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.
Highlights
Atmospheric CH4 has an important greenhouse effect (Myhre et al, 2013)
Among the two types of wet areas, the water level was lower in wet areas of sphagnum mosses than those of sedges (Fig. 2)
Our results show that CH4 emission from wet areas is expected to make a greater contribution to ecosystem-scale CH4 exchange at the taiga–tundra boundary on the Indigirka River lowlands
Summary
Atmospheric CH4 has an important greenhouse effect (Myhre et al, 2013). The largest source of atmospheric CH4 is the emission from natural wetlands, which is considered to be the main driver of interannual variations in the global CH4 emission, depending on meteorological conditions such as Published by Copernicus Publications on behalf of the European Geosciences Union.R. Atmospheric CH4 has an important greenhouse effect (Myhre et al, 2013). R. Shingubara et al.: Multi-year effect of wetting on CH4 flux at taiga–tundra boundary in NE Siberia air temperature and precipitation (Ciais et al, 2013). Dlugokencky et al (2009) reported that high temperatures in the Arctic and high precipitation in the tropics led to high CH4 emissions from natural wetlands, which caused the observed large growth rates in atmospheric CH4 concentration during 2007 and 2008. Atmospheric CH4 has been increasing from 2007 through the present (Nisbet et al, 2014)
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