Gabriel Johnson, a Ph.D. student co-majoring in Sustainable Agriculture and Agricultural and Biosystems Engineering at Iowa State, is a recipient of the 104(b) Program Grant (the Water Resources Research Act Program) for his project, “Stream Nitrate Load Monitoring for Watershed Scale Assessment of Edge-of-Field Practices.”

From Bettendorf, Iowa, Johnson was originally drawn to Iowa State for his undergraduate degree. He was interested in a variety of environmental, agricultural, and engineering fields and discovered that Iowa State’s Agricultural and Biosystems Engineering program was the best fit. Johnson went on to pursue a master’s degree at the University of Illinois, later taking the opportunity to work toward a Ph.D. at Iowa State through the Graduate Program in Sustainable Agriculture. This is an interdisciplinary degree program, which trains both natural and social scientists to integrate knowledge from across various disciplines to solve the complex challenges facing agriculture and food production.

“I went into this field because I have always been passionate about the natural world and protecting the environment,” Johnson said. “I’m also a passionate vegetable gardener, so I tied these interests together into a career trying to solve the big question, ‘how can we sustainably produce food and minimize negative impacts on the environment?’ Beyond that, as I progressed further into my studies, I’ve become even more fascinated by soil and water and their natural processes, such as nutrient cycling, flooding, stream morphology and others, that impact how we as humans use these natural resources.”



Johnson’s upcoming project will involve quantifying the nitrate load for a small watershed with near 100% treatment of tile drains with edge-of-field practices. The recent “Batch and Build” efforts in Polk County have resulted in very high implementation rates of saturated buffers and denitrifying bioreactors across the Alleman Creek Watershed. Johnson and his Ph.D. advisor, Dr. Tom Isenhart in the Department of Natural Resources Ecology and Management, currently monitor nitrate load reduction for three saturated buffers in this watershed.

For the upcoming project, they will be adding nitrate load monitoring of Alleman Creek to assess changes from the widespread implementation of edge-of-field practices throughout the watershed. They will measure stream flow and nitrate concentration of Alleman Creek to determine the annual mass of nitrate leaving the watershed. Their findings will provide empirical data to assess the effectiveness of edge-of-field practices at scale.

In simpler terms, the project aims to quantify water quality improvements from individual practices installed at a larger scale. In Iowa, and across much of the Midwest, there is a large amount of subsurface tile drainage – pipes installed below agricultural fields to drain excess water. These aid farming by helping fields dry out faster, allowing equipment to drive in the fields and protecting crops from being drowned. However, the systems also transport dissolved in the drainage water nutrients (nitrogen and phosphorus) directly to streams and rivers. This results in poor water quality both for human use (recreation and drinking water) and for the natural ecosystems. Fortunately, there are various in-field and field-edge practices that can reduce nutrient loss. These practices are becoming more widespread, and now we can assess how well they work when installed across a small watershed.

Presently, the project is in the beginning stages. As part of their existing research, Johnson and Isenhart are monitoring three saturated buffers at the outlet of the watershed and collecting water samples in the stream to determine stream nitrate concentration. Later this summer, they will be installing stream flow monitoring equipment at the site to determine the total volume of water and mass nitrogen transported by the stream.

“I submitted this project because there was a unique opportunity to enhance my current research,” Johnson said. “In addition to improvements in individual practice effectiveness for saturated buffers and denitrifying bioreactors, we also need to assess performance when they are installed at scale across a watershed. The ‘Batch and Build’ construction provided by this opportunity at one of my existing sites, and I want to keep thinking about the bigger picture. This award will help me achieve my project goals because it provides funding for supplies and equipment and additional transportation to the site. Our end goal is to improve water quality in Iowa, and I wanted to start measuring progress at a large scale.”

Johnson hopes to provide valuable data to the water quality efforts in Iowa and around the Midwest upon the completion of his project. He also looks forward to continuing to grow his network with water quality professionals in the state.