Structure and seasonal dynamics of phytoplankton of the Kizhi Island area of Lake Onego

An investigation into the phytoplankton condition in the area of Kizhi skerries of Lake Onego during the spring, summer and autumn of 2023 revealed a high level of microalgae development. The quantitative indicators of the phytocenosis characterise this area of Lake Onego as mesotrophic. The classification of the water type in the Kizhi skerries area of Lake Onego is determined by the indicator values of phytoplankton found during the study period and their quantitative development. The water type is thus classified as a β-mesosaprobic pollution zone with water quality class 3, i.e. satisfactorily clean. The most significant increase in quantitative development was observed during the spring and autumn periods, with diatoms and cyanobacteria being the dominant phytoplankton species. In contrast, during the summer months, cyanobacteria, along with golden and green algae, were the primary components of the phytoplankton community. Furthermore, silicon concentrations was decreased from spring to autumn that was caused by increasing ofabudance and biomass of diatom algae. At the same time, lower values in the ratio of общal nitrogen to total phosphorus can be applied as indicator of active production of cyanobacteria. The intensive vegetation of phytoplankton in the Kizhi Island area is related to the area’s natural conditions.