The use of salt to melt snow and ice from slippery roads has an environmental downside that can affect a widespread area long after winter has passed, scientists say.
Nancy Karraker, a New York-based scientist, visited the University of Maine this week to share her research into how road salt can affect amphibians in small seasonal wetlands called vernal pools located as far as 550 feet from roads.
Stephen Norton, a UMaine professor, said salt can be responsible for changes in water chemistry many miles downriver from a road crossing. "You can see the effects all the way down to the ocean," he said.
New Hampshire began the practice of salting its roads in 1938. But the use of salt increased sharply after the interstate highway system was built in the 1950s and `60s.
In Maine, 104,000 tons of salt have been used so far this winter, according to Brian Burne, an Augusta-based highway maintenance engineer for the Maine Department of Transportation. Nationwide, more than 13 million tons are applied annually, according to the federal Environmental Protection Agency.
There has been relatively little research on how all this road salt, which frequently contains dyes and other chemicals, is affecting the environment. "It's nasty stuff, and nobody pays much attention to it," Douglas Wilcox, a U.S. Geological Survey researcher, recently told a Midwestern magazine.
Scientists know that road salt can kill trees and that white pines are particularly sensitive. Sometimes, road salt puts such a strain on native species that hardier invasive plants and animals take over.
Researchers, including Norton, have learned that excess salt changes stream chemistry, causing certain minerals to leach out of soils. At high enough concentrations, salt can increase the acidity of water, causing some of the same negative effects as acid rain.
Studies have shown that road salt attracts deer and moose, causing collisions with vehicles. Other scientists have learned that some amphibians refuse to cross salted roads and, as a result, can be separated from their traditional breeding areas.
Karraker found that high salt concentrations affected the ability of wood frogs and spotted salamanders to survive, with eggs and embryos dying in experiments when subjected to the high end of salt concentrations she saw in the wild.
Scientists who study road salt's effect on the ecology do not advocate leaving icy roads untreated. They hope to learn more about how to prevent salt's negative impacts without sacrificing public safety.
Maine has sought to cut down on the use of road salt in recent years primarily to reduce costs, but also for environmental benefits, said Jerry Waldo, regional manager for the DOT's Bangor office.