EGU22-11190
https://doi.org/10.5194/egusphere-egu22-11190
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The size matters: aerobic methane oxidation in thermokarst lake sediments in Western Siberia

Maxim Dorodnikov1,5, Rinat Manasypov2, Lichao Fan1, Oleg Pokrovsky2,3,4, Michaela A. Dippold5,6, and Yakov Kuzyakov1,7
Maxim Dorodnikov et al.
  • 1University of Göttingen, Büsgen-Institute, Soil Science of Temperate Ecosystems, Göttingen, Germany (mdorodn@uni-goettingen.de)
  • 2BIO-GEO-CLIM Laboratory, Tomsk State University, 36 Lenina av., 634050 Tomsk, Russia
  • 3GET UMR 5563 CNRS, 14 Avenue Edouard Belin, 31400 Toulouse, France
  • 4Federal Center for Integrated Arctic research, Institute of Ecological Problem of the North, 23 Nab. Severnoi Dviny, 163000 Arkhangelsk, Russia
  • 5Department of Biogeochemistry of Agroecosystems, Georg August University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany
  • 6Department of Geosciences, Geo-Biosphere Interactions, University of Tübingen, Schnarrenbergstrasse 94-96, 72076 Tübingen, Germany
  • 7Department of Agricultural Soil Science, Georg August University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany

Thermokarst lakes of permafrost peatlands in Western Siberia are among the most important sources of greenhouse gases (GHG) such as CO2 and CH4 because of current permafrost thawing due to climate change. Field measurements demonstrated the increase of dissolved GHG concentrations with the decreasing lake size due to higher concentration of coastal-derived organic C in water of small lakes. However, the size-dependent mechanisms of the GHG production and consumption (e.g. CH4 oxidation) in the sediments of these lakes remain poorly known. We estimated aerobic CO2 production and CH4 oxidation potentials based on natural 13C abundance and 13C labeling in two layers of upper 20 cm sediments of three thermokarst lakes: small (~ 300 m2), medium (~ 3000 m2) and large (~ 1 km2). We hypothesized that i) specific CO2 production (per gram of sediment) decreases with increasing lake size, but CH4 oxidation increases, and ii) both processes are more intensive in the upper 10 cm of sediments than in deeper 10–20 cm, due to naturally occurring O2 gradients and the available C. As expected, CO2 production in the upper layer was 1.4–3.5 times higher than in the deeper layer and the rate of production increased from large (170 nmol CO2 g-1 d.w. h-1) to medium (182) and small (234) lakes. In contrast to CO2, CH4 oxidation in the uppermost sediment layer was similar between lakes, while the deeper layer in the large lakes had 12- and 73-fold higher oxidation rates (5.1 nmol CH4-derived CO2 g-1 d.w. h–1) than in small and medium lakes, respectively. This was attributed to the fact that the O2 concentration in the water of large lakes is higher than in smaller lakes due to the intense turbulence caused by wind and waves. Due to the ongoing and future thawing of permafrost, smaller lakes will increase in size, so that a large part of the CH4 produced in the sediments will be oxidized. However, this process can be (over)compensated by the increased formation of new small lakes. From an ecological perspective, the sediments of shallow thermokarst lakes in the discontinuous permafrost zone of Western Siberia could oxidize up to 0.48 Tg C as CH4 in the summer period, with the largest contribution coming from the large lakes. This confirms the key role of the thermokarst lake ecosystems as a global hotspot of GHG turnover.

Acknowledgement. This work was supported by RSF grant No. 21-77-10067 and the German Academic Exchange Service (DAAD).

How to cite: Dorodnikov, M., Manasypov, R., Fan, L., Pokrovsky, O., Dippold, M. A., and Kuzyakov, Y.: The size matters: aerobic methane oxidation in thermokarst lake sediments in Western Siberia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11190, https://doi.org/10.5194/egusphere-egu22-11190, 2022.