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

Continuous observations of methane (CH 4 ) mixing ratios in combination with the atmospheric 222 Rn activity and stable isotope ratios of carbon and hydrogen in atmospheric CH 4 at a remote midcontinental monitoring station at Fraserdale, Ontario (49°53′N, 81°34′W) are used to characterize and quantify the regional CH 4 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 CH 4 at Fraserdale were used to determine the isotopic signature of the regional wetland CH 4 source to be δ 13 C VPDB = (−60.0±3.2)‰ and δD VSMOW = (−442±142)‰. These integrated values are regarded as representative of several hundred square kilometers. The atmospheric 222 Rn daughter observations made during the months of September and October 1994–1996 were used to estimate total CH 4 emission rates in the region of Fraserdale. The fluxes of CH 4 for September and October were (11.5±1.2) mg CH 4 m −2 d −1 and (4.7±2.7) mg CH 4 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].