MIDDLETOWN, Wis. — Farming has been taking much of the blame for the amount of phosphorous – which causes harmful algal blooms – in bodies of water, but a new study by Dr. Dale Robertson claims the source of the problem depends on the area.

“The amount of phosphorous varies greatly by lake and especially by tributaries,” said Robertson, a research hydrologist with the U.S. Geological survey out of Wisconsin, whose research deals with the Great Lakes and bodies of water in the Midwest.

“If you go into something like the Maumee River Basin, it is still dominated by agriculture. If you go into some of the rivers that are draining, for instance, the city of Detroit, those are dominated by point sources. When you put it all together and when you look at the United States side of Lake Erie, it is about equal between agriculture and point sources like sewage treatment plants and such.

“In some ways, it is easier for a city to clean up, but more expensive,” Robertson added. “In agriculture, the techniques are out there to improve things ... Maybe it is a little easier for a point source to fix things, but it is expensive.”

Treatment plants right now are designed to get down to maybe 1 milligram of phosphorous per liter, Robertson said. Technology can push it down to about 71 milligrams per liter, but that is a major step and very expensive to do.

Once a total maximum daily load (TMDL) is established, municipalities often find it is cheaper to continue releasing phosphorous while paying someone else to reduce that share for them. The idea is, it is cheaper to reduce phosphorous levels on farmland than in a municipality – but that is not always the case, Robertson said.

The models say the reduction is possible, but many times when farmers actually implement all of the strategies, the loads don’t come down as much or as fast as expected.

“When farmers change their practices, studies show it takes longer than expected to reduce that load,” Robertson said. “The thing I have been catching from the people around Lake Erie is that the conclusion really varies by tributary.

“If you’re looking at the Maumee River and you start pointing your finger at point sources, it’s probably not the right finger to point – that land throughout the Maumee River basin is driven by agriculture. What we found is the dominant source of nutrients really varies by tributary.”