METHANE AND NITROUS-OXIDE FLUX IN A WYOMING SUB-ALPINE MEADOW

The atmospheric concentrations of the greenhouse gases nitrous oxide and methane continue to increase. Since both gases are derived primarily from the soil, soil source/sink relationships in a variety of ecosystems must be understood before complete global source/sink budgets can be accurately made. Little information exists about soil/atmosphere exchange of nitrous oxide and methane from subalpine, forests and forest meadows. A transect of flux measurement sites was established across a subalpine meadow and adjacent forest in southeastern Wyoming, and CH4 and N2O fluxes were measured at least weekly from snow melt in June until the winter snow covered the meadow in October during 1991 and 1992. Nitrous oxide emissions from the meadow were small both years, averaging only 2.5 and 1.3 ug N m-2 h-1 in 1991 and 1992, respectively. Fluxes were larger during the wetter year and varied from point to point, generally in response to soil moisture conditions. Methane flux varied across the meadow and over the season, also in response to changing soil moisture conditions. During the time of rapid snow melt when water was flowing freely across the meadow, the meadow acted as a net source of CH4. After snow melt was completed and the soil dried, the entire meadow became a sink for CH4. The mean snow-free seasonal CH4 flux for the meadow was -3.5 and -21.4 ug C m-2 h-1 during 1991 and 1992, respectively. As a whole, the meadow served as a sink for atmospheric methane, but sites within the meadow served as a net source of CH4 during the snow-free part of the year.