Methane emissions from a wetland region within the Hudson Bay Lowland: An atmospheric approach

Continuous observations of methane (CH4) mixing ratios in combination with the atmospheric 222Rn activity and stable isotope ratios of carbon and hydrogen in atmospheric CH4 at a remote midcontinental monitoring station at Fraserdale, Ontario (49°53′N, 81°34′W) are used to characterize and quantify the regional CH4 emissions from the Hudson Bay Lowland (HBL). Large diurnal variations are observed in both trace substances during the summer which are due to emissions from ground level sources accumulating during strong nocturnal inversions. Diurnal changes of the stable isotopic composition of atmospheric CH4 at Fraserdale were used to determine the isotopic signature of the regional wetland CH4 source to be δ13CVPDB = (−60.0±3.2)‰ and δDVSMOW = (−442±142)‰. These integrated values are regarded as representative of several hundred square kilometers. The atmospheric 222Rn daughter observations made during the months of September and October 1994–1996 were used to estimate total CH4 emission rates in the region of Fraserdale. The fluxes of CH4 for September and October were (11.5±1.2) mg CH4 m−2 d−1 and (4.7±2.7) mg CH4 m−2 d−1, respectively, with an estimated absolute uncertainty of ±30%. These values are well comparable with summer flux measurements performed during the 1990 NOWES campaign using static chambers [Roulet et al., 1994] as well as using eddy correlation measurements performed on a tall tower [Edwards et al., 1994].