Journal
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION
Volume 53, Issue 6, Pages 1251-1266Publisher
WILEY
DOI: 10.1111/1752-1688.12569
Keywords
tile drainage; hydrology; nitrate export; SWAT; denitrification; soil nitrogen
Funding
- EPA's Initiative Enhancing State and Tribal Wetland Programs grant program [CD-97723301-0]
- Iowa Department of Agriculture and Land Stewardship
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Tile drainage significantly alters flow and nutrient pathways and reliable simulation at this scale is needed for effective planning of nutrient reduction strategies. The Soil and Water Assessment Tool (SWAT) has been widely utilized for prediction of flow and nutrient loads, but few applications have evaluated the model's ability to simulate pathway-specific flow components or nitrate-nitrogen (NO3-N) concentrations in tile-drained watersheds at the daily time step. The objectives of this study were to develop and calibrate SWAT models for small, tile-drained watersheds, evaluate model performance for simulation of flow components and NO3-N concentration at daily intervals, and evaluate simulated soil-nitrogen dynamics. Model evaluation revealed that it is possible to meet accepted performance criteria for simulation of monthly total flow, subsurface flow (SSF), and NO3-N loads while obtaining daily surface runoff (SURQ), SSF, and NO3-N concentrations that are not satisfactory. This limits model utility for simulating best management practices (BMPs) and compliance with water quality standards. Although SWAT simulates the soil N-cycle and most predicted fluxes were within ranges reported in agronomic studies, improvements to algorithms for soil-N processes are needed. Variability in N fluxes is extreme and better parameterization and constraint, through use of more detailed agronomic data, would also improve NO3-N simulation in SWAT. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.
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