Abstract
M.Sc. Aquatic Health)
The Klip River runs past heavy urbanization and industrialization as a consequence it is possibly one of the most abused river systems in Gauteng and perhaps the country as a whole. Eight sites were selected along the course of the Klip River for biomonitoring purposes. The sites were selected to represent the upper, middle and lower reaches of the river, while sites representing point source pollution sources were also included. Various biomonitoring techniques have been included to determine the present ecological state of the Klip River. This includes biotic indices to assess the ecological integrity of the fish and invertebrate communities and the habitat. In addition, fish health was assessed using a variety of histological, biomarker and bioaccumulation based assessments.
From the results it is evident that the sites on the Klip River represent the three main regions of a river including headwaters, middle reaches and a mature river. These natural changes in river ecology also caused natural variations in the habitat availability and the resultant biotic communities. There were, however, many changes not related to these natural variations but rather the numerous anthropogenic activities present on the river.
The most noticeable change has occurred due to alteration in the flow regime. These changes are brought about by the many weirs and bridges in the system, return flow from the numerous settlements and agricultural activities and the various WWTW. These alterations in flow have caused serious erosion of the stream banks and may lead to siltation of the system. It is clear from the results of the sediment particle size analysis that there is an increase in the percentage contribution of medium and very fine sand below site 3. This is a good indication that the increased flow below the Olifantsvlei WWTW is already causing siltation. Ultimately this can lead to loss of riffle habitat within the river. These flow alterations have also caused an alteration to habitat availability and quality and as a result caused a modified invertebrate community. The macroinvertebrate community at all the sites (below site 1) consisted of taxa that are tolerant to pollution. This is also reflected in the poor SASS 5 and ASPT scores observed at the various sites. These tolerant organisms probably occur in the system due to an altered habitat template and a change in water quality. It is important to note that although the values obtained for the water quality variables are within the TWQR that the oxygen saturation at some sites decreased. These sites included the sites below the Olifantsvlei WWTW, after the confluence with the Rietspruit and the last monitoring site. The Fish Health Assessment Index scores were the highest at site 3 and decreased to site 8. This indicated that the fish condition improved from site 3 to site 8. However, there was a large variation in the index scores from the individual specimens. The results of this assessment cannot be compared to other studies as no fish health assessment index has been applied on the Klip River. This study will serve as a baseline assessment for future studies of the fish health of the Klip River. The results of the metal analysis in the fish muscle tissue indicated relatively low levels that correspond to levels measured by Kotze (1999) while still being lower than fish sampled from the polluted Olifants River.
It is therefore recommended that further studies be completed on the fish health of the Klip River and that the fish health of specimens in the Klip River is compared to those of the Vaal River to determine the impact of the Klip River system on the Vaal River. As it has become clear that the Rietspruit also influences the water quality of the Klip River it is recommended that further studies be completed on the Rietspruit to determine the cause of the impacts.
Because the histological alterations identified may be the result of a range of different biological and/or chemical stressors, it is difficult to assign specific causative agents for the various alterations identified. Based on the selected parameters investigated, the results show that fish in the Klip River appears to be in a relatively healthy condition and the organs seem to be in a functional state. Establishing a histology-based monitoring programme for fish health in the Klip River, by incorporating appropriate sample sizes and various fish species is recommended. Monitoring of biological responses for assessing the significance of pollutants has become a reasonable measurement in biomonitoring, and use of biomarker responses has played a significant role in this aspect. However, no biomarker has been validated as a unique tool to determine the effects of pollutants on organisms. Furthermore, it is necessary to understand how bioaccumulation and biomarkers relate to each other on exposure to specific pollutants and how it varies between species, to interpret the effects of pollutant exposure in both the field and laboratory. The results obtained in this study indicate that there are definite impacts on the entire system, although these have not altered fish biology and functionality to a large extent. However, sample size should be considered when evaluating individual biomarker responses, as a larger sample size will be more representative of the resident fish community’s response to the pollutants and other stressors. It is difficult to assign specific stressors for the various biomarker responses identified. It is recommended that further biomarker studies be undertaken on the Klip River to increase the level of confidence in the results obtained.