THE USE OF CESIUM-137 MEASUREMENTS TO ESTABLISH A SEDIMENT BUDGET FORTHE START CATCHMENT, DEVON, UK

Caesium-137 (Cs-137) measurements have been used to investigate the de livery of sediment from the hillslopes to a lake which marks the downs tream limit of the small agricultural Start basin in Devon, UK. Total Cs-137 inventories and Cs-137 depth distributions in sediment cores we re used to estimate that the eroded sediment stored within the fields and on the flood plain of the main river was equivalent to sediment yi elds of ca. 21 and 30 t km(-2) year(-1), respectively. Based on publis hed information on sediment accumulation in the lake, the minerogenic sediment yield from the basin was estimated to be ca. 29 t km(-2) year . The erosion rate on the hillslopes in the basin, calculated as the s um of the sediment yield to the lake and the two storage components, i s ca. 80 t km(2) year(-1). Of the soil eroded from the slopes more tha n 60% is stored at intermediate locations and the sediment delivery to the lake is less than 40%. The calculated soil erosion rare for the S tart basin is consistent with an estimate of the erosion rate for the basin of the nearby Old Mill Reservoir of ca. 63 t km(-2) year(-1).