Understanding A Globally Unique Nexus Of Acid Mine Drainage, Karst And World Heritage Site

The Cradle of Humankind World Heritage Site (COH WHS), South Africa, is the only UNESCO-protected karst landscape in the world that is under threat from acid mine drainage (AMD). This has generated wide and considerable concern for the preservation of the fossil sites and karst ecosystems of the WHS. A recent assessment of the water resources environment and continued water resources monitoring has better informed this situation, providing support for management efforts to protect the aquatic environment and outstanding universal value of the site. Allogenic recharge of AMD (salinity \u3e300 mS/m, pH 7, PO4-P ~4 mg/l, E. coli ~240 000 cfu/100 ml) at ~3 megalitres/d on average from losing surface drainages, combined with a mean autogenic recharge of ~30 megalitres/d from natural precipitation, define the principal inputs to the karst hydrosystem. Their combined impact on the hydrophysical environment is manifested as a rise in groundwater levels of as much as 6 m in the space of a few years. Each input adds a characteristic hydrochemical signature to the associated recharge component that imprints itself variedly on the karst groundwater chemistry. The association of an observed ~3 m rise in Sterkfontein Caves water level with an AMD impact, however, is contradicted by a weak mine water signature in the cave water chemistry (salinity ~60 mS/m, pH ~8). The paper explores the new understanding that informs these circumstances and a hydrovulnerability assessment of each fossil site