Greenhouse Gas Production and Transport in Desert Soils of the Southwestern United States

摘要

Deserts comprise a large portion of the Earth's land area, yet their role in the fluxes and cycles of greenhouse gases is poorly known and their likely response to climate change largely unexplored. We report a reconnaissance investigation of the concentrations and fluxes of CO2, CH4, and N2O along two elevation (climate) gradients in the southwestern United States. In-soil concentrations of CO2 increased with elevation (up to 5,000 ppm). Concentrations of CH4 declined with depth in all soils (to less than 1 ppm), but the rates of decrease with depth increased with elevation. In contrast, concentrations and depth trends of N2O varied erratically. Soils were net CO2 sources (0 to >1,500 kg CO2 center dot ha(-1).year(-1)), and net CH4 sinks (0.2 to >3 kg CH4 center dot ha(-1).year(-1)). The small and variable N2O fluxes were inconsistent with the trends in soil N delta N-15 values, which decreased by 5 to 6 over about 1,000 m of elevation. The high soil N delta N-15 values (up to nearly 17 at the lowest elevation) indicate that there is a soil N loss mechanism that is highly depleted in N-15, and gaseous losses-either NH3 or N2O/N-2-are suspected of driving these values. In summary, there appears to be a strong climate control on both soil CO2 and CH4 concentrations and to a lesser degree on calculated fluxes. The soil N trace gas concentrations indicate that deserts can be either small sources or sinks of N2O and that there may be significant consumption of arid soil N2O.