A comparative evaluation of ecosystem health of selected water bodies in the Olifants and Limpopo River systems using the health assessment index and parasite diversity as indicators

Abstract

South Africa's water resources are limited and scarce in global terms, due to the fact that the country's climate varies from desert to semi-desert in the west to sub-humid along the coastal area. The country is also expected to experience further variability in rainfall, reduced precipitation and increased evaporation as a result of climate change. At the projected population growth and economic development rates, it is unlikely that the projected demand on water resources in South Africa will be sustainable. An additional concern is the declining water quality due to domestic, mining and industrial pollution, and eutrophication as well as salinisation due to agricultural pollution. Thus, aquatic ecosystems must be protected, monitored and managed to ensure sustainable resource use. The aim of the study was to evaluate and compare possible environmental deterioration by analysing fish health and parasite diversity in three dams within the Limpopo and Olifants River Systems by using the fish Health Assessment Index (HAI) and the Inverted Parasite Index (IPI). The intention of the study was to substantiate the theories behind the HAI and IPI in a bid to augment strategies to manage water quality, fish health and aquatic biodiversity. Seasonal surveys were carried out between April 2008 and April 2010 at three localities. The Luphephe-Nwanedi Dams are in a Nature Reserve located in a rural catchment, the Flag Boshielo Dam in an industrualised and mining catchment whereas the Return Water Dam is located on a platinum mining premise. Clarias gariepinus (Burchell, 1822) and Oreochromis mossambicus (Peters, 1852) were collected with the aid of gill nets and used as indicator fish species. Fish were examined for external parasites after which they were weighed and measured. Blood was drawn and skin smears were made. The skin smears were examined with a dissecting microscope for the presence of parasites. Fish were killed, dissected and then examined as prescribed in the fish HAI. From the ecto- and endoparasite data collected, infection statistics and ecological parameters were calculated. The HAI values were calculated for each fish species at each sampling site. To verify the results of the HAI, water quality was included in the studyThe nutrients and mining related pollutants of the three dams differed to a great extent and showed a similar increasing trend in the order: Luphephe-Nwanedi Dams < Flag Boshielo Dam < Return water Dam. Our results were consistent with previous work describing Luphephe-Nwanedi Dams as essentially unimpacted and Flag Boshielo Dam as impacted with a combination of mining and agricultural effluents. The results have shown that the Return Water Dam is an extremely polluted site with high levels of nutrients and metals. Fish health of both species responded similarly to polluted sites although mean population HAI results showed that C. gariepinus was more affected in terms of haematocrit necropsy-related alterations. The top six metrics that correlated most to fish health scores were nearly the same for both species (i.e. haematocrit values, inverted ectoparasite index, condition of the kidney, liver, gills and skin). The parasite community of C. gariepinus comprised 19 metazoan species. Seventeen parasite species were recovered from fish sampled from Luphephe-Nwanedi Dams compared to 11 at Flag Boshielo Dam and four at the Return Water Dam. The parasite community of O. mossambicus comprised 20 metazoan species. A total of 19 species, 17 species, and 4 species of metazoan parasites from O. mossambicus were obtained from Luphephe-Nwanedi Dams, Flag Boshielo Dam and the Return Water Dam, respectively. In both fish species, the Shannon Wiener Index, the inverse Simpson Index, equitability and the number of metazoan parasite individuals were highest in fish from Luphephe-Nwanedi Dams. The results of this study emphasized the negative impacts of urbanization, agricultural and mining activities on the environment. The fish hosts collected in the mining premise supported the poorest and least diverse parasite communities of all sampled sites, with virtual depletion of both heteroxenous and monoxenous species. The Return Water Dam may therefore be regarded as a simulation model for a severely environmentally deteriorated, impoverished habitat, in which all or part of the intermediate hosts have been depleted, enabling the survival of hardy parasite species only. Further studies should address the identification of parasite life stages that are more sensitive to pollutants