In response to the Announcement of Funding Opportunity by the CSCOR/COP South Florida Ecosystem Restoration Prediction and Modeling Program (SFP) we conducted a two year study of the circulation and exchange processes that regulate the residence times and flushing rates within the NE basin of Florida Bay (Fig. 1). This project was conducted through CIMAS, Task 3, Theme 3: Coastal Ocean Ecosystem Processes. The overall goal was to improve understanding of the effects of modifying fresh water supply to the Everglades as part of Everglades restoration plans. It was uncertain how proposed changes in water delivery, with increased fresh water flows to Shark River and Taylor Slough would affect salinity variability within Florida Bay. The primary objectives were to quantify the circulation and exchange rates influencing salinity variability in the eastern regions of the Bay that directly receive fresh water discharge from a series of small rivers along the northern border (Fig. 1) and to determine their interactions with connecting regions, as well as to identify the controlling physical processes. This information is needed to aid evolution and evaluation of hydrodynamic models for prediction of future water deliveries.
Fig. 1. Measurement strategy for Whipray basin including mooring locations for current, temperature and salinity, moored bottom pressure, sealevel, drifter release sites and vessel survey track
Currents, salinity, and temperature were measured in the flow channels connecting WB with the surrounding basins during dry (Mar 28 to Jul 19) and wet (Sept 3 to Nov 19) seasons of 2001 (Fig. 1). Currents were measured with Sontek Argonaut SL side-looking acoustic current meters that averaged currents at mid-depth over a horizontal distance of 2-3 m from the transducers with a sample interval of 5 min and averaging time of 2 min. Each current meter was also equipped with a SeaBird SBE 37 MicroCat conductivity and temperature recorder set to a 30 min sampling interval. All time series data were smoothed slightly with a 3 Hour Low-Pass (HLP) filter and subsampled at hourly intervals. Due to mechanical problems at Crocodile there was a loss of 1.5 months of data at the end of the record during the dry season and 1.3 months at the start of the wet season. There was also a two week data gap in the middle of the Twisty record of the wet season. Along-channel transports were measured with an RDI 1200 kHz Acoustic Doppler Current Profiler (ADCP) mounted between the hulls of a shallow draft catamaran, the R/V Virginia K, using WinRiver software provided by the instrument manufacturer. Ensemble average transports were made from 4 to 6 ADCP transects per ensemble. Each transect took about 4 min at Topsy and 12 min at Twisty, resulting in ensemble averaged transports over 16 to 24 min periods at Topsy, and 48 to 72 min periods at Twisty. Data recovery of ADCP velocity profiles typically ranged from 80 to 100% for water depths greater than 1.2 m and boat speeds less than 2.5 ms-1. At Crocodile and Dump locations the shipboard ADCP technique could not be used due to the shallow water depths and narrow channel widths. Therefore, transport time series were derived at these locations by multiplying the cross-sectional area times the measured along-channel currents. The missing transport time series at Crocodile (from gaps in current measurement) was filled using a linear regression with the highly coherent Dump transports, which accounted for about 80% of the Crocodile transport variability during the dry season and 90% during the wet season. A similar approach was used to replace the missing two week period of transports at Twisty during the wet season with a regression on the east-west wind, which accounted for 70% of Twisty’s transport variance. These reconstructed transport time series provide an expanded data set of equal length that is more representative of seasonal time durations.
Synoptic spatial surveys of WB salinity patterns were made throughout the dry and wet seasons using a SeaBird 21 thermosalinograph mounted on the R/V Virginia K with a 7 sec sampling interval. The vessel survey speed was kept near constant at approximately 10 ms-1, which resulted in a spatial resolution of measured parameters of about 70 m. It generally took less than 2 hours to complete a detailed survey of the entire basin and adjacent regions. Synoptic salinity surveys of the entire Florida Bay were conducted monthly from the R/V Virginia K using a continuously recording thermosalinograph. Each survey was completed in two days, one day for the outer portion of the bay and one for the inner area (Fig. 2).
Fig. 2. Satellite photograph of the North-Central Basin subregion of Florida Bay including Whipray Basin and surrounding shallow mud banks (light brown).
Tidal excursion lengths are quite small in the interior of the bay and spatial salinity patterns were found to have little variation on daily time scales. Vertical CTD profiles were collected at a network of 40 stations within basin interiors, together with a suite of water quality parameters. Salinity contouring from gridded fields, as well as basin average salinity, were determined using Golden Software's "Surfer" routine. Surface current trajectory patterns were observed several times during each season using specially designed shallow water drifters consisting of small discs that floated at the surface with drogued skirts that extend 0.75 m below the discs. GPS positions were recorded internally and transmitted to ARGOS satellite. Sea level variability for WB and the Florida Bay as a whole was determined from the ENP monitoring network. Local wind time series were obtained from CMAN and SeaKeys monitoring stations in the Florida Keys and northwest Florida Bay as part of a cooperative agreement between Florida Institute of Oceanography (FIO) and NOAA/NDBC through the SEAKEYS Program. Synoptic winds are highly coherent over the study area. River discharge of fresh water into Florida Bay was measured by USGS for all significant input locations. Daily average discharges for 2001 were provided by C. Hittle, USGS, unpulb. Data. Subtidal time series of all current, transport, sea level, and wind data sets were computed using a 40 Hour Low-Pass (HLP) Lanczos filter to remove tidal, sea breeze, and inertial fluctuations to better understand low-frequency variations.
This approach was repeated in the North East Basin that receives most of the freshwater discharge from a series of small rivers on the northern boundary during the wet season of 2002 and dry season of 2003. The western basins of Rabbit Key and Twin Key Basins were studied with the same approach during the wet and dry seasons of 2005.
Data (Florida Bay Central Basin Project)
Deployment Period #1 Central Basin Dry Season: Mar 28 2001 – Jul 19 2001
Deployment Period #2 Central Basin Wet Season: Sept 3 2001 – Nov 19 2001
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