U.S. Waterways Are Getting Dangerously Saltier, Study Finds

Pam Wright
Published: January 12, 2018

Communities across the nation are quick to treat roads with salt and other chemicals ahead of and during winter storms, but that practice has made our rivers and streams dangerously salty and alkaline, a new study says.

According to research published Monday in the Proceedings of the National Academy of Sciences, the increased salt in waterways threatens drinking water supplies for millions of Americans. The increased corrosiveness of the water from the salt also poses a threat to infrastructure and the ecosystem.

The researchers used 232 U.S. Geological Survey sites to look at chemical changes in freshwater bodies across the United States for the past half-century. They determined the waterways were becoming saltier and more alkaline.

"Many people assume that when you apply salt to the landscape it just gets washed away and disappears," Sujay Kaushal, a professor of geology at the University of Maryland and lead author of the study, said in a press release. "But salt accumulates in soils and groundwater and takes decades to get flushed out."

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This map shows changes in the salt content of fresh water in rivers and streams across the United States over the past half-century. Warmer colors indicate increasing salinity while cooler colors indicate decreasing salinity. The black dots represent the 232 US Geological Survey monitoring sites that provided the data for the study.
(Ryan Utz/Chatham University)

Previous studies have looked solely at the levels of sodium chloride – the primary component of de-icers used in the U.S. – in waterways. This study, led by researchers from the University of Maryland, is the first to look at all forms of salt, nutrients from fertilizers and other compounds to see how they interact.

"These 'cocktails' of salts can be more toxic than just one salt, as some ions can displace and release other ions from soils and rocks, compounding the problem," Kaushal said. "Ecotoxicologists are just now beginning to understand this."

According to the press release, the water crisis in Flint, Michigan, is a good example of how salty, alkaline water can corrode pipes, leading to disastrous consequences.

The leading cause of salty waterways varies by region, the scientists found. In the Northeast and mid-Atlantic, road salt is the primary culprit. In the Midwest, nutrient-rich runoff from agricultural fields is a major contributor, while in other regions, mining waste and weathering of concrete is a factor.

"We found that the pH of some rivers started increasing in the 1950s and '60s – decades before the implementation of acid rain regulations," said Michael Pace, a professor of environmental sciences at the University of Virginia and a co-author of the study. "We also observed increased salt concentrations in the Southeast, where they don't apply road salts. These surprising trends presented a puzzle that our team worked together to solve."

The researchers say the findings call for changes in how communities address de-icing and land-use management. Recommendations include using brine instead of sodium chloride in treating roads, updating the outdated infrastructure used to spread the salt on roadways and implementing better land-use strategies.

"The trends we are seeing in the data all suggest that we need to consider the issue of salt pollution and begin to take it seriously," said Kaushal. "The Environmental Protection Agency does not regulate salts as primary contaminants in drinking water at the federal level, and there is inconsistency in managing salt pollution at the local level. These factors are something communities need to address to provide safe water now and for future generations."

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