The Legacy of Mercury in Lake Superior

The northern Great Lakes are praised for being clean, but these aquatic systems don’t exist in a vacuum. Contaminants still find their way into lake water and sediments. Mercury is of particular interest because of its toxicity and persistence.

In a new study published in the Journal of Great Lakes Research in February, an interdisciplinary team from Michigan Technological University examined the legacy of mercury in Lake Superior.

Currently, the National Atmospheric Deposition Program reports low levels of mercury deposition across most of the upper Midwest. However, those figures don’t account for past mercury deposition and what that might mean for heavy metal contamination. In fact, when mining was booming around the lake in Michigan, Minnesota and Canada in the 1800s and 1900s, the researchers found mercury input was higher than expected. 

“We document that the mining effort was discharging mercury at 1,000 times the normal deposition rate in the region,” says W. Charles Kerfoot, a professor of biology and director of the Lake Superior Ecosystem Research Center at Michigan Tech. “We set out to quantify this deposition—and it was a real wake-up call.”

Mine Tailings

Kerfoot collaborated with Noel Urban, a professor of civil and environmental engineering and director of the Center for Water and Society at Michigan Tech. Together they dug into mine tailings buried at the bottom of local waterways near campus to start piecing together the region’s mercurial history.

Booms and busts rocked not just the area’s economy, but also heavy metal fluxes. Naturally, some metals—including mercury—make their way into water bodies. Mining speeds up that process, and the more mining, smelting and processing taking place, then the more heavy metals get deposited. In the Keweenaw Waterway and Torch Lake, lakebed sediments record these mercury-rich layers in lighter bands.

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Taxonomy

• Water Pollution
• Pollution
• Lake Management