How winter storms, road salt and increasing salinity in our creeks and river impact our aquatic resources

This image taken by Michael Kinney on Jan. 13, 2022, shows a wintery scene along Loyalsock Creek.

​Last winter, the Pennsylvania Department of Transportation applied 12.3 million gallons of salt-based brine to the state’s roadways and has spread an average of 807,766 tons of rock salt a year over the last five winters.

“They are just one entity that spreads road salt in Pennsylvania, but there is a comparable amount of additional road salt spread by municipal and private entities,” said Ben Lorson, Watershed Analysis Section Chief for the Pennsylvania Fish and Boat Commission. “When someone says road salt, you think PennDOT, but it is just one part of a larger problem.”

That problem, Lorson added, is closely tied to bigger issue – increased salinization of our freshwater resources across the state.

“There is this trend of increasing ionic concentrations in our waterways. There quite a bit of recent literature out there pointing to this, and it has really been more prevalent over the last couple decades,” he said. “Some of the major sources of that increased salt content – beyond road salt spread in the winter months – includes fertilizer, sewage and industrial effluents, marcellus waste and the general weathering of our built infrastructure.”

Matt Wilson, of Susquehanna University’s Freshwater Research Institute, has noticed similar trends when it comes to road salt usage and increasing salinization of freshwater systems.

“The increase (of salinity) has been pretty dramatic, and it is something that concerns me,” he said. “Our road salt application has continually increased each year while the average snow accumulation has not.”

According to PennDOT Press Secretary Alexis Campbell, the agency uses rock salt, made of sodium chloride, as a deicer and crushed natural aggregate (such as limestone and sandstone depending on geology of the region) as an anti-skid or abrasive material.

“This combination is a regular practice that is widely used among state and municipal highway maintenance organizations to improve surface traction during winter weather events,” she said. “The amount of anti-skid used in any case follows the same standards used by other states and varies with the type of highway, necessary level-of-service and the present weather conditions. In typical winter conditions, rural areas with less traffic tend to use salt/anti-skid mixtures to reduce salt consumption and the cost of winter maintenance.”

Sodium chloride is the same compound found in table salt, “but they use a courser rock salt form that isn’t as refined as table salt,” said Lorson. “It can be spread in various forms. A brine is rock salt dissolved in a water solution that can be applied as a pre-treatment. They also have a form where they just wet the salt with water enough to round the edges so it doesn’t scatter as much.”

PennDOT works with partner agencies, such as the Department of Environmental Protection (DEP) to “address any issues or concerns related to waterways and will modify treatment guidelines accordingly,” said Campbell. “PennDOT continues to employ nationally-recognized best practices for the reduction and conservation of salt in an effort to minimize our impact on the environment while balancing safety needs for travelers.”

However, the connection between road salt usage and salinization issues in waterways continues to be an issue, according to Lorson.

Immediate impacts tend to be “greatest after a storm where salt has been spread and then there is some type of runoff event, whether it be a followup rain or rapid melting situation where an increased concentration of salt enters the waterways,” he said. “Where you see the greatest impacts are along roadways that run parallel to a waterway, so there is a long distance where that water runs straight off the road and into a stream.”

Ben Lorson, Watershed Analysis Section Chief for the Pennsylvania Fish and Boat Commission, talks about his role with the agency and his concerns about road salt use and increasing salinity of our freshwater systems in the newest episode of the Middle Susquehanna Riverkeeper Podcast:

Check out the Pennsylvania Department of Transportation's Winter Maintenance page and various resources by clicking here.

Check out the PDF version of Ben Lorson's recent presentation for the PA Fish and Boat Commission's Habitat and Environmental committee meeting titled "Road Salt Impacts and the Salinization of Freshwater Systems" by clicking here.

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Check out various studies about salinity in waterways and potential impacts, as provided by the PFBC's Ben Lorson:

kaushal2021_article_freshwatersalinizationsyndrome.pdf
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kaushal_et_al_2018.pdf
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road_salt_review.docx
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​Aquatic impacts
“The critters that live in freshwater streams are just like us,” said Wilson. “They are much healthier and happier when they drink fresh water instead of salt water.”

Impacts in different species depend on their sensitivity to outside contaminants, according to Lorson.

“We have seen some chloride concentrations much higher than what we know the tolerance can be for certain aquatic species. Even within those species, there can be a range of tolerance,” he said. “Certain macroinvertebrates and fish are more likely to be impacted first. We know that amphibians can also be very sensitive, as well as mussels.”

As salinity increases in streams, “the more sensitive species are affected first, while the more tolerant species persist. “Over time, this causes decreasing diversity within our aquatic communities where you have the highest levels of road salt (contamination).”

Salt can have a varying impact on different life cycles within the same species, as eggs and fry can be more susceptible than adults, so species that spawn earlier in the spring can see more of an immediate impact. Increased salinity can also suppress feeding and growth and can be more detrimental if mixed with other external ions or contaminants.

Trout specifically is a species of concern when it comes to salinity. Lorson referenced a study out of Maryland where no brook trout were found in waterways that exceeded 280 mg/L of chloride, and could be found in the highest density in streams with chloride below 100 mg/L.

In another study he shared – focused on mayfly toxicity in Delaware and Pennsylvania streams – showed  that some waterways contained more than 1,000 mg/L of chloride ranging as high as 11,000 mg/L.

“It is a general increasing trend over the course of the year. While we may see spikes after winter storm situations, the increasing salinity is not just a seasonal issue,” said Lorson. “Road salt and fertilizers get into the soil and can be released over time and get into the groundwater. So, if we are spreading it today, it could wind up in our waterways years, or even decades, down the road.”

Wilson agreed.

“Increased salt applications over time have led to build-up in ecosystems so that we even see increased salinity of streams in the summer now,” he said. “This isn’t just a winter problem – it’s becoming a year-round problem that adds additional stress on top of our other impacts from land use and climate change that we have thrown at our streams.”
 
Solutions not simple
A change in our road salt usage would require a change in human behavioral trends, according to Lorson.

“People feel the need to maintain their daily, normal life during the winter season. To do that, they need safe roads where everyone can drive wherever and whenever they want without concern of someone getting sued,” he said. “Right now, the way we try to maintain that lifestyle is to increase salt usage vs. learning how to slow down and properly drive on snow-covered roads. For any real change, it will take a lot of public education and a shift in behavior.”

Wilson agreed that current practices are driven by our “increasingly on-demand culture.”

“If we want to be able to drive 100 percent of the time straight through the middle of a storm, then yes, it might be easy to see why we’ve increased salt use,” he said. “But if we give the crews who are working around the clock in treacherous conditions during storms a chance to do their job, be patient and accept that we might need to sit at home for a few hours during those storms – then perhaps we can simply apply less salt to our roads.”

Some states have started taking steps to reduce salt usage as they notice decreases in water quality and macroinvertebrate communities, according to Wilson.

“Some states have started using porous pavement, which not only decreases ice formation, it actually creates a 77 percent decrease in the need for salt application,” he said, adding that there are other solutions that don’t require a change in infrastructure.

“Using a brine solution instead of salt crystals can decrease salt by over 20 percent,” he said. “Other including biodegradable additives to the salt that increase traction and decrease the melting point of ice, making the salt more effective. Some options that have proven effective include adding beet juice or molasses.”

When making decisions on how to treat a parking lot, your driveway or a sidewalk in terms of salt use, Lorson suggested mindfully cutting back.

“Use as little as possible – just enough to get the melting started,” he said, illustrating it with an example provided by a PennDOT winter maintenance chief used in training for PennDOT staff.

“They have three similar-sized blocks of ice. On the first one, they put one shot glass of salt. With the second one, two shot glasses of salt and three on the third one,” said Lorson. “By the end of the training, a couple of hours down the road, they pull out those bottles of frozen water and regardless of how much salt was put on, there was the same amount of melted ice in each container.
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“It is an example that more salt is not always better. The more salt we put on our roads, driveways, parking lots and sidewalks, the more eventually winds up in our waterways.”