Determining the origins and history of sedimentation in an underground river system using natural and fallout radionuclides.

Murray, AS; Stanton, R; Olley, JM; Morton, R

CSIRO Div. Water Resour., G.P.O. Box 1666, Canberra, A.C.T. 2601, Australia

Journal of Hydrology (Amsterdam) vol. 146, no. 1-4, pp. 341-359, 1993 ISSN 0022-1694

Natural and anthropogenic radionuclides were used to characterize the source of sediment reaching the underground river in the karst system at Jenolan, New South Wales, Australia. It was found that the relationship between super(226)Ra and super(232)Th concentrations, in both spatially averaged soil samples and transported sediments, distinguished between two of the most likely source subcatchments. Sedimentary sequences, collected from within the underground system, showed that contemporary deposition was made up of an equal mixture of sediment from these two sources. However, at least three earlier deposition periods were also identifiable, each with different relative contributions from the source catchments. The first appearance of super(137)Cs in the sedimentary sequence and correlations with historical information provided a chronology for these changes, and it is concluded that the contemporary phase was initiated in the early 1950s, most probably by forestry activities. This work demonstrates that natural radioactivity can be used as a tracer of the origins of sediment, providing an important new approach to problems in sediment supply, transport, and deposition.