Biogeochemical processes of methane cycle in the soils, swamps and lakes of Western Siberia

The biogeochemical processes of methane production and oxidation were studied in the upper horizons of tundra and taiga soils and of raised bogs and lake bottom sediments nearby the Tarkosalinsk gas field in western Siberia. Both in dry and water-logged soils, the total methane concentration (in soil particles and gaseous phase) was an order of magnitude higher than in the soil gaseous phase alone (22 and 1.1 nl/cm3, respectively). In bogs and lake bottom sediments, methane concentration was as high as 11 microliters/cm3. Acetate was the major precursor of the newly formed methane. The rate of aceticlastic methanogenesis reached 55 ng C/(cm3 day), whereas that of autotrophic methanogenesis was an order of magnitude lower. The most active methane production and oxidation were observed in bogs and lake sediments where the delta 13C values of CO2 were inversely related to the intensity of bacterial methane oxidation. Methane diffusing from bogs and lake bottom sediments showed delta 13C values ranging from -78 to -47@1000, whereas the delta 13C value of carbon dioxide ranged from -18 to -6@1000. In these ecosystems, methane emission comprised from 3 to 206 mg CH4/(m2 day). Conversely, the dry and water-logged soils of tundra and taiga took up atmospheric methane at a rate varying from 0.3 to 5.3 mg CH4/(m2 day). Methane consumption in soils was of biological rather than of adsorptive nature. This was confirmed by the radioisotopic method and chamber experiments, in which weighting of methane carbon was observed (the delta 13C value changed from -51 to -41@1000).