NWT RESEARCH DATABASE

Regions: Dehcho Region, North Slave Region, South Slave Region

Tags: mercury, lakes

Objective(s): We will leverage a large spatial dataset of over 200 near-surface lake sediment samples in the central Northwest Territories to better understand controls on biogeochemical cycling of Hg and other elements of concern. Characterization of lacustrine sediments and peatlands in studied watersheds will be used to determine the: 1) distribution of Hg and other elements of interest; 2) climatic history; 3) fire history; 4) hydrological history (e.g., changes in water table depth, timing and magnitude of freshet); 5) vegetation history; and, 6) changes in primary productivity.

Project Description: This licence has been issued for the scientific research application No. 5927. We will leverage a large spatial dataset of over 200 near-surface lake sediment samples in the central Northwest Territories to better understand controls on biogeochemical cycling of Hg and other elements of concern, and analyze lake sediment and peat cores to obtain a temporal perspective of metal(loid) accumulation. Characterization of lacustrine sediments and peatlands in studied watersheds will be used to determine the: 1) distribution of Hg and other elements of interest; 2) climatic history; 3) fire history; 4) hydrological history (e.g., changes in water table depth, timing and magnitude of freshet); 5) vegetation history; and, 6) changes in primary productivity. These data will be synthesized to understand the cumulative effects of climate change on biogeochemical processes that affect the mobility and fate of Hg (and other elements) in northern lakes and understand recent changes to environmental baselines for Hg. We will leverage a large spatial dataset of near-surface lake sediment collected across a 5 degree latitude transect in the central Northwest Territories, combined with analysis of at least 1 existing lake sediment core from the same region, and combined with analysis of newly collected lake sediment core(s) and peat monolith(s) from targeted areas of interest to industry partners Nighthawk Gold Corp. (now STLLR Gold Corp.) and Tli?cho communities. Lake sediment cores will be collected using freeze coring to obtain undisturbed sedimentary sequences from lake bed(s) where possible or open-tubed gravity coring where freeze coring is not feasible, and peat monoliths will be collected using a spade and trowel method. If possible, a CRREL drill core may also be used. The newly collected materials will be frozen and shipped to laboratories for analysis using the following methods: Total inorganic Hg determination (thermal decomposition followed by AAS), trace and major element concentration determination (ICP-MS/ES), light stable isotopes analysis (d13C, d2H, d15N, d18O) to reconstruct hydrological change, micropaleontological analyses to reconstruct depth to water table (testate amoebae) and paleoclimate parameters such as temperature (e.g., diatoms, chironomids) and vegetation and fire history (palynology). Plant macrofossils and macroscopic charcoal will also be used to reconstruct fire and vegetation history. Polycyclic aromatic hydrocarbons (PAHs) will also be assessed for fire history reconstruction. Organic matter, particularly important for Hg mobility, will be assessed using sequential pryolysis and organic petrology. Results will be combined with metadata such as lake bathymetry, morphometry, watershed characteristics, bedrock geology, etc. to produce a multivariate dataset. We will analyze the resulting data statistically to determine factors that affect and control biogeochemical cycling of Hg in the surficial aquatic environment. The twinned peatland-lake sediment approach will help us to characterize potential watershed sources of Hg to the lacustrine system. Communication has already begun with the Tli?cho Government who have already provided input on which lakes and areas are of concern to the communities for targeted study if logistically feasible for this project. In addition, we presented our project proposal in an online workshop hosted and facilitated by the Tlicho Government Department of Culture and Lands Protection (May 09, 2024; see correspondence summary). Our on-going communication plan will include: 1) annual "open house" workshops for researchers and community members to exchange knowledge (possibly to be held in conjunction with the Yellowknife Geoscience Forum and pending managerial approval and budget for Galloway and colleagues travel); 2) presentation(s) and meeting(s) at the Yellowknife Geoscience Forum; 3) production of plain language summaries translated into English, French, and Tli?cho (and other languages as requested); 4) frequent "virtual" communication with Tli?cho Government and any other interested communities; 5) travel to Tli?cho communities by researchers, as welcomed and requested, for meetings, "open-houses" and workshops (pending Galloway and colleagues managerial approval and budget approval). The fieldwork for this study will be conducted from: January 1 - December 31, 2025