CARBON TRACE GAS FLUXES ALONG A SUCCESSIONAL GRADIENT IN THE HUDSON-BAY LOWLAND

Patterns and controls of carbon trace gas emissions from wetlands may vary depending upon the spatial and temporal scale being examined. The factors affecting these emissions are thought to be hierarchically re lated according to their respective scales of importance. A hierarchic al model of processes controlling methane emissions from wetlands is p resented and examined here. During the 1990 Northern Wetlands Study (N OWES) methane (CH4), carbon dioxide (CO2), and non-methane hydrocarbon (NMHC) fluxes were measured in static chambers along a 100 km transec t in the Hudson Bay lowland (HBL). Environmental variables, vegetation abundance, and ecosystem age and structure were also quantified at ea ch sampling site. The findings indicate that CH4 emissions from peatla nds (e.g., bogs and fens) and other wetlands (e.g., salt marshes) in t he region were low, and were nil or negative (i.e., CH4 uptake) in for ests and bog forests dominated by aspen and black spruce. Site to site variations in mean CH4 flux appeared to be most closely related to me an water table and sedge productivity, both of which are intercorrelat ed. Seasonal changes in CH4 flux tend to follow soil temperature fluct uations. Instantaneous CO2 and CH4 daytime fluxes exhibit a negative c orrelation, suggesting that photosynthetic assimilation of carbon may be related to CH4 emissions, although the processes of CO2 and CH4 pro duction are occurring at somewhat different temporal scales. No diurna l variations in CH4 flux could be detected. While soil water pH trends rue not fully explored, there is some indication that high CH4 fluxes are concentrated around pH 4 and pH 7. Soil temperature closely follo ws the seasonal progression of CH4 flux. Estimated CH4 seasonal flux ( 1.5-3.9 g CH4 m(-2) season(-1)) and estimated aboveground net primary productivity (NPP) (90 - 400 g dry weight m(-2) season(-1)) show syste matic changes along a successional sequence which are consistent with patterns predicted from successional theory. Estimated seasonal NMHC e missions (0.5-1.4 g C m(-2) season(-1)) exhibit an increase along the succession from salt marsh to Sphagnum bog communities. Data from seve ral studies were combined to estimate seasonal CO2 flux from three sit es. The estimated fluxes range from a net uptake of 23 g CO2 m(-2) sea son(-1) to a net loss of 77 g CO2 m(-2) season(-1), although there are large uncertainties in these estimates. It is inferred from the asses sment of ecosystem age and structure that disturbance effects and succ essional changes occurring over hundreds to thousands of years in the HBL strongly control regional CH4, CO2, and NMHC emissions by influenc ing NPP, species composition, community structure, soil (peat) develop ment, and landscape hydrology. Given this, it is likely that models of carbon trace gas flux based on succession models may be useful in pre dicting climate change-landscape change feedbacks.