Trophic state of the Kizhi skerries area of Lake Onego and water quality assessment based on summer phytoplankton indicators

Abstract

The study of summer phytoplankton (July-August 2020 and 2022) in the Kizhi skerries area of Lake Onego revealed high quantitative indicators of phytoplankton development, which characterises this area as meso-eutrophic. The phytocenosis was characterised by high species diversity, which is typical for the summer phytoplankton community of Lake Onego. However, at the time of the study, the indicator species of β-mesosaprobic pollution zones (water quality class 3, satisfactorily clean) exhibited the greatest quantitative development. Notable species with the potential to produce cyanotoxins were observed, although their quantitative development was relatively limited. The analysis of multi-year changes revealed an increase in the abundance of cyanobacteria, green algae and euglena algae. The total biomass of phytoplankton increased as a result of the proliferation of numerous, small-celled cyanobacteria and a limited number of large-celled, benthic and planktonic-benthic diatom algal species. The marked proliferation of phytoplankton in the study area is attributable to the prevailing natural conditions. Further research is required to ascertain the precise reasons for the observed increase in phytoplankton quantities in recent years.