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 for 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 mobilisation, transfer, storage and output. In the last 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 use of this approach has focussed on relatively small areas, such as individual fields or small catchments. There is a need to explore the potential for upscaling the approach to larger areas or catchments. This paper reports an attempt to use the fallout radionuclides 137Cs and 210Pbex to explore further the relationship between sediment mobilisation, sediment transfer and storage and sediment yield for a medium-scale (31.61 km2) catchment located in Calabria, southern Italy. The results emphasise 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.