Atmospheric CH 4 oxidation by Arctic permafrost and mineral cryosols as a function of water saturation and temperature

• Published in: Geobiology 2016-07, Vol.15 (1)
• Main Authors: Stackhouse, B., Lau, M. C. Y., Vishnivetskaya, T., Burton, N., Wang, R., Southworth, A., Whyte, L., Onstott, T. C.
• Format: Article
• Language: English
• ISSN: 1472-4677; 1472-4669

Abstract The response of methanotrophic bacteria capable of oxidizing atmospheric CH 4 to climate warming is poorly understood, especially for those present in Arctic mineral cryosols. The atmospheric CH 4 oxidation rates were measured in microcosms incubated at 4 °C and 10 °C along a 1‐m depth profile and over a range of water saturation conditions for mineral cryosols containing type I and type II methanotrophs from Axel Heiberg Island ( AHI ), Nunavut, Canada. The cryosols exhibited net consumption of ~2 ppmv CH 4 under all conditions, including during anaerobic incubations. Methane oxidation rates increased with temperature and decreased with increasing water saturation and depth, exhibiting the highest rates at 10 °C and 33% saturation at 5 cm depth (260 ± 60 pmol CH 4 gdw −1 d −1 ). Extrapolation of the CH 4 oxidation rates to the field yields net CH 4 uptake fluxes ranging from 11 to 73 μmol CH 4  m −2 d −1 , which are comparable to field measurements. Stable isotope mass balance indicates ~50% of the oxidized CH 4 is incorporated into the biomass regardless of temperature or saturation. Future atmospheric CH 4 uptake rates at AHI with increasing temperatures will be determined by the interplay of increasing CH 4 oxidation rates vs. water saturation and the depth to the water table during summer thaw.