| dc.description.abstract | The Mooi River catchment area has been the sole water source for Potchefstroom (North-West Province) since 1842. The Mooi River and the Wonderfontein Spruit are subjected to a substantial number of detrimental impacts which result in, amongst others, the influx of metals that are deposited and adsorbed on the sediment. Anthropogenic activities, such as agricultural and mining activities in the catchment area, not only reduce the diversity of macroinvertebrate assemblages, but also the community structure. According to the literature, aquatic macroinvertebrates are well known for their sensitivity towards extensive organic pollution, habitat transformation and selected physico-chemical factors and therefore utilising them for the assessment of the ecological health of rivers is a widely recognised method.
The aim of this study was to determine the aquatic macroinvertebrate diversity and the possible influences that selected physico-chemical factors may have on the macroinvertebrates. This will contribute towards a meaningful assessment of the current state of environmental (water and sediment) and ecological (macroinvertebrate) quality of the Mooi River catchment.
Three surveys were conducted at 11 preselected sites in the Mooi River, Gerhard Minnebron and Wonderfontein Spruit. Macroinvertebrates were collected from the vegetation, as well as the substratum by using standard sampling procedures. Sediment and water samples were also collected at each of the sites, while electrical conductivity (EC), pH, temperature, turbidity and flow-rate were measured in situ at all sites. Whenever possible, macroinvertebrates were identified up to species level in the laboratory, otherwise identification was done up to genus or family level. Subsequently, all specimens were counted and classified. Sediment samples were digested, sieved and sent for Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analyses, X-Ray Diffraction (XRD), as well as Scanning Electron Microscopy (SEM)-analyses to determine the metal concentrations, mineral composition and elemental composition, respectively. Water samples were filtered and acidified, where after the samples were sent for ICP-MS analyses to determine the metal concentrations. In addition, selected macroinvertebrate taxa were digested and sent for ICP-MS analysis to determine the metal concentrations.
Thirty four (34) and 31 metals were detected in the water and sediment samples, respectively. Only those metals that may be, according to literature, potentially toxic to macroinvertebrates were included. The results indicated that, although some metal concentrations measured in the water and sediment samples may have been affected by the mining effluent originating form Site 1B, the presence of the majority was probably as a result of natural weathering of the minerals and rocks present in the catchment area, as well as soil erosion due to the agricultural activities around the rivers. The concentrations of the metals in the water and sediment could thus not be attributed to the adverse effects of the mining effluent.
Regarding the macroinvertebrate taxa, a total of 142 taxa belonging to 66 families were collected at the 11 selected sites during the three surveys. The majority of these families were classified as highly tolerant. Only one highly sensitive family was collected during this study, suggesting that organic enrichment is present throughout the catchment area. Although the levels of organic enrichment observed at some sites during this study could be advantageous for those families known to be tolerant to, or have a preference for such environments or conditions, these levels were probably not to such an extent as to exclude the less tolerant families from these sites. Different biotope types and selected parameters (specifically flow-rate and EC) played a decisive role in the distribution of the families in the Mooi River catchment area.
The results obtained from the metals measured in the macroinvertebrates taxa revealed that, in contrast to the limited variations in metal concentrations measured in the pelagic organisms, of which the majority were classified as predators, a substantial variation in the metal concentrations measured in the benthic macroinvertebrates was evident. The majority of macroinvertebrates that associated with the benthic environment had the highest metal concentrations, which may be ascribed to the ingestion of sediment and organic particles, direct contact with sediments or contact with interstitial water | en_US |
