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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]

Tides, wind and the Florida Current affect the dynamics of the South Florida continental shelf over a range of scales. Two field experiments in the winter (LARGO1) and summer (LARGO2) employed a high-frequency (HF) Ocean Surface Current Radar (OSCR), moored current meters and a boat-mounted Acoustic Doppler Current Profiler (ADCP) to study the circulation over the southeast Florida Shelf. The OSCR measured near-surface currents over an approximately 30 km by 30 km grid, with 1-km horizontal resolution, covering the shelf and extending offshore of the shelf break. By using observed 20-min surface vector field time series to backward track patches with defined volumes of shelf water, their recent origin was identified. The proportion of surface volume flux past various points on the shelf that originated offshore, along the shelf edge and inshore was then estimated. Onshore winds were linked to periods of transport of offshore water all the way to the inner shelf during both the summer and winter seasons. In LARGO2 the exchange of offshore water with water over the middle and inner shelf was closely linked to onshore and downcoast winds. Simulated particle trajectories revealed that Florida Current spin-off eddies caused off-shelf water to be advected onto the middle (LARGO1) or outer (LARGO2) shelf. However, because eddies had short residence times and small spatial scales their contribution to the overall exchange was much smaller than the wind. [Copyright &y& Elsevier]

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.

Swimming in ocean water, including ocean water at beaches not impacted by known point sources of pollution, is an increasing health concern. This study was an initial evaluation of the presence of indicator microbes and pathogens and the association among the indicator microbes, pathogens, and environmental conditions at a subtropical, recreational marine beach in south Florida impacted by non-point sources of pollution. Twelve water and eight sand samples were collected during four sampling events at high or low tide under elevated or reduced solar insolation conditions. The analyses performed included analyses of fecal indicator bacteria (FIB) (fecal coliforms, Escherichia coli, enterococci, and Clostridium perfringens), human-associated microbial source tracking (MST) markers (human polyomaviruses [HPyVs] and Enterococcus faecium esp gene), and pathogens (J'ibrio vulnjficus, Staphylococcus aureus, enterovirus, norovirus, hepatitis A virus, Cryptosporidium spp., and Gwrdia spp.). The enterococcus concentrations in water and sand detennined by quantitative PCR were greater than the concentrations determined by membrane filtration measurement. The FIB concentrations in water were below the recreational water quality standards for three of the four sampling events, when pathogens and MST markers were also generally undetectable. The FIB levels exceeded regulatory guidelines during one event, and this was accompanied by detection of HPyVs and pathogens, including detection of the autochthonous bacterium V. vulnificus in sand and water, detection of the allochthonous protozoans Giardia spp. in water, and detection of Cryptosporidium spp. in sand samples. The elevated microbial levels were detected at high tide and under low-solar-insolation conditions. Additional sampling should be conducted to further explore the relationships between tidal and solar insolation conditions and between indicator microbes and pathogens in subtropical recreational marine waters impacted by non-point source pollution. [ABSTRACT FROM AUTHOR]

Enterococci are used to evaluate the safety of beach waters and studies have identified beach sands as a source of these bacteria. In order to study and quantify the release of microbes from beach sediments, flow column systems were built to evaluate flow of pore water out of beach sediments. Results show a peak in enterococci (average of 10% of the total microbes in core) released from the sand core within one pore water volume followed by a marked decline to below detection. These results indicate that few enterococci are easily removed and that factors other than simple pore water flow control the release of the majority of enterococci within beach sediments. A significantly larger quantity and release of enterococci were observed in cores collected after a significant rain event suggesting the influx of fresh water can alter the release pattern as compared to cores with no antecedent rainfall., (Copyright © 2011 Elsevier Ltd. All rights reserved.)