Salt in the wound

Natural History, Dec, 2005 by Stephan Reebs

This winter, as you drive on ice-free roads flanked by drifting snow, ponder this: In winter, some streams in urban and suburban Baltimore have become one-fourth as salty as seawater. In areas where more than 40 percent of the ground is covered with structures that are impermeable to water, such as roads, parking lots, and buildings, surface waters are now saltier than recommended for the protection of sensitive freshwater life. Those conclusions come from a recently published study by Sujay S. Kaushal, an ecologist at the Institute of Ecosystem Studies in Millbrook, New York, and a team of collaborators.

Kaushal's group blames the accumulation of salt on the de-icer dumped on roadways in winter. During the five-year period of the study (1998-2003), Baltimore spread more than 82,000 tons of sodium chloride on its roads. By contrast, rural areas of Maryland, New Hampshire, and New York have long used less de-icer, and so the salt content of rural streams in these areas is less extreme. The ecologists found, however, that the saltiness of rural streams has increased steadily for the past thirty years.

Perhaps "greener" ways of making roads safe in winter will someday be adopted. But if the current rate of annual winter salinization continues, Kaushal and his colleagues warn, much of the surface water in the northeastern United States will become toxic to freshwater life and unfit for human consumption in a century or two. (PNAS 102:13517-20, 2005)--S.R.