| dc.description.abstract | Acid mine drainage (AMD) is a global environmental concern that persists long after mining activities cease and poses challenges for remediation efforts. Understanding the behaviour of AMD-related metal(loid) contaminants such as arsenic (As), copper (Cu) and zinc (Zn) in the aqueous and sediment phase is vital for protecting affected catchments, especially under differing hydrogeochemical conditions and their interaction with seawater upon entering coastal zones. This thesis aimed to investigate the sources, pathways, and sinks of contaminants within an AMD-affected river system (the Carnon River, UK). The mining history and short length (14 km) of the Carnon River catchment allowed an extensive investigation into the behaviour of the aqueous phase metal(loid)s from source (AMD) to sink (estuary).
Contaminant sources, loads, and transport mechanisms were assessed through a 12-month sampling of water and over 22 years of data from the UK Environment Agency. Sediment samples were also collected along the Carnon River and analysed for their spatial and particle size distribution of metal(loid)s and mineralogy.
Decadal (22 years) water quality monitoring revealed increasing As and iron (Fe) export to the coastal zone and ongoing AMD generation (and Cu and Zn release) at the County Adit (AMD input). The one-year (2021-2022) more detailed study recorded substantial load contributions of unfiltered and filtered Cu (59-81%), Zn (46-83%), and Fe (49-86%) from the County Adit to the cumulative load of the Carnon River. The main drivers of release were found in this study to be riverine discharge for Cu and Zn, while pH and Eh controlled As and Fe behaviour in the Carnon River.
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Aqueous- and sediment-phase As speciation analysis revealed a downstream shift, where aqueous As (III) became dominant and the proportion of As (V) decreased in the sediment phase. This process likely via reductive dissolution of Fe oxides and sequestration by sulfides in the estuary.
Maximum (filtered and unfiltered) contaminant loadings into the coastal zone were recorded at 742 kg/month (Cu), 3430 kg/month (Zn), 354 kg/month (As), 1960 kg/month (Fe) and 128,000 kg/month (sulfur, S). Sediment analysis revealed As, Cu and Zn concentrations were concentrated in both coarse (>2 mm) and fine (<0.063 mm) particles. The >2 mm particles were likely detrital phases remobilised instream ore and mine waste. The <0.063 mm particles were most likely a mix of detrital and secondary Fe (oxy)hydroxides and other phases.
Overall, this study addresses knowledge gaps in AMD-affected river systems, informing future research and intervention strategies to address the environmental challenges posed by AMD contamination. | en_GB |
