Salt might make our roads safer, but it's also threatening hundreds of lake ecosystems around North America.
Lakes near roads or parking lots are the most at-risk, but even a small amount of pavement close by increases a lake's salination, according to a study published Monday in the Proceedings of the National Academy of Sciences.
The study looked at 371 freshwater lakes in the Midwest and Northeastern U.S. It found that as little as one per cent of impervious land cover — roads, sidewalk or any other hard surface that prevents salt from soaking into soil — meant that a lake would have a high chloride concentration. Over the past few decades, 44 per cent of the studied lakes got saltier.
“These results are likely an underestimation of the salinization problem, as a number of regions with heavy road salt application, such as Quebec or the Maritime provinces of Canada, had no long-term lake data available,” study co-author Sarah Bartlett said in a release from the University of Madison-Wisconsin.
Road salting became a standard practice in the '40s, the study notes. Over the following 50 years, the amount of salt used in the U.S. increased from 0.15 metric tons per year to more than 18 million.
In Canada, an average of five million metric tons of road salt was used every year between 1995 and 2001.
In the U.S., 27 per cent of large lakes are surrounded by at least one per cent of roadway or sidewalk, meaning that they are at a high risk of hurting local ecosystems, drinking water and fisheries. The study estimated that 7,770 lakes are in trouble across North America.
Salty drinking water can hurt people with kidney disease, and lakes with high salinity slowly kill off freshwater fish.
Cities trying to use less salt
The study recommended that local jurisdictions set up long-term monitoring to keep freshwater lakes "fresh."
Canada's government published a code of practice for reducing the use of road salts in 2004.
Toronto reduced its salt use by a mean of 37,000 tons over two years after implementing a new training program for employees. Municipalities like Cowansville, Que., and Williams Lake, B.C., have started using beet juice to reduce the salt's environmental impact.
However, cities aren't the only problem.
“What I don’t think people realize is that a large quantity of road salt – in some areas more than 50 percent – is applied by private citizens and businesses, to sidewalks and parking lots, and there has to be an effort to reduce this load as well," researcher Hilary Dugan told the University of Madison-Wisconsin.
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