Estimation of Indicators of Phytoplankton Development and Water Quality of Peipsi–Pskov Lake in Modern Conditions

Currently, the acute problem of pollution of the hydrosphere, which results in a drop in the stability of ecosystems, destruction of the signaling links of biocenoses, and food pyramid violation, is of great importance. The results of our monitoring of the current state of phytoplankton communities and water quality of Peipsi–Pskov Lake, a large transboundary reservoir located in the northwestern part of Pskov oblast are presented. During the growing season of 2022, 221 phytoplankton taxa with ranks below the genus from eight phylums were identified. The average abundance of phytoplankton over the entire period of our study was 11.6 million cells/L, and the average biomass was 1.6 g/m3. An ecological and geographical analysis was carried out, according to which widespread freshwater planktonic forms of microalgae predominated in the lake, preferring stagnant-flowing weakly alkaline waters. According to the Sjörensen–Chekanovsky index, the degree of commonality of the species composition of the planktonic algal flora in Pskov and Peipsi lakes was 73.2%. Saprobiological analysis showed that the waters of the study area in 2022 were slightly polluted (class II of water quality).