CH₄emission from different stages of thermokarst formation in Central Yakutia, East Siberia

The present study was carried out to evaluate the effect of permafrost thawing on methane (CH4) emission from different development stages of thermokarst formation in Central Yakutia, East Siberia. Four stages of thermokarst, "Bullar,""Dyede,""Tuumpu" and mature "Alas," differing in age, depth of depression and water presence, were selected for examination. The emission of CH4 was measured at each thermokarst in forest, dry grassland, wet grassland and on the pond surface. The forest plots were CH4 sinks and uptake ranged from −1 to −34 μg C m−2 h−1. The CH4 fluxes from dry grasslands ranged from −5.4 to 0.9 μg C m−2 h−1, and in wet grasslands CH4 fluxes substantially increased, ranging from 3.6 to 285 μg C m−2 h−1. Pond surfaces had the highest CH4 emissions, ranging from 657 to 8.0 × 103 μg C m−2 h−1. The amount of CH4 stored in the permafrost (up to a depth of 15 m) was estimated to be approximately 0.259 g C m−2. This value was small compared with the current CH4 emission from pond surfaces (4.3–16 g C m−2 growing season−1) in thermokarst depressions. Accordingly, the release of CH4 trapped in the permafrost was not significant compared with the high CH4 emission from the pond surface in young thermokarst depressions. The formation of thermokarst involving permafrost thawing could influence the regional CH4 budget significantly by forming thermokarst wetlands that produce and emit CH4 as a result of current microbial processes under anaerobic conditions.