Can vegetation “buffers” on farm fields effectively trap nutrients in the Maumee River watershed, limiting runoff that leads to harmful algal blooms? Researchers led by Dr. Kevin Czajkowski of The University of Toledo, funded by the Harmful Algal Bloom Research Initiative, recently investigated this issue.

Filter strips, also known as vegetative buffer zones, are often placed along the edges of agricultural fields to slow runoff, absorb nutrients, and improve water quality. However, prior projects and discussions with state agencies in Ohio suggest that these strips aren’t always efficient throughout the Maumee River watershed, resulting in a greater risk of nutrient loss or runoff from fields than assumed.

Water movement off of a field after a rain event doesn’t flow equally through all filter strips, but rather forms channels of concentrated water flow that can bypass the filtering process. This concentrated flow, often called preferential flow, needs to be evaluated, as filter strips are one of the best management practices promoted by the state’s H2Ohio program and are a tool farmers are comfortable utilizing as a nutrient reduction strategy.

Based on this concern Czajkowski’s team set out to evaluate the nutrient trapping capacity of these filter strips within the watershed. The goal was to identify locations where nutrient trapping can be improved on agricultural fields, and to explore opportunities to install new filtering practices to intercept agricultural runoff as it travels downstream.

Through the project, the team used remote sensing data from multiple sources, including lidar and high-resolution imagery, to map and study filter strips. They also collected field data to confirm imagery and build a model that estimates how Ohio filter strips are being utilized.

Researchers were able to successfully create a dataset identifying drainage networks, vegetative buffer zones, points of concentrated flow, and other features across the entire Maumee watershed. Combining the results with prior research, they were able to map priority areas with strong potential to reduce nutrient losses, identifying sites that have the best “bang for the buck” in reducing runoff.

“I was amazed to see how many concentrated flow paths we were able to detect using lidar data,” said Czajkowski, adding that the paths are areas where water flows off a farm field into a ditch or stream. “It seemed like almost every buffer on farm fields had at least one or more concentrated flow path.”

Data from this project is supporting the refinement of hydrological models that track water and phosphorus movements at a higher resolution and are improving nutrient pollution monitoring and control. This work is also providing farmers with insight into nutrient runoff, helping them take steps to enhance best management practices.

Additionally, results will be able to help inform management decisions by local agencies, focusing on reducing nutrient release from less efficient nutrient-trapping buffer zones and developing more impactful filtration techniques. Several promising sites were found on land managed by the Ohio Department of Transportation where filtration systems could substantially lower nutrient release.

“This project is a start. I hope that it contributes to decisions made about how to reduce nutrient runoff in the Maumee River watershed,” Czajkowski added.

To learn more about this HABRI project, contact Czajkowski at kevin.czajkowski@utoledo.edu or watch his recent Freshwater Science Webinar.

Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.