Nano- to catchment-scale investigations of metal transport processes in mining-impacted river systems

Abstract

Millennia of metal mining has left across the world an extensive physical legacy of contaminated mine waste and a substantial impact on the environment. In mining-impacted rivers, efforts to monitor metal mine contamination and remediation strategies to achieve good water quality are often of limited efficiency and success due to the variability of processes which control metal dispersion. This thesis aims to identify nano- to catchment-scale drivers of metal dispersion by: assessing the role of river catchment geomorphology in metal storage; quantifying metal sources across streamflow conditions; and investigating the metal-bearing nanoparticle flux in the river water. This study investigated metal dispersion at the Nant Cwmnewyddion and the Nant Magwr, two rivers draining the abandoned lead and zinc mining area of Wemyss and Graiggoch Mines (central Wales). Sediment geochemistry and metal content were characterised and combined with river catchment geomorphological descriptions to identify areas of metal storage. A multi-tracer approach, which combined continuous tracers with slug (gulp) injections, allowed metal sources to be apportioned at a highly resolved spatial scale, enabling variations in metal load across streamflows to be accounted for. Metal-bearing nanoparticle flux was quantified using a novel, efficient sampling method and their size, morphology and chemistry characterised with a multi-method approach with the employment of several instruments. The findings of this study suggest that river catchment geomorphology can influence on sediment geochemical processes (such as redox and dissolution), and highlight areas of metal source transformation. Descriptions of river catchment geomorphology can therefore be employed as a low-cost approach to initially identify potential metal sources and focus geochemical sediment analysis. The multi-tracer method successfully estimated point and diffuse metal source contributions throughout the river and across streamflows. These estimates were only possible due to the multi-tracer methods, therefore, the integration of this method in monitoring protocols is proposed for future studies of metal dispersal in rivers. Furthermore, the study provided important information concerning environmental nanoparticle chemistry, particle size distribution, and aggregation state within the river, allowing their role in metal transport to be better understood. In conclusion, this research extended the understanding of the spatial and temporal variability of zinc and lead dispersion mechanisms and showed the high potential of adopting a multi-method approach to apportioning metal sources at the catchment scale.