An assessment of the effects of water quality on the ichthyofauna of the Ga-Selati river, Limpopo, South Africa

M.Sc. (Aquatic Health)The lower Olifants River within the Kruger National Park is regarded as an environmentally sensitive area which has been found to exhibit high levels of aquatic diversity. The biodiversity in this lower section of the Olifants River is under threat as a result of the cumulative impacts upstream within the catchment. These impacts are apparent in water pollution, siltation and reduced stream flows as a result of agriculture, mining, industry and power generation. Although the impacts within the upper catchment have been well documented, it was the numerous fish kills within the river which brought the issue of river health into the public eye. Due to the intensive industrial activities on the Ga-Selati River, a tributary of the Olifants River, and its close proximity to the Kruger National Park, much focus has been placed on the river’s water quality, especially industrial effluent containing high concentrations of pollutants. Currently bi-annual monitoring of the aquatic ecosystems associated with the industries along the Ga-Selati River is being conducted, providing information of the ichthyofaunal communities within the system. In addition to this, the separate industries collect water quality data as frequently as weekly. The aim of this project is to lay the foundation for understanding the state of the Ga-Selati River, and to determine what water quality variables may be influencing the ichthyofaunal structure within the river. Analysis of water quality data showed that elevated levels of salts are evident, with a downstream increase in concentrations being observed along the length of the Ga-Selati River at a given point in time. Over the eight years of data considered, the overall trend indicates a general water quality improvement (decreased concentrations). A reoccurring trend showed an increase in salts between two of the sites, suggesting a source of contamination within this area. A statistical analysis of the fish community data and environmental data showed there to be a clear distinction between historical (2003, 2004 and 2005) and recent surveys (2009 and 2010). During the first time period, Site 1 showed the lowest diversity and showed to be significantly different from the remainder of the sites. During the second time period, diversity at Site 1 increased, and it was noted that overall, there was greater variability within the data. In general it was observed that upstream species richness was lower compared with downstream sites. This trend is likely linked to the proximity of the Olifants River, which allows migration into the lower reaches of the Ga-Selati River. The historical monitoring data revealed that water quality and in particular salts are influential in the structuring of ichthyofaunal communities. This change can be substantiated by identifying that an improvement in water quality has resulted in a positive shift in ichthyofaunal community structure. The analysis of this information will contribute towards the improved management and conservation of the Ga-Selati River system. Although mining houses/industries are collecting and sharing water quality data, it would be valuable if a strategic approach to sample collection and management was perused. A centralised database will increase the understanding of the driving variables behind ichthyofaunal community structure within the river and would lay the foundation for future closure plans. It is imperative that an excellent set of water quality data is available during the design of appropriate rehabilitation and treatment facilities