Linking land use, erosion and sediment yields in river basins

Results obtained from erosion plots and catchment experiments provide clear evidence of the sensitivity of erosion rates to land use change and related human activity. Evidence for the impact of land use on the sediment yields of world rivers is less clear, although examples of rivers where sediment yields have both increased and decreased in recent decades can be identified. The apparent lack of sensitivity of river sediment loads to land use change reflects, at least in part, the buffering capacity associated with many river basins. This buffering capacity is closely related to the sediment delivery ratio of a river basin, in that basins with high sediment delivery ratios are likely to exhibit a reduced buffering capacity. Investigations of the impact of land use and related human activity on sediment yields should consider the overall sediment budget of a catchment rather than simply the sediment output. Information on the sediment budget of a drainage basin is difficult to assemble using traditional techniques, but recent developments in the application of fingerprinting techniques to establish sediment sources and in the use of environmental radionuclides, such as caesium-137 and lead-210, to document sediment storage offer considerable potential for providing such information. Sediment storage within a river basin can give rise to environmental problems where sediment-associated pollutants accumulate in sediment sinks. The accumulation of phosphorus on river floodplains as a result of overbank sedimentation can, for example, represent an important phosphorus sink.