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Salt spikes in streams after icy roads are cleared in winter pose health threats to developing salmon, new research shows.
The amount of road salt, or chloride levels, can be ten times higher than provincial limits during a particularly sensitive time for salmon development, said Clare Kilgour and Carley Winter, zoology student researchers at the University of British Columbia.
The pair have analyzed water quality data in more than 30 Lower Mainland streams and conducted lab experiments to mimic the impacts these “salt pulses” have on coho salmon eggs.
Their preliminary research shows road salting often coincides with the return of spawning chum and coho salmon to the region’s freshwater streams in the late fall, Kilgour said.
“Between November and March, we're seeing these absolutely massive spikes in salt getting into streams.”
The salt levels can reach up to 10 times the chloride levels set out by the province, which is 600 mg/L., especially in urbanized areas where more roads and concrete parking lots drain into streams, where salt spikes may be occurring up to three times a week, she added.
Such high salt levels in the lab are proving lethal to young salmon, Winter said.
The lab experiments aimed to isolate the impacts of salt levels in water on the fish to determine what concentrations were dangerous and when salmon were most vulnerable, Winter said.
Impacts to salmon egg survival began when chloride levels reached double the provincial guideline. Salt levels between four to eight times the provincial threshold result in the coho salmon eggs dying at an average of 50 to 70 per cent, Winter said.
“So that’s a huge, huge percentage of mortality with just one 24-hour exposure,” she said.
Eggs that lived despite high chloride concentrations weren’t necessarily left unscathed.
“If they were lucky enough to survive, there were higher percentages of deformities,” Winter said, noting coho eggs are most sensitive to salt contamination during the first 24 hours to a week of their development.
“If embryos survived a salt pulse of three times the recommended level, we found about four per cent of them were deformed and would not survive in nature,” Winter said.
The two UBC masters students are three years into a wider five-year study that also involves Simon Fraser University, British Columbia Institute of Technology, numerous community scientists and stream-keeper groups, as well as Fisheries and Oceans Canada (DFO).
To determine how much salt was making its way into streams, the UBC team dug into information from nearly 40 water quality monitoring devices across the Lower Mainland.
“They collect the salt concentration in water every 10 minutes,” Kilgour said.
“So, we have a really good idea what the salt levels are at any given time in all these different locations.”
SFU researchers will conduct in-stream studies that evaluate egg development in natural conditions, while exposed to salt spikes as a complement, and contrast to UBC’s findings, Winter said.
Municipalities and households can make a big difference to salmon health by using salt in icy conditions sparingly, the researchers stressed.
Road salt use in Canada has climbed by 2.5 per cent annually, while B.C. dispersed 830,000 tonnes between 2020 and 2021 — with approximately 6,000 tonnes used in Metro Vancouver alone.
While road or public safety can’t be ignored, it can be maintained with less harm to fish, the researchers noted.
“I think the ideal outcome is just to advocate for smarter salt use,” Kilgour said.
Municipalities can examine how and where to reduce use or opt to spray brine rather than rock salt, which sticks to the road better and contains half the chloride, she said. The added bonus is brine is also cheaper than using rock salt.
Clearing sidewalks and driveways before they are icy means less salt can be used to greater effect.
Avoiding the use of salt in areas where water runs off into storm drains or streams and creeks is also helpful.
“Community members can also just be salt-aware and use only as much salt as they need,” Kilgour said.
“You only need about two tablespoons per square metre for your driveway.”
Moderating salt use is a comparably easy fix to help struggling salmon stocks dealing with a range of different stressors, Winter said.
“Pacific salmon are facing various threats, but road salt is one area that we could make a change and see immediate results around the concentration in streams.”
Rochelle Baker / Local Journalism Initiative / Canada's National Observer
Comments
Now the stuff has eaten a Calgary watermain, maybe they'll pay more attention. Hate to put it that way, but millions of dollars in losses and a summer without gardening water may have a way of focusing attention that salmon have not.