An examination of the influence of thermokarst activity on methane production in Arctic lakes

Accelerated warming in the Arctic contributes to the formation of landscape features known as thermokarsts, or ground surface collapses created by the thermal degradation of permafrost.   We designed an experiment to determine how thermokarst features may impact arctic lake sediment methanogenesis.  We investigated 3 lakes with the presence of a thermokarst feature adjacent to their banks, and 3 lakes without this landscape feature in the foothills of the Brooks Range, Alaska.  Using a sediment core incubation method, methanogenesis, methane oxidation and net sediment methane flux to the atmosphere were compared between lake types.   Although a significant difference in methane production was not found between lake types, a strong negative trend was found between methanogenesis and distance from shoreline in both lake types.   Sediment traps served as a proxy for material delivered by an adjacent thermokarst feature.  Although sedimentation rates were significantly greater in traps near a thermokarsting shore than those opposite, the organic matter content in the traps was lower near thermokarsts.  A significant portion of the global carbon pool is stored in high latitude ecosystems.  However, our study does not suggest that thermokarst activity along lake shores enhances methanogenesis in lake sediments.