Abstract. Low affinity methanotrophic bacteria consume a significant quantity of methane in wetland soils in the vicinity of plant roots and at the oxic-anoxic interface. Estimates of the efficiency of methanotrophy in peat soils vary widely in part because of differences in approaches employed to quantify methane cycling. High resolution profiles of dissolved methane abundance measured during the summer of 2003 were used to quantity rates of upward methane flux in four peatlands situated in Wales, UK. Aerobic incubations of peat from a minerotrophic and an ombrotrophic mire were used to determine depth distributions of kinetic parameters associated with methane oxidation. The capacity for methanotrophy in a 3 cm thick zone immediately beneath the depth of nil methane abundance in pore water was significantly greater than the rate of upward diffusion of methane in all four peatlands. Rates of methane diffusion in pore water at the minerotrophic peatlands were small (<10%) compared to surface emissions during June to August. The proportions were notably greater in the ombrotrophic bogs because of their typically low methane emission rates. Methanotrophy appears to consume entirely methane transported by pore water diffusion in the four peatlands with the exception of 4 of the 33 gas profiles sampled. Flux rates to the atmosphere regardless are high because of gas transport through vascular plants, in particular, at the minerotrophic sites. Cumulative rainfall amount 3-days prior to sampling correlated well with the distance between the water table level and the depth of 0 µmol l −1 methane, indicating that precipitation events can impact methane distributions in pore water. Further work is needed to characterise the kinetics of methane oxidation spatially and temporally in different wetland types in order Correspondence to: E. R. C. Hornibrook (ed.hornibrook@bristol.ac.uk) to determine generalized relationships for methanotrophy in peatlands that can be incorporated into process-based models of methane cycling in peat soils.

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.

[1] Rates and d 13 C values of CH 4 flux are reported from an upland blanket mire (Blaen Fign) situated in Wales UK. The d 13 C values of CH 4 flux were similar from Sphagnum and vascular flora dominated areas despite flux rates being an order of magnitude greater from the latter. Methane flux was 13 C-depleted relative to belowground CH 4 , indicating that transport occurred predominately via passive diffusion through vascular flora and that pore water diffusion and ebullition contributed little to CH 4 flux. The strong influence of vascular flora abundance on CH 4 flux strength suggests that any factors altering vegetation assemblages in blanket mires will likely impact CH 4 emission rates. Methane flux from Blaen Fign was highly 13 C-depleted compared to emissions from minerotrophic wetlands, suggesting that d 13 C values may be useful for tracing CH 4 flux from blanket mires and other types of ombrogenous peatlands to the global CH 4 budget.Citation: Bowes, H. L., and E. R. C. Hornibrook (2006), Emission of highly 13 C-depleted methane from an upland blanket mire, Geophys. Res. Lett., 33, L04401,

Abstract. Low affinity methanotrophic bacteria consume a significant quantity of methane in wetland soils in the vicinity of plant roots and at the oxic-anoxic interface. Estimates of the efficiency of methanotrophy in peat soils vary widely in part because of differences in approaches employed to quantify methane cycling. High resolution profiles of dissolved methane abundance measured during the summer of 2003 were used to quantify rates of upward methane flux in four peatlands situated in Wales, UK. Aerobic incubations of peat from a minerotrophic and an ombrogenous mire were used to determine depth distributions of kinetic parameters associated with methane oxidation. The capacity for methanotrophy in a 3 cm thick zone immediately beneath the depth of nil methane abundance in pore water was significantly greater than the rate of upward diffusion of methane in all four peatlands. Rates of methane diffusion in pore water at the minerotrophic peatlands were small (<10%) compared to surface emissions during June to August. The proportions were notably greater in the ombrogenous bogs because of their typically low methane emission rates. Methanotrophy appears to consume entirely methane transported by pore water diffusion in the four peatlands with the exception of 4 of the 33 gas profiles sampled. Flux rates to the atmosphere regardless are high because of gas transport through vascular flora, in particular, at the minerotrophic sites. Cumulative rainfall amount 3-days prior to sampling correlated well with the distance between the water table level and the depth of 0 μmol l−1 methane, indicating that precipitation events can impact methane distributions in pore water. Further work is needed to characterise the kinetics of methane oxidation spatially and temporally in different wetland types in order to determine generalized relationships for methanotrophy in peatlands that can be incorporated into process-based models of methane cycling in peat soils.