Contemporary erosion rates in the Kruger National Park, South Africa, inferred from reservoir siltation surveys

Reinwarth, Bastian GND

Soil erosion by water is a major environmental issue that affects about 70% of South Africa's land surface and leads to significant environmental and economical costs. In the view of soil conservation, erosion caused by natural conditions (e.g., climate, relief, soils) must be considered largely unavoidable, while accelerated soil erosion due to various forms of land use appears to be 'manageable'. Information about contemporary 'natural' erosion rates in South Africa is, however, still limited which complicates the definition of realistic management goals. In this thesis, mean rates of contemporary erosion are presented for the near-natural savanna landscape of the southern Kruger National Park (KNP) in the northeast of South Africa. Erosion rates were quantified through the investigation of 15 small (≤350 × 103 m3) intermittently dry reservoirs with an operational lifetime of 30 to 65 years and a catchment size of <1 km2 to about 100 km2. The amount of sediment that accumulated within the reservoir basins was quantified based on high-resolution surveys (differential Global Navigation Satellite System and terrestrial laser scanner), sediment mapping (Pürckhauer-type augers), and dry bulk density samples (core rings and clods). The sediment trap efficiency of reservoirs was estimated through modeling. The propagation of uncertainties arising from field work and modeling was examined. The results indicate that erosion rates in the KNP are typically ≤190 t km 2 yr 1. This is comparable to previous results from plot-scale studies on natural erosion rates in South Africa. Erosion rates that were reported for cultivated reservoir catchments outside the KNP are by an order of magnitude higher. At the same time, contemporary erosion rates within the KNP are >4 times higher than long-term (≥105 years) denudation rates ascertained from cosmogenic beryllium-10 concentrations. These results have notable implications concerning tolerable soil loss rates in the vicinity of the KNP.


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