The relative importance of methanogenesis in the decomposition of organic matter in northern peatlands

Using an isotope‐mass balance approach and assuming the equimolar production of CO 2 and CH 4 from methanogenesis (e.g., anaerobic decomposition of cellulose), we calculate that the proportion of total CO 2 production from methanogenesis varies from 37 to 83% across a variety of northern peatlands. In a relative sense, methanogenesis was a more important pathway for decomposition in bogs (80 ± 13% of CO 2 production) than in fens (64 ± 5.7% of CO 2 production), but because fens contain more labile substrates they may support higher CH 4 production overall. The concentration of CO 2 produced from methanogenesis (CO 2‐meth ) can be considered equivalent to CH 4 concentration before loss due to ebullition, plant‐mediated transport, or diffusion. Bogs produced slightly less CO 2‐meth than fens (2.9 ± 1.3 and 3.7 ± 1.4 mmol/L, respectively). Comparing the quantity of CH 4 present to CO 2‐meth , fens lost slightly more CH 4 than bogs (89 ± 2.8% and 82 ± 5.3%, respectively) likely due to the presence of vascular plant roots. In collapsed permafrost wetlands, bog moats produced half the amount of CO 2‐meth (0.8 ± 0.2 mmol/L) relative to midbogs (1.6 ± 0.6 mmol/L) and methanogenesis was less important (42 ± 6.6% of total CO 2 production relative to 55 ± 8.1%). We hypothesize that the lower methane production potential in collapsed permafrost wetlands occurs because recently thawed organic substrates are being first exposed to the initial phases of anaerobic decomposition following collapse and flooding. Bog moats lost a comparable amount of CH 4 as midbogs (63 ± 7.0% and 64 ± 9.3%).