Abstract

MCCARTHY, T.S.; ARNOLD, V.; VENTER, J.  and  ELLERY, W.N.. The collapse of Johannesburg's Klip River wetland. S. Afr. j. sci. [online]. 2007, vol.103, n.9-10, pp.391-397. ISSN 1996-7489.

The Klip River wetland south of Johannesburg has long been economically important to the region, initially as a source of water, and latterly as a purifier of polluted water arising from the western section of the Witwatersrand urban-industrial-mining complex. A geomorphological investigation into the current state of the wetland has revealed that the upper reaches, which receive polluted water from old gold mines, are in reasonable condition, apart from a few sections that have been severely degraded by peat mining. The lower reaches, however, are in an advanced stage of collapse. A network of irrigation canals, dug to support intensive agriculture during the early part of the last century, provided nuclei for the development of major channels as discharge of treated sewage water increased in the latter portion of the century. The channels have become interconnected, and an almost continuous, single channel has formed downstream of the sewage works. The problem is likely to have been exacerbated by a falling water table in the area due to excessive groundwater extraction. The wetland's ability to remove phosphates and nitrates from the water has been seriously compromised, and eutrophication problems can consequently be expected to arise in the Vaal River above the Barrage. In addition, it is anticipated that the reed beds flanking the single channel will degrade over the coming years, releasing sequestered heavy metals, organic load and phosphates into the Vaal River system.

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