Arsenic mobility in a changing northern climate: Implications for geochemical baselines and long-term stability of contaminants in lake systems

Climate change is influencing the biogeochemical dynamics of lake systems in northern Canada. These changes may affect the loading and cycling of naturally occurring metal(loid)s and the long-term stability of mining-derived contaminants in sub-Arctic lakes. Arsenic (As) concentrations of lakes in the Courageous Lake Greenstone Belt (CLGB), Northwest Territories, Canada, are elevated from the weathering of mineralized bedrock and/or the operation of historical gold mines (Tundra and Salmita mines). In this region, the cumulative effects of resource extraction and modern climate warming make it difficult to discern between anthropogenic impacts and baseline geochemistry. This study integrates As geochemistry, organic petrography, paleoclimate proxies (particle size, organic matter (OM) type and quantity), and radiometric dating (14C and 210Pb) to determine the influence of past and present climate warming on the long-term stability of As in lakes surrounding Tundra Mine. The findings of this study demonstrate baseline As concentrations in lake sediments ranging from 28 to 170 mg·kg−1 (median: 40 mg·kg−1; n = 102) and provide evidence that weathering of mineralized bedrock and terrigenous material provides an ongoing source of naturally derived As to some lakes of the CLGB. An increased accumulation of OM in the near-surface sediment, as a result of climate warming, influences redox dynamics and results in As release from minerals to pore waters via reductive dissolution of As-bearing minerals (i.e. scorodite and Fe-(oxy)hydroxides). Under these changing redox conditions, solid phase OM mediates the diffusion of dissolved As to overlying surface waters by providing a substrate for As sequestration and facilitating the precipitation of authigenic As-bearing minerals (i.e. framboidal pyrite, As-sulphides, Fe-(oxy)hydroxides). However, the effect of these changes will differ between lakes as the long-term stability of As is influenced by the source and primary hosts of As in lake sediments. Knowledge from this study will help predict future climate-driven changes to metal(loid) cycling in sub-Arctic lakes and improve environmental monitoring and remediation strategies at northern metal mines. The possibilities and benefits of weaving traditional knowledge with our research and teaching of geological sciences and engineering are also explored in this thesis, based on hands-on experience gained through this study.
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