Sulfides and Methane in Bottom Sediments and Flooded Soils of the Tsimlyansk Reservoir

The Tsimlyansk reservoir is a source of greenhouse gases into the atmosphere, for example, methane, which is formed mainly under anaerobic conditions of bottom sediments. The deposits of artificial reservoirs are represented by modern sediments and buried soils. The aim of the work is to establish the distribution of methane and sulfide sulfur contents in sediments formed after filling the reservoir bowl and in the underlying flooded soils. The work is based on data obtained during the expeditionary work on sampling bottom sediments in the Tsimlyansk reservoir, conducted in the fall of 2023. The concentrations of CH4, sulfide sulfur, density, humidity, pH, and Eh were determined over the horizon in the obtained samples. It is shown that the processes of methanogenesis and sulfide formation combined in time and space take place in the bottom sediments of the reservoir. A noticeable decrease in the contents of CH4 and Ssulfide was found during the transition from modern reservoir sediments to well-visually diagnosed structurally flooded soils, which is caused by the depletion of labile organic matter in soils and, as a result, the attenuation of the processes of methanogenesis and sulfate reduction in them. Based on the location of the boundary between modern precipitation and flooded soils, the sedimentation rate at the station located in the central part of the Tsimlyansk reservoir was calculated at 0.52 cm/year.