Total Phosphorus Reductions in the Huron River 

The City of Ann Arbor is under a federal mandate to reduce phosphorus loading to the Huron River in order to meet water quality standards. Regular sampling of Huron River phosphorus levels by University of Michigan scientist Dr. John Lehman and a team of graduate students shows significant decreases in total phosphorus levels in 2008 and 2009 when compared to a pre-ordinance reference period.  Source: Huron River Phosphorus Study

In the graph above, total phosphorus measurements for 2008 and 2009 are expressed as percentages of the measurements collected during a 2003-2005 reference period. The measurements were collected at sample site B, an experimental site located on the Huron River downstream of Geddes Pond. This site drains 36 square miles of Ann Arbor.

The graph shows that for all months during the growing season (May-September), with the exception of September 2009, total phosphorus levels were below the measurements recorded during the reference period (i.e., below the 100% line). On average, TP reductions were 28% in 2008 and 17% in 2009. 

What is phosphorus?

Phosphorus (P) is a naturally occurring element that exists in minerals, soil, living organisms and water. In plants, phosphorus promotes healthy root development.

How does phosphorus affect the Huron River?

Too much phosphorus in lakes, streams, and reservoirs stimulates excess plant growth and may contribute to algal blooms. The excess growth and blooms create vegetative mats that block sunlight needed by other organisms and deplete the dissolved oxygen required by fish and other aquatic species for survival. Nuisance vegetation can also impair recreational uses, while certain types of algae can produce toxins that are harmful to humans and animals.

Excess phosphorus enters the Huron River from both point and non-point sources. Even though the Ann Arbor Waste Water Treatment Plant removes most of the phosphorus from treated water before discharging it into the river, it still accounts for 43% of Ann Arbor's phosphorus load. Non-point sources of phosphorus are soil and fertilizer run-off. Allen, Malletts, Millers, Swift Run, and Traver creeksheds all contribute high phosphorus loads to the Huron River in Ann Arbor.

Is the manufactured fertilizer ordinance helping reduce phosphorus levels in the Huron River?

Research supported by the city and performed by University of Michigan ecologist Dr. John Lehman and his graduate students is showing measurable reductions in phosphorus in the Huron River in the two years post-ordinance compared to a 2003-2005 reference period. The city is cautiously optimistic because these reductions are coincident with the City Council enactment of the phosphorus fertilizer ordinance. While this research does not demonstrate that the ordinance is the cause, the reductions appear to be real, on average 28% in 2008 and 17% in 2009. Other contributing factors to the observed reductions may be decreased construction activity in the Ann Arbor area, increased infiltration of rainwater resulting from stormwater infrastructure improvements, and greater environmental awareness by residents.

For more information

Ann Arbor Phosphorus Fertilizer Ordinance

Frequently Asked Questions about Phosphorus and Fertilizer (pdf)

Year 1 Progress Report (Summary Version - pdf)

Year 1 Progress Report (Detailed Version - pdf)

John Lehman's Huron River Study webpage