Bottom sediments of the Shershnevskoye reservoir: Physicochemical characteristics and toxicity

\nThe Shershnevskoye reservoir (ShR) is the main source of drinking water supply for the city of Chelyabinsk, which, since 2003, has been experiencing serious environmental problems caused by eutrophication processes. The purpose of this work was to study the bottom sediments (BS) of the ShR. BS were sampled in 4 locations of the ShR in the spring of 2024. We determined the 5 physicochemical parameters of the BS, the content of humic substances and gases (CO, CO2, CH4), 25 hydrochemical parameters and the toxicity of pore waters. It has been established that the bottom sediments of ShR are sandy silt, they have an average density of 1.008 g/cm3. In the longitudinal section of the reservoir, a trend towards an increase in the content of organic matter and methane in the BS from the upper reaches to the dam is observed. The pore waters belong mainly to the first (I) hydrochemical facies (Ca2+–Mg2+–Cl-–SO 2-) according to the Back (1961) classification. In the reservoir section, there is a clear trend of replacing bicarbonate ion with sulfate ion, and the concentration of chloride ion was minimal (from 0.1 to 1.1 mg/L). According to the results of biotesting using Scenedesmus quadricauda and Daphnia magna, all BS samples exhibit chronic toxicity, and two samples also exhibit acute toxicity, probably associated with the release of toxic products of organic matter mineralization.\n