Nutrient Runoff in a Livestock-Dense Watershed: A Case Study of the Grand Lake St. Marys Watershed


Stream Restoration at Mercer County Elks Golf Course, 2019

Grand Lake St. Marys (GLSM), located in Ohio, has experienced harmful algal blooms for decades.  In 2010, a massive algal bloom shut down the Lake for the entire summer season. In 2011, the GLSM watershed was declared “distressed,” requiring a new set of rules imposed upon livestock producers in the watershed. These rules required each farm that produced over 350 tons of solid manure or 100,000 gallons of liquid manure per year to create and maintain a nutrient management plan. There was also a winter manure application ban enacted, which prohibits manure application from December 15 to March 1 of each year. These rules still apply to the watershed today.

What Did We Do?

Coldwater Creek Treatment Wetlands, established 2016 (Photo Summer 2021)

An influx of federal and state funds was poured into the watershed to assist the approximately 135 farms with constructing additional manure storage and other best management practices to improve manure management. Over 130 manure storage structures, 80 feedlot covers, 15 waste treatment systems, 20 leachate collection systems and 5 mortality compost structures were built from 2011 through 2019.

KDS Separator Pilot (Swine Manure Solids), March 2018

Other local efforts to improve water quality in GLSM include the restoration and creation of new wetlands to treat stream flow prior to entering GLSM.  Since 2010, we have more than doubled the acreage of wetlands along the south side of the lake and have seen an incredible diversification of wildlife in the area. Additional best management practices have also been installed, such as stream restoration projects, saturated buffers, tile phosphorus filters, double cropping, cover crops and much more. Mercer County has also expended a considerable amount of effort to research manure nutrient recovery technologies throughout the last six years. Manure nutrient recovery is challenging due to cost; however, many technologies can achieve a 90+% recovery of phosphorus from manure.

What Have We Learned?

Long-term monitoring data is collected on two streams feeding GLSM, Chickasaw Creek (installed in 2008) and Coldwater Creek (installed in 2010). The data from Chickasaw Creek was used to determine the effects of the best management practices installed along with the effects of the winter manure application ban. The data showed a reduction of 10-40% of nitrogen and phosphorus because of these improved practices (Figure 1).

Figure 1.  Nutrient Reduction Trends Pre and Post Distressed Watershed (Pre-Condition 2008-2011; Post-Condition 2012-2016) Jacquemin, etal (2016).

Future Plans

Nutrient management planning is an ongoing effort in the Grand Lake St. Marys watershed and will continue as long as the watershed remains distressed. Research and collaboration continue on manure nutrient recovery and development and adoption of technologies. Monitoring of stream and effectiveness of treatment wetland will also continue to ensure that maintenance and management is conducted appropriately. Additional conservation projects, including wetlands, stream restoration and more are planned in the coming years.


Theresa A. Dirksen, PE, Mercer County, Ohio Agriculture & Natural Resources Director

Additional Information

Jacquemin, Stephen J., Johnson, Laura T., Dirksen, Theresa A., McGlinch, Greg. “Changes in Water Quality of Grand Lake St. Marys Watershed Following Implementation of a Distressed Watershed Rules Package.” Journal of Environmental Quality, January 12, 2018.

Jacquemin, Stephen J., McGlinch, Greg, Dirksen, Theresa, Clayton, Angela. “On the Potential for Saturated Buffers in Northwest Ohio to Remediate Nutrients from Agricultural Runoff.” PeerJ, April 12, 2020.

Link to wetland monitoring data summaries:


Dr. Stephen Jacquemin, Wright State University Lake Campus

Mercer Soil and Water Conservation District

Grand Lake St. Marys Restoration Commission


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