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Research Project: MANAGING AGRICULTURAL WATER QUALITY IN FIELDS AND WATERSHEDS: NEW PRACTICES AND TECHNOLOGIES

Location: Agroecosystems Management Research

Title: Agricultural conservation planning framework: 1. Developing multi-practice watershed planning scenarios and assessing nutrient reduction potential

Author
item Tomer, Mark
item Porter, Sarah
item Boomer, Kathleen - Nature Conservancy
item James, David
item Helmers, Matthew - Iowa State University
item Isenhart, Thomas - Iowa State University
item Mclellan, Ellen - Environmental Defense

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2015
Publication Date: 4/27/2015
Publication URL: http://handle.nal.usda.gov/10113/60765
Citation: Tomer, M.D., Porter, S.A., Boomer, K.M., James, D.E., Helmers, M.J., Isenhart, T.M., McLellan, E. 2015. Agricultural conservation planning framework: 1. Developing multi-practice watershed planning scenarios and assessing nutrient reduction potential. Journal of Environmental Quality. 44:754-767.

Interpretive Summary: The need to develop and implement watershed improvement plans is becoming more pressing as continental-scale water quality issues in the Great Lakes and Gulf of Mexico continue to become more acute. This paper reports on a new aid for watershed planning, the Agricultural Conservation Planning Framework (ACPF), that only requires data inputs that are becoming widely available. In particular, the availability of Light Detection and Ranging (LiDAR) survey data makes it possible to map watershed topography with high resolution. The ACPF leverages this capability, and comprises a series of spatial mapping algorithms that provide candidate locations to place a variety of conservation practices throughout a watershed. These results provide an inventory of conservation opportunities that conveys no planning prescription, but can be used to develop watershed plans at the local level. In two watersheds in differing landform regions, we show how the results can be used to identify and compare planning alternatives in terms of potential nutrient reduction, using only the input spatial data and a spreadsheet approach. In both watersheds we identified planning alternatives with potential to achieve a 40% N reduction while taking less than 5% of the watersheds' croplands from production. The tools used to develop the conservation opportunities inventory will be made available, with a user's guide, for download to assist local planning efforts in headwater watersheds of the Midwest. This information and the downloadable ACPF spatial analysis tools will be of interest to agricultural and conservation groups, agricultural engineers, rural sociologists, farmers, and watershed planners and modelers.

Technical Abstract: We show that spatial data on soils, land use, and high-resolution topography, combined with knowledge of conservation practice effectiveness, can be leveraged to identify and assess alternatives to reduce nutrient discharge from small (HUC12) agricultural watersheds. Databases comprising soil attributes, agricultural land use, and LiDAR-derived digital elevation models were developed for two Midwestern HUC12 watersheds: Iowa’s Beaver Creek watershed has an older dissected glacial landscape, and Lime Creek in Illinois has recent, poorly dissected, glacial deposits. Subsurface (tile) drainage is common in both watersheds. We applied a recently published framework to identify locations for conservation practices in both watersheds, including in-field practices (e.g., grassed waterways), edge of field practices (e.g., nutrient-removal wetlands, saturated buffers), and practices that address tile drainage (e.g., drainage-water management), by applying terrain analyses, geographic criteria, and cross-classifications to field- and watershed- scale geographic data. Planning scenarios were developed from the results, including cover crops assigned to fields randomly, without geographic prioritization. To assess nutrient reduction potential of the scenarios, a spreadsheet approach was used to calculate the average nutrient-removal efficiency required among the practices included in each scenario in order to achieve a targeted percent nutrient reduction goal. Results were evaluated in the context of the Iowa Nutrient Reduction Strategy. In both watersheds, planning scenarios were identified with potential to achieve a 40% nitrate-N reduction, while removing <5% of cropland from production. Cover crops and nutrient removal wetlands were common to these scenarios in both watersheds. This approach provides an interim technology to assist watershed planning wherever local staff have intermediate GIS skills. In a research context, planning scenarios could be evaluated and further developed using watershed simulation models. A set of ArcGIS tools and a user’s guide were written to enable transfer of this mapping technology to others; a website for download is provided.