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Modified APEX model for Simulating Macropore Phosphorus Contributions to Tile Drains
Author(s) -
Ford William I.,
King Kevin W.,
Williams Mark R.,
Confesor Remegio B.
Publication year - 2017
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2016.06.0218
Subject(s) - macropore , tile drainage , tile , environmental science , hydrology (agriculture) , apex (geometry) , soil science , geology , chemistry , soil water , geotechnical engineering , materials science , botany , biology , composite material , mesoporous material , biochemistry , catalysis
The contribution of macropore flow to phosphorus (P) loadings in tile‐drained agricultural landscapes remains poorly understood at the field scale, despite the recognized deleterious impacts of contaminant transport via macropore pathways. A new subroutine that couples existing matrix‐excess and matrix‐desiccation macropore flow theory and a modified P routine is implemented in the Agricultural Policy Environmental eXtender (APEX) model. The original and modified formulation were applied and evaluated for a case study in a poorly drained field in Western Ohio with 31 months of surface and subsurface monitoring data. Results highlighted that a macropore subroutine in APEX improved edge‐of‐field discharge calibration and validation for both tile and total discharge from satisfactory and good, respectively, to very good and improved dissolved reactive P load calibration and validation statistics for tile P loads from unsatisfactory to very good. Output from the calibrated macropore simulations suggested median annual matrix‐desiccation macropore flow contributions of 48% and P load contributions of 43%, with the majority of loading occurring in winter and spring. While somewhat counterintuitive, the prominence of matrix‐desiccation macropore flow during seasons with less cracking reflects the importance of coupled development of macropore pathways and adequate supply of the macropore flow source. The innovative features of the model allow for assessments of annual macropore P contributions to tile drainage and has the potential to inform P site assessment tools. Core Ideas The field‐scale APEX model is modified to account for macropore P contributions. APEX modifications significantly improve hydrology and P simulations for a case study. Macropore flow contributes approximately 48% of flow and 43% of P annually. The model has potential for informing pathway partitioning in P site assessment tools.