Organic matter control on the distribution of arsenic in lake sediments impacted by ∼65 years of gold ore processing in subarctic Canada

Climate change is profoundly affecting seasonality, biological productivity, and hydrology in high northern latitudes. In sensitive subarctic environments exploitation of mineral resources led to contamination and it is not known how cumulative effects of resource extraction and climate warming will impact ecosystems. Gold mines near Yellow knife, Northwest Territories, subarctic Canada, operated from 1938 to 2004 and released N 20,000 t of arsenic trioxide (As2O3) to the environment through stack emissions. This release resulted in elevated arsenic concentrations in lake surface waters and sediments relative to Canadian drinking water standards and guidelines for the protection of aquatic life. A meta-analytical approach is used to better understand controls on As distribution in lake sediments within a 30-kmradius of historicmineral processing activities. Arsenic concentrations in the near-surface sediments range from 5 mg.kg(-1) to over 10,000 mg.kg(-1) (median 81 mg.kg(-1); n = 105). Distance and direction from the historic roaster stack are significantly (p < 0.05) related to sedimentary As concentration, with highest As concentrations in sediments within 11 km and lakes located downwind. Synchrotron-based mu XRF and mu XRD confirm the persistence of As2O3 in near surface sediments of two lakes. Labile organic matter (S1) is significantly (p < 0.05) related to As and S concentrations in sediments and this relationship is greatest in lakes within 11 km from the mine. These relations are interpreted to reflect labile organic matter acting as a substrate for microbial growth and mediation of authigenic precipitation of As-sulphides in lakes close to the historic mine where As concentrations are highest. Continued climate warming is expected to lead to increased biological productivity and changes in organic geochemistry of lake sediments that are likely to play an important role in the mobility and fate of As in aquatic ecosystems. (c) 2017 Elsevier B.V. All rights reserved.