A study by a Dartmouth College
graduate student and 14 collaborators from throughout North America found that
44 percent of the 371 lakes analyzed had “undergone long-term salinization” as
a result of salt run-off from roads, driveways and parking lots.
Flora Krivak-Tetley said that 26 of
the lakes had salt concentrations over 100 milligrams per liter, more than five
times that of rain water. “Salt at high levels like that starts to be directly
toxic to large lake organisms like fish and amphibians,” she said. “For the
most part, our lakes here in New England are below that level and aquatic life
can handle it.”
But 14 of the lakes in the study are
predicted to increase to levels above the Environmental Protection Agency
criterion that places aquatic life at risk.
“Our big question, though, is what
happens at lower salt concentrations, those between 20 and 100 milligrams per
liter and slowly rising over time,” Krivak-Tetley said. “Phytoplankton and
zooplankton communities might not be directly killed, but it may cause shifts
in community composition.”
She said that smaller organisms can
lose their ability to compete against others for resources in high salt
environments. And because many of the less common native species tend to be
intolerant of salty conditions, she believes that increasing salt
concentrations could lead to a loss of biodiversity.
In a research paper published in the Proceedings of the National Academy ofthe Sciences, Krivak-Tetley and her colleagues found that the primary
drivers of increased salt in lakes was a high density of roads and parking lots
around the water bodies.
“Impervious surfaces around lakes
puts them at risk,” she said. “Even as little as one percent impervious surface
correlated to rising salinity. That may seem like a small number, but a small
amount of development around a lake and the use of salt in that area is having
an impact on most lakes.”
The good news, she said, is that
most of the lakes studied in the Northeast, especially those in the Adirondack
region and in Vermont and New Hampshire, are not in highly developed areas,
especially compared to those in the urbanized Midwest.
“It’s nice to see that we have a lot
of lake systems that are really healthy in our area, and even some of those
that are increasing in salt concentration are still pretty low,” Krivak-Tetley
said. “So if we make a point of good management and limit development around
our lakes, or if homeowners around the lakes don’t over-salt their driveways,
then that can make a difference and help keep our ecosystems in good shape.”
This article first appeared in the winter 2018 edition of Northern Woodlands magazine.
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