A comparative study on the biotic integrity of the rivers supplying a polluted, hyper-eutrophic freshwater system: A multi-indicator approach

The aim of this study was to use an integrated, multi-indicator approach to assess and compare the biotic integrity of the polluted rivers flowing into the hyper-eutrophic Roodeplaat Dam. This included seasonal assessments of physical, chemical and biological parameters of the water and sediment, as well as a habitat, macro-invertebrate and histology-based fish health assessment. The results showed that all three rivers are polluted by metals and faecal coliform bacteria and high nutrient levels which explains the eutrophic status of the receiving impoundment. The Edendalespruit showed higher metal concentrations while the Pienaars River showed higher nutrients and Chlorophyll-a levels. Semi-volatile organic compounds were detected in sediment samples from all three rivers. The macroinvertebrate assessment confirmed that the water quality of the rivers are negatively impacted with most of the sites classified as "fair" to "poor" based on the number of taxa identified and their sensitivity scores. The histological assessment of six different target organs of two indicator fish species indicated a definite tissue response, especially in terms of the liver alterations in Clarias gariepinus. The percentage prevalence of alterations varied across rivers and seasons with no discernible pattern identified. The assessment of both abiotic and biotic indicators indicated that this system is plagued by a number of negative impacts and that management initiatives should focus especially on the activities influencing the Pienaars River to mitigate the continuing eutrophication of the Roodeplaat Dam.