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Abstract: Alkaline rocks (phosphate deposits in particular) of igneous origin are currently being mined in Zimbabwe. Exploitation of these deposits, which are associated with metals and non-metals, provides a potential for changing the river water quality in the surrounding areas by increasing metal and phosphates levels in the water, thereby endangering the beneficial use of the river. The aim and objectives of this paper are to enumerate the current impacts associated with mining alkaline rocks on Save River water quality in Zimbabwe using the Dorowa mine as a case study. Though there are several impacts associated with the mining of alkaline rocks, this paper deals only with impacts on water quality. A preliminary assessment of the water quality in the Save River downstream of the Dorowa phosphate mine showed an increase in conductivity, iron content, manganese content, nitrates and hardness when compared to those taken before mining activity began. However, there was no notable increase in phosphate and metals except for Fe and Mn. A plausible explanation for the low phosphate values in the water is that the phosphates are precipitating and settling as sediments. Phosphate is known to effectively remove metals from the surface water through the formation of metal–phosphate minerals. Thus, various pollutants may be adsorbed into sediments accumulated on the bottom of the river. These sediments may accumulate pollutants over long periods and act as new pollutant sources to the overlying water when phosphate desorbs from sediments due to changes in water conditions. Therefore, the sediments can act as a source of water pollution in the future. [Copyright &y& Elsevier]

Abstract: The objective of the study was to investigate the role played by the natural environment in protecting the transboundary Save River from the impacts of metals derived from phosphate mining at Dorowa. The study is a follow up study from a previous one that noted that there is natural attenuation at Dorowa. Water and sediment samples were collected in the Save River and the streams that drain the Dorowa dumps. Inductively coupled plasma mass spectrometry (ICP–MS) was used to analyze the cations (Na+, K+, Ca2+, Mg2+, Cu2+, Co2+, Fe2+, Ni2+, Zn2+, Pb2+, Sn2+, Mn2+, Cd2+) in the samples. Major anions Cl−, and were analyzed by standard chromatography whilst and were determined by titration. pH was measured on site. Geochemical modeling of the water composition was conducted with Visual Minteq. The results show that natural attenuation is being achieved through precipitation of solids from the water and subsequent deposition onto the sediments. Six of the metals are almost completely precipitated (Cu 99.99%, Fe 99.39%, Ni 91.24%, Pb 99.87%, Sn 99.99% and Zn 88.66%). However Mn, Co and Cd remain in solution. Thus the natural environment is protecting the Save River which is a transboundary river from the impacts of mining through precipitation of the metals. Users downstream of Dorowa mine are therefore not being affected by mining pollution. This study demonstrates that besides being a legitimate and important user of water, the natural environment can also play a significant role in protecting water quality by attenuating metals naturally. By analyzing costs incurred in several places where alternative methods are employed to remediate metal related pollution the study concludes that natural remediation at Dorowa is saving the nation in environmental costs. Therefore the paper advocates for appreciation of the role that the natural environment plays in protecting ecosystems from the impact of human developments and environmental costs. Subsequently, this calls for recognition of natural environment’s role in water resources management for the sustenance of ecosystems and peoples livelihoods. [Copyright &y& Elsevier]