North America's freshwater lakes are getting saltier due to growing development and exposure to road salt, according to a new, large-scale study involving Michigan State University.
The study, published in PNAS, is the first to evaluate 371 lakes and show that many Midwestern and Northeastern lakes are experiencing increasing chloride trends, with about 44 percent of the lakes sampled in these regions experiencing long-term salinization.
Nicholas Skaff, an MSU doctoral student in the Department of Fisheries and Wildlife, is one of 15 researchers who co-authored the study as part of the Global Lake Ecological Observatory Network, or GLEON, Fellowship Program.
“This paper touches on a delicate problem,” Skaff said. “There’s a careful balance between protecting public safety on icy roads and ensuring that lake ecosystems, and all the important services they provide, are safeguarded long term.”
Each year, some 23 million metric tons of sodium chloride-based deicer is applied to North America's roads to melt away snow and ice. Much of this road salt washes into nearby water bodies where it’s recognized as a major source of chloride pollution to groundwater, streams, rivers and lakes.
Elevated chloride levels have been shown to alter the composition of fish, invertebrates and the plankton that form the base of the aquatic food web. In extreme cases, salinization can prevent lakes from mixing, which causes low oxygen conditions that smother aquatic life and reduce water quality.
"In the North American Lakes Region, where road salt is a reality, roads and other impervious surfaces within 500 meters of a lake's shoreline are a recipe for salinization,” said co-author Kathleen Weathers, co-chair of GLEON and an ecosystem scientist at the Cary Institute of Ecosystem Studies. “We need to manage and monitor lakes to ensure they are kept fresh and protect the myriad of services they provide, from fisheries and recreation to drinking water supplies."
If current salinization trends continue, many North American lakes will surpass EPA-recommended chloride levels in 50 years. Within this study, 14 North American Lakes Region lakes are expected to exceed the EPA's aquatic life criterion concentration of 230 mg/L by 2050, and 47 are on track to reach chloride concentrations of 100 mg/L during the same time period.
The study's authors recommend extending shoreline management practices beyond a lake's perimeter. Zoning regulations in many states and municipalities are often only enforced within 300 meters, and many lakes lack the monitoring programs needed to adequately track lake health.
“I don’t think that we should stop applying salt during the winter, but I think this paper supports the idea that municipalities, businesses and individual homeowners should take a thoughtful approach when deciding when, where and how to apply salt,” Skaff said. “Believe it or not, private homeowners and businesses can make a big difference. They’re responsible for more than 50 percent of road salt applications in some areas.”