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What Risks Do Past and Present Mining Activities Pose to Salmon?

Flathead Lake Biological Station researchers Erin Sexton (right) and Chris Sergeant watch spawning salmon in a groundwater channel of the mine-impacted Tulsequah River in British Columbia. Credit: Photo by Jonathan Moore, Simon Fraser University.

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Recently, a group of 23 science and policy experts from the U.S. and Canada published a review of mining risks to watersheds ranging from Montana to British Columbia and Alaska.

The paper in the journal Science Advances brought together experts in salmon ecology, watershed science, mining impacts and mining policy to integrate knowledge across research fields that often work independently from one another. Led by UM researchers at the Flathead Lake Biological Station, the team found past and present mining pressures are extensive across the region and often overlap with important populations of salmon, trout and char.

“Our paper highlights the mosaic of more than 3,600 active and abandoned mines sitting amongst some of the most valuable fish habitat in western North America,” said Chris Sergeant, an FLBS research scientist and the paper’s lead author. “The largest of these mines processes around 160,000 metric tons of earth every day.”

Sergeant said not all mines pose the same level of risk, but their review revealed that harm from mining can be severe and long-lasting. The extent of mining pressures on these watersheds underscores the importance of accurately assessing risk to water, fish and communities.

The study reviewed the ecological complexity of rivers and how mines can impact culturally and economically important fish species such as salmon by contaminating waters with heavy metals, burying stream habitat and diverting water for processing ore. When not managed properly, these cumulative impacts can be impossible to reverse and degrade landscapes for decades to centuries.

“Unfortunately, in some cases, we are learning the hard way that mines can have profound impacts on aquatic ecosystems, leaching far down the watershed from the actual mine site, at scales that were not anticipated in the original impact assessment”, said Erin Sexton, a paper co-author and FLBS senior scientist. “For example, impacts from the Elk Valley coal mining complex in southeast British Columbia have been documented over 155 miles downstream of the mines, crossing the U.S.-Canada international boundary.”

The authors emphasize that up-to-date and transparent science has an important role to play in managing the potential impacts of mines. Emerging science on salmonid ecology, cumulative effects and how climate change is altering these landscapes can improve risk assessment of mines.

The authors highlighted four key issues that will be foundational to modern, science-based risk assessment and mitigation: understanding stressor complexity and uncertainty, accounting for cumulative effects of mining activities across a mine’s life cycle, developing realistic mitigation strategies and recognizing the potential for climate change to magnify risk.

“Emerging science is revealing the complex realities of how salmon watersheds work in this era of climate change and also the many different risk pathways posed by mines,” said co-author Jonathan Moore of Simon Fraser University in British Columbia. “Informed decision-making will need risk assessments that embrace these challenging topics, ranging from cumulative effects to climate change.”

While a low-carbon future will depend to some extent on mined minerals, it is important to consider whether current and future mining projects are operated in such a way that protects fish, water and well-functioning watersheds.

“Our paper is not for or against mining, but it does describe current environmental challenges and gaps in the application of science to mining governance,” Sergeant said. “We identify a need and opportunity for strong science-based and transparent risk assessment, as well as the integration of goals and values of impacted communities. In the end, it is possible that some specific places might just be too valuable to risk with major mines.” 

Reference: Sergeant CJ, Sexton EK, Moore JW, et al. Risks of mining to salmonid-bearing watersheds. Sci Adv. 2022;8(26):eabn0929. doi:10.1126/sciadv.abn0929

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