METHANE FLUXES, CONCENTRATIONS, AND PRODUCTION IN 2 ADIRONDACK BEAVER IMPOUNDMENTS

We measured methane release into the atmosphere, concentrations and fluxes of dissolved methane, and rates of methane production by peats in two beaver impoundments in the Adirondack Park region of New York to determine whether such impoundments are a significant source of atmospheric methane. In 1990, methane release rates were similar between impoundments and averaged 705 and 600 pmol cm-2 min-1 (i.e. 162 and 138 mg CH4 m-2 d-1). Water-column concentrations of dissolved CH4 were lower in one impoundment (33 muM) than in the other (158 muM). Rates of CH4 production by underlying peats were similar between impoundments and averaged 34.7 and 25.1 pmol cm-3 min-1. In both impoundments, CH4 oxidation in the water and at the sediment-water interface seemed to be an important factor controlling its release. Moss-dominated wetlands adjacent to the impoundments had at least tenfold lower release rates for CH4 and fivefold lower concentrations of dissolved CH4. Beaver impoundments in woodland streams appear to be important local sources of atmospheric CH4. Enhanced CH4 cycling in these systems compared to that in local wetlands could be due to altered hydrology, increased retention of sediment and organic matter caused by beaver activities, or both.