Variability in methane emissions from wetlands at northern treeline near Churchill, Manitoba, Canada

This paper reports on a 2-yr study of methane emissions to the atmosphere made in a high subarctic wetland region at treeline near Churchill, Manitoba. Emissions were monitored from a treed bog, tundra fens, a coastal marsh and shallow ponds, which are wetland terrain types that dominate the region. There were substantial emissions from the fens, marsh, and ponds but very small emissions from the bog. Variability was large, both spatially and temporally. This included variability in measurements at a specific site, between sites, over the course of a single season and between years. Such variability was a response to edaphic factors which control methane production and consumption, differences in ground water levels and pond depths which determine whether conditions are aerobic or anaerobic, and variability in air and soil temperatures. During the cool, moist summer of 1990 there were moderate to strong correlations of log normalized methane emissions with depth to water table or pond depth and with air temperature. In the warmer and drier summer of 1989 correlations were more weakly developed. Some of this behavior is explainable by the relation between methane production under anaerobic conditions and consumption under aerobic conditions. During 1990, the methane production on a site by site basis was comparable to coincident measurements made in the southern Hudson Bay Lowland and in the mid-boreal region of Ontario. In 1989, the emissions were about three-fold less than in 1990.