for the Odra lagoon and the beaches of Usedom - IKZM-Oder

International Journal
of Hygiene and
Environmental Health
Int. J. Hyg. Environ. Health 203, 417-433 (2001)
© Urban & Fischer Verlag
http://www.urbanfischer.de/journals/intjhyg
The consequences of the Odra flood (summer 1997)
for the Odra lagoon and the beaches of Usedom:
What can be expected under extreme conditions?
Christiane Fenske1, Helmut Westphal3, Alexander Bachor4, Elke Breitenbach2, Wladyslaw Buchholz5, Wolf-Dieter Jülich6,
Peter Hensel6
1
2
3
4
5
6
Zoological Institute, University of Greifswald, Greifswald, Germany
Geological Institute, University of Greifswald, F.-L.-Jahnstraße 17a, D-17487 Greifswald, Germany
Energiewerke Nord GmbH, Postfach 1125, D-17507 Lubmin, Germany
State Agency of Environment, Nature & Geology Mecklenburg-Vorpommern, Goldberger Straße 12, D-18273 Güstrow,
Germany
Maritime Research Institute Szczcecin, Monte Casino 18a, PL-70467 Szczecin, Poland
Landeshygieneinstitut Mecklenburg-Vorpommern, Außenstelle Greifswald, Lange Reihe 2, D-17489 Greifswald, Germany
Received September 13, 2000 · Accepted March 20, 2001
Abstract
The exceptional flood of the river Odra in July/August 1997 caused severe damage, especially on
the Polish side of the Odra valley. An additional 5 km3 of water were discharged during the flood.
This represents about a third of the normal annual Odra discharge of 17 km3.
Large agricultural and industrial areas were submerged, as well as towns and villages. However,
as regards the Odra lagoon and the beaches of the Isle of Usedom, the substances transported, such
as nutrients and pollutants, did not cause much damage, due to strong dilution. Hygienic investigations (human pathogenic bacteria and viruses) showed that the water had bathing quality during
the whole flood.
Key words: Odra flood – Odra lagoon – nutrients – heavy metals – pesticides – bacteria –
viruses – suspended matter
Introduction
The Odra lagoon (= Szczecin Lagoon) acts as a link
between the river Odra and the Baltic Sea. It has been
investigated with regard to its genesis, hydrographical
conditions, sediments, heavy metal concentrations,
suspended matter, nutrients, primary production, and
macrozoobenthos (Lampe 1998a, Leipe et al. 1998).
In summer 1997, investigations concerning bacteria
and viruses have been intensified. Besides the regular
bi-weekly monitoring, samples for hygienic investigations were taken daily during the Odra flood at bathing places on the beaches. Moreover, daily measurements of nutrients, chlorophyll-a, phaeophytine, and
primary production were carried out in order to evaluate the effect of the extraordinary event.
Floods of the river Odra have occurred before
(Gocke 1988, von Berg 1997), usually after a typical
meteorological situation developing in late June, therefore named “St. John’s flood” (Rosenthal et al. 1998).
Corresponding author: C. Fenske, Zoological Institute, University of Greifswald, Johann-Sebastian-Bach-Straße 11–12,
D-17487 Greifswald, Germany, phone ++ 49 3834/86 4260, fax ++ 49 3834/86 4252, E-mail: [email protected]
1438-4639/01/203/5-6-417 $ 15.00/0
418
C. Fenske et al.
However, the 1997 flood was by far the strongest since
the commencement of the records (Oppermann 1997).
Two main reasons caused the flood:
1) high precipitation of up to 400 l/m2 in the source
area of the river in the mountains between Poland and
the Czech Republic (Siegel et al. 1998); this amounted
to 6 km3 in the catchment area from July 3rd to 9th and
another 4 km3 from July 17th to 21st (Rosenthal et al.
1998); strong winds from NE (6–7 °B) hindered the
outflow of the water into the Baltic (Lysiak-Pastuszak
et al. 1998);
2) anthropogenic factors such as melioration, lack of
inundation areas, deforestation and the consequent
erosion. After the heavy rainfalls the level of the Odra
rose quickly within a few days in July 97.
A marked outflow from the Odra Lagoon into the
Baltic started on 20 July 1997, due to a change in water
level. The floodwater from the Odra started to fill the
Grosses Haff (Zalew Wielki) on 23 July 1997, maximum inflow occurred on 7 August 1997. The water of
Grosses Haff was replaced by water from the river
after about 5 days. The Kleines Haff, on the contrary,
was later effected and not to the same extent. The
floodwater reached the western end of the lagoon
around 13 August 1997 (HELCOM 1998a). Maximum current velocities of up to 3000 m3/s were measured, compared to average discharges of 540 m3/s.
Measured and modelled water transport in the Odra
lagoon for the period of July/August 1997 are presented by Rosenthal et al. (1998) and Müller-Navarro et al.
(1999).
Daily observations of Sea Surface Temperature (SST)
images (derived from data of the Advanced Very High
Resolution Radiometer (AVHRR) working on NOAA
weather satellites) showed the warm and low-salinity
plume of the floodwater intruding into the Pomeranian
Bay, north of the Swina (Siegel et al. 1998). WIFS
(Wide Field Sensor) images even revealed the distribution of suspended matter and showed again that most
of the water flowed directly through the eastern part of
the lagoon into the Baltic Sea, without previous horizontal mixing with water from the western part. A simulation of the spatial behaviour of the Odra plume in
the lagoon and the Baltic Sea (Pomeranian Bight) was
also carried out by Schernewski et al. (in press).
During the flood the content of suspended matter in
the western part was much higher than that in the eastern part, thus indicating biological activity and particle formation in comparably stagnant water, whereas
the eastern part was characterized by very strong discharges. The outflow was so intense that most of the
microscopic algae in the Pomeranian Bay originated
from the Odra lagoon and were not formed autochthonously. Markers such as chlorophyll-a or fucoxanthin (marker pigment for diatoms) showed conserva-
tive mixing patterns (Humborg et al. 1998), thereby
proving the dominance of the outflow against biological activity in the Baltic Sea. An exception was found
with zeaxanthin, which is included in high amounts in
pico-cyanobacteria that make up a large part of pelagic autotrophic biomass during the summer in the open
Baltic. Zeaxanthin showed non-conservative mixing
patterns because only minor amounts of this pigment
could be built up in cyanobacteria in the river due to
the lack of light. It is likely that most of the zeaxanthin
originated from the standing stock of pico-cyanobacteria in the Baltic (Humborg et al. 1998).
Investigation area
The Szczecin Lagoon (= Oderhaff or Odra lagoon,
Fig. 1) has a size of 687 km2 and a volume of approx.
2.6 km3. It represents a natural reception pool for water from the rivers Odra (= Oder), Peene, Zarow and
Uecker. The largest water supply comes from the river
Odra (approx. 17 km3/a), compared to 0.76 km3/a
from the Peene, 0.19 km3/a from the Uecker, and
0.11 km3/a from the Zarow (Lampe 1993).
The western part (277 km2) is German (Kleines
Haff); the larger eastern part (410 km2) is Polish
(Grosses Haff or Zalew Wielki).
Average salinity in the lagoon lies between 1 and 3
PSU (practical salinity unit), with extreme values of 0.2
and 6.4 PSU. The slope of the Odra lagoon bottom
(from the mouth of the river Odra to the Baltic Sea
(approx. 40 km) is 22.7 cm (Herr, quoted after Brandt
1894/96) and there are only three narrow outlets, therefore the flow velocity of the water masses is slowed
down, before they enter the Baltic through the three
straits (Swina, Peenestrom, Dziwna). On average, 70 %
of the overall water exchange takes place through the
Swina and Piastowski channel, whereas the Peenestrom
and the Dziwna contribute approx. 20 % and 10 % respectively. These relations stayed the same, even during
the flood (Rosenthal et al. 1998). Only in September 97
did the ratio between the different branches vary more
strongly due to changing weather conditions.
Some of the imported substances, mainly heavy metals, can sediment in the lagoon. Former statements
characterizing the inner coastal waters as important filter and buffer zones had to be modified: long-term investigations showed that the coastal lagoons in this
area hold back only 2–5 % of the nutrients imported,
and 15 % of the metals (Lampe 1998b).
Usually the Szczecin Lagoon is well mixed due to its
average depth of only 3.8 m. A high nutrient content
causes a strong development of phytoplankton, which
in turn is responsible for the high turbidity (Secchi
depth of only 50–60 cm in summer).
The consequences of the Odra flood
419
Fig. 1. Investigation area: the Szczecin Lagoon (= Oderhaff) near the Baltic
Sea. Sampling stations during the Odra flood (summer 1997); P. c. = Piastowski channel.
Water movements (currents and convection) are
mainly influenced by wind.
The Pomeranian Bay is characterized by sandy shallow bottoms (0–20m) and a salinity of 6–8 ‰ near the
coast (Powilleit et al. 1995; for a review on transport
and modification processes between the lagoon and the
Pomeranian bay see von Bodungen et al. 1995). The
beaches on the Isle of Usedom at the southern edge of
420
C. Fenske et al.
the bay are intensively used by tourists. Water quality
is monitored bi-weekly and has been very good so far,
with only very few exceptions when the hygienic limiting value was exceeded locally.
Methods
Besides the monitoring carried out by the State Agency for
Environment, Nature, and Geology Mecklenburg-Vorpommern (LUNG), several parameters were measured continuously by the GKSS research centre (sea level, wave height,
current direction and current velocity, wind direction and
speed, air and water temperature, turbidity and salinity). Additionally, a special measurement programme was carried out
at the time of the flood (July–September 1997) in the Odra
Lagoon and the adjoining Pomeranian Bight of the Baltic
Sea.
The following parameters were measured:
Meteorological and hydrological parameters: wind direction
and speed, water and air temperature, current direction and
velocity, salinity, oxygen saturation, turbidity
Biological parameters: bacteria (Rheinheimer 1981), chlorophyll-a and phaeophytine (Rohde and Nehring 1979, Gocke
1988), primary production (radio carbon method after Gocke
1988), viruses (Jülich et al. in press); sampling for hygienic investigations was bi-weekly (bacteria) or daily (viruses).
Geochemical parameters: concentrations of nutrients: dissolved inorganic nitrogen = DIN, dissolved inorganic phosphate = DIP (Rohde and Nehring 1979 , Autorenkollektiv
1982), dissolved silicate, heavy metals, hydrocarbons, pesticides (methods described in Gewässergütebericht Mecklenburg-Vorpommern (GGB-MV) 1996/97).
Seston analysis: total particulate carbon (TPC), particulate
organic carbon (POC) and particulate inorganic carbon
(PIC) were measured using a C/S-Analyser METALYT CS
(firm ELTRA). The procedure is described in Fenske et al.
(1998).
The stations for the measurements were located as follows
(Fig. 1 and BSH 1999):
Kleines Haff:
Tonne H3
53° 49.50N
14° 03.30E
centre
53° 49.50N
14° 06.00E
German-Polish border
53° 48.50N
14° 14.10E
near Kamminke (Kam)
53° 51.60N
14° 12.30E
Ueckermünde (Ueck)
53° 45.40N
14° 05.10E
near Mönkebude (Moe)
53° 49.50N
14° 00.60E
Karnin
53° 50.40N
13° 51.50E
Grosses Haff/Zalew Wielki:
Karsibor (Kars)
Tor 1
Tor 2
Tor 3
Tor 4
Odra mouth
Tonne MeW
53° 52.00N
53° 48.50N
53° 45.70N
53° 42.90N
53° 39.95N
53° 39.80N
53° 46.40N
14° 16.80E
14° 20.55E
14° 24.30E
14° 28.20E
14° 32.00E
14° 32.20E
14° 29.10E
The water samples for the hygienic investigations were taken from piers in the sea resorts of the island of Usedom at
19 stations along the coastline of 36 km. A further 8 stations
are situated in the Achterwasser and the Peenestrom, i. e. the
inner coastal waters. One station was the central Kleines
Haff (Tonne H3). For the evaluation of health risks only the
stations fairly close to the Odra water were included: those
were no. 724–727 and 729–730 at the beaches of Usedom
close to the Swina mouth, and stations no. 707, 709, and
714 at the Peenestrom (Fig. 1). It was assumed that if no critical concentrations of potentially harmful bacteria and viruses were detected close to where the Odra water flows into
the Baltic, then beaches farther away should not be endangered.
Results
Nutrients
Comparing the amounts of nitrate, orthophosphate,
total nitrogen, and silicate transported into the Pomeranian Bay from June to August 1995 and 1997, the
effect of the Odra flood can clearly be seen (Fig. 2). In
1997 loads were up to 7.8 times higher (silicate),
nitrate occurred in 4.7 fold amounts compared to
1995, and the load of orthophosphate and total-N
more than doubled.
The high amounts of nutrients are likely to come
from agricultural areas that were involuntarily flooded
and released manure and/or fertilizers. Moreover, 56
water treatment plants in Poland closed temporarily
during the flood because they no longer could handle
the water masses, thereby allowing all the discharge to
flow downstream untreated.
However, at the Piastowski channel, the main outlet
of the lagoon, inflows of water from the Baltic sea were
measured again in mid September and found to be carrying about 2.5 t/d of DIN and 6t/d of DIP (Fig. 3). On
18/9/97 the current direction changed during the day
so that after an inflow a strong outflow was recorded,
exporting about twice the load that had been imported before (–1.45 versus +3.44 t DIN, and –3.79 versus
+7.97 t DIP). Undoubtedly, large amounts of nutrients
were transported into the Baltic, but as regards concentrations, these were not extraordinarily high due to the
strong dilution. For orthophosphate (= dissolved inorganic phosphorus, DIP), similar concentrations were
measured in both parts of the lagoon. Usually the
Grosses Haff has a much smaller DIP concentration in
summer than the Kleines Haff. During the flood, DIP
concentrations in the Kleines Haff were only half the
average level of 6–8 µmol/l (Fig. 4) whereas concentrations of 5 µmol/l in the central part of the Grosses Haff
represent a six-fold increase as compared to 1996
(0.8 µmol/l). However, this increase disappeared after
the flood: at the end of September concentrations of
The consequences of the Odra flood
about 2.5 µmol/l were measured in the central part of
the Grosses Haff, compared to 4.45 µmol/l in 1996.
Nitrate in the Kleines Haff reached concentrations
of 26 µmol/l during the flood (Fig. 4), compared to a
maximum of over 100 µmol/l that had been measured
in the years before.
Total dissolved inorganic nitrogen (nitrite, nitrate
and ammonium) in the Grosses Haff ranged between 6
and 31 µmol/l during the time of the investigation
(22/7–25/9/97). An even higher range (5–55 µmol/l)
was measured at the mouth of the river Odra (before
entering the lagoon).
Compared with our data from 1996 and data from
other authors (Vietinghoff et al. 1995, GGB-MV
1996/97), the concentrations of DIN during the Odra
flood in 1997 were not extraordinarily high. In the central part of the Grosses Haff concentrations of
35 µmol/l DIN were found in June/July 1996 and
26.4 µmol/l in September 1996 (Fenske et al. 1998).
The input of DIN was positively correlated to the
amount of river water transported.
Considering the river discharge, the Odra transported a load of 6–65t/d DIN into the Grosses Haff.
Silicate concentrations (max. 213 µmol/l in the
Kleines Haff) were much higher than in other years.
This is probably due to the fact that phytoplankton
populations, especially diatoms, did not have enough
time to keep pace with the amount of nutrients supplied. However, silicate is a naturally occurring mineral and even higher amounts do not cause harm.
Although the Kleines Haff and Grosses Haff are connected by a broad stretch of water, they do not always
show the same reactions. Concentrations of different
substances varied between these two different parts of
the lagoon, probably because a large part of the water
flows directly from the Odra via the Grosses Haff into
the Baltic, without efficient mixing with the water from
the Kleines Haff. The currents between the Kleines and
the Grosses Haff do not follow a clear pattern. Synchronous measurements along the German-Polish border showed that at different points water either flows
east-westwards, west-eastwards, south-northwards or
does not move at all. Near the bottom there are also
north-southwards currents. The latter are of particular
importance because they transport saline water from
the Baltic into the lagoon.
For further details about nutrient concentrations
and other parameters measured during the Odra flood
in both parts of the lagoon see Fenske et al. (1998).
Chlorophyll-a, phaeophytine, and primary production
With one exception (4/8/97: 198 µg/l) chlorophyll-a
contents were not higher during the flood than usual.
Concentrations of 40–90 µg/l were measured in the
421
Fig. 2. Nutrient loads transported into the Pomeranian Bay during June–
August 1995 and 1997 (HELCOM data).
Grosses Haff and 30–110 µg/l in the Kleines Haff.
Both values correspond to our average concentrations
observed over several years as well as to the data acquired in the projects GOAP (Westphal and Lenk
1998) and PIONEER (Fig. 5). A large steady phytoplankton population could not develop, presumably
because the current velocity and the water discharge
were too high.
Larger differences in chlorophyll-a contents within a
few days can be explained by concentration of algae at
the surface of the water. The algae population was
mainly composed of coccal cyanobacteria and coccal
Chlorophycea (Hübel, pers. comm. ).
As expected, the results for Secchi depth and
chlorophyll-a content were reciprocal. In comparison
with other inner coastal waters, the Odra lagoon contains enormous amounts of algae, even in “normal”
years. The Greifswald Bodden, which is comparable in
size and volume (510 km2, 2.960 km3) but has a
422
C. Fenske et al.
Fig. 3. Water discharge, loads of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) in the Piastowski channel during the flood in
1997. The negative discharges on 15/9 and 18/9/97 signify an influx from the Baltic Sea into the lagoon.
stronger exchange with the Baltic Sea, has an average
chlorophyll-a content that is only one fifth of the value for the Odra lagoon (10 µg/l compared to 50 µg/l;
(Westphal and Lenk 1998))
Phaeophytine, indicating the amount of inactive
chlorophyll, was measured in relatively high amounts
(max. 22 µg/l) in the central part of the lagoon during
the main wave of the Odra flood (Fig. 5). At the Odra
mouth near Trzebiez there were always increased concentrations of phaeophytine. This means that a great
part of the algae was damaged. In other years no phaeophytine was detected during summer.
Concentrations of chlorophyll-a during the flood
were normal for the time of the year, indicating no
extraordinarily high primary production. Comparing
summer ‘97 with spring ‘98 and autumn ‘98, the results
for primary production lie in the same range (Fig. 6).
In the Grosses Haff an average primary production
of 280 mg C/m2 h (range 100–680 mg C/m2 h)
was determined (radio carbon method, simulated in
situ). The average primary production in the Kleines
Haff was 250 mg C/m2 h (ranging between 23 and
840 mg C/m2 h) during the course of the year 1997.
Fluctuations in the carbon assimilation on different
days were caused by the differing light intensity (PAR).
Combining our results with other measurements not
presented here, we assume a primary production of
500 g C/m2 a.
Heavy metals
Overall concentrations of the trace metals such as zinc,
copper, nickel, lead, and cadmium have been measured
routinely in unfiltered water samples in the central area
of the Kleines Haff (station “centre”) since 1992. During the period of the Odra flood, measurements were
also done at the other six stations of the Kleines Haff.
The zinc, copper and nickel concentrations were
lower in July and August 97 than during the first half
of the year. All three elements showed similar changes,
e. g. a relatively distinct decrease on July 8 and an increase on August 11. By this date the Odra flood had
reached the central part of the Kleines Haff. However,
the mid August concentrations of zinc, copper, and
nickel were about 50 % lower than at the beginning of
the year.
The consequences of the Odra flood
423
Fig. 4. Concentrations of nutrients (nitrate, nitrite, orthophosphate, and silicate) in 1997 at the German-Polish border within the lagoon: no extraordinarily
high results during the flood, except for silicate. Orthophosphate is diluted during the flood and goes up to normal level after the flood.
In contrast to this, concentrations of lead, cadmium, and mercury increased during the flood, thus indicating higher inputs from the Odra water. Usually,
high concentrations of heavy metals occur in winter
or spring in times of high discharge (GGB-MV
1996/97). In 1997, the situation was reversed: high
concentrations were detected in summer, during the
flood.
On July 31, the highest concentrations of lead
(3.3 µg/l) since the beginning of measurements (1992)
were registered in the central part of the Kleines Haff.
On the other hand, the Odra water reached this part of
the Szczecin Lagoon only on August 11. Therefore the
main input of lead into the Szczecin Lagoon must have
taken place before the flood reached its peak (Röpke et
al. 1998). This result is supported by direct measurements in the Odra river carried out by the State Agency of Environment Brandenburg (Landesumweltamt
Brandenburg 1998).
Results for cadmium are similar to those for lead
(Fig. 7). 98 and 92 ng/l were measured on July 31 and
August 4 respectively. This value is 5 times higher than
the detection limit. However, cadmium concentrations
even above 100 ng/l had already been registered earlier in the Kleines Haff.
In general, mercury is hard to detect in water. Signals
above the analytical detection limit are very rare. During the Odra flood this was the case. On one single day
(August 11), an extraordinarily high concentration of
mercury (210 ng/l) was registered in the central part of
the Kleines Haff. Two days later we also found mercury concentrations between 76 and 88 ng/l (significantly above the detection limit) at three stations in the
eastern part of the Kleines Haff.
The increase of heavy metals could have been caused
by contaminated sediment transported from upstream
riverbanks and by effluents from flooded industrial areas. Contamination can be expected to originate from
mining and smelting operations at industrial centres
between Katowice and Glogow (Müller 1998).
Organic contaminants
During the special investigation concerning effects of
the 1997 Odra flood in the Szczecin Lagoon several organic contaminants were analysed for the first time at
424
C. Fenske et al.
Fig. 5. Chlorophyll-a and phaeophytine in the Zalew Wielki (Grosses Haff) during the Odra flood: High values for phaeophytine in summer are unusual.
two stations in the Kleines Haff. Out of 26 pesticides,
four (atrazine, simazine, desethylatrazine and 2,4
dichlorphenoxy-acetic acid) appeared in concentrations above the analytical detection limit.
Atrazine, which it has been forbidden to use in
Germany since 1992, was detected during the flood
in the eastern part of the Kleines Haff. Concentrations increased from 28/7 to 4/8/97 from 0.11 µg/l to
0.19 µg/l and decreased after 15/8/97 (Fig. 8). Concentrations in the central part of the Kleines Haff
were lower: 0.02–0.11 µg/l. Higher values close to
the German-Polish border indicate that the pesticide
arrived with the Odra water. In most of the rivers of
Mecklenburg-Vorpommern, including the rivers
Uecker and Zarow, atrazine was not detected at all
in 1997. Only in the river Elbe concentrations were
above 0.10 µg/l measured (GGB-MV 1996/97). In
1998, atrazine was detected again in the Szczecin
Lagoon (Fig. 8) but in much lower concentrations
(max. 0.04 µg/l). Due to its long life time of 28 years,
atrazine and its metabolites desethylatrazine and desisopropylatrazine are still in the ground water following their widespread use as a herbicide in maize
fields.
Desethylatrazine was found in concentrations up to
0.06 µg/l on 4/8 and 6/8/97 in the eastern part of the
Kleines Haff. Traces of simazine near the detection limit (0.02 µg/l) were measured only at the border station.
2,4 dichlorphenoxy-acetic acid was found in concentrations between 0.05 and 0.09 µg/l in the eastern part
of the Kleines Haff throughout the whole period of the
special investigation. At the central station in the
Kleines Haff it was detected later and in lower concentrations. The amounts of herbicides detected in the water were below the guideline values of the WHO for
drinking water.
A strong input of hydrocarbons from mineral oil
proved the influx of contaminated Odra water at the beginning of August 1997. This may have been heating oil
from flooded houses. After a short peak with a duration
of a few days, hydrocarbons were no longer detectable.
Suspended matter
Not only as a carrier for heavy metals but also for bacteria and viruses, suspended matter (SPM) plays an important role in the ecosystem. Most of the potentially
harmful substances occur absorbed by or adsorbed to
The consequences of the Odra flood
particles. Usually the amount of SPM is highly correlated to the wind velocity (Pearson correlation factor
for the time period 18/7–11/8/97 in the Kleines Haff:
R = 0.76). During the flood, however, this correlation
was not so strong. The maximum concentration of
SPM was 45 mg/l (Fig. 9).
Concurrently with the arrival of the flood wave in
the Kleines Haff a decrease of the SPM content was detected, starting on 7/8/97. This was probably due to the
dilution of SPM. A minimum of 15 mg/l was measured
on 14/8/97 (Fig. 9).
At the same time, contents of particulate organic
carbon (POC) and total particulate carbon (TPC) increased slightly. Wind is always able to cause resuspension of the sediment, thereby increasing the amount of
SPM (20/7 and 28/7/99).
However, the changes in the SPM content of the water in the Odra lagoon during the flood were within the
usual annual variations.
Microbiological investigations
Regular bacteriological investigations (daily, later 2–3
times per week) during the Odra flood showed no harmful situations. Results were similar to those from previous years. An impairment of the water quality could not
425
be detected, neither at bathing places of the Achterwasser nor at the Baltic beaches of the isle of Usedom. All
bathing places had a good water quality. The few occasions when the EU-guideline limit was exceeded occurred as rarely as in the years before or after the flood
(Fig. 10). Faecal Streptococcus species were never detected. Eighty-eight isolated bacteria strains were investigated for their resistance against antibiotics. Each of
them was sensitive, i. e. there were no hints of the existence of multiresistant species of bacteria.
Investigation of Enterovirus, cultivated from ultrafiltrated 10-l water samples in of FL (fibroblast-like) cells,
showed that the particular conditions of the Odra flood
hindered the occurrence of Enterovirus. Comparing the
virus contents of the Odra and the water at the beaches
of Usedom in June/July and August 97, there were fewer
infectious units in the water during the flood (Fig. 11).
Two factors are considered as important: 1) strong dilution by the water masses 2) inactivation during the transport, e. g. by UV radiation (Jülich et al. in press). Moreover, there might have been virus-inhibiting substances
such as acrylic acids or polyphenoles produced by the
phytoplankton (Burger 1995), thus preventing the development of viruses that could have been a danger for
human health. Harmful substances such as pesticides or
heavy metals also have a destroying effect on viruses.
Fig. 6. Chlorophyll-a concentrations and primary production in the Zalew Wielki (Grosses Haff). Comparing summer 97 with spring 98 and autumn 98, the
results lie in the same range, i. e. there was no marked effect of the flood.
10.12
5.11
3.9
20.8
13.8
11.8
6.8
4.8
31.7
28.7
8.7
3.6
21.5
8.4
11.3
C. Fenske et al.
20.2
426
Fig. 7. Heavy metal concentrations and salinity in the Szczecin Lagoon (station “centre”): a) Cadmium b) Lead. Both metals have clear peaks at the time of
the Odra flood (late July/ early August) Salinity decreases during the whole summer until the end of October.
Discussion
The Odra lagoon, situated at the end of the polluted
river Odra, is predestined by nature to become eutrophic. The Odra is a major source of pollution of the
Baltic Sea (HELCOM 1998b). A large part of the load
(e. g. heavy metals) is imported with suspended particulate matter (SPM) and accumulates in the sediments
of the lagoon. Especially zinc is found in very high concentrations in the SPM of the Odra estuary (1997:
1200 mg/kg, 1998: 937 mg/kg). Increased concentrations were also detected for cadmium which is known
The consequences of the Odra flood
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taminated sedimentary sources and polluted regions
(Lehmann et al. 1999, Damke et al. 1999). However, the
median concentrations of suspended particulate matter
did not exceed the values of older samples taken during
mean discharge conditions between 1989 and 1995,
and correspond to those of the river Elbe in 1990. The
heavy-metal load of the Odra strongly decreased from
1988 to 1997 (Zn by 85 %) (Niemirycz 1999). But still
the Odra is categorized as “very highly contaminated”
with regard to Zn (Eidam et al. current investigation).
The accumulation of heavy metals in sediments and
SPM of the Odra lagoon usually shows maximum values at the points close to the Polish border, confirming
that the input comes from the river Odra. Concentrations of heavy metals in fine-grained sediments (20
µm) of the Kleines Haff are up to three times higher than
the concentrations in the Greifswald Bodden (GGB-MV
1996/97). Target values for Cr, Cu, Hg, Ni, Pb, Zn, and
Cd in SPM were by far exceeded in the Kleines Haff both
in the flood year 1997 and in 1998 (Eidam et al. 2000).
During the flood (5 weeks) approximately 1⁄3 of the
usual annual particular load of Cu, Pb and Zn was
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to be very toxic for organisms (1997: 3.7 mg/kg, 1998:
4.3 mg/kg) (Eidam et al. 2000). The joint project
GOAP (Greifswald Bodden and Odra Estuary Exchange Processes, 1993–1997) showed that the sediments of the estuary were so polluted with nutrients
and heavy metals that the vast majority of these substances freshly arriving with the Odra water were
transported into the Baltic without much transformation or storage in the estuary (Lampe 1998 a, b, 1999).
Because of the sediments’ pollution, it was not clear
what the additional very high input of the Odra summer flood in 1997 would bring about.
A flood wave adds to the usual disturbance of the
sediment, thereby increasing the concentration of suspended matter and remobilising heavy metals. However, the flood sediments along the whole river Odra were
also able to absorb contaminants, due to their specific
composition, especially their contents of organic matter and clay minerals (Damke et al. 1999).
The contents of heavy metals in the river water and in
the SPM as well as in the sediments developed irregularly, because of the successive flooding of differently con-
427
Fig. 8. The pesticide atrazine in the Kleines Haff (summer 1997–winter 1998): During the flood extraordinarily high concentrations were detected especially
close to the border (i. e. closer to the river mouth), confirming the influence of the Odra. However, even the high concentrations are one order of magnitude
below the WHO guideline value for drinking water.
428
C. Fenske et al.
Fig. 9. In the Kleines Haff the amount of suspended matter (SPM) is positively correlated to the wind velocity. The amounts of inorganic and organic carbon
in SPM vary within their normal ranges, even at the time of the Odra flood.
transported (Müller and Wessels 1999). For the total
loads of dissolved trace elements temporary increases
at Hohenwutzen ranged from 4-fold (Cr) and 5-fold
(Pb) to 16-fold (Zn) and 17-fold (Cd), comparing conditions before (10 July) and during the flood 1997
(Lehmann et al. 1999).
Investigating the sediments of the Odra river basin
in November 1997, Müller and Wessels (1999) found
maximum concentrations for Cu and Pb not in the
Odra lagoon but in the downstream part of the river.
This illustrates the retention potential of the sediment
and explains why the consequences for the lagoon
were milder than assumed.
The strong outflow of the flood’s water masses
swept the heavy metals into the Baltic, where they were
taken up by macrozoobenthic animals. Since 1994
mussels (Mytilus edulis) in coastal waters of Mecklenburg-Vorpommern have been investigated for their
content of heavy metals and organic contaminants. Investigations of Mytilus edulis on the Odra bank (in the
Pomeranian Bay) showed that the contents of lead,
cadmium, chromium and arsenic after the flood were
about twice as high as in the years 1994–96 (GGB MV 1996/97). For the recruitment of mussels (Mytilus
edulis in the Baltic, Dreissena polymorpha in the Odra
lagoon) the level of SPM might also play an important
role. Ruth (1998) found in laboratory experiments that
the growth of Mytilus larvae from the North Sea was
inhibited by sediment concentrations in the water
0.5g/l. As mortality rates of mussels are inversely
proportional to their size, growth in the first year of life
is a crucial factor. Although the water in the Odra lagoon is often very turbid, especially in summer, the
concentration of SPM during the flood was lower than
usual, and the threshold value of 0.5g SPM/l was never reached.
Thus, in the lagoon it is not the concentration of
SPM itself but the heavy-metal contamination of SPM
that is likely to have affected the mussels. In the fraction 20 µm, the metal content (Zn, Pb, Cu, Cd, Co,
Ni, Cr, Mn, Fe) was significantly higher than in the
whole sediment (Helios Rybicka and Strzebonska
The consequences of the Odra flood
1999), probably due to the higher surface/volume ratio of small particles. Zebra mussels (Dreissena polymorpha), however, prefer smaller particles (15–40 µm)
and are therefore exposed to higher concentrations
than that of the total SPM. Moreover, the composition
of SPM is likely to have changed during the flood to
higher amounts of fine-grained and more strongly polluted particles (Lehmann et al. 1999). One mussel
may filter up to 2.4 l of water per day in order to obtain food (Claudi and Mackie 1994). In this process, more than 100 mg of more or less polluted SPM
might be taken up per day. A long-term survey would
be necessary to assess the flood impact on the population.
Not only heavy metals occurred in higher amounts,
but also phosphorus and nitrogen. Müller (1997) and
429
Müller and Wessels (1999) found for the lower Odra
(near Schwedt) that during the flood these nutrients in
SPM occurred in amounts 2 and 5 times as high respectively as compared to 1996. This large increase was
also measured in the Pomeranian Bight (Fig. 2), comparing the nutrient load in 1995 and 1997. However,
the actual concentrations were not extraordinarily
high.
While most of the phosphorus input comes from
point sources (73 %), the nitrogen input is dominated
by diffuse sources (59–67 %) (Behrendt et al. 1999).
But the actual nutrient loads are rather low as compared to the inputs. With regard to nitrogen, a flood
in summer causes less trouble than in winter because
the plants can use nitrate and therefore less nitrogen
gets into the river and into the sea. A lot of the nutri-
Fig. 10. Hygienic quality of the bathing water: Investigation of coliform bacteria showed no hazard during the flood. EU-limiting values were not exceeded
in 1997 at the beaches of Usedom and only twice (= 5.1%) at the Achterwasser. These transgressions, however, did not happen during the flood.
430
C. Fenske et al.
Fig. 11. Comparison of the concentration of potentially harmful viruses (pathogenic for humans) in the water of the Odra lagoon and at the beaches of Usedom: During the flood lower amounts of infectious units per litre were found. This is probably due to dilution and inactivation by UV radiation, heavy metals
or secondary plant metabolites.
ents are retained within the river system of the Odra.
Maximum retention of particulate matter in a polder
area of the Lower Odra Valley National Park during
the flood was more than 80 % (Engelhardt et al.
1999). The advantage of a flood in summer is that
there is more vegetation in the polders to hold back
particles. In normal winter floods retention varied
between 33 and 70 %.
The self-purification could be further enhanced if the
course of the river was developed more naturally with
more areas that could be flooded in times of high discharges. One favourable side effect of more floodable
areas would be that a lot of bird species such as grey
herons (Ardea cinerea), common snipes (Gallinago gallinago), lapwings (Vanellus vanellus), spotted redshanks (Tringa erythropus), greenshanks (T. nebularia), wood sandpipers (T. glareola), several duck species
and many others could use the habitat for resting
and feeding. The Odra flood in summer ’97 destroyed
many nests, so that corncrake (Crex crex), spotted
(Porzana porzana) and little crake (P. parva) lost their
broods completely (Dittberner 1998). But the conditions afterwards with large flooded areas were ideal for
many species, including migratory birds.
Gromisz et al. (1998), who investigated the composition of phytoplankton in the Pomeranian Bay during
the flood, found that four potentially toxic species (Anabaena spiroides, Aphanizomenon flos-aquae, Micro-
cystis aeruginosa, and Nodularia spumigena) occurred,
but not in “bloom” quantities. The same cyanobacteria species were detected again in summer 1999 (Cuypers, pers. comm.) with lower concentrations in Ahlbeck (close to the Swina outlet into the Baltic) than at
the stations further north. It can thus be assumed that
even during the Odra flood the beaches of Usedom
were not endangered by microalgae.
The hygienic investigations of the water along the
beaches of Usedom also resulted in good quality values, therefore swimmers or bathers were not at risk,
even during the flood.
However, routinely applied tests for wastewater
monitoring such as tests with algae, Daphnia or photogenic bacteria proved to be not sensitive enough to
show effects of the flood on aquatic organisms (Oetken 1998). It is therefore necessary to develop more sensitive biotests with reversible adverse effects (Jülich et
al. in press). Moreover, we recommend to include potentially toxic microalgae and viruses in the regular EU
bathing water investigations. So far only bacteria are
routinely tested.
In order to finally assess the impacts of the flood on
aquatic species, it would be necessary to investigate the
reproduction of sensitive species. Only the fact that
they are able to reproduce properly in the habitat over
several years would prove that the short-term effect of
the flood does not harm the population.
The consequences of the Odra flood
Conclusion
With regard to the Szczecin Lagoon the flood of the
river Odra had no disastrous effects. Although some
substances (DIN, DIP, lead and cadmium) occurred in
higher concentrations during the flood, these were only
short peaks. The concentrations of most of the substances analysed did not exceed the results of the longterm investigations. However, atrazine and lead in the
Kleines Haff occurred in extraordinarily high concentrations. Pb concentrations reached a new maximum
(3.3 µg/l), but it could be shown that the lead had not
been transported with the Odra flood. The floodwater
arrived in Kleines Haff only 11 days later. Atrazine,
which is thought to be carcinogenic, was even at peak
concentration (0.19 µg/l) one order of magnitude below the WHO guideline value for drinking water
(2 µg/l). Most of the substances imported were simply
washed into the Baltic, partly due to the difference in
water level caused by the specific wind situation. Extraordinarily high concentrations of nutrients or pollutants and their negative effects that might have been
expected in the Szczecin Lagoon did not occur, due to
the dilution by the water masses and some retention in
downstream regions of the river. As regards the polluted sediments of the lagoon, the flood can even be considered as a fortunate event because a lot of it may have
been exported after being stirred up by the enormous
amount of water. Even during the flood there was no
health risk for swimmers at any time, either in the inner coastal waters or on the beaches of the Baltic (Isle
of Usedom).
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