Soil-atmosphere gas exchange across an Alpine tundra landscape

The alpine, while not extensive in global area, has several advantages for trace gas research, particularly the spatial landscape heterogeneity in soil types and plant communities. This variation can be viewed as a “natural experiment,” allowing field measurements under extremes of moisture and temperature. While the atmospheric carbon dioxide (CO2) record at Niwot Ridge extends back to 1968 (chapter 3), and NOAA has done extensive measurements on atmospheric chemistry at the subalpine climate station (e.g., Conway et al. 1994), work on tundra soil-atmosphere interactions were not initiated until recently. In 1992, studies were begun on Niwot Ridge to gain a comprehensive understanding of trace gas fluxes from alpine soils. Our sampling regime was designed to capture the spatial and temporal patterns of trace gas fluxes in the alpine. In addition, we coupled our studies of trace gas fluxes with ongoing studies of nitrogen cycling on Niwot Ridge (Fisk and Schmidt 1995,1996; Fisk et al. 1998; chapter 12). Methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) were studied because of their role in global environmental change and because they could be easily monitored at our remote sites. On a per-molecule basis, CH4 and N2O are much more potent as greenhouse gases than CO2 is (Lashof and Ahuja 1990; Rodhe 1990). In addition, N2O plays a role in ozone depletion in the stratosphere. The global CH4 and N2O budgets are still poorly understood and the relative importance of soils in these budgets is even less clear. For example, estimates of the global soil sink for CH4 range from 9.0 to 55.9 Tg per year (Dörr et al. 1993). This range is large compared with the approximately 30 Tg of excess CH4 that is accumulating in the atmosphere every year. To better assess the role of soil in trace gas budgets, our work focused on investigating landscape patterns of gas fluxes (CH4, N2O, and CO2) and environmental controls on these fluxes.