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TitleMediation of arsenic mobility by organic matter in mining-impacted sediment from sub-Arctic lakes: implications for environmental monitoring in a warming climate
AuthorMiller, C B; Parsons, M BORCID logo; Jamieson, H E; Ardakani, O HORCID logo; Patterson, R T; Galloway, J MORCID logo
SourceEnvironmental Earth Sciences vol. 81, 137, 2022 p. 1-20, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200025
Mediapaper; on-line; digital
File formatpdf; html
ProvinceNorthwest Territories
Lat/Long WENS-111.2833 -111.0667 64.1083 64.0333
Subjectsenvironmental geology; surficial geology/geomorphology; geochemistry; mineralogy; Science and Technology; Nature and Environment; Economics and Industry; mining; mines; metals; mine waste products; liquid waste disposal; surface waters; lakes; lake sediment geochemistry; lake water geochemistry; arsenic geochemistry; environmental studies; environmental controls; climate effects; lake sediment cores; grab samples; pore water samples; microorganisms; sulphides; remobilization; minerals; organic carbon; Tundra Mine; Mining industry; lacustrine sediments; Climate change; cumulative effects
Illustrationslocation maps; geoscientific sketch maps; geochemical profiles; bar graphs; photomicrographs; Venn diagrams; spectra; profiles
ProgramEnvironmental Geoscience Metal Mining: northern baselines
Released2022 02 16
AbstractArsenic (As) is commonly sequestered at the sediment-water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulfides. The results of this study demonstrate that the accumulation of organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories, Canada. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially derived OM (e.g., cutinite, funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulfide minerals (e.g., goethite, orpiment, lepidocrocite, and mackinawite); however, grain-scale synchrotron-based analysis shows that As is also associated with amorphous OM. Mixed As oxidation states in porewater (median=62% As (V), 18% As (III); n=20) and sediment (median=80% As (-I) and (III), 20% As (V); n=9) indicate the presence of variable redox conditions in the near-surface sediment and suggest that post-depositional remobilization of As has occurred. Detailed characterization of As-bearing OM at and below the SWI suggests that OM plays an important role in stabilizing redox-sensitive authigenic minerals and associated As. Based on these findings, it is expected that increased concentrations of labile OM will drive post-depositional surface enrichment of As in mining-impacted lakes and may increase or decrease As flux from sediments to overlying surface waters.
Summary(Plain Language Summary, not published)
At high northern latitudes, 21st century climate warming has resulted in increasing temperature and duration of ice-free seasons, promoting increased primary productivity and transport of organic matter to lakes. In this study, sediment and porewater samples were collected from three lakes downstream of the former Tundra and Salmita gold mines, Northwest Territories, to examine the association between arsenic and solid phase organic matter. The results show that organic matter plays a major role in controlling the mobility of arsenic in lake sediments, by providing a substrate for arsenic sequestration and facilitating the precipitation of arsenic-bearing minerals. As climate warming continues and leads to increased fluxes of organic matter to northern lakes, this study suggests that arsenic concentrations will increase in near-surface lake sediments. This natural enrichment of arsenic will make it increasingly difficult to distinguish between mining impacts and the influence of current warming trends in the sub-Arctic. It is therefore important that environmental monitoring programs consider the influence of natural, climate-driven processes on metal(loid) mobility when examining mining impacts and contaminant stability in lake sediment.

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