Why's That: What Does Road Salt Do to Fishes?
Even mild winters sometimes get icy. People throw salt on sidewalks and roads, and unless it’s really cold the ice melts.
“But then obviously that liquid goes somewhere at some point,” says Western Michigan University chemistry professor Andre Venter.
This story has been updated.
Venter figures that in Kalamazoo, the salt water from the roads eventually reaches the Kalamazoo River.
“I’m wondering if our fish are getting brined,” he says.
Researchers at Western know that some local lakes do get large doses of road salt. Woods Lake lies below Oakland and Parkview, two busy streets in Kalamazoo. Once a month, grad students Emily Sprague and Danielle Dupuis row out to take samples. This involves a tube-shaped device that Dupuis drops over the side of the boat.
“We can lower it to a certain depth and drop the weight and then it snaps closed so we get the water from just that depth,” she explains.
Dupuis is a student of WMU professor Carla Koretsky, who’s shown that some local lakes have so much dissolved salt in their depths, the water’s not turning over like it’s supposed to. But what about rivers and the salt’s effect on fish?
To find out, Venter and I visited two more experts at Western: Joyashish Thakurta, an assistant professor in the Department of Geosciences and Devin Bloom, an assistant professor in the Department of Biological Sciences and the Institute of the Environment and Sustainability.
Bloom specializes in fish biology. We’re at his lab, where one student’s sequencing DNA on a computer while others examine fish samples. Cardboard boxes at the back hold the fish Bloom’s borrowed from museums.
Before we talk about how road salt affects fishes, we’ll go over some geology. We know some ponds and lakes have a problem with road salt. Thakurta says salt in rivers is different in that the water is moving.
“The average concentration measured in the river would not be that high,” he says [see comments from Korestky, below.]
But Thakurta adds that even in a river the water moves at different speeds.
“There might be isolated pockets within the river belt which might be closer to the banks where the salinity will be higher than the other areas,” he says.
Thakurta notes that fishes can swim away from those banks.
But, says Bloom, “Most fish biologists and any fisherman knows what he’s doing will tell you that’s where most of the fish hang out.”
Road salt is hardly the only concern for fish in the Kalamazoo River. They also face dams, fertilizer runoff and PCBs, and the river went through a major oil spill in 2010. But Bloom says even if it’s not the biggest threat, if you dump a bunch of salt into fresh water, that’s definitely a concern.
“So if you increase the amount of salinity in a particular habitat like say a river or a lake, a fish that’s not adapted to that higher level of salinity is going to end up taking on extra amount of salt into its body,” he says.
And that can pull moisture out of a fish’s cells. Some species might tolerate extra salt. But it could still cause them problems. Maybe those fishes eat bugs that can’t deal with higher salinity.
“Or maybe you have two fish that compete for limited resources and one fish is able to tolerate slightly increased salinity levels and another isn’t. That fish is now going to outcompete the other species,” Bloom says.
But to know those things, you’d have to look at each species of fish individually. That’s research that Bloom says just isn’t being done. As for fixes, Bloom says a number of states with harsh winters do not salt their roads. But then drivers have to do things like put chains on their tires. There’s sand, but that causes its own problems for water. Sand can also pollute the air.
“There’s no simple solution or I’m sure we would have probably implemented it by now,” Bloom says.
Andre Venter, who wanted to know if local fish were getting ‘brined’ by road salt, thought that storm water went through treatment before draining to a river. Bloom and Thakurta say: no. Roadside storm drains flow directly to the river or creeks that drain to the river (or in some cases, ditches). Venter is sorry to hear that.
“And I’m even more concerned about salt running into the water than I was when this first occurred to me,” he says.
“That’s usually what happens in science, right?” Thakurta asks. “You answer one question, you have ten more questions that pop up. “
Update: WMU Geosciences Professor Carla Koretsky, who has extensively researched the presence of road salt in waterways says that rivers do sometimes contain very high levels of salt, though not always for very long.
"A number of studies have shown ‘pulsing’ of extremely high salt concentrations with snow melt and salt runoff – far higher than you would see in a lake, where the salt is more diluted by the volume of water, although the concentrations are of course more fleeting because the water moves quickly, as Joyashish pointed out," Koretsky says.
The levels of salt in rivers "can be several hundred times higher than in lakes and way above the chronic and acute toxicity thresh holds for freshwater organisms," she adds.
"All of that salt does go somewhere – ultimately, around here it goes to Lake Michigan. And as large as Lake Michigan is, a study by Chapra et al. a few years ago showed demonstrably elevated salt levels due to road salt runoff, which is truly something."
Finally, "Even treated wastewater does not have any salt removed. Wastewater treatment plants are simply not designed for desalinization. Likewise, wetlands and other remediation to control nutrient loading have no effect on salt."