Controls on CH4 emissions from a northern peatland

We examined the controls on summer CH4 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 CH4 flux, determined by static chambers on collars, ranged from 22 to 239 mg CH4-C m(-2) d(-1) and was related to peat temperature. There was an inverse relationship between water table position and CH4 flux: higher water tables led to smaller fluxes. The determination of anaerobic CH4 production and aerobic CH4 consumption potentials in laboratory incubations of peat samples was unable to explain much of the variation in CH4 flux. Average net ecosystem exchange of CO2 ranged from 1.4 to 2.5 g CO2-C m(-2) d(-1) and was strongly correlated with CH4 flux; CH4 emission averaged 4% of CO2 uptake. End-of-season sedge biomass was also strongly related to CH4 flux, indicating the important role that vascular plants play in regulating CH4 flux. Determination of isotopic signatures in peat pore water CH4 revealed average delta(13)C values of between -50 and -73 parts per thousand and delta D of between -368 and -388 parts per thousand. Sites with large CH4 emission rates also had high CO2 exchange rates and enriched delta(13)C CH4 signatures, suggesting the importance of the acetate fermentation pathway of methanogenesis. Comparison of delta D and delta(13)C signatures in pore water CH4 revealed a slope shallow enough to suggest that oxidation is not an important overall control on CH4 emissions at these sites, though it appeared to be important at one site. Analysis of C-14 in pore water CH4 showed that most of the CH4 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 CH4 emissions from these wetland sites through influences on the availability of fresh plant material for methanogenesis, rhizospheric oxidation, and plant transport of CH4.