Using Sediment Archives to Reconstruct the Historic Risk of Legacy Contamination from Gold Mine Emissions to Lakes Near Yellowknife, NT

Abstract

In the last 150 years, the City of Yellowknife has transitioned from an area of traditional subsistence living to the largest city in the Northwest Territories (Canada) due to the economic influence of resource extraction. As resource extraction in the area boomed, large quantities of pollutants from mine tailings and emissions from roaster stacks adjacent to gold mines were deposited on the landscape, leaving a known legacy of elevated surface water, sediment, and soil metal(loid) concentrations. Most of the research to date has focused on arsenic in the region, and my thesis expands the body of knowledge to include other metal(loids) of interest, including antimony, lead, and mercury. My thesis's main objective was to determine the spatial and temporal extent of legacy mining emissions near Yellowknife and assess the associated biological risk from these historic emissions. I analyzed select intervals from 20 lake sediment cores for time constrained metal(loid) contaminants of concern. I used a combination of paleotoxicity and paleoecotoxicology methods to establish a spatial and temporal footprint of biological risk associated with historic gold mining activities in the Yellowknife region. I determined that lakes close to the mine exhibited a low-level hazard to aquatic communities before mining, while the onset of mining increased the hazard posed by sediments deposited to acute levels. I also discovered that lakes within 5 km of Giant Mine exceeded guideline values for sedimentary mercury during active mining. Further, I developed methods in paleoecotoxicology that indicated a concordance between time deposited, estimated risk, and observed mortality of native Daphnia sp exposed to time-constrained sediment archives. My thesis demonstrates that paleotoxicity and paleoecotoxicology are effective methods to separate historic and modern influences of industrial development on aquatic biota. Additionally, my research has application extensions for policymakers, remediation scientists, Indigenous Peoples, and those proposing new industrial ventures.