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In common with other natural systems, aquatic ecosystems provide a wealth of economically valuable services and long-term benefits to society. However, growing human populations, coupled with increased aspirations for improved quality of life, have lead to intense pressure on the world's finite freshwater resources. Frequently, particularly in developing countries, there are both perceived and genuine incompatibilities between ecological and societal needs for freshwater. Environmental Flow Assessment (EFA) is essentially a tool for water resources management and its ultimate goal should be the integration of ecological and societal systems. While other ecological components (i.e. biological and geomorphological) are equally important to EFA, this thesis investigates the role of the hydrological cycle and the hydrological regime in providing the ecosystem goods and services upon which society depends. Ecological and societal systems operate at different temporal, spatial and organisational scales and hydronomic zoning or sub-zoning is proposed as an appropriate water resources management technique for matching these different scales. A major component of this thesis is a review of the South African water resources management framework and, in particular, the role of the Reserve (comprising a basic human right to survival water as well as an ecological right of the aquatic resource to maintain ecological functioning) in facilitating ecologically sustainable water resources management. South African water resources management is in the early stages of water allocation reform and the Department of Water Affairs and Forestry has stated that "the water allocation process must allow for the sustainable use of water resources and must promote the efficient and non-wasteful use of water". Thus, new ways of approaching the compromise between ecological and societal needs for freshwater water are required. This thesis argues that this requires that the focus of freshwater ecosystems be extended beyond the aquatic resource, so that societal activities on the catchment are linked to the protection of instream flows. Streamflow variability plays a major role in structuring the habitat templates that sustain aquatic and riparian ecological functioning and has been associated with increased biodiversity. Biodiversity and societal well-being are interlinked. However, there is a need in EFA for knowledge of the most influential components of the streamflow regime in order that stakeholders may anticipate any change in ecosystem goods and services as a result of their disruption to the hydrological cycle. The identification of high information hydrological indicators for characterising highly variable streamflow regimes is useful to water resources management, particularly where thresholds of streamflow regime characteristics have ecological relevance. Several researchers have revisited the choice of hydrological indices in order to ascertain whether some indices explain more of the hydrological variability in different aspects of streamflow regimes than others. However, most of the research relating to hydrological indices has focused primarily on regions with temperate climates. In this thesis multivariate analysis is applied to a relatively large dataset of readily computed ecologically relevant hydrological indices (including the Indicators of Hydrological Alteration and the South African Desktop Reserve Model indices) extracted from long-term records of daily flows at 83 sites across South Africa. Principal Component Analysis is applied in order to highlight general patterns of intercorrelation, or redundancy, among the indices and to identify a minimum subset of hydrological indices which explain the majority of the variation among the indices of different components of the streamflow regimes found in South Africa. The results indicate the value of including several of the IHA indices in EFAs for South African rivers. Statistical analysis is meaningful only when calculated for a sufficiently long hydrological record, and in this thesis the length of record necessary to obtain consistent hydrological indices, with minimal influence of climatic variation, is investigated. The results provide a guide to the length of record required for analysis of the high information hydrological indices representing the main components of the streamflow regime, for different streamflow types. An ecosystem-based approach which recognises the hydrological connectivity of the catchment landscape in linking aquatic and terrestrial systems is proposed as a framework for ecologically sustainable water resources management. While this framework is intended to be generic, its potential for application in the South African Water Allocation Reform is illustrated with a case study for the Mkomazi Catchment in KwaZulu-Natal. Hydronomic sub-zoning, based on the way in which societal activities disrupt the natural hydrological processes, both off-stream and instream, is applied to assess the incompatibilities between societal and ecological freshwater needs. Reference hydrological, or pre-development, conditions in the Mkomazi Catchment are simulated using the ACRU agrohydrological model. Management targets, based on the statistical analysis of pre-development streamflow regimes, are defined to assess the degree of hydrological alteration in the high information hydrological indices of the Mkomazi Catchment as a result of different societal activities. Hydrological alteration from predevelopment conditions is assessed using the Range of Variability Approach. The results indicate that the proposed framework is useful to the formulation of stakeholder-based catchment management plans. Applying hydrological records (either observed or simulated) as an ecological resource is highly appropriate for assessing the variability that ecosystems need to maintain the biodiversity, ecological functioning and resilience that people and society desire. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Although the use of pesticides is necessary to meet the socio-economic needs of many developing countries, especially in Africa, side effects of these bio-active chemicals have contributed to contaminating aquatic and terrestrial ecosystems. Environmental water quality degradation by pesticides interferes with ecosystem health and poses numerous risks to aquatic life. In South Africa, glyphosate-based herbicides are frequently used to control weeds and invading alien plants, but ultimately end up in freshwater ecosystems. However, there are no South African-based environmental water quality management strategies to regulate these bio-active chemicals. Therefore, this study sought to provide a sound scientific background for the environmental water quality management of glyphosate-based herbicides in South Africa, by conducting both laboratory and field investigations. In the laboratory investigations, aquatic ecotoxicological methods were used to evaluate responses of the freshwater aquatic shrimp Caridina nilotica exposed to Roundup® at different biological system scales, and the responses of multiple South African aquatic species exposed to Roundup® through species sensitivity distribution (SSD). In the field investigations, the effect of Kilo Max WSG on the physicochemical and biological conditions of three selected sites in the Swartkops River before and after a spray episode by Working for Water were evaluated through biomonitoring, using the South African Scoring System version 5 (SASS5) as a sampling protocol. Both Roundup® and Kilo Max WSG are glyphosate-based herbicides. All the data were subjected to relevant statistical analyses. Findings of this study revealed that Roundup® elicited responses at different biological system scales in C. nilotica, while SSD estimates were used to derive proposed water quality guidelines for glyphosate-based herbicides in South Africa. The biomonitoring revealed that using glyphosate-based herbicides to control water hyacinth within the Swartkops River had a negligible impact on the physicochemical and biological conditions. Based on these findings, a conceptual framework that can be used for the integrated environmental water quality management of glyphosate-based herbicides in South Africa was developed as part of integrated water resource management (IWRM). The combined data sets contribute to a sound scientific basis for the environmental water quality management of glyphosate-based herbicides in South Africa.

Freshwater resources are increasingly subject to pollution because of escalating human population growth, accompanied by urbanisation, industrialisation, and the increased demand for food. Consequently, freshwater quality, and aquatic ecosystem structure and function have been severely impaired. The Swartkops River, which drains an urbanised and industrialised catchment in the Eastern Cape of South Africa, is no exception. An integrated environmental water quality (EWQ) approach is needed to measure the impacts of deteriorating water quality on its aquatic ecosystem structure and function to sustain these vital ecosystem-attributes. In this study, an integrated EWQ approach, which included i) analysis of water physico-chemical variables; ii) macroinvertebrate-based family-level taxonomic- and traits-based community analysis; iii) Chironomidae species-level taxonomic- and traits-based community analysis; iv) Chironomidae deformity-based sub-lethal analysis; and v) experimental investigation of long-term wastewater effluent effects, using model stream ecosystems, were applied to investigate environmental water quality in the Swartkops River. One upstream reference site and three downstream sites in the Swartkops River were monitored over a period of three years (August 2009 – September 2012). The family-level taxonomic community responses based on the South African Scoring System version 5 (SASS5) and a newly developed Swartkops multimetric index indicated very poor river health conditions for the three downstream sites, compared with the good condition of the upstream site. The Chironomidae species-level responses in the three downstream sites provided evidence of differences in biotic impairments, which were not evident with the family-level taxonomic data at these sites, thus highlighting the importance of species identification in freshwater biomonitoring. The family-level traits-based approach (TBA) showed that macroinvertebrates with gills and lungs were more abundant at the upstream site, decreasing markedly at the downstream sites. The relative abundance of macroinvertebrates relying on aerial and tegument respiration increased at the downstream sites compared with the upstream sites. The results of the family-level TBA highlighted the inextricable link between the traits-based approach (TBA) and taxonomic identification, clearly showing that the TBA is additional to, and not an alternative to, taxonomic recognition because important traits, e.g. reproductive cannot be used at a coarse taxonomic identification. A novel chironomid species traits-based functional strategies approach developed in this study, based on species combining similar sets of traits, proved sensitive in diagnosing the main abiotic water physico-chemical stressors. The functional traits responded predictably to deteriorating water quality and provided an adaptive and mechanistic basis for interpreting chironomid species occurrences at the four sampling sites, providing insight into why certain chironomid species occurred at one site but not at the other. Chironomid deformities provided evidence of sub-lethal in-stream biological response to deteriorating water quality. A newly developed deformity-based extended toxic score index proved sensitive, enabling the discrimination of the sampling sites, indicating that a biomonitoring tool based on sub-lethal effects could be used to assess the effects of deteriorating water quality before it reached lethal levels. Empirical evidence based on the taxonomic, traits and sub-lethal responses suggested that the changes in macroinvertebrate community structure were caused chiefly by the discharge of wastewater effluents into the river. This was supported by the model-stream ecosystem results indicating significant effects of effluents on the macroinvertebrate community structure, similar to the observed in-stream responses. The model stream results indicated that improved physico-chemical effluent quality compliance after 50% effluent dilution did not significantly reduce the effects of the effluent on the macroinvertebrate communities, showing that ecologically-based methods rather than physico-chemical measures alone are necessary to assess effluent quality. Finally, the results of the multi-criteria approach were integrated to propose tools to manage environmental water quality in the Swartkops River, and the benefits of the study were highlighted in the context of biomonitoring in South Africa.

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