How Does the Area of a Thermokarst Lake Influence on Methane Emissions? (A Case Study from the West Siberian Tundra)

Thermokarst lakes are a significant source of methane, the second-most important greenhouse gas. At high latitudes, the rise in air temperature increases the total area of thermokarst lakes. This can enhance methane emissions from permafrost regions. The area of thermokarst lakes grows especially strongly in Western Siberia. We assess poorly studied local variability in methane emission from lakes in the region and its drivers, focusing on lake area. We measure methane flux at the summer peak on four small (0.1–1.0 km2) and five extra-small (<0.1 km2) lakes, considering possible variability within the lakes and two methane transport pathways to the atmosphere (diffusion and ebullition). Contrary to widely observed patterns, fluxes from larger lakes are higher than from smaller lakes: the mean methane flux measured by the chamber method is 4.1 and 2.1 mg CH4 m–2 h–1, and the median flux is 1.3 and 0.43 mg CH4 m–2 h–1 for small and extra-small lakes, respectively. Higher temperatures of bottom sediments, higher photosynthetic activity of algae, more intense ebullition in larger lakes, and equal depths and oxygen concentrations in lakes of different area categories could all explain the observed pattern. Results can improve predictions of methane emissions from the West Siberian tundra.