Study: Geneva Lake shows elevated levels of salt

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Xavier Ward
Monday, April 17, 2017

LAKE GENEVA—Geneva Lake doesn't have a sea monster, but what lurks in the water could bite lakeside communities in other ways.

It's salt.

Geneva Lake is a freshwater lake, but runoff from rock salt applied to roads during the winter has increased the lake's salt levels, said Hilary Dugan, a researcher at UW-Madison.

It's happening in lakes across the United States, not just Geneva Lake, Dugan said.

Dugan and a research group looked at 294 freshwater lakes from Minnesota to Maine and measured the salt content in each lake. She said Geneva Lake was in the upper part of that group for salt content.

“Once you put road salt down, there's nothing that actually removes it,” she said, noting that the salt eventually washes into lakes, rivers, streams and even seeps into groundwater.

“We only have about a 15-year data set, but what we see in that time is chloride levels increasing,” Dugan said.

Ted Peters, director of the Geneva Lake Environmental Agency, said there hasn't been a concerted effort to reduce the lake's salt levels by any one community.

However, many lakeside municipalities have taken steps to reduce salt use, Peters said.

Williams Bay uses a sand and salt mixture, and the town of Lynn employs a wetting agent to maximize the efficiency of its rock salt, he said.

In Lake Geneva, salt use is left to the discretion of the street department, Peters said.

Tom Earle, director of public works for Lake Geneva, said his department doesn't apply more than 300 pounds per lane mile.

The department also tries to salt during snowstorms to maximize efficiency, but it doesn't use sand or mix anything with the salt.

“We're very close to the lake, and a lot of our storm sewers drain into the lake. Sand will actually clog up the drain,” Earle said.

Earle said cars tend to throw sand off the road, rendering it useless.

“We have to keep the roads safe, and it's a balancing act to use less salt but use enough to be effective,” he said.

Peters said Geneva Lake measures at roughly 48 milligrams of salt per liter of water.

The federal threshold for dangerous levels of salt in freshwater is 230 milligrams per liter, Dugan said.

While the levels in Geneva Lake are nowhere near dangerous, elevated salt content can have negative effects.

“All of these changes will filter through the food web, eventually up to fish, but we're still at freshwater concentrations, and that's not going to be killing fish anytime soon,” Dugan said.

She said increased salt levels can make the water more susceptible to invasive algae species, which could affect other lake organisms.

“If we change that environment, we're actually making it a lot more favorable potentially to exotic invasive species whose homes are saltier,” Dugan said. “If the environment is more favorable to these toxic breeds of algae, that's going to have ramifications.”

The lake can reduce its own salt levels naturally.

“The good news is lakes and rivers are routinely flushed out by streams and rivers,” Dugan said.

But people can play a role in reducing salt levels, too. While many cities focus on reducing salt as part of their municipal services, much of the salt that seeps into freshwater lakes comes from residential use, such as someone salting a sidewalk, Dugan said.

“It's amazing how little road salt you need for it to be effective,” she said.

The UW-Madison study yielded the largest data set available on salt in freshwater lakes, Dugan said.

“It's really just the tip of the iceberg in understanding some of these longer-term changes in lakes.”

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