popescu et al., 1998), followed by the blooms of calcareous dinoflagellate genus Thoracosphaera and of the nannofossil Braarudosphaera bigelowii, indicating strong salinity
fluctuations. In the investigated offshore drilling there was
no trace of the lithological signature of the K/T boundary
(e.g. ejecta layer, Iridium fallout laminae, microtektites, etc.)
The Upper Cretaceous chalk deposits are overlain, in the
Tandala, by Eocene sediments. A marine sequence was recorded within the Middle Eocene (Lutetian) – Early Miocene
(Burdigalian) interval in the studied drilling from the Black
Sea offshore area.
The Eocene sediments are characterized by a carbonate-rich deposition, related to a shallow shelf environment.
It is to be assumed that during the Middle - Late Eocene
interval there were warm, well oxygenated surface waters,
as indicated by the high frequency of Tethyan nannofloral
genera Discoaster and Sphenolithus, recorded in the studied cores. The progressive shift of warm calcareous nanno-
87
plankton taxa, along with the increase in cosmopolitan and
mostly eutrophic ones, reflected the climatic deterioration
(i.e.,progressive cooling) towards the end of the Eocene.
A sharp change in sedimentation was identified in the
Tandala Well within the Early Oligocene (Rupelian), the carbonate-rich sediments being replaced by a bituminous clay
deposition, probably related to an outer shelf environment.
This event is synchronous with a marked global cooling
(Savin, 1977; Jovane et al., 2004), as well as with the first separation of the Paratethys Domain (including the present-day
Romanian territory) from the Mediterranean Realm (Rusu,
1988; Rögl, 1998).
The Early Oligocene calcareous nannofloral assemblages of the Tandala Well reflected these paleoclimatic and palaeogeographical changes: endemic taxa occurred together
with cosmopolitan ones, while the typical Tethyan species
vanished. There was high productivity in the surface waters and low oxygen levels in the bottom waters. The Early
Rupelian laminitic coccolithic limestones, contain blooms
of endemic taxa, as well as of Braarudosphaera bigelowii,
suggesting a strong decrease in the salinity. Notably, the
youngest laminitic coccolithic limestone identified in the
Chattian deposits of the Tandala Well contains only blooms
of cosmopolitan nannofloras; no endemic taxon was recorded. These facts support a re-connection between the
semi-isolated Paratethys basin with the Mediterranean one,
within the Late Oligocene. The re-occurrence of the Tethyan
taxa, during the same interval, also suggests a warmer period, more stable environmental conditions and probably
a higher amount of nutrients at surface waters. These features persist into the earliest Miocene (Aquitanian - Early
Burdigalian).
In the Tandala Well, the earliest Miocene sediments are
overlain by Middle Miocene (Lower Sarmatian) detrital deposits of an inner shelf. In the Volhinian outcrops of Southern Dobrogea, levels with marine faunas (Ionesi & Ionesi,
1973) and nannofloras are interbedded with brackish faunal
levels, indicating strong salinity fluctuations in the Central
Paratethys semi-enclosed basin (including the investigated
area) and/or several sea-level changes.
The Middle Miocene deposits are followed, in the Tandala Well, by Upper Miocene sediments. All the substages of
the Pontian (namely, Odessian, Portafferian and Bosphorian)
were separated based on ostracod communities (Olteanu in
Popescu et al., 1998).
The faunal associations indicate prevailing brackish conditions during the Late Miocene, but short marine influxes
are present within the Late Pontian (Bosphorian- NN11b
Calcareous Nannoplankton Zone, Mărunţeanu in Popescu
et al., 1998). Some authors (Tătărâm et al., 1977; Ion et al.,
2005) consider that the entire Southern Romanian Black Sea
onshore and offshore was an emerged land during Pontian
times. Moreover, the Dobrogea seems to be a source (a mi-
88
nor one, the main being the Carpathian Domain) of Pontian
sediments for the Dacian Basin (Jipa, 2005).
The Pliocene deposits traversed by the Tandala Well
onshore are characterized by a continental sedimentation,
with minor brackish episodes (Popescu et al., 1998). An
important change in the sedimentary regime took place
within the Pliocene/Pleistocene boundary interval, when
the fresh-waters of the Kuyialnikian were replaced, in the
Black Sea basin, by a dominant marine Quaternary deposition (Wong et al., 1994, Panin, 1997), characterized by very
high sedimentation rate (Panin et al., 2005). Brackish marine
episodes within the Middle Holocene of the NW Black Sea
(where monospecific nannofloral assemblages with Braarudsophaera bigelowii) were reported (Oaie et al., 2005).
An important transgression took place during the Late
Holocene (Olteanu, 2005), marine faunas and floras being
recorded in the Tandala Well sediments.
CONCLUSIONS
The Late Jurassic (Tithonian) to Neogene history of the
Southern Romanian Black Sea onshore and offshore reflects
multiple depositional episodes of different sedimentological regimes, separated by several hiatuses of varying duration. These hiatuses may reflect periods of slow deposition
and/or erosion.
• The oldest sedimentary sequence recovered by the studied drillings is latest Jurassic (Tithonian) - earliest Cretaceous (Berriasian - Valanginian) in age. This sequence is
followed by a hiatus of more than 15 MA.
• The next depositional cycle, in stratigraphic order, is
Late Barremian - Early Aptian in age.
• A hiatus of around 45 MA was evidenced in the studied
drilling of the offshore Black Sea area, covering the Early
Aptian - Early Campanian interval.
• In the onshore area, after a shorter hiatus (up to 10 MA),
a fluvial-lacustrine formation was deposited, within the
Middle - Late Aptian interval.
• The Upper Cretaceous sequence covers the Campanian
– Earliest Paleocene interval on the offshore drilling and
the Santonian - latest Maastrichtian interval.
• In the offshore area, a hiatus, of around 13 MA (earliest
Paleocene – Middle Eocene) was pointed out, while in
the offshore zone, a hiatus of more than 10 MA (Early
Miocene - Middle Miocene) was recognized.
• The next sequence is represented by the Middle Miocene (Lower Sarmatian).
• Offshore, a hiatus up to 4 MA follows.
• The youngest sequence identified (in the offshore Tandala Well) covers the Upper Miocene (Pontian) – Quaternary interval.
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90
DACIAN BASIN ENVIRONMENTAL EVOLUTION
DURING UPPER NEOGENE WITHIN THE
PARATETHYS DOMAIN
Radu OLTEANU (1), Dan C. JIPA (2)
(1) “Emil Racovitza” Speleology Institute, 13, 13 Septembrie St, Bucharest
(2) National Institute of Marine Geology and Geo-ecology (GeoEcoMar), 23-25 Dimitrie Onciul St, 024053 Bucharest, Romania
Abstract. The present paper describes the paleoecological evolution of the Dacian Basin starting with the Sarmatian time. The Uppermost Sarmatian is
strongly regressive with freshwater faunas. However, the Meotian is transgressive and it is characterized by a Congeria fauna (indicating reduced salinity)
and ostracoda of marine origin. Both groups disappeared at the end of the Meotian (a freshwater episode). The transgression of the Pontian brings about
a new fauna (with new morphological structures). During the Middle Pontian, the biodiversity is maximal and the Pontian Sea extends to the Panonian
Basin. During the Upper Pontian – Lower Dacian interval, there is a regressive phenomenon which gradually isolates the Dacian Basin from the Euxinian
Basin. Two bioprovinces with distinct morphogenetic evolution take shape. In the Romanian, the Dacian Basin is a freshwater lake.
Key words: Dacian Basin, paleoecology, ostracoda, mollusc
INTRODUCTION
The Tethys Ocean was an equatorial basin. Starting with
the Paleozoic, it separated the unique protocontinent, Pangea, dividing it into the Laurasia and Gondwana supercontinents.
The Austrian geologist Eduard Suess coined the name
Tethys and introduced the idea into scientific literature in
1893. The sea Goddess Tethys, whose name was chosen by
Seuss, is, in Greek mythology the personification of the fertile
ocean.
The Tethys ocean, as conceived by Eduard Suess, has altered significantly with time. Initially, Tethys was imagined as
a continuum, uniform oceanic body, encased in the Paleozoic
continent Pangea. Later on (Metcalfe, 1999), Tethys was seen
as a series of aquatic basins which had occurred and supposedly closed down in the Paleozoic-Mesozoic times.
A collision of the continental plates during the Upper
Eocene fractured the Tethys ocean. The current Mediterranean area is its present remnant. The new sea, spread between
the two continents (Fig.1), taking shape North of Tethys, was
called Paratethys (Laskarev, 1924). Its history, the history of
the events that marked the progress of the geologic time, is
mostly that of the faunas undergoing periodical change with
every palaeoecologic opportunity (changing from marine to
brackish, and, often, to lacustrine). In other words, the history
of the Paratethys belongs with the palaeoecologic history.
Configured as an inland sea, the Paratethys spreads from
the Alps to beyond the Aral sea. Senes (1979) and Steininger,
Papp (1979) subdivided its domain as follows:
• The Western Paratethys (the Rodanian Basin)
• The Central Paratethys (the Panonic and Dacian basins)
• The Oriental/Eastern Paratethys (the Euxinian and AralCaspian basins)
Paleobiologic and geodynamic considerations enabled
Senes and Marinescu (1974) and Rusu (in 1988) to distinguish
four periods in the development of Paratethys: the ProtoParatethys, the Eo-Paratethys, the Meso-Paratethys, and the
Neo-Paratethys (Fig. 2).
The intracontinental Paratethys area separated into a
number of basins which often developed independently. It
was during the Oligocene that the Paratethys (Fig. 3) evolved
as a geographical, even faunal, unity (Rusu, 1977, 1988;
Baldi, 1979, 1980), when links with the Mediterranean Sea
91
R. Olteanu, D.C. Jipa - Dacian Basin environmental evolution during Upper Neogene within the Paratethys domain
were diminishing in the South. Moreover, there were differences occurring between the Western (Alpino-Carpatian or
Central Paratethys) area and the Eastern one (spreading to
the North and East over the North Sea and the Caspian Sea
= Scitic Sea and even further East, the Turanic Sea). It was for
the first time that the brackish-water biotypes occurred (in
Solenovian=Oligocene) and also the first Euxinian facieses (in
Maikopian= Upper Oligocene – Early Miocene) together with
the first endemic elements of faunas. Its connections with
the Mediterranean basin (Tethys) are discontinous while the
fauna is mostly influenced from the North.
The Lower Miocene is predominantly marine as a consequence of reestablishing connection with Mediterrana
through the pre-Alpine pass. East of the Caspian Sea, a fluvial-lacustrine sedimentation (and fauna) was evolving. Starting with the Middle Miocene, the Eastern Paratethys tends to
isolate itself, first, ecologically and then, geographically, also.
From the beginning of the Late Konkian (“Veseleanka Beds”),
the water turns brackish (while the links with the ocean are
diminishing). Davidaschvili (1932) found almost 50 endemic
mollusc species including the new Mactrae, Cardium, Ervilia,
Modiola, Cerithium, Mohrenstermia species.
Starting with the Sarmatian, the Paratethys separates itself for good from the Mediterranean Sea, as all connections
close down, turning it into a brackish intracontinental sea – a
facies which has continued, with certain intermissions, up to
the present (the relict basins of the Black and Caspian Seas).
From then on, there were two ecosystems evolving at the
same time (the brackish one, in Paratethys and the marine, in
the Mediterranean basin), with totally different faunae and,
consequently, two biostratigraphical scales which are difficult to correlate.
THeAPPeARANCeANDeVOlUTIONOfTHe
PARATeTHYsDOMAIN
The final phase of the tethys domain
(Upper Eocene, 37 – 34 Ma)
The paleogeographic image can be explained entirely
through faunas, while their development is traced in the
epicontinental areas, littoral and sublittoral, mostly. During
the Late Eocene, some domains have become ‘classic’ due to
the abundance and diversity of their fauna – all the basins of
Paris, Vincentin, Pannonic, Transilvania, Crimea, developed on
the edge of the alpine zones, consolidated by the Cretaceous
– Paleocene orogenesis.
Fig. 1 Paleogeographic configuration during the final existence of the Tethys Domain (Late Eocene, 37-34 Ma). Simplified after Popov S.V., Shcherba, I.G., Stolyarov, A.S., (in: Popov et al., 2004)
92
Fig. 2 Critical phases of the Paratethys time scale
Until the end of the Tethys Ocean (during the Upper
Eocene), the European continent was mostly covered with water. The Black Sea, the Caspian and the Mediterranean seas are
the depression zones. There were wide connections between
them and a significant faunal unity (Fig. 1) while the faunal differences between the boreal and the Atlantic-Mediterranean
area are still insignificant. The faunas in the Parisian and the
Belgian basins, as well as the ones in the North of Germany are
quite similar to the faunas in Aquitania and the Mediterranean
Sea areas. The connections of the basin with the Northern Sea
are cut off during the Upper Lutetian and the basin is totally
isolated later. The Stampian is transgressive with Northern faunae. In the Upper Oligocene, the basin is cut off again turning
into a freshwater lake whereas the Belgian area is wide open to
the North (the Kassel clays, Chattiene).
As regards the intra-Carpathian area (in Transilvania), the
post-Senonian and before Middle Lutetian ‘lower red clays’
sequence reaches over 1,500 m in width (with Timiriazevia
punctata Clemens, a common species in Wealdean). The
‘marnes with Anomia tenuistriata’ is the first marine sequence.
Throughout the Lutetian interval, the benthonic faunae (molluscs and ostracoda) belong almost exclusively to the mesogeene bioprovince; it is in the Priabonian (the “Cluj limestone’
and the Numulites fabianii complexes) that the faunae exhibit
an obvious Northern influence.
At the end of Eocene, there are differences occuring between a West European kind of fauna (in Transilvania and the
Panonian basin) and an East Mediterranean one (in Dobrogea
and the Varna-Tracia basin) (Sonmez-Gokcen, 1972). That dif-
93
ference suggests distinct influences and affiliation. Thus the
existence of an ‘Anatolian bioprovince’ can be substantiated.
Proto-Paratethys (the Lower-Middle Oligocene)
At the end of the Eocene, movements of the tectonic
plates (the drift towards the North of the Indian continent
which collides with Asia; the simultaneous rotation of Africa
and the compression between Africa and Europe generate
the deep reorganization of the Tethys domain and the occurrence of two new marine domains (Fig. 1): the Paratethys domain, in the North and the Mediterranean one, in the South
(a relict of the Tethys ocean).
In the Paratethys area, there starts an intensive phase
of continentalization. The Eastern Paratethys no longer has
communication with the Indian Ocean. Episodic connections
with the Northern Sea occur instead (through the “Polish
Strait” and the “Rhine Rift”), while the connections with the
Mediterranean Sea of the Western and Central Paratethys diminish significantly (are restricted merely to the “Slovenian
corridor”). The connections are interrupted in the Late Chattian, when in the “Renan depression” brackish and freshwater
faunas start to flourish.
North of the Black Sea area, the facies pertaining to the
Euxinian Sea of the Maikopian Series are forming. It is a Mediterranean fauna in Eocene, but it attains distinct characteristics starting with Oligocene when the Northern influences
intensify. It is connected through the Northern Ukrainian
platform and through the Polish basin. During the Rupelian
time there is a slow regression, the waters withdrawing towards the Black Sea depression. A new transgression takes
place during the Poltavian (=Chattian).
A strong process of faunal endemism begins in some areas (for example, in Transilvania, where brackish insertions
occur) due to a tendency towards regional isolation.
During the Upper Oligocene (Fig. 3) the Paratethys Sea
reopens to the world ocean. The North European influence
continues to be dominant on the fauna in the Western Paratethys which connects with the North Sea through the “Rhine
Rift“. The central Paratethys connects with the Mediterranean
Sea through the “Slovenian corridor” until the end of the Badenian.
After a brackish water episode (in Solenovian), the marine regime is restored in the Eastern Area. The still randomly
intermingling three European bioprovinces i.e., the North-Atlantic, the Mediterranean, and the Ponto-Caspian (“Oriental
Paratethys”) are finally taking shape. At this point, the biostratigraphic discrepancies become apparent (in the compositions of the fauna and of the desynchronization of the
“events”).
Hereon, the biostratigraphy turns prolix. The classic layers are being discussed, dismissed, and replaced by other layers, said to be more accurate. In the literature, there are more
than 50 new stages in the European space referring to the Mi94
ocene and Pliocene intervals only. That is creating confusion
and raises the problem of redefining the “biostratigraphical
taxonomy” from a thouroughly different viewpoint.
In the intercontinental area of the Central Paratethys a
new biostratigraphic scale was drafted (Senes and Cicha,
1968), apart from the Oriental Paratethys one.
The Oligocene-Miocene boundary is set within the Egerian, while the Miocene-Pliocene limit is placed either somewhere in the Pontian or at the Pontian/Dacian boundary. The
demarcation line to the Pleistocene is conventionally agreed
upon at 1.8 Ma because the attempt to find a geologic event
occuring symultaneously all over the continent has failed.
The boundary between the two main time sequences,
ranked as epochs, namely the Oligocene and the Miocene,
has generated a debate yet to be settled. In the central area
of the Paratethys, the boundary is set at the end of the “Buda
Marls”, when the Miogypsinoides complanatus and the Paragloborotalia opima opima species occur, as well as, at the
end of the Nannoplancton NP-24 zone, which both mark the
beginning of the Egerian (Baldi 1969,1979, 1984). In Transilvania, the existence of a specific episode called Merian (Moisescu 1975, 1989) is pointed out. Its upper limit would be set
at the “Cardium lipoldi level” synchronized with the base of the
nannoplankton NP-23 zone.
The faunal evolution in the late Oligocene to early Miocene is influenced by Mediterranean and Indo-Pacific connections (Rogl, 1996). The molluscs community seems to
demonstrate similarities during the Egerian and the Caucasian stage.
During the Aquitanian, in the Atlantic bioprovince, sediments, mostly sandy, accumulated with an exceptionally rich
fauna. The Bazas and Saucats falunae become the stratotype
of the Aquitaine and the Burdigalian. In the Helvetian stage of
this area noticeable tropical influences become apparent.
During the Burdigalian (Fig. 4), the Western Paratethys
was connected to the Mediterranean Sea through the “PreAlpine Pass”. In the Central and Oriental Paratethys there is
ample regression. With the Burdigalian, the “faunas with giant Pectinids” occur; they are considered to be of “indo-pacific, subtropical” origin (Rögl, 1988). This horizon is a world
wide stratigraphic marker level (according to Addicott, 1974,
Steininger et al., 1976, Rogl, 1996).
The dissimilarities between the three (aquatic) bioprovinces remain, moreover, they become more prominent which
indicates a diminishing faunal “flow”. Still, many species, are
known to be familiar both with the North Sea and Aquitania,
while, the boreal faunas enter the Pannonic area through the
“Silesian passage”. In the North-German area, after a regressive stage (with coals), the sea advances with a faunal minority of Mediterranean origin. From now on, the fauna becomes
entirely holoarctic.
Fig. 3 Paleogeographic configuration during the initial stage of the Paratethys Domain (Early Oligocene, 34-32 Ma). Simplified after Popov S.V., Shcherba, I.G.,
Stolyarov, A.S., (in Popov et al., 2004)
Fig. 4 Paleogeographic configuration of the Paratethys Domain during Early Burdigalian (20.5-19 Ma). Simplified after Popov S.V., Shcherba, I.G., Stolyarov, A.S.,
(in Popov et al., 2004)
95
In the Carpathians flysch-type sedimentation continues.
The disoxic and anoxic conditions persist (regionally) in the
deep water environments (North of the Black Sea depression,
the “Maikop Strata” are formed).
A major event is the Ottnangian-Kotsakhurian. The sudden “burst” of the Rzehakia species, together with the Congerii, Melanopsidae and Eoprosodacnae validates the existence
of a brackish-water biofacies resulting in their excessive and
mostly exclusive growth. The extension of that ecologic episode across Paratethys supports the hypothesis of a general
event (generated by isolation as well as by a huge regression
along with the setting up of certain detrimental facies that
favoured the “eruption” of those eccentric, unknown or previously minor faunae).
Meso-Paratethys (Karpathian – Badenian)
According to the fossil faunas, the Karpathian from the
Central Paratethys is a Late-Burdigalin sequence. Meanwhile, numerous species of foraminifera and ostracoda (Zorn,
1995) generate the luxuriant Badenian fauna. Obviously, the
boundaries are no more – and cannot be any more – than
merely “transitional”.
A large transgressive phase (Rögl, 1996) in the entire Circum-Mediterranean area generated a new basal Badenian
fauna. The Langhian correlates with the Lower Badenian due
to the existence of Praeorbulins (Cita & Premoli Silva, 1968)
and of the Orbulina universa species in both areas. (including
the Serravallian stage). Within intra-Carpathian area, the Pannonian basin was flooded during the Lower Badenian (Moravian). The occurrence of the first evaporites throughout the
Paratethys domain is equally important to substantiate the
existence of a warm climate (with Orbulina suturalis) (Fig. 5).
The faunas of the Eggenburgian – Badenian time interval
are similar to the ones found in the Pad Valley, the Rhone Depressions and the Vienna basin. That supports the idea that
permanent links existed through the Drava-Sava-Vincentin
corridor (the transdinaric or Slovenian corridor).
Within the Paratethys, the faunal segregation process increases. The central Paratethys was separated from the Western
one when the “Bohemian massif” emerged; it connected instead,
with the Mediterranean through the ‘Slovenian corridor’.
The Oriental Paratethys is clearly quasi-isolated, with
its faunae and its distinct stratigraphy (the Sakaraulian,
Fig. 5 Paleogeographic configuration of the Paratethys Domain during Early Badenian (16 - 15 Ma). Simplified after Goncharova, I.A., Shcherba, I.G.,
Khondkarian, S.O., (in Popov et al., 2004)
96
Tarkhaninan, Tschocrakian, Karaganian and the Lower Konka
levels, all of them, considered nowadays contemporary with
the Miocene).
The Sakaraulian correlated to the Acvitanian-Burdigalian
and the Eggenburgian. Many ostracod species are common
(Cytherella postdenticulata Oertli, Senesia philippi (Reuss),
Hermanites sakaraulensis Schneides (closest to H. haidingeri), Loxoconcha punctatella (Reuss), Cushmanidea bradiana
(Lnkls.), Cytheretta ovata (Egger), Xestoleberis tunida (Reuss),
Krithe galericum Schneider etc) (Schneider, 1963). After the
Kotsakhurian brackish-water episode the Tarkhanian transgression restored the marine conditions (Nevesskaya et al.,
1984, 1987, fide Rogl, op. cit.).
The Tarkhanian is marine (with marine species: Pterigocythereis calcarata, Costa edwardsi, Bosquetina carinella, B.
zalanyi, Loxoconcha carinata, Eucythere alexanderi, Schneider,
1956, and Flexus plicata, F. triebeli, Bythocypris lucida, “Trachyleberis” prestwichiana, Suzin, 1965). Andrusov, (1918) and
Davidaschvili, (1932), (fide Amitrov, 1975) found molluscs species: Nucula placentina Lamarck, Pecten denudatus Riss, Nassa
tamanensis n sp, N. rosticorum n sp, four Turboniella species,
Leda fragilis Chemn., Ostrea cochlear Poli. etc, all of them suggesting the pre-Lower Badenian time. During the Lower Badenian two new taxa appeared, Acanthocythereis histrix (Reuss)
and Verrucocythereis verrucosa (Reuss). The ostracod community is larger (Mutylus (?) polyptichus (Reuss), Cytherella postdenticulata Oertli, Bythocypris lucida (Seguenza), Mutilus aff
deformis (Reuss), Aurila philippi (Reuss), Urocythereis seminulum (Reuss), Quadracythere sulcatopunctata (Reuss), Bosquetina carinella (Reuss), Costa reticulata (Reuss), Flexus triebeli
(Ruggieri), Cushmanidea longa (Reuss), Occultocythereis bituberculata (Reuss), Cytheropteron vespertilio (Reuss), Eucytherura pygmea (Reuss), Hemicytherura aff. videns (G.W.Muller),
Ruggieria tetraptera tetraptera (Seguenza), Loxoconcha punctatella (Reuss), Loxoconcha aff hastata (Reuss).
Likewise, the marine Tschokrakian faunas correlate admirably with the Middle-Upper Badenian (similar with the Costei
ostracod and foraminifer community, from Transilvania).
Schneider (op. cit.) found an ostracod community with:
Paracytheridea aff triquetra (Reuss), Phlyctenophora kalikzii
(Schneider), Leptocythere rugosa (Schneider), Pontocythere
suzini Schneider, Pseudocytherura aff caudata Sars, Semicytherura filicata (Schneider), Semicytherura aff acuticostata
(G.W.Muller), Semicytherura aff inversa (Seguenza), Ruggieria
tetraptera tetraptera (Seguenza), Costa edwardsi (Roemer),
Falunia plicatula (Reuss), Cytheridea mulleri (von Munster),
Eocytheropteron inflatum Schneider, Loxoconcha aff carinata
(Lienenklaus), Loxoconcha carinata alata Schneider, “Trachyleberis” prestwichiana (Jones – Sherborn).
In 1956, Suzin completed it with: Pontocythere vitrea Suzin, Paradoxtoma eusiforme Brady, Semicytherura aff reticulata
(Lienenklaus), Cytheropteron obesum Schneider, Cushmanidea lithodomoides (Bosquet), Cytherella aff compressa (von
Munster), Cytherella gracilis Lienenklaus.
Davidaschvili (op. cit.) offers a long list of molluscs, most
of them, endemic elements (almost 50 species). Dominant
taxa are: Venus konkensis Sokolov, V. marginata Hoernes, Mactra bajarunasi Andrusov, Donax tarchaniensis Andrusov, Tapes
vitalianus Andrusov, Spaniodontella intermedia Andrusov şi
S. crassidens Andrusov, Modiola volhinica Hoernes, M. marginata (Eichwald), Ervilia praepodolica Andrusov, E. trigonula
Sokolov, Mohrenstermia inflata Andrusov, Cardium (six endemic species), Cerithium (five species), Trochus (12 endemic
species and subspecies), Leda (4 species). All of them suggest
that the beginnings of the ecologic isolation process occured
before the Central Paratethys areas (salinity reduction).
During the Karaganian time, that results into a poor fauna,
presumably generated by a sharp decline in salinity. Ossipov
(1932) found seven Spaniodontella species, and some Unio,
Mohrenstermia, Sandbergeria, Nassa, Planorbis, Lymnea and
Helix species, suggesting an oligohaline restricted biotop.
Such community with brackish and lacustrine species shows
a regional facies with fluvial-continental influences.
Schneider (op. cit.) found some ostracod species: Candona
ex gr candida Muller, Herpetocypris reptans (Baird), Darwinula
stevensoni (Brady & Stevenson), Loxoconcha truncata Schneider, “Cythereis” declivis Schneider (both are juvenile specimens), Loxoconcha aff bairdii Muller (new species).
The Konkian (biostratigraphically matched with the Kosovian, Rogl, 1998) and its thoroughly marine fauna suggest a reopening of the Paratethys towards the marine West
(Nevesskaya et al., op. cit.). It is the time of the ecosystem
change in two steps, “Venus konkensis Beds”, belong to Konkian s. str. and “Veseleanka Beds” belong to the Buglovian
stage). A significant reduction in biodiversity occurred, 316
mollusc species and almost 200 ostracod species within the
Upper Badenian and 140 mollusc species and 41 ostracod
species within the Konkian. During the last sequence of the
succession (“Veseleanka Beds”) the community is more reduced. The following mollusc species are dominant: Acanthocardia andrussovi, Venus konkensis, Mactra basteroti konkensis
and Ervilia pusilla – trigonula - podolica, Congeria sandbergeri,
Cardium kokupicum, C .praeplicatum, C. ruthenicums, Cerithium
konkensis, Mohrenstermia etc. (Ossipov, op. cit.).
Schneider (op. cit.) described the following ostracod community: Cytheridea muelleri (von Munster), Pterigocythereis
calcarata (Reuss), Falunia plicatula (Reuss), Mutilus deformis
(Reuss), Aurila punctata (von Munster), Carinocythereis carinata
(Roemer), Hermanites haidingeri (Reuss), Aurila similis (Reuss),
Cytheretta aff tenuipunctata (Bosquet), Loxoconcha aff bairdi
Muller (new species), Loxoconcha aff laevatula (Normann) (new
species), Bairdia explicata Schneider, Phlyctenophora affinis
Schneider, Hemicytherura videns Muller, Semicytherura bacuana
(Schneider), “Cytheridea” parangusta Zalany (juvenil), Pontocythere mediterranea Schneider, Amnicythere tenuis (Schneider).
During the Konkian s. l. a new fauna “wave” appeared.
Most of them are endemic species characterized by larger
intrapopulational variability. It is another type of community
97
generated by a particular ecology, a slow transition between
the marine ecosystem and the brackish-water ecosystem. The
process occurred on the Volhino-Podolian area.
We think that it was not an actual geographic isolation
(geographic barriers like the continental spaces), but rather
an ecological one. The Eastern Paratethys area has slowly
started to turn brackish, while in the Western part, the faunal
communities are exclusively marine. The faunae were restrictively and selectively migrating in all directions, which made
the biostratigraphical correlation hardly possible.
South-West of Transylvania, there are several Badenian
fossiliferous deposits which are an indicator of a large and direct connection with the Mediterranean; similarly, West of the
Dacian basin. By contrast, the rest of the Carpathic area (that
is, Northern Transylvania and the central part of the Dacian
basin) is characterised by a specific litho- and bio-stratigraphical sequence: the “marls (tufa) with globigerinae”, “salt breccia”, “radiolar schists” and “marls with Spiratella”. The existence
of salt supports the hypothesis of dessication in Transilvania
and in the sub-Carpathian fosse from Moldavia to Muntenia.
The fossiliferous deposits from Lăpugiu, Coştei, Delineşti
(in that order of succession) in the South-Western Transylvania,
correlated well to the Badenian from Vienna Basin (Nussdorf,
Kostel etc, Brestenska & Jiricek, 1975). The literature assumes
the closing of the “Slovenian corridor” during the Upper Badenian (Fig. 6). The existence of the luxuriant mollusc fauna
(Rado-Moisescu, 1965, more than 350 species) and ostracoda
from Buituri (Latest Badenian) invalidates such an assumption
At the “Buituri level” there is an extremely rich Mediterranean fauna (Hemicytherura videns (G.W.Muller)*, Semicytherura sanmarinensis Ruggieri, Semicytherura retipunctata
Ruggieri, Falunia (Hiltermanncythere) hartmanni (Caraion)*,
Carinocythereis carinata (Roemer)*, Costa edwardsi edwardsi
(Roemer), Costa napoliana Puri*, Pseudocytherura calcarata
(Seguenza), Aurila convexa (Baird)*, Aurila aff. cicatricosa (Reuss), Mutilus badenicus Olteanu, M. aenigmaticus Olteanu,
Cytheridea acuminata (Bosquet)*, Loxoconcha rhomboidea
(Fischer)*, L. quadricornis Ruggieri, Semicytherura punctata
(G.W.Muller)*, Costa edwardsi runcinata (Baird)*, Henryhowella
assperrima (Reuss)*, Pterigocythereis jonesi, (Baird)*, “Cythereis”
polygonata Rome*, Ruggieria tetraptera unicostata Olteanu,
Bythoceratina unica Olteanu) (*nowadays species from the
Black Sea, Schornikov, 1969), while the “marls with Spiratella”
show links with the Eastern area. Such segregation brings to
mind the existence of an ecological barrier.
Fig. 6 Paleogeographic configuration of the Paratethys Domain during Late Burdigalian (14 - 13 Ma). Simplified after Ilyina, L.B., Shcherba, I.G., Khondkarian, S.O.,
Goncharova, I.A. (in Popov et al., 2004)
98
The features that differentiate the faunae of the Central
and Eastern Paratethys are significant indeed. Yet, there are
enough shared traits to support the random connection between them.
NEO-PARATETHYS (SARMATIAN-RECENT)
The Neo-Paratethys is characterized by specific faunae at
all levels of the faunal spectra. Beginning with the Sarmatian
time (Fig. 7) the biggest intercontinental brackish basin in the
geological history of Europe took shape. During the Volhinian, it
displayed the maximum areal extension and a clear faunal uniformity. The Sarmatian begins ca 13 Ma (Rogl op. cit.) but it ends
differently in the two areals. The correlation is questionable.
In Eastern Paratethys Saulea et al. (1969), Saulea (1995)
emphasize the significance of the presence and migration
of the Chisinau-Orhei-Camena barrier reef. The movement
towards the South (which takes place beginning with the Upper Badenian up until the Middle Sarmatian) is evident with
intense subsidence in front of the Eastern Carpathians. This
reef facies suddenly ceases during the Middle Basarabian.
It is followed by a strong regression which simultaneously
affects both the South Dobrogean promontory and the Eastern end of the Dobrogean ridge.
The facies, that Saulea et al. (op. cit.) called “continental-deltaic” which emerged in the Lower Sarmatian, in the Septentrional part of the Carpathian avantfosse, extends into the Upper
Sarmatian covering the foreland also. This leads to the closing of
the aquatic basin of the avantfosse in the North. Consequently, it
may be said that the paleogeographic area configuration of the
Dacian basin was completed in the Upper Sarmatian.
The major processes that led to the configuration of the
Dacian Basin were the following:
• the broadening of the sedimentation area of the Carpathian avantfosse. It started to extend (to the East and
to the South) in the Upper Badenian continuing during
the Lower and Middle Sarmatian;
• the closing of the aquatic basin of the Carpathian fosse
during the Middle and Upper Sarmatian due to the emergence of the Northern part of the avantfosse and the setting up of a continental facies.
The occurrence of the Dacian Basin as an independent
aquatic unity is one of the consequences of the movements
pertaining to the attic phase (Saulea et al., 1969). The separation of the Dacian Basin from the Pannonian Basin is another
consequence of the attic movements. Meanwhile, the connection between the Dacian Basin and the Oriental Paratethys continues into the Upper Pontian.
Fig. 7 Paleogeographic configuration of the Paratethys Domain during Sarmatian s.l. (12 - 11 Ma). Simplified after Paramonova, N.P.,
Shcherba, I.G., Khondkarian, S.O., (in Popov et al., 2004)
99
In the Central Paratethys area (including the Dacian basin), the Sarmatian is transgressive. In the Eastern Paratethys
(Volhinia, Bassarabia, Northern Black Sea) only, there is a
gradual succession from the marine to the brackish faunas,
with all the faunal changes generally encountered starting
with the Upper Konkian.
Gradually, the new ‘residual’ eurihaline communities become dominant and the intra-specific diversification processes increase. Distinct philogenetic lineations occur, with
distinct morphogenetic directions, starting from several
previous typologies while the ‘opportunist’ species of marine
(Badenian) origin are slowly disappearing.
The cases of the Limnocardiidae, of some of the ostracoda
or some of the foraminifera shows a remarkable ‘selection of
species’ when the new brackish ecosystem is established. The
Volhinian had still preserved a great number of previously existing foraminifera and ostracoda. The Basarabian is an epoch
of maximum biodiversity (dominated by new mollusc, ostracoda and foraminifera species), their morphogenesis following
individual tracks. At the Lower and Middle Sarmatian level, the
faunas display uniformity and quasi-unity both in the central
and in the Eastern Paratethys basins. Throughout, littoral or
deep to shallow areas are identified. They are examples of local
or regional situations which do not alter the overall image (i.e.,
metacommunity). The regional biotope with Congeria on the
Moldave platform is an example (Jeanreanud, 1963).
The Upper Sarmatian (Chersonian) is a short and atypical
temporal sequence for the general evolution of the faunas. The
diversity of the faunas on the whole is sharply reduced (the existence of several small sized Mactrae and of several species of
ostracoda). There are only some endemic foraminifera species
known (Bica Ionesi, 1968, Natalia Paghida-Trelea, 1968). The
Late Sarmatian ends with freshwater facies (with Candona,
Cypris, Darwinula) resulting in the extinction of all the “Sarmatian type” faunas (more precocious in the Moldavian Platform,
called “the Balta-Paun formation”, Ionesi et al., op. cit.).
The post-Sarmatian period, in the Paratethys area is characterized by the following processes:
• The colmatation of the aquatic basins in the Central Paratethys (the Pannonic and Dacian basins)
• The action of ample eustatic movements in the EuxinianCaspian region
• The almost entire separation of the Black Sea from the
Caspian.
As compared to the Sarmatian Sea, the geographical area of
the Neo-Paratethys diminishes sharply during the Maeotian.
Fig. 8 Paleogeographic configuration of the Paratethys Domain during Early Meotian (8.5 - 7 Ma). Simplified after Ilyina, L.B., Shcherba, I.G., Khondkarian, S.O.,
100
It is asserted that during the Upper Miocene (Maeotian,
8.5 to 7 Ma) (Fig. 8), in the Eastern Paratethys, a “corridor”
opened towards the Indian Ocean (Chepaliga, 1995). There
are no concrete examples (with one exception, namely, Abchazia, the Atapi Valley, where the marine-level (with Mutilus
polyptichus (Reuss), Hemicytheria sp.n., Callistocythere sp.n,
and Loxoconcha sp.n) in the Lower Meotian is intercalated
among brackish faunas with two morphotypes of Cyprideis
sp.). Nevertheless, the Maeotian community in the Northern-Black Sea area appears to be uniform and relatively compact (it is symbolically named “the Dosinia complex”). The
fact that such uniformity is not to be found in the Western
areas (in the Dacian basin) suggests that the “marine influx”
originates from the East (South of the Caspian Sea?) and not
entirely from the South (from the “Aegean” Sea, Gillet, 1961,
Semenenko & Ljulieva, 1978). In the Dacian Basin, after the
Uppermost Sarmatian fresh-water levels a new brackish-water community appeared (with Drobetiella, Severinella, Hemicytheria, Loxoconcha, Maeotocythere species). It was followed
by the “Dosinia level” (with Modiola incrassata, Ervilia minuta,
Pirenella caspia, P. disjunctoides, Caspia minor and two ostracod species Mutilus parabulgaricus Olteanu and Maeotocythere sulakensis Suzin only), a fresh-water level (with Leptanodon-
ta), a large level with brackish ostracods (Hemicytheria - 22
species, Loxoconcha, Xestoleberis, Maeotocythere, Stanchevia)
and finally, the last two short fresh-water levels, with Unio,
Helix and Reticulocandona and the second one, with Congeria
novorossica-navicula-panticapea, this with frequently Pontian
ostracods in Eastern and central areas of the basin). The history of the Dacian Basin during the Maeotian time was a successive opening and isolation phases with “cosmopolite” and
endemic taxa, respectively. The absence of Limnocardiids and
foraminifers (except for Ammonia beccari) and the last occurence of Mutilus, Hemicytheria, Xestoleberis species are the
specific features of the Maeotian metacommunity. The luxuriant Congeria species evolution suddenly interrupted.
No Maeotian taxa crossed the Pontian boundary.
The correlation of the Pontian with Mediterranean scale is
disputable (Khondkarian et al. 2004).
In the Lower Pontian (the Upper Messinian) (Fig. 9), the Gibraltar closes down while the Mediterranean Sea becomes an
enclosed lake (5.8 Ma). On the edges, evaporites and gypsum
are being deposited. During the next time (5.8 – 5.6 Ma) the
sea level rises forming the so-called “Lago mare” with brackish waters (and implicitly brackish faunas). Eventually, 5.6 Ma,
Fig. 9 Paleogeographic configuration of the Paratethys Domain during Early Pontian (6.1 – 5.7 Ma). Simplified after I.G., Khondkarian, S.O. Shcherba, S.V. Popov
101
the sea level decreases sharply and massive areas of land are
exonded. Still, the brackish faunas which occur meanwhile
invade the Eastern Paratethys across the Aegean Sea and
the Pre-Pontida (or the area located just North of it). In other
words, there are several separate phases: the first is a phase
characterized by hypersalinity, followed by the refilling of the
basin and the dilution of the water to the brackish “Pontian
type” (around 0.010% salinity). Similarly, we must remember
that the (hypersaline) Dead Sea still receives river influx from
the Jordan Valley without turning brackish. Likewise, the salinity of the Caspian Sea does not decrease under 0.06%. It is
true though, that the warm climate and the intense evaporation are responsible for it (but the Mediterranean had the
exact same conditions at the time).
The Early Pontian is strongly transgressive. A new wave
of fauna migration spread through the Eastern seas (neoLimnocardiids as Chartoconcha, Pseudocatillus, Prosodacna,
Pachydacna, Tauricardium, Caladacna, Pontalmyra, Phyllocardium etc. and new ostracod types as Bacunela, Pontoniella,
Euxinocythere, Pontoleberis). It is possible but unlikely they
originate from the Pannonian area.
The question of the origin of the brackish faunas in the
South of France, the Italian Peninsula and the Aegean basin
remains a mystery. The question is whether those influences
and movements or morphogenetic evolutions, respectively,
are unique to this area (Olteanu, 2000, 2003). The maximum
sea extent occurred in the Pannonian Basin in the Portaferrian time.
The semi-enclosed Dacian basin continues to be under
the „faunal umbrella” of the Euxinian bioprovince, in spite
of the fact that, starting in the Upper Pontian, it tends to
become isolated. In its Western region, more fresh levels appeared. During the Post-Pontian, there is a gradual, but persistent retreat and freshening of the waters, as, after the Middle Pontian, the Moldavian Platform is emerging (Ionesi et al.,
2005). Lacustrine formations occur. The flora is an indicator of
warm climate (Ionesi et al., op. cit.).
The Euxinian basin is the only one which stays brackish
throughout this interval. The Pontian can be directly correlated with the Dacian basin fauna (and the Portaferian fauna,
with the Pannonian basin). The differences occur in Post-Pontian, when the biostratigraphic nomenclature becomes cor-
Fig. 10 Paleogeographic configuration of the Paratethys Domain during Late Romanian (3.4 – 1.8 Ma). Simplified after I.G., Khondkarian, Paramonova, N.P., S.O.
Shcherba, (in Popov et al., 2004)
102
respondingly intricate (and more accurate). In the Northern
Euxinian area, the first freshwater episode to appear is in the
Kuialnikian time. (Contrary to the Black Sea deep basin, which
stayed brackish, as it was in the Kimmerian, preserving the
same type of evolutionary line of the fauna. Consequently,
the Kuialnikian cannot be accepted but as a marginal, shallow final facies of the Kimmerian stage, a facies which presumably continued the „Azov Beds” dominated by the Congeria species). During the Late Dacian time, the Dacic Basin was
isolated. Its low brackish-water rich fauna (Olteanu, 1995) is
different from the Kimmerian fauna (three common species
only). There are two directions in fauna evolution in the two
bioprovinces with different (paleo) ecology, low salinity in the
Dacian Basin and higher and constant salinity in the Euxinian
Basin.
The upper limit of the Pontian was conventionally set to
coincide with the Miocene/Pliocene boundary, which should
begin with the Zanclean (in the Mediterranean Sea), with
the Dacian (in the Dacian basin), with the Kimmerian (in the
Euxinic basin) and the Babadzhanian (in the Caspian area),
around 5.3 Ma (Popov et al., 2004).
During the Romanian stage, the Dacian basin was isolated.
It became a large lake with a rich community of fresh-water
molluscs (Unionidae, more 70 endemic species, Melanopsidae
and Viviparidae) and ostracods (Candona s. l., Cypris s.l.). The
Middle Romanian is characterized by a specific ostracod community: Cypris mandelstami, Zonocypris membranae, “Eucypris” famosa, Kowalevskiella sp. (that community includes Upper Pliocene species existing also in the Caspian area).
A variety of ecosystems are known for the Dacian basin
development, from marine (Badenian), through all the brackish phases (Sarmatian - Dacian) to the fresh-water ecosystem
(Romanian).
In the Upper Pliocene (3.4 – 1.8 Ma) (Piacentian and Gelasian in the Mediterranean basin; Romanian, in the Dacian
basin and Akchiaghilian in the Pontic-Caspian area), in the Paratethys domain, the Pliocene orogenic movements shaped
the general features of the present-day geography (Fig. 10).
After the “Congeria rhomboidea Beds” (Portaferrian), the
Pannonian basin was almost completely filled up, except for
two regional depressions.
In both areas there is the abundant, but exclusively endemic ostracoda and mollusc species. In Slovenia, the “Paludinae Beds” represent an essential break up from the previous community, while in the satellite “Baraolt basin” (Jekelius,
1932) a “residual fauna” with the (dominant) Pachidacna fuchsi, and the P. abichiformis (inherited from the Pontian fauna)
and few new taxa, together with the last species of “Hungarocypris” and with deviant forms of Caspiolla and Amplocypris
(Olteanu, 2003) survived to prove the continuity of the faunal
evolution in the Post-Pontian or even newer oligohaline and
lacustrine facies. In the final part of the sequence (at Racos
and at Bodos-Baraolt) forms of Unio - looking like certain spe-
cies from the Romanian of the Dacian basin (in the Pristinunio
pristinus and P. mutabilis group) (Olteanu, Lubenescu, in press)
- were found. The above support a most likely correlation
(with the Romanian and the Pleistocene) as our knowledge
deepens and extends.
The Euxinian basin is isolated although there occur random connections with the Caspian basin through the Manici
corridor (Northern Caucasus). The Kuialnikian-Gurian-Ceaudian episodes (conspicous in the NE area of the Euxinian basin),
each of them with specific community, (Imnadze, 1971) imply
an intense eustatic „play” and an implicit hydrochemical one
(yet, it cannot be claimed that the area turned „lacustrine”.
Ancient or recent, the Black Sea has never been a freshwater
lake).
The Caspian basin (as well as the whole geographical
area belonging to the Paratethys) is now a low salinity one
(as compared to the Pliocene average). The water level movement compared to the present-day level of the Black Sea,
reaches high levels (up to 500m). In the „Akchiaghilian Episode” a lower level and a freshwater upper level occur (confirmed by ostracoda, Mandelstam et al., 1962). In the middle
level of the Akchiaghilian, the sea extends towards the North
(along the Volga - Ural depression axis), for nearly 2,200 km
and Westwards towards Taman-Crimea across the Kuban
depression. The Black Sea boreholes brought to light ‘exotic’
faunal elements of a rather high salinity (of marine origin in
a Sarmatian “typology” (Avimactra, Avicardium, Miricardium,
Andrusella, Kirkiziella) which naturally, raises the question:
Where did they come from? Likewise, where did the Mediterranean brackish fauna come from?). (Olteanu, 2001). The mollusc fauna suggests that the salinity exceeded the Pliocene
average. That brackish insertion-transgression (along with its
specific fauna of uncertain origin) seems to be generated by
a South Caspian possible corridor through the Upper basin of
the Eufrat that would have linked that basin to the Southern
marine area (Steininger et al., 1985, Chepalyga, 1995).
The likely cronostratigraphic correlation between the
Romanian and the Akchiaghilian was generally agreed upon,
while the next episode, Apscheronian, belongs to the Lower
Quaternary. The boundary with the Pleistocene is again conventionally set (at 1.8 Ma) just because it is generally impossible to put together a correlation of any kind of geological
‘events’.
The Dacian Basin area was ephemerally invaded by
the Euxinian waters during the Upper Dacian (in the Lehliu – Alexandria area is the one constant level, 0.10cm with
Kimmerian ostracods) and, for the last time, during the Apscheronian (with the mollusc fauna in Barbosi – Galati, Macarovici, Costetchi, 1973, with Didacna crassa, D. aff pseudocrassa, Adacna plicata, Corbicula fluminans, Viviparus sadleri,
V. pseudo-sadleri, V. diluviensis etc and Bandrabur, 1960, Unio
pictorum, Unio sp.). The ostracoda fauna in Barbosi sequence
is particularly rich: Amnicythere precaspia (Livental), A. quinquetuberculata (Livental)*, A. multituberculata (Livental)*, A.
103
bacuana (Livental)*, A. striatocostata (Schweyer)*, A. cymbula
(Livental)*, A. propinqua (Livental)*, A. variabituberculata propinqua (Livental), A. unicornis (Schweyer), Euxinocythere bosqueti (?) propinqua (Livental), E. aff ergeniensis (Schweyer), E.
post-kuialnica n. sp., Candona mandelstami (Schweyer), C. liventalina (Evlachova), C. elongata (Schweyer)*, Limnocythere
(Scordiascia) aff sharapovae (Schweyer), Tyrrhenocythere pontica (Livental), Loxoconcha petasa (Livental), L. eichwaldi (Livental), Cytherissa new sp.(*recent species in the Black Sea). It
suggests a large western lagoon of the Black Sea.
During the Karangatian (the Riss-Wurm interglacial period) the Bosporus opens up and the Black Sea area is invaded by organisms from the Mediterranean basin, including many marine ostracod species: Pterigocythereis jonesi,
Carinocythereis carinata, Loxoconcha aff granulosa, L. lepida,
L. aff eliptica, Semicytherura aff sanmarinensis, S. aff acuticostata, Mediocythereis n. sp., Sclerochilus n. sp., Echinocythereis
n. sp., Hemicytheria n. sp. etc. The second opening of the
Bosphorous takes place during the Sourozkian episode: Leptocythere multipunctata, L. macallena, Loxoconcha granulata,
Cytheridea aff acuminata, while the last opening, during the
Upper Neo-Euxinian: Hemicytherura videns, Callistocythere
diffusa, C. flavidofusca, C. mediterranea, C. ramosa, C. fabaeformis, Costa edwardsi runncinata, Urocythereis margaritifera, Loxoconcha rhomboidea, Aurila convexa. (three brackish
ingressions in the Danube Delta) (Olteanu, 2004). Three moments, three migration waves and three types of colonists
signify different ecological features during the Black Sea
recent history.
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105
Geoelectrical Measurements Applied
to the Assessment of Groundwater Quality
Vlad RĂDULESCU (1), Florian RĂDULESCU (2), Ioan STAN
(3)
(1) National Institute of Marine Geology and Geo-ecology (GeoEcoMar), 23-25 Dimitrie Onciul St 024053, Bucharest, Romania
(2)
S.C. Intel 91 S.R.L. , 12 Valea Buzaului St, Bucharest, Romania, [email protected]
(3) Institutul de Studii şi Consultanţă Energetica S.A., Bucureşti, Romania
Abstract. The aim of this paper is to convince both the specialists in the drilling fields and those in the environmental protection field to use the geophysical methods of investigation, especially in the field of water supply. It is almost essential to use geophysical methods especially in the geoelectrical domain
when you have drilled for water if you take into consideration the possibility this method gives of an optimum setting for estimating the quality of these
waters. Below we are laying before you some examples of water quality estimation through geophysical methods. We are also mentioning that applying
this geoelectrical method important savings can be realized, concerning the performing of same drillings for potable water
Key words: geoelectric, resistivity, groundwater, VES, well log, drill, borehole
INTRODUCTION
Geoelectrical measurements are very often used to identify the underground aquifers, their geometrical characteristics, groundwater quality, aquifer porosity layers and even
the direction and flow velocity of the groundwater.
Generally, the geophysical and especially the geoelectrical techniques (Buselli et al. 1990) were successfully used in
realizing the image of a very wide feature variation, including: the heterogeneity of the aquifers lithology, the under
pressure aquifer layers width, position of the hydrostatic level, the depth to the aquifers bed , presence of the clay lenses,
fracture zone identification, the geometry of underground
cavities concerning the cavernous limestone, as well as the
characteristics of the contamination lenses with both organic
and inorganic compounds (Castany 1972, Gheorghiu 1969).
In order to satisfy the requirements of drinking water,
a series of boreholes have generally been made at medium
depths (50 -100 m) lately. For an optimum placement it is
compulsory to make a geophysical measurement mainly
the standard electrical logging, which is a cheap, rapid and
precise geophysical method. Resistivity measurements in
boreholes can present useful information, not only regarding
the existence of an aquifer horizon or geological information
with compact characteristic (sandstones, limestones), but
also regarding groundwater quality.
In the following chapters, we will present some typical
situations regarding the groundwater quality estimations using both geoelectrical surface and borehole measurements.
1. GEOELECTRICAL MEASUREMENTS
Rocks and geological formations can vary in their capacity of conducting the electrical current, a capacity which is
usually called electrical resistivity. Electrical current implies
electricity moving electrical loads, in the case of geological
formations these louds being either electrons or ions, ions
moving through the fluids of spongy space of rocks. Experimental results have shown that water consistency has the
most important contribution to the electrical current conduction through rocks and sedimentary geological formations.
According to the electrical resistivity variations of underground formations, some hydrogeological characteristics
may be identified.
The surface alternative of geoelectrical research (Modin
et al., 1997) can supply regional or local information about
the distribution of aquiferous formation at depth, over their
development and the degree of mineralization in groundwater pollution estimations.
107
V. Rădulescu, F. Rădulescu, I. Stan - Geoelectrical measurements applied to the assessment of groundwater quality
In the electrical logging, the information is local, the degree of accuracy in determining the aquifer horizon is to the
nearest centrimetre and the contact, almost direct between
measurement device and aquifer horizon, may lead in many
times to almost exact estimates of the groundwater quality
especially when, in the case of drilling for water, the existing
geological situation may be easily surveyed during drilling.
As we know, water conductivity is influenced by the content of free electrical charge that may be electrons, in case of
the existence of chemical elements with some iron content,
or free ions, in case of azoth and a azothates. Delimitation of
the type of water mineralization cannot be done using geoelectrical data. This method indicates, in a qualitative mode,
the existence of a certain degree of water mineralization.
2. RESEARCH METHODOLOGY
Geo-electrical measurements in boreholes have been taken
using a GEOLOGGER 3000 logging installation. General results
consisted in 3 curves, two of them representing resistivity correlations and one is a potential curve (PS). While the first two curves
make evident the resistivity of the formations, penetrated by the
boreholes, the PS curve shows the electro-chemical processes
inside those geological formations. As a result, the total potential has the form of a ponderate average between diffusion and
absorption potential, oxido-reduction potential and electro
filtration potential (Gheorghiu, 1969). In the case of geological
sedimentary formations the diffusion and absorption potential
is mainly present. The prevailing rocks of this type are: clayish
sands, fine or coarse sands and broken stones; all these do have
water in their content. The PS curve is very useful in analyzing
geophysical data, especially in locating the aquifer horizons but
only if it being correlated to the resistivity curve.
Surface geo-electrical measurements have been taken
with Intel91 V3 resistivity meter that uses Schlumberger disposal (Mundry 1980). Data interpretation and management is
done using the self modelling program for VES (Simulation 2).
3. DATA ANALYSIS
As previously presented, geological formation resistivity
depends on mineralogical composition, water content and
the degree of mineralization in the water. The geo-electrical
perspective shows that, (in the case of sedimentary formations), apparent resistivity measured using electrical logging
is as follows:
• clay and marl
5-10 ohmm
• dry sands
> 150 ohmm
• sandstone
> 150 ohmm
• limestones
> 500 ohmm
• sandy clays
10 – 15 ohmm
• clayish sands
10 – 25 ohmm
• aquiferous sands
50 – 100 ohmm
• mineralizated water 0 – 0.1 ohmm
The values presented above have only an informal character, occasional major modifications being possible due to either
108
Fig. 1 Well log H = 110 m - Vela
layer thickness penetrated by the electrode, the composition
of the mud drilled or the mineralogical groundwater composition or the specific conditions for that particular borehole.
The geophysical well log presented in Fig. 1 was recorded
in the Dolj area. From a lithological point of view, this area
is mainly argillaceous, horizons with aquifer sands being located (using the electrical logging results) in-between 19-23,
48-52 and 61-70 m. Due to the fact that the average value for
resistivity is 70 ohmm, we have considered that the groundwater deposited in sandy horizons is not mineralized and is
accordingly drinkable. We must also mention that in-between
55-61 m, high levels of apparent rezistivity (200 ohmm) indicate the presence of some compact sands; the same result
being obtained during the drill process.
Close to Ramnicu Valcea city quite an opposite situation
was noted from the groundwater quality point of view. The
well log presented in figure 2 indicates the presence of a sandy
horizon within 0-18 m interval. After this interval, the resistivity
curve remains constant around 2 – 5 ohmm although the PS
indicates the presence of some sandy horizons. In this condition, we can definitely identify the mineralized groundwater.
Because the salt concentration (NaCl) within this borehole was so dense, it was quite impossible to separate the
salty water horizons from possible drinkable water horizons.
In order to solve the problem some surface measurements
were taken (VES). The results obtained from these measurements are presented in the figure 3.
After the interpretation of SEV, the existence of two very
conductive horizons between 17-37 m and 47-70 m and of a
resistive horizon between 37 and 47 m was noted. The first
two horizons were composed of salty sands and the resistive
one was composed of a volcanic tuff. This last horizon was
also identified during the drilling process.
Fig. 4 Well log H = 50 m - Movilita
Fig. 2 Well log H = 70 m – Rm. Vâlcea
Fig. 5 Well log H = 30 m - Movilita
Fig. 3 Vertical electrical sounding (VES) – Rm. Vâlcea
The boreholes taken in the Movilita region at depths of
about 50 m (Fig. 4 and Fig. 5) present very low resistivity,
which proves that the groundwater retained especially in the
clayish sands (prevalent in this area) is very well mineralized.
Fig. 6 presents the state of the Liscoteanca region. There,
the groundwater source is situated in the clayish sands at 540 m depth, but also in two small sandy horizons (of about
20-30 cm) within a 60 m interval. The lowest resistivity values
indicate the presence of a very strongly mineralized water.
Fig. 6 Well log H = 80 m - Liscoteanca
109
CONCLUSION
The aim of this article is to demonstrate that the groundwater quality may be measured using geoelectrical measurements, before using cased boreholes. In this way it is possible to reduce the costs of drilling if drinking water is desired.
When a decision regarding groundwater quality is needed, it
is recommended to gain all the information about that area
(some geological information, hydrological or geophysical
information). It is also recommended to use surface geoelectrical measurements, in order to locate the optimum water
drilling, especially in areas where there is a lack of hydrogeological information or in areas where there are doubts about
the groundwater quality.
References
Barker, R. D., 1990 - Improving the quality of resistivity sounding data
in landfill studies . In:Ward, S. H. (ed.).Geotechnical and Enviromental Geophysics, 2, SEG, Tusla, Oklahoma, 245-251
Buselli, G., Barber, C., Davis, G. B., Salama, R.B., 1990 - Detection of groundwater contamination near waste disposal sites with transient
electromagnetic and electrical methods, in: Geotehnical and
environmental geophysics, Vol.2, 27-39, Society of Exploration
Geophysicists
Castany, C., 1972 - Prospectarea şi explorarea apelor subterane , Editura Tehnică, Bucureşti
Gheorghiu, Fl., 1969 - Investigarea găurilor de sondă prin metode geofizice - Editura tehnică, Bucureşti
Kelly, W. E. 1976 - Geoelectric sounding for delineating groundwater
contamination. Ground Water, 13, 418-427
Modin, I. N., V.A. Shevnin, A.A. Bobatchev, D. Bolshakov, D.A. Leonov,
M.L., Vladov, 1997 - Investigations of oil pollution with electrical prospecting method, in Proc. 3rd Meeting, edited by N.B.
Chridtensen 267-270 Environm. and Eng. Geoph. Soc. Europ.
Section
Georgescu, P., 1977 - Three-dimensional models for resistivity data,
Rev. Roum. Geophy. et Geogr., serie de Geophysique, 21,1
Mundry, E., 1980 - The effect of a finite distance between potential
electrodes on Schlumberger resistivity measurement – A simple
correction graph, Geophysics, 45, (12), 1872-1875
Georgescu, P., Gavrilă, I., 1989 - Influence of electrical prospecting arrangement on apparent resistivity anomalies, Rev. Roum. Geophy. et Geogr., serie de Geophysique, 33,1
Ştefănescu, S. S., Ştefănescu, D., 1974 - Mathematical models of conducting ore bodies for direct current electrical prospecting. Geophysical Prospecting, 22,1
110
MS Excel Built-in Program for Flow
and Channel Profile Determination
Florian PĂUN, Mirel Ciprian PĂUN
National Institute of Marine Geology and Geo-ecology (GeoEcoMar),
304, Mamaia Blvd., 900581 Constantza, Romania
e-mail: [email protected]
Abstract. The results of the program are the following: a quick display of the flow through a transversal section; display of the section’s area and of its
profile, all these in the same worksheet as the input data (bathymetric data, speeds and depths measured on a minimum number of at least 3 “verticals”
on each profile). Also, the possibility to use then, for processing and presenting output data, all the graphical and tabular MS Office facilities for selecting,
copying, pasting, resizing, moving, font formatting, aligning, coloring, text-tables and graphics transferring between applications, sorting, filtering, reports
and pivot-tables realization... as the main purpose of direct MS Excel “built-in” programs, is to allow work as if everything would have been programmed by
Microsoft itself, from the raw data input, intermediate and final processing to the final results presentation, all in a single Workbook, by mere mouse clicks
on a toolbar’ buttons, independent but absolutely similar to the Excel original ones.
Key words: flow, transversal section area, channel profile, speeds and medium speeds, depths, GPS assisted positioning
This complex program performs:
1. transversal section area’s integral computerized calculus
for any running water,
2. channel profile’s graphical represen- tations (depth dependent on the left/right border distance, expressed in
meters or geographic coordinates), based on bathymetry
results and on a small number of measurements on selected profile’s verticals,
3. the section’s flow calculus, by many methods, based on
different hydrological models (and the program’s authors
can easily implement, on request, any other desired model, for any researcher that will address to them).
The program has routines for computerized preparation
of all input data, results, in different formats and combinations, from other programs and devices, such as:
• routine for synchronizing bathymetry (depths) data and
GPS position, their processing in the format desired for
the next stage, by retaining the useful columns only
(from the multitude of columns given by GPS),
• routine for filtering bathymetry data at intervals desired
by different end-users, (the bathymetric data sorting at
•
•
•
•
10 or 20 or 30 seconds only, for example, from the very
big data number offered by the bathymetric device, at
every second, generally),
routines to parcel out and process by columns separated
on degrees, minutes and thousandths, the latitude and
longitude geographical coordinates; obtaining any desired formats for those,
different subroutines included in the main routine for
areas and flow calculus, for coordinates and distances to
borders calculus for the projection points of all bathymetry as well as of all “verticals” for depths-speeds on the
straight line that join the two marks previously chosen on
the two river borders,
routine for on screen bathymetric complete profile instant display, in coordinates and depths, in order to allow fast selection, immediately after finishing preceding
bathymetry, of the best positions for the “verticals” of the
speeds-depths measurements by the flow meter or other adequate device; these selected positions will be given
to the ship’s commander for a most precise positioning of
the ship on the desired coordinates, for the next stage,
routine to determine on “vertical” mean speed, by a corresponding specific calculus formula,
111
F. Păun, M.C. Păun - MS Excel Built-in Program for Flow and Channel Profile Determination
•
•
•
routines to determine the 6-degree polynomial functions
that approximate the channel profile’s real curves,
routines to implement the desired hydrological models,
routines to compute the partial and total areas, and partial and total flows, based both on bathymetry (with as
few or as many filtered data as one wishes), as well as on
the “verticals” only (minimum 3, but the precision obviously grows with the number of “verticals” on each profile).
Once the input data (already pre-prepared by using the
first routines anteriorly presented: depths, East and North geographical positions, and in the bottom part, of the “verticals”,
the mean speeds’ column is also completed) is adequately introduced, a simple mouse click on the (built-in Excel) DEB
button is needed, which will start practically instantly the
automated achievement of all tabular and graphical desired
results, presented in Figs. 1 and 2 and in Table 1.
The program is exemplified with the Sf. Gheorghe
km108.4 profile from the 2004 campaign.
First, the final desired results, coloured in red automatically by the program for their immediate emphasizing are
presented;
These are the total flows of: 2423.62 (m3/s) – computed
based on the given profile by the 5 “verticals” only, and then
2718.35 (m3/s) and 2706.87 (m3/s), respectively. They are computed based on the much accurate profile, from much more
depths, supplied by the preceding bathymetry, but restricted
to the same number of 5 mean speeds only, for the 5 “verticals”. The mean speeds are distributed by the program to the
multitude of bathymetry points, according to two models,
md1- based on the principle of proximity to the verticals, and
md2-, the model of the linear variation of the speed between
two successive “verticals”; Any other speeds variation model,
imposed by hydrological studies is easy to implement, but
the variations do not exceed very few percentages. There is a
greater difference only from the first value, in which the channel profile is approximated by just 5 depth measurements, on
the 5 “verticals”.
Immediately to the left of the total flows’ red values’, there
are the red figures of the total section’s areas, namely 3035.41
(m2), computed based on bathymetry’s dozens of points, and
2779.56 (m2). The latter is an obviously smaller and less accurate value, as it is calculated based on a smaller number
of depths: those corresponding to the “verticals” chosen for
the speeds’ measurement in 6 layers (speed horizons) and on
mean speed computation.
In figure 1, the 4 graphics automatically obtained are included, simultaneously with table 1, with titles according to
the presented data, namely
112
1°-Lat.N-Long.E, with the measurement points’ geographic positions (in thousandths of degree) as well as with their
projections on the line joining the two borders marks;
2°-Depths(m)-Distances(m):
3°-Depths(m)-Eastern Longitude
4°-Depths(m)- Inverse Distances (m)
In figure 2, the Depths(m)-Distances(m) presentation is
resumed, this time at exactly the same scale on ordinate as
well as on the abscissa, in order to have the real, undistorted
profile image, without the horizontal compression from the
last 3 previous graphics. We do that because, though in metres too, the depth and the distances from the borders differ
substantially by an order of magnitude, from 20…30 metres
for maximum depths to 300…900 metres for channel’s profile width.
The table is structured on an upper side, for the bathymetry points, and a lower one, for the “verticals” points (minimum 3 and maximum as many as the fuel cost allows), separated by the two points of the two border marks coordinates.
Those points also border each of the two groups for bathymetry and “verticals”, in order to close the profiles at the river
borders, where the depth and river speed are considered
null.
As the columns’ significance is identical, the units of measurement are displayed only once, in the intermediate part of
the two zones (i.e., bathymetry and “verticals”), in magenta,
but they aren’t crucially necessary, all data and computations
being made in the SI units (m, m2, m3, m3/s).
Detailing the program’s presentation, here are, from left
to right, the table’s columns significance:
45, in the first cell, [A1], tells to the program to use the degree-minute-thausandths of minute transforming relations
that are valid for the 45° latitude parallel, of Sf.Gh.km108,
which exemplifies the program,
E, on column 1, A, signifies the East coordinate, the longitude, used as abscissa in the first two graphics, on the left
side.
N, on column 2, B, the North coordinate, the latitude,
used as ordinate in the first graphic, left-up corner, from the
4, to which the b letter is attached for the upper zone, of the
bathymetry, the D letter for the line joining the two river borders marks (on this line both the bathymetry’s points as well
as the 3…5 or even more “verticals” measurement points are
projected, by drawing perpendiculars) and the v letter for the
lower zone, of the “verticals” measurements by the “handmill”
(flow-metre ) or other device, in the 6 layers or continuously,
thus obtaining the titles Nb, ND and Nv.
np, the ordinates at the origin, in the East-North plane,
of the perpendicular lines drawn, from the bathymetry’s and
verticals’ points, on the line joining the two border points, orange coloured line on the first, trajectories’ graphic.
Fig.2 The actual shape of the Danube basin in the studied section (the same horizontal scale for the distances from the border and depths)
Fig.1 The 4 graphics automatically drawn by the program togther with the calculs of the section area and of the water flow into the section
113
Ebpr and Nbpr, columns 4 and 5, the E and N coordinates
of the light blue projection points on the orange line, of the
dark blue bathymetry’s points, from the columns 1 and 2 of the
upper part of the table.
Evpr and Nvpr, columns 4 and 5 of the lower side, the E
and N coordinates for the orange points of projecting on the
same line the Verticals’ red points from columns 1 and 2 of the
lower part of the table.
D and Dinv, columns 6 and 7, the distances of each bathymetric point or vertical measurement, to one border and to the
other border, respectively.
Ab and Av, respectively, on column 8, of bathymetric
depths - up and of Verticals, down, respectively, is the column
of input data.
Vm, column 9, for mean speeds, is automatically completed
by the program, in the upper part, the Bathymetry part, with
the speed mean values read from the lower part, the Verticals’
part (input data), according to the criterion of the proximity of
each bathymetric point (its projection on the straight line, to be
more exact) to the closest speed measure-ments vertical (that
is, a mean speeds repartition to all the bathymetry points, according to the criterion of proximity to the flow-metre Verticals
measurements, as well as Vlin, in the last column, 13, contains
the repartition into the bathymetry points for the same mean
speeds, but according to another model, for comparison, the
model of linear speed variation between verticals; any other
hydrologic model can be attached).
Column 10, Arii, (areas), calculates the elementary areas, between two successive bathymetric points in the upper zone, between two successive Verticals in the lower zone, respectively.
Column 11, Debite, (Flow), calculates the elementary flow
for each elementary surface, multiplying the elementary areas
by their respective elementary surfaces (DebiteB, up, in the
bathymetry zone, and DebiteV, down, in the Verticals zone).
Likewise, DebL, in column 12, calculates the elementary flows
based on the model 2, of mean speeds linear variation, from
column 13, Vml.
Under the latter semi-columns, in red, there are the sums
of the total areas and flows, as final results (with which we, in
fact, begun our presentation).
The first graphic, I, upper-left, “Trajectories”, was already
entirely described, when the table was presented, and the 3
subsequent graphics from Fig.1. display the channel’s profile
as follows:
The second graphic, II, in the bottom-left corner, represents
additionally, in blue, the bathymetry projections curve; in red,
the 5 Verticals projections depths (with the values enclosed),
and in black, the curve of the 6 degree polygon. It best approximates, as a function, the blue bathymetric curve, while
the equation of the 6 degree function is written, just in the
middle of the 3 functions, under the table: the first function,
of degree 1, is, obviously, the equation of the line joining the
two borders, on which the bathymetry and the Verticals profile are projected, while the last, third function is the polynomial function of also of degree 6, (the maximum degree with
114
which Excel and its incorporated language, VBA, work), which
best approximate the red, Verticals profile curve. The writing of
these functions was programmed for their further use in the
most precise areas calculus by integrating these functions between the limits of the borders, after a separate mathematicalphysical discussion. The ordinate of this second graphic, i.e., II,
(depths graphic) is obviously depth, while its abscissa is the
East latitude, in thousandths of a minute (exactly in the same
way as for the first graphic, I).
The last two graphics, III and IV, in right side, also represent the depths, in metres, but not as functions of the East
geographic coordinate, but as function of the distances to the
two borders, in metres (D, to a border, and Dinv to the other
border).
All the last 3 graphics clearly show smaller areas closed
by the red (Verticals depths) curves, than the areas closed by
the blue (bathymetry) curves, which is based on many more
measurement points, that is on a much better approximation
of the channel bed profile, thus graphically justifying the bigger values, in red, based on bathymetry, than those based only
on a few Verticals in approximating the bed channel profile
and its section area.
A still better approximation, still closer to the real values,
can be obtained by using in the upper, bathymetry part, all
registered bathymetric points, 5 time more numerous, a value
at every 2 seconds as compared to the method presented until
now, in which the bathymetric values were filtered from 10 to
10 seconds, as required. Only the final results of this new
calculus is directly given, based on the entire bathymetric registration, 3026.35 (m2) for the total area and 2749.48 (m3/s) for
the total flow, (without the entire table type 1 and the entire
figure type 1 for the entire bathymetry), all that only to emphasize the fact that these values, naturally the most accurate,
are however with only 1.27% more precise for flows and with a
still smaller percentage for the total area, a fact that completely
justifies the bathymetry points filtering (“decimation”) use, at
every 10 seconds instead of every 2 seconds, as the total registration is made. The line’s equation is normally the same, while
the 6 degree curves’ equations differ by the small, insignificant
powers only, (1 and 2, at the most 3 powers). It should be emphasized that our method for areas calculus is most accurate,
approaching, in fact, the integral’s definition (just the Darboux
sums, in fact, before passing to the “limit” process).
On the first table’s line, at the right of latitude’s degrees’
value (45, in our exemplification), the program automatically
completes a series of intermediate values, very useful for the
next calculations, as well as for controlling the accuracy of the
results’ (by the programmer and user), such as the straight
line’s slope, its origin ordinate, the slope of the perpendicular
projections on this line which join the channel’s borders, the
values in meters, on latitude and longitude, at the exact value
of the sample’s latitude, etc.
It should be mentioned that the program is very, very precise when using a maximum number of decimals. Yet the final
results’ precision essentially depends on the precision of the
input data, that is on the precision of the devices, on the methods used and on the specialist who works with it.
Tab.1 The input, intermediate and output data. The final form triggerred by a click on the DEB button
115
It should be again underlined that a national and even an
international collaboration for establishing the best profiles
on the Danube, the good marking of all these profiles with
good marks on both borders (stable and visible, at least electronically, in the worst weather and environmental conditions,
flood and tempest including), stable for the following dozens
of years, with precisely known coordinates, would distinctly
improve and facilitate the Danube’s and its tributaries flow
and profile monitoring. So, a database can be created which
would permit the positioning always not only on the same profiles, but also on the same verticals in the profiles. The year on
year comparisons would be thus done based on just a single
annual Vertical only.
The measurements, both bathymetrical and by flow meter, can be more accurately made using very small boats, more
precisely positioned and more easily preserved on the chosen
positions.
More precise results can also be obtained by doubling the
number of the devices, on both boat borders, and also doubling the Verticals measurements for the same number of positions of the boat, that is, for the same fuel consumption.
Another most important special desideratum is to place
the GPS and the bathymetry devices as near as possible to the
flow-metre emplacement, for the place of the measurements
to coincide. Also, a complex transducer, for depth and speeds
in the same unit, would eliminate any other supplementary
errors, especially when measuring the depth based on hydrostatical pressure (that is, apart form the current speed and
angle between the vertical and the transducer’s cable). The detailed and chronological algorithm to use this program is the
following:
• the Debite toolbar display (Excel standard proceeding:
VIEW, Toolbars, Debite), that contains two incorporated
buttons: DEC and DEB.
• bathymetry data processing (in a sheet named, for example, BatOrigin) at a simple click on the DEC (“decimation”)
button.
• the processing of these results according to the prototype
from TransformPunctVirg.xls (which keeps the needed
transform formulae in its second line), by mere rolling the
mouse, from up to down, for the second selected line, over
all data.
•
•
•
from the new results, only the further useful ones are copied [Depths, E-thousandths, N- thousandths] and Past on a
new sheet, renamed, for example [ E, N, Ad ]
the completion of the first cell with the value of the parallel
on which the profile is situated, in order that the program
reads it from here and automatically uses it in transforming the geographical coordinates in metres, for the correct
distances, areas and flow calculus. In our example, [A1].
value=45
the minus sign is assigned to the entire depths column (for
a correct graphic representation of the column under the
axis) and the depths are moved to column 8.
Conversion to NUMBER-format of the columns [1:2], that
is [E,N], in order not to be treated as text. Their selection,
with or without title, and the realization of a preliminary diagram, according to the Excel std. method (INSERTCHART,
type=xyScatter), the elimination of the edges (“S” trajectory’
curvatures) in order to keep only the trajectory’s linear part;
the appropriate elimination of the Parasite data from the beginning and end of the bathymetry trajectory.
• the adding of the borders coordinates, MS and MD, left and
right border.
• selection of E (East) and Ab (bathymetry depths) and
quick display of the bathymetry diagram (INSERTCHART,
type=xyScatter) for selecting immediately the Verticals positions, that will be given to the ship’s commander to best
position its boat, using these data and the GPS.
• completion, under bathymetry, two lines by two columns,
for the line joining the borders marks, MS, MD; further
completion, with data obtained by the Verticals’ measurements, (minimum 3, but better, 5 or even more, depending
on the complexity of the profile, channels or sub-channels), also bordered, up and down, with the two borders
values, for curves’ closing.
• completion with mean speeds, by averaging flow-metre
data.
• click on the special Excel built-in DEB button, to compute
flow, and the Table 1 and the 4 graphics of Fig.1 are instantly automatically completed, together with a new graphic,
for the real profile’s shape. Here, the same metric scales are
used horizontally and vertically, that is, for horizontal distances and vertical depths.
References
F.l. Păun, M.C. Păun, 2004 – MSExcel built-in Program for Analytic and
Synthetic Ecological Indices Describing Ecosystems,Geo-EcoMarina 9/10 2003-2004
*** Microsoft Excel User’s Guide
*** Microsoft Excel Visual Basic User’s Guide
116
*** Microsoft Excel Visual Basic Reference
*** Microsoft VBA (Visual Basic for Applications)
*** Microsoft OLE Automation with Applications (MSWord, MS-Excel, MS-Project).
BOOK REVIEW
“DANUBE DELTA Genesis and Biodiversity” by Claudiu TUDORANCEA and Monica M. TUDORANCEA (eds),
2006, Backhuys Publishers, Leiden: 444 pp ISBN 90-5782-165-6
The publishing of a new book is an event that should be
greeted. It is a challenge; a challenge meant to lead to improvement, to further work on the weaker points of the book
and finally to a new and better book. That is the reason why we
welcome the publishing of this monographic volume “DANUBE DELTA Genesis and Biodiversity” edited by Professor
Claudiu Tudorancea, who is supported by his wife Monica M.
Tudorancea, and we recommend it to all those interested in
both deciphering the „secrets” of wetlands in general, of the
Danube Delta – an European and world asset in particular,
and making a comparison with the situations in other deltas
of the world. And if in the analysed paper there are some slips
somewhere, omissions, inadvertences, overlaps, imbalances,
redundancies etc., we hope that specialists will come with a
better book in the future.
The book, published in the collection “Biology of Inland
Waters” - Series Editor K. Martens, is a monographic paper
concerning one of the most important deltas of Europe, the
Danube Delta, a wetland of global importance, designated a
biosphere reserve and, part of it, a zone of the world natural heritage. It is worth mentioning the effort of the Editor
of this series of books on the biology of inner waters and,
unquestionably of the volume editors, to highlight a unique
European area, most of it still unaffected by anthropogenic
influences.
The book is the result of a fruitful collaboration of 20 authors, most of them specialists with rich knowledge and practice of the Danube Delta ecosystems.
In the Preface of the volume, the Distinguished Emeritus Professor H. B. N. Hynes (University of Waterloo, Ontario Canada) considers that the work is of large interest to
limnologists and various other specialists in environmental
protection, fishermen - ichthyologists, bird watchers – ornithologists; the Professor mentions that the book is the first attempt to deal comprehensively both with the limnology and
the general biology of a river delta and abounds in a variety
of points of view on the diversity of the topics – the origin
of the delta and its physical-geographical problems, water
chemistry, the phytoplankton, zooplankton, its vegetation or
bacteria living on sediments etc., with some overlaps, inevitable in a work with so many authors.
Following the “Preface”, the “Acknowledgements” and the
“Authors’ Addresses”, there is a short introduction by C. Tudorancea, on the history of the Danube Delta knowledge (Chapter 1 – Introduction), which comprises the main coordinates,
including two maps, and surveys the major bibliographic reference points.
We present below the contents of the other 15 chapters
of the book, all of them containing, with a few exceptions, the
subchapters “Introduction”, “Conclusions” and “Bibliography”,
together with some comments.
Chapter 2 - Danube Delta geology, geomorphology and
geochemistry (N. Mihăilescu) comprises, besides an introduction, a few subchapters which analyse the origin - the
Pleistocene and evolution of the Danube Delta during the
Holocene, the recent lacustrine deposits, the lakes of the fluvio-marine area of the Danube Delta (the Roşu-Iacub-Lumina
and Razelm-Sinoe depressions), the lakes of the fluvio-lacustrine area of the Danube Delta (the Matiţa-Trei Iezere, Gorgova-Isacova and the Meşter-Lungu-Fortuna depressions). The
conclusions reveal that the form and dynamics of the Danube
Delta are the effect of the climatic evolution during the Upper Pleistocene and Early Holocene.
Chapter 3 - Physiography and climate (Vasile Torică) synthetically presents the physical and geographical factors
characterizing the Danube Delta: location, area, boundaries,
relief, then paleo-geological, climatic and pedo-geographic
elements, followed by the climate, the radiative and dynamic
factors for the 1961 – 1999 interval (the mean monthly and
annual values of the sunshine period, nebulosity, the regime
of atmospheric pressure, air temperature, winds and humidity/precipitations etc.), as well as the unusual meteorological
117
Book Review
phenomena connected with the radiative or advective atmospheric processes.
on the characteristic structures – the Macrophytes cover and
the reed community, the phytophilous fauna.
Chapter 4 - The hydrological regime of the Danube River
in the deltaic sector (I. A. Irimuş) briefly deals with the hydrological relations within the aquatic components of the
Danube Delta and the hydrological budget of this system as
well, presenting comparative data concerning the evolution
of knowledge in the field; at the end, the chapter presents a
major practical problem, the long term hydrological forecast
of the summer-autumn minimum flow in the deltaic sector of
the Danube River.
The complex problems of the Danube Delta ecosystems
still require more attention, more research, and more efforts.
The study of the chemical characteristics and dynamics
of the ecosystem complex in the Danube Delta, presented in
Chapter 5 - The chemistry of the Danube Delta (Carmen Postolache) focuses on two major aspects: a. the development
of the trophic state of the delta ecosystems and b. pollution
– heavy metals and pesticides.
By using the historical approach, the author differentiates
three periods in the trophic state of the deltaic ecosystems: 1.
before 1980 - a state of relatively low nutrient concentrations
and variations (DIN:TRP > 10), characteristics typical of meso
and early eutrophic conditions; 2. the period 1981 – 1990 – a
state of higher concentrations and a wider range of nutrient
fluctuation (DIN:TRP < 10), characteristics typical of eutrophic
and hypertrophic conditions, and 3. the period 1990 - present
– characterized by the reduction of nutrient load, but without
any clear tendency in the trophic state development of the
ecosystems.
Pollution with heavy metals has become an important
problem in the last 15 – 20 years, not for the Danube in particular, but especially for the ecological effects recorded far
away from the emission source. No severe contamination was
signalled along the lower Danube; in this sector, as well as in
the most important lakes of the delta a significant reduction
in the concentration of heavy metals was recorded in the majority of the ecosystem compartments along the West – East
geographical gradient.
An important bioaccumulation of most heavy metals, together with an active accumulation in the bottom sediments,
occurs in the delta lakes in comparison with the channels
where the processes are very slow. The chapter on the
Danube Delta chemistry stands out as one of the most successful parts of the book.
Chapter 6 - The Danube Delta ecosystems (Nicolae
Găldean & Dorel M. Ruşti) briefly mentions some generalities,
however redundant as information, which become important when the concept of ecosystem is applied in a practical
and specific way. The authors consider that the delta ecosystems can be grouped as follows: the Danube branches, shallow ponds and channels, lakes, lagoons, river banks, marshes,
marine sand banks, land plains, marine shore and calcareous
islands. In a logical sequence based especially on literature,
the subchapters deal with the aquatic ecosystems, focusing
118
Chapter 7 - Phytoplankton and its primary production in
the Danube Delta (Ioan Cărăuş & Nicolae Nicolescu) r e p r e sents a substantial part of the monographic volume, which
consistently analyses the qualitative structure (specific
composition - 1098 species, 37.98% Chlorophyceae, 30,69%
Diatomaceae, 16,12% Cyanobacteria) and the quantitative
structure (abundance, biomass, comparative analysis of different physio-geographical units), then the elements of phytoplankton productivity and its development to the level
characteristic of eutrophication processes.
It is worth mentioning that the authors pay great attention to the delta - sea ecotonal zone, which represents a
mosaic with different proportions of the stenohaline or eurihaline freshwater forms and eurihaline or stenohaline brackish water species. The chapter ends with the analysis of the
distribution and role of the phytoplankton in the Danube
Delta. The species of algae identified in the Danube Delta are
presented in Appendix 7.1, which is praiseworthy, but the
pieces of information are difficult to follow because they are
not included in a table (typographically space-consuming,
but easily accessible).
In Chapter 8 - Aquatic Macrophytes (Anca Sârbu), the author presents and characterizes, in order, the Danube Delta
aquatic vegetation by categories:emerged macrophytes
(Typha angustifolia, Schenoplectus lacustris or Phragmites
australis), macrophytes with floating leaves (Nuphar lutea,
Nimphaea alba, Trapa natans, Hydrocaris morsus-ranae and
Nymphoides peltata), natant macrophytes (Salvinia natans,
Lemna minor, L. gibba, Spirodella polyrrhiza, Azola caroliniana,
A. filimicoides, Adrovanda vesiculosa, Utricularia australis) and
submerged macrophytes (Batrachium, Ceratophyllum, Elodea,
Hippuris, Lemna, Myriophyllum, Najas, Potamogeton, Utricularia, Vallisneria şi Zannichellia), then the changes in species
composition, density dynamics, biomass, nutrient cycling,
the role of aquatic Macrophytes in the ecosystem feedback
mechanisms. The chapter contains numerous interesting
quantitative data, some of which could be better structured
in the future. Sometime methodology should be described so
that the reader might grasp the text more easily: for instance,
in Fig. 8.2 – Changes in frequency (F%) and abundance (A%)
of submerged macrophytes species… the frequency values
over 100% are questionable.
In Chapter 9 - The zooplankton structure and productivity in Danube Delta lacustrine ecosystems (Victor Zinevici &
Laura Parpală), after a concise introduction and the general
characterization of the Danube Delta lacustrine zooplankton, the authors present the multiannual values of the structural and functional parameters, the spatial, seasonal and
interannual dynamics, then, they proceed by analysing the
lacustrine zooplankton under the natural evolution of the
Book Review
trophic state of ecosystems; at the end, the authors describe
the structure and productivity of the Danube Delta lacustrine zooplankton under the impact of eutrophication. The
chapter abounds in information, containing, for instance,
the list of recorded species, some values of the number of
species in definite situations, values of population density,
biomass, productivity etc. In the period 1975 – 1995, 562
components were identified in the lacustrine zooplankton
of the Danube Delta, having the mean general values as follows: 659 indvs.L-1 for density, 4.7 mg.wet weight.L-1 for biomass, 0.5 mg.wet weight.L-1/24 h for productivity, and 9.4
days for biomass cycling time. The analysis of multiannual dynamics showed three distinct periods in the development of the delta zooplankton, revealing the evolution
of the eutrophication process: 1975 – 1980, a period of less
impacts, 1981 – 1990, a period of maximum impact, 1991
– 1995, a period of slight decrease in impacts.
Chapter 10 - Benthic fauna of the Danube Delta (Claudiu
Tudorancea), is an attempt to summarize the knowledge of
the different aquatic ecosystems in the delta. The author focuses on three major problems: 1. the composition of benthic
fauna, supported by a list of species, well-organized and very
useful (Table 10.1 – The occurrence and distribution of benthic species in the major types of aquatic ecosystems in the
Danube Delta), 2. benthic habitats and their fauna (the Danube branches, lakes and ponds, new marine lagoons), and 3.
trends in the dynamics of benthic fauna.
After 1983, the benthic communities in the Danube Delta
are characterized, as a rule, by the presence of Chironomidae
and Oligochaeta populations, which shows a severe reduction in benthic fauna diversity.
The important ecological role of Oligochaeta populations
in the last decades (numerical dominance up to 60% and biomass dominance up to 47% of the total benthic fauna) made
it necessary that the book should include a special section
on this issue. Chapter 11 - Structure and function of the
Oligochaeta communities in lentic ecosystems of the Danube Delta (Geta Rîşnoveanu), analyses in detail, starting from
the studied lakes located between the three Danube arms,
the structure, dynamics and role of the dominant species in
the communities of reference. Then, the author provides extremely important information on the role of Oligochaeta in
the energetic flow and in the cycling processes of nitrogen
and phosphorous, suggestively illustrated by diagrams (Fig
11.6 and Fig. 11.7).
Another section of the book deals with an issue less tackled – the invertebrate fauna of the substratum represented
by the submerged vegetation; thus Chapter 12 - Weed-bed
fauna of the Danube Delta (Constantin Ciubuc & Ovidiu
Ciolpan) includes, in a table occupying 55% of its length, the
identified taxa, the studied area and the species composition of the vegetation substratum (Table 12.1 – The list of
macro invertebrates in the thickness of the Danube Delta
submerged vegetation). Phytophilous fauna is characterized,
as a rule, by relatively low specific diversity (sometime 16 species appear to the utmost) and great variations in space and
time; the most abundant taxonomic groups were Chironomidae – 22%, Gastropoda – 16%, Coleoptera – 14%, Odonata
– 9%, then Oligochaeta - 8%, Trichoptera - 8% etc.
Chapter 13 - Benthic microbial communities (Doina
Ionică), presents the results of consistent studies performed
on 16 deltaic lakes along a period of over 20 years (1975
– 2000). The structural characteristics of benthonic heterotrophic microorganisms are related to the number and/or
the biomass of the population, while the functional aspects
are analysed in terms of the rates of microbial processes or
micro biota activity. Beside the microbial numerical density,
the author focuses on the seasonal dynamics and the horizontal and vertical distribution of heterotrophic bacteria. The
bacterial biomass in sediments recorded large variations (5.8
– 20.3 μg wet mud), with the highest values in summer. The
subchapter dealing with the activity of the micro organisms
living in sediments briefly tackles the problems of aerobic
and anaerobic decomposition, the coefficient of heterotrophic activity and the dehydrogenaze activity. When analysing the relationship between microorganisms and nutrient
cycling, the author first underlines the bacteria taking part
in the nitrogen cycle, then the role of bacteria in the carbon
and sulphur cycle. The important role of benthic microorganisms in assessing the trophic state of the Danube Delta lakes
is shown when the author presents the following aspects: the
total number of viable cells, the density of different physiological groups of microorganisms, the rate of aerobic decomposition of organic matter in sediments and the coefficient
of heterotrophic activity. The conclusions confirm the data in
the field literature and, at the same time, show an increasing
tendency in the numerical density of bacteriobenthos in the
lake complexes of Roşu-Puiu and Matiţa-Merhei during the
period 1975 – 2000.
The world of the fishes is largely presented in Chapter 14
- The ichthyofauna of the Danube Delta (K. W. Battes & F. Pricope), through two major aspects, namely fish taxonomy (species, interspecific hybrids, races, intraspecific hybrids) and
fish ecology. It is worth mentioning that the authors present
an orderly list (Table 14.1 – List of the Danube Delta fish species – after Nalbant, 2003), which comprises 82 species, and
a list of bibliographical synthesis of species recorded in three
different habitats (Table 14.2, which should have included
not only the English common names of the species, but also
the Romanian vernacular). The ecological aspects comprise
first the zoogeographical problems of the fish populations,
fish migrations, then aspects of growth biology, reproductive and feeding biology. An important subchapter, containing statistical data from various sources, deals with fish yield
and the control factors influencing it. The assessment of the
state of deltaic ichthyofauna reveals the major changes in the
structure of various fish species, characterized especially by
the general tendency of severe decrease in the deltaic fish
resources.
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Book Review
The amazingly varied world of birds, an emblem of the
Danube Delta, is presented in Chapter 15 - The Danube Delta
avifauna (Dan Munteanu), in which the author analyses the
bird populations by taxonomic order and species. Special attention is paid to migration and the influencing factors of the
deltaic avifaunistic structure from the biogeographic point
of view (geonomic factors, palaeoecological, ecological and
anthropogenic factors); the author concludes that the deltaic
avifauna includes elements of great zoogeographical diversity, some of these elements, the ones of Asian and Sarmatian origin, making the link with the European avifauna. The
subchapter presenting the habitats of the Danube Delta avifauna is particularly interesting from a didactic point of view
and it should be further developed. The final subchapter, rich
in information and very well organized, refers to changes and
change tendencies, most of them regressive, the qualitative
and quantitative modifications in the structure and functioning of avifauna communities in the Danube Delta. The author
considers that, during the 20th century, the avifauna of the
delta, lost up to 7 breeding species (plus 4 more species in the
lakes complex), but gained 18 species by recent immigration.
In the period 1961 – 1970, a drastic decrease in the number
of colonial birds was registered; after 1970 – 1975 the populations of some species (Phalacrocorax carbo, Ph. pygmaeus,
Ardeola ralloides) recovered, while other species recorded the
continuous diminishing of their populations (Plegadis falcinellus, Ardea purpurea); in the 1980s the number of colonies decreased, but the number of individuals in the remaining colonies increased; after 1990 (the year when the Danube Delta
Biosphere Reserve – DDBR was established) some species
become more abundant (Phalacrocorax carbo, Ph. pygmaeus,
Ardeola ralloides, Egretta garzetta, Nycticorax nycticorax, even
Plegadis falcinellus), while other species maintained the same
low levels (Ardea purpurea, Egretta alba).
The last part of the book, Chapter 16 - Human presence
in the Danube Delta (Monica M. Tudorancea) presents, after
some historical data, the main economic activities characteristic of the Danube Delta (fishing, agriculture - especially
cattle breeding, reed harvesting and eco-tourism), then the
activities after 1990 when the law establishing DDBR was
passed by Parliament. Finally, the author underlines the strategies concerning the protection and ecological recovery of
the Danube Delta, starting from the causes of the ecological
disturbances in the delta and upstream.
120
At the end of the volume, one can find a Subject index
and a Taxonomic index of all cited species, both of them of
great use to readers.
•
•
•
•
•
•
•
•
•
Weak points:
The occurrence of titles in the original in the lists of literature, without the corresponding English translation;
Overlaps or redundant information;
Absence of final conclusions with regard to the state of
the Danube Delta ecosystem complexes;
Insufficient information on the impact of anthropogenic
activities in the Danube Delta;
Insufficient data on the management in the DDBR in the
last years (concerning deltaic ecosystems and their biodiversity, ecological restorations included);
Absence of a chapter presenting the marine zone in front
of the Danube Delta, which, in fact, belongs to the Danube Delta Biosphere Reserve;
Some important titles on the Danube Delta missing from
chapter bibliographies;
Imbalance in including more recent papers into the bibliography; the knowledge of some authors, regarding recent problems in the Danube Delta is limited;
Heterogeneous presentation of biodiversity – sometimes
in tables, sometimes in rows or included as enumerations
in the text.
The paper gives an image of the Danube Delta biome,
which is more or less static, with grey shades whose occurrence should challenge the “shooting” of a film that might
achieve better links between compartments and describe
the real dimension of the huge flow of substances and energies at the confluence of the Danube and the Black Sea.
Despite the inherent weak points of such a comprehensive task undertaken by Professor Claudiu Tudorancea, the
book deserves to be praised as a reference benchmark and
appreciated as being useful to a large range of specialists and
students, to ecologists, hydrobiologists, geographers, specialists in nature protection and in the management of protected areas; finally, the book is an efficient instrument and a
challenge for future studies.
Professor Marian-Traian GOMOIU
GeoEcoMar National Institute &
“Ovidius” University - Constanta

ISSN 1224-6808

Transcription

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