Modeling phosphorus export from agricultural fields in the mid-Atlantic coastal plain: The FHANTM-MACP model (Delaware).

摘要

In southern Delaware's Inland Bays watershed, loss of phosphorus (P) from agricultural soils is a significant non-point source pollutant of surface waters. To control this pollution, it is necessary to identify areas that have a high risk for P export. Computer simulation models are one way to achieve this goal. The F&barbelow;ield H&barbelow;ydrologic and N&barbelow;utrient T&barbelow;ransport M&barbelow;odel, Version 2.0 (FHANTM 2.0), which was developed in Florida to simulate field-scale Pin the Lake Okeechobee watershed, was acquired for use in Delaware because the hydrology for which FHANTM 2.0 is applicable is similar in both states. However, it was necessary to modify the model's components for soil P processes to represent Delaware soils instead of Florida soils. First, The Revised Universal Soil Loss Equation (RUSLE) was incorporated into FHANTM 2.0 to predict sediment loss in runoff. Equations to calculate an enrichment ratio that accounts for P loss with eroded sediment were also incorporated. Other modifications included estimating the size of the labile P pool from routine soil test data, estimating the relationship between labile P in the soil and soluble P in solution, estimating a P availability index for inorganic P pools, and estimating soluble P concentrations in runoff.; Following these modifications, the revised FHANTM 2.0, FHANTM-MACP, was calibrated and verified against field data taken from a study conducted from 1995 to 1997 on a poultry-grain farm in southern Delaware's Inland Bays watershed. Two sets of field data were used to calibrate and verify the hydrology of FHANTM-MACP, depth to water table measured in monitoring wells and discharge of water in ditches. Estimates of P export made during the field study were also used to assess the ability of FHANTM-MACP to accurately simulate fieldscale P export. Results of the calibration and verification procedures showed that FHANTM-MACP could simulate hydrology with reasonable accuracy, and that P export in runoff, erosion, and drainage as simulated by FHANTM-MACP was in the range of P export values estimated during the field study. Although, it is clear that a field study designed specifically for the calibration and verification of FHANTM-MACP is still needed, FHANTM-MACP currently represents an important tool for simulating field-scale P export in southern Delaware and throughout the Mid-Atlantic Coastal Plain.