Water temperatures are a fundamental water quality component, and a key abiotic determinant of fish distribution patterns in rivers. A river 's thermal regime is the product of a multitude of thermal drivers and buffers interacting at different temporal and spatial scales, including, inter alia, air temperatures, flow volumes (including groundwater flows and lateral inputs from tributaries), channel geomorphology and riparian vegetation. "Healthy" river systems are self-sustaining, with adequate thermal variability to maintain biotic diversity. Temporal variability of flow volumes and water temperatures, and how these change along the longitudinal axis of a river, contribute towards a rivers "signature". Rivers that have had their signatures altered through anthropogenic impacts may no longer be sustainable, and require varying levels of management. Successful river management should include a quantification of these signatures , a definition of the "desired" state which management aims to achieve, associated "thresholds" of change or concern, and monitoring programmes. Such an approach requires flexibility and adaptability, as well as appropriate tools being available to natural resource managers. Indices, the utility of which are enhanced when included in predicative modelling systems, are a common means of assessing system variability and change. The degree of confidence placed in such tools depends on the level of fundamental science, and the degree of system understanding, underpinning them. This research contributes to the understanding of the ecological significance . of water temperatures in variable semi-arid river systems, using the Sabie River (Mpumalanga, South Africa) as a case study, and indices derived from biological indicators (Chiloglanis , Pisces: Mochokidae) to quantify the effects of cumulative changes in heat units against a hypothesised critical water temperature threshold. Hourly water temperatures for 20002002 collected at nine sites in the main rivers of the Sabie catchment, together with biannual surveys of relative abundances and community patterns of fish collected using standard electrofishing techniques, were used to provide the basis for a modelling system which aims to provide river managers with a tool for quantifying changes to the thermal regime of the Sabie River. This modelling system consisted of a suite of pragmatic models, including multiple linear regression models for simulating daily maximum water temperatures, and simple cause-and-effect relationships between biological indices (change In condition factor and change in the ratio of relative abundances of two species of Chiloglanis) and annual metrics of time-of-exposure to heat stress. It was concluded that changes in the thermal regimes of the rivers in the Sabie catchment are likely to lead to changes in fish distribution patterns, and a decline in river health. Inherent system variability suggests that management decisions will be made in the face considerable uncertainty. Indirect management of water temperatures may be possible through maintenance of flow volumes and flow variability. However, the most appropriate management approach for maintaining fish diversity within these rivers is to ensure that obstacles to fish migration are minimized, to maximise the ability of river biota to respond to thermal changes, by accessing suitable alternative habitats or refugia. Future research should focus on extending the time series of water temperatures from such river systems, and further understanding the drivers and buffers contributing to the thermal regimes of variable semi-arid river systems in South Africa. Additional testing of the validity of the hypothesized relationships between abiotic processes underpinning biotic patterns should be undertaken. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.

No abstract available Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Plant Science / unrestricted

Whole Effluent Toxicity (WET) testing has been identified as one of the tools in the management of complex effluents in aquatic ecosystems. In South Africa, toxicity testing has not been required for regulatory purposes. Recently, the Department of Water Affairs and Forestry has adopted WET testing as a tool to evaluate the suitability of hazardous effluent for discharge into receiving environments. This has necessitated suitable procedures to be established for use in the South African situation. With the implementation of the new National Water Act (No 36 of 1998), industries have to comply with set standards to protect the aquatic environment. However, the South African Water Quality Guidelines for Aquatic Ecosystems have been set using international toxicity data, and it is not known if they are comparable with South African conditions. The aim of this study was to investigate the tolerances of selected indigenous riverine invertebrates to complex saline effluents. The study investigated the effects of kraft mill effluent to Tricorythus tinctus, a tricorythid mayfly from the Sabie River, Mpumalanga, and the effects of a textile effluent to baetid mayflies of the Buffalo River, Eastern Cape. Indigenous riverine invertebrates were chosen as test organisms, as there is no toxicity data in South Africa which could be used to evaluate the level of protection afforded by the South African Water Quality Guidelines for Aquatic Ecosystems. The use of indigenous riverine invertebrates added the challenge of variability of a wild population, and the use of a complex effluent as toxicant added the variability of effluent composition. In this study, WET testing was used to determine the dilution of whole effluents required for discharge. Hazard-based guidelines were developed for the disposal of kraft and textile effluents. The level of environmental hazard posed by different effluent concentrations was ranked, and was related to the River Health Class. This indicated effluent concentrations that may be allowed to enter the aquatic environment, e.g. 3% effluent concentration guideline for both general kraft effluent and general textile effluent for the protection of a Class A river. This approach could contribute to the use of an Environmental Risk Assessment, approach for the management of complex effluents. A number of acute 96 hour toxicity tests were conducted following an unreplicated regression design, using kraft and textile effluents as toxicants, mayfly nymphs as test organisms, and river water as diluent and control. Test organisms were sampled from unimpacted, flowing-water riffle areas, and were exposed in recirculating artificial streams (or channels) to a range of effluent concentrations. Mortality was selected as end-point and observed twice daily. The experimental results showed the variability and acute toxicity of both kraft and textile mill effluents. Baetids were more sensitive (mean LC50=16% effluent concentration) to General Textile Effluent (GTE), but less sensitive to Post Irrigation Textile Effluent (PITE). Textile effluent (PITE) held in a holding dam were therefore less variable and less toxic; suggesting that stabilization of the effluent could have contributed to reduced toxicity. Effluent composition, e.g. higher calcium levels, may also have contributed to lowering toxicity. T. tinctus was sensitive to kraft effluents, but showed less variable responses to Irrigation Kraft Effluent than General Kraft Effluent. Toxicity test data indicated that GKE, IKE and GTE should not enter the aquatic environment without treatment, as they can cause adverse effects to aquatic biota. Both kraft and textile effluents must therefore be treated before discharge. Different responses to different effluent batches were probably due to effluent variability. The use of indigenous organisms, and not a standard laboratory organism, could also have contributed to variability. A hazard-based approach could be useful, as it will provide a consistent basis for deciding on the acceptability of impacts, while allowing natural site-specific differences to be taken into account.