How Do Road Salts Impact Roadside Microorganisms?
Study examined impacts of varying levels of beet brine and road salt
By John Lovett – Jan. 15, 2025
IMPACT STUDY — Caroline Anscombe, left, stands with Brynnen Beck and Claire Meara at Niokaska Creek in Fayetteville, Arkansas as part of water quality studies with Shannon Speir, assistant professor of water quality. (U of A System Division of Agriculture photo by Paden Johnson)
FAYETTEVILLE, Ark. — Salt is essential to keeping our roads and walkways safe when it snows. But when salt is washed off the roads, how does it impact nearby microorganisms?
Water quality researcher Shannon Speir and her students have been conducting studies to measure the impact that road salt and beet brine, a common eco-friendly alternative, have on freshwater ecosystems that receive the roadway runoff. Their initial results were not entirely expected.
Beet brine is a liquid solution of salt and beet molasses, which helps the solution stick to the road. Road salt is mostly salt mixed in with a small amount of calcium chloride or magnesium chloride.
Speir is an assistant professor of water quality in the crop, soil and environmental sciences department for the Dale Bumpers College of Agricultural, Food and Life Sciences at the University of Arkansas and the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture.
Speir said her team’s experiments showed road salt and beet brine did not significantly impact overall leaf litter decomposition even though decomposition rates were decreased in the presence of high levels of beet brine during the first week of the study only.
“Beet brine has less salt than road salt since it is in a solution, but it also has a lot of added nutrients like nitrogen, carbon and phosphorus,” Speir said. “So, we’re reducing our salt application, but what does this mean in terms of added nutrient application and potential runoff to waterways?”
Caroline Anscombe, one of Speir’s graduate students at the University of Arkansas, put the question to the test. She conducted a study in partnership with researchers at the University of Notre Dame to examine the impact beet brine and rock salt have on leaf litter decomposition using recirculating aquatic mesocosms. Aquatic mesocosms are water enclosures designed to replicate natural conditions where environmental factors can be realistically manipulated.
“They look kind of like oblong donuts,” Speir said of the aquatic mesocosms. “It circulates the water around and around using a paddle wheel to simulate natural stream flow.”
Anscombe’s experiments aimed to measure the impact of varying levels of beet brine and rock salt on leaves that were either tough or soft. They chose post oak leaves, which are harder for microbes to break down, and sugar maple leaves, which are easier for microbes to decompose. She exposed the leaves to low and high levels of road salt and low and high levels of beet brine to get a broad comparison of different treatments.
Testing the hypothesis
Going into the study, Speir and Anscombe predicted that the nutrients in low levels of beet brine might stimulate microbial activity. Higher levels of beet brine, however, were hypothesized to hinder microbial decomposition activity due to excessive salt concentrations. Similarly, road salt was predicted to decrease microbial processing, Speir said.
Contrary to expectations, preliminary results suggest that decomposition rates were not significantly affected by the various treatments over the experiment’s two-week duration. Beet brine decreased decomposition rates for maple leaves more than traditional road salt in the first seven days but did not significantly impact leaf litter decomposition overall for the oak and maple leaves. And microbial colonization of oak leaves increased by each of the deicing treatments.
Beet brine had a larger effect on leaf litter decomposition and respiration than the equivalent concentration of traditional road salts. However, they did not see differences between low and high salt treatments in any of their response metrics.
The results, especially the lack of a significant impact on decomposition from beet brine treatments, were surprising and did not align with the initial hypotheses, Speir said. Since they found that beet brine has the potential to impact decomposition, particularly in areas where it is continually applied throughout the winter, Anscombe said future studies may be needed to quantify the effects of repeated deicer treatments and the residence time, or how long these products are staying in the environment, to determine their potential impacts of beet brine products on freshwater ecosystems.
Two undergraduate students in Speir’s lab — Brynnen Beck and Claire Meara — are currently conducting related studies on the impacts of road salt and beet brine on microbial respiration, which is a measure of microbial activity, and the conversion of nitrates to atmospheric nitrogen, also known as denitrification.
“It’s a very understudied area considering the widespread application of salt to roads without really understanding what the benefits, the risks and tradeoffs are,” Speir said. “It’s not to say that road salt and beet brine are not tools you should use. It’s just that if we’re going to wholesale apply it on areas, and water quality is something of importance, we really want to make sure that we understand all the tradeoffs.”
WATER QUALITY — Shannon Speir is a water quality researcher whose work includes investigating nutrient cycling and microbial processes. (U of A System Division of Agriculture)
Practicing ‘Smart Salt’
While this study showed that beet brine and road salt did not significantly impact leaf litter decomposition, Speir said more public education is needed to address proper application of salt to roads, driveways and walkways. Too often, Speir said, people use too much salt around those areas.
In the United States, the most drastic increases in salinity have occurred in the Midwest and Northeastern regions, driven by winter road salt application, Speir said.
The Conservation Foundation, a northern Illinois nonprofit that promotes a practice called “Smart Salt” recommends making a brine with 3.5 cups of road salt per gallon of hot water to spray on driveways and walkways. Following is a list of brine application tips from The Conservation Foundation.
- Don’t apply brine if rain is forecasted before the snow.
- Use the sprayer to make lines back and forth across the pavement; you don’t need to cover all of the pavement.
- Brine can be applied 24-48 hours before a storm is predicted.
- Agitate or shake the sprayer to keep the salt from settling out – especially if the sprayer has been sitting for a while between storms.
- Brine left over at the end of the season can be stored in a clean jug for the next winter. Excess brine or rinse water shouldn’t be dumped onto the lawn or down a storm drain or sink drain.
To learn more about the Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website. Follow us on 𝕏 at @ArkAgResearch, subscribe to the Food, Farms and Forests podcast and sign up for our monthly newsletter, the Arkansas Agricultural Research Report. To learn more about the Division of Agriculture, visit uada.edu. Follow us on 𝕏 at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit uaex.uada.edu.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on three campuses.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs to all eligible persons without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
WATER QUALITY — Shannon Speir is a water quality researcher whose work includes investigating nutrient cycling and microbial processes. (U of A System Division of Agriculture)
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