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.
Bibliographical noteWe appreciate discussions with M. Firestone and S. Blazewicz. We received assistance in the field and lab from K. Smetak, H. Dang, and A. McDowell. This research was funded by grants to W.L.S. from the U.S. National Science Foundation (ATM-0842385 and DEB-0543558) and the California Department of Fish and Wildlife (CDFW) and California Department of Water Resources (DWR) contract 4600011240. The data used are listed in the references, tables, supporting information, and the Illinois Digital Environment for Access to Learning and Scholarship (IDEALS) repository at https://www.ideals.illinois.edu/.
- gross methane fluxes
- methane oxidation
- Sacramento-San Joaquin Delta
- stable isotope pool dilution