Road Salt is Turning North America's Freshwater Lakes into Saltwater

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The road salt sprayed from the rear ends of trucks in winter—a staple of the season in the Northern US and Southern Canada—melts ice and keeps cars from careening off the road, but it also makes our freshwater lakes salty and possibly unsuitable for the things we need them for most: drinking water, irrigation, habitat for fisheries and more.

In a recent study examining the scale of freshwater lake salinization in North America, Scientists from the University of Wisconsin found that lakes near any kind of impervious surface— “as little as one road,” limnologist and lead author Hilary Dugan told Motherboard over the phone—are at high risk of becoming too salinized within the next 50 years for either freshwater life or human use. This includes 27 percent of all large lakes in the US.

The study is published in Proceedings of the National Academy of Sciences.

Dugan’s team looked at 371 freshwater lakes across North America—284 of which are in the Northeast and Midwest US, and Ontario, Canada. Road salt has been dumped heavily in these areas since the 1940s—5 million metric tons a year in Canada between 1999 and 2001, and almost 18 million metric tons a year in the US by the 1990s.

“Road salt is not removed from the environment, so it’s either going to be stored in soils, or in our waters.”

“Road salt is not removed from the environment, so it’s either going to be stored in soils, or in our waters,” said Dugan. “High levels can have both an effect on the taste of drinking water, but can have really negative implications for people who need low sodium diets, including people on dialysis. And it’s incredibly expensive to remove salt from water,” she said.

Salt is benign in low concentrations—10s of milligrams per liter of water (mg L-1)—but becomes detrimental to freshwater aquatic ecosystems as it builds up over time. High salt concentrations can alter the algal composition of aquatic ecosystems, causing cascading collapses of fish communities and booms of toxic cyanobacteria. Cyanobacteria appeared in Toledo Ohio’s drinking water in 2014 and cost millions of dollars to clean out.

The researchers found that 44 percent of the 284 lakes sampled have undergone long term salinization and that 26 of them are already at salt concentration levels over 100 mg L-1. If long term salinization follows current trends, many lakes will venture beyond the EPA’s safe concentration threshold of 250 mg L-1 by 2050.

Dugan said state and city government agencies are acutely aware of the environmental and infrastructural damages rock salt causes (think corrosion of cars and bridges)—because it costs them money—and are working to decrease use of it. The city of Toronto and other Canadian municipalities, for example, have started using a beet juice mixture instead of traditional rock salt as road de-icer.

“There’s been dramatic improvement in how much salt is laid down by cities,” she said, “but I don’t think people realize how much rock salt is thrown down by private citizens and businesses.”

It behooves citizens then, she said, to “just be a little more environmentally conscious when you go out and de-ice your own sidewalk. You really don’t need that much to be effective.”

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