November 18, 2012

Watersheds suffer from rock salt runoff

By Matt Hongoltz-Hetling mhhetling@centralmaine.com
Staff Writer

Salt has serious effects on watersheds, according to a University of Maine study.

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Waterville Public Works Director Mark Turner on Friday holds a handful of salt used on city roads.

Photo by Jeff Pouland

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"Road salt tends to show up on a regional scale to impact most areas," said Sarah Flanagan, of the U.S. Geological Survey. Flanagan released a study earlier this year on the quality of water in New England's rock aquifers.

"You think about the one chemical that's used a lot, it has to be road salt," she said.

What starts as rock salt on the pavement turns into sodium and chloride, which are found in heightened levels in surface water and ground water. It also increases the salinity of ponds and changes the chemistry of the soil, causing the release of magnesium and other elements.

By a complicated process, sodium can have an impact on the aquatic environment by changing nutrient concentrations and reducing the ability of water to manage acids.

Studies show that temporary freshwater pools that are home to salamanders, frogs and other amphibians can become so salty that the eggs of those species are destroyed. In addition, some amphibians will avoid crossing salty roads, which can cut them off from breeding grounds.

Many native tree species, notably white pines, are also affected by road salt, which can also kill birds and mammals that ingest it. Native salt-sensitive species weaken or die, opening the door to invasive salt-tolerant ones.

The net effect is a loss of diversity in the watershed, and the chronic effects can require decades to reverse.

More sodium in the water is also a human health concern, as those who are trying to reduce their sodium intake are unwittingly foiled by contaminated wells. A high sodium intake contributes to hypertension, which causes 7.6 million premature deaths each year, according to a report from the International Society of Hypertension. The Centers for Disease Control finds that a majority of Americans, 57 percent, have high blood pressure or borderline high blood pressure.

Salt can also corrode concrete reinforcing rods in roads and bridges. With the cost of such corrosion placed around $16-19 billion annually, according to a 2006 study, managing road salt in a way that reduces corrosion is also important.

Vehicles are also corroded by road salt, but the dollar value of the damage is difficult to isolate and quantify. The University of Maine study said that there is ample anecdotal evidence suggesting that the damage to vehicles has increased as salt use has increased.

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