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What Are the Recommended Phosphorus Reduction Targets?

Western Basin: Modeling showed that spring loading of phosphorus from the Maumee River is the determining factor in the production of cyanobacteria in the open waters of the Western Basin of Lake Erie. The GLWQA Nutrients Annex Subcommittee found that to achieve 2012 conditions in the Western Basin in nine out of 10 years, there should be a reduction of 40 percent in spring loads of both total and dissolved phosphorus from the Maumee River. A 40 percent reduction to the Maumee equates to a target spring load of 860 metric tons per year of total phosphorus and 186 metric tons per year of soluble reactive phosphorus under high spring discharge conditions. The GLWQA Nutrients Annex Subcommittee has defined spring as the period between March 1 and July 31 each year.

Central Basin: Modeling showed that phosphorus concentrations in the Central Basin of Lake Erie are the result of loadings from sources discharging to both the Western Basin, including those along the Huron-Erie corridor, and the Central Basin. To achieve a minimum concentration of dissolved oxygen of 2 mg/L in the bottom waters of the Central Basin, there should be a reduction in the load of total annual phosphorus to the Western and Central Basins to 6,000 metric tons per year. This is a 40 percent reduction from the 2008 load.

Eastern Basin: For the Eastern Basin, the work group has not recommended a target to address nuisance algae (Cladophora) at this time. Additional science is required to link phosphorus loadings to changes in algal production prior to recommending phosphorus reduction targets for this area of the Lake. Nonetheless, it is important to note the targets that have been recommended for the Western and Central Basins work in concert, not in isolation.  Because all tributaries to Lake Erie, including the Detroit River and the Huron-Erie Corridor, contribute phosphorus loads to the Eastern Basin, the reductions needed to address algal blooms and hypoxia will lower the phosphorus concentrations in the Eastern Basin as well. This will help address nuisance algal issues in the Eastern Basin, while maintaining enough nutrients to support the fisheries.

Nearshore Waters: In some nearshore areas, including river mouths and embayments,phosphorus loads from the watershed contribute to localized blooms of cyanobacteria. Reducing spring total and soluble reactive phosphorus loadings in these watersheds by 40 percent is expected to reduce localized blooms of cyanobacteria in those areas. The working group has identified the following watersheds where localized cyanobacteria blooms are a concern: in Canada, the Thames River and Leamington area watersheds; in the U.S., the Maumee River, River Raisin, Portage River, Toussaint Creek, Sandusky River and Huron River watersheds.  These watersheds are different from each other; as programs are implemented, and research and monitoring efforts increase knowledge and understanding of phosphorus movement in these tributaries and the nearshore, reductions less than or greater than 40 percent may be required in each of these watersheds to resolve the associated nearshore cyanobacteria blooms.

Map of Lake Erie Priority Watersheds. Created by U.S. Environmental Protection Agency.

Why Aren't Phosphorus Concentration Objectives Being Recommended?

The GLWQA Nutrients Annex Subcommittee has focused its recommendations on phosphorus loading reductions, not on phosphorus concentrations.

Phosphorus concentration objectives were established in the past for the Great Lakes. However, the GLWQA Nutrients Annex Subcommittee found that phosphorus concentrations in the nearshore and open waters vary considerably over space and time, making them very difficult to track in a meaningful way through monitoring programs.

As a consequence, the GLWQA Nutrients Annex Subcommittee is recommending that phosphorus concentration objectives not be established for Lake Erie at this time. However, the GLWQA Nutrients Annex Subcommittee has estimated the phosphorus concentrations expected to result from the recommended phosphorus load reductions:

Substance Objectives for Total Phosphorus Concentration in the Open Waters of Lake Erie (µg/L)
BasinInterim Objectives
Great Lakes Water Quality Agreement Annex 4, Section C
Expected Outcome from Implementation of Proposed Load Reduction Targets
Lake Erie (Western Basin)1512
Lake Erie (Central Basin)106
Lake Erie (Eastern Basin)106