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

The influence of trophic status on CH(4) 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 CH(4) in both pore water and emissions to the atmosphere were notably (13)C-enriched compared to the ombrogenous bogs. Highly negative delta(13) C values (- 95 to -82%) for CH(4) flux from the acidic rainfed peatlands likely resulted from a combination of CO(2)/H(2) methanogenesis and isotope effects associated with diffusion of CH(4) through aerenchymatous tissue of vascular flora. The delta(13) C values presently attributed to CH(4) flux from northern wetlands in isotope-weighted mass balance budgets of the CH(4) cycle may be too positive. Methane flux from northern bogs and fens should be assigned different delta(13) C values because CH(4) is notably more (13)C-depleted in the former, albeit emission strength typically is weaker.