Stores, impacts and dispersal of sediments contaminated by mining legacy in rivers and estuaries induced by climate change effects

The history of mining exploration has left a significant stock of legacy contamination in the UK’s river sediments. Flood events have contributed to the erosion of upstream sediment deposits and widespread the contamination throughout river basins, carrying mining legacy sediments to lowland rivers and estuaries. This thesis investigates how the increase of climate change effects could disturb the mining legacy deposits and the consequences for the river health. The physical characteristics and the proximity to the Tamar Estuary makes the mining legacy sediments in the Cotehele a good site to understand the dispersal and impacts of such sediment to rivers and estuaries. The metals Cu and Pb were the most explored metals in upstream mines. In terms of magnitude, the sediment deposits presented concentrations ranging between 38 to 140 times higher than background values for Cu and 2 to 16 times above background values for Pb. A bioaccumulation experiment exposing snails to re-suspended sediments in waters with different salinities was performed. The aim was to understand how different salinities can influence the uptake of metals. The bioaccumulation experiment demonstrated that the disturbance of sediments released metals at a concentration that may cause deleterious ecotoxicological effects. Modelling simulations demonstrated that the worst-case scenario would spread Cu concentrations above EQS (Environmental Quality Standards) in areas with high potential for bioaccumulation for a prolonged time. After agriculture, pollution from abandoned mines is the second main reason for the deterioration of the Lower Tamar. The results demonstrated that the impacts of climate change could bring further challenges to the improvement of the Lower Tamar water quality.