Net ecosystem CO2 exchange in a boreal peatland, northern Manitoba

Net ecosystem CO2 exchange (NEE) was measured by a chamber technique from J une to September, 1994, at five peatland sites where the water table was cl ose to the peat surface, ranging from ombrotrophic bog to minerotrophic fen , near Thompson, Manitoba. NEE measurements were made during three 10-14-da y periods, and CO2 exchange relationships with photosynthetically active ra diation (PAR), air and soil temperatures, and water table were used to mode l net ecosystem productivity (NEP) for the season. Daily NEE ranged from -3 to 5 g CO2-C m(2) d(-1), with positive values indicating uptake by the lan d surface. Two of the sites became sources of CO2 during the late summer, a ssociated with plant senescence and falling water tables. Average NEP for l une to August ranged from 1.4 to 2.5 g CO2-C m(-2) d(-1). Both water table position and end-of-season above-ground sedge biomass were strong predictor s of NEP during each measurement period as well as over the lune to August period Sites with high NEP had high aboveground sedge biomass (75 to 100 g m(-2)) and low water tables (seasonal average -5 to -10 cm).