Evaluating the Classical Versus an Emerging Conceptual Model of Peatland Methane Dynamics

Methane (CH₄) is a potent greenhouse gas that is both produced and consumed in soils by microbially mediated processes sensitive to soil redox. We evaluated the classical conceptual model of peatland CH₄ dynamics—in which the water table position determines the vertical distribution of methanogenesis and methanotrophy—versus an emerging model in which methanogenesis and methanotrophy can both occur throughout the soil profile due to spatially heterogeneous redox and anaerobic CH₄ oxidation. We simultaneously measured gross CH₄ production and oxidation in situ across a microtopographical gradient in a drained temperate peatland and ex situ along the soil profile, giving us novel insight into the component fluxes of landscape-level net CH₄ fluxes. Net CH₄ fluxes varied among landforms (p < 0.001), ranging from 180.3 ± 81.2 mg C m⁻² d⁻¹ in drainage ditches to −0.7 ± 1.2 mg C m⁻² d⁻¹ in the highest landform. Contrary to prediction by the classical conceptual model, variability in methanogenesis alone drove the landscape-level net CH₄ flux patterns. Consistent with the emerging model, freshly collected soils from above the water table produced CH₄ within anaerobic microsites. Even in soil from beneath the water table, gross CH₄ production was best predicted by the methanogenic fraction of carbon mineralization, an index of highly reducing microsites. We measured low rates of anaerobic CH₄ oxidation, which may have been limited by relatively low in situ CH₄ concentrations in the hummock/hollow soil profile. Our study revealed complex CH₄ dynamics better represented by the emerging heterogeneous conceptual model than the classical model based on redox strata.