Methane and carbon dioxide flux from a macrotidal salt marsh, Bay of Fundy, New Brunswick

Fluxes of methane (CH4) and carbon dioxide (CO2) to the atmosphere at 52 sites within a salt marsh were measured by a dark static chamber technique from mid July to mid September. Mean CH4 fluxes ranged from 0.2 mg m(-2) d(-1) to 11.0 mg m(-2) d(-1), with an overall average of 1.6 mg m(-2) d(-1). Flux of CH4 was inversely correlated (r(2) = 0.23, p = 0.001) with salinity of the upper porewater at the site, suggesting the dominant role of SO42- in inhibiting methanogenesis in salt-marsh sediments. The combination of salinity and water table position was able to explain only 29% of the variance in CH4 emission. Mean soil flux of CO2 ranged from 0.3 g m(-2) d(-1) to 3.7 g m(-2) d(-1), with an overall average of 2.5 g m(-2) d(-1); it was correlated with aboveground biomass (positive, r(2) = 0.38, p = 0.001) and position of the water table (negative, r(2) = 0.55, p = 0.001). The combination of biomass and water table position accounted for 63% of the variance in CO2 flux. There were high variations in gas flux within the six plant communities. The sequences were CH4: upland edge > panne > pool > middle marsh > low marsh > high marsh, and CO2: middle marsh > low marsh > upland edge > high marsh > panne > pool. Compared to other salt-marsh systems, this Bay of Fundy marsh emits small amounts of CH4 and CO2.