Methanogenesis in Peat Bogs – Insights from 14C Data Synthesis and Modeling

Abstract:

Depth profiles of Δ¹⁴C found in peat bogs are similar across latitudes. Solid peat radiocarbon ages increase with depth, young or modern DOC is found in porewater at all depths, and dissolved methane has an intermediate age. Using traditional mixing models, this pattern has been explained as methane produced from roughly half peat and half DOC. However, these models do not account for the advection and diffusion of dissolved gases, which plays an important role in peatlands. We develop a model that includes these transport pathways and individually models ¹²C, ¹³C and ¹⁴C during the transformation and transport of DOC, DIC, and methane. We test the model against existing data from several field sites, in bogs as disparate as the Glacial Lake Aggasiz Peatlands and Brunei Darussalam. Our model suggests that in bogs with typical Δ¹⁴C profiles, where the methane age is intermediate between that of peat and DOC, DOC advected from the surface does not contribute significantly to methane production. Instead, peat decomposition is the primary carbon source. The younger apparent ages of methane compared to peat at the same depth result from vertical advection of the dissolved gases, rather than consumption of DOC for methanogenesis. This is consistent with the finding that DOC found in these bogs is recalcitrant. The model reproduces vertical patterns of DOC, DIC and methane found in both tropical peatlands and northern bogs, emphasizing the similarities in hydrological and geochemical processes across latitudes.