Permafrost Thaw Induces Methane Oxidation in Transitional Thaw Stages in a Subarctic Peatland

Abstract:

Rising temperatures in the subarctic are accelerating permafrost thaw and increasing methane (CH₄) emissions from subarctic peatlands. Methanotrophs in these peatlands can consume/oxidize CH₄, potentially mitigating CH₄ emissions in these peatlands. Oxidation rates can exceed 90% of CH₄ production in some settings, depending on O₂ and CH₄ availability and environmental conditions. Malhotra and Roulet identified 10 thaw stages in Stordalen Mire near Abisko, Sweden (68°21'N,18°49'E ) with variable vegetation, environmental conditions, and associated CH₄ emissions. We investigated potential methane oxidation rates across these thaw stages. Peat cores were extracted from two depths at each stage and incubated in 350ml glass jars at in situ temperatures and CH₄ concentrations. Headspace samples were collected from each incubation jar over a 48-hour period and analyzed for CH₄ concentration using flame ionization detection gas chromatography (GC-FID). Oxidation rates ranged from <0.1 to 17 μg of CH₄ per gram of dry biomass per day. Water table depth and pore water pH were the strongest environmental correlates of oxidation (sample size = 56, p < 0.001). The highest potential oxidation rates were observed in collapsing palsa sites and recently collapsed sedge-dominated open water sites near palsa mounds. Our results suggest that permafrost thaw induces high CH₄ oxidation rates by creating conditions ideal for both methanogenic and methanotrophic microbial communities. Our results also reinforce the importance of incorporating transitional thaw stages in landscape level carbon budgets of thawing peatlands emphasized by Malhotra and Roulet. Forthcoming microbial analysis and stable isotope analysis will further elucidate the factors controlling methane oxidation rates at Stordalen Mire.