The ability of wetlands to improve water quality an investigation of the upper catchment of the Blesbokspruit in Gauteng, South Africa.
Maphakela, Phyllis Matshwene
Maphakela, Phyllis Matshwene
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Abstract
Wetlands are transitional between terrestrial and aquatic systems, where the water table is usually at, or near the surface, or where the land is periodically covered with shallow water. Wetlands play an important role in the regulation of river flow, they filter out pollutants and also provide a habitat for plants, insects and birds. Although wetlands play an important role in reducing pollutant levels of the inflowing water, they require protection as they act as water sources. This study aimed to look at the effectiveness of the Blesbokspruit wetland in reducing some water pollutants in the Blesbokspruit River. Six sampling sites were selected based on the activities affecting the wetland downstream. A paper mill, gold mine, wastewater treatment plant and acid mine drainage treatment plant are some of the major water users discharging into this wetland and impacting the water quality. Grab samples of water were taken each month to the laboratory for analysis of cations, including metal ions, anions and microorganisms. On-site measurement of physical parameters such as: pH, dissolved oxygen (DO) and electrical conductivity (EC) with a multi probe meter were conducted. Water quality results obtained from on-site analysis demonstrate that pH remained relatively constant for the entire study period at all sites investigated with a minimum value of 6.3 and maximum of 9.8. The dissolved oxygen remained significantly low for a better part of the study at minimum of 0.4 mg/L, while the EC was significantly higher at sampling sites that were downstream of the paper mill, gold mine and acid mine drainage treatment plant, at maximum value of 217 mS/m. From these results, it can be concluded that during the study period, there was a deterioration in dissolved oxygen across the entire study area of the wetland and the conductivity levels at sites situated downstream of mines and industries were significantly higher. The wetland at the outlet was able to reduce chemical oxygen demand, to concentrations of minimum of 11 mg/L in winter and a maximum of 33 mg/L in summer; NH3 from 0.3 mg/L in winter and 1.5 mg/L in summer; Cl- from 62 mg/L in summer to 90 mg/L in winter and NO-3 from 0.2 mg/L in summer to 0.7 mg/L in winter. Although chemical oxygen demand, EC and NH3 was introduced into the wetland, average levels declined significantly towards the outlet of the wetland showing that the wetland was capable, to some extent, of reducing these pollutants. Total coliforms were high in all four seasons from the inlet of the catchment to the outlet, averaging values of 28712 MPN/100 ml. The Blesbokspruit wetland appears to be overloaded with certain pollutants such as phosphates and sulfates that appear to impact on the wetland with little reduction observed at the outlet. A rehabilitation plan for this wetland is recommended in order to improve the status of the water quality in this catchment and to avoid overloading.
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Submitted in partial fulfilment of the requirements for the degree, Master Technology Chemistry, in the Department of Chemistry, Faculty of Science at the Tshwane University of Technology
Date
2018-10
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Tshwane University of Technology
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Keywords
Wetlands, Water quality, Upper catchment, Blesbokspruit, South Africa