Using Anthropogenic Radioisotopes to Estimates Rates of Soil Erosion by Wind.

Erosion of soil by wind and water is a degrading process that affects millions of hectares worldwide.  Atmospheric testing of nuclear weapons and the resulting fallout of anthropogenic radioisotopes, particularly Cesium 137, has made possible the estimation of mean soil redistribution rates.  The peak fallout levels occurred in the early 1960s.  Cesium 137 has a relatively short half-life of 30.2 years, limiting its use for future studies.  Radioisotopes of Plutonium were also created during the period of atmospheric testing and were deposited onto the earth’s surface at less than 1/50th the rate of Cesium 137, but recent advances in analytical techniques have made Plutonium isotope measurements relatively quick and cost-effective.   The half-lives of Plutonium 239 and Plutonium 240 are 24,100 years and 6,500 years, respectively, making them ideal tracers for future erosion estimates.  Further, the ratio of these two isotopes is easily measurable and may be used to validate the contribution from stratospheric fallout rather than from local sources of contamination.  We sampled a system of locations with documented wind erosion and deposition histories by depth and analyzed the samples for Cesium 137 and for Plutonium 239+240.  Models developed for Cesium 137 predicted redistribution rates very well when a particle size correction factor of 1.18 was used for eroding surfaces.  Plutonium 239+240 activities and distribution patterns correlated very well with those of Cesium 137, strongly indicating the usefulness of these radioisotopes for future studies of soil redistribution in semi-arid environments.