Detection and prediction of sediment sources in catchments: use of Be-7 and Cs137

Activities of the naturally occurring isotope Be-7 and the bomb produced Cs-137 were measured in the soils and sediments of two small agricultural catchments at Wagga Wagga in NSW. Similar measurements were also made on soils and sediments from a number of runoff/erosion plots undergoing different cropping-tillage treatments. The results indicate that together the two isotopes provide a means of locating the sources of eroded soil. Analyses of soil and sediment particle size fractions and their isotopic activities also permit discrimination between sheet, rill, and gully erosion mechanisms. These isotopic methods would not be as effective if either isotope were measured in isolation