Protecting the Waters:
The Issue of Phosphorous

Causes and sources
Problem extent
History
Efforts and progress
Looking to the future



Rain to Rivers Program

UWEX Natural Resources Education

 

A History of Monitoring, Research and Modeling


Research History

Work and research in the Red Cedar Basin focused on the issues of algal blooms and water quality have been ongoing for decades. As far back as 1972, the US EPA had determined that Tainter Lake was highly eutrophic - the nutrient-rich condition that promotes the growth of algae and cyanobacteria. From 1989 to 1990, WDNR collected monitoring data on the Red Cedar and Hay Rivers and in Tainter Lake to update phosphorus load estimates to the lake. A report on this work and on the modeling derived from it was issued in 1992, and recommended a comprehensive watershed management plan to address phosphorus sources in the watershed. More research was done in the 1990s, including a SWRRB (Simulator for Water Resources in Rural Basins) model which studied the transport and delivery of phosphorus in the Red Cedar Basin.

Total Maximum Daily Load (TMDL)
In 2001 WDNR began the process of writing a TMDL, or Total Maximum Daily Load, for Tainter Lake. A TMDL is a prescriptive document, usually based on monitoring, research and modeling, that describes the maximum amount of a pollutant a water body can receive and still meet water quality standards. Fourteen individuals representing lake groups, private interests, and state and local government were part of the work group focused on this task. The TMDL process was suspended for a period, then begun again, adding Lake Menomin as well. The TMDL makes recommendations for necessary phosphorus load reductions from both point sources (such as effluent pipes from waste water treatment plants), and non-point sources (such as agricultural fields). A comprehensive strategy for implementing such reductions is then necessary in order to reduce the frequency and intensity of algal blooms on these lakes and improve the overall water quality.

Until recently, the state had no water quality standards for phosphorus. These were finally established in 2010 and are now in place. Other indicators of water quality include chlorophyll-a concentrations (a pigment in algae), and the water's clarity, which is measured using a black and white disk (called a Secchi disk), lowered into the water to see how far down it will go before it is no longer visible.

The final TMDL for Tainter and Menomin Lakes was released in May of 2012, and approved by the US EPA in September 2012. The initial goal recommended by the TMDL was for a Basin-wide phosphorus load reduction of 45% from levels measured in 1990. Since the statewide phosphorus standard has been established, WDNR, in consultation with US EPA, has modified this goal. Currently, goals include a 65% reduction in non-point-source phosphorus loads upstream of Tainter Lake, and a 45% non-point-source phosphorus load reduction from the watershed contributing to Lake Menomin. Point sources are capped such that they never constitute more than 10% of the total annual load. To put things in perspective however, there will still need to be a reduction of several hundred thousand pounds of phosphorus flowing to Tainter and Menomin Lakes in order to reach these water quality goals.

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