Lower reaches of rivers as well as estuaries are regarded as South Africa’s most productive ecosystems due to the important functions such as providing nursery areas and feeding sites for juvenile macro-invertebrate and fish species they perform. Furthermore, ecologically healthy estuaries are not only of critical importance since they facilitate the provision and recirculation of nutrients, they also provide conduits for fish migrations into the fresh water system and act as buffers during floods. In South Africa, these functions are continuously being threatened by residential and/or industrial developments. It is thus essential to determine the ecological integrity (structure and function) of these systems. An Ecological integrity study was carried out on the selected rivers in Kwazulu Natal between 2015 and 2017. This study was assessed in terms of selected abiotic drivers on specific biological responses.
The study was carried out according to the guidelines of the ecological determination methodologies and the resource directed measures for aquatic resources as set out by the Department of Water Affairs and Forestry, South Africa. Surveys were carried out during summer and winter seasons. Abiotic and biotic monitoring was carried out at four sites along each estuary. The abiotic component such as sediment composition and physio-chemical properties of the water was analyzed using standard methods. The biotic and abiotic components were analyzed using various indices, where applicable. The ecological integrity of the system can be accessed on the basis of its ability to carry out its natural functions. Results showed the various anthropogenic activities in the upper reaches of each river contributed to the high modified state of some of these rivers’ unacceptable water quality, loss and/or modification of habitat and an altered hydrological pattern due to impacts by agricultural, industrial and domestic uses. The ecosystem services of the lower areas of the rivers under investigation are used extensively through sugarcane agricultural activities and heavy industries works inclusive of sand mining and rural sewage-treatment. These activities affect the ecological integrity of the rivers and ultimately the estuaries. This study aimed at determining the current state of ecological integrity of five selected rivers in KwaZulu Natal and to establish trends between current and historical periods for the evaluation of changing trends in ecological integrity. Abiotic and biotic indicator components were used to ascertain changes in the surrounding environment as well as to determine the ecological integrity of these rivers. Monitoring of water quality, sediment grain size, moisture and organic content as well as habitat state, macro-invertebrates and fish assemblages was undertaken.
The following variables water temperature, chemical oxygen demand (COD), electrical conductivity (EC), pH and total alkalinity (TAL) as well as salts, nutrients and toxics were investigated to provide indications as to the state of the water-quality of these rivers. The Target Water Quality Requirements (TWQR) as developed by the Department of Water Affairs and Forestry for domestic use (Volume 1) and Aquatic Ecosystems (Volume 7) were used to evaluate the quality of the water sampled in this study. Historical data obtained from previous studies of similar study areas have also been evaluated. Sediment analyses were performed according to the protocol set out by the United States Environmental Protection Agency.
As a result of the abiotic drivers, results showed that the invertebrate reside in modified state. Physio-chemical, geomorphological and hydrological changes in this system resulted in the rivers’ suffering a loss in both biological and ecological function as well as aesthetic value. It is apparent from the above that there is not a need for rehabilitation but also a need for effective and continuous management strategies. These strategies can only be successful if the bio-monitoring of the system includes the effects at both economical and social levels. The water quality of the rivers under this investigation was found to be in a slightly modified state with the majority of water quality parameters falling within the target values. Water quality parameters of the lower Thukela River, not within the required target, was highly elevated and could possibly cause negative impacts on the river functionality. The water quality parameters of Umvoti river, Umdloti river and uMngeni river were seriously modified. The sediment clearly indicated that the organic content of the all the rivers was low and directly relating to the possibility of erosion and transportation taking place in the Rivers. The removal of riparian vegetation by agricultural activities, sand mining and water abstraction contributed to the destruction of the habitats along all these rivers.
The South African Scoring System, version 5 (SASS 5), the Macro-invertebrate Response Assessment Index (MIRAI) and multivariate statistical analyses were implemented in order to determine the ecological integrity of the rivers. Results revealed that the SASS 5 integrity classes were generally one class higher than the integrity classes of MIRAI. The Fish assemblage methods used to determine fish samples included electro-narcosis and a 5m wide 12mm meshed seine net.
Impacts on the ecological integrity of the Rivers under investigation have been assessed by various sources. To protect the current ecological integrity and further destruction of the rivers under investigation, direct involvement by the relevant authorities is of paramount importance. / Agriculture and Environmental Science / D. Litt. et Phil. (Environmental Science)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:unisa/oai:uir.unisa.ac.za:10500/24845 |
| Date | 09 1900 |
| Creators | Mbanjwa, Sibonelo Thanda |
| Contributors | Coopoosamy, M |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1 online resource (ix, 158 leaves) : color illustations, color maps, color graphs |
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