Methane dynamics of a northern boreal beaver pond

The production, oxidation, and transport of methane (CH4) from a boreal beaver pond were measured during the ice-free period in order to explain the observed flux of CH4 between the pond and the atmosphere. The study pond was located in the northern study area (NSA) of the Boreal Ecosystem Atmosphere Study (BOREAS), near Thompson, Manitoba. Three pathways transported the CH4 produced in the rich, organic anaerobic sediments. In order of importance they were: bubble flux (ebullition), diffusion, and plant transport. The water-air flux of CH4 was related to windspeed and sediment temperature, whereas the bubble flux also showed a degree of synchronicity with changes in atmospheric pressure and water level. By mid-June the storage of CH4 in the sediments reached a quasi steady-state, and production minus oxidation approximated the water-air exchange. Since the dominant pathway of ebullition is little affected by oxidation, the mean unit area flux of CH4 for the vegetated and open portions of the beaver pond (155 and 320 mg CH4 m−2day−1) were larger than the flux observed in most wetlands of the NSA. CH4 in bubbles from vegetated sites was significantly enriched in 13C and significantly depleted in 2H relative to bubbles from open water sites, consistent with a shift in methane production mechanism from acetate fermentation to CO2 reduction for the vegetated and unvegetated sites, respectively. The radiocarbon content of methane was not different between the two types of sites (114.7 ± 4.2pMC, vegetated versus 108.1± 6.5pMC, open water).