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A.R.M. Loxahatchee National Wildlife Refuge Enhanced Water Quality Program - 4th Annual Report

July 2009

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 is used in management decisions to better protect Refuge resources. The enhanced water quality monitoring network complements the 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. Monthly grab samples have been collected at 37 to 39 sites located in the marsh and canal since June 2004. Further, continuous measurements of conductivity have been collected along seven transects, four of which extend from the canal near surface water discharge points into the interior. This report is the fourth annual report, with analyses of the period from January through December 2007 with comparison made to the preceding years (2004 through 2006). This period of record includes a significant range of environmental conditions, from average to drier conditions. Drought conditions for South Florida began in late 2005 and continued through 2007. These drier conditions have not lead to decreases in total phosphorus (TP) concentrations over the entire Refuge (mean for the marsh and canal combined) during the extent of this program (2004 - 2007).

Analyses of canal water intrusion into the Refuge marsh and water quality 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 2007 canal water intrusion analysis 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, Xyris spp. negative 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 ecosystem functionality alterations.

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. In 2007, when inflows to Refuge canals were greater than outflows from Refuge canals, and when canal stages were greater than marsh stages, intrusion extended between 1 and 2 km (0.6 and 1.2 miles) into the marsh interior. Additionally, this report documents a positive relationship between structure inflows and canal TP concentrations, reflecting stormwater treatment area discharges into the Refuge. When combined with our understanding of canal water intrusion's 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 to the long-term TP level, as defined by the Federal Consent Decree, occurred in October 2007 (Lehr 2008). Rainfall was greater than one inch (25.4 mm) in July. Daily canal inflows increased, beginning in July, and were greater than 2,500 cfs (3,083 acre-ft; 3,801 ML-1) by the beginning of October. Marsh and canal stages increased more than 0.6 ft (0.18 m) since the September 2007 sampling event. Canal water intrusion into the marsh increased as canal inflows and stages increased. By late August 2007, canal water intrusion (movement of water from the perimeter canal into the marsh interior) was observed at 1 km or greater into the marsh on both the east and west sides of the Refuge. Concentrations of TP, total nitrogen, chloride, and sulfate in the Canal and Perimeter Zones increased above the annual means for each parameter along with the increase in canal water intrusion. In October 2007, most of the monitored concentrations in the Canal and Perimeter Zone peaked, and canal water intrusion increased to 2.3 km on the west side of the Refuge, representing the highest level of recorded intrusion in the west over the past three years. Intrusion increased to 1.7 km on the east side of the Refuge - the highest intrusion recorded on the east side of the Refuge in 2007. Increased canal water intrusion was coincident with increased inflows of long durations (greater than six consecutive weeks) which were not matched by similar outflows. The excursion of the long-term TP level occurred coincident with these hydrologic conditions.

Nutrient and mineral-enriched water has negative consequences on vegetation dynamics in the Refuge interior. The fringe of the marsh is most susceptible to canal water influence because of its proximity. Seed bank germination research identified differences in plant species response to different levels of mineral enrichment, including germination failure of non-preferred native species (e.g., Mikania scandens, Typha spp.) when marsh soils are not enriched by canal waters. These findings coincide with the observation of cattail (Typha spp.) in the western marsh fringe where cattails are densely distributed up to 1.5 km into the marsh from the canal on the west side of the Refuge. This area is the most influenced by canal water intrusion.

A simple water budget model was developed to predict canal and marsh volumes and stages. Statistical analyses demonstrate the ability 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, including an effort to better define the Refuge's water needs. 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 ft) - 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 to allow 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 continues to provide 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)


 

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Acknowledgments

The authors thank the following contributors, without whom this report would not have been possible: Angela De'Bree, Marcie Dixson, Rebekah Gibble, April Ostrom, Serena Rinker, 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; Dr. Paul McCormick (formerly with USGS) for assistance with the ecological effects research; SFWMD for the use of DBHYDRO for data availability; Laura Brandt, Paul Conrads, James Entry, and Dan Schiedt for extensive review of this report. We would also like to thank James Entry for unit conversions. 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 2007 was obtained from Everglades National Park through the DOI Critical Ecosystem Studies Initiative program.

This report should be cited as:

USFWS, 2009. A.R.M. Loxahatchee National Wildlife Refuge - Enhanced Water Quality Program - 4th Annual Report - July 2009. LOXA09-007, U.S. Fish and Wildlife Service, Boynton Beach, FL. 106 pp.

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