Spatial and temporal variations in the transport and storage of trace metal contaminants in the upper Rio Pilcomayo, southern Bolivia

摘要

Mining of the Cerro Rico de Potosi precious metal-polymetallic tin deposits of Bolivia began in 1545 and has led to severe contamination of water and sediments of the upper Rio Pilcomayo drainage system. Detailed geomorphological, stratigraphic and geochemical analyses show that the downstream transport and deposition of sediment-borne trace metals from Cerro Rico vary among three types of river reaches. Reach types, called process zones, are characterised by a semi-homogeneous set of landforms and geomorphic processes. The potential for trace metals to be remobilised and negatively impact the riverine ecosystem also differs between these process zones. The analysis, then, demonstrates that the assessment of trace metal contamination within rivers that drain the eastern flank of the Andes, and other high relief terrains, requires an interdisciplinary approach that integrates an understanding of both geomorphological and geochemical factors.