ECOSYSTEM AND PHYSIOLOGICAL CONTROLS OVER METHANE PRODUCTION IN NORTHERN WETLANDS

Peat chemistry appears to exert primary control over methane productio n rates in the Canadian Northern Wetlands Study (NOWES) area. We deter mined laboratory methane production rate potentials in anaerobic slurr ies of samples collected from a transect of sites through the NOWES st udy area. We related methane production rates to indicators of resista nce to microbial decay (peat C:N and lignin:N ratios) and experimental ly manipulated substrate availability for methanogenesis using ethanol (EtOH) and plant litter. We also determined responses of methane prod uction to pH and temperature. Methane production potentials declined a long the gradient of sites from high rates in the coastal fens to low rates in the interior bogs and were generally highest in surface layer s. Strong relationships between CH4 production potentials and pest che mistry suggested that methanogenesis was limited by fermentation rates . Methane production at ambient pH responded strongly to substrate add itions in the circumneutral fens with narrow lignin:N and C:N ratios ( partial derivative CH4/partial derivative EtOH = 0.9-2.3mg g(-1)) and weakly in the acidic bogs with wide C:N and lignin:N ratios (partial d erivative CH4/partial derivative EtOH = -0.04-0.02 mg g(-1)). Observed Q(10) values ranged from 1.7 to 4.7 and generally increased with incr easing substrate availability, suggesting that fermentation rates were limiting. Titration experiments generally demonstrated inhibition of methanogenesis by low pH. Our results suggest that the low rates of me thane emission observed in interior bogs during NOWES likely resulted from pH and substrate quality limitation of the fermentation step in m ethane production and thus reflect intrinsically low methane productio n potentials. Low methane emission rates observed during NOWES will li kely be observed in other northern wetland regions with similar vegeta tion chemistry.