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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #329880
Title: Multisite evaluation of APEX for water quality: 1. Best professional judgement parameterization

Author
item Baffaut, Claire
item NELSON, NATHAN - Kansas State University
item LORY, JOHN - University Of Missouri
item SENAVIRATNE, G.M.M.M. ANOMAA - University Of Missouri
item BHANDARI, AMMAR - Kansas State University
item UDAWATTA, RANJITH - University Of Missouri
item SWEENEY, DANIEL - Kansas State University
item HELMERS, MATT - Iowa State University
item VAN LIEW, MIKE - University Of Nebraska
item MALLARINO, ANTONIO - Iowa State University
item WORTMANN, CHARLES - University Of Nebraska

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2016
Publication Date: 4/13/2017
Citation: Baffaut, C., Nelson, N.O., Lory, J.A., Senaviratne, G., Bhandari, A.B., Udawatta, R.P., Sweeney, D.W., Helmers, M.J., Van Liew, M.W., Mallarino, A.P., Wortmann, C.S. 2017. Multisite evaluation of APEX for water quality: 1. Best professional judgement parameterization. Journal of Environmental Quality. doi: 10.2134/jeq2016.06.0226.

Interpretive Summary: The Agricultural and Policy Environmental Extender (APEX) is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of agricultural management practices. The program requires hundreds of input parameters that describe the field and control how processes are simulated. Current parameterization practice is to adjust some of these parameters based on the comparison of simulated flow and water quality with measured data, which requires resources and data that are not always available. The objective of this study was to compare annual simulated flow, sediment and phosphorus transport under two parameterization strategies: a best professional judgment (BPJ) parameterization based on readily available data and a fully calibrated parameterization based on site specific soil, weather, event flow and water quality data. The analysis was conducted using data from 12 sites at four different locations representing poorly drained soils and management systems covering row crop under different tillage systems. Although the BPJ model performance for flow was acceptable, calibration using site specific data improved it. Acceptable simulation of sediment and total phosphorus transport was obtained only after full calibration at each site. Given the unacceptable performance of the BPJ approach, uncalibrated use of APEX for planning or management purposes may be misleading; scientists and water resource managers should be aware that model calibration for water quality prior to APEX use for simulating sediment and total phosphorus loss is essential.

Technical Abstract: The Agricultural and Policy Environmental Extender (APEX) model is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of management practices. The current practice is to fully calibrate the model for each site simulation, a task that requires resources and data not always available. The objective of this study was to compare model performance for flow, sediment and phosphorus transport under two parameterization schemes: a best professional judgment (BPJ) parameterization based on readily available data and a fully calibrated parameterization based on site specific soil, weather, event flow and water quality data. The analysis was conducted using 12 datasets at four locations representing poorly drained soils and row crop production under different tillage systems. Model performance was based on the Nash-Sutcliffe efficiency (NSE), the coefficient of determination (r2) and the regression slope between simulated and measured annualized loads across all site years. Although the BPJ model performance for flow was acceptable (NSE = 0.7) at the annual time step, calibration improved it (NSE = 0.9). Acceptable simulation of sediment and total phosphorus transport (NSE = 0.5 and 0.9, respectively) was obtained only after full calibration at each site. Given the unacceptable performance of the BPJ approach, uncalibrated use of APEX for planning or management purposes may be misleading. Model calibration with water quality data prior to using APEX for simulating sediment and total phosphorus loss is essential.