Challenges For Sustainable Water use in Dolomitic Mining Regions of South Africa—A Case Study of Uranium Pollution Part II: Spatial Patterns, Mechanisms, and Dynamics

Abstract

Surface and groundwater resources in the Wonderfonteinspruit (WFS) catchment are of increasing importance as future sources of water supply to a growing population in the region. However, deep-level gold mining over more than a century has impacted adversely both the availability and quality of ground- and surface water. This paper analyses spatial patterns, mechanisms, and dynamics associated with the fluvial transport of uranium. Previous studies found elevated levels of dissolved U along the entire watercourse and also detected significant secondary accumulations of U in fluvial sediments. The degree of sediment contamination seems to be determined less by the distance to the source of U pollution than by the sorption capacity of sediments and certain site-specific mechanisms removing U from stream water. U concentrations in stream water were found to fluctuate by up to several orders of magnitude between two weekly measurements. This highly dynamic behavior of U in stream water is caused by complex interactions of natural and anthropogenic processes differing in frequency and magnitude. Such processes include diurnal and seasonal photosynthesis cycles, rain events, and pumping regimes of mines discharging uraniferous effluents. It is recommended to adjust sampling intervals of existing monitoring systems accordingly, because current protocols systematically underestimate the true extent of stream pollution.