UC Berkeley

Abstract 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 CO 2 , CH 4 , and N 2 O along two elevation (climate) gradients in the southwestern United States. In‐soil concentrations of CO 2 increased with elevation (up to 5,000 ppm). Concentrations of CH 4 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 N 2 O varied erratically. Soils were net CO 2 sources (0 to >1,500 kg CO 2 ·ha −1 ·year −1 ), and net CH 4 sinks (0.2 to >3 kg CH 4· ha −1 ·year −1 ). The small and variable N 2 O fluxes were inconsistent with the trends in soil N δ 15 N values, which decreased by 5‰ to 6‰ over about 1,000 m of elevation. The high soil N δ 15 N values (up to nearly 17‰ at the lowest elevation) indicate that there is a soil N loss mechanism that is highly depleted in 15 N, and gaseous losses—either NH 3 or N 2 O/N 2 —are suspected of driving these values. In summary, there appears to be a strong climate control on both soil CO 2 and CH 4 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 N 2 O and that there may be significant consumption of arid soil N 2 O. Plain Language Summary We conducted the first comprehensive study of how greenhouse gas production and consumption varies with climate and season in the deserts of California and Nevada. Desert soils are significant consumers of atmospheric methane, an important greenhouse gas. Soils are both small producers and small consumers of nitrous oxide. Given the small nitrous oxide emission rates, there must be an unidentified gaseous loss of nitrogen occurring in desert soils. Finally, the carbon dioxide emission rates, coupled with the amounts of organic carbon in the soils, suggest that deserts—like many ecosystems—will lose organic carbon due to global warming and will in turn act to accentuate greenhouse gases in the atmosphere. Key Points We present measurements on the soil carbon dioxide, methane, and nitrous oxide concentrations and fluxes in the Great Basin and Mojave Deserts of California and Nevada The desert is a significant methane sink There appear to be fairly large, but unidentified, gaseous losses of N from desert soils