By Mike Polhamus,
Lake Champlain is growing increasingly salty, and researchers say winter snow maintenance is the likely culprit, according to a new study published April 10.
Salt in the lake can promote the spread of blue-green algae, according to scientists.
The current salinity level of Lake Champlain isn’t high enough to harm aquatic life, or high enough for humans to taste, scientists say.
Lake Champlain is one of two of the 20 Vermont lakes in the study that are experiencing increasing salinity, and that trend worries some researchers, said Mindy Morales-Williams, a scientist with the Rubenstein Ecosystem Science Laboratory. Morales-Williams will begin teaching as an assistant professor at the University of Vermont in August.
“I think the concern is the increasing trend, and the potential for it to continue to rise,” she said. “It’s currently not at the level [in Lake Champlain] where it would hurt aquatic life … but the problem with salt is that it’s really hard to remove from water, and it’s really hard to remove from soil.
“Even if you stop salt application … it continues to leach” from soil, Morales-Williams said.
Moreover, she said, “larger lakes like Champlain take longer to recover than small lakes because the residence time is longer, meaning things that enter the lake stick around a lot longer than it would in a smaller lake with a shorter residence time.”
The lake has a long ways to go before it reaches what the Environmental Protection Agency defines as the “aquatic life threshold criterion,” which is at 230 milligrams per liter. This concentration, Morales-Williams said, is the point at which “most freshwater aquatic life cannot survive.
“Your lake is basically dying at that point; you’re severely impacting ecosystem function,” she said.
Sampled sites from Lake Champlain show a mean concentration of 11 milligrams per liter.
Even at lower concentrations, salt can affect the balance that exists between organisms living within freshwater water bodies, Morales-Williams said.
Toxic blue-green algae, which as the result of phosphorus pollution throughout the state blooms annually in Lake Champlain, tolerates salt better than most freshwater plant species, Morales-Williams said.
Also known as cyanobacteria, these plants can handle up to a third of the salinity found in ocean water, she said.
As a result, cyanobacteria in salty freshwater lakes can potentially outcompete other, less salt-tolerant species, Morales-Williams said.
“Increasing salinity … may promote blue-green algae” as a result, she said.
The study, published in the scientific journal Proceedings of the National Academy of Sciences, found that impervious surfaces, such as asphalt and concrete, are closely linked with trends of increasing salinity. The study found long-term salinity increasing in lakes where as little as one percent of the area within 500 meters of the shoreline is covered with an impervious surface.
Road salt is the most likely culprit, the study found.
But as much as 50 percent of the salt found in some lakes in the study is thought to have come from individuals and businesses applying their own salt, Morales-Williams said.
Lily Pond, in Dover, is also undergoing long-term salinization, Morales-Williams said. The concentration of salt there was measured at less than one milligram per liter, but it showed a long-term increasing trend, she said.
The other 18 Vermont lakes that were included in the study did not show trends of increasing salinity, according to the study’s results.
“Overall, concentrations across the state were quite low, except in Lake Champlain,” Morales-Williams said.
The study includes 371 North American lakes in total, spread out through the United States and Canada.
As a whole, the study indicates a need to carefully weigh the utility of road salt against its consequences in nearby freshwater water bodies, Morales-Williams said.
“We really need to have society work on balancing our needs with how we affect local ecosystems,” she said. “We want ice-free roads right away, but we’re really doing damage to the quality of our water resources.”
The Vermont Agency of Transportation applied 66,821 tons of salt to state roads over the winter spanning 2015 and 2016, according to the VTrans 2017 Fact Book.
During the same period VTrans applied 2,496 cubic yards of sand to road surfaces.
The previous winter VTrans applied 131,684 tons of salt and 6,489 cubic yards of sand.
On average over the past five years, VTrans has applied 114,607 tons of salt each winter, and 5,530 cubic yards of sand.
Road salt, according to the VTrans 2017 Fact Book, “is the primary material used on the majority of roads maintained by VTrans. Salt is used to prevent the bonding of snow and ice onto the pavement surface, and to melt snow and ice that cannot be removed by plowing.”
Salt is generally used when pavement temperatures measure 15 degrees Fahrenheit or above; at lower temperatures, VTrans uses sand “when necessary for temporary traction.”