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Ask the expert: Is road salt making the Great Lakes saltier?

"Ask the Expert" articles provide information and insights from MSU scientists, researchers and scholars about national and global issues, complex research and general-interest subjects based on their areas of academic expertise and study. They may feature historical information, background, research findings, or offer tips.  

Anthony Kendall, a research assistant professor in the Department of Earth and Environmental Sciences in the College of Natural Science, found a surprise as he was studying contaminants in Lake Michigan and discovered a slow but steady increase in the level of chloride found in the water.

1. How does salt get into the Great Lakes?

There are some natural sources of chloride (an element found in salt) such as the ancient ocean that used to lie underneath Michigan. When that water evaporated, salt was left behind, which can seep into the deep reservoirs of our groundwater, streams and tributaries that feed into the Great Lakes. Pumping groundwater for cities and farms can also pull this deep groundwater to the surface.

However, most of the chloride reaching the Great Lakes comes from direct human-caused sources. The largest of these are road salt applications and salt from water softeners.

2. How much salt is in the Great Lakes?

The Great Lakes are freshwater ecosystems. Traditionally, Lake Michigan, for example, has been a very low-salt lake, with levels around one milligram of chloride per liter of water. Over the years, due to our increased salt use, that level has steadily but gradually climbed up to 15 milligrams per liter. This means that Lake Michigan is still a very low-salt lake compared to our oceans (which is closer to 35 grams of salt per liter), but we are forcing change faster than nature and the environment can adapt.

3. Why should we be concerned now?

Salt is very difficult and expensive to remove from water and the salt cannot be removed directly from the lake. The water would need to go through a wastewater treatment plant, where we would need to use something like a reverse osmosis filter that would cost a lot of money. But in our groundwater and streams, the only way to reduce chloride levels is through dilution with fresher water. We need to reduce how much salt we apply to the landscape before we create a problem that is even more difficult for future generations to deal with. We need to identify the places we need to be most concerned about right now. 

4. What is being done now?

The easiest solution is to use less road salt, and Michigan’s Department of Transportation is actively looking for ways to apply less salt on roads during the winter while keeping roads clear and safe for motorists. The most direct way is to put salt on fewer roads. In some cases, sand or ash is used as an alternative to rock salt in lower-traffic areas. The DOT and MSU’s campus are using a liquid brine made from salt dissolved in water to create a barrier between roads, sidewalks and winter weather. The brine can be applied at a lower rate and spreads more evenly on the ground than road salt.

For more information, check out Kendall’s research


Banner image: Most of the chloride reaching the Great Lakes comes from direct human-caused sources. The largest of these are road salt applications and salt from water softeners. Credit: Shutterstock/Tom Fawls