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projects > water flows and nutrient fluxes to the southwest coast of everglades national park, florida > abstract
Synopsis of Flows and Nutrient Fluxes to the Southwest Coast of Everglades National Park, Florida, 1996-99The mangrove estuaries along the southwest coast of Everglades National Park (ENP) are dependent on receiving adequate freshwater and optimal nutrient concentrations to minimize adverse impacts to the habitat they provide for many organisms. The mangrove swamps and estuaries seem far removed from the land and water use practices of urban and agricultural areas of south Florida. However, land use, water use, and flood control practices in south Florida have altered the amount and timing of water flows that reach the estuaries on the southwest coast of ENP. As an element of the U.S. Geological Survey South Florida Ecosystem Program, a study was initiated to describe hydrodynamic characteristics and quantify water flows and nutrient fluxes of selected estuarine streams that receive water from the Shark Slough drainage area. These data are needed for hydrologic system models under development by local and federal agencies to be used for evaluating ecosystem restoration impacts. The Broad, Harney, and Shark Rivers receive flows from the Shark Slough and were established as monitoring stations in 1996 for determining water flows and nutrient fluxes. Monitoring stations at Lostmans Creek and North River were added in 1999. Stations are equipped to record water velocity, water level, specific conductance, and water temperature at 15 minute intervals. Water velocities are measured using upward-looking acoustic Doppler current sensors. Water levels are measured using vented pressure transducers. Specific conductances near the surface and near the bottom of the water column are measured using four-electrode conductance sensors, and water temperatures are measured using integral thermistors in the conductance sensors. Stations are visited every 4 to 6 weeks for sensor calibrations, stream discharge measurements, water-quality sample collection, and data retrieval from the data logger. Stream discharge measurements at the Broad, Harney, and Shark Rivers began in February 1997 and will begin in May 1999 at the Lostmans Creek and North River stations. Discharge measurements are made using a boatmounted acoustic Doppler current profiler. Water-quality sampling began in February 1997 at the Broad, Harney, and Shark Rivers and will begin in May 1999 at the Lostmans Creek and North River stations. Water-quality samples are collected using a modified equal-width-increment method. Top, middle, and bottom temperature, specific conductance, pH, and dissolved oxygen are measured using a submersible multiparameter sensor during water-quality sample collection. The water samples are analyzed for total and dissolved nitrogen and phosphorus concentrations and specific conductance by the USGS water-quality laboratory in Ocala, Florida. The streams are affected by mixed tides (semidiurnal and diurnal) that cause the flows to reverse direction one to two times per day. The instantaneous discharges show a long-duration ebb flow (toward the Gulf of Mexico) and a greater magnitude, but shorter duration flood flow (away from the Gulf of Mexico). Instantaneous discharge magnitudes are similar for the Harney and Shark Rivers and have ranged from approximately -8,000 to +8,000 ft3/s, whereas the instantaneous discharge magnitudes for the Broad River are less and have ranged from approximately -2,000 to +2,000 ft3/s. Tidal effects on the instantaneous discharge data are removed using a low-pass filter that attenuates the tidal signals that are less than about 30 hours in duration. The filtered data are used to estimate the residual flows.
Preliminary analyses of the residual flow data show seasonal and short-term variations. The Harney and Shark Rivers data show that larger pulses of residual flow (approximately 2,000 ft Water-quality data for the Broad, Harney, and Shark Rivers show significant relations between nutrients and specific conductance and that the majority of nitrogen and phosphorus occurs in a dissolved form. The Harney and Shark Rivers dissolved nitrogen concentrations are inversely related with specific conductance (significance level 0.02), and may indicate that the majority of dissolved nitrogen is transported from the upgradient areas to the estuarine rivers as fresher water flows into these streams. In contrast, the Broad River total and dissolved nitrogen concentrations are directly related with specific conductance (significance level 0.01) and may indicate that the higher concentrations are transported from the waters in the Gulf of Mexico to the river estuary. Total and dissolved phosphorus concentrations for all three rivers are directly related with specific conductance (significance level 0.02) and may indicate that the rivers are receiving higher concentrations of phosphorus from the Gulf of Mexico than from upgradient areas.
(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)
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| U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology This page is: http://sofia.usgs.gov /projects/nutrient_load/nutrientabsfrsf.html Comments and suggestions? Contact: Heather Henkel - Webmaster Last updated: 11 October, 2002 @ 09:30 PM (KP) |
