June 2018 Vol. 26, No. 2

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Northern North American lakes are getting saltier

Hilary Dugan has studied long-term changes in the chloride content of more than 400 lakes in North America and Europe. In a nutshell, she found that, as a result of winter road salt application, chloride content has increased in North American lakes.

Dugan showed the following standards for chloride content in lakes:

Chronic Mg/L Acute Mg/L
US EPA 230 860
Wisconsin 395 757
Canada 120
North American lake
Photo: Shutterstock

The 230 mg/L standard is very little salt: equivalent to one teaspoon of salt in 5 gallons of water. “The more salt we put in our water, the more stressed our ecosystem is going to be,” she said. “And while salinization of lakes comes from multiple sources, including water softeners and some fertilizers, far and away, road salt is the leading cause of chloride in these lakes.”

In addition to studying chloride content in North American and Swedish lakes, Dugan looked for correlations between each lake’s chloride content and its surroundings: Was the lake near roads? What was the ground cover: forest? agriculture? And how big was the lake?

The results are troubling. Dugan found that chloride levels are increasing in many lakes studied in 10 U.S. states plus Ontario—both urban and rural. And when the amount of impervious surface (mostly due to paving) near lakes was correlated with the chloride levels in those lakes, “almost every lake with increasing chloride had high levels of impervious surfaces—and lakes with decreasing chloride had no impervious surfaces nearby.”

But in Sweden, Dugan found that in all but two of the 114 lakes studied—even those close to roads— chloride levels have remained low, around 5 to 7 mg/L, since the 1980s. “Sweden has lots of roads and lots of snow—but no chloride problems in their lakes. What chloride content was in their lakes correlated with climate. In drought years, there was slightly higher chloride from evaporation. In years with lots of rain, chloride went down; the lakes got flushed out. That’s what we should see naturally. But we don’t see that in North America because the precipitation signal is drowned out by the road salt signal. The result of the study was that 1% impervious surface [near a North American lake] was enough to cause these problems because we put down road salt everywhere.” Of 38,000 lakes in the 10 U.S. states, she estimates 11,000 are at risk.

zebra muscle in salt
Invasive species such as zebra mussels thrive in salt water. (Photo: Shuttershock)

Next, Dugan addressed biological impact: “The question I always get is: Are the fish going to die? No! There will always be fish, but they may be different fish. They may be species that adapt much better to saline conditions. What we should be worried about is our native species that are adapted to fresh water—from plankton to mussels to fish. They will have a harder time the more salt you put in the water. What’s really good at living in salt water are the invasive species like zebra mussels.”

When an audience member asked whether the lack of salt use on roads in Sweden correlates with less safe roads, Dugan said, “I think it comes down to how they manage their roads. There’s almost no salt use in general. They plow their roads, and they use a lot of sand. They drive more slowly. And liability is a very different topic in Scandinavia. They don’t think about the risk of being sued if someone slips. That’s just part of winter there. It was probably like that here 50 years ago, but now we’ve moved into this more litigious mindset. That’s why we’re using so much salt—especially in commercial applications. Passing laws that limit liability would go a long way to making it possible to use less salt.”

Richard L. Kronick, LTAP freelancer