Estimating residence times of sediment in rvier channels using fallout Pb-210
The residence time of fine-grained sediment (<10 mm diameter) within river channels is often assumed to be short, and has been rarely quantified. Here we investigate a new approach to estimate residence times of such material. Fine-grained sediments collected from along the Brisbane River, Queensland, Australia, have higher excess 210Pb activities and 210Pb/137Cs ratios than sediment eroded from uncultivated, cultivated and channel bank sources in the catchment. We explore the possibility that these higher 210Pb activities are related to residence of the sediment within the channel and propose a method for using this data to make a residence time calculation. The method gave a range of residence times of 0–21 years for the Brisbane sediments. Data from the adjacent Logan River system provide a range of 0–9 years, although both ranges were dependent on a number of assumptions regarding sediment thickness and 210Pb fallout rates and amounts.
The Structure, Function and Management Implications of Fluvial Sedimentary Systems
Geomorphology and Regolith and Landscape Evolution