Impacts of Artisanal Small-Scale Gold Mining on Water Quality of a Tropical River (Surow River,Ghana)

摘要

Rivers in Ghana provide environmental and economic services such as fishery and farming, and are also the main sources of clean drinking water. Artisanal small-scale gold mining (ASGM), a significant industry in Ghana, typically occurs near streams and rivers in order to obtain a source of water for processing and waste discharge. ASGM is subsistence mining carried out by individuals or small collectives using rudimentary technologies for both extraction and processing of ore. Using small quantities of mercury for gold extraction, ASGM also releases high quantities of sediment, (along with metals and other contaminants) into local water bodies, posing environmental and downstream human health risks. In Ahafo, Ghana, we undertook a detailed assessment of the effect of ASGM on the water quality of the Surow River over one year (January 2013 to April 2014). Physico-chemical properties of the water at 11 sites along the river (above and below ASGM sites) were measured monthly. Our research indicates that the impacts of ASGM extend beyond Hg contamination, with the main effects of ASGM on river systems being changes in water conductivity, sediment loads, and metals, as well as alteration of river morphology. Dewatering water was responsible for significant increases in conductivity. We did not detect mercury above drinking water standards, with the exception being at the headwaters, presumably from natural sources. In general, we found that sites with associated ASGM activities had water qualities that did not meet Ghanaian national standards for drinking water, with manganese at particularly high concentrations. We also saw temporal variability in water quality parameters, likely due to the combination of fluctuating ASGM activities and the natural seasonal hydrology of tropical river svstems.