Michigan uses tons of road salt each year, and while this de-icer helps keep the roadways safe, it also pollutes the natural ecosystem – particularly lakes and other waterways.
Dr. Carla Koretsky, College of Arts and Sciences dean and professor of geological and environmental sciences, and Dr. Kathryn Docherty, associate professor of biological sciences, recently conducted a project funded by Michigan’s Department of Environmental Quality that studies road salt contamination in Kalamazoo-area urban lakes.
“When road salt washes away, it dissolves in water and eventually ends up in the lowest point in a watershed – usually a lake,” Docherty says. The salt disrupts a critical process known as turnover. “Normally, as temperatures change during spring and fall, water from the top of the lake sinks to the bottom, carrying dissolved oxygen with it. This is the reason why animals such as fish and insects can survive at the bottom of the lake in winter.”
When road salt enters the lake, it can fail to mix seasonally, causing the bottom to remain deprived of oxygen. “Lakes impacted by road salt create the perfect habitats for anaerobic microorganisms, some of which ‘breathe’ in chemicals like hydrogen and carbon dioxide and produce methane,” Docherty says. “If these lakes are producing more methane, then we could be underestimating their importance as methane sources in models that predict the effects of climate change.”
Road salt contamination also comes with major consequences for recreational fishing. “Once the salt is dissolved, it’s virtually impossible to remove,” Docherty says. “As lakes continue to receive salt inputs, the lack of turnover will limit deep-water oxygen for fish during the winter. As a result, lakes may not be able to sustain fish populations year-round.”
While Docherty says much research is needed in order to better understand the impacts of road salt contamination, she hopes to see more regulation of its application, as well as alternative forms of de-icers. “There are many ways to move forward with this research,” she says. “It will be interesting to see whether we can include urban lake methane production into climate change models.”
To learn more about WMU researchers' work in freshwater science and sustainability, view the 2018 issue of Arts and Sciences Magazine.