Up-scaling the Application of Fallout Radionuclides to Support Catchment Sediment Management Programmes

The application of fallout radionuclides in soil erosion and sedimentation investigations has provided a valuable tool for improving the understanding of erosion and sediment transfer processes. However, most studies using fallout radionuclides have focussed on small areas. Increasing acceptance of the important role of fine sediment in degrading aquatic habitats and in the transfer and fate of nutrients and contaminants within terrestrial and fluvial systems has emphasized the need for sediment management programmes in many areas of the world. Such programmes commonly focus on the catchment scale and an understanding of the sediment budget of a catchment represents a key requirement for developing effective sediment management strategies. Although the need for information on catchment sediment budgets is clear, obtaining such information faces many practical problems. While fallout radionuclides offer considerable potential for use in documenting sediment budgets for small areas, there is a need to up-scale their use to provide information at the catchment — and larger scales. To date there have been few attempts to develop and implement such upscaling. This paper describes the results of three studies undertaken by the authors to address this need. These examples include, firstly, the use of caesium-137 (137Cs) measurements to provide the data required for a national scale soil erosion inventory; secondly, the use of areawidescale spatially distributed sampling of 137Cs inventories to assemble information on catchment sediment budgets; and finally the use of 137Cs and excess lead-210 (Pbex) measurements to establish sedimentation rates on river floodplains.