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A.R.M. Loxahatchee National Wildlife Refuge
Enhanced Water Quality Monitoring and
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Canal Sediment and Water Quality Characterization
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Water Quality Modeling

In cooperation with the University of Louisiana-Lafayette, the Arthur R. Marshall Loxahatchee National Wildlife Refuge (Refuge) developed and applied a suite of hydrology and water quality models. The models were formulated with varying levels of spatial resolution. The water quality model with the least spatial resolution has three concentric marsh cells and a single canal cell; the highest spatial resolution model represents the marsh as 3,494 active computational cells. These models improve our quantitative understanding of mechanisms affecting timing and levels of water depth, and water quality throughout the Refuge canal and marsh. Each model has specific advantages and limitations. Professional judgment is essential in using any model. Version 1 of our simplest model was freely available for download in June 2007, and versions of all models are currently available upon request.

In 2010, we concluded our intensive model development efforts which have produced a suite of four hierarchical models predicting stage (water surface elevation) and water quality (chloride, sulfate, and total phosphorus). The modeling team completed responses to comments and incorporated suggestions provided by the Technical Advisory Panel in May 2009. Release of final model versions followed soon after these comments were addressed (Table 1).

Table 1. Summary and status of models.
MODEL Version / Status Canal Cells Marsh Cells Stage Water Qualitya
SRSMb 4.0 Complete 1 1 / 3c
9-Box 1.0 Complete 3 6
39-Box 1.0 Complete 11 28
Mike-Flood Hydrodynamic 2.0 Complete 269 3,494  
Mike-Flood Advection-Dispersion 2.0 Complete 269 3,494  

a Includes chloride, sulfate, and total phosphorus concentrations.
b SRSM is the Simple Refuge Screening Model.
c Aggregates marsh into a single cell for stage simulation, and 3 cells for water quality.

Background - At the July 24, 2003 TOC meeting, the committee forwarded recommendations to the Consent Decree principals that included an enhanced monitoring and modeling program for the Refuge. In FY04, Congress funded our modeling program which was implemented via a work plan (Brandt et al. 2004). A cooperative agreement was established with the University of Louisiana - Lafayette (Principal Investigator Dr. Ehab Meselhe), to provide model development and application. A separate cooperative agreement with Tennessee Tech University (Principal Investigator Dr. Vince Neary) provided for an independent Technical Advisory Panel. Although the Refuge's modeling project is broader than the 2003 TOC recommendations, it remains consistent with those recommendations.

Agency and public involvement - Prior to selecting the models for use, public meetings were announced to interested agency representatives and stakeholders, and to the TOC. Attendees included representatives from the South Florida Water Management District, Florida Department of Environment Protection, US Environmental Protection Agency, US Geological Survey, the Miccosukee Tribe, and members of the public. Later, in 2005, the Technical Advisory Panel first met in a public session.1 Again, attendees represented diverse agencies as well as the public. The panel held their third review and advisory meeting at the Refuge on May 11, 2009. The panel meeting again was open to the public, and meeting time was provided for public questions and discussion of model issues with the modeling team and advisory panel. In addition, since 2005, modeling workshops have presented details of modeling efforts and accomplishments to a broad range of agency representatives and the public.

Applications - The models have been used already by the Refuge for several applications to better understand Refuge needs for inflow quantity and timing. For example, modeling was applied to an analysis of alternatives proposed in the EAA Regional Feasibility Study. This analysis revealed that proposed diversion would reduce the period of inundation (hydroperiod) for much of the Refuge. Modeling also was used by the TOC sub-group on Refuge water needs to extend the range of modeling scenarios beyond those available using the South Florida Water Management Model. Sulfate modeling, undertaken to test, constrain, and add credibility to the hydrodynamic model formulations, additionally has provided understanding of how sulfate transformation within the Refuge is related to sulfate concentration and loading.

It is important that model users understand the basis of model formulations (e.g., a report on model kinetics is available on the website), their capabilities, and their limitations. Application of the highly aggregated SRSM can examine quickly a broad range of alternatives, but is not appropriate for site-specific projections. Even site-specific model results of the Mike-Flood model must be interpreted with an understanding of the uncertainty introduced by local topography and other local conditions beyond the resolution of the model input data. While the models reasonably mimic phosphorus fate and transport in the Refuge, users need to be aware that these models are deterministic, which means that they do not simulate statistical probabilities of occurrences. Direct application of model results to statistically derived properties, such as the Refuge total phosphorus levels defined in the Consent Decree, therefore would not be appropriate. The suite of models can, however, provide insight and understanding of conditions that are common at times of excursions.

1 Agendas and presentations from advisory panel meetings and these modeling workshops are available at http://loxmodel.mwaldon.com/.

For additional information please contact:

Yongshan Wan, Ph.D.
Ecologist, Everglades Program Team
U.S. Fish and Wildlife Service
A.R.M. Loxahatchee National Wildlife Refuge
10218 Lee Road
Boynton Beach, FL 33473
Voice: 561-735-6006
email: yongshan_wan@fws.gov

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