Simply Science: cleaning Powderhorn Lake with barley straw

MINNEAPOLIS, Minn. -- Powderhorn Lake has had an algae problem for decades.

That's where Steve McComas with Blue Water Science comes in.Working with the Minneapolis Park District, McComas stakes bags of barley straw throughout the lake.

Without adding nutrients that feed algae, the barley straw feeds the lake's microorganisms. These microorganisms are key in clearing up the water.

"They're using the organic carbon in the straw, but there aren't enough other nutrients like phosphorous," explains McComas. "So they're taking phosphorous out of the water. And in fact, as they grow then, they're taking out so much phosphorous, or enough phosphorous, that the concentration in the whole lake decreases."

It's phosphorous that feeds algae. When all the barley straw is gone, the bags are removed from the lake.

"When you're done, there's nothing left in the water. And the barley straw decomposes to about zero," says McComas.

The algae still grows with the barley straw in the lake, just not as abundantly. As a result, the water clears up and more sunshine penetrates the water's surface, promoting native aquatic plants to grow on the lake bottom. That's another key step in the process.

"Those rooted aquatic plants can help sustain good water clarity. And someday we can stop using the barley straw," says McComas.

The whole process is a natural way to clear the lake without using chemical algaecides, which can be toxic to fish and plants.
The barley straw treatment began in 2004, when it was difficult to see even a foot below the water's surface. Today, we can see down more than five feet, and even to the bottom in many locations.


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