A comparative study of chemical and physical water quality along the Crocodile River in the Gauteng and North West Provinces, South Africa

M.Sc. (Geography)The Crocodile River drains a highly developed catchment, with 25% of the South African Gross Domestic Product (GDP) being produced in the Crocodile-West Marico Water Management Area (WMA). The industrial, agricultural and mining sectors that mostly contribute to GDP are however greatly dependent on the water resources within the Crocodile-West Marico WMA and therefore it is important to monitor the status of these water resources carefully. This study aimed to determine whether there is a positive correlation between changes in land-use and changes in water quality in the Crocodile River catchment area across both a spatial and temporal scale. Water quality was defined by measurement and analysis of both pure quantitative changes in water quality parameters as well as qualitative changes in water quality as related to the end use of the water. In general water quality in the study area, as measured in terms of the variables used for this study, was found to still be within acceptable range for domestic use, irrigation, livestock watering and Industrial Cat. 3 and 4 water uses. The majority of variables were however above the Aquatic Target Water Quality Range (TWQR). In terms of aquatic ecosystems, the study area is however not very sensitive with only a few catchments and sub-catchments classified as freshwater ecosystem priority areas. The freshwater ecosystem priority areas are also located in mostly the upper catchment where water quality is generally fair to good i.e. as confirmed by water quality results from Water Monitoring Stations (WMS) 90195 and 90165. It was confirmed that spatial and temporal changes in land use had a definite impact on physical and chemical water quality as measured at each WMS. The variables used to determine water quality changes due to land use change were however not ideal to determine certain land use impacts. Urban, industrial and mining impacts would for example have been easier to identify by means of metal and heavy metal concentrations as well as other toxic organic and inorganic constituents. To this extent it was a challenge to link specific industries or industrial areas to water quality changes. This was mostly due to the fact that industrial processes differ vastly, with a range of pollutants being emitted and discharged into the environment. It was however evident from the results that nutrient enrichment mostly originates from point sources, specifically Wastewater Treatment Works (WwTWs), and that salinization is mostly caused by intensive crop irrigation. Build-up or urban areas mostly resulted in lower levels of salts and dissolved solids, possibly due to limited exposed ground surfaces. It was further found that mining related to Platinum Group Metals (PGMs) resulted in and increase chloride, dissolved major salts, electrical conductivity, total hardness, potassium, magnesium, sodium and sulphate concentrations..