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projects > salinity and turbidity patterns within Estero Bay Aquatic Preserve > 2001 Proposal

Salinity and Turbidity Patterns within Estero Bay Aquatic Preserve, Lee County, Florida

Project Proposal for 2001

Author: Eduardo Patino


Estero Bay is a shallow estuary, across which salinity gradients from freshwater to saltwater occur over short land-sea distances. Such gradient compressions can result in a highly variable salinity environment and affect a diverse range of estuarine flora and fauna when even a small change in watershed runoff occurs. Rapid development within the bay's watershed has a changing effect on the amount, timing, and quality of runoff into the bay. Currently there is no information available to assess the effect that these alterations of runoff may have on the bay and its biota, nor to define watershed runoff and loading limits that provide desirable ranges in salinity and water quality at historical, current, and potential locations for seagrass, oysters, and other species of concern. To manage and preserve the Estero Bay ecosystem, it is necessary to: (1) understand the salinity patterns of the bay in relation to freshwater inflow and water exchange with the Gulf of Mexico; (2) describe the mixing and freshwater residence times within the bay; and (3) study the effects on light penetration from increased Total Suspended-Solids (TSS) load and re-suspension. Results from this study will facilitate management decisions geared toward defining flow and sediment loading limits that provide desirable ranges in salinity and water quality by providing necessary hydrological information.


The objectives of this study are to: (1) collect the necessary information within Estero Bay to delineate the salinity and turbidity patterns of the bay in relation to freshwater inflows (tributary flow and rainfall) and tidal exchange with the Gulf of Mexico; and (2) further study the use of acoustic and turbidity instruments for the estimation of TSS concentrations in estuarine environments. All the information generated through this study will be made available for the development and calibration of hydrodynamic and water quality models of Estero Bay.


The study is designed as a 3 1/2-year project, starting in April 2001 and ending in September 2004, and is divided into a research component and accompanying monitoring component. The research portion of the study includes describing the effects that freshwater runoff has on the salinity and turbidity patterns within the bay in relation to water exchange with the Gulf of Mexico and San Carlos Bay and to further test the feasibility of using continuous acoustic and turbidity data at three inflow points for estimating time-series of TSS concentration, which will aid in the calculation of sediment load into the bay. To carry out the objectives of the study, a network of monitoring stations will be established and will include: (1) the monitoring of flow, water level, salinity, temperature, Acoustic Backscatter Strength (ABS), and turbidity near the mouth of three of four tributaries flowing into Estero Bay; (2) monitoring of water level, salinity, temperature, turbidity, wind speed and direction, and barometric pressure at one location inside the bay; (3) monitoring of water level, flow, salinity, temperature, and ABS at three of four tidal exchange points with the Gulf of Mexico along the barrier islands; (4) monitoring of water level (depth), salinity and temperature at one open-water location in the Gulf of Mexico. All USGS data will be stored in the Miami Subdistrict database and will be available for the development and calibration of hydrodynamic and water-quality models being planned for the bay.


Description of salinity and turbidity patterns

The description of salinity patterns for Estero Bay will be accomplished by determining freshwater residence times within the bay and by analyzing salinity data collected at the freshwater inflow points, the inner-bay, barrier islands boundary, and the open-water station. Analysis of turbidity data will be limited to inflow and inner-bay stations. Freshwater runoff residence times will be calculated by determining the period of time it takes for salinity to return to levels existing prior to storms or runoff events (managed releases at control structures). The significance of effects from hydrologic events on salinity patterns will be evaluated by measuring the extent of salinity variations prior, during, and after storms at all monitoring stations within the study area, and the effects on turbidity by measuring variations at inflow points due to increased flow and at the inner-bay by analyzing turbidity data in relation to wind speed and direction (sediment re-suspension). Freshwater flows from tributaries flowing into the bay will be determined from data currently collected and computed by the Fort Myers USGS Field office personnel in conjunction with calculated net flow data from tributary stations. Due to the location of the proposed sites and the availability of rainfall data from other agencies in areas nearby the study area, rainfall data will not be collected as part of the monitoring effort.

Verification of ABS/Turbidity to TSS relation

The equation forms developed to describe TSS to ABS and turbidity relations for monitoring stations within the St. Lucie River Estuary will be used here as the starting point. Given the fact that these equations are site-specific empirical equations, and the possibility of varying suspended material composition in conjunction with differences in flow, salinity, and color characteristics of these streams as compared to the St. Lucie River, changes to the equation forms may be necessary. The following are the baseline ABS and turbidity equations to be used in this study:

For ABS, TSS = 10{ABS*[A + B * log (salinity) - C * log (temperature)] - D}
    where A, B, and C are regression coefficients and D a constant.

For turbidity, TSS = A * turbidity + B
    where A is a regression coefficient and B a constant.

Water samples for TSS and SSC analyses will be collected near the mouth of the three tributaries flowing into Estero Bay. Both laboratory analyses will be done with duplicate samples in order to address possible bias as described in WRI 00-4191 "Comparability of Suspended-Sediment Concentration and Total Suspended Solids Data" by John R. Gray, G. Douglas Glysson, Lisa M. Turcios, Gregory E. Schwartz. Continuous ABS and turbidity data will be collected at the three tributary sites and regression analyses will be used to determine if correlation can be obtained and time-series records of TSS concentrations produced.


All monitoring will be done according to USGS protocol, methods, and techniques. Flow monitoring stations will be equipped with acoustic instrumentation for the measurement of water velocity and an Acoustic Doppler Current Profiler (ADCP) will be used for discharge calibrations during different hydrologic and tide conditions.


The mission of the Water Resources Discipline is to provide reliable, impartial, and timely information needed by decision makers to understand, protect, and enhance the Nation's water resources for human health, aquatic health, and environmental quality. The Estero Bay Estuary is a State Aquatic Preserve and is also part of the Charlotte Harbor National Estuary Program and the work proposed within this study is consistent with the accomplishment of our mission and work elements described in the Florida District's Science Plan. In addition to providing information relevant to the protection and preservation of Florida's coastal ecosystems, this study includes the development of new techniques for the calculation of time-series records of suspended solids that can have a great impact on the implementation and monitoring of TMDLs across the country.


  1. Water Resources Investigations Report "Salinity and Turbidity Patterns within Estero Bay Aquatic Preserve, Lee County, Florida".
  2. Open-File Report "Hydrologic Database for Estero Bay Aquatic Preserve, October 2001 - September 2005".


Patino, Eduardo, Hittle, Clinton D., Zucker, Mark, 2001 (in review), Freshwater flow into northeastern Florida Bay: U.S. Geological Survey Water-Resources Investigations Report.

Thevenot, M.M., and Kraus, N.C., 1993, Comparison of acoustical and optical measurements of suspended material in the Chesapeake Bay Estuary: Journal of Marine Environmental Engineering, v. 1, p. 65-79.

Patino, Eduardo, 1996, Feasibility of using acoustic velocity meters for estimating highly organic suspended-solids concentrations in streams: U.S. Geological Survey Open-File-Report 96-137, 28 p.

Patino, Eduardo, and Byrne, M J., 2001 (in preparation), Using acoustic and optic instrumentation for estimating total suspended-solids concentrations in estuarine environments: U.S. Geological Survey Water-Resources Investigations Report.


Work element 2001 2002 2003 2004
3 4 1 2 3 4 1 2 3 4 1 2 3 4
Selection of monitoring sites, design gage-houses and obtain permits x x                        
Construction and instrumentation of monitoring stations   x x                      
Data collection, calibration of discharge sites, and data analysis   x x x x x x x x x        
WRI Report and Open-File Report annotated outlines           x                
Introduction and non-interpretive portions of reports               x            
Interpretative portions of reports                 x x        
Submit reports for review                     x x    
Revise reports                         x  
Obtain approval and publication of WRI & Open-File Reports                           x

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