Methane and Sulfide Sulfur in Water and Bottom Sediments of Watercourses of the Steppe Zone of the European Part of Russia

The results of long-term studies of the conjugate distribution of methane (CH₄) and sulfide sulfur (S_sulfide) concentrations in the bottom sediments of watercourses of the steppe zone of the European part of Russia are analyzed. In addition to CH₄ and S_sulfide, Eh and pH values, humidity and density were determined in different sediment horizons; CH₄, dry residue, and pH values were determined in water. Concentrations of CH₄ in the watercourses vary from <0.1 to 2007.0 μL/L (median 24.3 μL/L), with the largest number of values (72%) in the range 10.1–100.0 μL/L. The concentrations of CH₄ and S_sulfide in the bottom sediments of watercourses are quite high and vary, respectively, from <0.01 to 51.0 µg/g of wet sediment (median 1.35 µg/g) and from <0.001 to 4.50 mg/g of wet sediment (median 0.813 mg/g). Usually, the CH₄ and S_sulfide concentrations increase from the surface layer to the subsurface horizons, and then decrease. The difference between the distributions of S_sulfide and CH₄ is the more frequent occurrence of maximum concentrations of S_sulfide in less deep sediment horizons. Seasonal changes were recorded in the vertical distribution of CH₄ and S_sulfide not only in terms of their concentrations, but also in the position of maximum and minimum values. There is a weak positive correlation between the concentrations of CH₄ and S_sulfide, which indicates the synchronous formation of these gases in separate layers of sediments of the studied watercourses. The positive correlation established between the CH₄ concentrations in water and 0–2 cm layer of bottom sediments indicates that the sediments are an important source of CH₄ in water and its emission into the atmosphere.