Inland lakes with cyanobacteria should pay more attention to nitrogen levels
The same toxic bacterial blooms that shut down Toledo's drinking water system are a problem in Michigan's inland lakes too. New research suggests treating and preventing them may take a more comprehensive approach than is currently used for most inland lakes.
The Michigan Department of Environmental Quality does track harmful algal blooms when they get reports from the public or local governments, but there isn’t an exact count on how many lakes might have a cyanobacteria bloom.
“It’s certainly not rare,” said Alan Steinman, director of the Annis Water Resource Institute at Grand Valley State University, which is conducting the research.
Steinman has been studying the toxic cyanobacteria blooms on Spring Lake in Ottawa County for years. Most of his work has focused on the nutrient phosphorous, the main culprit in the toxic cyanobacteria blooms. But new research from the institute is looking how nitrogen, another nutrient, might be contributing to the nutrient-rich environment that helps the bacteria thrive. Scientists studying Lake Erie have also turned recently their attention to the role of nitrogen plays in toxic cyanobacteria blooms.
Both phosphorous and nitrogen can make their way to the lakes through runoff from farms or developed land. In many smaller inland lakes, Steinman says, old septic systems are partly to blame. He says the systems were built for small lakefront cottages.
"And now they're tearing down these cottages, they're putting up large homes, and the septic systems haven't changed, and they can't handle that amount of nutrients,” Steinman said.
Steinman says that Spring Lake had been dealing with toxic bacteria blooms starting in the late 1990s. He and his team figured out that it wasn’t just phosphorous coming into the lake from outside sources that was causing the them. A significant portion of the phosphorous was actually coming from the sediment at the bottom of the lake, so-called “legacy phosphorous.”
They found that applying an aluminum sulfate treatment to the sediment stopped the phosphorous from leaching from the sediment into the water. That meant that there was less phosphorous for the cyanobacteria to feed on, which helped cut down significantly on the lake’s blooms.
But aluminum sulfate isn’t an effective treatment for nitrogen. So while Steinman says that reducing phosphorous is still the first priority when it comes to preventing cyanobacteria blooms, he says people who manage lake water quality should take nitrogen into account as well.
But remediation isn’t going to solve the problem of toxic algal blooms, not to mention its incredibly expensive. Treating just half of Spring Lake with aluminum sulfate in 2005 cost $1.1 million.
“You’re treating the symptom and not the disease, and therefore this is not the long-term solution,” he said.
Ultimately, Steinman says, the best medicine is prevention and so preventing phosphorous and nitrogen from reaching lakes in the first place is the only way to solve the problem of toxic cyanobacteria blooms.