Annual cycle of CO2 exchange at a bog peatland

Eddy covariance measurements of the carbon dioxide flux from an ombrotrophi c bog near Ottawa, Canada, were made between June 1, 1998, and May 31, 1999 , Net ecosystem exchange of CO2 (NEE) showed a distinct annual cycle, with net daily uptake increasing rapidly after snowmelt, peaking in midsummer an d declining toward the fall. Summer (June to September) mean daily NEE flux was an uptake of -2.8 +/- 0.23 (standard error) g CO2 m(-2) d(-1) but dail y values ranged considerably from a loss of 4.8 g CO2 m(-2) d(-1) to a maxi mum uptake of -8.3 g CO2 m(-2) d(-1). Daytime fluxes of CO2 were closely re lated to the photosynthetically active radiation flux, with derived relatio nships varying monthly. A curvilinear relationship developed between nightt ime NEE and soil temperature produced a Q(10) value of 3.0. Throughout the late fall and the snow-covered periods (November 5 to April 6), mean daily fluxes showed a fairly constant efflux of similar to1.1 +/- 0.003 g CO2 m(- 2) d(-1). The integrated non-growing season CO2 loss was 183 g CO2 m(-2). H owever, this was offset by gains during the long growing period resulting i n an integrated annual NEE net uptake of 248 +/- 68 g CO2 m(-2) yr(-1) for this peatland, The growing season measurements of CO2 flux at this site wer e similar to those reported in the few previous studies on northern peatlan d ecosystems, but no previous annual estimates of NEE based on year-round m easurements have been published for other peatlands. Compared to annual mea surements at forest sites in North America, the net exchange at this site f alls between that of a small annual loss recorded at a northern boreal spru ce forest and the substantial uptakes measured at a temperate mixed forest and boreal aspen forest sites.