When snow and ice melt, road salt goes with them, washing into lakes, streams, wetlands and groundwater.
Tourist towns along the Lake Michigan shoreline love to proclaim the giant body of water “Unsalted and Shark-Free.” The slogan is plastered on t-shirts, magnets and bumper stickers — but, according to a new study, only one of those claims holds water.
Combined, the Great Lakes make up about 20 percent of all the available fresh surface water in the world. While it’s true that sharks aren’t swimming through that vast reservoir, the lakes aren’t as fresh as they used to be. Over the last 200 years, thanks primarily to the use of road salt to keep winter roads and surfaces ice-free beginning in the 1940s, the freshwater of the Great Lakes has seen salinity levels creep steadily upward.
While other studies have shown increasing salinity levels in smaller bodies of water, “we know big lakes aren’t immune to human pollution,” says Hilary Dugan, an associate professor at the University of Wisconsin–Madison’s Center for Limnology and lead author of the study published recently in the journal Limnology and Oceanography Letters.
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