Florida Bay is an estuary that covers approximately 1,100 square miles (2,850 square km) between the southern tip of Florida and the Florida Keys. It is located in a shallow platform lagoon where fresh water from the Everglades mixes with salt water from the Gulf of Mexico. Florida Bay is the bay located between the southern end of the Florida mainland (the Florida Everglades) and the Florida Keys in the United States. It is a large, shallow estuary that, while connected to the Gulf of Mexico, has limited water exchange due to the shallow mud banks that divide the bay into many basins or lakes.
The shores separate the bay into basins, each with their own unique physical characteristics. Florida Bay, which encompasses approximately one-third of Everglades National Park, covers an area of 800 square miles (2,100 km), 850 square miles (2,200 km), or 1,000 square miles (2,600 km). The bay has been described as a lagoon on the interior continental shelf. The northern edge of the bay is formed by the Florida mainland. The east and south edge of the bay is defined by the Florida Keys, with only a few natural passages between the islands that connect to the Atlantic Ocean.
The western edge of the bay is defined by the westernmost mud banks of the bay. Nearly all of Florida Bay is included in the Everglades National Park. The southern end, along the Florida Keys, is in the Florida Keys National Marine Sanctuary. While there is no definite boundary between Florida Bay and the Gulf of Mexico, the westernmost edge of Florida Bay can be approached by a line drawn from Long Key to Cape Sable on the mainland, which is very close to the Everglades National Park border line.
The northeastern end of Florida Bay is located on Jewfish Creek in Key Largo. Blackwater Sound, southwest of Jewfish Creek, is generally considered part of Florida Bay; Barnes Sound, on the other side of Jewfish Creek, is not. Barnes Sound is generally considered part of the Biscayne Bay system. Water flows between basins in narrow channels and over mud banks.
The bay is open to the Gulf of Mexico from the west, but the connection to the Atlantic Ocean from the east is restricted to narrow channels between the Florida Keys. The average tidal range along the western edge of the bay is 1 to 1.5 meters, but the tidal range decreases rapidly eastward in the bay due to restricted water flow between basins. The flow of fresh water to the bay is limited to Taylor Slough and Trout Creek, in the northeast corner of the bay, and represents only 10% of the bay's fresh water supply (rains provide the rest of the fresh water). Due to poor water circulation within the bay, salinity increases rapidly away from the shores of the bay, except in the northeastern part of the bay, where it receives fresh water from rivers.
The tides in Florida Bay are semidiurnal, with a range of 60 centimeters (24 inches) on the Atlantic side of the streams that connect the Florida Keys and Cape Sable. Tidal ranges are less than 15 centimeters (5.9 inches) behind the first line of mud banks and are absent in the northeast corner of the bay. Salinity is 30 to 40% near the open waters of the continental shelf, while salinity levels range from 4 to 70% in the northeast corner of the bay. Examination of the paleontology of biota in the sludge cores of Florida Bay has discovered that, historically, the salinity of water in Florida Bay has relied primarily on rainfall rather than on the flow of the Everglades. Florida Bay is the largest body of water in the Everglades National Park, with an area of more than 2,850 square kilometers (1,100 square miles) between the southern tip of Florida and the Florida Keys.
The bay, which consists of a series of shallow water basins, is located on a shallow platform where fresh water flowing from the Everglades mixes with salt water from the Gulf of Mexico. The coastline along the Florida Bay supports mangrove forests with waters close to the coast. dotted with hundreds of mangrove islands. The bottom of the bay includes extensive seagrass beds and hard-bottomed reef habitat.
Freshwater from the surface enters the bay through a continuous flow and flows directly from Taylor Slough from the southern part of the Everglades to Whitewater Bay. However, this flow of fresh water has declined considerably over the past century due to the construction of a series of channels in the Everglades. Freshwater also enters the bay through rain, surface runoff, and groundwater. This mix of saltwater and freshwater results in a salinity gradient across the bay, with salinities increasing from north to south.
In recent years, the waters of Florida Bay have been hypersaline, with salinities exceeding 35 parts per thousand (ppt). The Gulf of Mexico includes the westernmost coastal waters of the Everglades National Park. The dividing line that separates the Gulf of Mexico and Florida Bay extends from Long Key to the northwest. to Cape Sable.
Shark River Slough carries fresh water from the western Everglades to the Gulf of Mexico, creating brackish water estuaries along the coast, including mangroves and tidal rivers, as well as many small mangrove islands in an area known as the Ten Thousand Islands. Due to large changes in seasonal rainfall, the tidal rivers of Tampa Bay contain varying amounts of fresh water, brackish water, and bay waters with higher salinity throughout the year. Rivers also carry nutrients and debris from decaying vegetation in the downstream watershed. At the same time, tidal action from the bay sends saltwater to rivers, full of plankton and various chemical components.
As these waters combine, salinity ranges create different ecological zones in rivers and streams (see main illustration). The mud banks in the central part of the bay tend to run from northwest to southeast, which corresponds to the direction of approach of the cold fronts that cross the bay. During the Wisconsin glaciation, sea level was much lower than it is today, and the area that is now Florida Bay was dry land. The key to correcting this imbalance is getting more clean fresh water from Lake Okeechobee to the Bay of Florida.
Juvenile sports fish, such as tarpon and bass, are also dependent on having the right salt concentrations in Florida Bay. For all these and other reasons, it has long been understood that Florida Bay is a place that deserves and needs protection. Stabenau hopes that Everglades restoration projects can help achieve the right salt levels in Florida Bay. The Miami limestone of Florida Bay was formed during the Sangamon interglacial period, between the most recent glacial period, that of Wisconsin, and the previous one, in Illinois, which occurred about 125,000 ago years.
