Methane fluxes in wetland and forest soils, beaver ponds, and low-order streams of a temperate forest ecosystem

Studies in tropical and boreal regions suggest that wetlands and forest soils are important sources and sinks, respectively, for atmospheric methane. This study was conducted to determine whether temperate wetlands and forests play important roles in the global balances of atmospheric methane. Flux measurements for methane in several different wetland, forest, and open-water (e.g., beaver pond and low-order stream) sites were determined using collection chambers placed over the soil- or water-air interface. All of the sites were located in the Appalachian Mountain region of West Virginia and western Maryland. Between June 1987 and April 1989 the wetland sites acted as small sources of atmospheric methane, with emission rates for methane usually < 200 mg CH₄ m^-2 d^-1 consumption of atmospheric methane in the wetland soils was observed frequently. The forest sites were mostly atmospheric methane sinks, even though emission rates (< 40 mg m^-2 d^-1) were observed sporadically. Open-water sites were large sources of atmospheric methane, with emission rates often exceeding 1000 mg CH₄ m^-2 d^-1. Methane fluxes were poorly correlated with environmental variables including soil moisture, soil and air temperature, and cloud cover, thereby making it difficult to determine the factors controlling methane fluxes in these sites. Scenarios of future global climate warming due to an increasing greenhouse effect suggest that wetlands and forests in the southern boreal forest will begin to resemble present-day temperate wetlands and forests. The results of our studies suggest that methane emissions from these "temperatelike" ecosystems will not result in a large positive feedback that might exacerbate the rate of global climate warming.