Model estimates of interannual variability of the Lake Ladoga ecosystem characteristics in the period from 1980 to 2020

Numerous generalizations based on field studies show that the spatiotemporal coverage of Lake Ladoga with observational data is insufficient for a reliable quantitative assessment of the interannual variability of the characteristics and biogeochemical fluxes in the lake ecosystem. This paper presents estimates of the interannual dynamics of the main ecosystem characteristics and biogeochemical fluxes in the lake for the period from 1980 to 2020, obtained using a verified three-dimensional eco-hydrodynamic model of Lake Ladoga. The features of the lake ecosystem response to a 39 % decrease in the external phosphorus load during the study period, which is accompanied by a decrease in phytoplankton biomass and primary production by only 30 %, are revealed. The main mechanism explaining this response of the reservoir ecosystem is an increase in the recycling rate due to an increase in water temperature in the photic layer during the growing season, caused by climate change. The phosphorus turnover time in the lake was estimated to be approximately 5.4 years for the considered period of 1980–2020.