The purpose of this project has been to compile existing salinity observations from the diverse literature on Florida Bay and to use this information to characterize salinity dynamics in Florida Bay over the available period-of-record. Salinity along with associated temperature, DO, and pH observations from all sources were combined in a single database relating each observation to time and place. 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 (for example, the observation was not part of a fine interval time series or an average value taken over time or space); 3) the date and time that the observation had been made was known; 4) the latitude/longitude coordinates of 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 could be determined.

The quantitative record of salinity in Florida Bay begins in 1936. Earlier references to salinity in the Bay are qualitative. To date salinity observations have been gathered from sixty-one published and unpublished studies. The resulting salinity record includes over 18,000 discrete salinity observations from within Florida Bay. The temporal and spatial distributions of the data largely reflect long-term research interests and concern over perceived conditions and related management issues within the Bay. Effectively, a usable database exists from the mid-1950's. In 1981, long-term monitoring of salinity was initiated by Everglades National Park in northeastern Florida Bay. By 1988, this monitoring network was spatially extensive with good coverage over much of Florida Bay inside Park boundaries.

Since 1955, Florida Bay has behaved generally as a marine lagoon which is often hypersaline. Salinities within the Bay can be described along a southwest/west to northeast gradient. The Gulf of Mexico and Taylor Slough/C-111 Canal, the latter being the Bay's primary freshwater sources, serve as extremes, respectively. Generally at a site in Florida Bay, variation in salinity conditions decreases from east to west. In the west marine salinities have prevailed. Mean monthly salinity has averaged 36.1 ± 1.6 ‰ at Long Key and 35.9 ± 5.1 ‰ in Johnson Key Basin. In southwestern Florida Bay at Long Key, where Atlantic and Gulf conditions dominate, the range of salinity observed has been 28.7 to 40.2 ‰. In Johnson Key Basin, also in the west but a basin enclosed by shallow water banks, the range of salinity has been greater, 20.0 to 53.2 ‰. Persistent estuarine conditions in Florida Bay have been largely confined to the embayments and bays characterizing the Bay's northern margin. In the fringing bays bordering northeastern Florida Bay mean monthly salinities in Long Sound, Joe Bay, and Little Madeira Bay, immediately downstream of Taylor Slough and the C-111 Canal, have averaged 23.2 ± 11.6 ‰. Variation in salinity has been greatest in these shallow fringing bays where the observed range of mean monthly salinities has been 0 to 57.6 ‰ over the period-of-record. In contrast mean monthly salinities in the vicinity of Duck Key, immediately downstream of Joe Bay in Florida Bay proper, have averaged 34.2 ± 8.6 ‰ with a period-of-record range of 13.3 to 51.3 ‰.

Over the period-of-record, Florida Bay has often been hypersaline. Hypersalinity in the Bay occurs with cyclic drought conditions in South Florida. The highest reported salinity for openwaters in Florida Bay was 70 ‰. 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. Hypersaline conditions in Florida Bay appear first and have been most severe and persistent in its center near Whipray Basin where mean monthly salinities have averaged 40 ‰ (range = 21.2 to 57.3 ‰) over the period-of-record. During this period salinities in Whipray Basin have reached or exceeded 40 for almost 60 percent of the months when data was 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 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 to 1985.

Generally, interannual variation in salinity exceeds seasonal variation in Florida Bay. This results due to the complex geometry of the Bay, the relative dominance of marine influence over freshwater inflow, and the importance of the wet/dry cycle in south Florida. Variation in salinity due to water management is weak when compared to natural variation in salinity.

Back to Project Homepage