Recent changes in sediment sources in a catchment in the Eastern Cape Province, South Africa

In view of addressing the severe soil erosion and sedimentation challenges facing many catchments in South Africa, there is increasing recognition of the need to include sediment control strategies within catchment management. Information on the potential catchment sediment sources and their temporal variation is important if an integrated understanding of the impacts of land use and climate change on catchments is to be achieved and to help targeted measures for soil erosion and sediment control. Statistically verified composite fingerprints and a multivariate fingerprinting procedure incorporating Monte Carlo simulations were used to reconstruct sediment source dynamics in the floodplain of the Mgwalana Catchment in the Eastern Cape, South Africa between 1950 and 2010. The study showed that grassland (grazing) areas have consistently been a major source sediment for the floodplain since the 1950s (40 – 83%), followed by abandoned cultivated land (37 – 40%). Since 1965 the contributions from abandoned and cultivated land peaked slightly, although grassland areas still remained the dominant sediment source. The results were consistent with observations from other studies in relation to the impact of livestock grazing on soil erosion in the Eastern Cape. In terms of surface/subsurface sources, the general long term trend showed that surface sources (57%) were slightly more dominant than subsurface sources (43%). However, the contributions from subsurface sources showed a consistently growing trend since 1965. This trend indicates an increase in the importance of gully erosion from the late 1960s. This information should be considered as a significant advance in our understanding of the sediment source dynamics in the catchment