Search

Biscayne Bay, a marine lagoon along the southeast Florida coast, has been affected by altered freshwater input due to water management construction features and operations. The Comprehensive Everglades Restoration Plan aims to improve the quantity, quality, timing, and distribution of freshwater flow through central Florida to the southern coasts and to restore nearshore estuarine conditions in Biscayne Bay. The Biscayne Bay Simulation Model (BBSM) is used to evaluate the effects of proposed changes to freshwater flow on salinity in the bay. However, a recent version of the model has left out the groundwater component due to uncertainty in its quantity, a critical shortcoming considering the porous substrate connecting the bay to inland freshwater sources and historic evidence of fresh groundwater discharge. As a result, the BBSM had been unable to reproduce mean salinity and salinity variability along the shoreline. In the present effort, salinity data from an expanded set of monitoring stations were used to estimate the quantity of the fresh groundwater discharge component. Adjustments in friction in the shallow nearshore regions were also made to increase salinity variability to mimic natural conditions. The result, referred to as BBSM version 4, has improved salinity behavior in the critical nearshore region while maintaining previous salinity performance mid-bay. A substantial coastal freshwater component was required to simulate nearshore salinity during portions of the year. This is an interesting finding that suggests groundwater and other freshwater sources along the coast, including convection driven precipitation events, may have been underestimated and require further investigation. [ABSTRACT FROM AUTHOR]

Background: Microbial water-quality indicators, in high concentrations in sewage, are used to determine whether water is safe for recreational purposes. Recently, the use of these indicators to regulate recreational water bodies, particularly in sub/tropical recreational marine waters without known sources of sewage, has been questioned. The objectives of this study were to evaluate the risk to humans from exposure to subtropical recreational marine waters with no known point source, and the possible relationship between microbe densities and reported symptoms in human subjects with random-exposure assignment and intensive individual microbial monitoring in this environment.Methods: A total of 1303 adult regular bathers were randomly assigned to bather and non-bather groups, with subsequent follow-up for reported illness, in conjunction with extensive environmental sampling of indicator organisms (enterococci).Results: Bathers were 1.76 times more likely to report gastrointestinal illness [95% confidence interval (CI) 0.94-3.30; P = 0.07]; 4.46 times more likely to report acute febrile respiratory illness (95% CI 0.99-20.90; P = 0.051) and 5.91 times more likely to report a skin illness (95% CI 2.76-12.63; P < 0.0001) relative to non-bathers. Evidence of a dose-response relationship was found between skin illnesses and increasing enterococci exposure among bathers [1.46 times (95% CI 0.97-2.21; P = 0.07) per increasing log(10) unit of enterococci exposure], but not for gastrointestinal or respiratory illnesses.Conclusions: This study indicated that bathers may be at increased risk of several illnesses relative to non-bathers, even in the absence of any known source of domestic sewage impacting the recreational marine waters. There was no dose-response relationship between gastroenteritis and increasing exposure to enterococci, even though many current water-monitoring standards use gastroenteritis as the major outcome illness. [ABSTRACT FROM AUTHOR]

In the present study, a spectral analysis was applied to field data and a numerical model of southeastern Everglades and northeastern Florida Bay that involved computing and comparing the power spectrum of simulated and measured flows at the primary coastal outflow creek. Four dominant power frequencies, corresponding to the S1, S2, M2, and O1 tidal periods, were apparent in the measured outflows. The model seemed to reproduce the magnitudes of the S1 and S2 components better than those of the M2 and O1 components. To determine the cause of the relatively poor representation of the M2 and O1 components, we created a steady-base version of the model by setting the time-varying forcing functions—rainfall, evapotranspiration, wind, and inland and tidal boundary conditions—to averaged values. The steady-base model was then modified to produce multiple simulations with only one time-varying forcing function for each model run. These experimental simulations approximated the individual effects of each forcing function on the system. The spectral analysis of the experimental simulations indicated that temporal fluctuations in rainfall, evapotranspiration, and inland water level and discharge boundaries have negligible effects on coastal creek flow fluctuations with periods of less than 48 hours. The tidal boundary seems to be the only forcing function inducing the M2 and O1 frequency flow fluctuations in the creek. An analytical formulation was developed, relating the errors induced by the tidal water-level gauge resolution to the errors in the simulated discharge fluctuations at the coastal creek. This formulation yielded a discharge-fluctuation error similar in magnitude to the errors observed when comparing the spectrum of the simulated and measured discharge. The dominant source of error in the simulation of discharge fluctuation magnitude is most likely the resolution of the water-level gauges used to create the model boundary. [ABSTRACT FROM AUTHOR]

The variability in the supply of pink shrimp (Farfantepenaeus duorarum) postlarvae and the transport mechanisms of planktonic stages were investigated with field data and simulations of transport. Postlarvae entering the nursery grounds of Florida Bay were collected for three consecutive years at channels that connect the Bay with the Gulf of Mexico, and in channels of the Middle Florida Keys that connect the southeastern margin of the Bay with the Atlantic Ocean. The influx of postlarvae in the Middle Florida Keys was low in magnitude and varied seasonally and among years. In contrast, the greater postlarval influx occurred at the northwestern border of the Bay, where there was a strong seasonal pattern with peaks in influx from July through September each year. Planktonic stages need to travel up to 150 km eastward between spawning grounds (northeast of Dry Tortugas) and nursery grounds (western Florida Bay) in about 30 days, the estimated time of planktonic development for this species. A Lagrangian trajectory model was developed to estimate the drift of planktonic stages across the SW Florida shelf. The model simulated the maximal distance traveled by planktonic stages under various assumptions of behavior. Simulation results indicated that larvae traveling with the instantaneous current and exhibiting a diel behavior travel up to 65 km and 75% of the larvae travel only 30 km. However, the eastward distance traveled increased substantially when a larval response to tides was added to the behavioral variable (distance increased to 200 km and 85% of larvae traveled 150 km). The question is, when during larval development, and where on the shallow SW Florida shelf, does the tidal response become incorporated into the behavior of pink shrimp. [ABSTRACT FROM AUTHOR]

Reports on the development of a numerical model to describe the currents, residence times, salinity patterns and larval transport in a South Biscayne Bay, Florida lagoonal system. Inclusion of tides, wind and freshwater inflows in model forcing; Agreement of computed tidal currents with observations; Average difference of computed salinity.