BROOKINGS, S.D. - While road salt throughout the winter months is seen by most as a necessity in our part of the country, it can come at a cost, said David Kringen, SDSU Extension Water Resources Field Specialist.
"While the salination of South Dakota surface waters is not a water quality concern at this time, awareness of the issue could prevent it from being a concern in the future," Kringen said.
He explained that salt corrosion can not only cause damage to our infrastructure (roads and bridges) and vehicles, it can be harmful to our freshwater ecosystems as well.
Salination (or salinization), is the process where water-soluble salts accumulate in soils, or a body of water. It is typically measured by an increase in chloride, which is an anion of many salts (i.e. sodium chloride, magnesium chloride).
In soils, salination is a concern, Kringen explained, because excess salts hinder the growth of crops by limiting their ability to take up water.
"In freshwater ecosystems, increased salinity can significantly reduce both species richness (the number of species found in an ecosystem) and relative abundance (the abundance of a given species relative to the abundances of the other species) of aquatic plants and invertebrates; which in turn, affects the entire food chain," he said.
Salinity ranges, measured as a concentration (milligrams per liter), are categorized as fresh to highly saline and can be seen in the table.
The U.S. Environmental Protection Agency's nationally-recommended criteria for chronic (long-term) chloride toxicity exposure for freshwater aquatic life is 230 milligrams per liter.
In South Dakota, surface waters designated as coldwater permanent fish life propagation waters are assigned a numeric standard of 100 milligrams per liter for a 30-day average and 175 milligrams per liter for a daily maximum.
"Concentrations above these limits means the water body does not support the beneficial use assigned to it," Kringen said.
For surface waters designated as a domestic water supply, the 30-day average and daily maximum concentrations are 250 milligrams per liter and 438 milligrams per liter respectively.
What research shows
A recent study conducted in 2017 investigated long-term chloride trends in 371 freshwater lakes in North America. "Results indicated that the density of roads and other impervious land cover was a strong predictor of long-term salination in Northeast and upper Midwest lakes where the study was focused," Kringen said.
Other studies also recognize the link between the salination of water bodies with the application of road salts as metropolitan areas continue to develop and grow.
"Keep in mind, runoff that enters city storm sewer systems to be channeled away is discharged untreated and delivered directly to rivers and streams; rivers and streams that we use for domestic, commercial and recreational purposes," he said.
Courtesy of iGrow. This table shows how salinity ranges, measured as a concentration (milligrams per liter), are categorized as fresh to highly saline.