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Among oligohalobous, halophilous Epithemia turgida , E. sorex and Meridion
circulare were noted. In addition, Cocconeis hoffmannii belonging to euhalobous
as well as mesohalobous taxa Opephora mutabilis and Rhopalodia musculus were
observed.
Planktonic diatoms were rarely represented by single valves of riverine species
Aulacoseira granulata.
11.4 Discussion
Results of palynological studies as well as the lithological description of the sedi-
ments show that at the beginning of the Atlantic period most of the Vistula Delta
was a swampy area (Figs. 11.6 and 11.7 ) . Habitats with poor drainage prevailed
and caused the domination of alder ( Alnus ) associations with hazel ( Corylus ), elm
( Ulmus ), willow ( Salix ), ash ( Fraxinus ), poplar ( Populus ) and locally also elder-
berry ( Sambucus ) and viburnum ( Viburnum ). Alder forests are usually present in
flooded, fertilized areas where the water level remains high for longer time spans.
The presence of diatoms typical of shallow, eutrophic and poorly oxygenated water
(Fig. 11.8 ) supports the existence of an environment mentioned above. The admix-
ture of riverine plankton and acidophilous benthos species could either result from
riverine floods or be redeposited together with fluvial sediments and peat bogs. Drier
habitats in the close vicinity of the delta were probably occupied by deciduous
mixed forests with oak ( Quercus ), lime ( Tilia ), elm ( Ulmus ) and hazel ( Corylus ).
The pine-oak forest, most probably, grew on the driest areas, on the dunes or the
barrier which separated the low-lying delta from the sea. A similar composition of
the forest association is also known from the dunes of Łeba Barrier on the middle
Polish coast (Tobolski 1997 ) . The barrier could be periodically overwashed during
storm surges as indicated by the admixture of benthic allochthonous forms pre-
ferring more saline waters, i.e. oligohalobous, halophilous and mesohalobous, in
diatom composition (Fig. 11.9 ) .
Dendrochronological data (Fig. 11.5 ) indicate that the tree growth was not
terminated by one catastrophic event, but rather during several flood episodes.
According to the relative sea level curve for the southern Baltic, the water level in
the early Atlantic (8,000-7,900 BP) was about 20-19 m below present (Uscinowicz
2003 , 2006 ) . That means that the investigated area was lying about 2-4 m above
water level in the Gulf of Gdansk at that time. The termination of the vegetation
was probably caused by few river floods (spring high water stand and ice flow),
rather than by marine transgression. It could have happened during 200-300 years
before the sea did enter into the area. We may infer that the gulf's waters passed
the -16 m level no earlier than about 7,700-7,600 BP. This view is based on all
the evidences explained above (radiocarbon dates, results of pollen, diatom and
dendrological analyses).
Similar drowned swampy areas of Atlantic age have also been found close
to the edges of the Gulf of Gdansk (Miotk-Szpiganowicz 1997 , Uscinowicz and
Miotk-Szpiganowicz 2003 , Ł˛czynski et al. 2007 , Uscinowicz et al. 2007 ) aswell
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