SOURCE: Scientific American
DATE: December 6, 2018
SNIP: Salts that de-ice roads, parking lots and sidewalks keep people safe in winter. But new research shows they are contributing to a sharp and widely rising problem across the U.S. At least a third of the rivers and streams in the country have gotten saltier in the past 25 years. And by 2100, more than half of them may contain at least 50 percent more salt than they used to. Increasing salinity will not just affect freshwater plants and animals but human lives as well—notably, by affecting drinking water.
When Sujay Kaushal, a biogeochemist at the University of Maryland, College Park, who studies how salt invades freshwater sources, sampled the local water supply he found not just an elevated level of the sodium chloride, widely used in winter to de-ice outdoor surfaces, but plenty of other salts such as sodium bicarbonate and magnesium chloride.
How people use the land is another important factor. “Today, the saltiest streams are in the northern Great Plains,” scientist John Olson at California State University, Monterey Bay says. “Salinity is naturally high, and mining and oil and gas extraction are releasing more salt by exposing new rock and pumping out saline groundwater.” In those places, he adds, it is not unusual to find streams that are about half as salty as ocean water.
The largest predicted increases are in the arid Southwest, however. The combination of expanding agriculture and reduced rainfall there would require careful irrigation management, Olson says. In the Colorado River Basin, where several such projects are ongoing, the economic cost of salinization is estimated at $300 million per year, including damage totaling $176 million to crops and $81 million to households. In California salty water is costing the agricultural sector billions of dollars in yield losses annually.
The Stroud Water Research Center in Pennsylvania has a long tradition of testing water quality impacts on mayfly larvae. According to entomologist John Jackson’s latest research, as the salt level approaches about a tenth that of seawater, which is not unheard of in some streams, at least three of four species tested are likely to die.
Insects are not the only life-forms that will suffer, adds ecologist William Hintz of the Darrin Fresh Water Institute in New York State, who has studied salinity effects on rainbow trout. “Adult fish are quite resilient, but the young are vulnerable,” he says. “High salt levels may slow down their growth, which has negative effects on their survival and reproductive capacity.”