Road salt can harm life in our rivers and lakes
Ever since the 1950s, Canada has been adding about five to seven million tonnes of salt annually to our roads, parking lots, driveways and other public areas. “That salt washes directly into our waterways, and has already started damaging entire aquatic communities,” worries Dr. Norman Yan, of Friends of the Muskoka Watershed.
The Canadian government standard for water considered safe for aquatic life is 120 milligrams of chloride per litre. (The amount of salt in our waters correlates with its chloride level because chloride is a part of every salt molecule, and all the chloride in our lakes is associated with sodium.)
Dr. Yan thinks that this standard is far too high. He has many studies and considerable data to
support his position.
First, he points out, the amount of salt in our waters is rising annually. The salt level, for instance, in the lower portions of eight large rivers in the Muskoka River Watershed (where people live and salt the roads), has increased steadily since 1983—almost doubling in below the watershed in one of the rivers studied.
Second, salt levels vary from lake to lake and river to river. The more people in an area, the more roads built for that area, and the more salt from those roads accumulates in its waters. As a result, densely populated lakes near roads that are salted annually already have far more salt in them than remote lakes.
Third, the official “safe” 120 per milligram per litre of chloride is not based on studies in actual lakes and rivers, where nutrients, water hardness, food sufficiency and weather can vary considerably. It is based on studies in aquariums under stable, controlled conditions.
Real Ontario lakes, in contrast, are home to eight species of Daphnia, a tiny water flea. While small, this animal plankton has a mighty effect on the health of our lakes. “Daphnia is the dominant animal plankton that keeps our lakes clean,” explains Yan. “All our lake water is filtered through the stomachs of Daphnia and her crustacean cousins, in other words animal plankton.”
Its survival rate varies, depending on the conditions in the water. Nutrition levels, for instance, go up and down in our lakes. Daphnia does well in lakes with sufficient nutrition. It normally also survives through low nutrition periods. But if salt levels are higher than 40 to 50 milligrams of chloride per liter—less than half the Canadian standard—Daphnia cannot survive. “Animals that are ‘starving’ are less able to survive a toxin,” explains Yan.
The threat isn’t just to a single species of animal plankton. Studies of lake bottom sediment
demonstrate that damage to 30-40 different species of tiny crustaceans started 70 years ago, when road salting first began.
Also, the percentage of salt in our waters is cumulative. More arrives after every fresh winter snowfall. And climate change is increasing the frequency of freeze-thaw cycles every year, which will only exacerbate this problem. With more freeze-thaw cycles, we will have more days every winter when we add salt to the roads. We will also experience more “lake effect snow”—snow blowing off all the lakes in November—which again increases the frequency we add salt to our roads.
We need to take steps to “halt the salt,” says Yan. He proposes dropping the guideline to a maximum of 10 milligrams per litre to protect all eight species of Daphnia and other vulnerable species in our lakes. “Right now only about 75 per cent of Muskoka lakes meet that standard,” he says.
He also recommends cutting down on the amount of salt we use on our roads, and replacing road salt with dirt. We should use winter tires and wear proper winter footwear, so less salt is needed, and companies don’t need to oversalt parking lots to keep their price of “slip and fall” insurance down.
Plus, we can ask our municipalities to step up, as some already have, and brine their roads to use less solid salt.
Thanks to Norman Yan, who shared his Friends of the Muskoka Watershed research at the Parry
Nature Club’s November 16 meeting. You can support Friends of the Muskoka Watershed’s “Halt the Salt” efforts and learn more about its activities on its website. Go to the Parry Sound Nature Club Facebook page to see his presentation.