FLUX TO THE ATMOSPHERE OF CH4 AND CO2 FROM WETLAND PONDS ON THE HUDSON-BAY LOWLANDS (HBLS)

Ponds on peatlands of the Hudson Bay lowlands (HBLs) are complex ecosy stems in which the fluxes to the atmosphere of CH4 and CO2 were contro lled by interacting physical and biological factors. This resulted in strong diel variations of both dissolved gas concentrations and gas fl uxes to the atmosphere, necessitating frequent sampling on a 24-hour s chedule to enable accurate estimates of daily fluxes. Ponds at three s ites on the HBL were constant net sources CH4 and CO2 to the atmospher e at mean rates of 110-180 mg CH4 m(-2) d(-1) and 3700-11,000 mg CO2 m (-2) d(-1). Rates peaked in August and September. For CH4 the pond flu xes were 3-30 times higher than adjacent vegetated surfaces. For CO2 t he net pond fluxes were similar in magnitude to the vegetated fluxes b ut the direction of the flux was opposite, toward atmosphere. Even tho ugh ponds cover only 8-12% of the HBL area, they accounted for 30% of its total CH4 flux to the atmosphere. There is some circumstantial evi dence that the ponds are being formed by decomposition of the underlyi ng pest and that this decomposition is being stimulated by the activit y of N-2 fixing cyanobacteria that grow in mats at the peat-water inte rface. The fact that the gas fluxes from the ponds were so different f rom the surrounding vegetated surfaces means that any change in the ra tio of pond to vegetated area, as may occur in response to climate cha nge, would affect the total HBL fluxes.