The Huron River is looking much clearer thanks to a city ordinance enacted in 2006 that has led to a decrease in the accumulation of toxic and unsightly algae.

John Lehman, a professor of ecology and evolutionary biology, and a team of scientists proved that phosphorus levels in the Huron River have declined since Ann Arbor enacted an ordinance banning the use of all phosphorus-containing fertilizers in 2006. Their findings were published Aug. 14 in the journal Lake and Reservoir Management.

Phosphorus, nitrogen and potassium are three elements that are essential for agricultural production.
Lehman said that when people started commercializing fertilizers they would put all three elements into the product, thinking that would help plant growth. But this combination of elements became a detriment to the environment.

“If you are applying this fertilizer without any intention to what the soil chemistry is like, you may very well be over supplying one of those or two of those elements,” Lehman said. “You’re supplying something that isn’t needed.”
Lehman said the unnecessary use of phosphorus has caused an excessive growth of algae in waterways around the world.

“A lot of it is running off the landscape in part because there is an over application of fertilizers containing phosphorus to soils that don’t really need it,” he said.

He added the consequence is that “we’re creating environmental problems in our own backyard — fowling our own nest as we might say.”

An increase in phosphorus will stimulate the growth of algae on the surface of a river or lake. Some algae are poisonous and release toxic chemicals while others emit a fowl smell when they die.

Lehman said the algae create a nuisance for the public.

“Most people don’t really like their lakes full of soupy pond scum,” he said.

To reverse the damage, many municipalities have decided to enact laws banning the application of fertilizer with phosphorus.

But Lehman said there had been little or no scientific evidence proving that the laws have benefited the environment.
Last year, Lehman received a call from Matt Naud, Ann Arbor’s environmental coordinator, who asked him to detect if the ordinance had any effect on the phosphorus levels in the Huron River. Naud claimed that the phosphorus levels had dropped 22 percent but that he wanted Lehman to prove it.

Lehman agreed to do the research. Before starting, he performed statistical calculations that determined it would only take one or two years to witness a 25 percent reduction in the total amount of phosphorus present in the river.
Lehman and his team began taking samples once a week starting in May 2008.

“We didn’t really know what we would find, but we set up a sampling and measuring program of very strict quality control of the measurements,” he said. “By the end of the summer, we were seeing significant reductions in the total phosphorus at a couple of stations along the river.”

By last August, the scientists saw a 28-percent drop in phosphorus.

While the results were promising, Lehman conducted the study again this summer to try to reproduce the numbers.
“If the results from 2008 are confirmed and reproduced in 2009, we’re going to have even greater confidence in those results,” he said.

University alumn Kahli McDonald worked with Lehman to collect water and measure the phosphorus levels during the last two summers.

“We’re hoping to see that the phosphorus levels will either continue to go down or stay at the same level as last year,” she said.

Lehman said if the results are upheld, there is stronger evidence that the ordinances were directly related to the phosphorus level reductions and other cities may try to enact similar ordinances on fertilizers.

“If it turns out this actually has a beneficial effect in reducing phosphorus, maybe Ann Arbor (will) become a model for communities in the region,” he said.