NWT RESEARCH DATABASE

Regions: North Slave Region

Tags: contaminants, water quality, bioaccumulation, arsenic, hydrology, sediment quality, aquatic invertebrates

Objective(s): To investigate watershed and within-lake abiotic processes affecting the recovery of mine-impacted lakes in the Yellowknife area.

Project Description: The overarching objectives of this research are two-fold: 1) to investigate watershed and within-lake abiotic processes affecting the recovery of mine-impacted lakes in the Yellowknife area, including storage and release of arsenic from soils, seasonal dynamics of arsenic export in runoff, and fluxes of arsenic to and from lake sediments; and 2) to investigate the toxicological consequences of more than half a century of elevated contaminant levels on food chains in mine impacted lakes that show little sign of recovery. The key research questions for this project include: a) What are the current processes that are loading and removing arsenic from Yellowknife area lakes and how does this influence lake recovery? i) Continued loading: how much arsenic continues to be derived from watershed sources, i.e. catchment soils, inflow from upstream lakes, and fluxes between contaminated lake sediments and overlying surface waters? ii) Export processes: how much arsenic is exported downstream from the lake via lake outflow or retained in the lake through sedimentation processes? iii) How do these processes vary seasonally, and what are the most important seasons for transport? b) How do lake water conditions affect the diffusion of legacy arsenic from sediments and its speciation in the water column? i) How do oxygen at the sediment-water interface and temperature affect the diffusion of arsenic from contaminated lake sediments? ii) How do sunlight and water chemistry affect the speciation of inorganic arsenic in the water column? c) How is legacy arsenic accumulating in food chains of mine impacted lakes? i) What is the speciation of arsenic accumulating in fish and their invertebrate prey? ii) What tissues are the main stores of arsenic and metals in fish? iii) Are fish showing signs of toxicity at the cellular level? The research team propose to conduct a multi-disciplinary study that integrates a variety of methods to better understand the processes controlling the slow recovery of Yellowknife lakes from legacy arsenic pollution and the toxicological consequences to aquatic food chains. The activities outlined below, which involve both field measurements and laboratory experiments, will be conducted over a three-year period to generate sufficient data to address the complex research questions and achieve our objectives. Activity 1: Quantifying arsenic loading and removal processes in Yellowknife area lakes The research team propose to undertake detailed seasonal arsenic mass balance estimates for Lower Martin Lake in order to better understand the processes influencing lake recovery in the area. Mass balance models are an effective means of estimating and partitioning the relative fluxes of contaminants in watersheds and have been used successfully in past studies. The research team have selected Lower Martin Lake as the primary location of study because it is the last lake in the Baker Creek system before the Giant Mine site and Yellowknife Bay and consequently the lake acts as a mediator for upstream contributions. Inputs and outputs from the watershed will be measured across seasons. This is rarely done, but is likely highly important in subarctic watersheds, where spring snowmelt may account for the bulk of metal(loid) transport. In addition, under-ice winter processes may lead to substantial enrichment of lake water arsenic via cryoconcentration and diffusion from contaminated lake sediments under anoxic conditions. To carry out these mass balance estimates, the watershed will be divided into distinct terrestrial and aquatic ecosystem units so that potential source areas and fluxes between these areas can be quantified. Current atmospheric deposition of arsenic will be measured using rain collectors in the spring, summer, and fall and by measuring the chemical composition of the snow pack in late winter. Total arsenic concentrations will be measured in catchment soils from the various terrain units (open and closed canopy forests, bedrock outcrops, and wetlands). Arsenic mineralogy (i.e. solid state speciation) will be determined for a subset of samples (soil, sediments, stream particles) to identify the origin (natural vs anthropogenic) and mobility of arsenic in environmental reservoirs. Porewater arsenic concentrations in soils will be measured during summer and fall using piezometers and suction lysimeters in order to estimate the amount of water soluble arsenic available for transport. Lake waters will be sampled regularly to evaluate seasonal variations in lake water arsenic concentrations, including arsenic speciation. Regular sampling at lake inflows and outflows will be undertaken, with detailed sampling during freshet and during storm events, as these periods likely account for the bulk of arsenic transport in the watershed. Finally, the flux of dissolved arsenic from lake sediments will be estimated seasonally in the field using in situ measurements of lake sediment porewaters. Activity 2: Toxicological consequences to aquatic food chains. Arsenic bioaccumulation and speciation will be investigated in food chains of the study lakes to evaluate potential toxicological impacts on resident biota. Recent evidence from Pocket Lake indicates that arsenic loadings to water bodies adjacent to the mine were sufficient to eliminate a keystone invertebrate of aquatic food chains. Fish-bearing lakes (Long Lake, Lower Martin Lake) will be sampled for fish and their invertebrate prey (zooplankton, benthic invertebrates) using standard methods (Broad Scale Fish Community Monitoring Protocol). In fish-less lakes (e.g. Handle Lake), only aquatic invertebrates will be collected. The research team will collaborate with parallel work on contaminants in fish that is being conducted. This will include logistical collaboration during fish collection to maximize the amount of information collected on each fish. Fish tissues and aquatic invertebrates will be analyzed for arsenic levels and speciation, and compared to published arsenic thresholds from the literature for toxicity in invertebrates and fish. In addition, tissues will be examined at the cellular level using a novel approach termed sub-cellular partitioning of elements. Aquatic invertebrate and fish tissues will be analyzed to determine where within cells arsenic and metals are distributed and to what sub-cellular components those elements are bound. These measurements will identify if arsenic and metals are bound to more sensitive components within cells that may result in toxicological effects (such as organelles or cytosolic enzymes) or if the elements are being detoxified (by association with heat-stable proteins or granule structures). This research will provide indicators of potential toxicity of legacy pollution to fish and their food sources in mine-impacted lakes. The Yellowknives Dene First Nation (YKDFN) are active partners in the proposed project. YKDFN members will be involved in project planning, collection of field data, and reporting back to the community. The project team will provide regular updates to YKDFN staff of the Department of Lands and Environment and will be available to meet with chief and council should that be necessary. YKDFN staff will be provided with copies of all annual reports and presentations. The project team has worked extensively in the past with YKDFN staff from the Department of Lands and Environment, including providing plain language information via reports and presentations. Information generated from this project will be summarized in annual reports to Cumulative Impact Monitoring Program (CIMP) and these reports will be shared with community groups and regulatory boards. Follow up conversations with researchers will be initiated if there is interest. Since the PI for this project will be based in Yellowknife, he is readily available to discuss project details throughout the year. Results from the project will directly inform the regulatory permitting process for the remediation of Giant Mine and results will be made available to the Mackenzie Valley Land and Water Board, the Giant Mine Remediation Team, and the Giant Mine Oversight Board through CIMP annual reports and through presentations to these organizations as required. Project team members are also available to participate as experts in the permitting process of remediation activities at Giant Mine should their services be required. The fieldwork for this study will be conducted from January 11, 2018 to December 31, 2018.