**Acknowledgements**

The study was funded by the University of KwaZulu-Natal (UKZN), through a competitive grant, and the Department of Agriculture, Forestry and Fisheries (DAFF), through a research bursary. The views expressed in this article are not those of UKZN or DAFF. Staff of Umgeni Water provided assistance with site information and soil sampling, and Dr. C. Southway, of the Chemistry Discipline, UKZN, provided valuable inputs in sample analysis.
