Environmental Health - Toxic Substances
Are Deserts Still Drying Out Since the Ice Age?
Desert vegetation at the Amargosa Desert Research Site
The answer appears to be yes, and this information could influence hazardous waste disposal practices. USGS scientists and their university partners have found that the sediments beneath the Nation’s southwestern deserts have been drying out for 16,000 years, since the cold and wet conditions of the ice age began to change to the hot and dry conditions of today. Aided by computer models, the scientists have learned that the drying out of these thick layers of dry sediments called the unsaturated zone has resulted in moisture moving upward rather than downward as expected. Normally precipitation percolates downward and replenishes ground water. However, the arid climate and desert plants draw moisture upward from hundreds of feet down in the subsurface. What the scientists have learned has implications for long-term waste disposal in the desert’s extremely dry unsaturated zones, because it means that removal of native vegetation, disposal of liquids, or changes to a wetter climate could potentially allow water and contaminants to percolate downward. This understanding of moisture movement can also be used to design better covers for desert landfills that rely on native plants to dry out sediments. In addition, the absence of ground-water replenishment in desert areas has important implications for sustainability of scarce ground-water resources.
Aided by computer models, the scientists have learned that the drying out of these thick layers of dry sediments called the unsaturated zone has resulted in moisture moving upward rather than downward as expected. Normally precipitation percolates downward and replenishes ground water. However, the arid climate and desert plants draw moisture upward from hundreds of feet down in the subsurface.
Related Science Features
Toxics Program Unsaturated Zone Research
Other USGS Information on Unsaturated Zone Flow and Transport
Andraski, B.J., 1997, Soil-water movement under natural-site and waste-site conditions--A multiple-year field study in the Mojave Desert, Nevada: Water Resources Research, v. 33, no. 9, p. 1901-1916.
Nimmo, J.R., Healy, R.W., and Stonestrom, D.A., 2003, Aquifer recharge, in Stewart, B.A., and Howell, T.A., eds., Encyclopedia of Water Science: New York, Marcel Dekker, Inc., p. 22-25.
Scanlon, B. R., Keese, Kelley, Reedy, R. C., Simunek, Jirka, and Andraski, B. J., 2003, Variations in flow and transport in thick desert vadose zones in response to paleoclimatic forcing (0-90 kyr)--Field measurements, modeling, and uncertainties: Water Resources Research, vol. 39, no. 7, 1179, p. 3-1--3-17, doi:10.1029/2002WR001604.
Stonestrom, D.A., Prudic, D.E., Laczniak, R.J., Akstin, K.C., Boyd, R.A., and Henkelman, K.K., 2003, Estimates of deep percolation beneath irrigated fields, native vegetation, and the Amargosa-River channel, Amargosa Desert, Nye County, Nevada: U.S. Geological Survey Open-File Report 03-104, 83 p.
Walvoord, M.A., Phillips, F.M., Tyler, S.W., and Hartsough, P.C., 2002, Deep arid system hydrodynamics--2. Application to paleohydrologic reconstruction using vadose zone profiles from the northern Mojave Desert: Water Resources Research, v. 38, no. 12, p. 27-1 to 27-12.
Walvoord, M.A., Plummer, M.A., Phillips, F.M., and Wolfsberg, A.V., 2002, Deep system hydrodynamics--1. Equilibrium states and response times in thick desert vadose zones: Water Resources Research, v. 38, no. 12, p. 44-1 to 44-15.
Walvoord, M.A., Stonestrom, D.A., Andraski, B.J., and Striegl, R.G., 2004, Constraining the inferred paleohydrologic evolution of a deep unsaturated zone in the Amargosa Desert: Vadose Zone Journal, v. 3, no. 2, p. 502-512, doi:10.2136/vzj2004.0502.
Walvoord, M.A., Stonestrom, D.A., and Phillips, F.M., 2002, From multi-year observations to millennial inferences--Uncertainties in paleohydrologic reconstructions of deep unsaturated zones in the desert southwest, U.S.A.: Eos, Transactions, American Geophysical Union, v. 83, no. 47, Fall Meeting Supplement, Abstract H22F-07, CD-ROM.