Road salt from winter deicing is making freshwater streams, ponds and lakes saltier across the United States. Researchers at the University of Missouri’s College of Agriculture, Food, and Natural Resources, led by Rick Relyea, ran semi-outdoor experiments that combined a range of salt levels with the presence or absence of predator species to mimic real environmental conditions. Relyea points out that freshwater organisms have evolved in low-salt environments.
The study found that road salt became far more harmful when snails also experienced predator stress. At the highest salt levels, predator presence dramatically increased snail deaths, producing nearly 60% higher mortality compared with salt alone. The researchers observed that snails reacted to predators by eating less and moving less to avoid detection, while higher salinity forced them to expend more energy just to stay alive. Reduced feeding together with greater energy use appears to deplete snails and raise mortality. Scott Goeppner notes that these interactive effects often do not appear in typical laboratory studies, so the danger of common pollutants may be underestimated.
Although small, freshwater snails play key ecological roles: they help control algae, recycle nutrients and provide food for fish and birds. Goeppner warns that loss of snails could let algae grow unchecked and reduce water quality, affecting the waterways communities rely on. The team also suggests that current water-quality standards may not fully reflect these real-world interactions, and when pollutant effects are uncertain it is safer to be cautious.
Relyea says practical steps can reduce salt pollution without compromising safety. Communities can cut road salt use by up to 50% while still maintaining safe roads. Simple measures include:
- pretreating roads,
- calibrating salt trucks,
- applying salt more strategically.
The study appears in the journal OIKOS. Mitchell Le Sage at Rensselaer Polytechnic Institute is a coauthor. Source: University of Missouri.
Difficult words
- predator — animal that hunts and eats other animalspredators
- salinity — amount of salt dissolved in water
- mortality — rate or number of deaths in a group
- deicing — removal or prevention of ice on roads
- calibrate — adjust a machine to work at correct levelcalibrating
- pretreat — treat a surface before main treatmentpretreating
- interactive — acting on each other; producing combined effects
- underestimate — judge something as smaller or less harmfulunderestimated
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Discussion questions
- Do you think reducing road salt by up to 50% is realistic in your area? Why or why not?
- How could loss of snails and increased algae growth affect local communities and water use?
- Which of the suggested measures (pretreating roads, calibrating trucks, applying salt strategically) would be easiest or hardest to implement locally, and why?
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