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

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 m⁻²d⁻¹ in plant communities dominated by Chamaedaphne calyculata, an eficaceous shrub, to 11.5–209 mg CH₄ m⁻²d⁻¹ 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 (r _s = 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 m⁻² d⁻¹ ) 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.