Freshwater sources in the northeastern U.S. are becoming increasingly salty, mainly as a result of increased roadway construction, a new report suggests. The findings, published online this week by the Proceedings of the National Academy of Sciences, indicate that at the current rate of change, some surface waters in the region could become toxic to freshwater life within the century.

Researchers led by Sujay Kaushal of the Institute of Ecosystem Studies in Millbrook, N. Y. studied three locations in Baltimore County, Hudson River Valley and the White Mountains in New Hampshire. The team found that over the past 30 years levels of chloride had risen dramatically. Measuring chloride concentrations can detect an increase in salinization because the anion is an important component of many salts. (Table salt, for example, is sodium chloride (NaCl).) Already, many urban and suburban streams exceed the recommended limit for chloride, which is 250 milligrams per liter. Rural waterbodies, meanwhile, can exceed 100 milligrams per liter on a seasonal basis.

The increased amount of dissolved solids in the water is strongly correlated to the amount of impervious surfaces such as roads and parking lots. In some regions, the increased use of deicer compounds in the winter caused chloride levels to reach five grams per liter, approximately a quarter of that found in seawater. Because land-use changes so rapidly, the authors conclude that "salinization associated with increasing suburban and urbanization deserves attention as one of the most significant threats to the integrity of freshwater ecosystems in the northeastern U.S."