NWT RESEARCH DATABASE

Regions: South Slave Region

Tags: contaminants, mercury, climate change, hydrology, ecosystem impacts

Objective(s): To characterize existing levels of trace metals in surface-runoff dominated Slave River Delta wetlands in order to provide insight into contaminant status of systems influenced by local runoff versus flood-water dominated systems.

Project Description: This licence has been issued for the scientific research application No.5337. The objective is to answer key questions: 1. From the outer SRD (river-water dominated) to the apex of the SRD (runoff dominated), what is the current status of nutrients and contaminants in SRD wetland ecosystems? 2. How do trace elements (e.g., mercury) move through SRD wetland food webs? 3. How does water source affect the availability of nutrients and trace metals in SRD wetlands? Answers to these questions will inform the research team regarding the sensitivity of SRD wetland habitat quality to changes in water source. In addition, characterization of existing levels of trace metals in surface-runoff dominated SRD wetlands will provide insight into contaminant status of systems influenced by local runoff (supplied by local parent materials and long-range atmospheric deposition) versus flood-water dominated systems. Should trace metal enrichment be found in surface-runoff wetlands, this finding could inform future investigation of potential regional contaminant sources (e.g., Giant Mine). This study is focusing on representative waterbodies from the wetlands of the SRD. In 2022, the team will focus the efforts on Hook Lake which was unsuccessfully sampled in 2021. Wetlands in the SRD are generally small and shallow (<4 m) and are recharged mainly by either river floodwater or snowmelt, depending upon the height of the levee separating them from the river. We are samplng selected sites from flood-dominated (five sites total) and surface-runoff dominated wetlands (five sites total). This year will focus on sampling and subsequent analysis of wetland media. Sampling will occur in the late summer/fall with sampling of water, sediment, phytoplankton, zooplankton, benthic invertebrates and small-bodied fish from Hook Lake. Materials will be collected from a minimum of three stations suitably spaced apart for (e.g., minimum of 50 m). The scope of this work will be limited to residue analysis for each environmental compartment. Emphasis will be on mercury, with all samples archived for later trace metals analysis. The exceptions will include water samples and sediments, which will be analyzed for trace metals. Measurements will be collected using a combination of field techniques and laboratory analyses on bottled samples. A minimum of three water samples will be collected for each analysis. Variables measured will include temperature, turbidity, pH, hardness, alkalinity, conductivity, dissolved oxygen, trace metals content (dissolved), chlorophyll A, nutrients (nitrate, nitrite, ammonia, total P, soluble reactive P) and dissolved organic carbon. The top 1-cm of surface sediment will be collected using a grab sampler. Three samples per station will be pooled and homogenized. Sediment will be analyzed for total organic carbon content, particle size distribution, total phosphorus and P geochemistry, and 24 trace metals. Periphyton (as filamentous algae) will be scooped into wide-mouthed sample bottles. Samples will be immediately put on ice for later freezing, transport, and freeze-drying. Analysis will include stable isotopes of C, N and S. Benthic invertebrates (bottom-dwelling invertebrates) will be collected using a D-frame dip net. Zooplankton will be collected using vertical hauls of 64 um mesh netting. Where present, small-bodied and larger fish will be collected using D-frame nets, gill nets, or a beach seine. Identification will be performed by the sampler. Tissue samples will be immediately put on ice for later freezing, transport, and freeze-drying. Tissue analysis will include mercury and stable isotopes of C, N and S. These tissues will be archived for later additional trace metals analysis. Tissue analysis (plants and animals) will include stable isotopes of C, N and S to help understand food web structure (what eats what). The research team will file field trip reports shortly after each outing with all participating organizations. These will be very visual to facilitate communication to community members and the layperson. An annual report for 2022 results of all activities and findings will be provided to all participating organizations in January 2022. At least one scientific paper will be crafting in collaboration with lead participants and submitted to a peer-reviewed journal. All metadata, project reports and peer-reviewed outputs will be made available to CIMP and the public by uploading the information to the NWT Discovery Portal and the Mackenzie Datastream. The fieldwork for this study will be conducted from September 22, 2022 to December 31, 2022.