This workbook implements the model described in the following report:

Walker, W. & R. Kadlec, '"A Model for Simulating Phosphorus Concentrations in Waters & Soils Downstream of Everglades Stormwater Treatment Areas", prepared for US Dept of the Interior, August 1996.

This report can be downloaded from the EPGM website: http://www.wwwalker.net/epgm

The model is further described in the following publication:

Kadlec, R.H. & W. W. Walker, "Management Models to Evaluate Phosphorus Impacts on Wetlands", in Phosphorus Biogeochemistry in Subtropical Ecosystems, K.R. Reddy, G.A. O'Connor, C.L. Schelske, eds, Lewis Publishers, pp. 621-642, 1999.

The original model was coded in Lotus-123 and has been converted to Microsoft Excel 2003,with a few minor modifications & enhancements. The translated code may work with earlier versions of Excel.

The model is now more than 7 years old and is based primarily upon data collected in the early 1990's along the phosphorus gradient in WCA-2A. Substantial additional data collected since then in WCA-2A and other locations indicate a need to recalibrate the model and potentially revise its structure. Recent data suggest, for example, that the relationship between cattail density and soil P needs recalibration and that actual soil P thresholds for biological impacts are probably lower than reflected in the original calibrations. There are also issues relating to interpretation of and potential anomalies in the historical soil P calibration data attributed to variations in soil core collection method and definition of the soil/water interface (inclusion vs. exclusion of floc layer). There are also indications in the recent data of biologically-mediated vertical transport and/or mixing that are not reflected in the current model structure.

Generally, the above limitations have greater potential influences on soil P and cattail simulations, as compared with the water column P simulations, which are essentially identical to those provided by the steady-state STA design model. http://www.wwwalker.net/pdf/stadesign.pdf

Phosphorus settling rates higher than 10 m/yr may be appropriate for open-water sloughs or periphyton-dominated areas.

As described in the original documentation, the model is designed to simulate marsh enrichment (responses to increasing P load), not recovery (responses to decreasing in load).

EPGM will be recalibrated and revised to provide recovery simulations under the long-term DMSTA/EPGM workplan being conducted for the U.S. Department of the Interior. It is likely that a revised version of EPGM will be incorporated into DMSTA (Dynamic Model for Stormwater Treatment Areas) http://www.wwwalker.net/dmsta

While we believe that the code correctly reflects the fundamental mass-balance concepts, equations, and assumptions described in the 1996 report, it may not provide the most accurate forecasts potentially derivable using this type of model and all data currently available. We do not encourage use of the model (particularly, the soil P & cattail components) until it has been further evaluated. Users of this version do so at their own risk.

The sample input cases provided ("Inputs" Sheet) are identical to those described in the above referenced report.Additional data are now available for defining the initial conditions for these cases.

The option to specify time-variable settling rates in the first few years of the simulation is not provided. We no longer support this concept, at least as it was implemented in the 1997 version of the model.

This version evaluates soil P profiles relative to the criterion adopted by the FDEP in the EFA phosphorus rule (500 mg/kg). This criterion applies only to a 10 cm soil depth. The steady-state solution of EPGM's soil P model predicts that soil P will exceed 500 ppb in areas with water column concentrations exceeding ~ 3 ppb (see Figure 9 of the model development report). While this may be an accurate forecast, it is subject to the limitations of the EPGM calibration discussed above and to uncertainty in the derivation of FDEP's criterion. The inconsistency between FDEP's criterion and the 1990-1991 WCA-2A soil P data has been pointed out in the phosphorus criterion rule development proceedings. EPGM predicts that it would take ~50 years (~2013) for the -10 cm soil P gradient between 0 and 10 km south of the S10s to reach steady-state if loadings continued at historical levels. If the calibration is accurate, the criterion was derived during a period when the soil P levels were not at steady-state.

Animated output graphs are provided, allowing the user to view the simulated gradients as a series of snapshots over time (1 second = 1 year). This output can be viewed by selecting the 'Graphs_Profile' tab and clicking the 'Animate' button on the EPGM toolbar. Press 'Esc' to stop the simulation at any point. Development of the soil P gradient in WCA-2A is illustrated by animating the "S10s, 0-10 cm" case.

The program is operated from the menu sheet and/or EPGM toolbar at the top of the screen

Press Ctrl-m or click the 'EPGM Menu' button on the toolbar to return to the menu from any worksheet.

User input cells are in red. All other cells are formulas and should not be modified.

9/4/2004