National Research Program


Amargosa Desert

Studies of Nitrogen and Carbon

Deserts have long been thought to be nutrient poor, but most traditional studies of nitrogen cycling in terrestrial ecosystems have examined the biologically active soil zone, which is considered to extend to about one meter below the surface. Then, in 2003, a report by USGS and other scientists on the Amargosa and other deserts noted that substantial quantities of nitrogen as nitrate have accumulated below the soil zone over millennial time frames and that arid regions in the southwestern United States contain a large reservoir of bioavailable nitrogen that had been previously overlooked continues to generate considerable interest. Amargosa DesertAs a result of this discovery, it is believed that the earth's global reservoir of soil nitrate is up to 16% greater than previously estimated. Because the desert subsoils contain oxygen and are low in organic matter, microbial populations, and water content, denitrification is inhibited and nitrate accumulates. However, there is evidence that climate change or the irrigation of arid areas could result in the percolation of this newly discovered nitrate into and the subsequent contamination of ground-water aquifers.

In 2005, USGS scientists reported that natural unsaturated-zone gas profiles at the U.S. Geological Survey's Amargosa Desert Research Site, near Beatty, Nevada, reveal the presence of two physically and isotopically distinct CO2 sources, one shallow and one deep. The shallow source derives from seasonally variable respiration in the root zone. Scanning electron micrograph results indicate that at least part of the deep CO2 source is associated with calcite precipitation at the 110-m-deep water table. A new model of carbon-isotopic profiles provides a quantitative approach for evaluating fluxes of carbon under natural conditions in deep unsaturated zones.

For additional information see the references:
Walvoord,M.A., Phillips, F.M., Stonestrom, D.A., Evans, R.D., Hartsough, P.C., Newman, B.D., and Striegl, R.G., 2003, A reservoir of nitrate beneath desert soils: Science, v. 302, no. 5647, p. 1021-1024.

Walvoord, M.A., Striegl, R.G., Prudic, D.E., and Stonestrom, D.A., 2005, CO2 dynamics in the Amargosa Desert: Fluxes and isotopic speciation in a deep unsaturated zone: Water Resources Research, v. 41, no 2. (1421 KB , published 2005 by American Geophysical Union, not subject to U.S. copyright)

or contact Michelle A. Walvoord, walvoord@usgs.gov

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