Understanding the salinity dynamics of Florida Bay is central to its restoration. Salinity is an intermediate link in the cause and effect that connects upstream water-management activities to the structure and function of the Florida Bay ecosystem. Long-term regional water-management practices are widely thought to have reduced the quantity and shifted the distribution and timing of freshwater inflow leading to a marinification of Florida Bay. The perception of ecological decline in Florida Bay as evidenced by seagrass die-off, the onset of extensive turbidity/algal blooms, and corresponding declines in dependent fisheries, is often linked, at least in part, to salinity stress and long-term changes in salinity within the bay (Robblee and others, 1991; Boyer, and others; 1999; Browder and others, 1999; Fourqurean and Robblee, 1999). Prominent elements within the Florida Bay Restoration Program involve restoring historic freshwater flows; enabling predictions of salinity in Florida Bay based on upstream hydrology and water-management; and developing, as a possible restoration target, a model of the salinity regime in Florida Bay prior to water management (Armentano, 1994; Florida Bay Program Management Committee, 1997). The success of these restoration efforts requires an understanding of the historical salinity pattern in Florida Bay.

This project has several objectives: (1) to complete the existing salinity record for Florida Bay by conducting a comprehensive search for salinity data, published or unpublished literature referencing salinity, and anecdotal information interpretable in terms of salinity conditions within the bay; (2) to compile these data in a relational database searchable via the internet; and (3) to provide a synthesis characterizing salinity conditions in Florida Bay over the last century.

Figure 1. Map of Florida Bay showing five salinity reference areas used to capture east-west gradient in salinity patterns. Click for larger image.

The geographical scope of this study (fig. 1) has been defined as the region south of mainland Florida but including the semi-enclosed bays and sounds of the mangrove estuary, north and west of U.S. Route 1 from its junction with the mainland southwest through the Florida Keys to the southern tip of Long Key and east of a line between Long Key (80^o56.0’, 24^o48.1’) and East Cape Sable (81^o05.3’, 25^o07.0’). Generally this region includes the portion of Florida Bay as contained within Everglades National Park. However, salinity patterns in Florida Bay are dependent on processes occurring along its periphery. As such, data and reference material were included for Manatee Bay and Barnes Sound to the east, Largo Sound and the major passes through the Florida Keys south to Long Key, near vicinity Gulf of Mexico waters, and Whitewater Bay and the rivers and bays from Lostmans River south. Future efforts will extend this west coast search area north as far as Cape Romano.

To compile a comprehensive salinity database for Florida Bay, extensive searches for salinity data were conducted across a diverse body of literature and collections spanning more than 150 years. The primary aim of the search was to identify and locate salinity observations that met the following criteria:

• the observation was made within Florida Bay waters or in waters adjacent to the Bay;
• the measurement was a discrete observation (not an average value); the date and time that the observation was made is known;
• the location at which the salinity observation had been made was available or could be estimated; and
• the depth at which the observation was made could be determined.

A second aim of the search was to identify and retrieve reference and anecdotal materials containing information interpretable in terms of salinity conditions within the bay. Sources include both quantitative salinity values as well as anecdotal observations about salinity and related conditions (for example, direct observations of freshwater occurrences, fish kills, and other phenomena reflecting changes in water quality). A partial listing of resources searched is included as table 1.

This effort to compile a salinity record for Florida Bay began in 1987 and has continued intermittently since then (Robblee, 1989; Nuttle and others, 2000). With this study the effort has produced a database containing 232 references, including 70 sources of salinity data extending from 1936 (Davis, 1940) to the present. Spatially extensive data are available from the mid-1950's. Comprehensive salinity monitoring begins in the late 1980's. Less quantitative or anecdotal references to salinity conditions date back to the turn-of-the-century in the scientific literature, and to the mid-19^th Century in the historical record.

Figure 2. Monthly mean salinity for period-of-record, 1950-1999, for 5 reference areas in Florida Bay. Click for larger image.

A principal goal of this study is to integrate these diverse studies and observations into a relational database within which the data can be explored, data sets can be developed, and data files can be exported for further analysis. The database interface supports multiple types of queries, including geospatial, temporal, and reference. From the results of any query, searchers may retrieve both salinity data and annotated reference materials. Latitude/Longitude or UTM coordinates, basin, or place name, define location. Within the database, basins are defined according to the polygon structure employed in FATHOM (Cosby, Nuttle and Fourqurean, 1999). Place names are defined according to the U.S. Board on Geographic Names (Orth and Payne, 1997). The primary data for each study are available in the database. A data set of daily average salinity calculated for each station within each study forms the basis for integrated data searches. Integration of data sets differing widely in spatial and temporal scale has been achieved within the database using a series of decision rules. To expedite data searches, predefined data summaries will be available for monthly, seasonal (wet/dry), and annual time steps. Metadata records providing summaries of the study; geospatial and temporal coverage of the study; descriptive keywords and place names; and related references where applicable will accompany data retrieved in each search.

An initial analysis of the data in the database indicates that, over the period-of-record, Florida Bay has varied between being a positive (salinity decreasing west to east) and a negative estuary (salinity increasing west to east) (fig. 2). These patterns of salinity appear to be linked to the wet/dry cycle characteristic of south Florida. During periods of drought the Bay behaves as a hypersaline lagoon. The highest recorded salinity for open bay waters (70 psu) occurred in April of 1956 at Buoy Key east of Flamingo (Finucane and Dragovitch, 1959). Twice normal seawater, 70 psu, was observed again in May 1991 in Rankin Lake near Buoy Key at the end of the 1989-1991 drought. Hypersaline conditions appear first and have been most severe and persistent in central Florida Bay where salinities have reached or exceeded 40 psu for over 50 percent of the period-of-record. In contrast, Florida Bay behaves as a positive estuary less often. Episodic events associated with high rainfall such as tropical waves or depressions, hurricanes or periods of above average rainfall like the 1993-1995 high water period are needed for Florida Bay to be a positive estuary. Upstream water management may have achieved this effect as well. Increased flows through the C-111 Canal cutouts into Florida Bay due to operational changes upstream had the effect of maintaining Florida Bay as a positive estuary during the period 1983-1985, a period of significant below average rainfall in south Florida.

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report (PDF, 8.7 MB))

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