An overuse of road salt in the winter has potentially harmful effects for everything from wildlife to groundwater
The winter months can bring dicey travel conditions, but those can be made safer with shovels, plows, and deicers like road salts. For road salts, a little can go a long way in improving safety, but its use is not without consequences. Researchers from the College of Agriculture, Health and Natural Resources and the College of Liberal Arts and Sciences are working to better understand the numerous environmental impacts of using too much salt on roads and walkways.
Bigger Frogs, More Mosquitos
Department of Natural Resources and the Environment researcher Tracy Rittenhouse and her group are investigating the effects road salts on amphibians.
“Previous research showed that tadpoles tend to metamorph larger in size from salty wetlands and high salinity conditions,” Rittenhouse says. “Generally, we think larger size as a good thing but we’re not sure why they’re larger or how they might be different physiologically.”
Rittenhouse explains that frogs starting life in saltier conditions, though larger, don’t seem to have any advantages later in life, whereas frogs from lower salt conditions started life smaller but grew much faster and larger over time. These results show that not only are amphibians amazingly tolerant to salt, but that we have much to learn. Despite the quantities of salt entering wetland environments, this resilience is why we have not seen massive declines in amphibian populations, says Rittenhouse.
Another experiment completed by an undergraduate student in her lab group showed that juvenile frogs not only detect if soil is salty, they will consistently avoid those conditions.
“That project opened up this whole arena of what we really should be looking at is the juvenile and adult frogs and how they might be responding to salinity in the terrestrial environment,” she says.
Rittenhouse says there are other consequences to heavily salting the road, including disruptions in the food web that can harm some members of the ecosystem while benefiting others.
“For example, salt generally kills most of the zooplankton,” Rittenhouse says. “Zooplankton eat phytoplankton, and tadpoles eat phytoplankton, so with fewer zooplankton, the tadpoles have more food, because those competitors are gone. You get shifts in the communities, but it’s not all negative for everything. Another thing that tends to do well in high salinity wetlands is mosquito larvae. Although a lot of other things die in high salinity conditions, the mosquitoes can tolerate it fairly well too. Maybe that would be a motivator to use less salt.”
Rittenhouse cautions that unless the “more salt is better” mindset changes, we will start to see more negative effects.
Future Changes in Plant Communities?
UConn researchers Beth Lawrence, Ashley Helton, and Gary Robbins recently published a study in Ecosphere investigating the potential impacts of road salts on plant communities and biogeochemistry in wetlands. The road-dense and wetland-abundant landscape of the Northeast provides a perfect setting for this type of investigation, says Lawrence.
“Other studies have found higher invasive species abundance and shifts towards salt tolerant species,” she says. “Surprisingly, we did not see strong shifts in the vegetation even where we observe elevated salinity in the roadside. We saw that invasive species might have a competitive advantage near the road edge and we’re unsure if that was road salt-induced.”
To get a better idea of potential salinity thresholds, the researchers looked at the seed bank — dormant seeds in the soil waiting for optimal germination conditions. They collected soil from a nearby forested wetland and exposed the banked seeds to different salinities to study seedling emergence under varying conditions.
“We found increased salinity reduces numbers of seeds germinating, the seeding density coming out of the soil was lower, and the diversity of species coming up was reduced,” Lawrence says, “suggesting that there might be some plants that are more tolerant and more capable of germinating under higher salinity conditions.”
Fortunately, Lawrence says these experimental salinity levels are higher than field conditions which are currently not salty enough to elicit a strong response.
“If high rates of road salt continue to be applied, we certainly could surpass that threshold and see strong changes in the vegetation in the future.”
A Sodium-lowering Solution
Mike Dietz, an Extension educator and faculty member in the Department of Natural Resources and the Environment, is working to address high salt application rates. His research also monitors salinity levels around UConn Storrs, and he says the best time to revise application rates is now.
“From some of the monitoring that we have here on campus with Eagle Brook, once we implemented Green Snow Pro training, given by UConn’s T2 Center, application rates were greatly reduced, over the course of two years, we started to see salt concentrations in the stream come down,” Dietz says. “In Connecticut we have this ‘glacial till’ soil that the water moves through very slowly. For example, for water to travel from Storrs Hall to Swan Lake, it takes around 10 months, so it really is a delayed response as we reduce the application rates. It is going to be a year to two years before we see a drop.”
Major hurdles include social factors and expectations, which Dietz says is a largely un-examined issue.
“It’s a big issue. In the 1980s and 1990s, we saw a steep increase in road salt application rates. I think that is when expectations started to change. Whereas previously people would just stay at home after a winter storm, now everybody’s got to get out and get to work. There’s a lot to be considered there,” he says.
Dietz says this issue is getting the attention of state legislators after a road salt bill was proposed in 2021. Dietz and a state-wide chloride workgroup is now working with legislators to craft the best bill possible for the upcoming session. The bill would require private contractors to take the Green Snow Pro training, which Dietz says would be a step in the right direction.
“In New Hampshire about 50% of the salt load that goes down is on private properties,” he says. “Having the liability relief for contractors and property owners that go through this training would be huge, and would really make a difference in the amount of salt that gets applied in Connecticut.”
Robbins, a professor in the Department of Geosciences, agrees that this issue needs to be addressed, and says road salt contamination of groundwater is one of the biggest problems stemming from the overuse of road salt.
“We are not slowing down how much salt is applied,” he says. “The salt gets into the groundwater where elevated concentrations persist even in the summer. It could take a very, very long time for that salt to get out. We have done a lot of groundwater monitoring for salt over the years, and found that the salt concentration has been increasing, on average over ten times natural levels.”
Everyone can do their part to reduce salt use at home, as there are alternatives to dumping salt, says Dietz. Plowing or shoveling driveways and sidewalks will allow the sun to heat the surfaces and melt the snow and ice. It’s also important to ensure the meltwater can drain away, so it doesn’t later re-freeze on the surface. Dietz has had luck with this method, and says he doesn’t need to use any salt at his own home. If you do use salt, just make sure you don’t overdo it, he says.