Hydrophysical factors affecting the distribution of chlorophyll "a" in a small lake

Abstract

In recent years due to climate warming algal blooms have been observed in some boreal lakes during summer and autumn months, which reduces the quality of water. We studied the distribution of chlorophyll "a" in Lake Kroshnozero (North-western Russia) in 2021 and 2022. This lake has been used for fisheries for more than 50 years, and currently there is a trout farm there. We studied the influence of temperature, turbidity and transparency of water on the distribution of chlorophyll "a". Low water transparency limits photosynthesis to the upper 1.5-2.5 m layer. The stratification limits the transfer of algae cells along the water column, therefore, deeper than 2-3 m, the concentration of chlorophyll "a" decreases sharply. Water exchange causes the transfer of suspended solids from the southeastern basin, where the trout farm is located, to the northwestern one, where the maximum concentrations of chlorophyll "a" are observed. Additional stimulation of photosynthesis in the shallow and rapidly warming northwestern basin can occur due to the supply of nutrients from the catchment area. Features of the lake bathymetry contribute to the formation of bottom oxygen deficiency in the southeastern basin near the trout farm.