Vertical distribution of plankton under ice in relation to environmental parameters in eutrophic lakes

Winter vertical distribution of planktonic communities differs from the summer one due to reverse thermal stratification. The study aimed to test the hypothesis that the abundances of heterotrophic organisms, in contrast to phytoplankton, are higher at the bottom (warmer water layers) than at the surface (colder water layers). Phytoplankton (cyanobacteria and algae), protozooplankton (heterotrophic nanoflagellates and ciliates) and metazooplankton (rotifers and crustaceans) were investigated under the ice cover in three eutrophic lakes during two consecutive winters (with and without snow cover). All of the studied groups of organisms showed heterogeneous vertical distributions. The maximal abundances of phyto- and protozooplankton were observed at different depths depending on the lake and year of the study. In the shallow lake, phytoplankton reached the maximum at the bottom, while in deeper lakes it was the most abundant at the surface. In all lakes during both winters, the rotifer and crustacean abundances reached maximal values at the bottom. In winter with snow cover, chlorophyll a was the crucial factor determining the vertical distribution of protists, while temperature was responsible for the distribution of metazooplankton. In winter without snow, phytoplankton and protists were negatively related, while rotifers and crustaceans were positively related to dissolved organic carbon and total phosphorus.