Wider is not necessarily better: Iowa State research seeks to optimize saturated buffer design

February 2, 2023

Andrea McEachran, a recent master’s student in civil engineering, samples water at a monitoring well at a saturated riparian buffer study site. Iowa State University photo.

AMES, Iowa – The latest on saturated riparian buffers and how to optimize their design is the focus of an Iowa Nutrient Research Center (INRC) water quality research seminar, set for Wednesday, Feb. 8, from 3:10-4 p.m. The free event is open to the public and will be held virtually and in person in 1306 Elings Hall on Iowa State University’s campus. Those wishing to participate virtually must register to attend.

A saturated riparian buffer (SRB) is an edge-of-field conservation practice that reduces nitrate export from agricultural lands. The SRB intercepts tile drainage and reroutes the flow through soils and vegetation that treat the water before it exits into an adjacent waterway.  

This innovative conservation practice, developed over the last decade with leadership from scientists at Iowa State and the USDA Agricultural Research Service, is rapidly gaining a foothold across the Midwest. The practice is relatively low-cost and long-lived, with minimal need for maintenance. It also offers multiple benefits, such as providing habitat for pollinators and wildlife.

Because SRBs are relatively new, questions remain about their optimal design. Based on the federal conservation practice standard approved for the practice in 2016, an SRB needs to be at least 30-feet wide to be eligible for conservation cost share. However, new research at Iowa State has found that with a few design tweaks, a narrower SRB could often be just as effective and would reduce the costs of implementation.

Chris Rehmann, associate professor of civil, construction and environmental engineering, and Tom Isenhart, professor of natural resource ecology and management, will present the Feb. 8 seminar.

Rehmann led the recent INRC-supported study looking at ways to improve the SRB design. His team evaluated saturated buffers at six sites around Iowa, analyzing the patterns of flow into, within and leaving the buffers. They also compared the buffers’ potential to improve water quality. Findings from the project were published in articles in the Journal of Environmental Quality in 2023 and 2020. Co-authors included Andrea McEachran, a masters student in civil engineering, who assisted with the project and graduated in 2020.

Their main takeaway: A wider buffer is not necessarily better.

Current versus optimal saturated riparian buffer (SRB) width for six study sites. Error bars on the optimal width result from an uncertainty analysis. The minimum buffer width specified by the current USDA NRCS conservation practice standard (Code 604) is 30 feet, or 9.1 meters (2016). Iowa State University image, courtesy of Chris Rehmann and Andrea McEachran.  

As expected, they confirmed that a larger width allows for a longer residence time for tile drainage flowing into the buffer. This increases the opportunity to remove a higher concentration of nitrate from the water. However, they found that narrower buffers can be just as effective (or more) at treating the overall load of water and nitrate, depending on the slope of the buffer and the way it channels flow.  

“Refining knowledge of SRB function is an important step toward enhancing the design for improving water quality – and encouraging adoption,” Rehmann said. He has met with agency leaders to review SRB design standards in light of the project’s findings.

The current INRC water quality research seminar series highlights outcomes and impacts from a decade of INRC-supported projects, with two presenters on a related topic each month through spring 2023. Register to participate online or get more information on the INRC’s website.

Click here for recordings of past seminars. To learn more about SRBs, watch this INRC video with Tom Isenhart, one of the technology’s originators.

The Iowa Nutrient Research Center pursues science-based approaches to evaluating the performance of current and emerging nutrient management practices, providing recommendations on implementing the practices and developing new practices. Since 2013, the center has invested approximately $15 million in 127 nutrient-related water quality projects.

News Type: