The Zambezi River Basin in southern Africa is a high-quality waterscape. But current rapid development threatens the waters of the Zambezi, particularly its tributaries. The challenge will be to ensure that mitigation measures keep up with population and economic growth to avoid degradation of water quality degradation.
The Zambezi and Kafue Rivers in southern Africa still carry very clean water today. Only below dams do they suffer from increased water temperatures, lack of oxygen and loss of sediments. Smaller tributaries, however, are showing signs of pollution. These are the results of four field campaigns conducted by the aquatic research institute Eawag in central and southern Zambia in 2018 and 2019 in collaboration with the ETH Zurich and the University of Zambia. The results were published today in the journal Environmental Science: Processes and Impacts.
Scott Winton, lead author of the study and postdoctoral researcher at Eawag and the ETH Zurich, warns of the consequences of future development, for the catchment area of the two rivers is changing rapidly. Population and cities are growing quickly, agriculture is spreading and intensifying, and hydropower plants are being built. In the following interview, Scott Winton reports on the most important findings of the field campaigns and where the challenges for the sustainable development of the Zambezi River Basin lie.
Scott Winton, how did you experience the water landscape? Were you surprised by the high water quality of the two main rivers Zambezi and Kafue?
Scott Winton: Yes, coming from the USA and living in Europe, where with few exceptions major rivers show obvious chemical signatures of human pollution, it was a big surprise to see this huge river in Africa, the Zambezi, and find it so clean. People drink the river water without any treatment. And when we brought samples back to the Eawag laboratories, the technicians were shocked. The river water seemed to be even cleaner than the highly purified water used for laboratory processes.
What kind of pollution did you find in the tributaries?
In small tributaries draining from more densely populated areas, we found elevated nutrients and ions such as sodium and chlorine – pollutants typical of urban wastewater. Close to some industrial agricultural plots we found a stream with very high nitrate concentrations, indicative of fertiliser leaching.