Benjamin F. McPherson^1,2 and Arturo Torres^1
1U.S. Geological Survey, Tampa, FL, USA
²Retired

The U.S. Geological Survey (USGS) began a series of studies in 1995 to monitor the major rivers and creeks that discharge freshwater into northeastern Florida Bay and the southwestern estuaries of Everglades National Park (ENP). These studies provide: (1) flow, salinity, water temperature, and water-level data for research applications including model development and calibration; and (2) supply base-line information for other physical, biological, and chemical studies being conducted in these areas. Specifically, a network of 35 estuarine and wetland hydrologic monitoring stations has been constructed between the Everglades wetlands and adjacent coastal-marine ecosystem. The network provides data to study the interaction of dynamic tidal forces and wind, including flow exchanges and salinity fluxes between surface and ground-water systems.

Investigators have measured relatively low concentrations of phosphorus and nitrogen in wetlands of ENP with median values mostly < 0.01 mg/L total phosphorus (TP) and < 1.5 mg/L total nitrogen (TN). Both total phosphorus and dissolved nitrogen that flows into Everglades wetlands are rapidly removed, but total nitrogen remains mostly unchanged. Rudnick and others (1999) reported nutrient loadings from the southern Everglades watershed (Taylor Slough and areas south of the C-111 canal) of 7.1 g C m^-2, 0.46 g N m^-2, and 0.007 g P m^-2 annually. Levesques (2004) reported a total nutrient flux for 5 SW coastal tributaries (Shark, North, Broad, Harney, and Lostman’s) for August 1999 to January 2000 of 17 short tons TP and 1,280 short tons TN. These values were measured within the mangrove zone and reflect higher concentrations in mangroves and Gulf of Mexico compared with upstream marshes. Everglades TP fluxes are 3 to 4 orders of magnitude lower than published flux estimates from upstream wetlands influenced by terrigenous sedimentary inputs, reflecting the inherently low TP concentrations of Everglades freshwater marsh waters and the efficiency of Everglades carbonate sediments and biota in conserving and recycling this limiting nutrient (Sutula and others, 2003).

The seasonal variation of freshwater input to the watershed is responsible for major temporal variation in nutrient export, with approximately 99 % of the export to Florida Bay occurring during the rainy season (Sutula and others, 2003). Hurricanes and tropical storms can result in large spikes in tributary nutrient loading, wind-driven bottom sediment recycling, and significant changes in coastal water quality (Lovelace and McPherson, 1996). Following Hurricane Andrew in 1992, concentrations of ammonia, dissolved phosphate, dissolved organic carbon, turbidity, and phytoplankton increased and dissolved oxygen decreased in Florida Bay (Davis and others, 1994).

Contact Information: Benjamin F. McPherson, U.S. Geological Survey, 10500 University Center Dr. Suite 215, Tampa, FL 33612 USA Phone: 813-975-8620, ext 126, Fax:813-975-0839, Email: bmcphers@usgs.gov

(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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