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High Nitrate in the Desert? What's Going On?

Desert vegetation at the Amargosa Desert Research Site
Amargosa Desert, Nevada
(click image for a larger version)

USGS scientists and their colleagues have unexpectedly found large concentrations of nitrate in desert subsoils. This previously overlooked accumulation of nitrogen is surprising because desert ecosystems are known to have become adapted to a lack of nitrogen. However, the nitrate recently found is within a few meters of land surface and below the biologically active root zone. Contrary to conventional wisdom, small amounts of naturally occurring nitrate appear to have been leaching from soil layers and accumulating for thousands of years in the unsaturated zones of arid regions. Scientists are concerned about this high level (thousands of kilograms per hectare) of nitrate because

  • Irrigating desert soils, a change to a wetter climate, disposal of liquid wastes, or construction of dams could release large quantities of nitrate to ground water, which in turn could potentially threaten drinking-water supplies (high concentrations of nitrate can cause human health problems).
  • These accumulations will cause scientists to rethink the long-term movement of nitrate and how nitrate is used (or not used) by plants in desert environments.

This finding built upon an understanding of how water moves in deserts-an understanding that scientists are advancing at the USGS's Amargosa Desert Research Site. Working at the site, scientists discovered that deserts in the southwest have been drying out since the ice age.

Reference

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. 7, p. 1021-1024

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