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

Methane exchange between the atmosphere and subalpine wetland and unsaturated soils was evaluated over a 15-month period during 1995–1996. Four vegetation community types along a moisture gradient (wetland, moist-grassy, moist-mossy, and dry) were included in a 100 m sampling transect situated at 3200 m elevation in Rocky Mountain National Park, Colorado. Methane fluxes and 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 CH₄ efflux to the atmosphere) were: 0.3 to 29.2 mmol CH₄ m⁻² d⁻¹ wetland area; 0.1 to 1.8 mmol CH₄ m⁻² d⁻¹, moist-grassy area; −0.04 to 0.7 mmol CH₄ m⁻² d⁻¹, moist-mossy area; and −0.6 to 0 mmol CH₄m⁻² d⁻¹, dry 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 moisture 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 based on field measurements at the other sites were 0.12 mol CH₄ m⁻², moist-grassy area; 0.03 mol CH₄ m⁻², moist-mossy 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, moist-mossy, and dry sites, respectively.