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A.R.M. Loxahatchee National Wildlife Refuge Enhanced Water Quality Program - 6th Annual Report - Calendar Year 2009

October 2010

Executive Summary

(Note: entire PDF is available for download below)

Congress appropriated funds to the U.S. Fish and Wildlife Service in 2004 which funded 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 is used in management decisions to better protect Refuge resources. The enhanced water quality monitoring network complements the compliance network monitored as a part of 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. Monthly grab samples have been collected at 37 to 39 sites located in the marsh and canal since June 2004. The number of grab sample sites has reduced to 37 in recent years because two sites located near the canal were overrun with cattail making them inaccessible. Continuous measurements of conductivity additionally have been collected along seven transects, four of which extend from surface water discharge points in the canal into the interior. This report is the sixth annual report, with analyses focused on January through December 2009, and with comparisons made to the preceding years (2004 through 2008).

Water quality data and analyses of canal water intrusion into the Refuge marsh presented in this report documents continued 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 network surrounding the Refuge has been shown to negatively impact Refuge flora and fauna. Important insights gained from 2009 canal water intrusion analyses include:

Analyses of these data continue to support previously suggested management practices that have the potential to minimize intrusion. A few of these recommendations are summarized as balancing inflow and outflow volumes, reducing the duration of inflows, and reducing inflow rates when the canal stage is lower than the marsh stage.

Based on the surface water conductivity 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 continue to be different from, and more impacted than, the Interior Zone. Cattail expansion in the Refuge marsh, negative impacts to Xyris spp. in response to nutrient and mineral enrichment, and displacement of sawgrass in the canal water-exposed areas of the marsh are a few examples of marsh impacts.

This report continues to document that water movement between the canals and the marsh is influenced by rainfall, structure-controlled water inflow and outflow into perimeter canals, the difference between canal and marsh stages, and marsh elevation. When combined with our understanding of canal water intrusion influence on the marsh, these data continue to suggest that high-nutrient water is having a negative impact on the Refuge marsh (e.g., enriched soil TP, displacement of sawgrass by cattails, loss of Xyris spp., etc.).

An excursion of the long-term TP level, as defined by the Consent Decree, occurred in June 2009. Elevated inflows, rapid canal stage rise, and canal water intrusion were the environmental conditions leading to the June 2009 excursion. These conditions are consistent with most of the excursions that have occurred over the past five years.

The June 2009 excursion, coupled with the November 2008 excursion, is an exceedance of the long-term level. The TOC did not find that there was substantial evidence of error or extraordinary natural phenomena, therefore, this exceedance represents a violation of the Consent Decree's long-term level. Further, this exceedance is the first exceedance since the long-term level went into effect in 2007.

In 2009, we continued to investigate the growth and survival of native Florida apple snails (Pomacea paludosa) as a response to periphyton compositions from the Perimeter, Transition, and Interior Zones. We also continued to investigate how P. paludosa life histories are affected by water chemistry in the Northern Everglades. Analytical results will be available in the next annual report.

Refuge modeling progress in 2009 centered on the final meeting of the Refuge modeling Technical Advisory Panel (TAP) on May 11, 2009. After primary focus on development, calibration, and verification of the models, much of the modeling effort in 2009 was redirected toward model application and use. Refuge models have been used to analyze hydrologic impacts of the EAA Regional Feasibility Study, comparison of methods and results with the South Florida Water Management Model, comparison of alternative regulatory releases under the current regulation schedule, comparison of model water quality results using hourly rather than daily average inflows, analysis of potential impacts of a berm along the marsh bank of the L-40 Canal, and sensitivity of interior and peripheral marsh to changes in chloride, sulfate, and TP inflow concentrations. In the final months of 2009, a version of the aggregated model was applied in development, testing, and application of a high-stage hydrological performance measure for testing alternative water management scenarios.


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


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The authors thank the following contributors, without whom this report would not have been possible: Angela De'Bree, Marcie Dixson, Rebekah Gibble, April Ostrom, and Tiffany Trent for water quality sample collection and sonde deployments and collections; SFWMD and Columbia Analytical Services for water chemistry analyses; April Ostrom for extensive data quality assurance and control; Paul McCormick (formerly with USGS) for assistance with the ecological effects research; and SFWMD for the use of DBHYDRO for data availability. Laura Brandt and Mark Musaus provided valuable contributions to the initial phase of this overall program. Finally, we thank Refuge Manager Sylvia Pelizza and Deputy Manager Rolf Olson for their continued 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. Funding for 2009 was obtained, in part, from the Everglades National Park through the DOI Critical Ecosystem Studies Initiative program. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service or the National Park Service.

This report should be cited as:

USFWS, 2010. A.R.M. Loxahatchee National Wildlife Refuge - Enhanced Water Quality Program - 6th Annual Report for calendar year 2009 - October 2011. LOXA09-011, U.S. Fish and Wildlife Service, Boynton Beach, FL. 106 pp.

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