Elizabeth Johns and Doug Wilson – NOAA/AOML

Research Scientists: Elizabeth Williams – University of Miami/RSMAS

Ryan Smith – NOAA/AOML

Period Covered: Oct. 1, 2000 to Sept. 30, 2002

In response to the Announcement of Funding Opportunity by the CSCOR/COP South Florida Ecosystem Restoration Prediction and Modeling Program (SFERPM) a two year study of the circulation and exchange processes that regulate the residence times and flushing rates within the interior basins of Florida Bay will soon get underway. This project will be conducted through the Cooperative Institute for Marine and Atmospheric Studies (CIMAS), Coastal Ocean Ecosystem Processes; Task 3; Theme 3. Determination of rates and pathways of exchange between interior basins of Florida Bay and with the southwest Florida shelf is needed for predicting the effects of modifying fresh water supply to the Everglades as part of Everglades restoration plans. At present it is not understood how the proposed changes in water delivery, with increased fresh water flows to Shark River and Taylor Sloughs, will affect salinity variability within Florida Bay. However, it is generally agreed that the large seasonal and longer period variations of salinity within the Bay have significant impacts on the sea grass and plankton communities, and possibly also with adjacent marine ecosystems of the southwest Florida shelf and Florida Keys National Marine Sanctuary (FKNMS) due to transport processes linking the regions. Reliable model predictions of the physical and biological effects of Everglades restoration plans require a better understanding of the physical processes regulating water exchange and residence times within the Bay and with adjacent coastal regions. The planned research is designed to provide this information. The primary objectives are to quantify the circulation and exchange rates influencing salinity variability in the eastern, central and western subregions of the Bay and their interactions with connecting regions, and to identify the controlling physical processes, to aid evolution and evaluation of hydrodynamic models used to predict future water deliveries.

The methods to be employed consist of a combination of seasonal deployments of moored current, bottom pressure, conductivity and temperature recorders together with smallboat ADCP transects along shallow banks and synoptic high-resolution surveys of basin water mass properties to directly measure the volume and salt transports and changes of basin average salt. Thus the measurement program is designed for direct determination of the basin salt balance per season, which will provide an estimate of exchange rates. Cross-bank sea level slopes will be measured and compared to volume transports and interior circulation will be measured with specially designed miniature drifters using GPS technology and satellite transmission to investigate the influence of local wind forcing. The planned effort is highly coordinated with ongoing and planned projects that will place the local basin dynamics in the context of the larger Bay-wide processes, as well as the entire south Florida coastal system to better understand the linkages over different scales, which is important to management and restoration of the south Florida coupled ecosystems.

The measurement program will begin with deployment of moored instrumentation in a central basin (Whipray Basin) during the height of the dry season from late March to late May 2001 (Fig. 1). Small boat T/S surveys, drifter releases and ADCP sections parallel to the shallow banks will be conducted over 3-day periods every 2-weeks for the duration of the 2-month study (Fig. 2). These measurement will be repeated in Whipray Basin during the following wet season from mid August to mid October. The following year similar measurements will be made in the northeast basin during dry and wet seasons. Measurements in the western basin will be proposed for subsequent years.