Quantifying the Microbial Utilization of Methanogenesis and Methane Loss from Northern Wetlands

Abstract:

The importance of methanogenesis and percent of methane loss from the subsurface porewater in various northern wetland sites was quantified with isotope-mass balance equations. With equimolar amounts of CO₂ and CH₄ produced from methanogenesis, the amount of dissolved CO₂ produced from methanogenesis as compared to other decomposition processes can be calculated and is equivalent to the amount of CH₄ before loss due to ebullition, plant-mediated transport, and diffusion. This method was applied to porewater samples collected from various locations within permafrost collapse-scar bogs and northern peatlands. From the peatland sites, bogs produced less CO_2-meth than fens (2.9 ± 1.3 mM and 3.7 ± 1.4 mM, respectively). Methanogenesis was a more utilized decomposition process in the bogs than the fens. However, greater amounts of CO_2-meth found in fen sites was most likely due to the presence of more labile organic substrates resulting in greater overall production. More CH₄ was lost in fens (89 ± 2.8%) than bogs (82 ± 5.3%) from plant-mediated transport as fens are dominated by vascular plants (Carex) while bogs are dominated by Sphagnum mosses. In permafrost sites, mid-bogs produced twice the amount of CO_2-meth as bog moats (1.6 ± 0.63 mM and 0.82 ± 0.20 mM, respectively). Less methanogenesis was found in bog moats as recently thawed organic matter is exposed to initial decomposition processes and methane production grows over time. A similar amount of CH₄ was lost from bog moats as mid bogs (63 ± 7.0% and 64 ± 9.3%, respectively) likely due to the greater density of vascular plants found within a bog moat.