Water quality in the United States (US) has improved after the ban on lawn fertilizers, indicates a new study with evidence.
In an effort to keep lakes and streams clean, municipalities in the US are banning or restricting the use of phosphorus-containing lawn fertilizers, which can kill fish and cause smelly algae blooms and other problems when the phosphorus washes out of the soil and into waterways.
"It's one of those things where political organizations take the action because they believe it's the environmentally conscious thing to do, but there's been no evidence offered in peer-reviewed literature that these ordinances actually have a salutary effect," said John Lehman, professor of ecology and evolutionary biology at the University of Michigan.
Now, such evidence exists in a study done by Lehman and students Douglas Bell and Kahli McDonald.
The study shows that phosphorus levels in the Huron River dropped an average of 28 percent after Ann Arbor adopted an ordinance in 2006 that curtailed the use of phosphorus on lawns.
Phosphorus is naturally plentiful in southeast Michigan soils, so fertilizing established lawns with the nutrient is generally unnecessary.
Using statistical models, Lehman and undergraduate student Julie Ferris figured out how much sampling would be required to confidently detect a 25 percent decrease in phosphorus concentrations.
"We came up with the result that for most of the river that runs through Ann Arbor, we should be able to detect a change of that magnitude by sampling once a week for one summer or two summers, depending on the sampling station," said Lehman.
"Right away, we started to see decreases," Lehman said.
After the first year of data collection, it was clear that phosphorus concentrations were lower after the ordinance was enacted than before.
Though that explanation seems likely, public education efforts and general increased environmental awareness among Ann Arbor residents also may have entered in.
At any rate, the study already has attracted the attention of the Southeast Michigan Council of Governments (SEMCOG), which invited Lehman to present the study results at a meeting earlier this year, and may well generate interest beyond Michigan's borders.