Identifying terrestrial sources of mercury in streams of the Mackenzie River Basin, NW Canada

• The Mackenzie River, with a catchment >1 million km^2 and a mean water discharge of 10,000 m^3/s, is the largest conduit for freshwater and sediment delivery to the Beaufort Sea. During peak flow, the Mackenzie and its main tributaries have some of the highest Hg levels in freshwaters of the Canadian Arctic and subarctic (>> 10 ng/L). An unknown fraction of this Hg is derived from thawing permafrost soils in the northern reaches of the Mackenzie basin. This contribution is likely to increase as NW Canada warms up over the next decades at nearly twice the mean rate of the whole country. To better anticipate the future impact of warming on riverine Hg transfer to the Beaufort Sea marine ecosystem, a Swedish-Canadian research project was initiated to identify and quantify the terrestrial sources of Hg in streams of the Mackenzie basin. Water was sampled from the Mackenzie itself and selected tributaries during spring peak flow in 2018, and will also be sampled during the base flow period in 2019. Water samples are being analysed for isotopic ratios of O and H in water, C and Hg (dissolved and particulate), as well as the optical properties of dissolved organic matter, to help in the source apportionment of Hg between various terrestrial pools such as rocks and organic soils. These data will be used to constrain a mixing model of water properties, including Hg loads, created for the Mackenzie drainage system. The mixing model will be used to simulate future riverine Hg transfer rates to the Beaufort Sea under varying scenarios of Hg release from the different terrestrial reservoirs, such as permafrost soils. The study design, methods, and preliminary findings will be presented.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)

Keyword

Mercury

rivers

subarctic

Canada

Earth Science with specialization in Environmental Analysis

Geovetenskap med inriktning mot miljöanalys

Publication and Content Type

vet (subject category)

kon (subject category)