Using caesium-137 and unsupported lead-210 measurements to explore the relationship between sediment mobilisation, sediment delivery and sediment yield for a Calabrian catchment

Recent concern about the many environmental problems associated with the transport of fine sediment by rivers has generated a need to obtain spatially distributed evidence of the erosion rates operating within a catchment and to explore more explicitly the links between sediment mobilization, transfer, storage and output. In the past few decades, the fallout radionuclides caesium-137 (137Cs) and unsupported lead-210 (210Pbex) have been successfully used as tracers to estimate soil erosion and deposition rates in many areas of the world. However, to date, most studies using this approach have focused on relatively small areas, such as individual fields or small catchments. There is a need to explore the potential for up-scaling the approach to larger areas or catchments. The present paper reports an attempt to use the fallout radionuclides 137Cs and 210Pbex to explore further the relationship between sediment mobilization, sediment transfer and storage, and sediment yield for a medium-scale (31.61 km2) catchment located in Calabria, southern Italy. The results emphasize that the low value of specific sediment yield derived for the study catchment from measurements of the suspended sediment flux at the catchment outlet obscure the existence of appreciable erosion rates in many areas of the catchment. Much of this erosion is balanced by deposition and sediment storage, resulting in a relatively low sediment delivery ratio for the catchment.