EGU22-9286
https://doi.org/10.5194/egusphere-egu22-9286
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Thermokarst lake size controls greenhouse gases production but not its temperature sensitivity

Tianpeng Li1, Lichao Fan1, Rinat Manasypov2, Yakov Kuzyakov1, Klaus-Holger Knorr3, and Maxim Dorodnikov1,4
Tianpeng Li et al.
  • 1Department of Soil Science of Temperate Ecosystems, University of Göttingen, Göttingen, Germany (tianpengli199211@163.com)
  • 2BIO-GEO-CLIM Laboratory, Tomsk State University, Tomsk, Russia
  • 3Institute for Landscape Ecology, Ecohydrology and Biogeochemistry Group, University of Münster, Münster, Germany
  • 4Department of Biogeochemistry of Agroecosystems, University of Göttingen, Göttingen, Germany (mdorodn@uni-goettingen.de)

Thermokarst lakes formed form permafrost thawing under the global warming are an important source of greenhouse gases (GHG). However, the driving mechanisms and temperature sensitivity (Q10) of GHG emissions from the sediments of thermokarst lakes require deeper understanding. From existing studies of organic matter (OM) turnover and thermodynamic theory, it is known that more refractory OM has a higher temperature sensitivity of decomposition. To test the relevance of such effects in thermokarst lakes, sediments of two differently sized lakes (small = young, DOC rich; large = mature, DOC poor) from Western Siberia were anoxically incubated under three temperatures (4, 10, 16°C) for 49 days. We hypothesized that the Q10 of CO2, CH4 and N2O production increases with lake size as OM becomes increasingly refractory. Rates of CO2 production increased exponentially with temperature in sediments from lakes of both sizes, whereas the highest rates were observed for sediments of the small lake (4.2-9.7 μg C g-1 day-1), as expected for the more labile OM. However, the Q10 of CO2 production (1.8-2.2) was unexpectedly similar between two lakes. The small lake sediment emitted 2-3 orders of magnitude larger amount of CH4 (20-583 ng C g-1 day-1) as compared with large lake. The Q10 values and activation energy (Ea) of CH4 production in small lake sediment significantly decreased from 4-10°C (Q10 = 6.7; Ea = 124 kJ mol-1) to 10-16°C (Q10 = 3.1; Ea = 76 kJ mol-1). This suggests that methanogenesis is a strongly temperature-dependent process that is more sensitive in the low-temperature range. However, Q10 of CH4 production in the large lake did not reveal a sensitivity to temperature probably due to too low CH4 concentrations. In contrast to low CH4 production, the N2O emission rates were dramatically high (0.1-1.3 μg N g-1 day-1) in the sediment of the large lake. Interestingly, there was no N2O detected in the small lake sediment. Presumably, intensive denitrification in the large lake sediment outcompeted methanogenesis for substrate and energy, or enhanced CH4 oxidation occurred with NO3- as the electron acceptor. In summary, the temperature sensitivity of GHG production in thermokarst lake sediments depended more on gas species than on lake size. Nevertheless, the size of thermokarst lakes can serve as an indicator of biogeochemical processes in the sediments, as the small lakes are hotspots of CH4 and the large lakes are hotspots of N2O production.

How to cite: Li, T., Fan, L., Manasypov, R., Kuzyakov, Y., Knorr, K.-H., and Dorodnikov, M.: Thermokarst lake size controls greenhouse gases production but not its temperature sensitivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9286, https://doi.org/10.5194/egusphere-egu22-9286, 2022.