Temperature controls inter-annual variability of summer methane emission from polygonal tundra in the Lena River Delta, Siberia
Temperature controls inter-annual variability of summer methane emission from polygonal tundra in the Lena River Delta, Siberia
Previously Published Material: We plan to present our analysis of the multi-annual CH4 flux data set from the Siberian Lena River Delta also at the General Assembly 2015 of the European Geosciences Union (12 – 17 April 2015, abstract submitted).
Abstract ID#: 35724
English Abstract:
Methane (CH4) emissions from northern wetlands are thought to be at least partly responsible for the observed recent rise in the growth rate of atmospheric CH4 concentrations. The suggested causal relationship between northern wetland CH4 fluxes and atmospheric CH4 concentrations is so far only substantiated by indirect evidence, e.g. by space-for-time approaches using compilations of chamber flux measurements across different climates or by outcome of deterministic CH4 process models. However, empirical data covering the inter-annual variability of CH4 emissions are still rare. Here we present multi-annual CH4 flux data from the Lena River Delta in the Siberian Arctic (72°N, 126°E). The study site is characterized by polygonal wet tundra and a vegetation dominated by mosses and sedges. Seasonal eddy covariance CH4 flux measurements were conducted during the period 2002-2014. CH4 flux data overlap during 25 days (28 July - 21 August) for 9 years. Median CH4 fluxes during the overlap periods of the 9 years ranged between 36 and 64 µmol m-2 h-1 and were found to be positively linearly correlated to the date of thaw (r2 = 0.57, p < 0.05) and soil temperature at 10 cm depth (r2 = 0.66, p < 0.01) in wet polygon centers. These results are in line with plot-scale measurements and stable isotope signatures of emitted CH4, which indicate that (i) wet polygon centers contribute most to landscape-scale CH4 emissions and (ii) the bulk CH4 emitted from vegetated polygon centers is not significantly modified by CH4 oxidation during soil-atmosphere transport. Together, these findings suggest that a warmer climate and longer thaw periods stimulate the production of CH4, which is directly reflected in increased CH4 emissions. On the other hand, warming effects on CH4 oxidation appear limited because transport processes that bypass the soil oxidation zone, i.e. plant-mediated transport and ebullition, dominate CH4 emission from wet polygonal tundra.