APEX model simulation of edge-of-field water quality benefits from upland buffers

Authors: Baffaut, Claire; SENAVIRATNE, ANOMAA - University Of Missouri; LORY, JOHN - University Of Missouri; UDAWATTA, RANJITH - University Of Missouri; NELSON, NATHAN - Kansas State University; WILLIAMS, JIMMEY - Texas A&M University; ANDERSON, STEPHEN - University Of Missouri

Submitted to: Annual International SWAT Conference
Publication Type: Abstract Only
Publication Acceptance Date: 3/29/2017
Publication Date: 6/28/2017
Citation: Baffaut, C., Senaviratne, A.G., Lory, J.A., Udawatta, R.P., Nelson, N.O., Williams, J.R., Anderson, S.H. 2017. APEX model simulation of edge-of-field water quality benefits from upland buffers [abstract]. Annual International SWAT Conference, June 28-30, 2017, Warsaw, Poland. p. 63.

Interpretive Summary:

Technical Abstract: For maximum usefulness, simulation models must be able to estimate the effectiveness of management practices not represented in the dataset used for model calibration. This study focuses on the ability of the Agricultural Policy Environmental eXtender (APEX) to simulate upland buffer effectiveness for reducing P export. The study used 16 years of monitoring data (1993-2008) from three field-scale row crop watersheds: upland agroforestry buffers (grass plus trees), grass buffers, and control (no buffers). The data were split into two datasets: prior and after buffer establishment in the fall of 1997. Objectives were to: i) calibrate and validate APEX on each dataset, ii) evaluate the performance of APEX on the dataset for which it was not calibrated and validated, and ii) compare estimated buffer effectiveness with that calculated from monitoring data. After modification of the APEX code to improve simulation of infiltration in the buffers, we successfully calibrated APEX for event runoff and total P using each dataset. The model based on the prior buffer dataset performed poorly once buffers were established. In contrast, the model developed for buffer conditions performed adequately for runoff and TP for a scenario with no buffers. Buffer effectiveness was similar when estimated using a paired watershed approach using monitoring data or values simulated with the model based on the buffer dataset. Effectiveness estimated with the model based on the prior buffer dataset was larger than expected. These results highlight potential problems using APEX to evaluate conservation practices not included in the calibration dataset.