Validating the Use of 137Cs Measurements to Derive the Slope Component of the Sediment Budget of a Small Rangeland Catchment in Southern Italy

The sediment budget is a key concept and tool for characterizing the mobilization, transfer and storage of fine sediment within a catchment. Caesium-137 measurements can provide valuable information on gross and net erosion rates associated with sheet and rill erosion that can be used to establish the slope component of a catchment sediment budget. However, there is a need to validate the use of Cs-137 measurements for this purpose, because their reliability has sometimes been questioned. The study reported focuses on a small (304ha) steepland (mean slope 37%) catchment in Southern Italy. It exploits the availability of information on the medium-term sediment output from the catchment provided by the construction of a reservoir at its outlet in 1978 and the existence of estimates of soil redistribution rates derived from Cs-137 measurements made on 68 replicate soil cores collected from the slopes of a substantial proportion of the catchment in 2001, to validate the use of Cs-137 measurements to construct the slope component of the catchment sediment budget. An additional 50 replicate soil cores were collected from the catchment slopes for Cs-137 analysis, to complement the data already available. Nine cores collected from the area occupied by the reservoir were used to estimate the mean annual sediment input to the reservoir. In the absence of evidence that the poorly developed channel system in the catchment was either a significant sediment source or sink, it was possible to directly compare the estimate of net soil loss from the catchment slopes (733Mgha(-1)y(-1)) with the estimate of sediment output from the catchment provided by the reservoir deposits (752Mgha(-1)y(-1)). Taking account of the uncertainties involved, the close agreement of the two values is seen as providing a convincing validation of the use of Cs-137 measurements to both estimate soil redistribution rates and as a basis for constructing the slope component of the sediment budget of a small catchment. Copyright (c) 2015 John Wiley & Sons, Ltd.