A Holistic Assessment of Trace Metal Mobility Near Abandoned Mine Sites in the Wheaton River Watershed, Yukon, Canada

Abstract

The Wheaton River Watershed, located in southern Yukon, feeds Bennett Lake and ultimately the Yukon River, and has been heavily impacted by recreation and mining activities dating back to the Klondike Gold Rush (1896). This watershed is within the Traditional Territory of the Carcross/Tagish First Nation (C/TFN), who have stewarded these lands since time immemorial, and hold concerns over impacts of point source contamination on broader ecosystem health. Despite the common understanding of ecosystem connectivity among locals, assessments of trace metal mobility across multiple environmental media are overlooked when approaching research using perspectives exclusively rooted in Western Science. Despite this knowledge, no assessment of trace metal mobility has been conducted in the watershed, leaving questions surrounding the extent of contaminant point source impacts on the catchment as a whole largely unanswered.

Co-created with C/TFN staff and community members, this thesis took a holistic approach to assess the current distribution and potential for trace metal mobility on a watershed scale. Water, plant, scat and sediment samples collected at mine-impacted and downstream sites were analyzed for trace metals, focusing on those posing known risks to human and animal health (As, Cd, Hg, Pb, and Sb) to investigate the extent of metal mobility between media and throughout the catchment, supported by sequential extraction and stable isotope analyses. There were both region and metal-specific patterns of trace metal distribution and mobility, with most trace metals stored in sediments at mine-impacted sites. Metals in water samples followed similar trends to solid samples; however, lower concentrations, especially in the mainstem Wheaton River relative to mine-impacted samples, suggested either or both low mobility and dilution from other water sources as driving factors at this time. Flux analyses and yield calculations indicated that the cumulative Wheaton River trace metal exports into Bennett Lake were comparable or below western Arctic references. This thesis explores trends of multi-media metal mobility from mine-impacted sites on a watershed scale, informed by perspectives rooted in Western Science and Indigenous knowledge, highlighting the complex, connected, and dynamic nature of the watershed. Findings from this thesis will help inform land planning and stewardship initiatives led by C/TFN, remediation efforts, and guide future research in the region.