In the winter, road salt enters fresh water through road runoff from deicing. While we already know salt alone is harmful to freshwater animals, a new study shows it becomes more deadly to freshwater snails when combined with the fear of natural predators in the water.
For the new study, published in Oikos, the researchers conducted semi-outdoor experiments using different salt levels with the presence or absence of different predator species to better reflect snails’ natural habitats.
The researchers noticed that when snails sense nearby predators, they slow their eating and move less to avoid being noticed. At the same time, an increase in salty water forces them to use more energy just to stay alive. Together, these forces drain their energy. This combination of factors likely increases a snail’s risk of death.
“At the highest salt levels, we found that predator stress dramatically increased snail deaths, causing nearly 60% higher mortality compared to salt alone,” said co-author Rick Relyea, director of Mizzou’s Johnny Morris Institute of Fisheries, Wetlands and Aquatic Systems.
Although they are small, freshwater snails are abundant and important to aquatic ecosystems because they help control algae, recycle nutrients and provide food for fish and birds. If snails disappear and algae grows unchecked, water quality lowers.
Relyea said practical solutions to reducing salt pollution in waterways already exist.
“Communities can cut road salt use by up to 50% while still maintaining safe roads,” he said. “Simple steps such as pre-treating roads, calibrating salt trucks and applying salt more strategically can protect freshwater ecosystems while saving money for local governments and taxpayers.”
Data from University of Missouri-Columbia