Thaw Transitions and Redox Conditions Drive Methane Oxidation in a Permafrost Peatland

Abstract

Abstract Permafrost peatlands are a significant source of methane (CH 4 ) emissions to the atmosphere and could emit more CH 4 with continued permafrost thaw. Aerobic methane‐oxidizing bacteria may attenuate a substantial fraction of CH 4 emissions in thawing permafrost peatlands; however, the impact of permafrost thaw on CH 4 oxidation is uncertain. We measured potential CH 4 oxidation rates (hereafter, CH 4 oxidation) and their predictors using laboratory incubations and in situ porewater redox chemistry across a permafrost thaw gradient of eight thaw stages at Stordalen Mire, a permafrost peatland complex in northernmost Sweden. Methane oxidation rates increased across a gradient of permafrost thaw and differed in transitional thaw stages relative to end‐member stages. Oxidation was consistently higher in submerged fens than in bogs or palsas across a range of CH 4 concentrations. We also observed that CH 4 oxidation increased with decreasing in situ redox potential and was highest in sites with lower redox potential (Eh < 10 mV) and high water table. Our results suggest that redox potential can be used as an important predictor of CH 4 oxidation, especially in thawed permafrost peatlands. Our results also highlight the importance of considering transitional thaw stages when characterizing landscape‐scale CH 4 dynamics, because these transitional areas have different rates and controls of CH 4 oxidation relative to intact or completely thawed permafrost areas. As permafrost thaw increases the total area of semiwet and wet thaw stages in permafrost peatlands, CH 4 oxidation represents an important control on CH 4 emissions to the atmosphere.