Freshwater is getting saltier, threatening people and wildlife

By Tim Vernimmen, Scientific American
Science
Dec 9, 2018 12:48 PM EST

Salts that de-ice roads, parking lots and sidewalks keep people safe in winter. But new research shows they are contributing to a sharp and widely rising problem across the U.S. At least a third of the rivers and streams in the country have gotten saltier in the past 25 years. And by 2100, more than half of them may contain at least 50 percent more salt than they used to. Increasing salinity will not just affect freshwater plants and animals but human lives as well—notably, by affecting drinking water.

Sujay Kaushal, a biogeochemist at the University of Maryland, College Park, recounts an experience he had when visiting relatives in New Jersey. When getting a drink from the tap, “I saw a white film on the glass.” After trying to scrub it off, he found, “it turned out to be a thin layer of salt crusting the glass.”

When Kaushal, who studies how salt invades freshwater sources, sampled the local water supply he found not just an elevated level of the sodium chloride, widely used in winter to de-ice outdoor surfaces, but plenty of other salts such as sodium bicarbonate and magnesium chloride. He also found similar concentrations of these chemicals in most rivers along the east coast, including the Potomac, which provides drinking water for Washington, D.C. Where did all of it come from?

De-icing salts, Kaushal determined, are part of the problem, slowly corroding our infrastructure. Estimates put the cost of repairs at about $1,000 per ton of de-icing salt imposed on the environment. But he also found a link to acid rain, caused by the air pollution from burning fossil fuels in power plants and cars. “Decades of acid rain have dissolved not just portions of rock and soils but buildings and roads as well—all of which have added various salts to the water,” he says. Although the acidity of the rain is decreasing, it is still present. Meantime the amount of concrete and asphalt in the world have continued to expand.

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