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U.S. Department of the Interior
U.S. Geological Survey


Introduction | Effect of Freshwater Flow from Taylor Slough on Florida Bay | USGS Geochemical Studies | Additional Studies in Taylor Slough and Eastern Florida Bay


map of Taylor Slough Study area
Figure 2. Map of Taylor Slough area. [larger image]
Taylor Slough, located in the south eastern corner of the Everglades, Fla., (figs. 1 and 2), and the much larger Shark River Slough, farther to the west, are the principal natural drainages for the freshwater Everglades. The term "slough" (pronounced slew) is used to describe areas of the Everglades where there is slightly deeper water than in the surrounding marshes and where a slow, but measurable, current is present. In essence, sloughs are the broad, shallow rivers of the Everglades. Sloughs occupy areas of slight depressions in the limestone bedrock underlying south Florida and generally remain wet during the seasonal dry period (November to May). Sloughs are important refuges for aquatic wildlife during these dry periods.

Anyone entering Everglades National Park by car from Homestead, Fla., crosses over the northern (narrowest) portion of Taylor Slough on the main park road west of the Visitor's Center. Taylor Slough begins about 3 kilometers north of the park road crossover, near the L31W canal southwest of Homestead. The slough extends south for about 27 kilometers to Florida Bay, gradually widening along the way (fig. 2). At its southern extremity near Florida Bay, Taylor Slough widens greatly as it merges with a zone of mangrove trees; this zone indicates a transition from freshwater slough to saltwater (fig. 3). The mangrove transition zone at the mouth of Taylor Slough is characterized by numerous tidal channels and brackish water lakes, which are important habitats for seagrass, juvenile fish, and other marine organisms.

photo of a helicopter
Figure 1. Helicopters are used for sampling at remote sites in Taylor Slough. The view shows a typical sawgrass marsh environment with a tree island in the background at a mid-slough site.

Effect of Freshwater Flow from Taylor Slough on Florida Bay

Taylor Slough is much smaller than Shark River Slough in both areal extent and total water discharge but still plays an important role in regulating fresh-water flow and water quality in Florida Bay. Most of the freshwater from Shark River Slough is discharged to the Gulf of Mexico and has little influence on Florida Bay. In contrast, virtually all the freshwater discharged from Taylor Slough enters Florida Bay. Recent events of high-salt-content (hypersaline), water in Florida Bay may be at least partly tied to changes in the freshwater discharge from Taylor Slough. Hypersaline waters may cause stress in some organisms, making them more susceptible to disease, or they may simply kill salt-sensitive organisms and thus change the composition of the ecosystem. Other ecological problems in Florida Bay, such as massive algal blooms, seagrass dieoff, decline of commercial and sport fish, and mercury in fish, may be tied to changes in the quality of water discharged from Taylor Slough.

These changes in freshwater discharge and water quality are closely tied to human activities in south Florida over the last century. Extensive construction of canals throughout the Everglades has greatly altered the natural freshwater flow of the ecosystem. In the area of Taylor Slough, construction of the C-111 canal and associated structures has likely had the most pronounced effect on natural freshwater flow (fig. 2). The C- 111 canal shunts freshwater away from Taylor Slough and Florida Bay and to the east into Biscayne Bay and the Atlantic Ocean. Land is used extensively for agriculture to the north and east of Taylor Slough, and farming may contribute some chemical contamination (nutrients, sulfur, organic pesticides, and so on) to Taylor Slough and ultimately Florida Bay. Similarly, urbanization of the region north and east of Taylor Slough may be producing emissions that are contaminating Taylor Slough with toxic metals (especially mercury) and other urban pollutants.

Recent interest in the Taylor Slough area is a result of proposed physical changes to the freshwater flow in the region, including breaching of sections of the levee along the C-111 canal to increase freshwater flow to northeastern Florida Bay. The effects of these changes on water quality and biotic health of the ecosystem are unknown, and research is needed to provide land and water managers with information on the current geochemical balance in Taylor Slough, on the effect of increased freshwater flow from the C-111 Canal to Florida Bay on this geochemical balance, and on the effects of these changes on the biota of the ecosystem.

Geochemical Studies

In 1995, the U.S. Geological Survey (USGS) began conducting extensive studies of the geochemistry of the Taylor Slough area, with emphasis on sediment geochemistry. Sediments are an important repository of integrated information on the water quality and chemical composition of the slough now and in the past. In addition, sediments play an active role in regulating the water quality of the slough. Overall goals of the project are to (1) examine sources, sinks, and cycling of nutrients and the processes regulating water quality in the Taylor Slough/eastern Florida Bay region, (2) determine sources and cycling of sulfur and the relation of sulfur to methylation of mercury, and (3) use a geochemical approach to examine the history of ecological change in the ecosystem. Emphasis is being placed on studies of nutrients and sulfur - key chemical components for the biolocical resources of the ecosystem. Analyses of these chemical components in sediments, sediment pore water (water within the sediment), surface water, and aquatic vegetation are being conducted in support of the project objectives. The geochemical studies being conducted in the Taylor Slough/Florida Bay region complement ongoing geochemical studies by the USGS in the northern Everglades, thus providing a spatial perspective of the ecosystem. Results of this research will be used by land and water managers in determining the current geochemical status and health of the ecosystem and predicting the likely effects of restoration efforts on the water quality and biological resources of the region.

aerial view of the lower Taylor Slough near Florida Bay
Figure 3. Aerial view of the lower Taylor Slough near Florida Bay, with mangrove trees, tidal creeks, and brackish water lakes. This view is of the Taylor Creek area, where the USGS has established four sampling sites.

To date, 115 cores have been collected from sites in the Taylor Slough/Florida Bay area. Figure 2 shows the location of these sampling sites, which include 25 sites in the main Taylor Slough drainage, 2 sites in the former agricultural area north of Taylor Slough known as the Frog Pond, 6 sites in the marsh area between the C-111 canal and Taylor Slough, and 4 sites in eastern Florida Bay. Information currently available from this studv includes coordinates of all sampling sites, site descriptions (vegetation, sediment depth, surface-water depth), surface-water and pore-water chemistry (nutrients, sulfur, metals, anions, salinity), and sediment geochemistry (organic carbon, carbonate carbon, mineral-matter content, nutrients, and sulfur) for some sites. An example of nutrient data is shown in figure 4.

Note the sharp increase in pore-water phosphorus concentrations in the brackish water mangrove transition zone (E and F) compared to freshwater marsh areas (A to D), indicating the importance of the transitional mangrove zone for nutrient storage and recycling in the ecosystem. Additional work on this aspect of the study is currently underway.

The sulfur geochemistry of Taylor Slough is dominated by two processes: microbial sulfate reduction and reaction of sulfide (a byproduct of sulfate reduction) with sedimentary organic matter to form organic sulfur. Freshwater marshes in Taylor Slough have sulfide concentrations in pore water ranging from <1 to 100 parts per billion. In other regions of the Everglades, similar levels of pore-water sulfide have been shown to be permissive of significant methyl mercury production. Sources of sulfur to Taylor Slough include saltwater intrusion from Florida Bay, wind-blown marine aerosols, and urbanization and farming.

Dissolved reactive phosphate (micromoles per liter)
graphs of dissolved phosphate vs.
Figure 4. Pore-water phosphate concentrations in Taylor Slough from the north near the start of the slough (A) to a site near Florida Bay (F). Sites A-D are freshwater, and sites E-F are brackish water. See figure 2 for site locations. [larger image]

Additional Studies in Taylor Slough and Eastern Florida Bay

Additional USGS teams are conducting research in Taylor Slough in collaboration with and complementing the geochemical studies discussed above.

  • Work on sediment dating and paleoecology in Taylor Slough and Florida Bay is being conducted by USGS teams on cores from the same sites sampled for geochemical studies. This combination of approaches will provide detailed information on the past environmental (paleoenvironmental) conditions of the ecosystem, both chemical and biological. Information on the paleoenvironmental conditions of the ecosystem will provide land managers with a framework from which the goals of ecosystem restoration can be defined.
  • Work is also being conducted by another USGS team on the occurrence of metals (especially mercury) in sediments and vegetation from the same sites shown in figure 2. This work will contribute to our understanding of biogeochemical processes and paleoenvironmental conditions in Taylor Slough.
  • A USGS team is beginning work in Taylor Slough on processes involved in mercury methylation and the bioaccumulation of methyl mercury in aquatic organisms. This will complement and expand on their ongoing work on mercury in the northern Everglades, an issue critical to wildlife managers in Florida, where mercury contamination of wildlife is of growing concern.
  • Other USGS projects in the Taylor Slough area on hydrology, saltwater intrusion, evapotranspiration, and surface-water quality are also being placed on close collaboration with scientists from the South Florida Water Management District, the Florida Department of Environmental Protection, Everglades National Park, the Environmental Protection Agency, and other State and Federal Agencies.

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For more information contact:

William H. Orem
U.S. Geological Survey
956 National Center
Reston, VA 20192
Telephone: (703) 648 - 6273
E - mail: borem@usgs.gov

Related information:

SOFIA Project: Geochemistry of Wetland Sediments from South Florida

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Last updated: 04 September, 2013 @ 02:03 PM(TJE)