A three-year study of controls on methane emissions from two Michigan peatlands

Abstract

Abstract. We investigate temporal changes in methane emissions over a three-year period from two peatlands in Michigan. Mean daily fluxes ranged from 0.6-68.4 mg CH4 mm2 d-' in plant communities dominated by Chamaedaphnecalyculata, an ericaceous shrub, to 11 S-209 mg CH4 m-* d-' in areas dominated by plants with aerenchymatous tissues, such as Carex oligosperma and Scheuchzeria palustris. Correlations between methane flux and water table position were significant at all sites for one annual cycle when water table fluctuations ranged from 15 cm above to 50 cm below the peat surface. Correlations were not significant during the second and third annual periods with smaller water table fluctuations. Methane flux was strongly correlated with peat temperatures at -5 to -40 cm (rs = 0.82 to 0.98) for all three years at sites with flora acting as conduits for methane transport. At shrub sites, the correlations between methane flux and peat temperature were weak to not significant during the first two years, but were strong in the third year. Low rates of methane consumption (-0.2 to -1.5 mg CH4 mm2 d-l) were observed at shrub sites when the water table was below -20 cm, while sites with plants capable of methane transport always had positive net fluxes of methane. The methane oxidizing potential at both types of sites was confirmed by peat core experiments. The results of this study indicate that methane emissions occur at rates that cannot be explained by diffusion alone; plant communities play a significant role in altering methane flux from peatland ecosystems by directly transporting methane from anaerobic peat to the atmosphere.

Spatial and temporal variability in CH4 and N2O fluxes from a Scottish ombrotrophic peatland: Implications for modelling and up-scaling

“…The temporal response in CH 4 emissions to variations in temperature is consistent with previous studies (Frolking and Crill, 1994;Shannon and White, 1994;Laine et al, 2007) Net CH 4 flux is dependent on the balance between oxidation and production processes. As the temperature response in methanogens is generally greater than that of methanotrophs (Segers, 1998), the overall effect on net emissions is positive.…”

“…Although significant changes in water table depth (e.g. drainage or drain blocking) have repeatedly been shown to strongly influence CH 4 emissions Strack et al, 2004), a much weaker relationship is often observed with temporal water table variability in the field (Frolking and Crill, 1994;Shannon and White, 1994). In our study water table was a significant correlate only in the Hollow chambers, although soil moisture, which may provide a better measure of both current The drivers of temporal variability were not consistent across the study site.…”

Instream and riparian implications of weed cutting in a chalk river

“…This is either due to the longer acclimation periods that methanogenesis requires or suppression of methanogenesis from the mobilisation of sulphate during the more aerobic conditions present when the water level fell (Gauci et al, 2004). In fact, periodic lowering of the water table to 0.15-0.20 m below the surface (within the range observed here ; table 3) has been demonstrated to completely inhibit CH4 generation (Shannon and White, 1994;Altor and Mitsch, 2006). Therefore, weed cutting may have potential as a management tool to mitigate greenhouse gas emissions from riparian wetlands.…”

Methanogenesis and methane emissions: effects of water table, substrate type and presence of Phragmites australis

“…Dise et al, 1993;Shannon and White, 1994;Roslev and King, 1996). This is not surprising as the oxygen availability and hence potential for aerobic degradation of organic matter and CH 4 oxidation increase when the water table is lowered.…”

“…Enhancement occurs through production and release of organic matter (Holzapfel-Pschorn et al, 1986;Schütz et al, 1991), and by transportation of CH 4 via molecular diffusion or convective flow through the internal gas spaces of the plants, thus bypassing oxidation in the anoxic/oxic interface (Shannon and White, 1994;Sorrell and Boon, 1994;Shannon et al, 1996). Many species of emergent macrophytes possess a convective flow mechanism which is many times more efficient in transporting gases than diffusion alone (Brix et al, 1992), and hence these species may accelerate the emission of CH 4 from wetlands (Brix et al, 1996).…”