No description available.

No description available.

Carbon dioxide and methane fluxes were measured between May 2003 and August 2004 on vegetated surfaces and pools of three peatlands located in the La Grande Riviere watershed, James Bay lowland, Quebec, Canada. Gas flux measurements were made using static chambers on a variety of sites in the three peatlands, chosen to represent the different biotypes present, from hummocks with water table position 35 cm below the surface to pools 100 cm deep. / Average CH4 fluxes for the different biotypes on vegetated surfaces sampled during summer 2003 ranged from 3.5 to 197 mg m-2 d-1 while summer 2004 average floating chamber pool fluxes ranged between 6.2 and 3165 mg CH4 m-2 d -1. Mean daily CH4 fluxes on vegetated surface are strongly correlated (r2 > 0.75) with summer average water table depth, greater fluxes occurring where water table is close to the surface. The vegetated surface CH4 fluxes were also correlated with peat temperature as fluxes increase with increasing peat temperature during the summer. / Most net ecosystem productivity values calculated for the different biotypes in the three peatlands showed release of CO2 during both early and mid growing season periods. An annual budget calculated for the LG2 peatland showed that the peatland emitted CO2 to the atmosphere at a rate of 0.77 g m-2 d-1. The overall release of CO 2 may have been caused in part by dry conditions in the peatlands during summer 2003, due to high temperature and low precipitation.

A soil climate parameterization is designed for peatland environments in the Canadian Land Surface Scheme (CLASS). Three wetland soil classes account for the variation in the hydraulic characteristics of organic soils. Saturated hydraulic conductivity varies from a median of 1.0 x 10-7 m/s in deeply humidified sapric peat to 2.8 x 10-4 m/s in relatively undecomposed fibric peat. Average pore volume fraction ranges from 0.83 to 0.93. Parameters are derived for the soil moisture characteristic curves of fibric, hemic and sapric peat, using the Campbell (1974) equation employed in CLASS, and the van Genuchten (1980) formulation. Validation of modelled water table depth and peat temperature is performed for a fen in northern Quebec and a bog in north-central Minnesota. The new parameterization results in more realistic simulation than the previous version of CLASS, which was constrained to using mineral soil properties to approximate those of organic soils. / Two approaches are used to model methane emissions from northern peatlands using the new soil climate parameterization in CLASS. In the first module, the multiple regression equation of Dise et al. (1993) is used to simulate daily methane emissions from water table depth and peat temperature. In the process-based module, methane flux is divided into its component parts: plant transport, diffusion and ebullition. Each of these transport mechanisms is determined by methane concentrations, which are calculated from a series of processes related to peat temperature, water table level and rooting depth. The daily methane emissions predicted by the two models are similar and correlate reasonably with observations from a bog in north-central Minnesota.

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No description available.

The role of Eriophorum vaginatum in carbon dioxide (CO 2) and methane (CH4) dynamics of two restored peatlands in eastern Canada was examined. Sites were established in Riviere-du-Loup, Quebec from May to October of 1999 and 2000, and Shippagan, New Brunswick from May to October of 2001. / CH4 emissions from E. vaginatum collars were positively related to maximum photosynthesis in 1999 and 2001, when the water table was close to the surface. CH4 emissions were also positively related to end of season above ground plant biomass at both sites. CH4 emissions from E. vaginatum collars ranged from -0.015 to 14.7 mg CH4-C m-2 h-1 at Riviere-du-Loup and -0.15 to 5.4 mg CH4-C m -2 h-1 at Shippagan. It is likely that E. vaginatum provides substrate for methanogenesis through plant production and acts as a conduit transporting CH4 to the atmosphere. / Patterns of NEE from E. vaginatum depended on site-specific and year-specific conditions. E. vaginatum was a net sink for CO2 at high and low light levels at Shippagan, and a net source of CO2 at low light levels at Riviere-du-Loup.

No description available.