Trophic status impacts both the magnitude and stable carbon isotope composition of methane flux from peatlands

The influence of trophic status on CH4 production, emission and stable carbon isotope composition was investigated in two ombrogenous and two minerotrophic peatlands situated in Wales, UK. Methane production and emission rates were highest in the minerotrophic peatlands and CH4 in both pore water and emissions to the atmosphere were notably 13C‐enriched compared to the ombrogenous bogs. Highly negative δ13C values (−95 to −82‰) for CH4 flux from the acidic rainfed peatlands likely resulted from a combination of CO2/H2 methanogenesis and isotope effects associated with diffusion of CH4 through aerenchymatous tissue of vascular flora. The δ13C values presently attributed to CH4 flux from northern wetlands in isotope‐weighted mass balance budgets of the CH4 cycle may be too positive. Methane flux from northern bogs and fens should be assigned different δ13C values because CH4 is notably more 13C‐depleted in the former, albeit emission strength typically is weaker.