Holocene environmental changes recorded by diatom stratigraphy in the Vistula Lagoon

Four 6 m long sediment cores from the Vistula Lagoon were analyzed with respect to their content of diatoms. The aim was to detect changes of the composition of the diatom flora and to link these changes to Holocene climatic fluctuations and paleoecological stages of the Baltic Sea. The location of cores creates a good opportunity for reconstruction environmental changes both in the northern and southern part of the lagoon. Based on species composition of the diatom flora, distribution of salinity and habitat groups and stratigraphical information supported by 14C data and lithological analyses four diatom assemblage zones were distinguished in each core. The study shows that the area originally had a terrestrial environment, whereas its later evolution is linked with the marine stages of the Baltic Sea. The northern part of the lagoon originated due to input of marine waters through the Vistula Spit, which is indirectly connected with two Littorina transgressions. Next, probably in Late Atlantic-Early Subboreal period, the basin expanded southwards caused by intensification of marine water inflow during maximum Littorina transgressions. As a result the shallow, eutrophic, brackish water basin originated. In Subboreal period the basin became shallower and slightly brackish water. However, intensive Bauda river inflow caused locally decreasing of salinity. Moreover, symptoms of Post-Littorina transgression in Subatlantic chronozone were observed in the diatom record. Finally, the effects of eutrophication are recorded in subfossil diatom flora. Moreover, as a consequence of closing the Nogat river inflow, the stronger influence of marine waters from the Baltic Sea are observed in the lagoon.