Phyto- and zooplankton ratio in the Karelian isthmus lakes of different type

Results of summer plankton research of 50 the Karelian Isthmus lakes of different type in 2010-2015 are given. The structure and biomass of phyto - zoo - and protozoan plankton and also a ratio of their biomass have been analyzed. According to the nutrients and chlorophyll “a” content trophic state of lakes studied varied from ologotrophic to hypertrophic, the majority of lakes are mezotrophic. In process of eutrophication phytoplankton biomass and share of blue-greens increases. Biomass of zooplankton and protozoa also increases, but correlation with trophic factor is less accurate. Nevertheless, the ratio of zoo - and phytoplankton biomasses decreases with increasing of the trophic status to minimum in shallow hypertrophic lakes. Decrease of zooplankton activity in comparison with phytoplankton led to decrease of destruction activity and stability of ecosystems.