Multi-year effect of wetting on CH<sub>4</sub> flux at taiga-tundra boundary in northeastern Siberia deduced from stable isotope ratios of CH<sub>4</sub>
Abstract. The response of CH4 emission from natural wetlands to meteorological conditions is important because of its strong greenhouse effect. To understand relationship between CH4 flux and wetting, we observed interannual variations in chamber CH4 flux, and concentration, δ13C, and δD of dissolved CH4 in summers from 2009 to 2013 at the taiga-tundra boundary in the vicinity of Chokurdakh (70°37' N, 147°55' E) on the lowland of the Indigirka River in northeastern Siberia. We also conducted incubation experiments to interpret δ13C and δD of CH4 to investigate variations in CH4 production and oxidation processes. Methane flux showed large interannual variation in wet areas of sphagnum mosses and sedges (36–140 mg CH4 m−2 day−1 as emission). Increased CH4 flux was recorded in summer 2011 when a wetting event with extreme precipitation occurred. Although water level decreased from 2011 to 2013, CH4 flux remained relatively large in 2012, and increased further in 2013. Concurrently, dissolved CH4 concentration rose by one order of magnitude from 2011 to 2012, and increased further from 2012 to 2013. Large variations in δ13C and δD of dissolved CH4 were observed in 2011, and less variations were seen in 2012 and 2013, suggesting both enhancement of CH4 production and depression of CH4 oxidation. These multi-year effects of wetting on CH4 dynamics may have been caused by continued soil reduction across multiple years after wetting, which suggests that duration of water saturation in the active layer can be important for predicting CH4 emission following a wetting event in permafrost ecosystem.