An examination of the influence of thermokarst activity on arctic lake sediment methanogenesis

• Main Authors: Bostick, Matthew C., NC DOCKS at The University of North Carolina at Greensboro
• Language: English
• Published: 2009
• Subjects: Climate change $x Research; Global warming $x Research; Arctic; Arctic Lake; Brooks Range; Climate change; Global warming; permafrost; Thermokarst; Alaska
• Online Access: http://libres.uncg.edu/ir/uncg/f/Bostick_uncg_0154M_10209.pdf

Accelerated warming in the Arctic contributes to the formation of landscape features known as thermokarsts, or ground surface depressions created by the thermal degradation of permafrost. As a significant portion of the global carbon pool is stored in high latitude ecosystems, it is of concern that accelerated permafrost thaw and the resulting formation of thermokarst features along lake margins may act as a positive feedback to climate warming by influencing the delivery of methanogenic substrates to arctic lake sediments. 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 CH4 flux to the water column were compared between lake types. Although a significant difference in CH4 production was not found between lake types, a negative trend was found between methanogenesis and distance from shoreline in both lake types. Sediment traps served as a proxy to assess 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. Regression models suggested that the catchment area/lake area ratio, water column DOC (mg/L), dissolved oxygen (mg/L) and glacial till were the most useful variables for predicting sediment methanogenesis in arctic lakes. However, our study does not suggest that thermokarst activity along lake shores enhances methanogenesis in lake sediments.