Developing design criteria to test a new saturated waterway conservation practice
Grassed waterways planted in upland drainageways are a common conservation practice to slow rainfall runoff and reduce soil erosion from agricultural fields. Less recognized is that the subsurface materials in these lowland areas are often filled with organic-rich deposits that could serve as natural bioreactors for reducing nitrate concentration in groundwater and tile drainage. Previous work funded by the INRC documented that grass waterway locations at an eastern Iowa site contained soil and biogeochemical conditions conducive for denitrification to occur, and nitrate concentrations in waterway groundwater were 70% lower than observed in groundwater beneath cropped fields.
In this new study, subsurface soil and groundwater conditions will be characterized across a wider range of waterway sites in Iowa and a hydrologic model will be developed to test the potential for development of a new conservation practice that utilizes the waterway deposits for nutrient reduction. The proposed practice would alter drainageway tiles to reconnect upland groundwater to the organic-rich drainageway deposits for nitrate reduction as saturated buffers do in riparian zones.
Up to 30 different waterway sites will be investigated by Schilling and his team at the University of Iowa and information from the field investigation will be used by Arenas at Iowa State University to model the performance of a new saturated waterway practice under a wide range of geologic and hydrologic conditions. At the conclusion of the project, the design for a new grass waterway practice will be developed that could be installed and tested at an appropriate site.
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
Analyzing soil samples collected at 22 waterway locations for particle size and TN and TC. Developing Hydrogeosphere model to test design criteria for waterways (Arenas lead).
Presentation on project at SWCS meeting in Des Moines on August 8, 2023 (abstract attached).
During the initial project period, a project planning meeting was held where it was decided to focus study sites on Iowa State University research farms. During the fall of 2021, researchers Schilling and Streeter visited multiple potential sites. In all, eight sites were selected on ISU research farms across Iowa. Three non-ISU sites were also selected. In early April of 2022, the project team installed 22 shallow monitoring wells across the set of selected sites. At approximately 50% of the locations (where truck access was possible), continuous soil cores were collected using a Giddings soil sampler. Soil samples were also collected from each representative zone for lab analyses. Soil samples were analyzed for soil particle size (texture) and Total Nitrogen and Carbon. Following well installation, all wells were purged by overpumping with a Waterra and sampled for groundwater quality parameters.
During the initial project period, a project planning meeting occurred. It was decided to target Iowa State University research farms for project study sites since there is a strong working relationship between ISU and the Iowa Geological Survey and ISU farms are spatially dispersed across Iowa. During fall 2021, researchers visited multiple potential sites. In all, eight sites were selected on ISU research farms across Iowa. Two non-ISU sites were also selected.
In the spring, shallow monitoring wells will be installed, and waterway stratigraphy will be characterized at each of the selected study sites.