Title: Use of Anthropogenic Radioisotopes to Estimate Rates of Soil Redistribution by Wind Author
Submitted to: Aeolian Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 5, 2012
Publication Date: June 1, 2013
Citation: Van Pelt, R.S. 2013. Use of Anthropogenic Radioisotopes to Estimate Rates of Soil Redistribution by Wind. Aeolian Research. 9:89-102. Interpretive Summary: Wind erosion is increasingly scrutinized by regulatory agencies as a source of fugitive dust. Process-based predictive models have been developed that will allow land managers and action agencies such as USDA-NRCS to assess the potential impact of soil management on air quality and agricultural sustainability. In order to locally calibrate these models for optimal accuracy, the average rate of soil erosion for that location must be known. The time and cost of long-term wind erosion modeling precludes this approach in all but a very few existing long-term study sites. Atmospheric testing of nuclear weapons in the 1950s and 1960s resulted in globally distributed atmospheric fallout of previously non-existent chemical species that are strongly adsorbed to the soil. These anthropogenic radioisotopes, most notably cesium-137 have been widely used to estimate rates of soil redistribution by wind, water, and tillage. The previous work in this field was reviewed and a new, previously little-used pair of anthropogenic radioisotopes, plutonium-239 and plutonium-240 for this use is investigated and compared with cesium-137 at a wind erosion study site in the Southern High Plains of Texas. The anthropogenic radioisotope soil tracers plutonium-239 and plutonium-240 may, for many reasons, become the soil redistribution tracers of choice for decades, centuries, and millennia to come.
Technical Abstract: Wind erosion results in soil degradation and fugitive dust emissions. The temporal and spatial variability of aeolian processes makes local estimates of long-term average erosion costly and time consuming. Atmospheric testing of nuclear weapons during the 1950s and 1960s resulted in previously non-existent anthropogenic radioisotopes being injected into stratospheric global circulation and subsequently deposited on the earth’s surface. Many of theses radioisotopes are strongly adsorbed to soil particles and their movement on the landscape is a powerful method for investigating soil redistribution by wind, water, and tillage. The radioisotope method for assessing soil redistribution rates has many advantages, but also a few limitations. One of the major limitations occurs when local sources of radioisotope contamination, particularly 137Cs, mask the pulse from global fallout, making temporal estimates of redistribution difficult or impossible. Isotopes of Pu offer the advantages of much longer half-lives, increasing their useful life as tracers into the next millennium, and of the 240Pu/239Pu ratio of approximately 0.18 for global fallout, allowing for detection of local sources of contamination and verification of the validity of redistribution rate estimates. In this paper, I explore the importance, history, and applications of the radioisotopic technique, particularly as it applies to soil redistribution by wind, present previously unpublished data from a pilot study designed to test whether or not 239+240Pu can be used to estimate rates of soil redistribution by wind, and conclude that 239+240Pu may well be the anthropogenic radioisotope of choice for future soil redistribution investigations.