EXCHANGE OF NITROUS-OXIDE WITHIN THE HUDSON-BAY LOWLAND

The source strength of atmospheric trace gases from natural ecosystems must be quantified in order to assess the effect of such inputs on th e background tropospheric chemistry. A static chamber technique and a gas exchange technique were used to determine the emissions of nitrous oxide from five sites within the Hudson Bay Lowland, as part of the N orthern Wetland Study. Two mechanisms, one diffusive and the other epi sodic, were found likely to be responsible for the emissions of nitrou s oxide. The annual diffusive flux ranged from -3.8 mg(N2O)/m(2) in a treed bog to 7.9 mg(N2O)/m(2) in an open fen. The addition of the epis odic flux, increased this range to -2.1 mg(N2O)/m(2) and 18.5 mg(N2O)/ m(2) respectively. These episodic emission occurred in from 2.5% to 16 .7% of the samples during the late summer peak emission period. Since the gas exchange rate could not detect the episodic emissions, it was found to be a poor method for water emission rate determination within the wetland. LANDSAT-Thermatic Mapper (TM) imagery was used to scale the emissions, from the chamber level to an integrated average over th e entire Hudson Bay Lowland. The total emission rate of N2O from the H udson Bay Lowland, was determined to be 1.2 Gg(N2O)/year, of which 80% was attributed to episodic emissions.