Potential drought-driven metal(loid) release in Junction Creek: effects of legacy contamination and the impacts of lime treatment

Abstract

Acid mine drainage (AMD) is a serious environmental problem at legacy and active mine sites around the world. Climate associated drought and rewetting events can increase the severity of AMD impacts through oxidation and release of stored metal(loid)s and acidity from contaminated sediments. The area surrounding Sudbury, Ontario, with its massive mining and smelting complexes, appears especially vulnerable to such drought-driven effects. I used a paired subwatershed approach to assess the impact of drought-rewetting cycles in two subwatersheds of Junction Creek, a heavily contaminated system flowing through the centre of Sudbury. For this study I chose the Frood tributary which contains a large mine site and waste rock storage area, as well as the less contaminated Maley tributary as a reference site. Laboratory drying and rewetting experiments with sediment-cores collected from the Nickledale wetland in the Frood branch surprisingly showed no post-drought re-acidification. However, highest concentrations of many metal(loid)s were observed in the longest (60-day) drought treatment, suggesting a drought effect may still occur. Pre-drought lime treatments showed reduced concentrations of many metal(loid)s in-solution following re-wetting. However, sediment metal(loid) concentrations suggest that liming applications may cause release of some metal(loid)s through ion exchange processes. Analysis of available long-term monitoring (2004-2020) data showed annual fluxes in metal(loid) concentrations in both subwatersheds, but the expected strong seasonality of the metal export was best observed at the reference Maley site rather than at the industrial Frood site. Additionally, it was observed that surface water As concentrations were in fact highest at the reference site. Overall, this study provides preliminary data demonstrating that the remedial work at the mine impacted site has reduced the vulnerability of this subwatershed to the climate-driven impacts.