Dr. Norman Yan, PhD, FRSC
Chairman, Friends of the Muskoka Watershed
Friends of the Muskoka Watershed takes on the most widespread threats to our lakes that aren’t being adequately resolved, pointing the path forward to solutions. That is the basis of our ASHMuskoka project. We selected it because “ecological osteoporosis” (environmental calcium decline) was damaging almost half of our lakes.
So, other than climate change, what is the next most widespread anthropogenic threat to the health of our lakes? The answer may surprise you. I believe it is road salt, and its signature is the concentration of chloride in our lakes.
What is the evidence?
The graph below shows chloride levels rising over the last 35 years in Lake Muskoka. Chloride levels in remote undeveloped lakes in Muskoka are currently less than 1 mg/L, and they’d barely show on this graph. Chloride was first sampled in Lake Muskoka in 1983 downstream of Bala. At that time, levels were just under 3 mg/L, levels we can assume were typical of much of the lake. Since then, levels at four open water stations in the lake have risen to about 6 to 7 mg/L. Doing the arithmetic, the lake now holds about 15,000 tonnes of salt in its waters – 15,000 tonnes! While chloride levels have been pretty stable in the open waters of the lake over the last 20 years, they continue to rise in Gravenhurst Bay, indicating a rising local source.
Well. So what. Levels are now roughly 15 times above background in Gravenhurst Bay, but is this a problem? Recent work from Queen’s University scientists working with the FMW and MECP proves that it is. At levels of 5 to 40 mg/L of chloride, the death rates of 6 species of Muskoka water fleas increased and their production of offspring dramatically decreased. Daphnia and her cousins are the little living lawnmowers that help to keep our lakes clean by filtering the algae. Gravenhurst Bay has been the stage on which past pollution events have been played. In the 1960s phosphorus levels from municipal sewage were high enough that algal blooms were a common occurrence. If salt pollution is killing the water fleas that eat the algae, the risk of algal blooms is again on the horizon, this time not because of increased algal growth, but because of reduced grazing of algae by their predators – the animal plankton including Daphnia. Keep tuned to how the FMW plans to help confront this issue.
Data sources: MOE (1983 to 1995) and DMM (after 2000), thanks to Huaxia Yao, Andrew Paterson, and Rebecca Williston.