Biological monitorings of mining pollution in tributaries of the Olifants River in the Sekhukhune Area

Abstract

Water pollution has been one of the major concerns all over the world for at least the past two decades. In South Africa, the Olifants River System is one of the most polluted river systems. Anthropogenic activities being carried out within the Olifants River Catchment area pose threats to the aquatic ecosystem. The Upper and Middle catchments are being characterised by intensive mining, industries, agricultural practices and inadequate sewage treatments. Thus, the aim of this study was to investigate the influence of mining activities on the water quality and health status of the Steelpoort River, a tributary of the Olifants River System. This was achieved through assessing the quality of water by analysing physico-chemical parameters, macro nutrients and metals at four selected sites, determining the response of macro invertebrate assemblages to water quality using the South African Scoring System (SASS) version 5 and determining the diversity of fish using the Fish Response Assessment Index (FRAI). Sampling of water, sediment, macro-invertebrates and fish was done seasonally (August 2017 – May 2018) at four selected sites. Site 1 and site 2 were located upstream while site 3 and site 4 were located midstream and downstream respectively. Water and sediment samples were analysed by WATERLAB (PTY) LTD by means of Inductively Coupled Plasma Optical Spectrometry (ICP-OES). Macro-invertebrates were sampled following the SASS protocol. Macro-invertebrates were identified, counted and recorded then released back to the river. Fish were sampled following the FRAI index protocol. The results obtained indicated that the system variables; pH, water temperature, dissolved oxygen and total dissolved solids fell within the target water quality range (TWQR) for aquatic ecosystems. However, some concentrations of macro-nutrients recorded were above the TWQR. These include ammonium at site 3 and nitrogen at sites 2, 3 and 4 which indicated that there was a variation in the influx of macro-nutrients into the river at different river sections. The higher concentrations of ammonium and nitrogen may adversely affect the functioning and survival of biological communities. The metal results indicated that most metals (As, B, Ba, Cd, Cu, Pb, Ni and Cr) fell within the recommended water and sediment quality guidelines (DWAF 1996c; CCME 2012). Chromium concentrations recorded in sediment were above the sediment quality guideline at all the selected sites (CCME 2012). Iron and Zn were also above the guideline values at all selected sites. In terms of physico-chemical parameters and metal concentrations indicated that the water quality of the Steelpoort River was fairly good. The macro-invertebrates were also analysed; their abundance, distribution and family richness indicated that there was a deterioration of water quality from upstream to downstream which may be an indication of increase in influx of pollutants and modifications in the stream such as flow, cover and microhabitat. The highest macro invertebrate abundance and richness was at site 1 while the lowest was at sites 3 and 4. Site 3 was highly modified while site 1 was the least modified site. The Ephemeroptera, Plecoptera and Trichoptera index (EPT) and Ephemeroptera, Plecoptera and Trichoptera/Chironomidae ratio (EPT/C ratio) analysis also confirmed that the water quality of the Steelpoort River is deteriorating from upstream to downstream. Site 1 had the highest value of EPT while site 2 had the highest value of EPT/C. Site 3 had the lowest value for both EPT and EPT/C ratio. The higher EPT and EPT/C ratio indicate the presence of highly sensitive taxa. The Canonical Correspondence Analysis (CCA) indicated a strong correlation between metals (Pb, Cr, Mg, As and Se) and macro-invertebrates (Pleidae, Ecnomidae, Athericidae, Synlestidae, Lestidae and Pyralidae). The SASS 5 results also indicated deterioration of water quality from upstream to downstream with the highest values of SASS score and Average Score Per Taxon (ASPT) being recorded at site 1 followed by site 2 while the lowest SASS score and ASPT were at site 3 followed by site 4. The use of fish as biological indicator also supported the same pattern of water quality deterioration and influx of pollutants which was previously indicated as increasing from upstream to downstream of the Steelpoort River. Site 1 had the highest fish abundance, while site 4 had the lowest fish abundance. However, the fish species richness was highest at site 4 while the lowest species richness was at site 1. The Shannon Weiner Diversity Index also supported that site 4 had the highest fish species richness while site 1 had the lowest species richness. The FRAI results indicated that different sites were in different Ecological Categories (EC). The ECs showed a trend from higher EC category upstream to lower EC category downstream. Site 1 had an EC of C followed by site 2 with an EC of C/D, site 4 with EC of D and then site 3 with the lowest EC of D/E. This might serve as an indication of decrease in habitat availability, increase of pollutants input and increase in stream modification. The CCA showed a weak correlation system variables and fish species. However, a strong correlation was observed between most metals and most fish species with the exception of Mesobola brevianalis Boulenger, 1908, Chiloglanis pretoriae Van Der Horst, 1931, Labeobarbus marequensis Smith, 1841 and Enteromius neefi (Greenwood, 1962). In conclusion, the water in the Steelpoort River is still in relatively good condition. However, increasing mining, industrial and agricultural practices in the catchment area results in increase of pollutants input into the river system. All the four selected sites were contaminated to some degree, with site 3 being the most affected site and site 1 being the least affected site. For this reason, it is important to continuously monitor the health status of the Steelpoort River and to educate the nearby communities who rely on this river for water supply about the quality of the water from the Steelpoort River.