Application of environmental magnetism to estimate source contribution by lithology to Kruger National Park reservoirs

Sediment source fingerprinting using environmental magnetism has successfully differentiated between sediment sources in several studies in the Eastern Cape Province of South Africa. The method was applied in this study to the near-natural landscape of southern Kruger National Park (Mpumalanga Province) to trace sediment and determine sediment yields by lithology in four reservoir catchments that were underlain by igneous, metamorphic, and sedimentary rocks. The Park area has no history of cultivation and is a conservation area, so catchment sources were dominated by underlying lithologies. One sediment core was collected in the assumed deepest area of the reservoir. Source discrimination and apportionment were estimated using a common statistical protocol that includes a Mann-Whitney U or Kruskal-Wallis H test, mass conservation test, discriminant function analysis, and an (un)mixing model. A contribution from each lithology-defined source was estimated. Sediment yield by lithology was estimated by using published catchment area-specific sediment yields in combination with the (un)mixing model. Underlying lithology determined vegetation type and density, and vegetation appeared to play a crucial role in protecting soils and reducing erosion. Proximity to reservoir, that is, travel distance for eroded sediment, and connectivity were also important factors controlling the relative contribution from each potential source. The contributing area for sediment was found to be dynamic through time and was probably dependent on runoff and temporal variations in vegetation cover.