Geological Survey ofFinland Bulletin 370

Transcription

Geological Survey
ofFinland
Bulletin 370
Holocene development and peat growth of the raised
bog Pesänsuo in southwestern Finland
by Liisa Ikonen
Geologian tutkimuskeskus
Espoo 1993
Geological Survey of Finland, Bulletin 370
HOLOCENE DEVELOPMENT AND PE AT GROWTH
OF THE RAISED BOG PESÄNSUO IN
SOUTHWESTERN FINLAND
by
LIrSA IKONEN
with 18 figures, 2 tables and 2 appendices
by
Tuovi Kankainen: Appendix I . Radiocarbon analyses of Pesänsuo,
a raised bog in southwestern Finland
Carl-Göran Sten: Appendix 2. Macrofossils of the raised bog
Pesänsuo in southwestern Finland
GEOLOGIAN TUTKIMUSKESKUS
ESPOO 1993
Ikonen, Liisa 1993. Holocene development and pe at growth of the raised bog
Pesänsuo in southwestern Finland. Geological Survey 01 Finland, Bulletin 370,
58 pages, 18 figures, 2 tables and 2 appendices.
The natural history of the Pesänsuo raised bog (60°46.2' N, 22° 56.7' E, 87 m
a.s.l.) was studied using both biotic and abiotic palaeoecological methods including
211 radiocarbon dates.
Peat formation commenced on a centrally domed clay bottom with primary
mire formation at about 8300 14C-years BP (ca . 9200 cal BP), with a contribution
made by subsequent forest fires. Pesänsuo developed initially as a swampy sedge
fen with meso-eutrophie and meso-oligotrophic species and was replaced by true
ta ll-sedge fen with more oligotrophic vegetation at about 8000 years BP (ca. 8900
cal BP). The edaphic impoverishment continued with increasing peat depth and a
Sphagnumluscum bog phase was attained at 6400 yr BP (7300 cal BP) in the bog
cen ter and 5600 yr BP (6400 cal BP) at the margin.
Peat growth in the Carex peat section and at the end ofthe minerotrophic stage
was approximatelyequal both in the bog centerand at the margin. In the Sphagnulll
pe at section, a phase of divergent growth is evident. In the bog center between
7700 - 6050 years cal BP (6900 - 5300 BP) the average rate of peat increment is
I mm yr . " slowing down to 0.50 111m yr ., during the interval 6050 - 5000 years
cal BP (5300 - 4400 BP). Since 5000 years cal BP three phases (5000 - 4900, 4200
- 3800 and 2500 - 2400 years cal BP) with high rates (3.22, 1.12 - 2.08 and 2.27
- 2.50 mm yr ") and intervening low rates (average 0.50 mm yr ' ') are recognised.
During the last two thousand years pe at growth has been slow (average 0.22 mm
yr ' '). At the margin the rate of peat increment varies from 0.22 mm yr " to 0.95
mm yr " . The cumulative mass versus age curve for the bog center shows a slightly
convex trend , while the depth versus mass trend is linear, both of which contradict
the concave plot predicted for age against depth by Clymo's model of peat growth.
The alternation of thin highly humified streaks and slightly humified peat in
the peat strata resembles short-cycle Sphagnumluscul11 regeneration. The thicker
highly hllmified layers correlate with slow pe at growth and the dry phase in the
hydrology ofthe bog. The stratigraphical and hydrological changes observed were
influenced more by the natural sllccession and local phenomena, such as fires than
by climatic factors.
Key words (GeoRef Thesaurus , AGl): bogs, raised bogs, peat, growth,
stratigraphy, humification, paleohydrology , absolute age, Holocene, Pesänsuo,
Mellilä, Finland
Liisa Ikonen , Geological Survey
ISBN 951-690-509-9
lSSN 0367-522X
01 Finland,
SF-02150 Espoo, Fin./and
CONTENTS
Introduction ...... ......... ................. ........................ ............. ............. .... ... ......... ...................... 5
Ear li er studies .. .................................... .... ... .............. ............... ....... ... ... ............................. 6
Review of humification changes ................ .. ................. .. ..... ........ .. .......................... 6
Review of pe at g rowth .. ... ................ .. .... ... .. .......................... ... ... .. ..... ....... ... .. ... .. ... ..... 8
Study area ............................................ .... .. ... .... ....... ... ... ........................................ ... .. ........ 9
Geology .......... .................. ... .......... .......................... ...... ... ............................. ................. 11
Vegetation ....... ...... ............. .............. ...... .. ... ....... ....... .. .... ... .................. ........................... .. 15
Met hods ........ ........ .... .... ....................... .... .. ... .................. .................. ........ ... .. .. ............... 16
Field studies ......... ...... ......... .... .. ........... ........... .. ............... ................... ............ .. ...... ... 16
Laboratory procedures .............. ....... .. ...... .... .... ... ...... .. .... .... ..... ..... ....... ..... ..... ....... .. .. 17
Pollen diagrams and their zonation .................. ... ......................... .... ............. .. ....... 20
Results and interpretation ........................ .. .......... .. .. .... .. ...................... .... ...................... 24
Dating and interpretation of pollen stratigraphy .......................... .. ....... .............. 24
Diatom stratigraphy ... ...... .............. ... .............. ................ ........ .... ..... .... ...... ....... ...... .. 26
Peat stratigraphy ... .. .. .............. .. .. .... ... ........................ ................................................ 27
Changes in humification ..... ............................... .. ..................... .... ... .......... ...... ........ 30
Origin of black streak s ........... .. .......... ... ......... ....................... ..... ..... ................... 31
Mire type succession in the light of the macrofossil record ...... ... .... ................ 32
Rhizopod stratigraphy ............................ ... .. ...... .............. .. .. ..................................... 32
Hollow site .... ................................................... .. .... .. ...... ..... ... .. ...... ..... .. .. .............. 35
Dry/moist stages .. ....... ..... .. .. .... ...... .. ..... ........ ....... ..... ............... .............. .. ...... 35
Amphifrema and humific ation ..................... .......................... ... .. ...... .......... . 36
Fluctuation in Amphitrema and in the spruce curve ...... ....... .. ... ... .. ... ..... 36
Amphitrema and peat growth ........... ... ... ................. .... .. ..... ... ... .............. ...... 36
Hummock site ...... ............ ................. .............. .. .. ... ......... .. ... ..................... ............ 37
Peat growth .... ... .. .... ... ........................... .......... ........ ...... ....... .... .................. .............. .. . 38
Rate of peat increment .... ...... ..... ... ......................... .... .. ..... .................... ............ .. 38
Rate of apparent peat accumulation ......... ................... .... ............... ...... ... ... .. ... .41
Cumulative mass versus age ............. .. ...... .............. ... .. ... ............... ... ... .............. 42
Discussion ........... ... ............ ............ .. ......... ... .... .. ..... ...... ... ..... ............. ... ... ...... ................... 44
Palaeohydrology .... .. ... ..... ...... ........... ............ ............ .. .. .... ........ ..... .. ........................ .. 44
Changes at the center of the bog ... .. ......................................... ....... ......... .. .. .... 45
Formation of hummock/hollow patterns ............ ........... .. ...... .. .......... ......... .. .. .48
Younger changes in peat humifi cat ion ......... ... .... ....... ...................... ....... ....... .49
Changes at the bog margin ........... ................... .... .............. ................................ 50
Comparison of the bog center and the margin ......... ... ... ........ ... ...... ...... .. .. ..... 50
Conclusions ............. ...... ........................ ........ .... .. .. ..... ..... ... ..... .. ..... ..................... ............. 51
Acknowledgements ..................... .. .. .... ...... .. ... .......................... ... .......... .... .......... .... ...... .. 53
References .. .. ................. .... ............... .... ..................... ... .. ... .......... ....... .......... .. .......... ........ 53
Appendices :
Appendix 1. Radiocarbon analyses of Pe sä nsuo , a rai sed bog in southwestern
Finland by Tuovi Kankainen
Appendix 2. Macrofo ss ils of the raised bo g Pesän suo in so uthwestern Finland by
Carl-Göran Sten
5
INTRODUCTION
A considerable proportion of the carbon in
the terrestrial ecosystems of the Earth is fixed
in peat, i.e. partially decayed remains of the
plants on waterlogged soils. The role of peatlands in the global cycling of garbon dioxide
and other atmospheric gases has recently become more significant in relation to the problem of the greenhouse effect. While peatlands
sequester carbon dioxide from the atmosphere
by photosyntesis, they also emit large quantities both CO 2 and the other important greenhouse gas, methane. Undisturbed mires are
considered to have a positive carbon balance .
Human ac ti vities, artificial drainage and com bustion of pe at for fuel have affected this balance substantially by accelerating the oxidation
of stored carbon and its release to the atmosphere as CO 2• It has been estimated that the
predicted climatic warming could also affect
greatly the effecti veness of peatlands as carbon
sinks, especially in northern latitudes . Consequently, an understanding of the rate of carbon
aeeumulation has become increasingly important in estimating of the amount of these reserves. Data on the peat accumulation rate especially on the true rate of peat accumulation
- in the tropic peatlands are virtually nonexistent, and are also very scarse for the northern
peatlands as weIl (Sjörs 1981 , Armentano &
Menges 1986, Gorharn 1991 , Tolonen et al.
1992a). The aim of the present investigation is
to reduce this gap in our knowledge by a de-
tailed study of pe at accumulation in a small
domed raised bog in southwestern Finland.
The study on the Pesänsuo raised bog started
with the mapping of the Quaternary deposits in
the Loimaa map sheet area and with the national inventory of pe at resourees (Kukkonen 1978 ,
Sten & Svanbäck 1984, Tuittila et a1. 1988).
The first profile was taken from an open peat
face at the marginal slope of the bog. From this
profile a preliminary pollen diagram and a few
radiocarbon analyses were made . The radiocarbon analyses represent only those levels where
ehanges in humification were observed in an
open peat face. Two additional profiles were
subsequently eored from the center of the bog
in order to obtain a more detailed pollen diagram and for providing a continuous series of
radiocarbon analyses.
The objecti ves of this study are: (l) to delineate the changes in the natural hi story of the
mire on the basis of stratigraphic data ; (2) to
study the initiation of peat deposition; (3) to
analyze the hydroseral development of the mire
and the vegetation history of both the mire and
surrounding uplands by means of pollen and
rhizopod stratigraphy, and (4) to examine and
to interpret peat humification and peat growth.
The timing of these stratigraphical changes has
been analyzed for two peat profiles in the bog
center, based on a continuous series of radiocarbon analyses and also for one profile at the
marginal slope using a few separate analyses.
6
EARLIER STUDIES
Review of humification changes
The interpretation of the stratigraphie changes observed in peat strata have been under continuous re-evaluation in a number of studies,
especially regarding the problems of regeneration complexes and recurrence surfaces. In the
classical concept of the "Grenzhorizont", the
stratigraphic al shift from highly humified to
slightly humified peat, the climatic change
from tbe Subboreal to tbe Subatlantic was regarded as a primary factor (Weber 1911).
The idea of climatic control in tbe cbanges of
humification was modified by Granlund (1932)
wbo, in his study of south Swedish bogs , assumed that the ultimate form of mires could be
related to annual rainfall. The peat layers representing retarded growth and hi g h humification were thought to be due to an equilibrium
between effective rainfall, runoff and th e heigbt
of the bog cupo la. A recurrence surface represe nted rejuvenation of growth in a bog previ ously stagnating "at limiting hei ght" and the
rejuvenation was initiated by the transition to
a wetter climate. Granlund distinguished f ive
s ucc ess iv e recurrence s urfaces and argued that
they formed sync hronou sly in all tbe bogs studied and that the recurrence surface RY IU was
equi vale nt to the c lassica l Grenzhorizont.
Weber ' s and Granlund's hypothes is was
widely accepted, though divergent interpretations were presented soon afterwards (e .g. von
Post 1926, Conway 1948 , Kulczynski 1949,
Godwin 1954, Olausson 1957). According to
Conway ' s theory of "threshold c limates", the
effect of the macroclimate on peat formation
varies witb the size and hydrology of the indi vidua l mire, and hence the supposed climaticalIy dependent humification of the peat wi ll vary
much in time between different mires.
In hi s stud y of the Poles'ye bogs in Belarus
and Ukra in e , Kulczynski ( 1949) , while firm ly
supporting the o ld theory of bog regeneration,
proposed a new concept for exp lain in g the for-
mation of recurrence surfaces and rejuvenated
peat growth. He interpreted tbe different types
of peat sequences as resultin g not from climatic
change but from regional rises in tbe water
table caused by otber processes.
Granlund' s opinion that bog heigbt was a
causative factor in the formation of recurrence
s urfaces was strongly opposed by Godwin
(1954), according to whom all drai nage losses
are of minor importance compared with the
direct effects of precipitation and evaporation.
Granlund's hypothesis of climatically controlled changes in humification was also criticized
by Olausson (1957), who claimed that there is
no indisputable connection betwee n the maximum hei ght of a rai sed bog, preci pitation and
changes in humification . The changes in humification do not necessarily always indicate
c han ges in precipitation and are not syncbronous.
Subsequently, the examination of the exposed peat faces resulted in a variety of new
interpretations (Walker & Walker 196 1). The
stratigraphic studies o n Iri sh bogs showed no
conv incin g cyc lic regeneration in which pool
formation and hummock degeneration would
have been discrete stages. The hummock s and
the great majori ty of pools develop predominantly on mature surfaces. The principal system by which the bogs have regenerated involves periodic rejuvenation of the bog surface
under conditions of increased wetness , followed by a progression towards mature vegetation under constant or drying conditio ns. The
rejuvenation phases therefore represent a phenomenon simi lar to the estab lishment of recurrence surfaces, a lth o ug h "their stratigraphic
evidence is not so di stinct" (Wa lker & Walker
1961 ).
Even though the existence of a true regeneration complex was not demonstrated , " a shortcycle" regeneration complex in peat stratigra-
phy was , however, found, particulary as the
bog surface approached the mature phase. This
feature implies fluctuations in the relative im portance of Sphagnum, Calluna and Eriophorum vaginatum in a given place, and " whilst it
is undeniably possible that this is a self-regulating system under constant water conditions,
it seems more likely that the life-cycle of the
dominant plants are of greater importance"
(Walker & Walker 1961 p.184) .
In the course of time the number of studies
concerning recurrence surfaces increased greatIy; the studies generally confirmed the results
of Walker and Walker (1961) and revealed that
the number of recurrence surfaces was much
more numerous than previously presumed. The
concept that the age of recurrence surfaces was
not synchronous, even in a single bog , was also
considered (e.g. J. Lundqvist 1957; G. Lundq vis t 1962; Ni Isson 1964; Schneekloth 1963,
1965; Casparie 1969, 1972; Overbeck et al.
1957; Overbeck 1975; Aaby 1976 ; Aartolahti
1965; Tolonen 1971 , 1980, 1987 ; Tolonen et al.
1985).
In Finland the earliest documentations of
peat stratigraphical variations were made during the 1920 's - 1940 's (Auer 1924; Aario
1932, 1933, 1943 and Sauramo 1939). The first
study in which a comparison with the recurrence surfaces found in Sweden was attempted
was carried out by Brandt (1948) on the mires
of Southern Ostrobothnia. According to Brandt,
abrupt climate deterioration (e.g. strengthening
of continentality) led to the formation of recurrence surfaces. Deteriorations of short duration
affected the formation of regress ive mire types.
In contrast, the amelioration of climate, wh ich
was more prolonged, resulted in increasing
dryness and progressive development in the
mire. The peat layers then formed were much
thicker than those formed during the colder
ph ase. Altogether Brandt distinguished eight
recurrence surfaces, seven of which were dated
by using land uplift chronology.
The climatic control on peat stratigraphieal
changes was already questioned by Aario
7
(1932). Similar doubts were later expressed by
Aartolahti (1965) , who in his study of the
raised bogs from western Finland found a peat
stratigraphy wi th alternati ng highly humified
thin streaks and lightly humified peat layers in
numerous raised bogs.
The contribution of climate to the formation
of recurrence surfaces and the question of hummock/hollow regeneration were discussed in
further studies by Tolonen 1971, 1980, 1987
and Tolonen et al. 1985. In the study of the
Isosuo raised bog at Klaukkala , in southern
Finland, a thorough palaeobotanieal analysis of
the plant eommunities on the formation of recurrence surfaees was carried out and theil'
origin discussed (Tolonen 1971).
Amongst the data compiled for the regeneration of northern European bogs Tolonen
(1980) found only limited evidenee for a cyelic
succession of hummocks and hollows, but instead he found frequent shart-term ehanges in
the growth rate of hummocks and to lesser
extent, in that of hollows.
The same streak pattern observed in northern
European bogs was also found in raised bogs in
eastern North America (Tolonen et al. 1985) ,
the streaks reeording intervals varying from
several decades to about one hundred years.
According to the writers no climatic cycle of
sueh frequency nor repeated peatland fires
could aceount for these stratigraphie features .
The climatic contral on peal stratigraphy was
still strongly advocated by Barber (1981),
whose "phasic theory " aetually invokes more
wide-ranging climatic control, extending to
even small-scaJe features in bog stratigraphy.
The theory implies that the growth of a raised
bog is controlled above all by climate. Threshold factors may alter the change in peat stratigraphy from region to region and, to a lesse r
extent from bog to bog, but "the factors of
hydralogy and drainage , life-cycle of plants ,
pool size etc. are all subordinate to the elimate"
(Barber 1981 p . 206).
The non-c1imatic faetors influencing the peat
stratigraphy have been demonstrated in some of
8
the most recent studies. For example Foster and
Glaser (1986) stressed the i mportance of local
factors, which may produce features in the
vegetation very similar to those due to c1imatic
variations and thereby complicate the strati-
graphie interpretation. These intrinsic factors
include fire (cf. Pakarinen 1974 and Damman
1977) and changes in the water table resulting
from mire development and pool formation.
Review of peat growth
Only a few data compilations exist concerning the height growth in deeper peat deposits
for longer periods. The mean rates of vertical
peat increment in them are based either on 14C_
dates or correlations of pollen zones to other
dated profiles (e.g. Walker 1970, Tolonen 1973
and 1979, Aaby & Tauber 1975, Overbeck
1975, Zurek 1976). These estimates are generally gi yen as average growth rates over periods
of several hundred years and therefore do not
reveal any possible short-term f1uctuations. In
only a few cases have peat sections been dated
using shorter intervals, the most detailed ex ample of a 14C_age against depth profile being
that for Draved Mose, where 55 14C ages have
been obtai ned (Aaby & Tauber 1975).
Walker's (1970) data compiled for rates of
accumulation in a number of different types of
organic sediments in the British Isles did not
reveal any significant differences between sediment types and between various Holocene substages; a modal rate of 21 - 60 cm per 1000 year
was reported.
Tolonen's (1973) results from some Finnish
peatlands showed more fluctuation in the rates
of pe at increment: an average rate of 0.5 mm
yr-I between 8000 - 6000 years BP, a slow rate,
with a minimum less than 0.2 mm yc l between
6000 - 2000 years BP and a subsequent increase in the rate of peat increment, to an average of about I mm per year, in the period
since 2000 years BP. According to Tolonen,
the lower degree of compaction in surface peat
may have been contributed to the increasing
rates in the latter period.
According to Aaby and Tauber (1975) the
calculated figures for the average peat increment in a number of north European ombrotrophic mires were generally 10w between
about 8000 - 3500 years BP, after which they
rose steadily , reaching a maximum in the period after 2500 years BP. They also stated that
the general tendency towards lower rates of
peat increment for older peat layers may partly
be explained by autocompaction, although
within individual periods the calculated variations in the rates are nevertheless considerable. According to these authors , these variations can hardly be due to statistical errors
alone, but presumably reflect real variations in
the rates of peat increment. The variations
show no clear geographical trend , so that varying rates in individual bogs within the same
time interval may rather reflect local climatic,
ecological and biological conditions.
Zurek' s (1976) results for Eurasian peatlands showed the same tendency of growth as
those of Tolonen (1973) and Aaby and Tauber
(1975). A reduction in the rates of peat increment was observed simultaneously in different
profiles and different peatlands between about
6500 - 5000 years BP and 4000 - 2500 years
BP. On the other hand the humid and cool
c1imate in the period since 2500 years BP contributed to increasing rates in the mires studied. Furthermore, alternating stagnation and
rejuvenation stages were observed in raised
bogs for the period since 5000 years BP.
Geological Survey of Finland, Bullet in 370
9
STU DY AR EA
The Pesänsuo raised bog is situated in the
Mellilä district In southwestern Finland
(60°46.2' N, 22°56.7' E), one kilometre south of
the Mellilä railway station (Fig. I). The bog is
nearly circular in shape (Fig. 2). The original
area of the bog is estimated to have been more
than 20 hectares , of which today about 18 hectares remain. The elevation of the bog is 87 m
above sea level and that of surrounding terrain
about 80 m a.s.l. The bog is borde red by open
farmlands and the stream Niinijoki, which is a
tributary of the Loimijoki river, runs north ,
north-east of the bog.
According to the regional distribution of
mire complex types in Finland the Pesänsuo
bog lies in the zone of the concentric raised
B
PESÄNSUO, Mellilä
Fig. I. A. Generallocation of the study area in southwestem Finland ; the Pesänsuo raised
bog is marked by a 1arge dot · . Zones ofmire complex types: I. Plateau bogs, 2. Concentric
bogs, 3. Eccentric and Sphagnum fuscum bogs, 4. Southem aapa mires (according to
Ruuhijärvi 1982). B. Location of Pesänsuo bog showing the main transect A and the crosstransect A 300 with coring sites at intervals of 100m (black dots), drainage ditches (lines
with arrows), peat cuning areas in 1970 (cross-hatched area), bog expanse (marked with
dotted line) and the hollows on it. Coring sites A 300-a and b are situated at the intersection
ofthe main and cross-transects. Sketched from air photo no 701 !7B/l5 by C-G. Steno
10
Fig. 2. Air photo (no 70 117BII 5) of Pesänsuo in Mellilä (1970). Publi shed with the permission of National Board of Survey.
bogs (Ruuhijärvi 1982). The bog ex pan se in a
longitudinal direction is an almost planar surface sloping gently to the southeast, with a
gradient of 80 cm over a di stance of 300 meters
(Fig. 3). This contrasts with the southwestnortheast direction , in which the gross form is
rather convex (Fig. 4) . The marginal slope is
exceptionally steep, with the gradient of the
northeastern sIope of the cross-transect being
4.3 m/IOO m and that of the southwestern slope
5.9 m/100 m. The gradient of the southeastern
slope along the main transect is 5.6 m/100 m
and that of northwestern slope 7.8 mlI 00 m.
The central part, namely the Sphagnum fuscum bog with hollows, comprises about 45 %
of the whole bog area, of wh ich the proportion
of kermi area is about 85 % and that of hollow
area about 14 %; pools are totally lacking (Figs.
I - 2). Kermi-formations are broad and both
their heights and those of individual hummocks
generally range from 20 cm to 30 cm, aithough
they occasionally reach 40 cm. The hollows on
the contrary are areally restricted and vary in
length from 4 m to 19 m (mean 10.3 m), with
widths ranging from 2.7 m to 6.5 m (mean 4.5
m). The hummocks and hollows show no clear
alignment. However, in peripheral parts so me
kermis show concentric arrangement (Fig. 2).
The vegetation of the marginal slope is that
of a true dwarf shrub pine bog . The lagg surrounding the bog has been c1eared for cuItivation. A thin-peated herb-rich forest, which is no
longer in a natural state occupies a narrow strip
around the bog.
The mean annual temperature in the area is
+ 4.5 °C, the yearly precipititation 600 mm, the
length of the growing season 170 days ( >5 °C),
effective temperature sum during the growing
II
season 1200 degrees [ L(T m - 5°C)] and duration
of snow cover about 125 days (Atlas of Finland, Climate 1987).
In terms of forest vegetation, the area belon gs to southern boreal vegetation zone (Ahti
et al. 1968). The original forest landscape has
been substantially modified and the c1ay district is nowadays characterized by wide, open
farmlands.
The most common mire site types in the
natural state in the Mellilä district are hummock-Ievel bogs/pine mires (52 % ), of which
Sphagnum fuscum bogs consist 17 %, dwarf
shrub pi ne bogs 15 % and Sphagnum fuscum
bogs with hollows 8 % . The proportion of flark
or intermediate-level bogs is 25 % , of which the
most common are short sedge intermediate-Ievel bogs 10 % and f1ark-level bogs 7 %. The
most common types of spruce mires (5 % ) are
poor birch fens 3 % (Sten and Svanbäck 1984).
GEOLOGY
The Pre-Quaternary bedrock of the Mellilä
area consists of strongly metamorphosed and
granitic rock types . The outcrops in the immediate vicinity are mainly Proterozoic Svecofennian granitoids: quartz diorites and granodiorites
(Salli 1953, Huhma 1957).
Clay deposited at the bottom of the BaItic
Sea covers the Mellilä area to a depth of about
14 m. Sand and gravel deposits are present
within the SE-NW trending Koski-Mellilä esker. Till is only exposed in small areas in the
vicinity of the bog (Kukkonen 1978).
The Loimaa area was deglaciated at about
9800 years BP aga (Glückert 1976 p. 8 sensu
Sauramo 1923). The oldest and topographically
highest shore line in southwestern Finland belongs to the Yoldia phase of the Baltic Sea. In
the study area the oldest Yoldia shore lies at
about 124 m above sea level at Hevonlinnankukkula (Auro1a 1938). During the Yoldia
phase the study area and also the whole LoimaaMellilä area were submerged.
At about the same time as the Ancylus lake
became isolated from the Baltic basin waters
the highest lying till deposits eastward and
south-eastward from the study area emerged.
During the early Ancylus Lake phase the Koski-Mellilä esker and later the lower Iying clayarea (ca. 80 m a.s.l.) also emerged. The highest
Ancylus Lake shoreline is situated at 97 - 98 m
a.s.1. (Aurola 1938, G1ückert 1976). Pesänsuo
was isolated from the Ancylus Lake about 8300
4
1 C years aga on the basis of the date 8290±60
yr BP (Su-285) obtained from the peat at the
isolation level. The gyttja-clay layer just above
the Ancylus c1ay gives too old an age , wh ich is
evident from the conflicting dates for the total
(8480±80 yr BP, Su-250) and humin (8780±80
yr BP, Su-287) fraction. The contamination of
older allochtonous material in the gyttja-clay
NW
SE
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1.00
1.50
500
81
80
600m
550
C-G
82
St~n
1979
'"
-.J
0
1' 1~~1 2 ' II~JI
loB
. <? <?
3.[1]
,·rn 5·1"'-' ~I 6·D 7·U 8·
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::::':.1
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. + + + 16 . 1
::'::'
110
1. 2 0
1
:E: 1 3 U
M
..,'.... :.,'. :
:-:-: : :
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17· H 1- 3 L
:::.d H, [ITJ
B»»
..........
::::::::: :::: :::
BI:;;;;;;;;;;;;;;;;;;;;:
.:.:.:.:.:.:.:.:.:.:.:
Hl 5 10
[9
Fig . 3. Cross·section of the main transect A. The upper profile show s the distribution of peat types . Das hed line marks the hypothetica l limit of
peat cutti ng area. V indicates the pos ition of the bog surface at about 5700 yr BP in the center and at the marginal s lope of the bog. The lower
profile shows humification of peat deposits. Symbo ls used in cross-sections and in the stratum co lumn of the diagrams, Figures 6 . 16 and 18:
I. Sphagnum peal 2. Carex-Sphagnum peat 3. Carex peat 4. Sphagnum-Carex peal 5. Bryales peat 6. Eriophorum 7. Scheuchzeria 8. Dwarf shrub
9. Li gnid 10. Birch wood I I. Equiselum 12. Phragmiles 13. Men yanthes 14. Clay 15 . Gynja c lay 16. Sand 17. Degrec of humificati an accarding
to v. Past's ( 1922) J 0 grade sca le. Profile s canstructed by C-G. Sten 1979.
(1)
~
\0
-.J
0-,
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~ 2. t""':;'
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e!
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(1) C
CI>
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(1)
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(1)
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('j'
e:.
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:;
<
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'<
o....,
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:;'
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POl
c:
[
:;'
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-.J
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(1)
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w
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NE
mo.s.1.
mo.S.!.
87
1
87
~86
86
le
I
I
)
f-85
\
J,~ \)
{ \
83
81
0(1)
0
/\
85
8t.
-I>
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()Q
(i'
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8
t t.
:;
83
'<
CIl
<
(1)
~
."
82
S'
'"
81
"
J"t:O
S
;
80
"
'"0-J
mo.s.1.
87
86
~
c::z:::-:
85
8t.
83
~
82
o
,
50
,
,
A300
100
150
200
I
,
250
,
300
,
350
-+80
t.50m
C-G Stlln 1979
Fig. 4. Section through cross-transect A 300. The upper profile shows the distribution of peat types and [he lower one humification of peat types. Explanation of symbols in Figure 3.
Geological Survey of Finl and , Bulletin 370
15
VEGETATION
The bog is densely wooded ex ce pt for a small
area on the bog expanse (Fig . 5). The predominant tree species is Pinus sylvestris although
some stands and saplings of Betula pendula and
B. pubescens subsp. pubescens grow on the
bog. At the outermost margin so me stands of
Populus and Salix are present as well as birch
(Table I ) . The range in the height of pine stands
Fig. 5. View from the bog expanse. Eriophorum vagina/um
hollow in front and dwarf shrub covered peat ridge in background . Photo L. Ikonen 1992.
in ] 975 was 3.5 - 13 m, while the predominant
height was 5 - 6 m. The stands are quite young ,
since as late as the 1930' s the bog was sparsely
wooded by low pines and the eastern part of the
bog was almost treeless (Kivinen 1934).
The field layer on the hummock levels contains abundant dwarf shrubs: including Ledum
palustre, CaUuna vulgaris, Vaccinium uligino sum, Empetrum nigrum and Betula nana. Rubus
chamaemorus is the most common of the herbs.
At the bog margins Vaccinium vitis-idea , V.
myrtillus, Melampyrum silvaticum and Trientalis europaea also occur. In the hollows Eriophorum vaginatum and Andromeda polifolia
dominate (Table 2).
Amongst mosses , Sphagnum capillifolium
and Pleuro zium schreberi predominate on hummocks and Sphagnum balticum and S. tenellum
in hollows. Other common moss species in clude Digranum undulatum, Sphagnum fuscum
and S. angustifolium. Sphagnum rubellum,
Hylocomium splendens and Polytrichum Slric tum are less common. The dominant lichens are
Cladonia alpestris, Cl. rangiferina and Cl. silvatica col\. The other species found are Cladonia deformi s, Cl. grayi and Cl. sulphurina.
On the whole, the species composition corres ponds to that listed by Eurola (1962) for
ombrotrophic vegetation of bogs in southern
Finland. In Eurola·s classification of mires
(1962) Pesänsuo represent the Calluna -rich
type of anormal raised bog. The trend towards
dryness due to drainage and peat cutting is to
be seen both in the great number of "forest
mosses " particulary Pleurozium schreberi and
partly in the quite den se Pinus cover on the
bog.
The marginal area of the Pesänsuo raised bog
is nowadays (1992) surrounded by dense tree
cover and on the bog ex pan se itself the height
and density of pines has increased, along with
a trend towards dryness (e .g. the expansion of
lichen cover). This trend is a consequence of
peat cutting, which has been continuous
16
Table I. Numbers of trees and saplings within a radius of 10m from the center of the sampIe quadrats.
A
0
A
SO
6
I
2
A
93
A
100
A
ISO
13
J3
21
24
A
150+4 m
A
200
A
250
A
304
A
350
4
9
7
9
32
29
4
7
8
Trees
Pinus sylvestris
Picea abies
Populus tremula
Sa/ix caprea
Betula pubescens
Betula pendula
11
Saplings
Pinus sylvestris
BelUla pubescens
Betula pendula
16
2
throughout the whole period of field studies.
Peat cutting on the northeastern part covers an
area of about 2 hectares .
METHODS
Field studies
The material for the study was collected
during the years 1972 - 1975 and 1978 . The
survey line network selected for cori ng consists
of two transects (Fig. 1). The length of the main
transect (A) is 520 m and that of the crosstransect (A 300) 400 m. The levelling of the
bog was made at shorter intervals than usual in
order to map the surface topography more accurately. The peat stratigraphy was studied
using a Hiller sampIer and a small Russian pe at
sampIer at intervals of 50 m in the center of the
bog and of 20 m at the margin . Humification
was estimated according to the 10 degree scale
of von Post (1922). The basic fjeld work and
the humification and peat stratigraphy determination s were carried out by C-G. Sten and his
field assistants.
Pollen- , macrofossil- and '4C-samples were
taken by different methods from the points
studied . At the marginal slope, at point A 0
excavation was commenced using an excavator
and was completed by spade in order to ex pose
a vertical open face. On that face six tin boxes
(60xl0x5cm) were pressed from the surface to
bottom. The boxes were then cut and wrapped
in plastic. At point A 300-a sampIes were cored
with a piston sampIer 8 cm in diameter and 60
cm long. The middlemost 40 cm of each core
segment was used in investigation. At point A
300-b the sampIes were taken with aspade and
a knife from an open pit 1,5 m deep . The sampling was undertaken by C-G. Steno
SampIes for bulk den sity, ash , carbon , nitrogen and fiber content were cored at points A
300-a and 300-b with a large Russian peat sampier by K. Tolonen, C-G. Sten, E. Raikamo and
A
400
18
A
450
5
A
501+lm
21
A 300
-49
A 300
A 300
-100+0.5 rn-ISO
7
A 300
- 185
A 300
+50
6
10
5
A 300
+100
14
A 300
+150+lm
6
17
A 300
+200
Sum
7
160
I
2
2
2
I
14
12
21
16
26
30
2
4
2
4
38
32
5
18
2
7
7
300
5
61
I
11
3
L. Ikonen and analyzed using the methods
outlined in Tolonen and Saarenmaa (1979) and
Tolonen (1982) .
The vegetation analysis was done by L. Ikonen and C-G. Sten from sampIe quadrats (I m 2)
29
2
at intervals of 50 m along the main and crosstransects staked out on the bog (n=21) . The
calculation of tree numbers was done within a
radius of 10m from the center of each sampie
quadrat.
Laboratory procedures
Ash , carbon, nitrogen and fiber content and
bulk density have been measured from core A
300-a. From peat monolith A 300-b only bulk
density has been measured. All measurements
were carried out by K. Tolonen . The ash content of peat was determined by drying the sampies at +60°C and igniting them at +550°C.
Carbon contents were determined with a Urasdevice (Salonen 1979 , five replicates) and nitrogen by the Kjeldahl-method (two replicates).
For calculations C/N the N- values have been
corrected so as to correspond to organic material. The fiber content of the pe at was determined by the American wet-sieving method
(Sneddon et al. 1971 ).
Macrofossils have been studied by C-G. Sten
from the core A 300-a and the peat monolith A
o (see Appendix 2).
The sampies for pollen analysis were taken
from the same core and peat monoliths as those
for radiocarbon dating in order to avo id the
problems in correlation . The sediment profiles
were taken along the main transect (A) at points
A 0, A 300-a and A 300-b. Pollen sampIes of
organic material were treated with KOH and
those with mineral components with HF (Faegri
and Iversen 1975). For each sampIe 500 arboreal pollen grains were counted in profi les A
300-a and A 300-b with a sampling interval of
5 cm and 100 - 200 pollen grains in profile A
0, with a sampling interval of 10 cm or occasionally also of 20 cm .
The rhizopods were counted from the same
preparation s from which the pollen analyses
were performed.
The diatoms were studied from the mineral
18
Geologieal Survey of Finland, Bulletin 370
Table 2. Oeeurrenee of speeies in the sampIe quadrat s plaeed on the bog at intervals of 50 m along the main
A
0
A
50
+
+
+
A
93
A
100
A
150
+
+
+
+
+
+
+
+
+
and eros ,
A
150+4 m
A
200
A
250
A
304
A
350
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Dwarf shrubs and herbs
Belula nana
Ledum paluslre
Calluna vulgaris
Vaeeinium vilis -idaea
uliginosum
m y rlillus
axyeoeeos
microearpum
Andromeda polifo lia
Empetrum nigrum
Eriophorum vaginatum
Rubu s ehamaemorus
Melampyrum silvatieum
Rumex aeelosella
Trientalis europaea
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Mosses
Mylia anomala
Dieranum undulatum
Hylo eomium splendes
Pleuro z ium sehreberi
Polytriehum slrie/um
Sphagnum anguslifolium
S. ballieum
S. fuseum
S. eapillifolium
S. tenellum
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Lichens
Cladonia alpestris
C. deformis
C. grayi
C. rangiferina
C. silvatica coll.
C. sulphurina
+
+
+
+
soils in profile A 0 with a sampling interval of
10 cm. In diatom preparations the sampies were
bleached in diluted HP2 for 24 hours and then
subjected to repeated suspension and decantation. For each sampIe 100 - 200 diatom frustules were i ndentified . The diatom sampIes
were analysed by Tuulikki GrÖnlund.
Radiocarbon measurements were made at the
radiocarbon laboratory of the Geological Sur-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
vey of Finland by the late Aulis Heikkinen
during the years 1972 - 1976 and the calibration
was made by T. Kankainen (see Appendix 1).
The measurements are made from the total
organic material, humic acid and humin fractions in A 0 and from two humin and one humic
acid fraction in A 300-b. In A 300-a the measurements were made only from the humin frac tion.
I
Geological Survey of Finland , Bulletin 370
19
;- t ransect s.
A
400
+
+
+
+
+
+
A
A
A 300
450
501+1 m
-49
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
A 300 A 300
- 100+0.5 rn-ISO
+
+
+
+
+
+
+
+
+
+
+
+
+
A 300
A 300
-185
+50
+
+
+
+
A 300
A 300
+100 +150+1 m
+
+
+
A 300
+200
+
+
+
+
+
+
+
+
+
+
+
+
Number of
occurrences
8
18
15
10
15
3
7
2
10
15
13
7
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
I
1
J
3
10
+
+
+
+
+
+
+
+
+
3
13
1
17
I
+
The ages used in this study are generally
conventional radiocarbon ages (1 4C-ages yr BP)
obtained from the dated levels or ages read
from the curve of the moving averages of the
five subsequent dates. Where calibrated dates
have been used they are marked as cal BP.
In calculating the rates of vertical peat increment and of apparent peat accumulation the
ages used are the moving averages of the five
+
+
+
4
2
+
+
14
6
subsequent calibrated dates from the hbmi n
fraction in A 300-a and 300-b. In A 300-b,
where two analyses were made from the humin
ffaction, the mean of these dates was used. In
A 0, for which only a few analyses were made,
the ages used in the calculation of veftical pe at
increment are from the original, calibrated
dates from the humin fraction.
20
Geol ogical Survey of Finland, Bulletin 370
Pollen diagrams and their zonation
The construction of pollen diagrams follows
the recommendations of the IOCP Project 158
B Handbook (Berglund & Ralska-lasiewiczowa
1986) . Calculations are based on the total poIlen sum in terriphytic spermatophytes. Within the
groups of Pterido- , Limno-, Telma-Amphi- and
Bryophytes the percentages of particular taxa
were calculated on the basis of the total pollen
sum + the pollen sum of the species in que stion.
The terriphytic spermatophytes, which occur
only sporadically are indicated in the column
of Varia.
In the biostratigraphie zonation of Pesänsuo
four local pollen-assemblage zones (Pes I-Pes
4) have been distinguished: four in profile A 0,
three in A 300-a and one in A 300-b (Figs . 6
- 8). Description of the zones is based on the
pollen diagram A 0 for the two lowest assem-
PESÄNSUO. A 0
53 .6m
O . S .I.
w
.,
u
~
Q.
'"
z
5 i;~
.,z
g!d
I
~
o
~
ou.
~::l:x:~
3100:120
3870!60
4370 !50
48OO!70
5H)()!70
5660! 80
6830: 90
250
74BO!80
8010!80
300
, ,,
8290!60
%
10
Sum:
JO
~p
50
70
90
EZJ ~. [2] %.
Fig. 6. Pollen diagram from Pesänsuo bog, point A O.
zone is characterised by the dominance of pi ne
pollen, birch value s being under 30 %. The
presence of Ephedra di stachya and Potamogeton and the maximum abundances of Hippophae pollen are restricted to this zone. The
continuous Corylus-curve starts in the upper
part of the zone . The upper limit is defined by
the distinct decline of pine pollen and the increase of birch and alder.
Pes 3. Birch-pine-alder-zone (A 300-a, 160 607.5 cm, 3550 - 8200 yr BP). The lower limit
blage zones and on A 300-a diagram for the two
uppermost zones.
Pes 1. Birch-zone (A 0, 375 - 410 cm). A
birch maximum of up to 79 % of total pollen is
the dominant feature of this zone, while pi ne
pollen values are correspondingly below 20 %.
The amount of NAP is rather small. The zone
ends with an abrupt decline in Betula pollen
abundances and a concomitant increase in the
abundance of Pinus pollen.
Pes 2. Pine-zone (A _O, 312 - 375 cm). The
g
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~ :l'x '" ~ ~
~
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«
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«
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~
ü
«
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in
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ai
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iil
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r ffi
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po.
~
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u
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"=--
10
10
243
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209
13
209
04
04
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11
11
217
242
09
15
,
,,,
,03
07
24
21
209
P
p
10
11
14
32
1> ,' 22
«
j
3
PE S-4
50
' 00
11
~1!11!~~~~~-1~
' 50
PES- 3
16
9
200
11
11
11
•
12
250
10
16
28'83 '4
,2~:32
, ,9,
,,09 9
,
>-" ,
14
09
P
N
9
13
09'0 7 6
1,216
11
8
,10'06 "
,
,,,
r- P- p. p.
Fe
~
p.
=
p.
~
:0
12
10
12
2
2
t7
V
05
207
,,
,~~106 ~~
,
P.
~ tf: ~
?i
r
117'03 12
20'20 e 10
p.
p.
lf D
~
p.
z
0
..~ 8 '" :i' ~
I"....i......L~ L........L....o l..o..JL.........Ir........J I....o..Jr........JL...-Ir........JL......JI....o..Jr........JL....o...Jr........J'--Jr........JL....o...J
11
14
"
36
300
11
11
08
5
4
PES -l
3
3
400
Sum:::EP . n
Anal L Ikonen 1976
Fig. 6. cont.
21
J1
01
o
-.)
..!.J
-!,
g:
g
9
uo
0
0
0 0 0
J,
d'I
g:
g
Cf
JI
uo
0
~,l
~
0
0
g
W
0
0
g
Ul
Cf
Cf
0
W
m
0
~
,l
g:g
gj
Cf
<:;'
N
uo
0
N
0
0
uo
0
:;':;--;.·3~j I) Sf.!.;Ji'11 I I~IT~TI \~,Il(1 luYI' I I 11'1 I,'I~,,:,'\':'I ,----~~
"'"
~.
",,}
0-
:f!
"
1 1IIIIfil!!!""
3 Ö
~~
3
o=<'
g;
3
ri'
;g:
'"
§ ~
g
~
~o
B
»
g
9",
o
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CD
d
'!"
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"
w
~
8
§
--;!)-..:-
0
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..:
§g8
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,
9
uo
14C_ AGE yr BP
"' -0
OEPTH le rn)
3 l> '
o
0
~~.~. ,. " ..
" " " " ! " " ' ! ! ! " l l l l l i l l l l l l l l l l l 1 l l l l t l l l l l l l llllllllllll[llllllllllllllllllllllllllllIIIIII111111I111
lITHOlOGY
HU MIFICATIQN.SCALE 1-10
POLLEN 5AMPLES
TREES I SHRUBS I
DWARF 5HRUBS I HERBS
~
BETUlA
i!.
D
PINUS
w
~
C>
ALNUS
PICEA
ULMUS
aUERCU5
TlliA
FRAX INUS
FAGU5
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SALIX
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ERICACEAE
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Ana l L I konen '976
Fig. 7. cont.
23
24
PESÄNSUO. A 300 b.
87. 2m 0 . 5 . 1.
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i
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' 0 20 30 1.0
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10 20 JO
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m·/"
Fig. 8. Pollen diagram from Pesänsuo bog, point A 3OD-b.
of the zone is placed at the level where Ainus
exceeds 2 %. The zone is dominated by birch,
pine and alder. Ainus attains its maximum of 34
% in the lower part of the zone and decreases
slowly in th e upper part. The continuous UImus-curve starts with low values in the beginning and that of Tilia in the middle part of the
zone. Quercus pollen occurs sporadically with
low values in the lower part but is more common from the middle parts onwards. Fraxinus
pollen has been found sporadically throughout
the zone . The continuous Picea-curve starts in
the upper part of the zone.
Pes 4. Spruce-pine-zone (A 300-a, 0 - 160
cm, - 3550 yr BP) . The lower limit is defined
by a clear rise in the Picea-curve when Piceavalues exeed 5 %. Quercus- and Tilia-curves
are di scontinued at the beginning of the zone .
The decrease in Corylus pollen coincides with
the Picea maximum, while the Ulmu s-curve is
di scontinued later at the Picea-decline. At the
same level the Pinus-curve starts to rise. A
small amount of Carpinus and Fagus pollen are
found in the upper part of the zo ne.
RESULTS AND INTERPRETATIONS
Dating and interpretation of pollen stratigraphy
The upper boundary of the birch -zo ne, Pes 1
coincides with the tran sition from the Yoldia
Sea to the Ancylus Lake in the diatom stratigraphy. The pollen flora in that zone is mainly
of long-distance origin and redeposited. The
vegetational history in the area did not co mmence until during the Ancylus Lake phase ,
when the area finally emerged during the Ancylus regression, in pi ne-zone, Pe s 2 (Fig. 6) .
The rise in the Alnus-c urve coincides with
the beginning of pe at formation. The zone
boundary of pine-/birch-pine-alder-zo ne (Pes
2/Pes 3) is dated at 8290±60 BP (Su-285) in
profile A 0 (Fig . 6) and 8190±80 yr BP (Su-
'--'
::0
I~)
IL--->
1\
If
~/
7
~
7>
ww
ww
~
~
P-
,
,
!
!.
'LI
l" '2
~~t
~ 11
r-~
,
25
~ 70
D
:l
13
569 11.
5 35 13
5 19 10
5 18 12
5
~3 ~Z
5
5 26
5,
5 20
5 17
5 32
5 29
s 21
17
15
k+---t==-:;;z::::::::::=-----h
11
Ho
15
13
I
13
L
rri
li i
i
i
i
I
i
i
Ir
10 20 30 "0 SO 60 70
Anal
l
Ikonen 1976
Fi g. 8. cont.
319) in profile A 300-a (Fig. 7).
Coryius-values exceed 2 % at the rational
Ainus-limit and Uimus-values exceed the same
percentage later, at about 8000 yr BP in both
profiles. The beginning of the continuous Tiiia curve is dated at 6660 years BP and the one for
the rational Tilia-limit 5760 years BP in profile
A 300-a (Fig. 7). At the same time birch values
and the amount of Quercus pollen , which earlier in the zone were found only sporadically ,
increase. In the A O-profile the occurrence of
Tiiia and Quercus is much more fragmentary
due to the sparse sampling levels and fewer
pollen counted.
The beginning of the continuous Picea-curve
is dated at 451 0±80 yr BP (Su-402) in A 300a and 4370±50 yr BP (Su-271) in A O. The
boundary between the birch-pine-a lder and
spruce-pine zones (Pes 3/Pes 4) is dated at
3550±110 yr BP (Su-427) in A 300-a . The date
is supported by earlier dates of Picea-i nvasion
obtained from the bogs nearby in southwestern
Finland: Linturahka in Mellilä 3400± 11 0 yr
BP, Vähäsuo in Tammela 3780±115 yr BP
(Aartolahti 1966) , Loimansuo in Huittinen
3400±130 yr BP (Vuorela 1975), Raholansuo in
Aura 3220±240 yr BP (Glückert 1976) and
Kontolanrahka in Pöytyä 3370±100 BP (Korho la 1992).
Later changes in the forest composition are
only clearly apparent in the profile A 300-a. At
the Picea-m aximum , 3200 yr BP, the continuous Tilia-and Que rcus- curves are interrupted
and also the amount of Coryius pollen decreases somewhat. The continuous Uimus -curve is
discontinued [ater, about 2800 yr BP, in the
beginning of the first Picea -d ecline.
In the upper part of the spruce-pine-zone the
fluctuation of Picea-c urve is to be seen both in
A 300-a and 300-b although the Picea-curve
shows a tendency to generally decline towards
the surface. In A 300-b (Fig. 8), however, there
is a small rise in spruce curve in the surface
sampies. In A 300-a the first decline starts at
2800 yr BP and culminates at 2500 yr BP. The
beginning of the seco nd decline at a depth of 52
cm is dated at 2150 yr BP and the third , at a
depth of 22 cm corresponds to 1200 yr BP. In
A 300-b the declines in abundances at depth s of
80 - 85, 65 - 70 and 35 - 40 cm are correspondingly dated at 2450, 2050 and 1200 yr BP.
The same declining tendency of the Piceacurve has been noticed in many other Finnish
pollen diagram s (Vuorela 1972 and 1986, Tolo-
26
nen & Ruuhijärvi 1976a, Huttunen & Tolonen
1977, K. Tolonen 1983 and 1987, M . Tolonen
1978 , 1983 and 1985). According to K. Tolonen
(1983) the relative and absolute values of
spruce have greatly diminished during the last
2000 years. The main reasons for the decline
and later regeneration of spruce are natural
forest fires, slash-and-burn-cultivation or other
clearing of forests. Spruce is more vulnerable
to the effects of forest fires than other tree
species and its regeneration is much slower
than that of pine, alder and birch (Heikinheimo
1915).
A small abundance of charcoal particles and
charred plant fragments were found within
macrofossil analyses at the Picea- declines (see
Sten Appendix 2). These levels have been dated
at 900 - 1200, 1800 and 2600 yr BP in profile
A 300-a. Charcoal particles and charred plant
residues were also found in the top most 20
centimetres in A O-profile. In A 300-b where no
macrofossil data exists, only black burned poIlen were found in the uppermost 30 centimeters .
Whether these features indicate natural forest fires or human activity in the area is difficult to determine from the pollen record. The
earliest distinct evidence of cultivation is found
in the topmost 15 cm in the A 300-a and A 300b profiles , where Secale and other Cerealia
pollen and ash enrichment in A 300-a (Fig. 18)
were found. One Cerealia pollen was also
found in A 300-a at a depth of 42 cm, dated at
1700 yr BP. At lower levels the question is
much more complicated. There are occasional
finds or slight increases in anthropogenie indicators (Behre 1981): Rum ex aceloseIla coll.,
Epilobium, Galium, Polygonum aviculare and
Sp ergu la type appear simultaneously with the
beginning of declines in Picea.
The number of cultural indicators so far
identified is very smal!. Their scantiness may
be due to the relative strong influence of local
bog vegetation or a large quantity of regionally
derived tree pollen. Perhaps forest clearings
were very small, and the vegetation around the
cleared area could hinder the spread of pollen .
The burning of mires has actually been the
main method of clearing in the coastal clayey
area (Vuorela 1986). Also the sparse sampling
interval , 5 cm, corresponding to an age difference of 100 - 300 years between two successi ve
sampIes, could mean that a short period (25 40 years) involving a single rotation of crops
may have remained unrecorded (Vuorela
1986).
According to historical records , permanent
settlement in Loimaa area commenced at the
beginning of the 13th century (Laakso 1986).
The first clear evidences of cultivation also
appear in Pesänsuo at this time. The beginning
of cultivation in Loimaa in the 12th-13th century seems to be a relati ve late phenomenon,
since evidence of cultivation has been documented from Late Neolithic cultures in SWFinland (Pihlman & Seppä-Heikka 1985, Vuorela & Lempiäinen 1988). Slash-and-burn-cultivation in the neighbourin g region s had already commenced during the Bronze age and
elsewhere in southwestern Finland stable field
cultivation was practised from AD 500 onwards
(Tolonen et al. 1976b, Vuorela 1975). The
earlier phases of cultivation may therefore have
remained unrecorded . Nevertheless, the earlier
changes in forest composition and incidences
of fire in the Bronze and Iron ag es were probably the result of natural forest fires. The clay
soil area, where Pesänsuo bog is situated, was
not suitable for prehistoric se ttlement. Cultural
finds from Stone, Bronze and Iron ages have
not been made in this area (Laakso 1986).
Diatom stratigraphy
The diatom stratigraphy was studied from
site A 0 at the marginal slope (Fig. 9). The
basal clay, at a depth of 370 - 410 cm was
deposited during the Yoldia phase of the Baltic
27
Pesänsuo A 0
1i'
.
0:
~
1i'
VI
....
::>
"VI
:0:
W
z
--'
::>
g
z
cm
300
z
ii
"-
ö
11}1:
:1< 1 :El
----
- +- +-
350
I
""
/
~
. . . ... :-
POOR IN DIATOMS
~~
~
7/
~
/"
150L
A
N
c
y
L
U
5
'00
x
. 1.
% 10 20 30
'0 SO 60 70 8 0 90
0 2.
10 20 30 '0 50 60 70
10 20 10 20 30 10 20 30 W 50 60 70 10 10
~3.
10 10 205
Anal. T. Grön[und 1973
Fig.9. Diatom diagram from Pesänsuo bog, point A O. (I) sall-brackish, (2) freshwater and (3) Ancylus-Lake taxa. IsoL= Isolation
from the Ancylus Lake of the Baltic basin.
Sea. Only a few diatoms have been found in the
c lay: for examp le Aulacoseira islandica (0.
Müller) Simonsen, A. islandica ssp. helvelica
(0. Müller) Simonsen and Coscinodis cus ssp.
(fragrn.). The following Ancylus Lake phase, at
depths between 320 - 370 cm reveals a much
more abundant diatom flora . The most common
species are A. islandica ssp.helvetica, Melosira
arenaria Moore, Gyrosigma attenuatum (Kützi ng) Rabenhorst, Diploneis domblittensis (Grunow ) Cleve , D. mauleri (Brun) Cleve , Cymatopleura elliptica (Bn!bisson) W. Smith and
Opephora martyi Heribaud. Ln addition some ,
probably redeposited salt-brackish water speeies , such as Grammatophora oceanica Ehren -
berg and Coscinodiscus ssp. (fragrn.) were
found.
The isolation of the area from the A ncy lu s
lake corresponds to the boundary between clay
and peat, at a depth of 320 cm. At the isolation
leve l a very thin gyttja-clay and a thin sand
layer were deposited. The diatom flora in that
layer constitues mainly of smal l lake species,
the amount of Ancylu s species is only 8 %. The
most common species are Stauron eis phoenicentron (Nitzseh) Ehrenberg , Hantzschia amphioxy s (Ehren berg) Grunow and Epithemia
turgida (Ehrenberg) Kützing. The diatom
stratigraphy indicatin g isolation is also in
agreement with the dating of the emergence.
Peat stratigraphy
The Pesänsuo bog formed on a slightly
domed clay bottom with the highest point in the
center part of the bog . The e levation of the clay
bottom at the bog margin is 80.5 m and in the
center 81 m a.s.l. The formation of the bog was
initiated by primary mire formation. In the
Loimaa and Mellilä areas the formation of
mires commenced mainly by primm'y peatland
28
formation and paludifieation, and only 20 % by
terrestrialization (Tuittila et al. 1988). Chareoal diseovered in the Carex peat seetion indieates that paludifieation was later promoted by
forest fires. The stratigraphy in eross-seetions
along the transeets is outlined in Figures 3 and
4.
In the hollow eore A 300-a the basal peat
strata (between depths of 505 - 618 em) are
eomposed of Equisetum-Phragmites-Carex-,
Equisetum-Carex-, Sphagnum-Carex-peat and
highly humified Eriophorum-Sphagnum-peat
with dwarf shrub and woody remains. Isolated
remains of Polytriehum strierum were deteeted
at depths of 505 - 525 em.
In the upper pe at seetion (from a depth of 505
em to the surfaee) there is an alternation of pure
Sphagnum- and Eriophorum-Sphagnum-peat
with variable amounts of dwarf shrub remains,
the greater proportion of whieh are eoneentrated in highly humified streaks and layers.
Sphagnum fuseum is the main moss speeies in
the whole upper peat seetion. Other less eommon speeies include S. anguslifolium and S.
magellanieum. Hollow peat, in addition to that
of the surfaee hollow, was found between
depths of 280 em and 300 em , where the peat
is eomposed of Seheuehzeria paluslris , Sphagnum cuspidalum and S. ba/rieum. Sparse remains of Polyrriehum srrietum were found at
depths of 475 - 495 em and a greater amount at
the depths of 460 - 475 em. A large amounts of
fungal remains were deteeted on the top of the
highly humified layer at a depth of 102 em. The
humifieation, whieh in Carex peat is H 5 - H 6,
varies greatly in the Sphagnum peat seetion.
In the neighbouring hollow along the erosstranseet at a distanee of 30 m from the previous
one, the same type of f1uetuation in S. fuseum
and Eriophorum-S. fuseum peat in the ombrotrophie seetion is present. A S. euspidatum
seetion is also doeumented at the depth of 300
em. Seheuchzeria was also found in the eentral
part at the site A 300+50 at depths of 280, 330
- 370 and 410 em (Fig. 4).
In the short hummoek peat monolith A 300-
cm
50
100
150
200
250
300
Fig. 10. Photo of peat face section at the southeastern marginal
slope of the bog (profile A 0), where separate and more c10sely
spaced highly humified streaks can be observed. Photo C-G. Sten
1983.
AO
>-
A 3000
C
cm
H
1
~~
u~
10;!
:>.
3100'120
C L
cm
H
1
0
..J
0
~~
Cl
<{<l-
,<0
0
>-
H
1
I
'"
620
er
er
>-
'"
Vl
W
a:
u~
10"
A 300 b
'"
Vl
W
Vl
w
u~
1O;:!
>.
560
1530
~~~
50
50
3870,60
4370,50
100
,er
100
2580
4800,70
5100'70
'+
150
t,,
50
29
1470
0
...J
0
a:
0
>-
I
~
150
5660,80
200
*
200
er
6830,90
4000
rr
+ 250
250
r,
300
300
4630
350
5690
400
450
+
o
500
550
er
er
6960
DRY
I
I MO IST
600
Fig. I I. Profiles of changes in humifi cati on for Pesänsuo bog at poi nts A 0, A 300-a and
A 300-b. For sy mbols see Figure 3. Columns show occurrences of charcoal partieles (C),
where the abundance is expressed on ascale from rr (minimum) through rand +, to c
(maximum) and lichenous (L) fragments (open circles) based on the data ofSten (Appendi x
2). The ages in A 300-a and -b are mov ing averages calculated fro m the fi ve subsequenl
conventional I4C ages.
b, the basal Sphagnum fuscum pe at is overlain
by Eriophorum-Sphagnum fus cum peat and the
uppermost section is composed of nanolignidSphagnum fuscum peat.
In the peat monolith from the southeastern
marginal slope (A 0) , a thin basal gyttja-clay
layer is overlain by Phragmiles -Carex peat.
The following peat strata are composed of
Equiselum-Carex , Sphagnum-Carex peat and
highly humified Eriophorum-Sphagnum pe at
with dwarf shrub and woody remains.
The basal " lower black" peat, at depths between 180 - 240 cm (Figs. 10 and 11) is com posed of Eriophorum-Sphagnum (mainly S.
fuscum) peat with dwarf shrub remains . Between depths of 140 - 170 cm there is a Sphag -
30
numfuscum pe at section after which the formation of Eriophorum-S. fuscum peat recommences. The uppermost section of 20 centimetres is composed of Sphagnumfuscum pe at with
an abundance of dwarf shrub remains. In the
Sphagnum peat strata a considerable variation
in humification is observable, as in the hollow
core. No hollow peat section was detected at
this point. However, at the northeastern margin
a Scheuchzeria-hollow peat layer was found at
site A 300+150 at a depth of 120 cm (Fig. 4).
During the coring operations sporadic charcoal occurrences were documented. The greater
part of the finds is concentrated at two levels:
in the lower part of the Equisetum-PhragmitesCarex peat and at the contact of Carex and
Eriophorum-Sphagnum peat. There is also
charcoal futher up at sites A 500, A 450, A 100,
A 300-57 and A 300 - 50 at depths of 30 - 40,
330 an d 480, 25, 382 and 390 cm respectively
(e-G. Sten pers .co mm . 1993). At the sites studied charcoal was found during coring operations only in A 300-a at depths of 175 - 176 and
535 cm but none in A O. However, within macrofossil analyses charcoal fragments were
found in A 300-a and A 0 at several levels in
both the minerotrophic and ombrotrophic peat
sectio ns (Fig . 11). In A 300-b black , burnt
pollen was encountered in the top most 30 cm.
An earlier study had also been undertaken at
the steep marginal slope of the Pesänsuo bog.
The 2.4 m deep section consists of slightly
humified Sphagnum fuscum peat down to a
depth of 1.4 m, of more humified S. angustifolium-S. magellanicum peat some 20 cm thick,
which contains some residues of Andromeda
and Oxycoccus and a basal Carex-peat, in
which charcoal and burnt plant residues have
been found (Malm & Rancken 1916 p. 212).
Changes in humification
The changes in humification were st udied in
peat core A 300-a and peat monolith A 300-b
in the bog center as weIl as within an open peat
face abo ut three meters wide at point A 0 at the
marginal slope. In all three peat profiles a stratified peat structure was observed (Fig. 11) . [n
the classification of humification an increase
above H 4 was recorded. In the basal Carex
peat at points A 300-a and A 0 , humification is
between H 5 and H 6. In the Sphagnum peat
section, on the other hand , the humification
varies greatly , from H 1 - H 9. The frequency
of the highly humified layers and streaks in the
Sphagnum peat section is 16, 25 and 7 in A 0,
in A 300-a and in A 300-b respectively.
In A 300-a the main tendency seems LO be
that the thick, highly humified layers are concentrated in dry stages. Minute streaks were
observed both in dry and moist stages, on the
basis of rhizopod data. The greatest number of
minute streaks is concentrated in A 300-a in a
generally moist stage dated at 2800 - 3800
years BP.
The thickness of the highly humified streaks
or layers varies from several millimeters up to
10- 20 centimeters. The change in humification
seems to be abrupt, but in some thicker layers
the transition from slightly to highly humified
peat is gradual, but in the opposite direction
abrupt (in A 300-a).
How far the streaks extend and how continuous they are remains uncertain , due to the lack
of an open peat face through the bog. At point
A 0 (Fig. 10) , where an open peat cut of sma ll er
size is available, thin streaks seem to be generally discontinuous and of undulating character. At two levels however, dark peat sections
continue through the who le three meters length .
The stratigraphic column (Fig. 11) reveals that
the dark pe at sections are actually composed of
interspersed highly humified and weakly humified layers and the black colour results from the
closely spaced highly humified streaks. The
streaks are more distinct at the margins than in
GeoJogicaJ Survey of FinJand, Bulletin 370
the bog center (Figs. 3 - 4). The same feature
has been observed by Aartolahti (1965) in the
raised bogs from southwestern Häme and
northern Satakunta.
Origin of the black streaks
The botanical composition of the streaks is
not weil known, due to the high degree of humification, but dwarf shrub remains were nearly al ways present. In profile A 300-a Iichenous
residues (Fig . 11 ) were also encountered quite
commonly but their exact stratigraphic position
is uncertain because the macrofossil sampIes in
question have been a nalysed over a vertical
section of 10 cm. No hollow peat above or
below the streak formation was found. The peat
type between streaks is either slightly humified
S. fuscum (mainly) or Eriophorum-S. fuscum
peat.
A similar pe at stratigraphy with alternating
hi ghly humified streaks and slightly humified
peats was descri bed by Aartolahti (1965) from
the raised bog s in so uthwestern Häme . The
Sphagnum species do not usually change within
streaks, but they consist of more dwarf shrub
remains, especially those of Calluna, than the
intervening weakly humified layers . The streaks
do not extend uniformly through the bog, and
they are more di stinct at the margi ns than at the
bog center, where they may be totally ab se nt.
On the Sphagnumfuscum bogs with hollow s the
streaks are restricted to hummocks , while in
pools no clear, synchronous recurrence surfaces horizons are found. According to Aartolahti
( 1965 ) the formation of the streak s is more
likely to be anormal growth mechanism of peat
bog and more dependent on local factors (e.g.
size of bog , water discharge, topography , increase in height of bog peat and in bog diam eter) than on the climate.
Likewise, in the Isosuo raised bog at Klaukkala in southern Finland, a vertical alternation
of highly humified streaks, only a few millimeters to one centimeter thick, and interspersed unhumified peat have been detected in ex-
3J
posed peat faces (Tolonen 197 I) . The streaks,
numbering about 25 in all , consist of Calluna,
Eriophorum vaginatum and lichens, and the
rhizopods associated with them all belong to
tyrphoxene groups. In the light coloured
Sphagnum peat S. fuscum is usually the main
constituent. Dark streaks are also encountered
in abundance in Sphagnum cuspida tum hollow
layers , but their origin has not been s tudied.
According to Tolonen (1971 p . 163) "after the
peat growth had come to a complete standstill
during the streak formation , it started once
more on deposition of light-coloured Sphagnum layers . A Sphagnum fuscum sward was
usually responsible for the rejuvenation of the
peat surface." He termed the phenomenon a
fuscum regeneration.
The peat section exhibiting alternating humi fication in the Isos uo bog at Klaukkala is , according to pollen data , supposed to date from
3500 - 4000 years BP and the streak interval is
believed to represent about 90 years. On account of the great number and non-synchronous
character of the streaks Tolonen deduces that
they do not correspond to classical recurrence
surfaces , which are only eight in number. Some
of the streaks may be i nterpreted as recurrence
surfaces. However, the majority of them may
represent minor fluctuations in the macroclimate (especially in humidity ), or referring to
the studies of Walker and Walker (1961), " it is
possible, however, that the lifecycles of the
dominant plants mentioned in themselves offer
a simple exp lanation " (Tolonen 1971 p. 164).
The short-cycle regeneration of hummocks is
a common feature in all the areas containing
raised bog s throughout Europe (Tolonen 1980
and references therein). The changes appear as
thin undulating dark streaks and lenses rich in
hepaticsl dwarf-shrubsl lichens interspersed with
less humified peat sections. The origin of the
dark streaks in Sphagnum cuspidatum hollow
layers on the other hand, is partly due to the
peat mud s tages witnessed by "wet" rhizopod
assemblage found in many of them.
According to Tolonen (1980) the most im-
32
portant regulating faetors in the formation of
streaks, bands and lenses in open peat faees are
"both loeal hydrologieal events (Casparie 1969,
1972) or eyelie elimatie variations (Aaby 1975,
1976) and their variations in effeets from plaee
to plaee (Overbeek 1975)".
The same alternation of highly humified
streaks with slightly humified peat has also
been deteeted in two raised bogs from eastern
North Ameriea. Blaek and dark peat streaks
indieate former liehenous eommunities and the
intervening layers represent hummoeks or
lawns. The interpretation is supported eonvineingly by their eontrasting rhizopod assoeiations . The pattern is similar to the short-eyele
Sphagnum fuscum regeneration deseribed by
Tolonen (1971, 1980) from northern Europe,
the only differenee being that the moss speeies
are different (Tolonen et al. 1985).
Mire site type succession in the light of the macrofossil record
Mire development began with a swampy
sedge fen phase (TuN). The assemblage of
plant remains eonsists of the meso-eutrophie
reeds Phragmites australis, sedges Carex vesicaria, C. canescens, C. diandra, C. dioica and
the meso-oligotrophie sedges Carex roSlrata
and C. lasiocarpa. Among herbs the meso-eutrophie speeies Cicuta virosa, Pedicularis
palustris, Peucedanum palustre and POlentilla
palustris are predominant. The meso-oligotrophie herbs eonsist of Menyanthes trifoliata,
Stachys palustris, Ranunculus flammula, R.
repens and Equisetum (see Appendix 2, Figs. I
and 2). Both swamp and ne va influenee is ref1eeted in the speeies eomposition.
The meso-eutrophie speeies diminish in the
subsequent true tall-sedge fen phase (VSN).
The change begins at about 8000 years BP at a
depth of 560 em in the profile of the bog center
and at 285 em in the margin profi le. The predominant sedges are Carex chordorrhiza, C.
lasiocarpa and C. dioica.
Edaphie impoverishment with inerease in
peat depth is indieated in the peat stratigraphy
by the inerease in Sphagnum and Eriophorum
vaginatum. The open mire vegetation is replaeed by Eriophorum vaginatum pi ne bog
(TR) with bireh being dominant at depths of
530 em in the bog center and at 250 em at the
margin.
In the nutrient status of mire an oligotrophie
stage is attained at about 6800 years BP. At the
same time a transition to open mire vegetation
(TR/LkN) took plaee. The speeies eomposition
is very sparse: Sphagnum, Eriophorum vaginatum, Vaccinium oxycoccos, V. microcarpum
and Andromeda polifolia, whieh is the most
abundant speeies.
In the bog center the short sedge intermediate level bog (LkN) was replaeed by Sphagnum
fuscum bog (RaN) at a depth of 460 em , at 6400
yr B P and at the margi n, at a depth of 180 em ,
eorresponding to 5600 years BP. The last
change in mire site type, to Sphagnum fuscum
bog with hollows (KeR) took plaee at 4600
years BP in the bog center at a depth of 300 em.
At the margin the final, true dwarf shrub pine
bog phase (IR), manifested by the i nerease of
Calluna and other dwarf shrub speeies , oeeurred about 3000 years BP.
Rhizopod stratigraphy
Rhizopods were studied only from the profiles in the bog centre. The eomplete absence of
rhizopods in the minerotrophie and early ombrotrophie phases is partly due to the method
Fig. 12. Correlation diagram of rhizopod spectra from point A 300-a of Pesänsuo bog with Iithology, humitication, Picea and CaUl/na
pollen , Calluna seeds and rate of apparent peat accumulation.
Geo logica l S urvey of Finland, B ull et in 370
PESÄNSUO . A 300
a
87.0 m 0 . 5 .1.
N
E
~
.... z
z!:'
w ....
~
<t
a:"
.. ...J
<l."
U
V>
<l.:L
;i
B
c5U:
w
'::=>
0
<t"
u
<t
0
>:
b~
<t
ou
iO
Q.
33
I>:
<t
w
~I
a:
<t
zz
=>w
3~
~~
~~
~w
U
<tw
<to
UQ.
UV>
u.u
0"
w ....
......
"w
a:<l.
W
er
.... >:
~~
>:~
<tu.
w
'"<tQ.
' <D
~u ~
200
I
1000
" 2000
2500
3000
3500
200
1.000
1.500
300
5000
5500
6000
f 6500
7000
I
t I
7500
283~ 8000
297
," "
102030 '0
Sum=~P
,. ,.
,-;'"l:;-~'
102030
~5cm
=;:,;::;::,;-;r;:;,;:;':::;:',,-'::;:=;:;::;::,;:::;:;::,;'"
10 20
Sum=::t P
1020301.050 60 70 80
Sum
=100
~-~LJ~_- -Lr-r- -L!J
10
10
10
r
H
,~ , ;r~ J
"
50
100
150
200
TREE POLLEN
Anal. L. I konen 1979
2
Geo logical Survey of Fin land , Bul le tin 370
34
PESÄNSUO A 300b
Vl
.,
0
...J
...J
--:
0
~
w
~
<{
:::J
...J
U
Vl
Z
0
E
0
I
IQ.
W
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>- f=
<!l<{
Ou
...J ou.
I~
~ :::J
...JI
...J
...J
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Q.
<{
~
Cl:
<{
a::
<{
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Z
...J
...J
Q.
U
~
<{
I
,
Q.
<{
W
Vl
<{
<{
<{
U
::i
a::
I
<{
.L.............L L...........J
U
<{
Vl
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X
W
I
....
>-
w
0
0
<!l
a::
<{
<{
a::
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I-
>-
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Vl
...J
>-
<{
>-
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...J
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eil
>-
<!l
Q.
a::
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Q.
a::
I-
:::J
a::
0
Z
0
z
:::J
Vl
Vl
:::J
Vl
Vl
<{
,
~
z
...J
...J
I-
:::J
<{
<{
<{
...J
...J
aJ
:::J
Vl
Z
~
:::J
Vl
~
<!l
Z
U
Vl
w
W
U
:::J
0
...J
0
...J
a::
~
<{
IVl
:::J
:::J
:::J
Z
w
~
~
<{
I
I
L.........J
L.J
~I
...J
I
Cl
I
U
~
,
500
1000
1500
50
2500
'I
,.
10 20
Sum= ~P
"
r ,~T'-''--''~'
10 20 30
Sum
= ~P
-''""""T'~ ~.,.......,
r ,~,-,~T'
10 20 30
10
Sum = 500 TREE POLLEN
10
r-rI
10
r-' r--r-l I
5
10
i
I
'
I
10 20
Ana l. L. Ikonen 1979
Fig. 13. Correlation diagram of rhizopod spectra from point A 300-b of Pesänsuo bog wirh lithology, hum ification and both Picea
and Call/llia pollen. Hydrology: moi st (vertical lines) and dry (dots) stages.
used in preparation and also becau se the tests
of genera restricted to minerotrophic mires are
either dissolved 01' brea k down durin g the decomposition process (Tolonen 1986).
There are also some res trietion s upon the
interpretation of the rhizopod dia g rams (Figs.
12 - 13 ), where the rhi zo pods were s tudied
within poll e n analysis. Firstly, the abundance
of te sts is limited becau se the origin, distribution and accumulation of pollen grains are quite
different from that of the mos s- inhabiting
Testacea and secondly, the number of taxa are
restricte d because of the se lect i ve destruction
of tests in pollen preparation (Tolonen 1986).
While ma ny of the peatland specie s have their
optimal and maximal occurrence within fairly
narrow limits , the application of particular taxa
in the interpretation of moisture conditions in
th e bo g is neverth e less val id (Tolone n 1986). In
this ca se the f1uctuating values of Amphilrema
flavum in particul a r are used.
In raised bogs , Amphifrema fl avum is associated with th e moi st parts of the bog surrace
(Grospietsch 1953, Meisterfeld 1977 moi sture
class TI - III , Tolonen et a l. 1992b) and its
abundance us ually incre ases with increasing
humidity ex ce pt in cases of extreme wetness, as
a result of which it suffers (Harnisch 1927).
Although the ab undances or o ther rhizopod s
are very smalI, the occurrence of Amphitrema
wrigh tianum , Hyal osphen ia subflava, Tri gol70pyxis arcula and a rotifer Habrotro cha
angusticollis are worth mentioning. Amphitrema wrightianum is a strict bog species
(Meisterfeld 1977 moisture class lI-III, Tolonen et al. 1992b), which is mostly restricted to
bog pools (Heal 1964). Habrotrocha angusticollis is also a wet habitat species ( Meisterfeld
1977 moisture class IV , Tolonen et al. 1992b),
wh ich according to Steinecke (1927), indicates
the existence of adepression with open water.
The tyrphoxene species Hyalosphenia subflava
is not indigenous to bogs but is instead characteristic of drained peatlands and those overgrown with heather and of peatland marginal
areas (Grospietsch 1953 ). Trigonop yxis arcula
is a xerophilous species (Graaf 1956 moisture
class VI- VII) , which is positively correlated
with the highly humified dwarf shrub peat
s treaks in the "s hort-cyclic" regeneration of
Sphagnum fuscum peat (Tolonen 1971).
Hollow site
Rhizopods first appear in the A 300-a profile
(Fig. 12) at a depth of 510 cm and Amphitrema
f/avum is the mo st abundant species. In the
basal part, from 385 - 5 10 cm, the abundance
of Amphitrema f/avum is quite low , but two
minor increases occur at depths of 490 - 500 cm
and 430 - 440 cm. From 385 cm upwards five
distinct maxima of Amphilrema flavum are to
be found:
Depth cm
I.
2.
3.
4.
5.
22
47
I 10
227
340
-
35
97
215
290
385
I-lC-age yr BP
1200
2050
2800
4100
5350
-
1500
2600
3800
4500
5700
Amphilrema wrighlianul1l is present In the
uppermost three Amphirrema flavum maxima
and is most abundant during the second maximum. Habrorrocha anguslicollis was detected
from the fourth to the uppermost maximum,
and occurs in greatest concentrations in the
35
second maximum. In the section above the
uppermost Amphitrema maximum, only one
test of Arcella sp. and one of Amphitrema flavum were found , at the two uppermost sampling
levels .
Dry/moist stages
There seems to be a detectable correlation
between the occurrence of Calluna vulgaris
and the fluctuating values of Amphitrema flavum, with the Amphitrema maximum coinciding with the absence or minimal occurrence of
Calluna seeds. Conversely the minimum abundance of Amphilrema tests and the maximum
occurrence of Calluna seeds and, to lesser
extent the increasing amounts of Calluna poI len show a distinct inverse correlation (Fig.
12). Hence the occurrence of Calluna in this
case seems to indicate drier conditions in the
bog.
The first minor increase of Amphitrema tests
occurs within a shift in mire site type (TR/
LkN). In the following section , where the in crease in Ca/luna pollen and the first s parse
occurrence of Calluna seeds commence , the
abundance of Amphirrema is very low. The peat
is composed of Eriophorum-Sphagnum and
Po/yrrichum-Sphagnum with minor, hi g hly humified streaks. Small amounts of PO/Ylrichum
are already found in the Eriophorum-Sphagnum
section, and hence the whole section might
represent a dry phase .
The succeeding Amphirrema maximum , which
was of short duration , combined with the absence of Calluna possibly represents a minor
moist period at the beginning of the Sphagnum
fuscum bog phase (RaN). After that the slightly
decomposed Sphagnum fuscum peat with dwarf
shrub remains and the overly in g more humified
Eriophorum-Sphagnul1l fUSeLlm pe at show a decrease in the amount of Amphilrema, while the
abundance of Calluna seeds and pollen increases, indicating drier conditions.
According to the fluctuating va lues of Amphilrema f/avlll17 tests and peat strata at the end
36
of the minerotrophic phase and during the early
part of ombrotrophication a generally dry phase
or alternation of dry and minor moist phases
prevailed up to level of 385 cm. Since then six
moist and five intervening dry phases succeeded one another. The moist phases are dated at
5700 - 5350, 4600 - 4100, 3800 - 2800, 2600
- 2050, 1500 - 1200 yr BP and from 600 yr BP
up to the present.
Amphitrema and humification
In the upper part of the diagram, from a level
of 385 cm upwards, the increase of Amphitrema
flavum is accompanied by a fall in the degree
of humification while conversely, a decrease in
Amphirrema corresponds to a ri se in degree of
humification. The coincidence with thinner
streaks is not obvious, the reason for this probably being that the rhizopods have been counted from pollen sampIes, where no separation
between the minute streaks and the interspersing layers was made.
In the Draved Mose raised bog in Denmark,
where the same selective taxa as in Pesänsuo
have been studied, an increase in the amount of
Amphitrema is accompanied by decrease in
humification (Aaby & Tauber 1975). In the
Varrassuo bog in south Finland, where more
representative taxa has been studied, the same
correlation between Amphitrema flavum and
degree of decomposition has also been recognized (Tolonen 1979).
Since Amphitrema flavum is also weil preserved in highly humified peat, the reason for
its vertical variations in abundance does not
appear to depend on variations in the humification of the peat (Grospietsch 1953 , Tolonen
1966 and 1971), but more Iikely shows that
these more humified layers originate in a different type of peat (Tolonen 1971). Concerning
the relation between humification and the local
vegetation it has been shown that recent bog
plants cause different degrees of humification
(Overbeck 1947). Plants growing in moist conditions show lower degrees of humification
than species growing under drier conditions
(e.g. Ca/luna vulgaris). The change in the humification curve thus seems to depend on the
humidity or the dryness of the bog surface
(Aaby & Tauber 1975).
Fluctuations in the Amphitrema and the
spruce pollen curve
In the upper part of the diagram (Fig. 12) the
rise and fall of the Picea curve also seems to
be correlated with the f1uctuating values of
Amphilrema flavum and with the highly decomposed peat layers. The increase in Amphitrema
flavum corresponds to a rise in the Picea curve
and converse ly the decrease in Amphitrema
correlates with a decline in the Picea curve,
although a short delay in the rise and decline of
Picea is observed. The decline of the Picea
curve on the other hand is contemporaneous
with a rise in the degree of humification. The
same correlation between Amphitrema and Picea i also observable in profile A 300-b (Fig .
13).
The peat stratigraphical fire-record and the
signs of anthropogenic activity suggest that the
decline and subsequent regeneration of spruce
in this case might be a result of natural forest
fires and local clearing (see p. 25 - 26). The
regeneration of Sphagnum cover and a change
to wetter conditions recorded by an increase in
Amphitrema f/avum abundances indicates that
the fires probably also affected the bog itself.
Amphitrema and peat growth
In profile A 300-a of the Pesänsuo bog, a
positive correlation between the abundance of
Amphitrema tests and peat growth and a negative one between the degree of humification
and peat growth is observable , mainly in the
upper peat profile between depths of 35 cm and
380 cm. However, between depths of 50 - 65
and 110 - 150 cm areverse correlation in both
the cases is evident (Fig. 12). No meaningful
correlation is discernible in the lower part of
the profile nor in the uppermost section. In the
GeoJogicaJ Survey of FinJand, Bulletin 370
latter ca se the reason is probably secondary
compaction, resulting in diminishing growth
rates.
The same phenomenon had previously been
recorded from the Varrassuo bog (Finland) and
the Ageröd Mosse (Sweden), in which the stages characterised by faster peat growth and by a
abundant occurrence of Amphitrema flavum
tests are also concentrated in slightly decomposed peat layers (Tolonen 1979). According to
Tolonen this relationship indicates that the rate
of peat increment was most rapid in wet condi tions.
In Draved Mose on the other hand, no correlation between peat growth and degree of humification was noticed in sampies representi ng
hollow phases, which may be an artefact of the
sampling method. Sampling from an open peat
cut might have promoted an artificial shrinkage
of looser peat layers responsible to the co mpression (Tolonen 1979).
According to Tolonen (1979) it is difficult to
determine to what extent major differences in
the height increment of virgin peat profiles are
caused by uneven autocompaction of originally
distinct Sphagnum species. Both the results of
Olausson (1957) and those from Draved Mose
indicate that the compression of peat has been
greatest in S. cuspidatum hollow layers (Tolonen 1979) . In Pesänsuo the values of the bulk
density in S. cuspidatum layer do not differ
from the ones in S. fuscum layer above it.
The negative correlation between peat growth
and the degree of peat humification is also
demonstrable on a larger scale in southern
Sweden, northern Germany, southern and central Finland (Tolonen 1979), as weil as in mires
in Maine (Tolonen et al. 1988).
In their study of the Draved Mose raised bog
Aaby and Tauber (1975) on the other hand,
concluded that there was no obvious relation
between measured rates of peat increment and
degree of humification. They stressed the importance of autocompaction in ombrogenous
peal. Pe at formed under moist conditions is
more compressible than that formed in dry
37
conditions. According to Aaby and Tauber,
neither decay nor humification could be the
main cause of variation in growth rates, although they concede that some influence from
these sources is possible. In his study of Bolton
Fell Moss in Great Britain Barber (1981) also
found that in some cases the growth rate of
unhumified and humified peat was much the
same.
Compression of peat by the weight of the
overlying peat mass has been demonstrated e .g.
in the studies by Berry and Poskitt (1972),
Clymo (1978) and Johnson et al. (1990). There
are , however, other varying opinions concerning compaction; Kaye and Barghoorn (1964)
and Walker (1970) for instance claim that progressive compaction does not occur. Clymo
(1978) , despite the evident compaction in the
topmost 50 cm of Sphagnum peats reported in
his study, stated that the time scale of this
change is so short, however, that it is still
consistent with the conclusion of Walker and
Kaye and Barghoorn (cf. also Middeldorp
1986).
Hummock site
In the short hummock peat monolith A 300b (Fig. 13) rhizopods are much 1ess common.
At the bottom of the core, from 65 - 90 cm, the
abundance of Amphitrema flavum varies from
5 - 30 % but only severa1 percent of Assulina
muscorum, A. seminulum, Arcella spp. are
present, while in the basal sampie one Habrotrocha angusticollis was found. At depths between 50 - 65 cm only a few tests of Amphitrema and solitary tests of Arcella spp. and
Trigonopyxis arcula were found. Several percent of Amphitrema flavum and some tests of
Arcella spp. were present at depths of 40 - 50
cm. Between depths of 20 - 40 cm no rhizopods
were found, while in the uppermost 20 cm, the
dominant species are Trigonopyxis arcula and
Arcella spp. Some tests of Assulina seminulum
and Hyalosphenia subflava were also found.
The rhizopod association present in the low-
38
Geological Survey of Finl and , Bulletin 370
er part of the profile probably indicates a moist
phase , which might correspond to the moist
phase dated at 2600 - 2050 yr BP in the hollow
profile. The subsequent decrease and ultimate
absence of Amphitrema in the section of highly
humified Eriophorum-Sphagnum-peat with dwarf
shrub remain s coincides with the dry phase in
the hollow core. The slight increase in Amphitrema at 1600 - 1300 yr BP probably reflects
a moist phase, which coincides with the moist
phase detected in the hollow core. The tyrphoxene types found in the uppermost 35 cm suggest a very dry phase on the hummock.
Peat growth
Rate of peat increment
In the hollow core A 300-a the mean rate of
peat increment for the whole peat strata is 0.67
mm yr . 1, although it shows great variation (Fig.
14). Vertical peat increment figures for Carex
peat are very high , up to 2.72 mm yr -I . For the
whole Carex peat sec tion , however, an average
rate of 1.1 3 mm yr · 1 has been calculated on the
basis of the lowest a nd uppermo st dates. In the
highl y humified Eriophorum-Sphagnum peat
with dwarf shrub and woody rema in s the rate
was quite low, being 0.41 mm yr . 1.
In the Sphagnum peat strata two sections
with different rates of peat in crement can be
distinguished. In the 10wer section, at depths
of 330 - 505 cm, representing the period between 7700 - 6050 years ca l BP (6900 - 5300
BP), an average rate of I mm yr - I is inferred .
Higher rates, however, have been determined
for 7700 - 7750 and 6900 - 6850 years cal BP:
1.32 - 2.13 and 2.08 mm yr - I respectively . A
period of slower growth , namely 0.50 mm
yr-I is recorded for the interval 6050 - 5000
years cal BP (5300 - 4400 BP) .
The upper section, representi ng the period
since 5000 years cal BP is characterised by
alternations of high and low rates of peal increment. The average value for slow growth is
0.50 mm yr . 1, whereas during the rapid growth
phases at 5000 - 4900, 4200 - 3800 and 2500
- 2400 years BP the rates are 3.22 , 1.12 - 2.08
and 2.27 - 2.50 mm yr -I respectively. During
the last two thousand years a decreasing rate of
peat increment, averaging 0.22 mm yr - I is recorded.
The very slow rate of peat increament in the
upper peat profile could be explained by sec ondary compaction , which is consistent with
the increasing bulk density values down a depth
of at least 35 cm. The compaction is probably
due to the presence of widely spaced drai nage
ditc hes in the bog.
The average figures for the rate of peat increa ment in the hummock mon olith A 300-b
(Fig. 15) are low , around 0.3 mm yr - I, correspondin g the values obtained from the upper
part of th e hollow core A 300-a.
The rate figures for the bog margin , point A 0
(Fig. 16) are much lower than th ose determined
for the bog cen ter. [n the Carex peat the rate of
peat increment varies between 0.45 - 1.25 mm
yr -I . In the basal "b lack " peat, the EriophorumSphagnum seclion, at 7600 - 6450 years cal BP
(6800 - 5600 BP) the rate is still low at 0.48 mm
yr . 1, but increases to 0.95 mm yr - I in the
slightly humified S. fuscum peat at 6450 - 5900
years cal BP (5600 - 5100 BP) . A very low
value of 0 .22 mm yr - I is indicated for the high ly humified layer at depth s of I 15 - l25 cm at
5900 - 5600 years cal BP (5100 - 4800 BP). In
the upper " black" peat section at 4900 - 4300
years cal BP (4300 - 3800 BP) the rate of pe at
increment is 0.41 mm yr - I . Since 4300 years cal
BP, in the uppermost 50 centimetres the rate
has slowed down to 0.36 mm yr - I . At the bog
margin the peat cutting ha s caused considerable
secondary compaction and humification , which
hinders the evaluation of the peat g rowth in the
uppermost peat section.
The vertical peat increment figures calculat-
Geol ogica l Survey of Finland , Bulletin 370
PESÄNSUO. A 300
39
0
z
]
;:
20
0.
>- ... - I
Ö . ;{
Vl
g~-
Wo.
ou. W
I--'
0.
... :0:«
w _ :>u
0
BULK OENSITY 9 cm - 3
-,Iv>
0.02
0.06
0.10
0.11.
~~
RATE OF PE AT
RATE OF APPARENT
INCREMENT mm yr- 1
PEAT ACCUMULATION 9 m- 2 yr- 1
1.0
L-~~~-L-L~r,",L-11
2.0
3.0
50
100
150
~~-L-L~-,~~~~~-LLJ~'
u >~
200
100
l
250
50
~
,-
100
~'i
l;==-
150
200
250
300
500
1000
1500
2000 - 2000
2500
3 000
3000
1 ":-
-~
~~'
~~
/,
\'
150
,000
'
4000
"
250
"- ~;
300
,
-
t?i?-
3500
200
4500
1/ ~
350
9~
!j>-
~~~~-mmmrrrr--,----,----,
5~
50
Vl<D
W .
~ö
5000
5000
6000
350
'
,00
450
f,
{ -'
\' ' -
';"~
550
,
bf
I
,00
6000
7000
450
6500
~~~
500
500
7000
f?
m
l _____ __25.6 L--_L---'='~:~f
550
' ,
•,
•,
600
90j
8200
Fig. 14. Profiles for Pesänsuo bog, point A 300-a, of bulk density , rate of pcat incremcnt and apparent peat accumu lation caJculated
from ca librated "C dates. Rate of apparent peat acc umulation = bulk density x ratc of peat increment. Hydrology: moist (verticallines)
and dry (dots) stages . Timescalcs: Age read from thc curve of moving averages of thc five sllbseqllent conventional "C-ages and
cal ibrated I4C-dates. Bulk density figurcs revi sed from data published in Tolonen 1979.
ed for lon ge r periods in earl ier studies (see
lntroduction ) are much lower than those obtained from the Pesänsuo rai sed bog. The highest rates had been reported for the period since
a bout 2500 years BP. However, th e gro wt h rate
in Pe säns uo already increased markedly from
5000 yea rs cal BP (4400 BP). In the Munas uo
pl atea u bo g at Pyhtää , in so uthern Finland,
where the average vertical height increm e nt of
peat is 1.36 mm yr - I, a faster period of growth ,
namely 3.3 mm yr -I is recorded for the interval
I
5500
about 3900 - 3600 years cal BP according to the
radiocarbon data of Seppä 1991 (To lo ne n &
Vasander 1991 ).
Recent studi es carried out on geo log ically
old mires in Finland reveal that the vertical peat
increment was hi g h during the first two thousand yea rs, es pecially in the inte rval 9000 8000 yr BP. Durin g the subsequent five thousand years th e rate was very slow but rose again
durin g the last three thousand years (To lonen &
Vasander 1991) .
40
..
L
>N
I
PESÄNSUO A 300 b
A.
E
.
CJ>
Z
f-O
z-
L
wl-
>-
o..z
(/)
E
Z
W
u
[LW
0::>:
WW
1-0::
«U
o::~
0
J:
~E
f-
a..
u
...J
::::>
W
000>
0
0::«
«....J
0..::::>
0..::>:
«:::J
U
[LU
0«
WIf-«
«w
0::0..
f- E
«E
Wf-
>f-
0.14
0.10
0.06
0.02
0.5
0..
CD
L
>-
W
(!)
«
I
U
~
20 40 60
500
1000
1500
50
2000
2500
B.
T (CALIBRATED 1I.C_DATES cal. BP)
500
I
!
,
I
I
!
1000
I
I
1
I
I
1500
I
I
J
I
I
2000
I
I
!
I
!
2500
I
I
I
!
I
I
I
E
u
50 ~
0..
W
o
Fig. 15 A. Profiles for Pesänsuo bog, point A 300-b, of bulk density , rate of peat increment
and apparent peat accumulation calculated from calibrated 14C dates. Timescale: Age read
from the curve of moving averages ofthe five subsequent 14C-ages. B. Profile of calibrated
I4C-dates against depth as cumulative mass below surface. The dates used are the moving
averages of the five subsequent calibrated 14C-dates.
In the geologically young mires on the co ast
of Gulf of Bothnia, where the stratigraphy and
development are dependent on the time elapsed
since emergence from the Baltic basin waters,
it is difficult to detect any synchronous regularity in growth (Tolonen & Vasander 1991).
Likewise, according to Aario (1932) and Aartolahti (1965) stratigraphie features in the
mires of northern Satakunta and southwestern
Häme do not relate to climatic change but rather reflect a natural mire s ite type succession
as the mires age. The stratigraphical order of
pe at type successions from the basal parts to
the tops of mires corresponds to the zonation of
contemporary and present mire site types progressing from coastal area towards the more
elevated interior of the country. In addition to
the influence of the geological history of the
area, the development of bogs in so uthwestern
Häme and northern Satakunta has probably
been strongly dependent on the natural mire
succession and local hydrological changes
(Aario 1932, Aartolahti 1965).
In the old Häädetkeidas raised bog in northern Satakunta, the initiation of wh ich (8200±120
BP, 9160 yr cal BP, Tolonen 1992 pers.comm.)
was approximately simultaneous with that of
Pesä nsuo, the vertical peat increment is low at
41
PESÄNSUO A 0
3000
5000
7000
9000 " C-DATES
ca!. BP
- ' - _LI--'_-'----'---'-'_'---'-----'-----"_-'-----'---'_L'-
i = 0.35
h =0 .1.1
9 =0.53
f =O.22
e = 0.95
d= 0.1.8
c= 0.38
b= 0.1.5
0=1. 25
,
2000
I
1.000
I
5000
I
8000
"C - AGE yr BP
Fig. 16. Rate of peat increment fo r Pesänsuo bog, point A 0, on the basis of calibrated 14C_
dates (timescale above). Conventional 14C-ages (with error bars) against depth (timescale
below).
first but rises steadily from 6000 years cal BP
(5200 BP), the values obtained in thi s seetion
being 0.6 - 2 mm yr -, (maximum). After 4000
years cal BP (3700 BP) the rate figures diminish , but since 1500 years cal BP (1600 BP)
there has again been an increase in peat increment (K. Tolonen 1992 pers.co mm .).
Rate of apparent peat accumulation
The rate of apparent dry matter accumulation
at a specific site in a mire can be calculated
from peat columns of known bulk den sity.The
true rate of peat accumulation, however , is
lower because the slow decay which takes place
in the anoxie deeper peat layers is ignored in
this approach. The true rate of peat accumulation can only be obtained by mean s of "peat
accumulation model s", such as the one defined
by Clymo (1984).
The bulk density , which averages 0.06 g cm3
in Pesänsuo bog (profile A 300-a) shows only
minor vertical variations and no curvilinear
relationship with depth. The profiles of bulk
density and vertical pe at increment (Fig . 14)
show that the final but still apparent pe at accumulation is mainly determined by height increment. Only in a few cases have bulk density
values caused by a greater proportion of dwarf
shrubs and high decompo sition affected the
rate of apparent peat accumulation (for thi s
concept see Tolonen et al. 1992a). This is obvious for example at depth s of 380 - 430 cm in
profile A 300-a, where the accelerated rates
coincide with the Calluna-phase, macrofossilzone 4 .
The apparent dry matter accumulation in the
Sphagnum peat sec tion varies greatly : ranging
from 24 - 208 g m - 2 yr -' . The values obtained
for the period since 5000 years cal BP (4400
BP) are far greater than any other ex am pies
published from Finland.
42
Long-term estimates of apparent dry matter
acc umul ation in the raised bogs in southern
Finland have been earlier estimated at 25 - 48
g m -2 yr - I (To lonen 1977). Subsequent ly a
slightly greater range of J9 - 68 g m ·2 yr ·1 was
proposed for the Laaviosuo raised bog (Tolonen 1979) which, according to Tolonen , agrees
with the long-term accumulation figures of 40
- 50 g m -2 yr - I obtained for a southern Swedish
raised bog (cf. Mattson & Koutler-Andersson
1954). A much wider range of 7.4 - 133.6 g m-2
yr - I, on the other hand was determined for the
short-term variation of apparent dry matter
accumu lation in the Varrassuo raised bog using
an unsmoothed growth rate curve. The range of
accumu lation using the average polynomial
height increment curve was , however, of the
sa me order as that in the Laaviosuo rai sed bog
(Tolonen 1979).
Other calculations of average apparent accumu lation rates come from Manitoba , Canada
(27 - 52 g m -2 yr - I, Reader & Stewart 1972) ,
from G lenamoy, lreland (32 g m ·2 yr .1, Moore
1972), from Moor House, England (48 - 180 g
m -2 yr - I, Clymo 1978). Higher values of 46 70 g m -2 yr - I and 129 - 204 g m -2 yr - I have
been reported for two blanket bogs in central
and northern England (Jones & Gore 1978).
tion) of respecti vely 100, 500 and 150 years
duration having rapid accumulation are interrupted by longer periods of J 250 and 700 years
with slow accumulation. In the upper part of the
profile the curve is slightly convex due to a
retarded trend in the rate of peat increment. The
profile of depth against cumulative mass is
clearly linear (Fig. 17).
In the short hummock monolith A 300-b, the
same s lightly convex trend in cumulative mass
curve as in the upper part of the hollow core is
evident (Fig. 15). Plots of age against depth for
the A 0 profile also lie alm ost along a straight
line (Fig . J 6).
The best fits for the relationship between the
cumulative mass and age for the Sphagnum peat
section (down to a depth of 505 cm) p lot along
both linear and power regress ion curves in A
300-a. The equation is in the former case
y
R2
y
=
x
and in the latter,
Iny
R2
y
x
- 4.820 + 0.005 x, where
0.989
cumulative mass
time (cal 14C dates)
-7.944 + 1.2831nx , where
0 .994
cumulative mass
time (cal 14C dates)
Cumulative mass versus age
A generally linear long-term trend prevails in
the cumulative mass versus age curve (cumulati ve mass agai nst 14C dates cal BP) through the
Sphagnum peat section of the Pesänsuo bog
hollow core, A 300-a (Fig. 17). There is , however, an exception between 2400 - 5000 cal BP,
where three periods (in the downward direc-
The true rate of net peat accumulation can be
obtained when decay both in the biologically
active s urface layer (the acrotelm) and the
anoxie waterlogged peat (the catotel m) is taken
into account. The real acc umul ating system is
the catotelm and the fundamental values are
those of the parameters Pe and U e, the rate of
Fig. 17. A I. Profile for Pesänsuo bog, point A 3OO-a, of eali brated 14C-dates against depth as eumu lati ve mass below the surface.
Cumulative mass X at eaeh ealculation step k (k ... n) is calculated as folIows:
k
X, = L 0, (z; - Z; _I)/ 1000, where 0 = bulk density (g dm3), Z = depth (em)
i=1
The dates used are the moving averages ofthe five subsequent ealibrated I4C-dates. 2. Profile ofrelation between depth and e umulative
mass. The horizontalline in profiles land 2 marks the mire site type boundaryTR/ LkN. B. Profile ofealibrated 14C-dateseal SP against
depth. C . The eurve of the moving averages of the five subsequent ealibrated 14C-dales.
A 1
X (g/cm
2
B
)
0
OEPTH m
o
10
20
3
4
30
6
40
o
4
6
10
CALIBRATED 14C DATES CAL BP
50
0
2
4
6
8
CALIBRATED 14C-DATES CAL BP
10
A2
Cl
DEPTH m
"Öo
c
o
(JQ
ö"
~
OEPTH m
° l~
CIl
:;
<:
"
'<
2
o
....,
"Tl
3
5"
4
"
Pro
~
5
"~
6
o
5
w
-..l
o
7
4
8
8
10
CALiBRATED 14C DATES CA L BP
o
10
20
X (g/cm
2
30
)
40
50
..,.
w
44
Geological Survey of Finland, Bull eti n 370
input to the catotelm and the catotelm decay
parameter (Clymo 1984). According to Clymo 's peat accumulation model ( 1984) the slow
rates of decomposition within the deep peat
layers result in a concave plot for age against
depth in a peat profile and the peat ma ss tends
towards a steady state in which the rate of
accumulation at the surface is balanced by the
cumulative los s throughout all depth s.
In five peat profiles from Finland, Sweden
and Denmark studied by Clymo (1984), a concave age against depth as cumulative-mass
curve was found, in spite of temporary fluctuations. The assumed values for long-term , constant true dry matter input (Pe ) for the bogs
studied were 36 - 78 g m · 2 yr · 1 (about 10 % of
the net productivity of the vegetation) , with a
decay parameter (<Xe ) of about 0.000 I yr . 1.
According to Clymo thi s long-term trend cannot be exp lained by a change in bulk density
(wh ether caused by autocompaction or by other
processes), but there are several other possible
explanations, any of which or any combination
of which may be involved (C lymo 1984 pp . 623
and 624) .
In one of the bogs , Ageröds Mosse (based on
the data of Nilsson , 1964) studied by C lymo
(1984), however , the corrected age against
depth , both as distance and as cumulati ve mass ,
was approximately straight except for a section
betwee n about 3000 - 1700 years ago, in which
a phase of slower growth was followed by an
almost exactly compensating phase of more
rapid growth . The diverging curved line marking the lower 95 % confidence limit in the
equation Xe = p/<X e ( l_e·aeTe) is almost straight,
whereas the upper is marked ly co ncave. According to Clymo ( 1984 p. 621) there is little
reaso n for rejecting the hypothe sis that there
has been no decay (<Xc=O) since th e plant material passed into the catotelm, but it is also
possible that <Xc is not zero, and that <Xe and Pe
have both varied in a complicated and compensating way .
There are a number of recent studies where
Clymo's hypothese s about bog growth have
been tested. In some cases the data for lateral
extension or (and ) vertical growth seem to conform the assumptions but in others the devel opment of the bogs diverges from the situation
presupposed by the model (Lewis Smith &
Clymo 1984 , Foster et al. 1988 , Foster &
Wri g ht Jr 1990, Foster & Jacob so n 1990,
Warner et al. 1991, Tolonen et al. 1992a and
Korhola 1992). The results for vertical growth
in Pesänsuo , however, contradict the concave
plot predicted for age against depth by Clymo 's
mode l of peat growth.
DISCUSSION
Palaeohydrology
The dry hydroseral stage which commenced
in the Eriophorum vag inatum pine bog phase
(TR) was interrupted by a short moi st phase
after about 6800 years BP (Fig. 12) . During the
transition of mire site types (TR/LkN) both in
A 300-a and A 0 an abrupt change from highly
humified to slightly humified peat took place .
In A 300-a a rise in the rate of vertica l height
increment and of apparent peat accumulation is
also observed. The charcoal finds from the
upper minerotrophic peat sections both in the
bog center and at the margin suggest that the
hydrological change was induced by forest
fires in the vicinity of the bog . In the previous
study of the Pesänsuo bog charcoal particles
and burnt plant remains were also found in the
section from the marginal slope, from the base
through to the top of Carex peat (Malm &
Rancken 1916) .
According to Lukkala (1933) a change in bog
hydrolo gy caused by peatland fire can greatly
accelerate peat accumulation. Tolonen ( 1987)
has also described the same phenomenon from
three raised bog s from the Salpausselkä region ,
where the formation of the black/light pe at
contact and the onset of ombrotrophication are
attributed to severe peatland fires, which changed the hyd rological and edaphical conditions in
the bogs. While moist conditions and a ri sing
water level pro vided better growth conditions
for Sphagnum there was a concomitant slowing
of decomposition which caused peat acc umulation to increase ( Tolonen 1987).
Changes at the center of the bog
According to the rhizopod and stratigraphic
data generally dry conditions or alternations of
dry and minor moi st phases prevailed at the end
of the minerotrophic phase and durin g the early
phases of ombrotrophication. A change in hydrolo gy from dry to moist conditions set in at
about 5700 yr BP (macrofos sil zone shift 4/5,
Appendix 2, Fig. I ). Within the transition to
sIightly humified Sphagnum fuscum peat, the
rate of peat increment and, to a greater extent,
the rate of apparent peat accumulaton, both
diminish.
Thi s decline when compared to the preceding
section can be explained by differences in the
bulk density va lues in corresponding peat section s. The higher growth rate in the preceding
Eriophorum-Sphagnum fuscum section coincides with the Calluna phase (macrofossil-zone
4) . In contrast, the proportion of dwarf shrubs
is greatly reduced in the slightly humified
Sphagnum fuscum peat, where the bulk density
va lues are also lower than in the EriophorumSphagnum sec tion.
The effect of water content, degree of humi fication and botanical composition of peat are
decisive factors in determining bulk density
(e .g . Päivänen 1969, Tolonen 1977, Tolonen &
Saarenmaa 1979 , Korpijaakko et al. 1981). In
the present case the differences in bulk den sity
can be principally explained by variations in
45
botanical composition and to a lesser exte nt by
the degree of humification in co rre spondin g
peat section s. Thi s conclusion is a lso s upported
by the C/N ratio, which is higher in the Eriophorum -Sp ha gnum section containing dwarf
shrub remains (Fig. 18).
No climatic factor to account for th e hydrolog ical change at 5700 yr BP can be detected ,
nor do pollen data indicate any apparent changes in vegeta tion . The increas e of Tilia a nd
Quercus and continuing presence of other deciduous trees indicate that the Holocene climatic optimum s till prevailed . The charcoal finds
at the bog margin suggest that a peneco ntemporaneous hydrological change observed there
was probably promoted by local fires . In the
bog center however, no charcoal was found.
The moist phase ended around 5300 years BP
and durin g the subsequent dry ph ase, which
persisted for about 750 14 C years, a more humified Eriophorum-Sphagnum fuscum peat layer
was formed, in which low values in the rate of
vertical peat increment and of apparent peat
accumulation are found.
A transition to a new moist regime at about
4600 yr BP coincides with a change in peat type
from Eriophorum-Sphagnum fuscum pe at with
dwarf s hrub remains to Scheuchze ria-Sphagnum cuspidatum-S. balticum pe at. The section
represents the first hollow-phase in the development of the bog. The rate of vertical peat
increment and apparent peat accumulation,
which in the hollow section remain s slow ,
greatly increases with the formation of s lightly
humified Sphagnum fuscum peat about 4400
years BP.
According to Clymo (1965, 1978 ) and Damman (1979) peat accumulation is controlled by
slow decomposition and not by high production. Sjörs ( 1990 referring to studies concerning the decomposition property of Sphagnum
species (Clymo 1965 and 1983, Glaser 1987 ,
Karunen & Ekman 1982 and Kälviäinen &
Karunen 1984), presents evidence that confirms the idea that more peat is formed under
hummocks, despite their lower primary Sphag-
PESÄNSUO
DEPTH H1_10
cm
5
50
A 300 a
.j>-
aC% OW 1
C/ N
20
60
100
140
48
52
F IBER%
ASH% DW
56
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0.2
0.6
1.0
1 .8
2.2
20
~~,
40
60
80
100
Cl
--
50
""r;.:=..
-/
100
150
"Ö0
100
(/]
::;
<:
"
'<
150
....,
0
.,
::!1
:J
2DO
200
250
250
:J
.0-
c:o
;=:J
v.>
--J
300
300
350
350
400
400
450
450
2.66
2.69
500
550
1
1
• ••
1
600
1
1
2.69
3.74
3.76
3.66
3.72
3.79
5.31
6.4
8.56
32.51
500
550
600
Fig. 18. Profiles for Pesänsuo bog, point A 300-a, of CIN ratio, carbon, nitrogen, ash and fiber content. Carbon and nitrogen conte nt has been calculated from organic material and ash
content from dry weight. Fiber column: values (mean ofthree determinations) of % fiber conlenl over 0.20 mm mesh (solid line) and % fiber contenl over 0.15 mm mesh (broken line) .
One standard deviation for Ihree delerminations shown with I-I. All data from unpublished results by K. Tolonen , University of Joensuu , Finland.
0
num production and bettel' aeration. The more
rapid decay of Sphagnum cuspidatum in hollows than of S. fuscum in the hummocks has
been demonstrated in studies on the Äkhu lt
mire, southern Sweden (Johnson et al. 1990,
Johnson & Damman 1991). The studies also
showed that " the decay of these two Sphagnum
species appears to be primarily species-regulated rather than controlled by microhabitat condition " (Johnson & Damman 1991). The results
of Rochefort et al. (1990) corroborate the conclusion drawn by Johnson and Damman.
The slower rate of peat accumulation in the
hollow layer in the Pesänsuo bog might thus be
due to differences in the primary decay properties of the Sphagnum species in question.
There are, however contrary results, which
show that the hummock species S. capillifolium
and the hollow species S. cuspidatum may decompose at comparable rates when litter is transpIanted into same the habitat (Clymo 1965).
An allogenic factor for hydrological change
and accelerated peat growth might be a climatic
shift towards cooler conditions after the Holoce ne climatic optimum. In cooler and wetter
conditions evapotranspiration decreases, resulting in a rise in mean water level. The rate
of decomposition decreases and the rate of
input to the catotelm increases (Clymo 1984).
According to Clymo a rise in the water table of
only a few centimeters can drastically reduce
the rate of decomposition (Clymo 1965). Low
degree of decomposition in this peat section is
also manifested by a high C/N ratio (Fig. 18).
There are several features, which reflect the
cooling of climate in Europe since 5000 years
BP. In northernmost Fennoscandia a decline in
the pine forest limit occurs at about 5000 yr BP
(Aario 1943, Hyvärinen 1975, Eronen 1979,
Eronen & Hyvärinen 1982). The advance of
spruce from eastern Fi nland at 5000 - 5500 yr
BP i also attributed mainly to changing climate , cooling and continentality (Aartolahti
1966, Tolonen 1983). In north-east Finland a
new acceleration of the paludi fication process
coincides with the beginning of climatic de-
47
terioration at about 4500 yr BP (Vasari 1962
and 1965).
The importance of a climatic effect on hydrological changes has , however, been questioned
by Foster and Wright Jr (1990), who interpret
results from bogs in central Sweden to indicate
that hydrological changes , which take place
when bog shape is altered (e.g. lateral expansion and vertical growth) are more significant
than the effects of precipitation/evaporation
ratios.
The moist phase was interrupted by a new
dry phase of short duration (ca. 300 14C years) ,
during which a thin more humified peat streak
was formed. Duri ng this period a decrease in
the rate of vertical peat increment and of apparent peat accumulation is observed.
The moist conditions were re-established at
about 3800 years BP and with this change a
futher significant increase in the rate of peat
increment and of apparent pe at accumulation
are witnessed . The high C/N ratio (Fig. 18)
confirms the low degree of decomposition. The
phase corresponds with the macrofossil zone 6
(see Appeddix 2 , Fig. I), where no Calluna
seeds are found.
In the upper part of this generally moist
phase, representing the period commenci ng at
3500 years BP growth rate slows down and the
C/N ratio is also reduced. Peat is mainly composed of S. fuscum and Eriophorum-S. fuscum,
where minute , highly humified streaks are
more densely concentrated. The streak formation probably represent a short-cyclic Sphagnum fuscum regeneration as described by Tolonen (1971 and 1980). The retardation of pe at
growth during the streak formation may thus
explain the lower rate figures found in this
section .
In the subsequent dry phase , the initiation of
which (ca. 2900 years BP) coincides within the
macrofossi I zone shift 6/7, the recovering of
Calluna and the appearance of Pinus sylvestris
seeds are witnessed. In this highly humified
Sphagnum fuscum peat section with dwarf
sh rub remains, the rate of vertical peat in cre-
48
me nt is very slow.
In the upper part of the profi le the most
recent moist phase, in which an abrubt fall in
humification is succeeded by an increase in the
rate of peat increment and of apparent peat
accumulation, began at 2580 years BP (710 cal
BC). A decrease in the rate of peat accumulation in the upper part is also witnessed here as
in the previous moist phase.
In the succeeding peat strata growth is very
slow and no increase in the rates of peat increment within humification change is detectable.
The change in humification and the shift towards a moist phase at a depth of 35 cm is
dated at 1530 years BP (cal AD 510) and the
top of the uppermost strongly humified layer at
a depth of 10 cm is dated at 620 years BP (cal
AD 1360).
In the short hummock monolith the moist
phases , representing the intervals 2550 - 1950
and 1500 - 1300 years BP respectively, probably correspond to those observed in the hollow core. Since 1300 years BP only dry conditions are recorded but frequent changes in the
humification of the peat strata also occur on the
hummock (Fig. 11). Two of them, the first
being dated at 1470 yr BP (cal AD 570) and the
second one to 560 yr BP (cal AD 1390) might
correlate with the uppermost humification
shifts in the hollow core.
The increase in Calluna and other dwarf
shrubs both in the hollow and hummock profiles since about 1300 yr BP, and the appearence of tyrphoxene rhizopod association in
A 300-b in the upper 20 centimetres indicate a
trend towards drier conditions in the bog .
Formation of hummock/hollow patterns
The date of 4600 yr BP for the first hollow
section is more than 1000 years older than the
previously obtained dates of 3200 yr BP and
2100 yr BP for hummock/hollow formation in
southwestern Finland (Aartolahti 1967). In
Finnish Karelia and Central Finland the corre-
sponding change in microrelief was initiated at
about 3500 - 2500 years BP (according to poIlen analysis , Tolonen 1987). In northern Finland the formation of strings in aapamires and
of hollows in the raised bogs were probably
synchronous with the initiation of palsas at
about 3100 yr BP and 4100 yr BP (Ruuhijärvi
1962 and 1963 , Oescher & Riesen 1965). According to Seppälä and Koutaniemi (1985) , the
initial formation of string-pool topography on
the Liippasuo aapamire in eastern Finland commenced at 3000 - 2000 years BP.
The formation of hummock/hollow topography has been attributed to a variety of causes
including climatic change, physical forces, or
biological processes controlled by local hydrology (see review in Seppälä & Koutaniemi
1985).
The climatic explanation assurnes that the
surplus of moisture required for the formation
of hummock/hollow and string/flark topography depends on a regional change in climate
(Aartolahti 1967 , Ruuhijärvi 1963) .
According to the biological hypothesis , pool
formation is interpreted as originating from the
gradual flooding of vegetated hollows, where
the local water table is controlled by regional
water balance and the authogenic development
of the mire , i.e. horizontal extension and vertical accumulation of peat (Foster et al. 1983,
Ingram 1983, Foster & Fritz 1987, Foster et al.
1988, Foster & Jacobson 1990, Foster & Wright
Jr 1990). In this authogenic process the hydrodynamic model of mire formation based on
groundwater mound equations is essential
(Clymo 1978, 1984 and Ingram 1982) . "As the
mire enlarges and deepens, changes in slope
(hydrological gradient) , peat thickness and peat
structure (hydraulic conductivity) may cause
local changes in the height of the water table
that initiates pools by altering production/decomposition and species composition" (Foster
& Jacobson 1990 p. 22).
According to Sjörs (1990) the initiation of
the hummock/hollow and stringlflark pattern
was regulated by the climate of preceding mil-
lenia and "presumably few patterns , if any ,
existed in the warm mid-postglacial period (before 5000 years BP) " . The initiation of the
patterns , however, was not simultaneous and
both climatic changes , forest fires and the increasing enlargement of the mire could also
influence the pattern formation (Sjörs 1990
referring to Foster & Fritz 1987 and Glaser
1987 ) .
Younger changes in peat humification
The beginning of the moist phase dated at
2580 yr BP (710 cal BC) might be correlated
with Weber's classical Grenzhorizont, Granlund' s RY III and also with the recurrence SUfface dated at 700 - 800 BC in Germany , England , Sweden and Denmark (Overbeck 1975 ,
Nil sson 1964, Bahnson 1968) .
The deterioration of climate, cooling and
increase in wetness around 2500 years BP is
evidenced in many way s in Europe . The most
marked change seems to have been from 1200
to 700 BC (Lamb 1977). Prevailing temperatures between 500 - 700 BC must have been
about 2°C lower than they had been half a millenium earlier and there was a marked increase
in wetness north of the Alps (Lamb 1977 , p.
373 ).
There is also a general correspondence between the change in humification and hydrological condition dated at cal AD 510 (hollow)
- cal AD 570 (hummock) and the general climatic alteration in Europe (Lamb 1977 , p. 374),
as weIl as the recurrence surface dated to AD
600 in northwestern Germany , Denmark and
Sweden (Overbeck 1975, Bahnson 1968 , Granlund 1932, Nilsson 1964) . A recurrence surface
a little younger than the one in Pesänsuo bog
has been detected in three raised bogs from
southern Finland and has been radiocarbon
dated in Laaviosuo at 1280±90 yr BP, in Kaurastensuo at about 1000 yr BP and in Varrassuo
at 1400± I 00 yr BP (Tolonen 1987). According
to Tolonen (1987) the contact may correspond
49
to the recurrence surface RY II found in Sweden
and in Germany and also to the phase shift to
wet lawn phase surface wetness curve for Bolton Fell Moss in Great Britain (Barber 1981) .
A recurrence surface of approximately the
same age as the last change in humification in
Pesänsuo bog, about 600 yr BP ( cal AD 1300)
has been described from Sweden and Germany
(Granlund 1932, Nils son 1964, Overbeck 1975).
In Bolton Fell Moss a shift from a dry hummock
to a wet lawn stage is dated at about AD 1300
(Barber 1981 ). In Europe there was a renewed
warming from about AD 800 onwards wh ich
culminated between AD 1100 - 1300 (Lamb
1977, p. 374).
While the alternation of dry/wet and unhumified/humified stages recorded by stratigraphieal, rhizopod and macrofossil evidence since
2600 years BP coincides approximately with
the known climatic trends and recurrence surfaces observed in Scandinavia and Europe, they
must still be regarded with a certain degree of
caution. First and foremost the lack of open peat
faces inhibits the evaluation of the lateral continuity of these distinct horizons as weil as the
extent of hummock/hollow formation. Furthermore, the indications of fire found within the
three uppermost highly humified peat section s
(Fig. 11) and the subsequent Picea declines in
A 300-a, charcoal finds in the uppermost 20 cm
in A 0 and burnt pollen in A 300-b, all suggest
the possibility of hydrological change caused
by local factors.
The lichenous residues and charcoal fragments found in the hollow core within the three
uppermost highly humified peat sections suggest, that the stratigraphical changes might
have been induced by local fires. Fire tends to
increase the cover of xerophytic lichens at the
expense of mesic bryophytes. As a consequence
of fire , wetter hollow-vegetation can spread to
lawn and also partly to hummock sites (Pakarinen 1974) . At Pesänsuo the development of the
vegetation after fire resembles the model found
in the higher hummocks in Canadian raised
bogs, where S. fuscum s ucceeds again after the
50
hepatic stage. According to Pakarinen (1974)
the model corresponds to the short-cycl ic regeneration described by Tolonen (1971). The
same phenomenon has also been described
from raised bogs in southeastern Labrador
(Foster & Glaser 1986) . According to these
authors, the death and replacement of Sphagnum cover on hummocks by lichens, followed
by re-expansion of Sphagnum, will produce a
" recurrence s urface" .
increase in humification in the upper peat section confirms the progression towards a drier
mire s ite type with a final stage , low -s hrub pine
bog at about 3000 yr BP. At the northeastern
margin a Scheuchzeria-hollow peat layer was
found (Fig. 4). The core in question , however,
has not been studied, and therefore the hydroseral development in this part of mire can not
be inferred.
Changes at the bog margin
Comparison of the bog center and the
margin
At the marginal slope of the bog the change
from dark to light peat, which is perceptible in
the open peat face at a depth of 1.8 m (F ig. 10) ,
coincides with the hydrological change dated at
5700 yr BP in the bog center. The black section
is composed of Eriophorum-Sphagnum pe at
with dwarf shrub remains , mostly of Andromeda (macrofossil zone 3, see Appendix 2, Fig. 2)
and the light peat above it consists of s lightly
humified Sphagnum fuscum peat (macrofossil
zone 4). The rate of vertical peat increment
increases in the light peat and at the same time
a change in mire site type (LkN/RaN) to a
Sphagnum fuscum bog occurs.
Charcoal particles and charred plant fragments found at depths of 175 - 220 cm (Fig. 11)
s uggest that the regeneration of Sphagnum
cover and the increase in peat growth was probably induced by local fires.
In the subsequent peat sections the erfect of
fire on the changes in the humification and on
the regeneration of Sphagnum cover is also
inferred . This applies to the levels at depths of
120 cm and 50 cm (Fig. 11 ), below which the
highly humified peat sections dated respectiveIy at 5100 - 4800 yr BP and 4300 - 3800 yr BP
were found to contain charcoal particles.
lt is difficult to deduce in greater detail the
hydrological conditions at the bog margin because there are no data concerning rhizopod
associations. In the peat strata, however, no
hollow or pool sections have been found. The
The very early alternations in the hydroseral
development of the mire prior to the true short
sedge fen phase (about 6800 years BP) coincides in both the center of the mire and at the
margin. Later changes detected in the bog center are difficult to correlate with the margin due
to the sparseness of date s and deficiency of
hydrological data in the latter. Th e Sphagnum
fuscum bog phase was reached in the center at
about 6400 years BP and at the margin at about
5600 years BP, which coincides with the dry/
moist shift in the center profile. Two strongly
decomposed layers dated at 5 100 - 4800 and
4300 - 3800 years BP could be, however, correlated with concomitant dry phases in the bog
center. The latest changes, if they indeed took
place at the margin, are not apparent in the
profile because the uppermost section of the
margin has been affected by secondary humifi cation and compaction due to peat cutting.
The difference in the hydroseral development between the center and the margin could
be explained by the difference in the water
table which, due to its slope , lies at a g reater
depth at the margin than at the bog center. In
raised bogs , the deeper water tables beneath the
margin are a consequence of the greater slope ,
the steeper hydraulic gradient and the more
rapid drainage in that part of bog. This concept
is also reflected in the distribution of vegetation (Ingram 1983).
According to the basal dates the mire forma-
tion eommeneed from the marginal area upslope towards the slightly domed bog center,
where peat aeeumulation was initiated about a
hundred years later. The present extent of the
mire was already reaehed in the early minerotrophie stage. Sinee then the mire has grown
mainly vertieally with a very limited lateral
extension. A slightly domed gross form was
already attained at about 5700 years BP (Fig.
3).
Likewise, aeeording to Aartolahti (1965) the
raised bogs with symmetrie shape and steep
marginal slope in southwestern Häme and
northern Satakunta have expanded very !ittle
horizontally and have retained the symmetrie
shape throughout their development. The nearly exelusive vertieal growth in mires gave rise
to better drainage eondition at the marginal
51
areas where peat growth was eorrespondingly
retarded due to drier eonditions.
A similar, very rapid lateral expansion of
mires has been doeumented on raised bog s in
southern eoastal area of Finland (Korhola
1992). Aeeording to Korhola terrain gradients
and small seale variations in topography have
been signifieant regulating faetors in the initial
development of the mires eoneerned. The lateral expansion took pI ace largely at a time when
the mires were still entirely minerotrophie . The
mires with f1at basal topography and no barriers to lateral expansion reaehed a steady state
in the lateral growth in the early phases of their
development e.g. in Munasuo an area of 560 ha
was paludified within a thousand radioearbon
years eommeneing at 4300 years BP.
CONCLUSION
I . The forest history in the Mellilä area eonforms with the general seheme outlined in previous studies from southwestern Finland. The
arrival of Ainus oeeurred at about 8200 years
BP and that of Picea about 3500 years BP.
2. Mire initiation took plaee as a result of
primary mire formation after the area emerged
from the Aneylus Lake of the Baltie basin at
about 8300 years BP. The paludifieation was
later promoted by forest fires . The centrally
domed clay bottom and the basal dates from
both the bog center and southeastern margin
suggest that peat formation might have eommeneed about 100 years earlier in the marginal
area. In the initial stages of development
Pesänsuo was a swampy sedge fen and the
vegetation of the mire eonsisted of meso-eutrophie and meso-oligotrophie sedges and
herbs . The meso-eutrophie speeies diminished
during the tall sedge fen phase at about 8000
years BP and edaphie impoverishment proeeeded with the inerease of the peat depth . The open
mire vegetation was replaeed by an Eriophorum vaginatum pine bog with a dominanee of
bireh trees at about 7500 years BP.
3. The oligotrophie stage in the nutrient status of the mire was attained at about 6800 years
BP, during which proeess the mire was converted to true short sedge fen, where an Andromeda
lawn was apredominant feature. In the bog
center the Sphagnumjuscum bog phase set in at
about 6400 years BP and at the margin about
5600 yr BP . In the bog center a change to a
wetter mire site type represented by Sphagnum
juscum bog with hollows set in at about 4600
yr BP. The age of the surfaee patterning is more
than 1000 years older than the previously published dates of 3200 yr BP and 2100 yr BP for
hummock/hollow formation in southwestern
Finland. At the margin Sphagnum juscum bog
was replaced by a drier mire site type, namely
dwarf shrub pine bog at about 3000 years BP.
4. Up until the true short sedge fen phase the
development of the mire vegetation proceeded
simultaneously both in the bog center and at the
margin. After that the development was no
Ion ger synchronous. The differenee in the development in the mire site types and in the
52
hydrology between the sites may be explained
by differences in the water table which , due to
the slope of the margin, lies deeper than on the
bog expanse. The development of the gross
morphology of the Pesänsuo raised bog and its
expansion and symmetrie shape were the results of its initiation on a level planar surface
without any obstructions or irregularities . The
transgression of the mire, however, has been
very slow, resulting in a distinctly domed gross
morphology and steep marginal slope. The
marginal parts have been drier than the bog
center since the early phases of bog development.
5. In the peat strata of the peat monolith from
the marginal slope as weil as in the peat monolith and the peat core from the bog center, intense fluctuations in humification were observed . In the hollow core it was possible to
associate the thicker highly humified layers
with dry phases in the bog development and the
interspersed slightly humified peat to moist
phases and, in most cases with slow and fastened rates of peat increment respectively as
weil. The change in humification could be related to local hydrological change caused by
fires in the bog center at levels dated at 6900,
5700, 2580, 1530 and 620 yr BP and at the
margin at the levels dated at 6830, 5660, 4800
and 3800 yr BP. In contrast, the formation of
the surface pattering at about 4600 yr BP and
the subsequent increase of pe at growth , in addition to the natural succession of the mire, all
suggest that the climatic control was probably
involved as weIl.
6. The highly humified thin streaks were
found in all the profiles studied. The streaks do
not extend uniformly through the bog and they
are more distinct at the margins than in the bog
center. In the hollow core thin streaks were
found in both dry and moist phases, the greatest
amount of which were concentrated in the generally moist phase dated at 3800 - 2800 years
BP. Within thin streaks dwarf shrub remains
and lichenous residues are present (the stratigraphical position of which is not quite certain
in all streaks), but no charcoal were found.
There is no record of Sphagnum species in the
streaks due to high humification , but the interlayer peat is mainly composed of slightly humified S. fuseum or Eriophorum -S. fuseum .
7. According to the data from the center of
the Pesänsuo bog, the rate of peat increment
was rapid between 7700 - 6050 years cal BP
(6900 - 5300 BP) , but slowed down between
6050 - 5000 years cal BP (5300 - 4400 BP).
Since 5000 years cal B P three phases (5000 4900, 4200 - 3800 and 2500 - 2400 years cal
BP) with very high rates of peat increment and
interspersing low rates have been recognised.
The phases of rapid growth are also verified on
a mass basis (i.e. cumulative mass verus age
curve). During the last two thousand years a
decreasing rate is evidenced. For the whole
peat sequence a rate of peat increment of 0.67
mm yr . I has been calculated. At marginal areas, however, the rate of peat increment has
been consistently much slower than in the cener.
8. The distribution and zonation of mires in
Finland are principally dependent on the climate, e.g. the differences in temperature and
humidity (Ruuhijärvi 1960, 1983; Eurola 1962;
Solantie 1974). Furthermore, within mire complexes variations in peatland vegetation and
microtopography occur due to differences in
temperature and length of the growing season
(north-south variation) as weil as in the degree
of oceanity (east-west variation). However, in
estimating the importance of climatic control in
the develoment of the individual mires the interpretation of the stratigraphie record requires
critical examination. There are a number of
processes, such as blocking of water outflow,
peatland drainage, fires, natural succession and
human activity leading to plant cover changes,
as weil as to the stratigraphical changes of
peats , which cannot be regarded as a consequence of climatic changes. The stratigraphical
and hydrological changes in the Pesänsuo
raised bog were more influenced by the natural
succession and local phenomena such as fires
than by the climatic factors.
53
ACKNOWLEDGEMENTS
This work was earried out at the Quaternary
Department of the Geologieal Survey of Finland. In partieular, I would like to thank the
head of the department, Professor Matti Saarnisto for his eontinuous interest, adviee and
eneouragement during the work. I also gratefu lly aeknowledge Assoeiate Professor Kimmo
Tolonen who kindly put his unpublished data
on earbon, nitrogen, ash and fiber determinations at my disposal and with whom I also had
inspiring diseussions on the topie. For improving the manuseript I express sineere gratitude
to Assoeiate Professor Pentti Alhonen and Professor Veli-Pekka Salonen for their val uab le
notes and suggested amendme nts.
I am greatly indebted to my eolleagues Dr.
Tuulikki Grönlund for the diatom analysis,
Tuovi Kankainen for many useful diseussions
on radioearbon data and Carl-Göran Sten for
the field work and the stratigraphie and maerofossil data he kindly put at my disposal.
Many other members of the Geologieal Survey helped me with various ways. Sirkka Lojander and Boris Saltikoff advised me in data
handling, the diagrams and figures were earefully prepared for publieation by Satu Moberg ,
Liisa Vuorela patiently provided me numerous
papers and books for review and referenee and
Dr. Peter Sorjonen- Ward eorreeted the English
of the text. The English of Appendix 1 was
eorreeted by Gillian Häkli.
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Ap pe ndix 1
Geolog ical Survey of Fin land, Bulletin 370
Appendix 1: Radiocarbon analyses of Pesänsuo, a raised bog in southwestern Finland
by
Tu ov i K a nk a in e n
Introduction
The stud y site
Before th e introdu cti o n of the radi oearbo n
me th od , p alyno logieal reeord s were used as a
e hro nos tratig rap hie g ui de. Eve n today, Qu ate rnary researc h uses th e 14C me th od most ofte n
for da tin g stratigra phie e ha nges o bserved in
sedi me nt strata or vegetatio na l e ha nges fo un d
in pa lyno log iea l in vestigatio ns. Peat g rowth
rates are ge nerally eale ul ated from a few 14C
ages o bta ined from leve ls defined by po ll en
analysis. Variations in growth rates eaused by
loeal faetors or c1imatie e hanges may then go
unnotieed, and 14C ages obtained from a peat
profile with irreg ul ar growth may even be regarded as erroneous.
To my knowledge, there are no reports of any
peat profile so exhaustively dated as the
Pesänsuo bog, whieh has been submitted to 211
14C determinations. Two other peat deposits at
whieh single seetions have been fairly thoroughly dated are Draved Mose, Denmark (Aaby
& Tauber 1975) and Ageröds mosse, Sweden
(Nilsson 1964), with 55 and 33 14C dates, respeetively. The eurrent dating projeet serves as
a basis on whieh to interpret the stratigraphie
data eolleeted from the Pesänsuo raised bog
(Ikonen, this volume) . So me of the 14C determinations were made to resolve sources of error
in dating peat and to verify the reliability of the
dating results. This paper also diseusses the
reliability oF the resuIts of some earlier studies
on peat growth.
The 14C analyses were made at the radioearbon laboratory of the Geologieal Survey of
Finland in 1972-1976 under the direetion of the
late Aulis Heikkinen. As his sueeessor, I was
eommissioned to re port the results of the dating
projeet.
The Pesäns uo raised bog is sit uated in th e
muni eipa lity of M e llil ä, south wes te rn F inl a nd
(60 0 46.2'N, 22°56.7'E, 87 m asl), in th e zo ne of
eonee ntri e ra ised bogs. The bog li es on a sligh tIy do med e lay bo ttom w ith its hig hes t point in
the centre. Pesänsuo is a ty pieal ra ised bog, yet
th e ma rg in a l s lo pe is exeeptio nall y steep beeause the lagg s urro un d in g it has bee n c1eared
fo r eultivation. T he presen t area of the bog is
about 18 heeta res. Ikonen (this vo lume) has
given a detai led deseription of the Pesänsuo
bog a nd of the geo logy a nd vegetation of the
Me ll ilä area .
Ma t eri a l a nd meth ods
Sampling methods
The sampies for 14C analyses were taken
from point A 0 at the southeastern end of the
main transeet A at the bog margin, and from
points A 300-a and 300-b in the bog centre, at
a distanee of 300 m from point A 0 along the
main transeet (see Fig. I in Ikonen, this volurne). The sampies were taken by C-G .Sten and
A. Heikkinen in 1972 - 1975.
The only plaee at whieh the stratigraphy of
the peat deposit ean be reeorded reliably is an
open peat face; this is also the best site for
taking sampies for 14C dating. At point A 0,
peat was removed with an exeavator to expose
a :l.5-m-high open face , whieh was eleaned
with aspade and a knife. A peat monolith was
taken for miero- and maerofossil analyscs with
six 60x I Ox5-em boxes. The sampies for 14C
measurements were taken with a knife from the
2
side of this peat monolith. The sampies, 13 in
all, were taken from levels showing a change in
humification in the peat profile (sampie thickness 2 to 5 cm). Two sampies of wood found
in the peat face were also collected for dating.
At point A 300-a (a hOllow), the sampies
were taken with a piston sam pier 8 cm in diameter and 60 cm long. The middlemost 40 cm of
each core was used in investigations. Two parallel peat profiles were taken , one of which was
used for microfossil analyses and 14C dating
and the other for macrofossil analyses. 14C
dating was carried out on a contiguous series of
sampies 5 cm thick. The whole profile totalled
123 14C sam pies, from which I 19 ages were
obtained.
At point A 300-b (a hummock) , at a distance
of 5 m from point A 300-a, the sampies were
taken with aspade and a knife from an open pit
1.5 m deep. A peat monolith was extracted for
microfossil studies and 14C dating. All in all, 19
contiguous 14C sam pies were taken from the
surface to 90 cm depth. The sam pies were 3 cm
thick near the surface and 5 cm deeper down.
Laboratory methods
Before chemical pretreatment, the sam pie
were cleaned of all visible roots. The sampies
from A 0 and A 300-b were homogenized and
divided in two for separate pretreatment and
dating.
The pretreatment methods were compared
and evaluated by dating the sampies from point
A 0 on three different fractions: total organic
matter, humin and humic acids . The contiguous
sequence of sampies from point A 300-a was
dated on the humin fraction. The sam pies from
A 300-b were first dated on the humin fraction
and later, to assess the reliability of the dating
results of the laboratory, on both the humin and
humic acid fractions.
The total organic matter (TO) of peat was
pretreated by boiling apart of each sampie in
4 % HCI and washing it with distilled water to
Appendix I
pH 4-5. The humin (HU) and humic acid (HA)
fractions were extracted by keeping the other
part of each sampie in hot 2 % NaOH for five
minutes and centrifuging it. This was repeated
foul' times. The alkali insoluble part of the
sampie (HU) was then heated in 4 % HCI and
washed with distilled water to pH 4-5. The
centrifuged liquid, i.e. the alkali soluble fraction (HA), was precipitated by adding concentrated HCI to the alkali ne solution and heating
it to boiling point. The precipitate was washed
with distilled water to pH 4-5. One wood sampie , birch (Su -245) , was subjected to the same
pretreatment procedure as the TO fraction of
peat, and the other, juniper (Su-248), to the
pretreatment procedure of the HU fraction.
The measuring technique used was proportional counting of CO z as described by Heikkinen et al. (1974).
The Ö13 C values for all the sampies from A
o and for a few of those from A 300-a and 300b were measured by Or R. Ryhage , Karolinska
Tnstitutet, Stockholm. Only the 14C ages for the
sampies from point A 0 were corrected for
isotopic fractionation. The Ö13 C values obtained for the remaining sampies were too few
in number and showed too much variations for
isotopic fractionation to be estimated reliably.
Tf only the samples with measured Ö 13C values
had been corrected for isotopic fractionation ,
the resulting 14C ages would have been unequal.
Calibration of the 14C ages
The 14C ages were converted to calendar
years , for calculation of the rate of peat increment and the cumulative mass versus age. With
the exception of the oldest sam pies, the calibration was done with a computer program devised
by Stuiver & Reimer (1986) which is based on
the calibration curves and tables in the Calibration Issue of Radiocarbon (Stuiver & Kra
1986) . The program allows several 14C ages to
be averaged on sampies from the same period
Appendix I
of time and the detailed calibration curve to be
smoothed. For material representing many
years, such as peat, the detailed calibration
curve must be smoothed to an extent commensurate with the sampIe age span (Mook 1983,
also Kankainen 1992 and references therein).
Only the 14 C ages obtained for the humin fractions of the peat sampies in the Pesänsuo bog
were calibrated. The time-widths of the sampies were estimated roughly from the 14 C age
versus depth diagram; time-widths of 20 , 40,
60, 80 etc., years are accepted for smoothing by
the computer program used. The ages at point
A 300-b were calibrated by averaging the two
ages obtained for the humin fraction of one
sampie .
The accurate calibration curve of the 14 C ages
and the record of the computer program (Stuiver & Reimer 1986) extend to about 8200 14 C
yr BP. In this study the ages are computer
calibrated near the finite limit of the program,
at which point only the most probable date can
be obtained. Dates calibrated beyond this limit
are estimates. They are read from 14C age cali bration curves, which, although floating , are
cross -dated accurately enough to permit their
use for calibration (Kromer et al. 1986, Becker
etal. 1991).
Results
All the 14C ages and calibrated dates are listed
in Tables I - 3. The ages versus depth of the
wood sampIes and of the humin fraction of the
peat and gyttja sampies are shown in Figs. 1 3. The ages of HU fractions of peat are used in
the study of Ikonen (this volume). Peat types at
the levels dated are shown in the lithology
column of the diagrams by Ikonen (this volume,
ego Fig. 5).
At A 0, the gyttja and the peat sampIes (Table
1, Fig. I) were dated on TO, HU and HA fractions. TO is made up of HU and HA. The age
Geological Survey of Finland. Bulletin 370
3
differences between the three fractions of one
peat sampie are generally within statistical errors. Only the difference of 170 years between
the HU and HA fractions at a depth of 0.800.85 m is outside the 95% (2a) confidence
interval. On an average, HA is 53 years and TO
9 years younger than HU. The age difference
between TO and HU is smalI , because the
abundance of humin in the sampies was generally many times higher than that of humic acid.
The ages of the pieces of wood (Su-245 and Su248) are also consistent with the age of peat at
the same levels. The juniper (Su-248) may
have al ready been growing before the mire was
formed. According to the age of the lowermost
peat sam pIe peat began to form at about 8300
years BP. The ages of the HU and HA fractions
of the 2-cm-thick gyttja layer beneath the peat
differ from each other by 260 years, which
indicates that the sam pIe was contaminated by
older allochthonous organic material. The ages
are therefore unreliable. Peat cutting has
caused compaction and humification in the
uppermost section of the bog margin; hence the
high age of the uppermost sampIe of A 0 (0.200.23 m depth).
The 14C ages, the curve of moving averages
of five subsequent 14 C ages , and the curve of
moving averages of five subsequent calibrated
dates from point A 300-a are shown in Fig. 2.
The sampies were taken from this point with a
piston sampier. With this method great care
must be exercised to ensure that the core segments are exactly successive. There is no indication of any inaccuracy in the sampling
depths, as this would have been reflected in
higher variations in 14C ages at the ends of the
core segments (see Table 2, Fig. 2); the wiggles in the curve of age versus depth are real.
At A 300-b (Table 3 , Fig. 3) the sampies
were dated twice on ffaction HU and once on
fraction HA. All tpe differences between the
two HU ages are within the 95 % confidence
interval, and the differences between HU and
HA ages are as expected; at two depths (0.70-
Appendix 1
4
PESÄNSUO AO
Marginal sect ion
00r -__.-~'~OrOO~-.__~2~00~0~-.__~3~00~0~-.__~'~00~0__- .__~
50~0~0__- r__~60~0~0__- r__~70~0~0__, ,__~
80~0~0__. -__9~0~0~
0 __,
E
-+-
2
I
l-
n.
lJJ
o
-+-
WOOD
-+-
-+-
--
WDOD
RADIOCARBON AGE (years BPI
'000
2000
3000
.000
5000
6000
7000
8000
9000
Fig. I. Pesänsuo, marginal section A O. Conventional I4C ages versus depth for the humin fract ions of peat and gyttja and for wood
sampies.
0.75 m a nd 0.85-0.90 m) the difference is
larger than 20. Yet there is a tendency for HA
to be yo un ger th a n HU, the ave rage age differe nce bei ng 62 years.
The 14C activity of the A 300-b samp Ies from
the surface to 0.15 cm depth is higher th an that
of the modern standard, which shows that the
roots of modern vegetation reach a depth of at
least 0.15 m. Should these modern roots have
affected the 14C ages of deeper levels , the ages
of humin would be younger than those of humic
acid, because modern roots penetrating to deep er levels are less humified than the peat at those
levels. In fact, humin is you nger than humic
acid at a depth of 0.15-0.20 m, but not deeper.
Discussion
Reliability of radiocarbon dating of the
Pesänsuo bog
The reliability of 14C ages can be impaired by
careless sampling, unsuitable samp Ie. , imprecise and inaccurate dating results , or environ-
mental or natural processes. Distortions of age
ca used by nature are tried to avoid by dating th e
least contaminated f ract io n of the sam pI e.
Roots penetrating dow n to older leve ls a nd
water-so lubl e decomposition products of peatforming plants (humic and fulvic acids) are the
most obvious natura l sources of errors in the
14C ages of peaL
Comparison of the ages obtained from Pesänsuo showed that the sampIes were taken carefully. Most of them are also thin enough in
relation to the confidence intervals of the ages.
A sampIe with a thickness, say, 10 to 15 cm
might represent a growth of up to 500 years. lf
there were a lso big differences in humification
between the upper and lower parts of the sampIe , it would be difficult to infer which part of
the sam pIe the 14C age refers to; moreover, the
difference in age between the humin and humic
acid fractions would probably be considerable.
The assessment of the carefu ln ess of pretreatment and of the precision of dating results
was included in the dating project at Pesänsuo
bog. Such an assessment cannot , however,
PESÄNSUO A 300-0
Centrol core
DEPTH
(mi ,_---,--~
10TO~0--_,--~2~OrOO~--r_--3~OTO~0--_,--~4~OrOO~--._--5~OTO~0---.__~6~
00~0~--,_--7~OTO~
0 --_,---80,0-0----,_--9-0,00 --_, 0
~
CALIBRATED DATE (yeors col BP)
2
<l---
CALIBRATED DATES
3
RADIOCARBON
Cl
"ö0
(JQ
(S.
~
C/J
:;
<
"
'<
5
s.,
::01
\
I
;.;'"
'"
.P-
,
I;C
t:
\
I
6
I
RADIOCARBON AGE (yeors BP)
;
'"
VJ
-..J
o
1000
0
2000
3000
4000
5000
6000
7000
8000
9000
Fig. 2. Pesänsuo, cen tral hol low core A 300-a. Conventional " C ages versus depth for the humin fractions of contiguous series of peat sam pies. Curves ofthe moving averages
of five subseq uent " C ages and of the moving averages of li ve subsequent calibraled dates. The dashed line in the last-ment ioned curve shows the inlerval al which the
calibral ion is not cerla in , i.e. al deplhs of 0.45-0.90 m, from which no 14C ages are ava ilable, and from the base up to a depth of 5.50 m, from wh ich lhe ages are 100 old for
definite calibrati on. Core segments usecl in daling are marked in side lhe de plh co lu mn.
DEPTH m
DEPTH m
o
o
0 .2
0.2
0 .4
0.4
0 .6
0 .6
0 .6
0 .8
o
500
1000
1500
2000
2500
o
3000
500
CONVENTIONAL 14C AGES VR BP
DEPTH
1000
1500
2000
2500
3000
m
DEPTH
m
0
0
0.2
0 .2
0.4
0 .4
0 .6
0 .6
0.8
0 .8
;J>
'0
'0
('0
o
500
1000
1500
2000
2500
CONVENTIONAL 14C AGES VR BP
3000
o
:::I
500
1000
1500
2000
2500
3000
Fig. 3. Pesänsuo, central hummock monolith A 300-a. Conventional 14C ages (above,left) and ca librated dates (above, right) versus depth for the averages ofthe two humin fractions dated .
Lower diagrams show the curves of the moving averages of five subsequent conventional 14C ages (Ieft) and calibrated dates (right).
"><
Appendix I
show whether the results of the laboratory are
biased. This would mean that the results, no
matter how precise, are not necessarily accurate . The radiocarbon laboratory of the Geological Survey of Finland has taken part in several
international comparisons between radiocarbon
laboratories (International Study Group 1982,
Scott et al. 1990, Rozanski et al. 1992) , always
with good results . The measuring equipment
for the first of these comparisons (International
Study Group 1982) was the same as that used
to measure the Pesänsuo bog sampies; the same
people were also responsible for the pretreatment, burning and purification of the sampIes
for dating and for measuring the sampIe activities . Hence there is good reason to regard the
Pesänsuo ages as not only precise, as shown by
the confidence intervals, but also accurate.
The slight difference in the ages of the three
fractions dated on one sampIe is attributed to
mobile humic acids , rather than roots. Roots
penetrating deep in the peat strata are less
decomposed than the original organic matter at
this depth. Thus they would make the age of
humin younger than that of humic acids.
The number of 14C ages needed depends on
the frequency of the variations observed in the
peat strata to be dated and on the accuracy of
the 14C analyses. For example, the variations in
peat growth between the depths of 1.50 m and
2.90 m at point A 300-a in the Pesänsuo bog are
so great and so abrupt that they can only be
dated with sampIe intervals of 10 to 20 cm,
depending on the accuracy of the dating results.
In contrast, between depths of 3.30 m and 5.00
m the growth rate was so stable that a 0.5-metre
sampIe interval might have been enough, assuming that the dating results are sufficiently
accurate.
The same dating accuracy is obtained for the
14C age of a sampIe with one date if the standard
deviation is ± 50 years, with two dates if the
standard deviation is ± 70 years or with four
dates ifit is ± 100 years!
3
7
Comments on earlier studies of peat growth
14C ages obtained for peat are not always as
expected, and as a result the dati ng results are
often regarded as erroneous. Sometimes the
whole 14C dating method is, without any proof,
assumed to be more imprecise than the error
estimates of the ages would warrant. It is true
that many laboratories underestimate their errors and that the dating results are often biased
by 50 to 250 years, as shown by the intercomparisons of radiocarbon laboratories (International Study Group 1982, Scott et al. 1990,
Rozanski et al. 1992). But the vertical spread
of the dating results of some studies is so great
that they cannot be explained simply by vagueness in dating. For example the 14C ages obtained for Nälköönsuo, Haukkasuo and Varrassuo (Tolonen & Ruuhijärvi 1976) show
considerable unexplained variations. In these
cases, two to fi ve laboratories ha ve been involved in dating one peat strata, and the sampIes are from two or more corings performed at
different ti meso Donner et al. (1978) have obtained 23 dates for one peat profi le at Varrassuo . For this bog all the dates are from one
laboratory , which is al so seen in the smaller
fluctuations in the dates .
If the dating method is taken as the "scapegoat" , the other reasons for suspected errors ,
e.g. careless sampling, may have been passed
over. In the interpretation of the results, too
many ages have been omitted because they are
superfluous or of suspect validity , or because
they differ from the general curve to such an
extent that they are manifestly too old or too
young ; that way so me information on the
changes in peat growth may have been lost.
The results of many previous studies on peat
growth should be regarded with caution, and at
least the half-life basis and possible calibration
of the 14C ages should be verified. Many researchers (e.g. Overbeck 1975 , Tolonen et al.
1985) have used conventional 14C ages (based
on the " Libby half-life", 5568±30 yr) in their
8
calculations. Others (e.g. Nilsson 1964) have
multiplied the conventional ages by 1.03 for the
correction of half-life (to "new half-life" ,
5730±40 yr), and yet others (e.g. Aaby & Tauber 1974, Aaby 1976) have calibrated the ages,
as was done also in the Pesänsuo study. It
should go without saying that if calibration is
used, all data must be calibrated.
Errors arise easily, particularly when published data are used. Clymo (1984) regarded the
14C ages of Tolonen (1977, 1979) and Donner
et al. (1978) as calibrated, though in fact they
are either conventional 14C ages (Donner et al.
1978, Varrassuo; Tolonen 1979, Laaviosuo) or
partly based on ages obtained by "calibrating"
the estimated radiocarbon ages of pollen zones
(Tolonen 1977, Kaurastensuo). Overbeck
(1975, p. 386) refers to the usage of conventional 14C ages throughout the book. Yet his
work contains ages publi s hed by Nilsson
(1964), "corrected" by factor 1.03 , which was
also used in the calculation of peat growth.
ConcIusion
The peat strata of the Pesänsuo bog have
been dated so reliably that the res ults can be
used to calculate a peat growth rate (Ikonen ,
this volume), to estimate the effect of different
so urces of error in the 14C dating of peat, and
to compare earlier studies of a s imilar nature .
Detailed knowledge of the ages of all the
peat strata is aprerequisite for detecting variations in peat growth. Inaccurate 14C ages of
sa mpies representing several centuries ' growth
may conceal abrupt changes in the rates of peat
increment.
Dating has frequently been a weak point in
ea rlier studies of peat growth, with conclusions
being based on too few ages of too thick sampies. Calibration of the radiocarbon time-scale
ha s also caused problems and errors , and these,
too, are reflected in the calculated growth rates.
Appendix I
The growth rates of bogs reported in different
publications should not be compared with each
other before the time-scale used in the calculations has been established.
It is often claimed that Accelerator Mass
Spectrometry (AMS) dates would help solve
the problems encountered in dating peat (see
e.g. Tolonen et al. 1992, p. 321). However, peat
is a chemically heterogeneous material comprising original, more or less decomposed plant
constituents and microbial biomas s. For the
best dating results for peat, it would be advisable to da te thin slices in a conventional highprecision laboratory known to produce accurate
results . At present, the high-precision conventional laboratories are superior in dating accuracy to AMS laboratories. In calibration, the
accuracy of a dating result is as importa nt as the
time interval the sampie represents.
References
Aaby, B., 1976. Cyclic c limati c variations in c limate
over the past 5,500 yr reflected in raised bogs.
Nature 263, 281-284.
Aaby, B. & Tauber, H., 1975. Rates of peat formation in relation to degree of humification and loca l
environment, as shown by studies of a raised bog
in Denmark. Boreas 4, 1-17.
Becker, B., Kromer, B. & Trimborn, P., 1991. A
stable-isotope tree-ring timescale of the Late Glaciall Hol ocene boundary. Nature 353 , 647-649.
Clymo, R.S., 1984. The limits to peat bog growth .
Philosophical Transactions of Royal Society London B 303 , 605-654.
Donner, J.J. , Alhonen, P., Eronen, M., Jungner, H.
& Vuorela, 1.,1978. Biostratigraphy and radiocarbon dating of the Ho locen e lak e sediments of
Työtjärvi and the peats in the adjoining bog Varrassuo west of Lahti in southern Finland. Annales
Botanici Fennici 15, 258-280.
Heikkinen, A., Koivisto, A.-K. & Äikää, 0.,
1974. Geological Survey of Finland radiocarbon
measurements VI. Radiocarbon 16 , 252-268.
International Study Group, 1982. An inter-Iaboratory comparison of radiocarbon measurements in
tree rings. Nature 298, 619-623.
Kankainen, T., 1992. Pitfalls in the calibration of
Appendix I
radiocarbon ages. Laborativ Arkeologi 6, 7-10.
Kromer, B., Rhein, M., Bruns, M., SchochFischer, H., Münnich, K.O ., Stuiver, M. & Becker, B., 1986. Radiocarbon Calibration Data for the
6th to the 8th Millenia BC. Radiocarbon 28 (2B),
954-960.
Mook, W.G., 1983. J4C calibration curves depending
on sampie time-width. PACT 8, 517-525.
Nilsson, T., 1964. Standardpollendiagramme und
C' 4-datierungen aus dem Ageröds mosse im mittleren Schonen. Lunds Universitets Ärsskrift. N.F.
Avd.2. Bd. 59 (7) , I-52.
Overbeck, F., 1975. Botanisch-geologische Moorkunde. Neumünster: Karl Wachhotz Verlag, 719 p.
Rozanski, K ., Stichler, W., Gonfiantini, R. , Scott,
E.M., Beukens, R.P., Kromer, B. & van der Plicht, J., 1992. The IAEA '4C Intercomparison Exercise 1990. Radiocarbon 34 (3), 506 - 519.
Scott, M.E., Long, A. & Kra, R. (eds), 1990. Proc.
International Workshop on Intercomparison of Radiocarbon Laboratories. Radiocarbon 32 (3) , 167263.
Stuiver, M. & Kra, R. (eds.), 1986. Internat. " c
Conf. , 12th, Proc.: Radiocarbon 28 , No . 2B , Calibration Issue.
Stuiver, M. & Reimer, P.J., 1986. A Computer Pro-
9
gram for Radiocarbon Age Calibration. Radiocarbon 28 (2B), 1022-1030.
Tolonen, K. , 1977. Turvekertymistä ja turpeen tilavu uspainoista kolmessa etelä-suomalaisessa keidassuossa. Summary: On dry matter accumulation
and bulk density values in three south Finnish
raised bogs. Suo 28, 1-8.
Tolonen, K., 1979. Peat as a renewable resource:
long-term accumu lation rates in north European
mires. In: Classi fication of peat and peatlands , proceedings of International Symposium , Hyytiälä.
Helsinki: International Peat Society,.286-296
Tolonen, K., Huttunen, P. & Jungner, H., 1985.
Regeneration of two coastal raised bogs in eastern
North America . Annales Academiae Scientiarum
Fennicae Ser A III , 139. 51 p.
Tolonen, K. & Ruuhijärvi, R. , 1976. Standard poIlen diagrams from the Salpausselkä region of
Southern Finland. Annales Botanici Fennici 13 ,
155-196.
Tolonen, K., Vasander, H., Damman, A.W.H. &
Clymo, R.S., 1992. Rate of apparent and true carbon accumulation in boreal peatlands. In: Proceedings of the 9th International Peat Congress, Uppsala, Sweden, June 22 - 26, 1992, Vol. I. Uppsala:
The Swedish National Committee. 319-333 .
10
Appendix I
Table I. Pesänsuo, marginal section A 0 , 14C dating results. The calibrated date range is given with la (68 %)
probabi Ii ty.
Fractions: TO=total organic matter , HU=humin, HA=humic acids.
Su110.
Sampie,
fraclion
(yr)
Timewidth
Sampling
depth (m)
(m)
8 13 C
14C age
(%0)
(yr BP)
-27.1
-24.4
-27.4
Ca!. date
range (yr
ca!. BP)
Most prob.
dale (yr
ca!. BP)
2990± 70
3100±120
2940±110
3460-3200
3355
-26.2
-26.1
-27.9
3830± 70
3870± 60
3840± 60
4420-4230
4315
-25.0
-24.0
-28.2
4330± 90
4370± 50
4200± 50
5000-4870
4960 .. .4890
-24.2
-25.5
-26.2
4890± 70
4800± 70
4780± 70
5630-5470
5580
-23 .3
-25 .0
-24.1
5100± 80
5100± 70
5150±100
5950-5760
5905
-25.1
-24.7
-25.2
5640± 80
5660± 80
5660± 60
6560-6360
6455
-26.9
-23.9
-26.0
6940± 80
6830± 90
6900± 90
7720-7570
7625
2.50
-27.8
74 10± 80
2.55 -2.60
-25.4
-26 . 1
-27 .3
7300± 80
7480± 80
7320± 70
8380-8140
8325 ... 8225
-25.1
-26.4
-27.6
8030± 80
8010± 80
7930± 70
238
267
268
Peat , TO
" , HU
" , HA
60
0.20-0.23
239
269
270
Peal , TO
" , HU
" , HA
100
240
271
272
Peal , TO
" , HU
" , HA
40
241
273
274
Peat, TO
" , HU
" , HA
100
242
275
276
Peal , TO
" , HU
" , HA
100
243
277
278
Peal , TO
" , HU
" , HA
100
244
309
310
Peal, TO
" , HU
" , HA
100
245
Birch, TO
246
281
282
Peal, TO
" , HU
" , HA
100
247
283
284
Peal, TO
" , HU
" , HA
60
248
Juniper , HU
3.05-3.10
-24.5
8420± 80
249
285
286
Peal , TO
" , HU
" , HA
3.14-3.18
-33.6
-28.4
-26.6
8370± 80
8290± 60
8260±100
250
287
288
Gyltja, TO
HU
" , HA
3.18 -3.20
-34.2
-29.0
-29 .0
8480± 80
8740± 80
8420± 80
0.55-0.60
0.80-0.82
1.15-1.20
1.22-1.27
1.74-1.79
2.30-2.35
2.87-2.90
* Calibration program (Stuiver & Reimer 1986) gives only lhe mosl probable date.
** Calibraled dale is an estimate as read from Fig. I in Becker el a!. (1991).
8985*
9200 **
Appendix I
I1
Table 2. Pesänsuo, central core A 300 -a (hollow), 14C dating results. The calibrated date range is given with la
(68 %) probability. The core segments used in dating are marked by blank spaces.
Su no.
473
472
471
470
469
468
467
466
465
464
463
462
461
460
459
458
457
456
455
454
453
452
451
450
449
448
447
446
445
444
443
442
Sam pie,
fraction
Peat, HU
Peat, HU
Timewidth
(yr)
200
Peat , HU
40
Peat , HU
40
Peat, HU
100
Peat, HU
40
Sampling
depth
(m)
0.00-0.05
0.05-0. I 0
0-0.15
0 .1 5-0.20
0 .20-0.25
0.25-0 .30
0.30-0 .35
0 .35 -0.40
0.40-0.45
0.45-0.50
0.50-0.55
0.55-0.60
0.60-0.65
0.65-0.70
0.70-0 .75
0.75-0 .80
0 .80-0.85
0.85-0.90
0.90-0 .95
0.95-1.00
1.00- 1.05
1.05 - 1.10
1.10-1.15
1.15-1.20
1.20-1.25
1.25- 1.30
1.30-1.35
1.35-1.40
1.40-1.45
1.45-1.50
1.50-1.55
1.55-1.60
427
426
425
424
423
422
421
420
1.60-1.65
1.65-1.70
1.70-1.75
1.75-1.80
1.80-1.85
1.85 - 1.90
1.90-1.95
1.95-2.00
419
418
417
2.00-2 .05
2.05-2. 10
2 .1 0-2.15
ö 13 C
14C age
( %0 )
(yr BP)
Ca!. date
range (yr
ca!. BP)
Most prob.
date (yr
ca!. BP)
>Modern
140± 60
705± 70
1020± 70
1280± 70
1400± 80
1520±110
1750± 80
250-modern
720- 610
1010- 870
1290-1120
1380-1250
1540-1330
1780-1580
140 ... modern
680
955
1210
1325
1410
1665
1710±110
2050± 60
1760-1500
2100-1950
1620
2020
-23.7
2410±120
2520±120
2460±120
2730-2340
2770-2370
2750-2360
2380
2725
2495
-24 .9
2390±
2400±
2540±
2750±
2860±
2900±
2950±
70
70
SO
60
60
60
90
2500-2340
2700-2350
2750-2700
2910-2790
3070-2890
3160-2950
3270-2970
2370
2375
2730
2850
2980
3030
3135
3110±100
3250± 60
3280± 60
3290±100
3340± 90
3420± 60
3540±100
3610± 90
3440-3230
3570-3410
3600-3450
3650-3410
3690-3480
3740-3620
3980-3710
4080-3840
3360
3480
3500
3510
3595
3680
3850
3925
3550±110
3620± 70
3490±120
3650± 60
3710± 60
3610± 60
3740± 80
3740± 70
4000-3710
4080-3850
3920-3630
4090-3890
4160-3980
4000-3850
4250-3990
4240-4000
3855
3935
3820 ... 3750
3985
4090
3925
4105
4105
3800± 90
3760± 70
3780± 70
4370-4090
4260-4010
4280-4090
4220 .. .4180
4150 .. .4120
4165
-25.0
-22.2
-25.5
-25.8
-26.1
-25 .8
-26.0
-26.9
-25.7
12
Appendix I
Table 2 . cont.
Suno .
416
415
414
413
412
411
410
409
408
407
406
405
404
Sampie,
fraction
Timewidlh
(yr)
Samplin g
deplh
(m)
Peal, HU
Peat, HU
40
160
Peal , HU
40
2.15-2.20
2.20-2.25
2.25 -2.30
2.30-2.35
2.35-2.40
Peal, HU
80
2.40-2.45
2.45 -2.50
2.50-2.55
2.55-2.60
2.60-2.65
2 .65-2.70
2 .70-2.75
2.75-2.80
403
402
401
400
399
398
397
396
2 .80-2.85
2.85-2 .90
2.90-2 .95
2.95 -3.00
3.00-3.05
3.05-3 . 10
3.10-3.15
3. 15 -3 .20
376
375
374
373
372
37 1
370
369
3.20-3.25
3.25-3.30
3.30-3 .35
3.35-3.40
3.40-3.45
3.45-3.50
3.50-3 .55
3 .55-3 .60
Pea l, HU
60
368
367
366
365
364
363
362
361
3.60-3.65
3.65 -3.70
3.70-3 .75
3.75-3 .80
3 .80-3.85
3 .85-3 .90
3.90-3.95
3.95-4.00
360
359
358
357
356
4 .00-4 .05
4.05 -4.10
4.10-4.15
4.15-4.20
4.20-4.25
ö l3 C
14C age
(%0)
(yr BP)
-26.6
3790±
3970±
4110±
4390±
4320±
-26.3
-22 .3
-21 .3
-20 .0
-23.5
-24.4
-23 .8
-23 .6
-26.5
Ca!. date
range (yr
ca!. BP)
Mosl prob.
date (y r
ca!. BP)
70
80
70
80
70
4300-4090
4540-4340
4770-4520
5060-4870
4990-4840
4170
4455
4610
4985 .. .4915
4875
4380± 80
4350± 70
4340± 70
4410± 70
4360±120
4400 ± 70
4430±100
4350 ± 80
5060-4860
5000-4850
5000-4850
5230-4880
5230-4850
5060-4880
5280-4880
5020-4860
4970 .. .4900
4890
4885
4995
4 890
4990
5005
4895
4420 ±
4510±
4570±
4610±
4670±
4820±
4920±
4820±
70
80
90
90
70
90
90
60
5090-4890
5310-5010
5350-5070
5460-5170
5490-5310
5660-5470
5760-5600
5630-5490
5005
5255 .. . 5 I 10
5300
5320
5350
5595
5665
5595
5150± 90
5240± 90
5230± 90
5380± 90
5410±130
5380± 80
5410±130
5560± 90
5990-5790
6140-5930
6130-5930
6300-6030
6330-6020
6300-6030
6320-6010
6440-6290
5935
5980
5975
6210
6225
6210
6265 .. . 6215
6335
5470± 90
5610± 80
5630±100
5600± 90
5730±100
5860± 90
5660±100
5770±120
6340-6190
6480-6310
6540-6320
6480-6310
6690-6430
6800-6620
6620-6330
6740-6440
6295
6415
6430
6410
6540
6720
6450
6630
5780± 90
6010±100
5910±100
6100± 80
6080± 80
6730-6470
7010-6750
6870-6670
7160-6870
7150-6860
6635
6870
6750
7000
6955
Appendix I
13
Table 2. co nt.
Suno.
355
354
353
Sampie ,
fraction
Peat, HU
Timewidth
(yr)
Sampling
depth
(m)
ö 13 C
14C age
(%0)
60
4.25-4.30
4.30-4.35
4.35-4.40
-23.2
352
351
350
349
348
347
346
345
4.40-4.45
4.45-4.50
4.50-4.55
4 .55-4.60
4 .60-4.65
4 .65-4.70
4.70-4.75
4 .75-4.80
344
343
342
341
340
339
338
337
4.80-4.85
4.85-4.90
4.90-4.95
4.95-5.00
5.00-5.05
5.05 -5 . 10
5.10-5 . 15
5.15-5 .20
336
335
334
333
332
331
330
329
5.20-5.25
5.25 -5 .30
5.30-5 .35
5.35 -5.40
5.40-5.45
5.45-5.50
5.50-5.55
5.55-5.60
328
327
326
325
324
323
322
321
5.60-5.65
5.65 -5.70
5.70-5.75
5.75-5.80
5 .80-5.85
5.85-5.90
5.90-5.95
5.95-6.00
320
319
318
Peat , HU
60
Peat, HU
60
Clay/peat, HU
6.00-6 .05
6.05-6 . 10
6.10-6.20
-22.6
-25.6
-25 .6
-2 4.2
-24.5
(yr BP)
Cal. date
range (yr
ca!. BP)
Most prob.
date (yr
ca!. BP)
5980± 90
6050±100
6100± 90
6945-6735
7140-6800
7160-6860
6845
6900
7000
6360±100
6270± 90
6320± 90
6360± 90
6520±130
6570±110
6580± 90
6800±130
7360-7180
7280-7150
7300-7170
7350-7180
7500-7280
7530-7330
7520-7370
7720-75 10
7270
7 185
7205
7270
7425
7440
7445
7600
6870± 80
6710±100
6880±130
6900±100
6855±130
6980±100
6910±100
7160±140
7760-7590
7610-7450
7820-7580
7810-7600
7790-7570
7930-7680
7830-7600
8070-7810
7680
7560
7685
7695
7670
7775
7700
7960
7350±130
7400± 80
7710±130
7820± 140
7790±110
7930± 80
8020± 140
8030± 140
8340 -8030
8340-8070
8630-8380
8770-8430
8670-8430
8990-8620
8115
8 145
8450
8580
8555
8735
8985*
8990*
8080±100
8010±100
7970± 70
7920± 90
8200±110
8010±120
8210±100
8090±120
-26.0
9000-8650
8990-8580
81 10±110
8 190± 80
8180± 120
* Calibration program (Stu iver & Reim er 1986) g iv es only the most probable date.
** Calibrated date is a n estimate as read from Figure 4 in Kromer e t a!. (1986).
9010*
8985*
8905 ... 8775
8725
9040 ... 9120**
8980*
9040 ... 9130**
9010*
9000 ... 9030**
9040 ... 9110**
9040 ... 9110**
14
Appendix I
Table 3. Pesänsuo , central monolith A 300-b (hummock), 14C dating results. The 14C ages ">Modern" are given
as per mil enrichment with regard to modern standard. The calibrated date range is given for the average of the
IWO humin ages, with la (68 %) probabilily. Fractions: HU=humin , HA=humi c acids.
Suno.
522
594
595
Sampie,
fraclion
Timewidth
(yr)
Peat, HU
Sampling
depth
ol3C
14C age
( m)
(%0 )
(yr BP)
-25.3
-25 .5
+105± 2 %0
+ 126± 13 %0
+59± 20 %0
0.00-0.05
HA
523
596
597
2 %0
2 %0
2 %0
0.08-0.11
+36±
+37±
+40±
5 %0
4 %0
7 %0
0.12-0.15
50± 70
+7± 10 %0
105± 70
200
0.15-0.20
270± 70
260± 70
320± 70
370- 280
335
200
0.20-0.25
570± 90
540± 70
490± 60
600- 530
570
200
0.25-0.30
870± 70
870± 70
850± 70
840- 740
780
200
0 .30-0.35
1150± 70
1040± 70
1030± 70
1060- 970
1010
200
0.35-0.40
1280± 70
1170± 60
1180±110
1200- 1080
1135
200
0.40-0.45
0.40-0.45
1340±110
1250± 70
1230± 70
1270- 11 30
1210
200
0.45-0.50
1550± 110
1380± 70
1400± 70
1390-1300
1345
200
0.50-0.55
1600± 70
1590± 70
1570± 70
1560- 1430
1495
-26 .8
HA
Peat , HU
525
600
601
Peat, HU
526
602
603
Peal, HU
527
604
605
Peal , HU
528
606
607
Peal, HU
529
608
609
Peat, HU
530
610
611
Peat , HU
531
6 12
6 13
Peal, HU
532
614
615
Peat, HU
533
616
617
Peal, HU
"
"
"
"
"
"
"
"
"
"
, HA
, HA
, HA
, HA
-26.8
, HA
, HA
-26.4
, HA
, HA
, HA
, HA
Most prob.
date (yr
ca l. BP)
+55±
+58±
+35±
0.05-0.08
524
598
599
Cal. date
range (yr
cal. BP)
-25.6
Appendix I
15
Table 3. cont.
Suno.
Sampie,
fraction
534
618
619
Peat, HU
535
620
621
Peal, HU
536
622
623
Peat, HU
537
624
625
Peal, HU
538
626
627
Peat, HU
539
628
629
Peat, HU
540
630
631
Peat , HU
Timewidth
(yr)
Sampling
depth
(m)
200
0.55-0.60
200
0.60-0.65
200
0.65-0.70
200
/)13C
14C age
( %0 )
(yr BP)
Cal. date
range (yr
cal. BP)
Most prob.
date (yr
cal. BP)
1790± 50
1770± 70
1680± 70
1770-1650
1715
19 75± 90
1800± 70
1860± 70
1880- 1750
1810
1990± 70
2070± 70
1980± 70
2060-1940
1995
0.70-0.75
2205± 70
2200± 70
2010± 70
2290-2140
2210
200
0.75-0.80
2390±110
2300± 70
2230± 70
2410-2310
2370
100
0.80-0.85
2520± 70
2430± 70
2450± 70
2730-2420
2685 ... 2515
100
0.85-0 .90
2500± 70
2670± 70
2350± 70
2770-2730
2750
HA
HA
"
-24.2
, HA
HA
HA
"
"
, HA
, HA
-26.3
Appendix 2
Appendix 2: Macrofossils of the raised bog Pesänsuo in southwestern Finland
by
Carl-Göran Sten
In trod uction
Maerofossils have been studied from the bog
eenter (eore A 300-a) and from the marginal
slope (peat monolith A 0). The sampling methods are deseribed in ehapter "method s" in Ikonen (this volume). Sampies were taken from A
300-a in seetions of 10 em and from A 0 also
in shorter seetions of 2 em and 5 em. After
preliminary treatment (soaking the sampIes in
10 % nitrie aeid for about 24 hours and stirring
oeeasionally) the sampIes were washed through
three s ieves with meshes of 1 mm , 0.5 mm and
0.2 mm. The residual material from the sieves
was then transferred to dishes for examination.
The frequeneies of seeds, fruits, fruit seales,
leaves and other maerofossils are represented
in absolute numbers per sampIe. Aeeording to
variations in speeies eomposition maerofossil
diagrams have been divided into seven (A 300a) and six (A 0) zones respeetively.
In identifying the maerofossils, maerofos sil
photographs and drawings in the works of
Beijeri nek (1947) and Berggren (1969) and
referenee material in the eolleetions of the
Department of Quaternary Geology in Geologieal Survey of Finland have been used . In the
elassifieation of speeies and mire site types the
works of Ruuhijärvi (1960), Eurola and Kaakinen (1978, 1979) and Eurola et al. (1984) have
been referred to.
Macrofossil dia gram A 300-a
The following 7 plant maerofo ss il zones
were defined on the basis of dominant maero
remains (Fig. 1).
Zone 1. (555 - 618 em) Equisetum-Phrag-
mites-Carex and Equisetum-Carex peat. The
speeies eomposition is eharaeterized by mesoeutrophie swamp (luhta) vegetation, within
whieh shore speeies are abundant. Meso-eutrophie sedges inelude Carex cespitosa. C. canescens. C. diandra. C. dioica. and C. vesicaria. Oligo-mesotrophie tall sedges are represented by C. lasiocarpa and C. rostrata. of whieh
the former is the most abundant. Herb speeies
inelude Cicuta virosa. Menyanthes trifoliata.
Potentilla palustris. Pedicularis palustris. Ra nunculus flammula and Stachys palustris. Oth er maerofossils found are Cenococcum (the
asexual state of the fungus Elaphomyces) and
Daphnia pulex (water flea). Chareoal particles
were found between 580 em and 605 em (Tab le
1.).
Zone 2. (530 - 555 em) Sphagnum-Carex
peat. The speeies eomposition is greatly redueed , eonsisti ng mainly of an oligo-mesotrophie tall- sedge C. lasiocarpa. Of the remain ing meso-eutrophie and mesotrophie speeies
only Ca rex dioica and Potentilla palustris are
represented.
The following zones are eharaeterized by
neva and hummoek-level bog (räme) vegetation. The main eriterion used in subdividing the
zones is the variable abundanee of Andromeda
polifolia and Calluna vulgaris.
Zone 3. (430 - 530 em) Eriophorum-Sphagnum peat. The mire vegetation is definitely
oligotrophie. The zone is eharaeterized by a
dominanee of Andromeda polifolia. Other
dwarf shrubs inelude Empetrum nigrum and
Vaccinium oxycoccos/V. microcarpum. Eriophorum vaginatum first appears in this zone. In
the lower part of the zone, in the highly humified Eriophorum-Sphagnum peat with woody
remains (Betula), rare remains of Polytrichum
strictum between depths of 505 - 525 em and
2
ehareoal fragments from 500 - 505 em and 525
- 530 em are found. A few remains of Poly trieh um strietum are also deteeted at depths of
475 em to 495 em and a greater amount between 460 em and 475 em. Liehenous residues
are found at depths of 440 - 445 em and 505 em.
The speeies eomposition in the following
zones, 4 - 7 indieates ombrotrophie eonditions.
Zone 4. (38 5 - 430 em) Eriophorum-Sphagnum peat. The dominant speeies is Calluna
vulgaris. The abundanee of Andromeda seeds is
greatly redueed. Other dwarf shrubs found are
Empetrum and Vaccinium oxycoccoslV. microcarpum. Liehenous residues are deteeted at
depths of 410 em and 430 em.
Zone 5. (200 - 385 em) Sphagnum, Eriophorum-Sphagnum and Scheuchzeria-Sphagnum
cuspidatum-S. balticum peat. The dominant
dwarf shrubs are Andromeda and Calluna. The
abundanee of Vaccinium oxycoccoslV. microcarpum inereases and Eriophorum vaginatum
aehenes are found again . The oeeurrenee of
Betula pubescens appears in the zone. Some
seeds of Pinus sylvestris and fruit seal es of
Betula nana are found in the upper part of the
zone. Chareoal is found at depths of 225 - 230
em and liehenous residues at depths of 240 250 em and 270 - 295 em.
Zone 6. (105 - 200 em) Eriophorum-Sphagnum and Sphagnum peat. The dwarf shrub taxa
inelude Andromeda, Vaccinium oxycoccoslV.
microcarpum and Empetrum nigrum. Trees are
represented by Betula pubescens and Betula
pendula. Liehenous residues are found in nearIy every sam pie, exeept between depths of 140
em and 160 em.
Zone 7. (0 - 105 em) Sphagnum and Eriophorum-Sphagnum pe at. The dominant dwarf shrubs
are Andromeda. Calluna and Vaccinium oxycoccoslV. microcarpum. The abundanee of
Calluna seeds inereases greatly in the two upperm ost sampies, where Empetrum seeds are
also found. Chareoal is found at depths of 15
- 25, 40 - 45 and 90 - 100 em. Liehenous residues are deteeted at depths of 0 - 5, 45 - 60 and
95 - 105 em.
Appendix 2
Macrofossil diagram A 0
The following 6 plant zones were defined on
the basi s of dominant maero remains (Fig. 2).
Zone 1. (285 - 320 em) Phragmites -Carex
and Equisetum-Carex peat. The vegetation is
similar to that deteeted in the zone I of the
hollow eore. Meso-eutrophie sedges inelude
Carex canescens. C. dioica and C. vesicaria.
Oligo-mesotrophie tall sedges are C. lasio carpa and C. rostrata . The meso-eutrophie and
oligo-mesotrophie herbs are Cicuta virosa,
Menyanthes trijoliata. Pedicularis palustris.
Peucedanum palustre. Potentilla palustris. Ranunculus jlammula. R. repens and Stachys
palustris. Chareoal fragments are found at
depths of 285 - 300 em and 318 - 320 em.
Zone 2. (250 - 285 em) Equisetum-Carex and
Sphagnum-Carex peat. The oligo-mesotrophie
tall sedges C. chordorrhiza and C. lasiocarpa
are dominant. Meso-eutrophie sedge speeies
are no longer found. There are, however. so me
seeds of meso-eutrophie herbs deteeted in the
previou s zone. Chareoal partieles are found
between depths of 265 em to 285 em.
Zone 3. (180 - 250 em) Eriophorum-Sphagnum peat. The speeies eomposition is oligotrophie. Andromeda polijolia is the dominant
speeies. Other dwarf shrubs include Calluna,
Empetrum and Vaccinium oxycoccos. Eriophorum vaginatum first appears in this zone. In a
few sampies the fruits and fruit seales of Betula
pubescens are found. In the lower part of the
zone, in the higly humified seetion woody remains (Betula) were found. Chareoal is deteeted at depths of 180 - 220 em and 245 - 250 em.
The mire vegetation in the following zones,
4 - 6 represents an ombrotrophie type.
Zone 4. (95 - 180 em) Sphagnum and Eriophorum-Sphagnum peat. The dominant dwarf
shrubs are Andromeda and Calluna. Some
fruits of Betula pubescens and aehenes of Eriophorum. leaves and seeds of Va ccinium oxyco ce os are also found. Chareoal is present at
depths of 120 - 125 em and 175 - 180 em.
Zone 5. (25 - 95 em) Eriophorum-Sphagnum
Appendix 2
peat. Andromeda is the dominant species. Other
dwarf shrubs found are Calluna . Empetrum.
Vaccinium oxycoccos. The abundance of Betula
fruits and fruit scales increases. Charcoal partic!es are found between depths of 55 cm to 68
cm.
Zone 6. (0 - 25 cm) Nanolignid-Sphagnum
peat. The species composition of dwarf shrubs
is increased. Calluna is the dominant species,
other species present being Ledum palustre,
Vaccinium uliginosum and Betula nana. There
is also an increase in the abundance of Betula
fruits and fruit scales. Charcoal partic!es are
found in the uppermost 20 centimeters.
Conclusions
The assemblage of the macroscopic plant
remains at the beginning of the hydroseral
development represent a wet land community
developed directly above mineral soi!. The remains consist of meso-eutrophie and oligomesotrophic grasses, sedges and herbs. A general progressive development of the mire vegetation towards oligotrop hicati on and to a final
ombrotroph ic bog stage is evident at Pesänsuo.
The mire site type successio n both at the bog
center and at the margin follows the sequence:
swampy sedge fen, true tall-sedge fen, Eriophorum vaginatum pine bog, true short sedge
3
fen/short sedge intermediate level bog and
Sphagnum fuscum bog. In the bog center the S.
fuscum bog is replaced by a Sphagnum fuscum
bog with holiows and at the margin by true
dwarf shrub pine bog.
References
Beijerinck, W. 1947. Zadenatlas der nederl and ischen flora ten behoeve van de botanie. palaeontologie, bodem kultuur en warenkennis. Mede·
deeling No 30 van het Biologisch Station te Wisjster, Dr. Wa ge ningen: Veenman . 316 p.
Berggren, G. 1969. Atlas of seeds and small fruits of
Northwest- European plant species (Sweden, Norway. Denmark. East Fennoscandia and Iceland)
with morphological descriptions. Part 2. Cyperaceae . Stockholm: The Swedish National Science
Research Council. 68 p.
Eurola, S. & Kaakinen, E. 1978 . Suotyyppiopas.
Porvoo: WSOY. 87 p.
Eurola, S. & Kaakinen, E. 1979. Ecological criteria
of peatl and zonation and the finnish mire type system. In: Proceedings of the International Symposium on Classification of Peat and Peatlands Hyytiälä. Finland . September 17-21 , 1979. Helsinki:
International Peat Society. 20-32.
Eurola, S., Hicks, S. & Kaakinen, E. 1984. Key to
finnish mire types . In : P. D. Moore (ed.) European
mires. London: Academic Press. 11-117.
Ruuhijärvi, R. 1960. Über die regionale Einteilung
der nord finnischen Moore. Annales Botanici Societatis Zoologicae Botanicae Fennicae 'Vanamo' 31
(I), 31-44.
Appendix 2
4
PESÄNSUO , A 300
0
87.0 m a.s.!.
"
~
Q
'"
~
i!:
fu
"
00
~~C3
",,,,,,
w"
"-a.
r
r~
0"
"''''
"'''''''
0'0
~"" ~~~
I" a."ww
_wz
g~
~"
""
W
~~
W
~
a.
w
~~
a.ro'"
L.JLWww'
"'00
0",
Uu
Uo
000
"" ~~
'"z x"
"" ""
2'Z
~~ <a~ «~
~~
Z
W
'"u-;
'"
~
a.
ro
~
'"~
W
~CDro
!
!
I
I
I
I
I
!
I
I I
I
!
!
!
!
!
"
~u
UU
u'!
'!.
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102030
rrrrlrr-lr~rrrlrT'r'
102030 10205
105
1020305
10 10 5
Anal C- G Sten 1975
Fig. 1 Macro foss il diagram from Pesänsuo bog, point A 300-a, where seeds and fruits are marked with black bars and leaves in white.
Macrofossil zones I - 7. Zones of rnire site types : TuN= swampy sedge fen, VSN= trlle tall-sedge fen , TR= Eriophorum vagina/um
pine bog, LkN= trlle short sedge fenls hort sedge intermed iate level bog, RaN= Sphagnumfuscum bog, KeR= Sphagnum fuscum bog
with hollows, IR= true dwarf shrub pine bog. Timescale: Age read from the curve of moving average ofthe five subsequcnt 14 C-ages.
.."
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PEUCEDANUM PALUSTRE
POTENTILLA PALUSTRIS
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C. ROSTRATA
L COMPOSITAE SP
l
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L C, VESICARIA
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CAREX CANESCENS
C. CHORDORRHIZA
E C, OIOICA
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VAGINATUM
L TRICHOPHORUM CESPITOSUM
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E RANUNCULUS FLAMMULA
E R. REPENS
E STACHYS PALUSTRIS
ZONES
MIRE SITE TYPES
l Xlpugddv
6
Appendix 2
Table I. Oeeurrenees of ehareoal partie les in profiles A 0 a nd A 300-a of the Pesänsuo bog.
Abundanee of e ha reoal i s expressed on a seale from rr (minimum) , through r and +,
to e (maxim um ) .
A 300-a
Depth
(ern)
15 - 20
20- 25
40- 45
90- 95
95-100
225-230
500-505
525-530
580-590
590-600
600-605
Chareoa l
rr
rr
rr
rr
+
rr
rr
AO
Depth
(ern)
0- 5
5-10
10- 15
15-20
55-60
60-62
62-66
66-68
120-121
122-125
175- 180
180- 182
182- 185
185-186
C hareoa l
AO
Depth
(ern)
+
rr
e
rr
r
+
195-200
207-208
208-2 10
210-215
215-220
245-250
265-270
270-275
275-280
280-285
285-290
290-295
295-300
3 18-320
+
rr
Chareoa l
rr
+
+
+
+
rr
rr
+
+
+

Geological Survey ofFinland Bulletin 370

Transcription

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