CARBON-DIOXIDE FLUXES OVER A RAISED OPEN BOG AT THE KINOSHEO LAKE TOWER SITE DURING THE NORTHERN WETLANDS STUDY (NOWES)

Measurements of carbon dioxide concentration and flux were made above a raised open bog at Lake Kinosheo in the southern Hudson Bay lowlands during the Northern Wetlands Study (NOWES) experiment in 1990. The fl ux measurements were made using micrometeorological techniques. They p rovide the first nondisturbing, larger-scale CO2 flux measurements for this ecosystem and are the first to integrate the exchange over the w hole 24 hours of the day. Continuous concentration measurements by inf rared gas analyzers (IRGA) and spot flask samples were taken over the period July 1 to July 29. Afternoon CO2 values were only 5 to 7 parts per million by volume (ppmv) lower than measurements over the same per iod at Canadian background monitoring stations. This suggested that th ere was little draw-down by local photosynthetic sinks. CO2 fluxes wer e measured at 8 and 18 m by Bowen ratio and eddy correlation methods, respectively. The methods produced comparable results on averaged data but often diverged considerably on individual half-hour results. flux es were small. Daytime values averaged to -0.068 mg/m(2)/s by eddy cor relation and -0.077 mg/m(2)/s by Bowen ratio over the period June 25 t o July 28 (negative denotes downward flux), while at night, flux densi ties were +0.062 mg/m(2)/s and +0.085 mg/m(2)/ s. Integration of the m ean diurnal curve gave a net flux of -1.7 g/m(2)/d. Comparable data fo r this type of ecosystem were not found. However, Coyne and Kelley (19 75), measuring near Barrow, Alaska, over wet meadow tundra dominated b y sedges and grasses, found net fluxes of -7.2 g/m(2)/d. Typical net C O2 fluxes from other active temperate ecosystems have been found to be -10 to -20 g/m(2)/d (Monteith, 1976). Mean half hourly fluxes were al most constant at +0.06 mg/m(2)/s through the nighttime hours. About on e half-hour after sunrise the flux reversed direction. Uptake peaked a bout 0900 eastern daylight time (EDT) and then gradually declined but remained downward until near sunset. The early peak was interpreted to signify that the many plants in the bog experienced water stress duri ng the day as evaporative demand increased and nighttime dew was evapo rated.