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A.R.M. Loxahatchee National Wildlife Refuge Enhanced Water Quality Monitoring and Modeling Program - 3rd Annual Report

October 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 is the third annual report, and focuses primarily on the period from January 2006, through December 2006.

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 continue to support previously 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.

This report continues to document previous findings 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 (1,312 ft by 1,312 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.


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


Download PDF of entire report (5.1 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: Bruce Arrington, A. Camille Darby, Rebekah Gibble, Angela Markovich, Serena Rinker, Robert Smith, and Tiffany Trent for water quality sample collection and sonde deployments and collections; SFWMD and Columbia Analytical Services for water chemistry analyses; and SFWMD for the use of DBHYDRO for data availability; Leslie MacGregor for GIS assistance; Paul Conrads, Rebekah Gibble, Guoqing He, Callie Oblinger, Dilip Shinde and Hongqing Wang for extensive review of earlier versions of this report; and finally, Refuge Manager Mark Musaus and Deputy Manager Rolf Olson for their continuing support and leadership throughout this project. Funds to conduct the expanded monitoring network at A.R.M. Loxahatchee NWR were provided by the U.S. Congress in P.L. 108-108, the Department of the Interior and Environment Appropriations Act of 2004.

This report should be cited as:

USFWS, 2007. A.R.M. Loxahatchee National Wildlife Refuge - Enhanced Water Quality Monitoring and Modeling Program - 3rd Annual Report - October 2007. LOXA07-005, U.S. Fish and Wildlife Service, Boynton Beach, FL. 116 pp.

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