Model prediction of the effects of changing phosphorus loads on the Everglades protection area

Abstract

The Everglades Phosphorus and Hydrology (EPH) model was developed to simulate water movement and phosphorus transportin the Everglades Protection Area which is comprised of theEverglades National Park (ENP) and surrounding wetlands knownas the Water Conservation Areas (WCAs). Water flows from theEverglades Agricultural Area (EAA) through the WCAs intoEverglades National Park (ENP). The model is designed to represent the system as a series of cells in which water flowsfrom one cell to the next. The code allows for pumped inputsand pumped outputs of water as well as sorption and removal ofphosphorus through peat accretion. Model application involved dividing the system into twenty cellsrepresenting different segments of the WCAs. Inputs to each cellconsisted of water pumped from the EAA (where appropriate), flowfrom upgradient cells, and precipitation. Outputs included pumped outputs and flow out of each cell. Using data collectedby the South Florida Water Management District, the model wascalibrated by matching simulated and observed flows, water elevations, and phosphorus (P) concentrations for the period 1980–1988. The model was then validated for the 1988–1992 period using the same model parameters derived from the calibration process and comparing simulated and observed values.Reasonable agreement between simulated and observed values wasattained for both the calibration and validation periods. The calibrated and validated model was used to simulate the impacts on annual average total P concentrations in each cellresulting from the implementation of the management plan mandated by the Everglades Forever Act. This plan calls for the construction of six Stormwater Treatment Areas (STAs) to treat discharges from the EAA, hydrologic modifications of thesystem to promote sheet flow, and the implementation of BestManagement Practices to reduce P runoff from individual farms. In addition, the model was used to evaluate the impact of notbuilding one of the STAs (STA 3/4), and sensitivity analyseswere conducted to determine the effects of changing STA outletP concentrations throughout the system. Model results indicatethat phosphorus concentration reductions will occur in areas near EAA discharges in response to reductions in input P concentrations. However these measures will have little impacton phosphorus concentrations for 85% of the area of theWCAs and on the water entering Everglades National Park. The scenario analyses also indicate that phosphorus concentrationsthroughout most of the WCAs are similar with or without the construction of STA-3/4.