Arsenic cycling and speciation in mining-impacted sediments and pore-waters from Yellowknife Bay, Great Slave Lake, Northwest Territories

Radiometric dating of lacustrine sediments combined with a non-reactive mid-core Pb, Zn, Cu and Sb enrichment independently confirms the onset of metal(loid) contamination into Yellowknife Bay, NWT, was coincident with the beginning of Giant Mine activity adjacent to the bay. These anthropogenic inputs have also resulted in sediments and pore-waters with As concentrations as high as 10,000 mg/kg and 7450 pg/L, respectively.; The most important seasonal process affecting As cycling involves the attenuating efficiency of the oxic zone at the sediment-water interface (SWI). This oxic veneer contracts to less than one centimetre during the open water season resulting in the release of As to the benthic environment. Arsenic and Fe sediment chemistry show a very good correlation with enrichments at the SWI. The release of As to bottom-waters in the open water season is likely due to the reductive dissolution of Fe (hydr)oxides by labile organic matter originating from active primary production. After lake freeze and subsequent organic degradation over the winter season, the oxic veneer expands significantly and is able to attenuate upwardly diffusing As onto authigenic Fe and possibly Mn phase(s) much more effectively. (Abstract shortened by UMI.)...