METHANE EMISSIONS FROM WETLANDS IN THE MIDBOREAL REGION OF NORTHERN ONTARIO, CANADA

Methane (CH4) fluxes were measured by a static chamber technique from May to October 1991 at 19 wetland sites near Cochrane, northern Ontario, representative of the Clay Belt Midboreal region of central Canada. Seasonal average fluxes of CH4 from the peatlands ranged from 0.4 to 67.5 mg.m-2.d-1 (0.06-10.1 g.m-2.yr-1). Beaver ponds showed the highest fluxes of CH4, from both the open water section (seasonal average 290 mg.m-2.d-1, 44 g.m-2.yr-1) and the adjacent marsh areas where the water table rose close to or above the soil surface (91-350 mg.m-2.d-1, 13-53 g.m-2.yr-1). Seasonal mean water table position, particularly at the microtopographic scale of hummock and hollow, explained most of the variability in CH4 emission among wetlands (r2 = 0.74). Trophic status, such as pore-water Ca, Mg, and pH had little correlation with CH4 emissions. Broad-scale peatland classifications that do not account for hydrological differences at the microtopographic level are inadequate for predicting CH4 flux in boreal wetlands, particularly in forested ecosystems where conifer swamps are diverse and comprise the major peatland class. Based on areal estimates of the different wetland types in the Clay Belt, we estimate an annual CH4 flux of 3.4 g.m-2.yr-1, generally lower than that used in extrapolations to continental- or global-scale methane budgets.