The Application of Paleolimnological Methods and Geochemical Normalization to Establish Baseline Conditions for Metal Contaminants in Advance of Proposed Mining, Marian Watershed, Northwest Territories, CanadaTuesday, November 20, 2018 - 15:20 to 15:39 Theatre 2
The Marian Watershed Stewardship Program (MWSP), a community-driven aquatic ecosystem monitoring program, was developed by the Tłı̨chǫ Government to address concerns regarding the cumulative impacts of multiple potential stressors. In particular, the MWSP aims to develop methods that will be effective for detecting potential pollution from the proposed cobalt-gold-copper-bismuth NICO mine within Tłı̨chǫ Lands. In collaboration with the MWSP, we are using paleolimnological methods and geochemical normalization to establish pre-mine baselines of lake sediment metals concentrations across the Marian Watershed prior to mine development, which can be used to assess for pollution from surficial sediment once the mine becomes operational. Here we present stratigraphic sediment metal concentration results from four lakes normalized to lithogenic and biogenic elements (Al, Ti, OM, Corg). The application of normalizing techniques to metals within the stratigraphic record aims to account for natural variation as a result of (bio) geophysical processes that may affect sediment metals concentrations. Our application of this method results in a set of lake and metal specific baselines established for the four lakes. Results show metal concentrations are substantially higher in lakes on or adjacent to the ore body compared to lakes located in the surrounding granitic bedrock terrane. Temporal variations in the concentrations of many metals of concern are small, which provide values that can effectively serve as baselines for ongoing monitoring. An exception is arsenic, a metalloid of major concern, which increases variably in the latter half of the 20th century. There are multiple possible explanations for this trend, including far-field atmospheric emissions, increase in erosion of arsenic-bearing sources in the lake catchments, and/or post-depositional diagenetic mobilization in the lake sediment profile. Notably, increases in arsenic concentrations also occur in the early part of the past millennium likely indicating the potential for variation in the catchment-derived supply of arsenic to these lakes. Additional studies are required to further characterize processes that cause arsenic variations in these lake sediment records. Variation in sediment metals concentrations on both temporal and spatial scales in this region demonstrate the need for lake-specific baselines for accurate interpretation of contemporary sediment monitoring data. This paleolimnological approach may be may be expanded to other lakes in the region for additional monitoring. This unique opportunity allows for the development of a well-informed and robust monitoring program which applies a scientific approach to meet the needs of a northern community initiative.