The contribution of dissolved organic carbon (DOC) to mineral weathering was investigated under the changing Eh and pH conditions in three subarctic fens, near Schefferville, Quebec. No evidence of increased weathering rates nor different weathering patterns were found in the fen basal sediment despite DOC-rich and low Eh (0 to +200 mV) conditions. / Solutions containing 50 mg DOC/L derived from subarctic fen peat, and of 50 and 300 mg DOC/L, derived from deciduous leaf litter were used as weathering agents. Clinochlore, microcline and the Fe-rich basal till from the Schefferville fens were used as weatherable mediums. The DOC rich solutions and controls (made of distilled water buffered to the same initial pH) were used to investigate the relative weathering ability of DOC-rich waters under aerobic and anaerobic conditions. The relative ability was determined by comparing the changing cation concentrations in the solutions.

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The sources, sinks, fluxes, spatial distributions, and temporal variations of dissolved organic carbon (DOC) in subarctic fen catchments as well as the temporal patterns of DOC in streams draining subarctic fen catchments in the region of Schefferville, Quebec were investigated. / In June to August sampling, DOC concentrations averaged 17 mg/L in peat water, 2-16 m/L in stream water, 49-56 mg/L in canopy throughfall, 14-19 mg/L in understory throughfall, 122-187 mg/L in stemflow, 25-39 mg/L in lichen and moss mat water, and 35-42 mg/L in soil A horizon water. / Precipitation and canopy and understory throughfall were all significant DOC sources with seasonal DOC fluxes to the forest floor of 0.1-0.4, 0.5-1.3, and 0.8-1.7 g DOC/m$ sp2$ of forest, respectively. The lichen and moss mats and the A soil horizon were also found to be DOC sources, whereas the B soil horizon was a DOC sink. The soil column was estimated to export 0.4-0.5 g DOC/m$ sp2$. Peat, also a DOC source, released 1.2-2.1 g DOC/m$ sp2$. / DOC concentrations in streams draining ten fen catchments were found to be positively correlated with the percentage of fen area in the catchments.

Emissions of methane were measured by a static chamber technique at 9 sites on 5 wetlands in the Eastern Temperate Wetland Region, north of Montreal. Mean daily methane fluxes measured from May to October ranged from 0.18 to 1071 mg/m$ sp2$/d, and estimated annual flux ranged from 0.02 to 186 g/m$ sp2$/y. Laboratory incubations of peat samples showed potential anaerobic methane production rates which ranged from 0.00 to 9.12 $ mu$g/g/d, and potential aerobic consumption rates from 0.55 to 3.75 $ mu$g/g/d. Seasonal methane emission patterns are related to water table level and CH$ sb4$ production and consumption potentials in the peat profile. Episodic fluxes were found to be important at several sites, contributing a significant portion of the total emissions. / Analysis of spectral reflectance data from 20 sites on 2 subarctic fens was carried out to address the issue of scaling up CH$ sb4$ emissions using satellite imagery. Hummocks, lawns and pools were found to be spectrally distinct enough to be differentiated by band 5 of Landsat MSS and band 3 of Landsat TM sensors. The averaging of spectral information in mixed pixels proved unlikely to be able to distinguish between wet lawn and string and pool communities. Such weaknesses can be overcome with the use of higher resolution data.

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The objective of this study is to assess current distributional patterns of species within a community, while taking into account species' evolutionary histories, as reflected in their phylogenetic relationships. The hypothesis is that closely related species segregate along environmental gradients, either due to historic evolutionary divergence of their niches, or to ecological processes presently occurring within a community. Distribution along environmental gradients was compared to phylogenetic structure of the 27 sedge species (Cyperaceae) growing in the subarctic fen communities of Schefferville, northern Quebec. Field data suggest that within these fens, sedges mostly differentiate along gradients of rooting depth and pH. Species growing in similar (micro)habitats often belong to different taxonomic sedge clades, and species belonging to the same clade usually differentiate on at least one environmental gradient. Further comparison of natural distribution to responses under greenhouse experimental conditions for four selected Carex species suggests that the two relatives in section Limosae differ in their tolerance ranges to environmental conditions due to past evolutionary events, while the two members of section Paniceae differentiate along environmental gradients in nature due to ongoing ecological processes.

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