NWT RESEARCH DATABASE

Regions: North Slave Region

Tags: water quality, benthic invertebrates, water monitoring, fish population, lake sediment

Objective(s): 1) To determine if installing an aerator in Frame Lake, Yellowknife, NT, will increase dissolved oxygen levels in the lake such that fish can be reintroduced; and 2) if phase 1 proves successful, transfer fish into Frame Lake and monitor growth and reproduction to determine if the population is self sustaining.

Project Description: This licence has been issued for the scientific research application No. 5706. This research project has two objectives: 1) determine if installing an aerator in Frame Lake, Yellowknife, NT, will increase dissolved oxygen levels in the lake such that fish can be reintroduced; 2) if objective 1 proves successful, transfer fish into Frame Lake and monitor growth and reproduction to determine if the population is self sustaining. If phase 2 proceeds, fish population will also be studied. Research will be completed in collaboration with University Partners from the University of Waterloo and Wilfred Laurier University. A two-day program will be conducted in winter (late March) to collect in-situ water quality data, specifically dissolved-oxygen (DO) measurements, at multiple stations along transects throughout the lake. Ice thickness, snow depth, and under-ice water depth will be recorded at each station and a water quality profile will be taken, with measurements collected at 1.0 m intervals. The approved monitoring plan outlined that samples were to be collected in twice over the winter for two years. Water quality sampling will be conducted during open-water conditions in spring (mid-June, or one to two weeks after ice-out), summer (mid-August), and fall (late-September). Two to four composite samples (one or two from each basin) will be collected each season, plus a single quality assurance/ quality control (QA/QC) sample per season. Water quality samples will be collected seasonally as a composite of three near surface grabs from each basin in Frame Lake. Samples will be analyzed for physical parameters, biological oxygen demand, major ions, and total and dissolved metals. If the lake is found to be thermally stratified, samples will be collected as a composite of three grabs from each of the hypolimnion and epilimnion. Depth-integrated water samples will be collected for nutrient and a-Chlorophyll analyses from the euphotic zone. In-situ water quality parameters (DO, pH, temperature, and conductivity) will be collected at the deep location of each basin during each season and will be taken at 1.0 m depth intervals. Six composite sediment quality samples (four from the north basin and two from the south basin), plus a single QA/QC sample will be collected in the fall (late September). In the north basin, two samples will be collected from locations deeper than 3 m, and two samples will be collected from locations less than 3 m deep. In the south basin, only one sample will be collected from each depth. Composite samples will be composed of three Ekman grabs using the top 5 cm of sediment from each grab. Samples will be collected at nine stations (six in the north basin and three in the south basin) in the fall (late September) and will include three stations in profundal habitat, three stations in littoral habitat, and three stations in shoreline vegetation. At each station, three individual grab samples or net sweep samples will be collected to account for within-station variability, for a total of 27 samples collected. Samples from profundal habitat will be taken from greater than 3 m depth. Samples from littoral habitat will be taken from less than 3 m depth with no vegetation cover. Samples from vegetation will be collected by completing a two-minute net sweep at the water surface at shoreline locations with high macrophyte cover. To test the level of contaminants in potential food sources for fish, six benthic invertebrate and macrophyte tissue samples will be collected (three from the north basin and three from the south basin) in the fall (late September). Sampling will be exclusively collected at the water surface at shoreline locations with high macrophyte cover using two-minute vegetation sweeps. This will allow for sufficient sample volume for tissue analysis. Samples will be analyzed for total metals. After starting the aerator, intensive monitoring of DO conditions will occur during the ice-cover season to assess the suitability of the habitat present in Frame Lake to support overwintering fish populations. DO will be measured monthly from November 2022 to April 2023. DO profile measurements will occur along four transects established in Frame Lake. Of these, two transects will be centered over the deep location in the North Basin and two will be centered over the deep location in the South Basin. Sampling stations will be established at seven locations along each transect, within suitable depth contours where sufficient under-ice water depth is present (e.g., 1.5 m depth contours). One of the four transects will provide coverage of the area of Frame Lake connecting the two basins. Data from this transect will be used to evaluate the potential for fish movement under the ice between the two basins. Ice thickness, snow depth, and under-ice water depth will be recorded at each station and a water quality profile will be taken. To provide a continuous log of DO conditions over the full duration of the ice-cover season, three DO data loggers will be deployed in the North Basin in proximity (i.e., within 20 m) to the aerator. DO measurements will be logged at three locations in the water column for the duration of the ice-cover season: 0.5 m above the bottom, mid-depth, 0.5 m below ice surface. The DO loggers will be deployed in December 2022 and removed in April 2023. The results of this program will be reported annually to DFO and success of each phase of the project will be reported to the Participation Agreement (PA) communities, the GNWT and the City of Yellowknife. The fieldwork for this study will be conducted from: July 28 - December 31, 2023