Aspects of water quality, metal contamination of sediment and fish in the Olifants River, Mpumalanga.

M.Sc.Pollution of the earth is presently one of the most important environmental issues of the world and various attempts, including creation of public awareness have been initiated over the past few years to address this situation. There is especially a global concern about the progressive pollution of valuable freshwater systems which most organisms, including humans, are reliant upon. This includes South Africa's aquatic ecosystems, many of which have been degraded over the past few decades. The Olifants River in Mpumalanga is one of the most threatened river systems in South Africa. It is impacted by various anthropogenic activities, particularly mining in the upper catchment, and urbanisation, industrial and agricultural activities in the upper and lower catchments. Previous investigations have shown that these activities are responsible for the degradation of this river system. The broad objective of this study was to obtain data on water and sediment quality, as well as bioaccumulation of metals in fish via monitoring of the Olifants River. It formed part of a major study concerned with the experimental investigation of lethal and sub-lethal effects of metals on fish physiology, supported by a field investigation into the water quality and metal contamination of the biotic and abiotic components of the Olifants River system. Physico-chemical properties of the water as well as the concentrations of some metals (Al, Fe, Cu, Zn, Ni, Mn, Pb & Cr) in the water and sediment were seasonally investigated. The extent of bioaccumulation of these metals in selected organs/tissues (muscle, gills, liver & skin) of Oreochromis mossambicus and Clarias gariepinus from Loskop Dam (upper catchment) and Mamba Weir, Kruger National Park (lower catchment) was also investigated. High levels of various macro-constituents and metals were detected at many sites in the study area and in many cases they exceeded the guideline limits set for aquatic ecosystems. Localities 2, 3, 6, 8, 10, 12 and 17 were observed to be severely impacted (see Chapter 9- Table 9.1) by elevated concentrations of pollutants influencing variables such as TDS and sulphates. This confirms that these sites are being impacted by mining. This was further confirmed by low pH-values at localities 3, 5, 8, 9, 10 and 12 which indicate on acid mine drainage originating from the many coal mines in the upper catchment of the Olifants River. Nutrient enrichment (elevated levels of phosphates, nitrates and nitrites) occurred at many sites in the catchment but in particular at localities 3, 4, 6, 10, 11, 14, 15 and 17. Point source pollution from sewage treatment works and non-point sources from agricultural runoff and informal settlements are the main contributors to these elevated levels of nutrients. The Selati River, impacted in particular by elevated phosphate levels, is the main contributor to the high nutrient levels detected at locality 17. It is evident from the evaluation of the metal concentrations in the water and sediment (Table 9.2) that most of the sites in the Olifants River catchment are being impacted by metal pollution. Oreochromis mossamhicus and C gariepinus sampled at selected sites in the Olifants River accumulated selected metals in the following order; Fe>Zn>Al>Cr>Ni>Pb>Mn>Cu. Levels were generally high in the liver and gills, while much lower levels were detected in the skin and muscle tissues. Gill tissue is in direct contact with the aqueous environment and therefore gives a good indication of the extent of exposure. Skin tissues usually contained relatively low levels of metals (except for Zn). Although muscle tissues usually accumulated low metal concentrations it is an important tissue to monitor in bioaccumulation studies as it can lead to metal poisoning if contaminated muscle tissues are consumed by humans. Adult specimens were mostly sampled and within this range there was a slight decrease in Cu, Al, Fe, Ni, Mn and Cr concentrations with increasing age. Temporal variation in metal accumulation by fish possibly occurred due to variations in metal concentrations in the water and sediment at a locality. These differences were caused by seasonal variation in climatical conditions (eg. rainfall, temperature), as well as temporal fluctuations of pollutant inputs into the river system. Aquatic organisms at both localities 15 (Loskop Dam) in the upper catchment and 17 (Mamba weir, Kruger National Park) in the lower catchment are at present being chronically exposed to elevated levels of the investigated metals, compared to both the control site and results in literature. The impact of the highly polluted Selati River in the lower catchment was evident in the difference between metal concentrations detected in fish at locality 17, and at locality 19 (Phalaborwa Barrage) upstream of the Olifants-Selati confluence. The present study clearly indicates that the Olifants River is subjected to various sources of pollution which could be detrimental to the health of this aquatic ecosystem. It is recommended (see Chapter 9) that a multi-disciplinary approach including a biomonitoring programme, should be followed to ensure a sustainable freshwater ecosystem