ILLUMINATING GEOCHEMICAL CONTROLS OF METHANE OXIDATION ACROSS A GRADIENT OF PERMAFROST THAW

• Main Author: Perryman, Clarice R.
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2017
• Subjects: biogeochemistry; methane; peatlands; permafrost; Environmental science; Geochemistry; Abisko; Stordalen; palsa
• Online Access: https://scholars.unh.edu/thesis/1146; https://scholars.unh.edu/cgi/viewcontent.cgi?article=2145&context=thesis

Methanotrophic bacteria may consume 60 to 90% of methane (CH4) produced in thawing permafrost peatlands. Rates of aerobic methanotrophy are dependent on the availability of CH4, redox conditions driven by O2 availability, and methanotroph community composition. This study investigated potential CH4 oxidation rates across a permafrost thaw gradient in Stordalen Mire, near Abisko, Sweden (68°21'N, 18°49'E). Oxidation rates were determined through laboratory incubations under a range of CH4 concentrations. Field measurements of redox conditions and analytical measurements of redox-sensitive compounds were completed to elucidate geochemical environments where methanotroph communities thrive. Potential CH4 oxidation rate increases across the thaw gradient, but increases were most pronounced at the transition from semi-wet to fully thawed sites. These submerged sites are characterized by variable CH4 and O2 availability and moderately reducing conditions. Oxidation potential increases as conditions become more reducing. Peat from submerged sedge sites has a greater CH4 oxidation capacity across increasing CH4 concentrations than peat from palsa and Sphagnum sites. Differences in CH4 oxidation capacity between sites are most pronounced under high CH4 concentrations. These data suggest that submerged sedge sites host methanotrophs with differing CH4 and O2 affinities than the palsa and Sphagnum sites which appear to be able to survive moderately reducing conditions. The classical conceptual model that limits aerobic CH4 oxidation to the depth of the water table may need to be reevaluated to better approximate peatland CH4 dynamics to account for heterogeneity of redox conditions and overlapping microbial communities through the peat column.