Abstract:
Concentrations of pollutants were measured in water, sediment and algal samples collected along a
longitudinal gradient from a stretch of the Olifants River, South Africa, that receives AMD from the
Klipspruit River. The effects of AMD were determined through macroinvertebrate biotic indices
(SASS5) and multivariate analysis of macroinvertebrate communities. The acidic Klipspruit River
caused increased concentrations of total Al, Fe and Mn in the Olifants River. Upon mixing of the
Klipspruit with that from the alkaline Olifants River, Al and Fe precipitate rapidly, leading to lower
concentrations in the dissolved phase and higher concentrations in the suspended phase and in
sediment at sites in close proximity to the confluence. Similarly filamentous algae accumulated high
concentrations of Al, Fe and Zn immediately after the confluence. Mn remains in the dissolved phase
and sediment and algal concentrations increase with increasing distance downstream. Metal speciation
analysis indicate that Al is rapidly converted from more toxic forms (e.g., Al3+ and Al(OH)2+) to less
toxic forms (e.g., Al(OH)3(aq) and Al(OH)4-). In contrast, Mn remains in the soluble Mn2+ form.
Macroinvertebrate metrics and community structure showed clear signs of deterioration in water
quality in the Olifants River downstream of the point of AMD input . While total TDS concentrations
at all sites fall within ranges likely to affect macroinvertebrates, the relative composition of major ions
changes as a result of AMD input, which may also account for the observed changes in
macroinvertebrate communities. Further downstream, the Wilge River discharges into the Olifants
River, and significantly improves water quality downstream of the confluence. Future mining and
development activities in the Wilge catchment should be carefully managed and monitored so as to
ensure sufficient flows of acceptable quality to prevent further deterioration of water quality in the
Olifants River and downstream reservoirs.
