Controls on CH4 emissions from a northern peatland

Abstract

We examined the controls on summer CH 4 emission from five sites in a peatland complex near Thompson, Manitoba, Canada, representing a minerotrophic gradient from bog to rich fen at wet sites, where the water table positions ranged from −10 to −1 cm. Average CH 4 flux, determined by static chambers on collars, ranged from 22 to 239 mg CH 4−C m−2 d−1 and was related to peat temperature. There was an inverse relationship between water table position and CH 4 flux: higher water tables led to smaller fluxes. The determination of anaerobic CH 4 production and aerobic CH 4 consumption potentials in laboratory incubations of peat samples was unable to explain much of the variation in CH 4 flux. Average net ecosystem exchange of CO 2 ranged from 1.4 to 2.5 g CO 2−C m−2 d−1 and was strongly correlated with CH 4 flux; CH 4 emission averaged 4% of CO 2 uptake. End‐of‐season sedge biomass was also strongly related to CH 4 flux, indicating the important role that vascular plants play in regulating CH 4 flux. Determination of isotopic signatures in peat pore water CH 4 revealed average δ 13 C values of between −50 and −73‰ and δD of between −368 and −388‰. Sites with large CH 4 emission rates also had high CO 2 exchange rates and enriched δ 13 C CH 4 signatures, suggesting the importance of the acetate fermentation pathway of methanogenesis. Comparison of δD and δ 13 C signatures in pore water CH 4 revealed a slope shallow enough to suggest that oxidation is not an important overall control on CH 4 emissions at these sites, though it appeared to be important at one site. Analysis of 14 C in pore water CH 4 showed that most of the CH 4 was of recent origin with percent of modern carbon values of between 112 and 128%. The study has shown the importance of vascular plant activities in controlling CH 4 emissions from these wetland sites through influences on the availability of fresh plant material for methanogenesis, rhizospheric oxidation, and plant transport of CH 4.