Impact of acidification on structural organization of phytoplankton community in the forest lakes of the north-western Russia

The response of the phytoplankton to different degree of pH was studied by the example of 7 shallow weakly mineralized forest lakes located in the Darwin National reserve on the north shore of the Rybinsk reservoir (north-western Russia). With a decrease of pH the number of phytoplankton species decreased especially among centric diatoms,blue-greens and Euglenophyta, total biomass of phytoplankton and its seasonal dispersion declined. Green algae, chrysomonades and cryptomonades biomass correlated negatively with pH but diatoms and blue-greens biomass were related positively to pH. The drop in pH produced a decrease of Shannon-Weaver diversity index, obtained from biomass and cell volume of algae, increase of Simpson index and algae size. The growth of phytoplankton did not correspond the total phosphorus. The necessary modifications to the structural characteristics of phytoplankton by the acidification came about in the pH range from 6 to 5.