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The Merrimack River watershed, the fourth-largest watershed in New England, has a salt contamination problem, according to a study.

Road salt from many New Hampshire and Massachusetts winters has polluted the runoff pouring into the watershed’s rivers, creeks, and brooks, affecting wildlife in many of the smaller waterways.

A team of researchers from the University of New Hampshire found that more than 10 percent of streams in the watershed have high salt concentrations. The researchers also found that this contamination is highest in the summer, when there is no water melting from snow.

“There’s been a lot of evidence that there’s increasing concentrations in chloride in streams in the past several decades,” said UNH scientist Shan Zuidema, a water systems specialist and lead author of the study, published recently in the Journal of Environmental Quality.

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The water systems at the start of the watershed come from pristine streams in the White Mountains, where minimal road salt is applied, but the river becomes increasingly contaminated with chloride as it travels south, Zuidema said.

For animals and plants in the ecosystem, high salt concentrations can be deadly.

“Wildlife can start to basically die off or create dead zones in areas of streams and brooks,” said Rusty Russell, the executive director of the Merrimack River Watershed Council. “It all comes from road salt, at least in this area.”

Experts estimate that the United States spreads about 20 million tons of salt every year. Some states are trying alternatives. New Jersey experimented with pickle brine, Wisconsin turned to cheese brine, and Pennsylvania used beet juice.

In the past decade, New Hampshire has seen a sharp increase in the amount of water bodies with chloride levels that exceed the federal standard. In 2008, only 19 water bodies exceeded the standard. In 2016, there were 46, half of which are in the New Hampshire section of the Merrimack watershed, Russell said.

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To alleviate the problem, the state included conversations about reducing road salt use while planning the widening of Interstate 93. In 2013, the state developed the Green SnowPro program, an initiative to train salt applicators in the best environmental road salt practices and help them track their salt use over the winter.

Massachusetts has also sought to address contaminated runoff and storm management. The state’s Department of Environmental Protection released an online snow disposal guidance packet and has a list of suggested best management practices. Massachusetts also has specific reduced-salt areas close to sensitive ecological areas, several of which are in the Merrimack River watershed.

The Commonwealth deploys other salt management tactics, such as using updated equipment and advanced weather system tools and applying the salt in liquid form to minimize scattering. The state’s Department of Transportation has determined that these new technologies have led to a 30 percent reduction of road salt usage statewide, a MassDOT spokeswoman said.


Amelia Nierenberg can be reached at amelia.nierenberg@globe.com.