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EVIDENCE FOR LAND DEGRADATION FROM AEOLIAN SEDIMENT IN THE WEST-CENTRAL FREE STATE PROVINCE, SOUTH AFRICA

Authors


P. J. Holmes, Department of Geography, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa.

E-mail: holmespj@ufs.ac.za

ABSTRACT

Evidence for historical and recent/contemporary aeolian activity in the west-central Free State Province, South Africa, is here reviewed, synthesised and supplemented by new data. The evidence is derived from three sources, namely lunette dunes and their capping sediments, fence-line dunes and buried fences, and contemporary dust entrainment. Prior to settlement by farmers of European origin during the 18th and 19th centuries, this grassland biome supported significant populations of native herbivores and carnivores. Human impact was limited to grazing of cattle and small stock by indigenous inhabitants of the region, with limited subsistence agriculture. The first Europeans to inhabit these grasslands were itinerant trekboers, who hunted game and drove cattle. Subsequent to permanent settlement by farmers in the 19th century, the area was surveyed, title was acquired and commercial agriculture was introduced, further impacting on the environment. There is currently evidence in the landscape that this human impact may have led to enhanced aeolian activity. This paper reviews such evidence.

Numerous pans (playas) occur in the area, with sand/clay lunette dunes typically occurring on their downwind margins. At most sites, the lunettes are unconformably capped by sand. Optically stimulated luminescence dates from dunes at five localities reveal a suite of ages between 580 and 60 years, suggesting renewed aeolian sediment mobility in historic times. Further evidence for sediment mobility, which suggests dune building post ca. 1880, was derived from buried barbed-wire fences and recent fence-line dunes, which border land currently under the plough. Finally, there is evidence of mobile dust derived from dust traps used to monitor aeolian sediment mobility on agricultural land, as well as at a pan site. It is proposed that historic and current land-use practices have contributed to sediment mobility and, by implication, may promote land degradation in the area. Copyright © 2012 John Wiley & Sons, Ltd.

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