The Current Trophic State and Water Quality of Lake Onego

Abstract

The trophic state and water quality of Lake Onegо were assessed under climate warming and changes in anthropogenic load over the past 30 years. The water body retains its natural oligotrophic state during the summer stratification according to the concentration of chlorophyll a. A small amount of readily mineralizable organic matter in water determines the low level of development of saprophytic bacteria, corresponding to xenosaprobic and β-oligosaprobic waters. Only the Kondopogskaya Bay of Lake Onego is characterized by a higher level of trophy (mesotrophic) and water saprobity (β-mesosaprobic) due to pollution by wastewater from the pulp and paper mill and waste from trout farms. Local “bloom” of cyanobacteria of in the open area of the lake was observed during the anomalous heating of the epilimnion in the summer of 2022 for the first time in the 50-year history of research. The increase in the concentration of humic substances in the water of the bays as a result of climate warming at this stage did not lead to a change in the level of saprophytic bacteria.