Carbon emission related to thermokarst processes in wetlands of NE European Tundra

Emission of greenhouse gases (GHG) from inland waters is recognized as highly important and understudied part of terrestrial carbon (C) biogeochemical cycle. These emissions are still poorly quantified in permafrost regions containing a vast amount of surface C in frozen peatlands. This is especially true for NE European peatlands, located within sporadic to discontinuous permafrost zone which is highly vulnerable to thaw. For a first quantification of the C emission from lentic waters of the Bolshezemelskaya Tundra (BZT, 200,000 km²), we measured CO2 and CH4 concentrations and fluxes to the atmosphere in 98 depressions, thaw ponds and thermokarst lakes ranging from 0.5 to 5x10⁶ m² in size. The CO2 fluxes decreased by an order of magnitude when lake size increased by > 3 orders of magnitude, while CH4 fluxes showed large variability that were not related to lake size By using a combination of Landsat-8 and GeoEye-1 images we found that lakes cover 4% of BZT, and calculated the overall C emission (CO₂+CH₄) from the lakes of the territory to 3.8 Tg C y^-1 (99% C-CO₂, 1% C-CH₄). Large lakes (> 10,000 m²) dominated GHG emissions whereas small thaw ponds (< 1000 m²) had a minor contribution to overall lake surface area (< 2%) and GHG emission (< 5 % of CO₂; < 20% of CH₄). The results suggest that, if permafrost thaw in NE Europe leads to the disappearance of large thermokarst lakes and formation of new small thaw ponds and depressions, this will decrease GHG emission from lentic waters of this region. However, due to temporal and spatial variations of C fluxes, the uncertainties on areal GHG emission are at least one order of magnitude in small thaw ponds and a factor of 3 to 5 in thermokarst lakes.

This work was supported by the State Task AAAA-A18-118012390200-5, RFBR grant No. 18-05-70087 “Arctic Resources”, 19-07-00282, 18-45-860002, 18-45-703001 and 18-47-700001, and the Swedish Research Council (grant no. 2016-05275).