Beaver ponds are important parts of peatland landscapes and have high fluxes of CO2 and CH4. This study was undertaken in Mer Bleue Bog, Ontario, to determine the response of a beaver pond to drainage (lowering by 25 cm) as a sink or source of carbon. Plant distribution was changed in response to a new water table gradient. Each vegetation community and the remaining beaver pond were sampled for fluxes of CO2 and CH4 from mid-April to end-November, 1999, one year after the water table was lowered. / A flow-through chamber system was used to measure CO2 flux from vegetated sites. Mean daily CO2 flux ranged from 0.4--1.6 g CO2-C M-2 (positive denoting uptake from the atmosphere). Variations in CO2 flux amongst the sites along the gradient could not be related to differences in plant species composition, peat temperature, or water table. The mean daily CO2 emission measured by a static floating chamber on the pond area was -24.1 g CO2-C m-2. / A closed chamber was used to measure CH4 on vegetated sites. Daily CH4 fluxes ranged from 1 to -159 mg CH4-C m-2, increasing from the beaver pond margin to the open water surface. The water table explained 83% of the seasonal average CH 4 flux variability and the vegetation added another 11%. The mean daily CH4 flux measured by a static floating chamber on the pond area was -54 mg CH4-C m-2. / The seasonal measurements were integrated into an areal estimate of CO 2 and CH4 flux for the beaver pond area prior to and after drainage. The beaver pond area sequestered 96 g m-2 before drainage (104 g CO2-C m-2 and -8 g CH 4-C m-2), and the same area more than doubled the uptake to 231 g m-2 after being drained (233 g CO 2-C m-2 and -3 g CH4-C m -2).

The exchange of carbon and water between a temperate peatland and the atmosphere was studied directly for the vascular plants; Chamaedaphne calyculata, Kalmia angustifolia, Vaccinium myrtilloides, and Maianthemum trifolium and indirectly for the bryophytes; Sphagnum rubellum and S. magellanicum. In vascular plants, carbon and water fluxes were well coupled (∼2.27 mumol CO 2 mmol-1 H2O) except in the post-deciduous period where temperature constrained water flux more than carbon flux. The seasonal cycle of Sphagnum water content was driven by water table depth; rain depth, rain frequency and atmospheric vapor pressure deficit. In 2000, these factors combined to cause primarily over saturation with regard to optimal net photosynthesis in Sphagnum. Carbon and water exchange at the community scale was also studied and related to the leaf level patterns observed. Few leaf level patterns were observable at the community scale although the effects of species composition and leaf area index were well represented in the community signal.

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