The application of fallout radionuclides to determine the dominant erosion process in water supply catchments of subtropical South-east Queensland, Australia

摘要

Previous studies using fallout radionuclides (137Cs and 210Pbex) to determine the relative contributions of surface-soil and channelnerosion (including gullies and channel banks) to stream sediments have used a relatively small number of composite samplesn(<25) to characterize the source end members, and concentrations in each of the source end members have, through the use ofnmeans and standard errors, been assumed to be normally distributed. Here, we examine 137Cs activity concentrations to determinenthe erosion processes supplying sediment in seven water supply catchments in South-east Queensland. First, we test some of thenunderlying assumptions in the method using concentrations of 137Cs and 210Pbex in composite samples collected from 109nsurface-soil sites and 39 channel-bank sites. Paired composite samples, each consisting of 20 subsamples, from five sites arenused to demonstrate that this sampling approach was sufficient to average out any local variations in surface-soil 210Pbex and 137Csnconcentrations across the 300m2 sampled. We derive probability distributions for 137Cs and 210Pbex concentrations in the groupnof samples from each of the end members and show that only the distribution of 210Pbex in samples from surface soils is normallyndistributed. We use the probability distributions for 137Cs, which provides the greatest discrimination between sources, to shownthat the 137Cs concentrations on the river sediment samples are consistent with channel erosion being the dominant source.nConservation works aimed at reducing the supply of sediments in these catchments should therefore focus on rehabilitation of thenchannel network and decreasing the runoff to the channel network. These findings are consistent with other similar studies onntropical Australian rivers. Copyright © 2012 John Wiley & Sons, Ltd.