Existing salinity observations and salinity information for Florida Bay are being compiled in a relational database accessible via the Internet for the purpose of characterizing salinity conditions in Florida Bay over the last century. To compile this comprehensive salinity database, extensive searches for salinity data have been conducted across a diverse body of published and unpublished literature and collections spanning more than 150 years. A salinity observation was included in the database if the following criteria were met: 1) the observation had been made within Florida Bay waters or in waters adjacent to the bay; 2) the measurement was a discrete observation (not an average value); 3) the date and time that the observation had been made was known; 4) the location at which the salinity observation had been made was available or could be estimated; and 5) the depth at which the observation had been made was known or could be determined. At this time the domain of the database is being expanded to include the southwest mangrove coast of Everglades National Park and temperature data is being included when available.

The quantitative record of salinity in Florida Bay begins in 1908 (Moore, 1908). To date salinity observations have been gathered from seventy-two published and unpublished studies. Some data is available from the 1930’s and 40’s but effectively, a usable database exists from about 1955. Even at this data after 1955 are scattered in space and time. In 1981, long-term monitoring of salinity was initiated by Everglades National Park in northeastern Florida Bay. This monitoring network was expanded to include bay-wide coverage inside Park boundaries by 1988. More recently spatially synoptic salinity surveys are being conducted in the bay related to restoration of the Everglades. A significant database issue has been the integration of data sets differing greatly in temporal and spatial intensity.

Since 1955, Florida Bay has behaved generally as a marine lagoon that is often hypersaline. Salinities within the bay can be described along a southwest/west to northeast gradient. The Gulf of Mexico/Atlantic Ocean and Taylor Slough/C-111 canal, the latter being the bay’s primary direct freshwater sources, serve as endpoints on this gradient, respectively. Along this gradient the marine influence of the Gulf and Atlantic decreases from the west while evaporation in the increasingly shallow and confined waters of central and eastern Florida Bay becomes dominant particularly in dry years. Estuarine conditions in Florida Bay are largely confined to the bay’s northeastern margin near the freshwater source.

Salinity conditions along this gradient can be summarized for the period-of-record. In western Florida Bay relatively constant marine salinities predominate. Mean monthly (± 1 sd) salinity has averaged about 36 psu ± 2.0 psu in the vicinity of Long Key. This region of the bay is in close contact with the Gulf and Atlantic. In a region centered on Johnson Key Basin mean monthly salinities average about 36 psu ± 5.5 psu. Johnson Key Basin is located south of Flamingo sheltered by extensive shallow water banks. The range of monthly average salinities observed in these areas over the period-of-record was 28.7 psu to 40.2 psu and 20.0 psu to 53.2 psu, respectively. In the vicinity of Long Sound, Joe Bay and Little Madeira Bay in northeastern Florida Bay, immediately downstream of Taylor Slough and the C-111 Canal, mean monthly salinities averaged about 20 psu ± 11.7 psu. The range of observed monthly average salinities was 0 psu to 57.6 psu over the period-of-record. Extreme salinity changes occur in these fringing waters. In contrast mean monthly salinities in the vicinity of Duck Key, immediately downstream of Joe Bay in Florida Bay proper, averaged about 33 psu ± 9.4 psu with a period-of-record range of 13.3 psu to 51.3 psu. In Florida Bay salinity variability is greatest in the northeast declining to the west.

Generally, annual variation in salinity exceeds seasonal variation in Florida Bay with the exception of the upper estuaries, Long Sound, Joe Bay and Little Madeira Bay. This result is due to size and complex geometry of the bay, the relative dominance of marine influence over freshwater inflow, patterns of rainfall, and the importance of the wet/dry cycle in south Florida.

Over the period-of-record, Florida Bay has often been hypersaline. Hypersaline conditions in the bay occur in years of average or slightly below average rainfall; extreme hypersalinity occurs with cyclic drought conditions in south Florida (Thomas, 1974). The highest reported salinity for open waters in Florida Bay was 70 psu (Finucane and Dragovitch, 1959). This salinity has been observed twice near Buoy Key, east of Flamingo, at the end of the dry season, once in 1956 and again in 1991. During severe drought salinities exceed 40 psu occur over most of Florida Bay including Long Sound, Joe Bay and Little Madeira Bay. Characteristically hypersaline conditions in Florida Bay appear first and are most persistent in central Florida Bay in the vicinity of Whipray Basin where mean monthly salinities for the period-of-record have averaged about 42 psu ± 8.9 psu (range = 21.2 psu to 57.3 psu). During this period salinities in Whipray Basin have reached or exceeded 40 psu for almost 60% of the months when data is available. In contrast, estuarine conditions across Florida Bay are rare and usually associated with high rainfall episodic events such as tropical waves, depressions, and hurricanes or with periods of above average rainfall like the 1994 to 1995 high period. Water management has influenced these processes as well. Increased flows through the C-111 Canal due to upstream operational requirements lowered salinities across the bay during a period of below average rainfall in south Florida, 1983-1985. However, variation in salinity due to water management in Florida Bay is probably small when compared to the natural variation in salinity.

Finucane, J.H. and A. Dragovitch. 1959. Counts of red tide organisms, Gymnodinum breve, and associated oceanographic data from Florida west coast 1954-1957. U.S. Fish and Wildlife Service Special Scientific Report - Fisheries. No. 289:202-295.

Moore, H.F. 1908. The commercial sponges and the sponge fisheries. U.S. Bureau of Fisheries. Bulletin of the Bureau of Fisheries. 28 (part 1): 399-511.

Thomas, T.M. 1974. A detailed analysis of climatological and hydrological records of South Florida with reference to man's influence upon ecosystem evolution. Pages 82-122 In P.J. Gleason, ed. Enviroments of South Florida: present and past. Memoir 2: Miami Geological Society, Miami, Florida.

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(This abstract was taken from "Programs and Abstracts - 2001 Florida Bay Science Conference". (PDF, 6.8 MB))

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