Road Salt & Water Quality: Growing Concern in Some Northern States Back »

I recently came across an article from the Associated Press addressing road salt and the nation’s waterways. Many of you may have seen the article too as a number of local media outlets elected to carry it. While road salt is almost a necessity in our part of the country, it can come at a cost. 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.

Impact of Salination

Salination (or salinization) is the process where water-soluble salts accumulate in soils, or in this case, 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 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.

Measuring Salinity
Salinity ranges, measured as a concentration (milligrams/liter), are categorized as fresh to highly saline and can be seen in the table below. The US EPA nationally-recommended criteria for chronic (long-term) chloride toxicity exposure for freshwater aquatic life is 230 mg/L. In South Dakota, surface waters designated as coldwater permanent fish life propagation waters are assigned a numeric standard of 100 mg/L for a 30-day average and 175 mg/L for a daily maximum. Concentrations above these limits means the water body does not support the beneficial use assigned to it. For surface waters designated as a domestic water supply, the 30-day average and daily maximum concentrations are 250 mg/L and 438 mg/L respectively.

Salinity (mg/L) Category
< 1,000 Fresh
1,000 - 3,000 Slightly saline
3,000 - 10,000 Moderately saline
10,000 - 35,000+ Highly saline


The Big Picture

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. One 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. Other papers 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.

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