Methanotrophy potential versus methane supply by pore water diffusion in peatlands

Abstract

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.

Decomposition ‘hotspots’ in a rewetted peatland: implications for water quality and carbon cycling

“…From the microcosm results, sequential use of electron acceptors occurs relatively quickly after rewetting (in the short-term; Table 5) tending to increase pH (see discussion below), in line with the general consensus (e.g. Blodau et al, 2004;Hornibrook et al, 2008;Toberman et al, 2008;Knorr et al, 2009), and evidence for this can be seen in the field too. In the long-term though, SO 4 2-accumulated markedly, the reasons for which are unclear but could include SO 4 2-release from the peat matrix via sulphatase activities (see later), more efficient thiosulphate recycling (Heitmann et al, 2007), or an inhibition of sulphate reduction by competing anaerobic processes (Paul & Clark, 1989).…”

Effects of nitrate and sulfate on greenhouse gas emission potentials from microform-derived peats of a boreal peatland: A 13C tracer study

“…2, blue color). Several authors have reported positive correlation between CH 4 fluxes and CH 4 oxidation rates (Basiliko et al, 2007;Hornibrook et al, 2009). This may suggest that CH 4 oxidation is substrate (CH 4 )-dependent rather than limited by the availability of O 2 (Sundh et al, 1994;Saarnio et al, 1997).…”

Precipitation fuels dissolved greenhouse gas (CO2, CH4, N2O) dynamics in a peatland-dominated headwater stream: results from a continuous monitoring setup

“…Under water-logged and anoxic conditions (e.g., pristine and re-wetted peatlands), CH 4 is mainly produced by methanogens if other terminal electron acceptors are depleted, and oxygenated carbon compounds (e.g., CO 2 ) are available (Lyu et al, 2018;Gao et al, 2019). At anoxic to oxic interfaces, methanotrophic microbes can oxygenize CH 4 to produce energy and CO 2 (Hanson and Hanson, 1996;Hornibrook et al, 2009). These basic concepts of GHG production are also valid in aquatic ecosystems.…”