Frozen ponds: production and storage of methane during the Arctic winter in a lowland tundra landscape in northern Siberia, Lena River delta

• Published in: Biogeosciences
• Main Authors: M. Langer, S. Westermann, K. Walter Anthony, K. Wischnewski, J. Boike
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2015
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic; Ice; lena river; permafrost; Tundra; Siberia
• Online Access: https://doi.org/10.5194/bg-12-977-2015; https://doaj.org/article/6256622ef20d47b8b310f73903fcd61e

Lakes and ponds play a key role in the carbon cycle of permafrost ecosystems, where they are considered to be hotspots of carbon dioxide CO 2 and methane CH 4 emission. The strength of these emissions is, however, controlled by a variety of physical and biogeochemical processes whose responses to a warming climate are complex and only poorly understood. Small waterbodies have been attracting an increasing amount of attention since recent studies demonstrated that ponds can make a significant contribution to the CO 2 and CH 4 emissions of tundra ecosystems. Waterbodies also have a marked effect on the thermal state of the surrounding permafrost; during the freezing period they prolong the period of time during which thawed soil material is available for microbial decomposition. This study presents net CH 4 production rates during the freezing period from ponds within a typical lowland tundra landscape in northern Siberia. Rate estimations were based on CH 4 concentrations measured in surface lake ice from a variety of waterbody types. Vertical profiles along ice blocks showed an exponential increase in CH 4 concentration with depth. These CH 4 profiles were reproduced by a 1-D mass balance model and the net CH 4 production rates were then inferred through inverse modeling. Results revealed marked differences in early winter net CH 4 production among various ponds. Ponds situated within intact polygonal ground structures yielded low net production rates, of the order of 10 -11 to 10 -10 mol m -2 s -1 (0.01 to 0.14 mg CH 4 m -2 day -1 ). In contrast, ponds exhibiting clear signs of erosion yielded net CH 4 production rates of the order of 10 -7 mol m -2 s -1 (140 mg CH 4 m -2 day -1 ). Our results therefore indicate that once a particular threshold in thermal erosion has been crossed, ponds can develop into major CH 4 sources. This implies that any future warming of the climate may result in nonlinear CH 4 emission behavior in tundra ecosystems.