ROLE OF THE HUDSON-BAY LOWLAND AS A SOURCE OF ATMOSPHERIC METHANE

Based on point measurements of methane flux from wetlands in the borea l and subarctic regions, northern wetlands are a major source of atmos pheric methane. However, measurements have not been carried out in lar ge continuous peatlands such as the the Hudson Bay Lowland (HBL) (320, 000 km(2)) and the Western Siberian lowland (540,000 km(2)), which tog ether account for over 30% of the wetlands north of 40 degrees N. To d etermine the role the Hudson Bay Lowland as a source of atmospheric me thane, fluxes were measured by enclosures throughout the 1990 snow-fre e period in all the major wetland types and also by an aircraft in Jul y. Two detailed survey areas were investigated: one (approximate to 90 0 km(2)) was in the high subarctic region of the northern lowland and the second area (approximate to 4,800 km(2)) straddled the Low Subarct ic and High Boreal regions of the southern lowland. The fluxes were in tegrated over the study period to produce annual methane emissions for each wetland type, The fluxes were then weighted by the area of 16 di fferent habitats for the southern area and 5 habitats for the northern area, as determined from Landsat thematic mapper to yield an annual h abitat-weighted emission. On a per unit area basis, 1.31 +/- 0.11 and 2.79 +/- 0.39 g CH4 m(-2) yr(-1) were emitted from the southern and no rthern survey areas, respectively. The extrapolated enclosure estimate s for a 3-week period in July were compared to within 10% of the flux derived by airborne eddy correlation measurements made during the same period. The aircraft mean flux of 10 +/- 9 mg CH4 m(-2) d(-1) was not statistically different from the extrapolated mean flux of 20 +/- 16 mg CH4 m(-2) d(-1) weighted emission for the entire HBL using six wetl and classes is estimated as 0.538 +/- 0.187 Tg CH4 yr(-1) (range of ex treme cases is 0.057 to 2.112 Tq CH4 yr(-1)). This value is much lower than expected, based on previous emission estimates from northern wet lands.