The lake appears to be returning to health after a battle with dangerous phosphorous levels, but low water levels present other threats.
Tony Groves, a water quality specialist for Grand Rapids-based Progressive AE, said the $1.2 million alum treatment that was applied to the lake bottom in 2005 appears to still be effective.
Alum is designed to seal phosphorous into the lake bottom and prevent it from escaping into the water column.
The treatment was funded through part of a $2.2 million lake property assessment launched in 2005 that spans 10 years. The rest of the assessment revenue is being used to pay for ongoing water samples, invasive plant growth control and public education.
Groves said phosphorous control was the key element that fast-tracked the lake back to health. High levels of phosphorous upset the ecosystem, and lead to algae blooms and lack of oxygen for fish and other water wildlife — both of which were prevalent in Spring Lake prior to the alum treatment.
“We're seeing all sorts of good things,” Groves said of the recent tests, which showed more than a 50 percent drop in phosphorous levels since the application.
Numbers have dropped from an average of 73 to 30 parts per billion from the surface down to the lake bottom in as many as seven Spring Lake sampling locations, according to Groves.
But there are still dangerous chemicals flowing into the water from lawns and impervious surfaces such as parking lots, according to Al Steinman, director of Grand Valley State University's Annis Water Resources Institute.
“I think the numbers certainly have improved since the alum treatment, but we still have a ways to go,” Steinman said. “The phosphorous levels are higher than what they have been historically because of human activity.”
Ideally, the lake's phosphorus levels would be about 10 parts per billion less — or 20 parts per billion — than they are as a long-term average. Steinman said the current numbers are likely due to continued inflow from human development, including stormwater runoff.
About four years ago, Steinman conducted a study called “Rein in the Runoff.” It included possible solutions with cost/benefit analysis.
Steinman's study is available online. To see it, click here.
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