The effects of grain abrasion and disaggregation on Cs-137 concentrations in different size fractions of soils developed on three different rock types

Sediment that is transported fluvially is subject to the processes of sorti ng, abrasion and breakage. Each of these processes may affect the propertie s used to determine the origin of the sediment; so they should be evaluated in sediment tracer studies. As part of a study to determine the dominant s ources of sediment in Tarago Reservoir, southeastern Victoria, Australia, t he effects of disaggregation and grain abrasion on the distribution of Cs-1 37 With respect to particle size fractions were studied in soils derived fr om the three different rock types of the Tarago catchment. The main action of abrasion over short distances is aggregate breakage. In each soil, the m aterial produced by abrasion had approximately the same Cs-137 concentratio n as the corresponding size fractions of unabraded soil. The < 40 mu m size fraction, which is the dominant sediment size in the Tarago Reservoir, inc ludes material generated by partial disaggregation and grain abrasion as we ll as unabraded soil. Consequently, determining the sources of sediment in the Tarago Reservoir using Cs-137 is unlikely to be significantly affected by grain abrasion or disaggregation. These results improve the confidence w ith which Cs-137 can be used to trace the origin of sediment at other sites . (C) 1999 Elsevier Science B.V. All rights reserved.