Salt used on icy roads is contaminating lakes; 44% of 371 lakes studied showed salinization

North American lakes are at risk of long-term salinization from salt used on icy roads, says a study from researchers at multiple universities and agencies, published in Proceedings of the Natural Academy of the Sciences. Researchers found that "most urban lakes and rural lakes that are surrounded by more than one percent impervious land cover show increasing chloride trends." (Chloride trends for North American freshwater lakes)

Researchers studied 371 North American lakes, finding that 44 percent showed signs of long-term salinization, Ben Guarino reports for The Washington Post. They estimated that at least 7,770 lakes are at risk of elevated sale levels. Scientists, who said they could not directly measure how much of the chloride came from road salt, said that "if at least 1 percent of the surface circling a lake was impervious, the lake was at risk of high chloride concentrations."

Distribution of impervious land cover within a 500-m
buffer of all lakes >4 ha in the lower 48 U.S.

One problem is that "no federal body tracks how much salt gets spread on roadways or makes its way into our lakes," Guarino writes. "Impervious surfaces, critically, allow dissolved salt to slide into lakes rather than soaking into soil."

"Each lake in the report had chloride measurements going back 10 years or more, was at least four hectares in size (about nine football fields or larger) and was in a state that regularly salted its roads during winter," Guarino writes. "The study authors also analyzed what percentage of the lake was surrounded by an impervious surface. This could be any combination of roadways, sidewalk pavement, boat launches or other hard surfaces."

"Across all lakes, chloride concentrations ranged from 0.18 to 240 milligrams per liter, with a median of 6 milligrams per liter. (Seawater, by contrast, is much saltier — an average of about 35 grams per liter.)," Guarino writes. "The Environmental Protection Agency recommends that salt in drinking water exceed no more than 250 milligrams per liter, at which point water tastes salty."