Hydrochemical studies conducted at Lake Kroshnozero in 1953–1954, 1986–1987, and 2021–2023 differed by intensity of human economic activity at the reservoir and its catchment area, revealed changes in the chemical composition of the lake water and identified the restructuring of the lakes ecosystem over the past 70 years. In the early 1950s, Lake Kroshnozero was already eutrophic. The average annual concentration of Ptot in the lake water was 32 µg/l. River runoff plays the main role in the entry of biogenic elements (primarily phosphorus) into the lake. From 1950s till now, the Ptot load with river discharge has changed from 5.17 to 8.45 t/year. Currently, the phosphorus yield from the watershed amounts to 0.92 g/m year, which is 2.2 times higher than in the 1950s. In present days, under conditions of summer temperature stratification, acute O₂ deficiency in the bottom layers was observed in the deep-water areas of the lake, resulted in mobilization of P-PO from bottom sediments. Additional (internal) phosphorus load contributes to an increase in production processes in the reservoir. Kinetic patterns of transformation and circulation of substances in lake water are considered. It was found that the transformation of organic matter, N, P and Si occurs more slowly than the circulation of mineral forms of nitrogen compounds and phosphorus.
A.V. Sabylina (2025) studied this question.