Cold season CH4 And CO2 emission from boreal peat bogs (West Siberia): Winter fluxes and thaw activation dynamics

Abstract

The conventional chamber technique was used to measure CH4 and CO2 emission to the atmosphere from snow-covered ombrotrophic bogs (57°N, 82°E, Plotnikovo, West Siberia). The average ± standard deviation values for CH4 and CO2 fluxes in mid-February were found to be equal mg m-2 d-1 5.0 ± 3.7 and 69±52, respectively. The contribution of cold season to annual methane fluxes varied from 3.5 to 11% depending on the calculation method and was similar to that found in Alaska and northern Minnesota. The vertical profiles of gases in snow were linear implying the applicability of the simple diffusion equation under steady state conditions. The diffusion reduction factor due to porous resistance and tortuousity of snowpack was 0.18 and 0.29 for methane and carbon dioxide, respectively. Thus snow forms only a passive cap which controls the gas concentration at the snow-soil interface, while gas flux into the atmosphere is controlled by gas production in the soil. The fresh samples of frozen peat soil incubated under laboratory conditions at constant temperature -16°C displayed very slow, but steady respiration varied from 0.05 to 0.2 mg CO2-C d-1 dm-3 depending on peat sampling depth. Although this activity was 200-300 times lower than soil respiration in summertime, it was enough to support the observed in situ winter CO2 emission. The thaw and subsequent peat incubation at 15°C accelerated gas formation up to 2-5 mg CO2-C and 1.2 mg CH4-C h-1 dm-3 of peat after 3-4 days of incubation followed by a decline by 1 order of magnitude and approaching a new steady state level. Although the mechanism of freeze-thaw activation needs further clarification, it was nevertheless possible to simulate the observed activation dynamics by a mathematical model which accounts for the burst of microbial growth on nutrients released into soil from frost-damaged cells.