Концентрация и эмиссия метана и сероводорода в озере Баскунчак, ручье балки Улан-Благ и дегазирующих источниках подземных вод в весенний период

Abstract

For the first time, the distribution of methane in the brine and bottom sediments of Lake Baskunchak, as well as its tributary, the Ulan-Blag stream, in the beam of which the discharge of ascending degassing groundwater sources takes place, was studied. In addition to CH4, concentrations of total hydrogen sulfide (ΣH2S), Eh and pH values, humidity and density were determined in various horizons (up to 35 cm) of stream sediments. Concentrations of CH4, major ions and pH values were determined in the brine of the lake and stream; experimental measurements of CH4 emission by the chamber method were carried out on one of the debit fields where degassing sources are discharged. Brine mineralization in Lake Baskunchak is 312 g/dm3, which is 2.1 times more than in the Ulan-Blag stream; the water class in the stream and lake is chloride, the sodium group, type II and III, respectively. The fluxes of CH4 into the atmosphere from the surface of the studied degassing source vary in the range of 1.97–2.07 mg/(m2 h). In the brine of degassing sources, a high concentration of CH4 (up to 215 μl/dm3) is recorded, which is 1-2 orders of magnitude higher than in the brine of the lake. Low concentrations of CH4 in the brine of the lake are due to its insignificant flow from bottom sediments into the water due to the presence of a salt crust that prevents gas emission, as well as due to its small concentrations in the upper layers of sediments (0.01 μg/g). Low concentrations of CH4, despite the reducing conditions, are also characteristic of the sediments of the mouth of the Ulan-Blag creek (0.04–0.32 μg/g), which, at high concentrations of ΣH2S in them (0.06–1.32 mg/g), is probably caused by the suppression of methanogenesis in the sediments by sulfate reduction. In general, the distribution of CH4 and ΣH2S along the vertical of deposits is quite synchronous (r = 0.64) and correlates with the distribution of Eh values.