A reduction in mining and industrial effluents in the Blesbokspruit Ramsar wetland, South Africa: Has the quality of the surface water in the wetland improved?

Abstract

The Blesbokspruit Wetland, 40 km southeast of Johannesburg, South Africa, was listed as a Ramsar Wetland of International Importance in 1986. Following discharges of mine-waters in the mid-1990s, the wetland no longer complied with the Ramsar criteria. This paper reports on historical trends in surface water quality of the Blesbokspruit, as a step towards restoration to Ramsar status. Monthly water quality data (SO₄, Na, Cl and Mg concentrations, pH and EC values), from January 2000 to December 2011, were obtained from Rand Water for sites at: the stream inflow, just after the discharge point of pumped underground mine-water from Grootvlei mine, and the stream outflow point. The major ions were grouped into two distinct time-variation patterns (SO₄-Mg) and (Na-Cl). Despite extensive reports that the wetland had an acid mine drainage problem, the pH values over an 11-year period were constrained within a range of 6.7 to 8.8. In 2011, following the cessation of underground mine-water pumping operations, mineralisation of the Blesbokspruit showed a large stepwise reduction, in contrast to a slowly decreasing trend over the previous 10 years, in both the SO₄-Mg and Na-Cl groups, and EC. The stepwise reduction suggests that the pulping plant within the paper mill, a major source of Na-Cl rich effluent, had ceased operations coincidentally with the cessation of underground water discharges. This contradicts previous findings that underground mine-water discharge was the principal contributor to contamination of the Blesbokspruit Wetland. So, while the Blesbokspruit may have had a high mineralisation problem, this was not simply an acid mine drainage problem, but a combination of the effects of mining and industry.

Keywords: acid mine drainage, underground mine-water, Blesbokspruit, Montreux Record, Grootvlei Mine, water quality, circumneutral, Ramsar