METRO DETROIT — Each winter, as municipal workers make our icy roads safer, they could also be turning our famous freshwater lakes saltier.
An intensive study published by the Proceedings of the National Academy of Sciences in April observed long-term chloride trends in 371 freshwater lakes across the continent. It was determined that there were increasing chloride trends in most of the urban and rural lakes in the Midwest and Northeast surrounded by greater than 1 percent of impervious land.
The skinny on salt
What does that mean? Thousands of local lakes are at risk of long-term salinization, which could negatively affect an ecosystem that thrives on being “fresh.” Critical components provided by freshwater lakes include drinking water, fisheries, recreation, irrigation and aquatic habitat.
“You’re changing what can live there,” said Donna Kashian, associate professor of biological sciences at Wayne State University. “And in our economy, where people love to fish for those big trout and sturgeon, we could be messing with our economy if the water gets saltier.”
It’s estimated that approximately 44 percent of freshwater lakes in the North American lakes region — which encompasses Michigan, Wisconsin, Connecticut, Maine, Massachusetts, Minnesota, New Hampshire, New York, Rhode Island, Vermont and Ontario — have undergone long-term salinization.
“Considering that 27 percent of large lakes in the United States have (greater than) 1 percent impervious land cover around their perimeters, the potential for steady and long-term salinization of these aquatic systems is high,” the study states. “This study predicts that many lakes will exceed the aquatic life threshold criterion for chronic chloride exposure, stipulated by the U.S. Environmental Protection Agency, in the next 50 (years) if current trends continue.”
A major culprit is believed to be salt application pertaining to icy roadways — a common practice in Michigan, of course, along with other northern climates in both North America and Europe.
Roads were first salted in the U.S. in the 1940s, with salt sales increasing in a 50-year period from 0.15 metric tons per year to more than 18 million metric tons per year. Following application, salt dissolves and is transported into rivers and lakes through leeching and runoff.
That’s what makes salt a more potent contaminant than others, said Kashian, who recently contributed to a short video documentary on the topic called “Road Salt: Street to Stream.”
“When it dissolves, it becomes mobile and can wash off easily into nearby lakes and ponds, particularly those closest to the roads,” she explained. “Sometimes those are the water bodies that are most sensitive because they house species like amphibians.”
The science on salt
Nicholas Skaff, a doctoral candidate at Michigan State University’s Department of Fisheries and Wildlife and co-author of the study, said the study originated after the Global Lakes Ecological Observatory Network established a fellowship program — funded by the National Science Foundation — to bring together 12 graduate students from around the country to observe large-scale environmental problems related to lakes.
Skaff’s research involved studying ecological problems at big spatial scales, typically across multiple states and regions. In the past, he has researched spatial patterns in outbreaks of mosquito-borne diseases, and he used that knowledge to apply his expertise to the subject of lakes — both topics that require similar analytical skills, he added.
“We chose to work on this project in particular because even though salt-laden runoff has been a known environmental concern for some time, no one had attempted to look at how extensive the changes have been at broad scales,” Skaff said.
The study started in January 2015 and took more than two years to complete. Skaff said that as the salinity of a lake increases, major changes in the composition of lake species can occur. It is expected that more subtle variations will transpire in the near future — such as an increased frequency of toxic cyanobacteria blooms, because they are more salt-tolerant than phytoplankton.
That’s one of Kashian’s major concerns.
“You really don’t want to make the environment more attractive to invasive species,” she said, adding that the yearly process of lake “flipping,” where water switches density from top to bottom to distribute nutrients, could change with increased salt essentially killing a lake.
Invasive species are a threat in the near future, according to Skaff, but Craig Bryson, senior manager of communications for the Road Commission for Oakland County, thinks the future is now. Just take a look at the sides of the highway every spring.
“The foliage along freeways doesn’t do real well. The trees and other foliage in the medians of freeways, you can see it’s (dying), and I suspect that’s probably related to salt use.”
Additionally, the richness and abundance of aquatic species may decline and result in overall changes in the structure of the ecosystem.
The consequences of salt use on the natural environment have been discussed in the road maintenance field for decades, according to Bryson.
A good sign is that 14 of the lakes studied are expected to surpass the EPA’s aquatic life criterion concentration for chloride by 2050, which is the time period being used to evaluate intense risks to the majority of species in a water body.
The safety of salt
And that’s good, because Bryson doesn’t think there’s much to be done to control salt runoff anytime soon.
“Just based on what we see and hear at the Road Commission, we get a lot more complaints that the roads are slippery than we do that there’s salt in the environment. I can’t imagine in our current society — when people expect clear and dry roads immediately after a snow event — that people are going to be willing to give up a bit of mobility to protect the environment,” he said.
Residents also aren’t likely keen on spending more of their tax dollars to find a more eco-friendly melting solution either.
“There are some other products that are commercially available, but they are really cost prohibitive,” Bryson said, noting that beet and corn byproducts, along with some synthetic options, are all nearly 10 times the cost of rock salt. “And we’re often asked why we don’t use sand like some other states. For one, sand doesn’t melt ice; it just provides traction on top of it. And in urban areas where we have storm sewers, the sand causes clogs and problems in the spring with flooding.”
One thing is for sure, and that’s that de-icing the roads is a must.
“Safety is our No. 1 priority as an agency, and we know if we don’t salt the roads we will have crashes,” Bryson said.
“You have to balance the impact of salt (on the environment) with how it saves lives,” Kashian agreed.
The scope of salt
So, then why worry now — or at all? Kashian said salinization is just one of several factors we should be keeping an eye on in our freshwater bodies.
“You don’t get rid of the EPA, that’s the first step, but there’s no quick fix for this. Salt regulation or drastic invasive species programs might be another step, short of extreme measures like closing off the Great Lakes to commercial shopping,” she explained. “But we have to just continue monitoring and controlling additional pressures on a lake and take a little stab at all of the problems to reduce the overall stress piecemeal. If we contain them all, maybe one particular stressor won’t be so grand.”
The potential long-term impact of chloride on the nation’s water was not addressed directly in the study, though Skaff said potability could become affected in the long run.
“The most alarming information we gleaned from this study was that even very small amounts of human development — just 1 percent of the area around a lake — can lead to progressive rises in lake chloride concentrations over time,” he said. “As a result of this, we estimate that a huge number of lakes, over 7,000 lakes in the Northeast and Midwest U.S. alone, have been subjected to unnaturally elevated chloride levels from road salt applications.”
The Great Lakes were not part of the study, as their unique makeups do not accurately reflect broad lake trends. However, salinity in the five lakes has increased in recent years.