Phosphorus is the nutrient that most often stimulates excessive growth of aquatic plants, leading to a variety of problems known collectively as eutrophication. Elevated phosphorus levels are causing premature aging of many Michigan lakes.
In an attempt to address this problem, Michigan passed legislation several years ago that limited the phosphorus content of laundry detergents and more recently extended the ban to dishwater detergents. However, phosphorus in fertilizers remained a problem. Phosphorus is a key ingredient in many commercial lawn fertilizers and is commonly applied at rates well in excess of what is needed to maintain a healthy lawn. Excess phosphorus can run off into lakes and streams where a single pound of phosphorus can generate hundreds of pounds of aquatic vegetation.
With the passage of a new state law (PA 299 of 2010), Michigan has joined a number of other Great Lakes states in banning phosphorus in lawn fertilizers. The new law, which took effect on January 1, 2012, prohibits the application of lawn fertilizers containing phosphorus unless a new lawn is being established (and phosphorus is needed to promote root growth) or if a soil test indicates a soil phosphorus deficiency. The new law also regulates the application of lawn fertilizer near surface waters and prohibits lawn fertilizer applications on frozen ground or ground saturated with water.
Under the new law, fertilizer containing phosphorus can be applied on golf courses operated by staff members that have been certified by the Department of Agriculture as having completed training on best management practices for the proper use of phosphorus fertilizers. Agricultural fertilizer applications are exempt from regulation under the new law. Communities with existing phosphorus fertilizer regulations in effect prior to the enactment of the state mandate will be allowed to maintain their local regulations if they so choose. The state may impose civil or administrative fines on violators of the new law.
The Minnesota Experience
Minnesota was the first state to enact a phosphorus fertilizer law. Between 2002 and 2005, Minnesota phased in a state-wide phosphorus fertilizer ban similar to Michigan’s new law. In enacting the law, the Minnesota legislature required that research be conducted to evaluate the effectiveness of the fertilizer restrictions. The research culminated in a report entitled Effectiveness of the Minnesota Phosphorus Lawn Fertilizer Law. Report findings indicate the following:
Water Quality Benefits
It is anticipated Michigan’s fertilizer law will result in significant water quality benefits. While it will likely take many years to document water quality improvements in Michigan’s lakes and streams, a recent study conducted on the Huron River found that total phosphorus levels in the river dropped about 28% following a phosphorus fertilizer ban enacted by the City of Ann Arbor. In this report, it was noted that the phosphorus fertilizer ban was accompanied by a number of additional initiatives (such as programs to promote shoreline vegetative buffers) and it was not possible to single out the phosphorus fertilizer ban as the sole reason for the measured decline in river phosphorus levels. However, these initial results are encouraging.
One of the challenges in evaluating the impact of the new phosphorus law on water quality will be to design sampling protocols and programs that can differentiate between natural variability and actual trends in water quality. While additional studies over several years will be required to document the impact of Michigan’s phosphorus fertilizer law, the law is certainly a positive step toward protecting water quality.