Metal enrichment and contamination in a karst cave associated with anthropogenic activities in the Witwatersrand Basin, South Africa

The Wonderfontein Spruit has been severely polluted as a result of anthropogenic activities (i.e. mining and industry) in the Witwatersrand Basin (South Africa). Although the extent of metal pollution within this surface freshwater system has been well studied, no such efforts have been made with emphasis on the associated cave environments. The Wonderfontein Cave, a highly interconnected network of passages, is one such system exposed to metal pollution by the influx of water from the Wonderfontein Spruit. This not only poses a severe threat to the associated subterranean ecosystem, but also to freshwater resources as water within the Wonderfontein Cave drains into the underlying aquifer. Subsequently, this study was aimed at assessing enrichment (pollution) and contamination levels of selected metals within the Wonderfontein Cave. While enrichment was calculated using enrichment factors, the geoaccumulation index provided contamination levels. Sampling was undertaken during April and September 2013, which represented the high and low flow periods, respectively. Results from the multivariate analysis indicated that especially sediments collected from the Wonderfontein Cave were enriched with metals. Furthermore, Cadmium, and Uranium occurred in extreme contamination levels. The soils, however, were positively related to only Arsenic, Chromium, and Manganese enrichment with substantially lower contamination levels recorded. Furthermore, the observed spatial variation in metal enrichment and contamination was likely subject to the hydrological setting of the Wonderfontein Cave, while temporal variation could have been a result of fluctuating water levels (dilution effect). This study provides evidence that efforts should be made to better manage and conserve subterranean environments to preserve subterranean life and protect freshwater resources.