Deep down under

Natural History, Feb, 2004 by Avis Lang

Hydrologists have recently discovered that immense reservoirs of nitrogen have been accumulating for millennia beneath the western deserts of the United States. Michelle A. Walvoord of the U.S. Geological Survey in Lakewood, Colorado, and her colleagues now estimate that as much as 16 percent more nitrogen lurks in subsoil reservoirs worldwide than had previously been thought. It occurs as nitrate (N[O.sub.3.sup.-]), the same stuff that's used in making fertilizers and in curing ham and bacon. During infrequent heavy rains it has been washed out of the sparsely vegetated soil and has become increasingly concentrated as the rainwater evaporates or is drawn up into the roots of plants.

Walvoord and her colleagues warn that several scenarios--irrigation, the more frequent heavy rains that climate change may bring, and the construction of reservoirs--could push the nitrate ever deeper into the earth, where it would eventually contaminate groundwater. ("A reservoir of nitrate beneath desert soils," Science 302:1021-24, November 7, 2003)