Methane emissions from wetlands, southern Hudson Bay lowland

Abstract

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 CH 4 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 CH 4 m −2 . At the more complex bog ecosystem locations, CH 4 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 CH 4 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 CH 4 (1.4 g m −2 ). In terms of ecological succession along the transect, covering emergence over ≈ 4000 yr, CH 4 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 CH 4 flux and peat temperature and water table. However, there was a significant (r 2 = 0.44, p < 0.001) correlation between the seasonal CH 4 flux and the mean position of the water table over the complete range of sites, emphasizing the overall importance of hydrology in determining CH 4 flux. Laboratory incubation experiments were conducted to determine the capacity of the surface (0–20 cm depth) peat samples to produce CH 4 anaerobically and consume CH 4 aerobically. They revealed that many samples exhibited high CH 4 consumption rates, suggesting that although CH 4 production in the subsurface peat is high, CH 4 emissions from these wetlands to the atmosphere are limited to a large extent by CH 4 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.