NWT RESEARCH DATABASE

Tags: contaminants, mercury, aquatic ecosystems, bioaccumulation, fish, metals, metal concentrations

Objective(s): To characterize environmental processes that are potentially driving the increasing trends in metal bioaccumulation; and, to estimate the relative contributions of different sources and pathways to total metal loadings to aquatic ecosystems in the NWT.

Project Description: Recent increases in fish mercury concentrations in the Mackenzie River basin are an environmental and human health concern. In several cases, new fish consumption advisories have been released by the NWT Health and Social Services for some lakes in the NWT. It remains unclear what processes are driving these trends in metal bioaccumulation. Two dominant hypotheses are: 1) new sources of long-range atmospheric transport and deposition from Asia; and 2) increased mobilization of previously deposited metals driven by climate change. Clearly, a better understanding of the sources and pathways of metal deposition in the NWT is needed before mitigative action can be taken. 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 two-year project will involve summer field programs in 2013 and 2014 to measure metal concentrations (including lead, mercury, arsenic) and lead isotope ratios in different environmental compartments, thereby linking metal loadings to aquatic ecosystems with modeled 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. Two locations on Great Slave Lake and two small lakes nearby will be sampled (two sites per year). The "fingerprints" (lead isotope ratios) of potential pollution sources will be determined by a combination of local sampling, regional sampling in Alberta, and use of literature values for long-range global sources. Using mixing models, the research team will then estimate metal contributions from: 1) different pathways (watershed inputs vs. direct atmospheric deposition); and 2) local, regional and global lead pollution sources. 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. One or two indicator fish species will be chosen in consultation with the Yellowknives Dene First Nation. Burbot, northern pike and lake trout would be relevant indicator species because they are currently being monitored 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 eight metals (mercury, arsenic, lead, zinc, nickel, cadmium, copper, selenium) 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 research team have provided information to and solicited feedback from the Yellowknives Dene First Nation on our proposed study. The study was discussed at a meeting in February 2013 and some initial feedback on the study design was provided from the Yellowknives Dene First Nation. The research team will continue to consult with the Yellowknives Dene First Nation prior to initiating the field programs. The team will also meet with members in both years of the program to discuss the progress and findings from this project. The research team will communicate with the Yellowknives Dene First Nation throughout the duration of the project. For the field programs, the team will consult on the activities and work with a local guide. 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 September 1, 2013 to October 5, 2013.