Understanding and predicting mercury in Dehcho lakes, Northwest Territories

In this project, we are aiming to understand how landscape, lake, and fish ecology explain variation in fish mercury (Hg levels). Our results will identify critical variables for future cumulative impact monitoring, and enable more informed predictions of how fish Hg levels in the Dehcho region will respond to continued environmental change. Decision-makers will use our results to develop long-term monitoring strategies, identify lakes that are most vulnerable to future increases in fish Hg levels, refine consumption advisories, and identify lakes with the safest and healthiest sources of food fish. This data set is collected to support the project titled “Northern Water Futures, Objective 2". Northern Water Futures is a Pillar 3 project under the Global Water Futures Program funded by Canada First Research Excellence Fund

Samples/data collected by joint University-community monitor team during on the land camps in 2018-2020. Data Collection: a. Fish (15-20 individuals/species, up to 4 food fish species/lake: captured with gill nets and dissected) • Mercury concentration in fish flesh, stable isotopes of carbon and nitrogen in fish flesh, fish age. b. Benthic Invertebrates and sediments (min. 3 samples/taxa at 5 sites/lake) • Profundal and littoral invertebrates collected with Ekman dredges and kick nets; • Samples coarsely sorted in the field to Order, divided in half, and: i) preserved in ethanol for taxonomic identification; ii) frozen for stable isotope and total and methyl Hg analysis; • Sediments collected with an Ekman dredge, frozen for analysis of Hg and MeHg. c. Zooplankton (min. 3 sample/size fraction at 3 sites/lake) • Collected with vertical tows, size-fractioned in the field; • Half of each size fraction preserved in ethanol for community composition analysis, other half frozen for stable isotope and total and methyl Hg analysis. d. Water (min. 3 sites/lake – top and bottom) • Filtered and unfiltered water samples collected from each lake, and from influent streams and wetlands. Ultra-trace sampling methods used for mercury. e. Abiotic • Catchment size and slope, lake area and volume, % wetlands and hydrology in catchment, underlying geology determined using GIS. Laboratory Analysis: a. Standard water chemistry: University of Alberta (ions, nutrients, chlorophyll-a); b. Total and methyl mercury analyses: Western University (ISO-accredited); c. Stable isotope ratios of carbon and nitrogen: University of Waterloo; d. Fish age: AAE Tech (Manitoba).

Swanson, H., and Low, G. (2019). Understanding and predicting mercury in Dehcho lakes, Northwest Territories. Waterloo, Canada: Canadian Cryospheric Network (CCIN). Unpublished Data.

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