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 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 Impact of Experimental Temperature and Water Level Manipulation on Carbon Dioxide Release in a Poor Fen in Northern Poland

“…Samaritani et al (2010) showed that the strongest differences in soil respiration were observed during the warmer and drier periods. Long periods without rain may result in a sharper transition between unsaturated and saturated peat layers (Hornibrook et al 2008) and change diffusion coefficients and water saturation within the peat, which can slow down the transport of gases and solutes in the peat profile (Waddington and Roulet 1997;Fraser et al 2001;Limpens et al 2008). Our results show that the peatland carbon flux can be modified by even small changes in environmental conditions such as those induced by our treatments.…”

Anaerobic oxidation of methane: an underappreciated aspect of methane cycling in peatland ecosystems?

“…Recent evidence provides strong support for the occurrence of AOM in peat soils (Smemo and Yavitt, 2007), yet conclusive ev- (Smemo and Yavitt, 2006;2007), Smemo and Yavitt (2006), and Keller and Bridgham (2007). 2 values derived from Hornibrook et al (2009), Keller and Bridgham, (2007), Küsel et al (2008), and Loy et al (2004). 3 values derived from Beer and Blodau (2007), Billet and Moore (2008), Blodau et al (2007aBlodau et al ( , 2007b, and Shotyk (1997a, 1997b).…”

Annual emissions of CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O, and ecosystem respiration, from eight organic soils in Western Denmark managed by agriculture

“…Methane oxidation potentials appear to be highest near the oxic/anoxic interface. Hornibrook et al (2009) found that CH 4 dissolved in the pore water of four Welsh peatland soils was nearly always zero at the groundwater table and concluded that emissions observed were predominantly mediated by vascular plants. The ability of plants with aerenchymous tissue to transport CH 4 to the atmosphere when CH 4 concentrations build up around the roots is well established (Laanbroek, 2010), and typically occurs when the soil is near saturation (Strack et al, 2006).…”

“…No attempt was made to correct CH 4 fluxes, which depend on CH 4 production in saturated parts of the soil profile, and CH 4 oxidation that may also primarily occur near the groundwater table (Hornibrook et al, 2009). At this depth diurnal temperature variations are small, i.e., any error associated with sampling time would be small.…”