Skip to main content
ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #332801
Title: Multisite evaluation of APEX for water quality: II. Regional parameterization

Author
item NELSON, NATHAN - Kansas State University
item Baffaut, Claire
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 - Iowa State University
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: 10/2/2016
Publication Date: 3/30/2017
Citation: Nelson, N.O., Baffaut, C., 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: II. Regional parameterization. Journal of Environmental Quality. 56(5):2663-2674. doi: 10.2134/jeq2016.07.0254.

Interpretive Summary: Phosphorus (P) index assessment requires independent estimates of long-term average annual P loss from multiple locations, management practices, soils, and landscape positions. Because currently available measured data are insufficient, computer simulation models have been proposed as tools to generate the required data. However, these models have hundreds of input parameters that need to be specified. The objectives of this research were to develop a regional set of input parameters for the Agricultural Policy/Environmental eXtender (APEX) model to estimate edge-of-field runoff, sediment and P losses in restricted-layer soils of Iowa, Missouri, and Kansas and assess the resulting performance using monitoring data from multiple sites in this region. The regional set of parameters was developed from five parameter sets, each determined using one of five data sets at four locations within the region. The regional parameter set was then validated with seven additional datasets. Simulation of runoff with the regional parameter set was similar to that with the site-specific parameter sets. Simulation of sediment loss was very poor. This was influenced by generally low sediment loss that did not provide an adequate range of data to determine input parameter values. Simulation of total P loss with the regional parameter set was acceptable but lower than with the site-specific parameter sets. Runoff estimates with the regional parameter set were acceptable for P-index evaluation. Total P loss estimates should be used with caution due to poor simulation of sediment loss. These results give insight to modelers and conservation planners on the accuracy of APEX results when applied over a region.

Technical Abstract: Phosphorus (P) index assessment requires independent estimates of long-term average annual P loss from multiple locations, management practices, soils, and landscape positions. Because currently available measured data are insufficient, calibrated and validated process-based models have been proposed as tools to generate the required data. The objectives of this research were to develop a regional parameterization for the Agricultural Policy/Environmental eXtender (APEX) model to estimate edge-of-field runoff, sediment and P losses in restricted-layer soils of Iowa, Missouri, and Kansas and assess the performance of this parameterization using monitoring data from multiple sites in this region. Five site-specific calibrated models for four locations within the region were used to develop a regionally calibrated model, which was then validated with seven datasets. Performance of the regional model was similar to that of the site-specific calibrated models for runoff simulation and had Nash-Sutcliffe Efficiency (NSE) > 0.72 and absolute percent bias (|PBIAS|) < 18% for both calibration and validation. The regional model had very poor performance for simulation of sediment loss with NSE<0 and |PBIAS| >90%. This was influenced by generally low sediment loss that did not provide an adequate range of data to inform the model during calibration. The regional model had acceptable performance for simulation of total P loss (NSE>0.74; |PBIAS|<30%), but underperformed the site-specific calibrations. Runoff estimates with the regional model were acceptable for P-index evaluation. Total P loss estimates should be used with caution due to poor simulation of sediment loss.