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

The Everglades Phosphorus and Hydrology (EPH) model was developed to stimulate water movement and phosphorus transport in the Everglades Protection Area which is comprised of the Everglades National Park (ENP) and surrounding wetlands known as the Water Conservation Areas (WCAs). Water flows from the Everglades Agricultural Area (EAA) through the WCAs into Everglades National Park (ENP). The model is designed to represent the system as a series of cells in which water flows from one cell to the next. The code allows for pumped inputs and pumped outputs of water as well as sorption and removal of phosphorus through peat accretion. Model application involved dividing the system into twenty cells representing different segments of the WCAs. Inputs to each cell consisted of water pumped from the EAA (where appropriate), flow from upgradient cells, and precipitation. Outputs included pumped outputs and flow out of each cell. Using data collected by the South Florida Water Management District, the model was calibrated 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 was attained 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 cell resulting 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 the system to promote sheet flow, and the implementation of Best Management Practices to reduce P runoff from individual farms. In addition, the model was used to evaluate the impact of not building one of the STAs (STA 3/4), and sensitivity analyses were conducted to determine the effects of changing STA outlet P concentrations throughout the system. Model results indicate that phosphorus concentration reductions will occur in areas near EAA discharges in response to reductions in input P concentrations. However these measures will have little impact on phosphorus concentrations for 85% of the area of the WCAs and on the water entering Everglades National Park. The scenario analyses also indicate that phosphorus concentrations throughout most of the WCAs are similar with or without the construction of STA-3/4.