Agencies wrestle with phosphorus controlby Sea Stachura, Minnesota Public Radio
It's summer, so the algae is starting to bloom. Algae can turn a pristine lake into a gummy mess. It feeds on phosphorus, commonly found in fertilizer. The Minnesota Pollution Control Agency wants to restrict how much phosphorus gets into watersheds. One major source it doesn't control is farmland and the fertilizer that washes off it.
Lake Byllesby, Minn. — Gunther Moesler has a retirement home on Lake Byllesby in Dakota County. Lake Byllesby is about three miles long, and it's fed by the Cannon River. The river meanders for miles through the farmlands of Steele, Le Sueur, and Rice Counties before reaching Byllesby.
Moesler steers his pontoon to the end of the lake. He's monitoring the water's clarity. He pulls out a black and white disc, dips it into the lake until it's only just visible, and then measures the depth.
"Today it's really pretty good it looks like. We have, one, two, three, four and half feet," he says. At the center of the lake its clarity is only two and a half feet. The sediment clouding up Byllesby contains phosphorus, and that eventually leads to algae blooms. Over 1,000 of Minnesota's lakes are impaired by problems related to phosphorus.
Blue-green algae is toxic. It has killed dogs and cattle. And as it grows and then dies the algae cuts off the oxygen supply for other aquatic life.
"By the time we get the other side it will probably be a foot and a half," Moesler says.
And in fact, it is. During most of the boating season Byllesby is covered in algae.
"The way it is right now, within a week or two of having wet, warm weather like we have, it will start turning into floating filament. And then into pretty thick filament of green, green slime," Moesler says.
Part of the problem with Lake Byllesby is its large watershed. In a typical watershed five or 10 acres of land feed an acre of lake. Lake Byllesby's watershed is 500 acres of land to one acre of lake. Most of the land is agricultural.
The Minnesota Pollution Control Agency has been working to control phosphorus output from residential storm sewers, and waste water treatment plants. The Legislature has limited phosphorous-based fertilizer in urban areas. The MPCA's Mississippi River Basin Coordinator Norman Senjem says it has made noticeable progress.
But Senjem admits: "We don't have a good handle run-off from agriculture."
Byllesby is part of the Cannon River Watershed. Most of the year storm sewers and waste water treatment contribute far less phosphorus to the watershed than agricultural land.
Senjem says usually when it rains about 75 percent of phosphorus in the Cannon comes from places like agricultural land and urban run-off. During a dry season, ag land contributes much less, but Senjem says climate change has meant that even a brief rainfall can erode soil off the land.
"You're getting an inch of rain in half an hour instead of over a 24 hour period, and that has a lot more erosive power in dislodging soil particles," Senjem says.
The MPCA says it's a major problem when topsoil, loaded with phosphorus-based fertilizer, runs off into Minnesota's ditches and streams. However, under state regulation the agency has no control over fertilizer application.
Instead, the Minnesota Department of Agriculture oversees commercial fertilizer. Most farmers use commercial fertilizer instead of manure.
The Ag department's Unit Supervisor for Fertilizer Management Bruce Montgomery says the ag department doesn't limit fertilizer application, or how farmers till their fields because each field has different needs. Heavy tillage can lead to more soil erosion. But Montgomery says he's not sure how any department could regulate erosion.
Still, if an industrial producer poured used oil down a sewer drain, that producer would be penalized. When asked why isn't that the case when a farmer's field pollutes a lake, Montgomery responds this way.
"Part of the problem is these cropping systems are so complicated, and the approach always has been hands off, we'll try to provide the best technical assistance, but it's always kept on a voluntary level," Montgomery explains.
If a farmer is interested in conservation state agencies offer advice, but farmers get paid for production. In the meantime the MPCA is looking at other strategies to reduce phosphorous in Minnesota's lakes.
- Morning Edition, 06/28/2007, 7:25 a.m.