Methane emissions were measured by a static chamber technique at 39 sites along a transect from the James Bay coast at the southeastern tip of Hudson Bay to Kinosheo Lake, northwest of Moosonee, Ontario, Canada. These sites represented five major wetland ecosystems along a successional gradient from the coast inland. Measurements were made at ≈10-day intervals from early June to mid-August, and once in mid-September and mid-October 1990. Seasonal CH4 fluxes were small (<2 g m-2) at the recently emerged coastal marsh, coastal fen, tamarack fen, and interior fen ecosystems, except where there were shallow ponds and pools, which emitted 2--5 g CH4 m-2. At the more complex bog ecosystem locations, CH4 fluxes were small (0.3--2.0 g m-2) from hummock/hollow microtopography in the raised bogs and from the forested margin. The largest CH4 fluxes were recorded from the degrading peat sections forming shallow pools and the moss/sedge mats which were always close to saturation (1.8--16.6 g m-2). A deeper (1-m water depth) pool emitted less CH4 (1.4 g m-2).

In terms of ecological succession along the transect, covering emergence over ≈4000 yr, CH4 emission rates increase from marsh to fen and bog, primarily through the development of peat degradation and the formation of moss/sedge lawns and pools. There were very weak statistical relationships at each site between the daily CH4 flux and peat temperature and water table. However, there was a significant (r2=0.44, p<0.001) correlation between the seasonal CH4 flux and the mean position of the water table over the complete range of sites, emphasizing the overall importance of hydrology in determining CH4 flux. Laboratory incubation experiments were conducted to determine the capacity of the surface (0--20 cm depth) peat samples to produce CH4 anaerobically and consume CH4 aerobically. They revealed that many samples exhibited high CH4 consumption rates, suggesting that although CH4 production in the subsurface peat is high, CH4 emissions from these wetlands to the atmosphere are limited to a large extent by CH4 oxidation in the surface layers of the peat. Trophic status of the peat appeared to have little influence on emission rates, with the highest fluxes in the most acid (pH<3.5) samples.