Ecological Risk Assessment of Heavy Metals Pollution in the Loskop Dam of the Olifants River System, South Africa

The Loskop Dam is a major reservoir on the upper Olifants River in South Africa. Many human activities in the upper river catchment are causing contamination in the river including heavy metals. Although several studies have investigated water pollution in the river system, limited information exists regarding the spatial distribution and ecological risks of heavy metals in the Loskop Dam and their ecological implications. Seasonal heavy metal concentrations and ecological risks associated with heavy metal contamination in the dam were assessed. Though most of the heavy metal concentrations were below detection levels in the water, the concentrations were substantially higher in the sediments, with higher concentrations mainly recorded during winter than summer. Chromium and nickel concentrations in the sediments exceeded the permissible guideline values. Furthermore, contamination factor, enrichment factor and geoaccumulation index were used to determine the extent of chemical pollution, and ecological risk index was used to assess the potential ecological risks. The contamination indices found the sediments to be moderately to highly contaminated by Cr, Pb and Zn. However, the ecological risk values were low, indicating a low ecological risk of contamination posed by heavy metals in the dam. During winter, Cd had the highest ecological risk and during summer, the ecological risk was dominated by Pb, but the values indicated a low contamination (ER <40) and the potential ecological risk index values were also low (RI < 150). Nonetheless, effective conservation strategies are needed to prevent further degradation of the river system. Furthermore, the study reinforces the importance of addressing metal pollution and conservation of freshwater ecosystems, which aligns with the United Nations Sustainable Development Goal (SDG) 6, particularly in enhancing water accessibility and responsible sanitation management.