Methane flux in subalpine wetland and unsaturated soils in the southern Rocky Mountains

Methane exchange between the atmosphere and subalpine wetland and unsaturat ed soils was evaluated over a 15-month period during 1995-1996. Four vegeta tion community types along a moisture gradient (wetland, moist-grassy, mois t-messy, and dry) were included in a 100 m sampling transect situated at 32 00 m elevation in Rocky Mountain National Park, Colorado. Methane fluxes an d soil temperature were measured during snow-free and snow-covered periods, and soil moisture content was measured during snow-free periods. The range of mean measured fluxes through all seasons (a positive value represents C H4 efflux to the atmosphere) were: 0.3 to 29.2, mmol CH4 m(-2) d(-1) wetlan d area; 0.1 to 1.8 mmol CH4 m(-2) d(-1) moist-grassy area; -0.04 to 0.7 mmo l CH4 m(-2) d(-1), moist-messy area; and -0.6 to 0 mmol CH4 m(-2) d(-1), dr y area. Methane efflux was significantly correlated with soil temperature ( 5 cm) at the continuously saturated wetland area during snow-free periods. Consumption of atmospheric methane was significantly correlated with moistu re content in the upper 5 cm of soil at the dry area. A model based on the wetland flux-temperature relationship estimated an annual methane emission of 2.53 mol CH4 m(-2) from the wetland. Estimates of annual methane flux ba sed on field measurements at the other sites were 0.12 mol CH4 m(-2), moist -grassy area; 0.03 mol CH4 m(-2), moist-messy area; and -0.04 mol CH4 m(-2) , dry area. Methane fluxes during snow-covered periods were responsible for 25, 73, 23, and 43% of the annual fluxes at the wetland, moist-grassy, moi st-mossy, and dry sites, respectively.