Tracking the Aquatic Impacts of a Historical Metal Mine Using Lacustrine Protists and Diatom Algae

Two lake sediment cores collected near a closed Cu–Au mine were analyzed for testate amoebas, diatoms, and geochemistry to compare their utility for assessment and monitoring of aquatic impacts of metal mines. Geochemical profiles displayed the mine history as increases in mineral matter-related elements during the mining period, and as post-mining metal peaks. Biotic assemblages co-varied with geochemical shifts, and the most notable ecological changes coincided with the peaks in metal concentrations. Additionally, nutrient enrichment caused a major shift in biotic assemblages. According to the results, the mine affected the lake environment over a relatively large area but the changes were transient. Major ecological effects occurred only after the actual mining period as the tailings weathered, which delayed the metal release. This suggests that mine impacts can be significantly reduced by careful design and after-care of the waste facilities.