Multivariate Analysis of the Dynamics in Water Quality and Trophic Status of the Crocodile River and Hartbeespoort Dam

Abstract

Economic expansion coupled with population growth and associated anthropogenic activities are a threat to water resources globally. This study assessed the dynamics in water quality and trophic status of one of South Africa's hyper-eutrophic reservoirs, the Hartbeespoort Dam. Spatio-temporal variability in water quality parameters was determined on historical data spanning a period of forty years , with the aim of determining decadal changes in the Water Quality Index (WQI), the Water Pollution Index (WPI), the Canadian Council of Ministers of the Environment-Water Quality Index (CCME-WQI) as well as the Nutrient Pollution Index (NPI) and TN:TP ratios in the Hartbeespoort Dam as well as the Crocodile River. The calculated indices provide a single aggregated standardized score of water quality. The efficiency of a bioremediation programme (2007)(2008)(2009)(2010)(2011)(2012) implemented as a mitigation measure to combat eutrophication in the dam was assessed. The study also investigated the impact of rainfall on the variability of the concentration and level of selected physico-chemical parameters. The results of the study revealed that apart from turbidity, rainfall has no significant impact on the variability of other water quality parameters studied. Furthermore, the WQI, CCME-WQI, WPI, as well as the NPI classified the general water quality of the dam as extremely poor and highly polluted. Moreover, TN:TP showed an increase in TP over time, further exacerbating hypereutrophic conditions in the catchment. The study also showed that the bioremediation programme was effective in reducing external P loading, however, bioturbation resulted in the resuspension of historical internal P loads, thus maintaining high phosphate concentrations at the site downstream from the Hartbeespoort Dam.