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Emissions of CH 4 were measured by a static chamber technique (five chambers/site) at 23 sites in four fens near Schefferville, subarctic Quebec. At three intensively‐monitored sites along a transect from fen margin to central and flooded sites, mean CH 4 fluxes from June to August, 1989 were 65, 125, and 36 mg m −2 d −1 , respectively. Pore water CH 4 concentrations in the peat profiles to a depth of l m averaged 125 to 200 μM, with lower concentrations (generally <50 μM) at 0.1 m. Total, depth‐integrated storage of CH 4 in the peat profiles ranged from 3.5 to 4.3 g m −2 . Although CH 4 flux was only weakly correlated with either peat temperature at 0.1 m or water table position within each site, there was a strong association of flux and these variables among the three sites, indicating the value of ecological attributes in identifying patterns of CH 4 flux. A pulse of CH 4 was recorded at two of the three sites in mid‐August, associated with a degassing of the peat profile, based on pore water CH 4 concentrations. This pulse appeared to be initiated by the lowering of the water table by between 5 and 10 cm during a 3‐week period of low rainfall and is estimated to have contributed 18 to 65% of the seasonal CH 4 emission, depending on the location of the site. An estimate of the regional CH 4 flux from 130 km 2 of the Schefferville area was based on CH 4 flux measurements at 23 sites in the area, stratified by fen type (forested margin, margin, central, flooded, ridge, and pool). June to August regional CH 4 flux was 18 mg m −2 d −1 , for an area in which fen coverage was 29%. When extrapolated to the global scale, these results indicate that northern fens may contribute about 14 Tg yr −1 , somewhat lower than other recent estimates.
Moore et al. (Thu,) studied this question.