Research finds sidewalk salt is killing salmon. How can cities de-ice safely?

10 Feb 2024 3:19 PM | Smart About Salt (Administrator)

Research finds sidewalk salt is killing salmon. How can cities de-ice safely? (

In the January cold snap, the Lower Mainland leaped into action to clear the roads using salt, sand and snow plows. As the snow melted into the gutters though, it carried the salt with it.

It trickled into streams where Coho salmon were hatching from their eggs. The tiny salmon, or alevins, hide in the gravel near their nests (called redds), feeding off of their round orange yolk sacs.

For young salmon, road salt runoff can be deadly. A research project is using citizen science to monitor the impacts of road salting on freshwater fish in 30 streams in the Lower Mainland.

Provincial guidelines set allowable salt levels for salmon, but they aren’t regularly monitored or enforced.

Although the project is only in year two of a five year study, UBC zoology professor Dr. Patricia Dr. Patricia Shulte said the results so far are concerning.

“There's a lot of salt getting into streams when we salt the roads, and the streams very frequently exceed acute guidelines,” said Schulte, who is also a a Canada Research Chair in Responses of Fish to a Changing Environment. “Our data so far suggests that the answer is yes, that these levels are high enough to harm salmon, especially if the pulses occur at particularly sensitive stages.”

The study is a collaboration between staff from the Department of Fisheries and Oceans, UBC, SFU, BCIT and the Pacific Streamkeepers Federation. They’re taking their data to cities in the Lower Mainland to discuss how to minimize road salt use.

Volunteers measure streams’ salt content using bluetooth conductivity loggers, which measure the concentration of electricity-conducive salt ions. The data then goes to a public website that researchers and concerned citizens can monitor.

When Vancouver freezes in January and February, the road salt run-off coincides with Coho salmon and rainbow trout hatching.

According to Schulte, the salt is killing fish. The next step is figuring out exactly how the salt is harming them, and why it harms some more than others.

Fish maintain balance between water and salt concentrations through a process called osmoregulation.

“At the time they're hatching, there's so many other demands on [their] body that [they] just don't have the energy to osmoregulate properly, and that's what's killing them,” said Schulte. “Or, that’s the hypothesis we’re testing.”

Road salt use rising

In Canada, the amount of road salt has been increasing by 2.5 per cent each year for the past decade.

“The data does clearly show that the use of road salt is increasing over time, which probably has to do with more severe winter weather,” said Schulte.

While climate change is usually associated with warmer temperatures, some scientists theorize that the warming Arctic is disrupting the polar vortex and allowing cold weather systems to escape. This could contribute to cold snaps like the West Coast saw in January. While we can generally expect warmer winters going forward, we can also expect more unusual freeze events — requiring proactive and sustainable strategies to safely de-ice streets.

Vancouver allocates 3,000 tons of salt each winter — although the city aims to limit use, and encourages people to avoid salting their private property when possible.

Since campus isn't part of Vancouver, UBC Facilities has their own salt stash: "160 tonnes of road salt, 80 tonnes of salt/sand combo, 80 tonnes of sand, 500 bags of de-icing salt" and more, according to UBC Director of Municipal Services Jenniffer Sheel.

Starting at 4 a.m. on snow days, the de-icing team focuses on high-priority areas like medical clinics, childcare facilities and academic buildings to clear important sidewalks while trying to minimize salt use.

“The cities around here already have this on their radar as something that they should be doing,” said Schulte. “It’s just a matter of the best way to do it.”

The timing of road salt application is also important. Road salt only works when applied before the road ices over, as it lowers the freezing temperature of water.

"We apply preventative measures based on weather conditions (precipitation, temperature and wind) and where possible reduce our salt use with brine applications or a combination of salt/sand," wrote Sheel in an email to The Ubyssey. "Our priority is public safety and we have found salt to be the most effective application when we are battling ice."

Channels by the side of the road, called bioswales (like those on 16th Ave near campus), can also use plants and landscaping to absorb runoff before it enters the water system.

One of Schulte’s recommendations is to salt less, and only where it's most needed.

“It's unlikely that we’ll entirely stop using road salt because it's very important for safety, but we want to provide the data to show that we should be careful with how we use it.”

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