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Effect of Road Salt Additives and Alternatives on Aquatic Ecosystems

A recent study by researchers from the Jefferson Project at Lake George looks at the ecological impacts of additives commonly added to road salt, as well as commonly used alternatives to road salt.

The Jefferson Project is a collaboration between several organizations, which was initiated in the hopes of developing an technologically advanced environmental monitoring and prediction system that would help managers to better understand and conserve the Lake George aquatic ecosystem, and which could also be applied to other freshwater systems all over the world.

Road salt additives and alternatives that are commonly used in or to replace sodium chloride — the most widely used type of road salt — are typically marketed as eco-friendly, low-salt alternatives to the most common form of road salt used to keep roads ice-free. But, it turns out that these additives and alternatives may not be so environmentally friendly after all.

According to Rich Relyea, the director of the Jefferson Project at Lake George:

"Additives and alternative salts are presumed to be less environmentally harmful because they let us use less sodium chloride, but what about the potential impact of the additives and salt alternatives themselves? We know almost nothing about the impact of these additives and alternatives on aquatic ecosystems," he says.

According to the study, which was recently published in the Journal of Applied Ecology, organic additives routinely added to road salt alternatives — for example additives included in commercial road salt products such as Magic Salt and GeoMelt — serve as a fertilizer to freshwater systems, promoting algal growth and allowing algae eating organisms to thrive. While the road salt alternative, magnesium chloride, which is used in commercial road salt products such as Clear Lane, has been found to boost populations of tiny aquatic crustaceans that forage on algae, and which play an important role in food webs, supporting fish.

Relyea and his colleagues undertook several experiments to determine the impact that various types of road salt had on aquatic food chains, and their results were quite surprising. Research published earlier this year showed how a common zooplankton species is able to genetically evolve within a time frame of just 6 weeks to be able to tolerate moderate concentrations of sodium chloride in water. While research published towards the end of last year revealed that sodium chloride is able to change sex ratios in developing frog populations. Further research has been conducted on the impacts of various types of road salt on juvenile trout living in streams and wetlands.

In this latest research — a pioneering study comparing the impacts of road salt additives and alternatives on aquatic ecosystem — scientists outfitted 64 replicate aquatic ecosystems with key players in aquatic food webs, including phytoplankton, zooplankton, tiny crustaceans and snails. The team prepared five road salt "treatments":

• Rock salt (sodium chloride)
• Magnesium chloride
• Sodium chloride with low levels of magnesium chloride added (similar to that found in the commercial road salt product Clear Lane®)
• Sodium chloride combined with beet juice (similar to that found in GeoMelt®)
• Magnesium chloride combined with a byproduct of the distillation process (similar to that found in Magic Salt).

They then applied each of these treatments at three different concentrations commonly found in freshwater systems: 50, 100, 200 milligrams/liter of chloride, while using tap water containing 25 milligrams/liter of chloride as a benchmark control. After one month, they looked at the changes in these replicated ecosystems.

According to the study, "microbes digested some of the sugars in the beet juice and distillation byproducts, causing an immediate drop in dissolved oxygen levels." Microbes are also likely to have transformed an unusable form of phosphorus in the additives to a form that is more readily available for algae to use, thus boosting algal growth. The authors found that these algal blooms allowed zooplankton populations to triple in size, which in a natural aquatic ecosystem could allow fish and other predators of zooplankton to increase in both size and numbers.

"Organic additives are like adding food to the lake. They are broken down into nutrients and organisms eat them," said Matthew Schuler, a postdoctoral research associate and first author of the paper. "The additives in GeoMelt and Magic Salt act as a fertilizer for aquatic systems."

Low levels of magnesium chloride similar to those used in Magic Salt, Clear Lane and in the magnesium chloride treatments caused aquatic amphipod populations to more than triple in number.

"Our research shows that these chemicals can cause changes to the food web, but we can't tell you whether that is desirable or not," Relyea said. "More algae means more zooplankton and more fish, and the angler might like that. But more algae also means turbid water, and a homeowner may not like that. It's a subjective public question."

Journal Reference

Schuler, M. S., Hintz, W. D., Jones, D. K., Lind, L. A., Mattes, B. M., Stoler, A. B., Sudol, K. A. and Relyea, R. A. (2017), How common road salts and organic additives alter freshwater food webs: in search of safer alternatives. J Appl Ecol. doi:10.1111/1365-2664.12877

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