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Freshwater Is Getting Saltier, Threatening People and Wildlife

Freshwater Is Getting Saltier, Threatening People and Wildlife

Road de-icing, industrial activity and other culprits are pushing salt levels in rivers and streams to alarming levels

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.

Salts can free up other pollutants, too. In his own house near Washington, D.C., Kaushal once had black water coming from the tap. “The salts in the water were leaching manganese—a neurotoxin—from the old pipes in the neighborhood,” he says.

A similar issue recently arose in Flint, Mich., where the decision to start drawing drinking water from a saltier local river mobilized lead from pipes into the water supply. Nationwide, salts are crusting the insides of home boilers and the cooling tanks of power plants. They are also coating the land where crops grow. And they are stressing plants and animals in freshwater ecosystems, in some cases until they disappear.