Descriptions and Preliminary Report on Sediment Cores from the Southwest Coastal Area, Everglades National Park, Florida

USGS Open File Report 2005-1360

Abstract Introduction Methods Lithologic Description of Cores Depositional Env. Summary References Tables and Figures PDF Version

Currently, south Florida is undergoing a massive restoration effort guided by the Comprehensive Everglades Restoration Plan (CERP). One of the primary goals of the CERP is to restore the natural flow of water through the terrestrial Everglades and into the coastal zones. Historically, Shark River Slough, which flows through the central portion of the Everglades southwestward, was the primary flow path through the Everglades Ecosystem. This natural movement of water, however, has been dramatically reduced over the last century as construction of canals, water conservation areas and the Tamiami Trail either retained or diverted flow (Light and Dineen, 1994). The reduction in flow and changes in water quality through Shark River have had a significant effect on the freshwater marshes and the associated coastal ecosystems. Additionally, the flow reduction may have shifted the balance of fresh to salt-water inflow along coastal zones, resulting in an acceleration of the rate of inland migration of mangroves into the freshwater marshes.

Both the CERP and the Department of Interior Science Plan identify the importance of understanding freshwater flow into south Florida's estuaries, and the changes incurred in the estuaries due to anthropogenic alterations of freshwater flow. One of the three primary objectives stated in the DOI Science Plan is to “ensure that hydrologic performance targets accurately reflect the natural predrainage hydrology and ecology” (DOI Science Plan, 2004, p. 14). A historical perspective can be obtained by examining the record of the hydrologic and biologic components of the natural system preserved in the sediments of south Florida. This method has been successfully utilized by USGS researchers in Florida Bay and Biscayne Bay since 1995 (Brewster-Wingard and others, 2001; Ishman and others, 1998; Wingard and others, 2003, 2004) and has provided a general picture of changes that have occurred to the system. These data have been used by CERP teams (Florida Bay Florida Keys Feasibility Study and the Biscayne Bay Coastal Wetlands), and the Southern Estuaries sub-team of Restoration, Coordination, and Verification (RECOVER), to begin the process of setting salinity targets and performance measures for the estuaries.

In 2004, the USGS Ecosystem History of South Florida's Estuaries Project shifted research emphasis towards the southwest coastal area. The objectives of this research are to document impacts of changes in salinity, water quality, coastal plant and invertebrate communities and other critical ecosystem parameters on a decadal to centennial scale in the southwest coastal region (from Whitewater Bay, north to the Ten Thousand Islands), and to correlate these changes with natural events and resource management practices. Examination of these long-term (centennial scale) data sets will allow us to determine what the natural trends or cycles of change (such as rising sea-level or changes in climatic patterns) within the ecosystem were, and how anthropogenic alteration offset those natural cycles. By projecting the natural trends of the 19^th century forward through the 21^st century, we can estimate the unaltered natural conditions of the ecosystem. These forecast values can be used as targets for restoration, because the real aim of performance measures or targets should be to bring the ecosystem back in line with the natural patterns representative of an unaltered system.

Figure 1. Satellite image of the southwest coast of Florida, showing general location of cores. Yellow line marks approximate boundary of Everglades National Park. Red dots indicate location of May 2004 core sites; AL=Alligator Bay Core; LM=Big Lostmans Bay Core; BR=Broad River Bay Core; TB=Tarpon Bay Core; and RR=Roberts River Core from river mouth. Image cropped from John W. Jones and others (2001). Table 1 gives geographic coordinates of core locations and Figure 2 illustrates precise location of cores. [larger version]

The southwest coastal area is the downstream recipient of water flowing through the Shark River Slough, and is adjacent to cypress and marl prairie ecotones. The region is a complex network of channels, bays, coastal prairies, and mangroves (Figure 1). A northwest-southeast trending line of inner bays marks the transition between the coastal and terrestrial ecosystems; the Everglades National Park Wilderness Waterway follows these inter-connected bays. Four of the five cores (Alligator Bay (AB), Big Lostmans Bay (LM), Broad River Bay (BR), Tarpon Bay (TB)) were collected from these inner bays in order to understand the historical conditions and range of variability of this zone. Currently, this system is exposed to significant variability. Between 1995 and 2004, salinities in these bays have ranged from <1 ppt to > 30 ppt , with averages in the 4-7 ppt range (data summarized from http://www.sfwmd.gov/org/ema/envmon/wqm/wqprojects.html, accessed March, 2005; Table 1). A general trend of decreasing average salinity values can be seen moving from Alligator Bay southeast to Tarpon Bay, which may reflect the increasing influence of the Shark River Slough outflow. Preliminary, observations of the molluscan fauna indicate relatively low diversity and abundance in these transitional areas. The fifth core was collected from near the mouth of Roberts River (RR), where it empties into Whitewater Bay. Salinities near this site range from <1 ppt to 30 ppt, with an average of 8 ppt over the period from 1995-2005 (Table 1) and preliminary examinations of the molluscan faunal assemblages indicate similarities to analogous sites in Florida Bay.

 

Figure 2. Digital Orthophoto Quadrangles (DOQs) of core locations, arranged in order from northwest to southeast. A. AL=Alligator Bay core plotted on Alligator Bay SE DOQ. B. LM=Big Lostmans Bay Core plotted on Big Lostman's Bay NW DOQ. C. BR=Broad River Bay Core plotted on Harney River NE DOQ. D. TB=Tarpon Bay Core plotted on Tarpon Bay SW DOQ. E. RR=Roberts River Core from mouth of River plotted on Whitewater Bay east SE DOQ. All images obtained from http://edcsns17.cr.usgs.gov/ EarthExplorer/ [larger version]

 

We would like to thank Everglades National Park for their cooperation in this study; the work described here was conducted under Study #EVER-00141 and permit #EVER-2003-SCI-0053. This work was funded by the U.S. Geological Survey (USGS) Priority Ecosystems South Florida Study Unit. Rob Stamm and Marci Marot, USGS, assisted in the core collection; and Marci Marot supervised the core cutting process. Jim Murray, USGS, assisted in the processing of the cores. Joel Hudley, USGS, assisted in the preparation of the figures. Radiometric carbon analyses were conducted by Beta Analytic Inc. (Miami, FL). We would like to thank our reviewers Bruce Wardlaw, Bill Orem, and Joel Hudley (USGS) for their thoughtful and thorough reviews of the manuscript.