Comprehensive assessment of Lake Gusinoye, Republic of Buryatia, based on water, suspended particulate matter and bottom sediments geochemistry

Lake Gusinoye, the second largest lake in the Republic of Buryatia, is a key source of domestic and industrial water supply for the city of Gusinoozersk and nearby areas. It also serves as a recreational site and as a cooling reservoir for the coal-fired Gusinoozerskaya Thermal Power Plant. The lake is exposed to prolonged anthropogenic impact from adjacent pollution sources, including the power plant, overburden dumps of the Kholboldzhinsky coal mine, and a municipal solid waste landfill. This study aims to assess the current hydrochemical state of Lake Gusinoye based on a field survey conducted in July 2019. Sampling of water, suspended matter, and bottom sediments was carried out along three transverse and one longitudinal profiles covering the entire lake area, as well as in inflowing rivers and the plant’s discharge channel. Parameters analyzed included physico-chemical characteristics, major ions, nutrients, heavy metals, and metalloids (HMMs). Aeration of the water column observed during the study period was caused by wind-driven mixing and upwelling, while oxygen depletion was noted near the wastewater discharge zone. Nutrient levels indicated mesotrophic conditions, approaching eutrophic. Wind forcing facilitated a more uniform distribution of water mineralization and major ions across the greater part of the lake’s surface area. Increased water mineralization and sulfate, chloride, and sodium concentrations were confined to the northern part of the lake, where the main anthropogenic sources of readily soluble salts are located. Among HMMs, dissolved Zn, Sr, Mo, and Cu predominated, with maximum concentrations exceeding sanitary norms in the northeastern part of the lake, adjacent to pollution sources. Suspended matter was depleted in HMMs relative to regional lithospheric clarks, whereas bottom sediments showed higher concentrations, indicating continuous pollutant accumulation, especially in the eastern part of the lake.