摘要：The application of stable isotopes is an approach to identify pathways of methanogenesis, methane (CH4) oxidation and transport in peatlands. We measured the stable C isotopic characteristics (δ13C) of CH4 in peat profiles below hummocks, lawns and hollows of a Finnish mire to study the patterns of CH4 turnover. Porewater CH4 concentrations ([CH4]; at 0.5–2 m) increased with depth below all microforms. Emissions of CH4 from hummocks were the lowest, and increased with the increasing water-saturated zone, being ~10 times higher from hollows. Thus, the microtopography of the peatland did not affect the porewater [CH4] in the water-saturated part of the peat profile, but the CH4 emissions were affected due to differences in the oxidative potential of the microforms. There was a decrease in δ13C-CH4 with depth below all microforms indicating dominance of CO2- reduction over acetate cleavage pathway of methanogenesis at deep peat layers. However, estimated potential portions of transported CH4 comprised 50%–70% of the δ13C-CH4 enrichment on microforms at the 0.5-m depth, hereby masking the acetate cleavage pathway of methanogenesis. Stable C composition (δ13C) of CH4 proved to be a suitable (but not sufficient) tool to differentiate between types of methanogenesis in continuously watersaturated layers below microforms of a peatland. Combined flux-based and multi-isotopic approaches are needed to better understand the CH4 turnover process.
