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A.R.M. Loxahatchee National Wildlife Refuge Enhanced Monitoring and Modeling Program - 2nd Annual Report

February 2007

Executive Summary

(Note: entire PDF is available for download below)

Congress appropriated funds to the U.S. Fish and Wildlife Service in 2004 to develop an enhanced water quality monitoring network and hydrodynamic and water quality models to improve the scientific understanding of water quality in the Arthur R. Marshall Loxahatchee National Wildlife Refuge1 (Refuge). The network and models provide information that will be used in management decisions to better protect Refuge resources. The enhanced water quality monitoring network complements the existing water quality compliance network created under the 1992 Federal Consent Decree (Case No. 88-1886-CIV-MORENO) by characterizing the water quality of a larger Refuge area, particularly the fringe area potentially impacted by canal water intrusions. The expanded monitoring network, initiated in June, 2004, consists of monthly grab samples collected at 39 canal and marsh stations, and continuous measurements of conductivity along seven transects, four of which extend from the canal near surface water discharge points into the interior. This report focuses on the period from June 2004, through December 2005, but includes data from additional time periods.

Although only a limited range of climatic and hydrological conditions has been experienced during this study, data collected document intrusion of rim canal water into the Refuge interior, adding to a growing information base about canal water impacts to the Refuge. Intrusion of nutrient-rich and high conductivity water from the canal has the potential to negatively impact Refuge plants and animals. Analyses of these data have identified management practices that have the potential to minimize such intrusion.

Based on the water quality data, the Refuge was classified into four geographic zones: (1) canal zone; (2) perimeter zone, located from the canal to 2.5 km (1.6 miles) into the marsh; (3) transition zone, located from 2.5 km (1.6 miles) to 4.5 km (2.8 miles) into the marsh; and (4) interior zone, greater than 4.5 km (2.8 miles) into the marsh. Overall, water quality conditions in the perimeter and transition zones of the Refuge marsh were different from, and more impacted than, the interior zone. The transition zone had instances where canal water penetration may have functionally altered the Refuge ecosystem as supported by a previous study of cattail expansion measurements along a single transect across the Refuge. The perimeter and transition zones combined represent up to 60% of the Refuge interior.

This report concludes that water movement between the canals and the marsh is influenced by the canal-marsh stage difference, structure-controlled water inflow and outflow into perimeter canals, marsh elevation, and rainfall. When inflows to Refuge canals were greater than outflows from Refuge canals and when canal stages were greater than marsh stages, intrusion extended more than 1 km (0.6 miles) into the marsh interior. Even with a minimal difference between the canal and marsh stage and when marsh stage was greater than canal stage, canal water still intruded into the marsh interior. Additionally, this report documents a positive relationship between structure inflows and canal total phosphorus concentrations, reflecting both stormwater treatment area discharges and bypass inflows into the Refuge. When combined with our understanding of the influence of the canal water intrusion into the marsh, these data suggest an impact of high-nutrient water on the Refuge marsh.

A simple water budget model was developed to predict canal compartment and marsh compartment volumes and stages. Statistical analyses demonstrate the applicability of this model to predict temporal variation of water levels in both the marsh and the Refuge perimeter canal. This model already is being used for examining regional water management scenarios. A more complex hydrodynamic model allows examination of Refuge hydrology at a scale of 400 m by 400 m (1312 ft by 1312 feet) - a much higher resolution than the 2-miles by 2-miles hydrodynamic model presently available for the Refuge. Water quality constituents are being incorporated into both models, allowing for both a better understanding of water movement within the marsh and understanding phosphorus levels in the water column. An independent model advisory review panel has provided valuable insights that have been incorporated into the modeling program. Finally, a series of management scenarios has been identified for application of these modeling tools.

This report provides recommendations for specific management practices to minimize the potential of canal water intrusion into the marsh. These recommendations are practical, and could be implemented under the operational structures and rules that presently exist. Other recommendations focus on additional information needs to significantly improve understanding of the Refuge ecosystem for purposes of protecting this valuable remnant of the northern Everglades.


1 Public Law 108-108; see House Report No. 108-195, p. 39-41 (2004)


Download PDF of entire report (3.5 MB)
(You will need the free Adobe Acrobat Reader in order to view the file.)


The authors thank the following contributors, without whom this report would not have been possible: USGS peer reviewers Jess Weaver, Paul Conrad, Wade Bryant, and Callie Oblinger for an extensive and helpful peer review; Bruce Arrington, A. Camille Darby, Serena Rinker, Robert Smith, and Tiffany Trent for water quality sample collection and sonde deployments and collections; SFWMD for water chemistry analyses and for the use of DBHYDRO for data availability; Leslie MacGregor for GIS assistance; Bill Walker, Bob Kadlec, Paul McCormick, Dan Scheidt, Joffre Castro, Dilip Shinde, and Jim Entry for extensive review of earlier versions of this report; Jim for valuable global editing service; and finally, Refuge Manager Mark Musaus for his continuing support and leadership throughout this project.

This report should be cited as:

USFWS., 2007. A.R.M. Loxahatchee National Wildlife Refuge - Enhanced Monitoring and Modeling Program - 2nd Annual Report - February 2007. LOXA06-008, U.S. Fish and Wildlife Service, Boynton Beach, FL. 183 pp.

Acronyms and Abbreviations

ACME Special Drainage District
CERP Comprehensive Everglades Restoration Plan
cfs cubic feet per second
Cl chloride
cm centimeter
CV coefficient of variation
DBHYDRO SFWMD's web portal for water quality data
DCS depth to consolidated substrate
DOI Department of Interior
ENRP Everglades Nutrient Removal Project
ET evapotranspiration
EVPA Federal Consent Decree compliance network for Refuge
FVCOM Two-dimensional unstructured finite volume model
km kilometer
L liter
LOXA Refuge's expanded water quality monitoring network
LWDD Lake Worth Drainage District
m meter
mg milligram
Mg megagram (metric ton)
MIKE-FLOOD Coupled one and two-dimensional finite difference model
mm millimeter
msl mean sea level
NAD83 North American Datum of 1983
NAVD83 North American Vertical Datum of 1988
NGVD National Geodetic Vertical Datum
NGVD29 National Geodetic Vertical Datum of 1929
NOx oxides of nitrogen
ppb parts per billion (micrograms per liter)
POR period of record
RMSE root mean square error
s second
SFWMD South Florida Water Management District
SO4 sulfate
STA Stormwater Treatment Area
TN total nitrogen
TP total phosphorus
µS microSiemen (measure of conductivity)
USACE U.S. Army Corps of Engineers
USFWS U.S. Fish and Wildlife Service
USGS U.S. Geological Survey
WCA Water Conservation Area

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