• Big snow melt events may lead to chloride spikes.
• Roughly 56% of chloride entering Michigan waters annually comes from road salt.
• High chloride levels can be detrimental to macroinvertebrates and fish.
All the melty weather lately creates more than just piles of slush. It also releases road salts that are locked up in snow banks and flushes them into our freshwater.
That’s bad news for freshwater ecosystems. Elevated chloride levels are toxic to macroinvertebrates, which recycle nutrients and make up the base of freshwater food chains, plus fish, plants and amphibians.
In Michigan, most chloride pollution comes from road salt, but also from industrial agriculture, wastewater and residential water softening agents.
But recent research in northern Michigan shows chloride pollution doesn’t affect all watersheds equally. One study led by The Watershed Center Grand Traverse Bay just wrapped up a year of testing in the Elk River Chain of Lakes in Antrim and Kalkaska Counties – the biggest subwatershed of Grand Traverse Bay.
Heather Smith, who helped coordinate the research, says what they found surprised them.
“We don’t see chloride as a big issue, at least not now in the stream sites that we monitored,” she said.
Smith says chloride levels and conductivity (a measure of water salinity) were lower than expected — much lower than state standards and nearby watersheds, like Kids Creek in Traverse City.
She says that’s likely because the Elk River Chain of Lakes sample sites are more rural; there are far fewer impervious surfaces like parking lots and roads to de-ice in the area.
The study also looked at chloride and conductivity following “trigger events” like big melts like the one we’re experiencing now.
“We anticipated that we would see a significant difference during our trigger event monitoring … versus our routine monthly monitoring,” said Smith.
But that wasn’t the case.
Most of the data in the study was collected by volunteers, and Smith says it was a pilot project to test the viability of conducting other, similar research in the region.
The Elk River project was spurred on by ongoing sampling in Kids Creek in Traverse City, which showed alarmingly high chloride levels, particularly in winter months and after trigger events.
“The amount of the impervious surface upstream in the Kids Creek watershed is just immense: lots of parking lots, lots of road crossings,” said Smith. “But we’re not seeing that detrimental urbanization effect … in the Elk River Chain of Lakes watershed.”
Smith says The Watershed Center might work on sampling another, more urban water body next, like Mitchell Creek watershed.
She says it’s part of a broader push to better gauge chloride levels. The state department of Environment, Great Lakes, and Energy only developed numeric standards for the pollutant in 2019. The Kids Creek research is part of a monitoring program looking at about 250 streams statewide.
“Within the last decade or so there has been a lot of a lot more attention on this increased salinization of our freshwater,” said Smith. “Knowledge is power, and sometimes you just need to get out there and assess what the conditions are.”
