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

Abstract. The response of CH4 emission from natural wetlands due to meteorological conditions is important because of its strong greenhouse effect. To understand the relationship between CH4 flux and wetting, we observed interannual variations in chamber CH4 flux, as well as the concentration, δ13C, and δD of dissolved CH4 during the summer from 2009 to 2013 at the taiga–tundra boundary in the vicinity of Chokurdakh (70∘37′ N, 147∘55′ E), located on the lowlands of the Indigirka River in northeastern Siberia. We also conducted soil incubation experiments to interpret δ13C and δD of dissolved CH4 and to investigate variations in CH4 production and oxidation processes. Methane flux showed large interannual variations in wet areas of sphagnum mosses and sedges (36–140 mg CH4 m−2 day−1 emitted). Increased CH4 emission was recorded in the summer of 2011 when a wetting event with extreme precipitation occurred. Although water level decreased from 2011 to 2013, CH4 emission remained relatively high in 2012, and increased further in 2013. Thaw depth became deeper from 2011 to 2013, which may partly explain the increase in CH4 emission. Moreover, dissolved CH4 concentration rose sharply by 1 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 smaller variations were seen in 2012 and 2013, suggesting both enhancement of CH4 production and less significance of CH4 oxidation relative to the larger pool of dissolved CH4. These multi-year effects of wetting on CH4 dynamics may have been caused by continued soil reduction across multiple years following the wetting. Delayed activation of acetoclastic methanogenesis following soil reduction could also have contributed to the enhancement of CH4 production. These processes suggest that duration of water saturation in the active layer can be important for predicting CH4 emission following a wetting event in the permafrost ecosystem.

Isotopic compositions of ground ice in near-surface permafrost in relation to vegetation and microtopography at the Taiga–Tundra boundary in the Indigirka River lowlands, northeastern Siberia

“…Normally, snowmelt and active layer thawing start in the late May through to early June; the growing season is from late June to early August. The average thaw depth observed between 3 July and 9 August at the study sites was 31±12 cm [65], whereas the maximum thaw depth was found at the end of thaw season (the first half of September). The active layer begins to freeze in the second half of September through to October and freezes completely between November and December.…”

Soil carbon flux research in the Asian region: Review and future perspectives

“…These low C emissions are speculated to partly be caused by the distinct cold and dry weather of Siberia which is located in Asian Russia Table 4 . from water-logged forests in Siberia Shingubara et al, 2019 ; this is particularly the case in western Siberia which features 52.4 million ha of wetland Glagolev et al, 2011;Terentieva et al, 2016 ; this is 0.12 times the emission Glagolev et al, 2011 .…”

Response of Methane and Nitrous Oxide Emissions from Peatlands to Permafrost Thawing in Xiaoxing’an Mountains, Northeast China

“…However, they only observed less than two years of CH 4 fluxes and lacked interannual variations. Shigubara et al [66] found that soil thawing depth can partly explain the interannual variations of CH 4 flux in northeastern Siberia. Our results also showed that interannual variation of CH 4 fluxes may be controlled by the differences of maximum permafrost active layer thawing depths; however, more years of data are needed to confirm this conclusion.…”