Determination of the rate of sheet erosion on grazing land using caesium-137

Abstract

There is concern about the rate of sheet erosion in the catchment of one of Sydney's water-supply reservoirs. A survey of net soil loss using the caesium-137 technique was carried out in a 7-ha subcatchment near Goulburn, New South Wales, Australia. Caesium-137, a fallout isotope of atmospheric thermonuclear weapons tests, because of its useful radioactive half-life (30 years), and because it becomes rapidly and firmly attached to surface soils, can be used as a radiotracer of soil movement. A survey of three toposequences within the subcatchment revealed that the 137Cs distribution corresponded with a previously established 137Cs sediment hillslope model. An existing regression equation, relating long-term soil loss from plots to 137Cs loss, was used to calculate net soil loss within the basin. Results indicated that soil losses due to sheet erosion were between zero and 1093kgha −1yr −1.