Soil emission inventories of nitrogen oxide and nitrous oxide from natural ecosystems in Ontario

The purpose of this study was to determine a complete soil emission inventory of NO{dollar}sb{lcub}rm x{rcub}{dollar} and N{dollar}sb2{dollar}O for the Province of Ontario. The source strength of atmospheric trace gases from natural ecosystems must be quantified in order to assess the effect of such inputs on the background tropospheric chemistry. This was the first complete soil emission inventory available for the province, and required the determination of the emissions from the northern wetlands and boreal forests.; Canada contains approximately 54% of the world's {dollar}2.76 times 10sp6{dollar} km{dollar}sp2{dollar} of boreal and polar peatland, but NO{dollar}sb{lcub}rm x{rcub}{dollar} and N{dollar}sb2{dollar}O emissions from this ecosystem had never been previously measured. Nitrous oxide emissions were obtained along a transect from the coast of the James Bay to Kinosheo Lake, during the ice free season period of 1990. Two emission mechanisms, one diffusive and the other episodic, were found to be responsible for the emissions of N{dollar}sb2{dollar}O. The total emission of N{dollar}sb2{dollar}O from the Hudson Bay lowland was 1.2 Gg/yr, of which 80% were attributed to episodic emissions. The emissions of NO{dollar}sb{lcub}rm x{rcub}{dollar} from the northern wetlands were found to be very small, only one seventh of the uptake rate determined.; Boreal forests cover on the order of 55% of the Province of Ontario, and no previous measurements of the emissions of NO{dollar}sb{lcub}rm x{rcub}{dollar} and N{dollar}sb2{dollar}O were available. In the summer of 1992, emission measurements were made from an undisturbed forest, a drained forest, an upland forest and a clear-cut forest. Although the effects of drainage were slight for the emission of NO{dollar}sb{lcub}rm x{rcub}{dollar} and N{dollar}sb2{dollar}O, those of clear-cutting were significant. The uptake of N{dollar}sb2{dollar}O was clearly enhanced in the drainage ditches by the presence of algae, which also resulted in large CH{dollar}sb4{dollar} production.; With the data available from these major ecosystems, a soil emission inventory for the Province of Ontario was compiled. The annual emission of NO{dollar}sb{lcub}rm x{rcub}{dollar} in the province was determined to be 5.4 Gg, of which 82% were emitted from agricultural soils (5.5% of the land area). Emissions from forests accounted for 17% and 0.5% from wetlands. The annual emission of N{dollar}sb2{dollar}O in the province was determined to be 7.9 Gg, of which 68% was emitted from agricultural soils. Forests accounted for 17.8% and wetlands for 14.2%. Inventories such as this, are essential in developing a clear understanding of the role of natural emissions in both local and global air chemistry.