Cumulative impacts of metal deposition in the NWT: Using lead isotopes to trace local, regional and long-range sources
Principal Investigator: Chételat, John (3)
Licence Number: 15455
Organization: Environment Canada
Licenced Year(s): 2014 2013
Issued: Apr 10, 2014
Project Team: Drs. M. Richardson & B. Cousens (Investigators, Carleton University), Drs. D. Muir & M. Evans (Investigators, Environment Canada), J. Black & F. Sangris (Coordination and guiding, Yellowknives Dene First Nation)

Objective(s): To characterize environmental processes that are potentially driving the increasing trends in metal bioaccumulation in aquatic ecosystems in the NWT.

Project Description: Yellowknife Bay on Great Slave Lake is a water body of cultural, subsistence and recreational importance for the Yellowknives Dene First Nation (YKDFN) and residents of Yellowknife. The ecosystem health of Yellowknife Bay has been impacted by historical mining releases of metals (particularly arsenic), as well as long-range atmospheric transport of metals such as mercury from far-away human emission sources. There is local concern over arsenic exposure from legacy pollution and more recent observations of increasing mercury levels in fish of Great Slave Lake. Further, climate change may be exacerbating these stressors on water quality by altering the cycling of metals and creating new issues such as cyanobacterial blooms. This project will contribute to cumulative impact monitoring by: 1) characterizing environmental processes that are potentially driving the increasing trends in metal bioaccumulation; and, 2) estimating the relative contributions of different sources and pathways to total metal loadings to aquatic ecosystems in the NWT.

This multi-year project will involve summer field programs to measure metal concentrations (including lead, mercury, arsenic) and lead isotope ratios in different environmental compartments, thereby linking metal loadings to Yellowknife Bay and Great Slave Lake with modelled contributions from different lead sources. The research team will collect lake sediment cores (which are environmental archives) with a gravity corer to provide a historical perspective on metal deposition, tree lichens to estimate current atmospheric metal deposition, river and stream sediments (by hand-held corer or Ekman dredge) to detect watershed inputs to aquatic ecosystems, and fish (by gill net) to examine the biological fate of metals. Surface and deep samples of water will be collected for analysis of metals, including for mercury and arsenic speciation, at sites of varying proximity to Giant Mine. In addition, a sampling program will be conducted to investigate the presence of cyanobacteria and cyanotoxins, which may be stimulated by climate warming.

Fish will be sampled to examine the biological fate of metals in the study area and to evaluate the pathways and sources of metal uptake into the food web. Burbot, whitefish and northern pike will be used as indicator species because of their local consumption and/or current monitoring in other parts of Great Slave Lake under the Northern Contaminants Program. Fish will be collected by gill net and their tissue will be analyzed for a suite of metals (including mercury, arsenic and lead) as well as lead isotopes. Muscle will be analyzed for mercury because of its relevance for fish consumption, while other metals will be analyzed in liver, which is a key organ for metal accumulation. Fish muscle will also be analyzed for carbon and nitrogen stable isotopes to provide biological information that is relevant for metal bioaccumulation, namely dietary carbon sources and trophic position of the fish.

The Yellowknives Dene First Nation is concerned about legacy metal pollution in Yellowknife Bay and local members of the project team will participate in various project activities, including providing input and feedback on the study design, coordination and collection of field samples, and communication of findings. YKDFN perspectives and observations on the environmental health of Yellowknife Bay will be incorporated through discussions on the study design, collaboration on the field sampling and review of on-going progress of the project by telephone and face-to-face annual meetings. This project will build longer-term community capacity through involvement in the project and collection of new information on specific concerns of the YKDFN. Knowledge of the ecosystem health of Yellowknife Bay is an essential step towards greater confidence in food security and local resource use by the community.

The research team will visit the Yellowknives Dene First Nation office to meet and discuss the progress and findings during the field programs and again during each annual northern meeting. The research team will attend the annual Cumulative Impacts Monitoring Program results workshops to present on the project and provide results to community members, other northern researchers and decision makers. The final report and project metadata will be made available for upload to the NWT Discovery Portal. The research team will also register the project and provide metadata to the Polar Data Catalogue. The intention is to submit papers from this study for publication in scientific journals.

The fieldwork for this study will be conducted from June 1, 2014 to October 1, 2014.