The Everglades, a vast wetland ecosystem in South Florida, is not simply a freshwater or saltwater environment. It is a dynamic system with a range of water types, resulting from freshwater flowing from inland sources and saltwater encroaching from the coast. This creates diverse aquatic conditions across its expansive landscape.
The Everglades’ Water Composition
The Everglades features distinct zones of freshwater, brackish water, and saltwater. Freshwater dominates the northern and central regions, originating from the Kissimmee River basin and Lake Okeechobee. Water from these sources flows southward, historically as a wide, shallow sheet, through the “River of Grass” towards the coast.
As this freshwater sheet approaches the coast, it mixes with seawater, forming brackish water in transitional zones. This brackish water, characterized by salinity levels between 0.5 and 30 grams of salt per liter, is found in estuaries where rivers meet the ocean. Along the southern and southwestern edges, particularly in Florida Bay and the Gulf of Mexico, saltwater environments prevail.
Life Thriving in Varied Waters
The diverse water conditions within the Everglades support a wide array of plant and animal life, adapted to freshwater, brackish, or saltwater environments. In freshwater marshes and wet prairies, species such as American alligators and wading birds like egrets and wood storks are common. These areas also host plant communities, including sawgrass.
In brackish zones, organisms capable of tolerating fluctuating salinities, known as euryhaline species, are prevalent. Mangrove trees, for example, are adapted to brackish conditions, with some species able to filter salt through their roots or excrete it from their leaves. This transitional area serves as a nursery ground for various fish, crustaceans, and shellfish. In the saltwater regions of Florida Bay, marine species and extensive seagrass beds flourish, providing habitat for a multitude of fish and other marine life.
Influences on Water Salinity
The salinity levels across the Everglades are influenced by natural processes and human activities. Natural factors include seasonal rainfall, which can dilute saltwater intrusion by increasing freshwater flow, and tidal cycles that regularly introduce saltwater inland. The interaction between the southward flow of freshwater and the push of oceanic tides creates a dynamic and constantly shifting salinity gradient.
Human modifications have significantly altered natural water flow and salinity patterns. Canals and levees, designed for drainage and flood control, have diverted freshwater from historical paths, reducing the volume reaching coastal areas. This reduction allows saltwater to intrude further inland, impacting freshwater habitats and underground aquifers. Additionally, rising sea levels also contribute to this inland shift, causing vegetation changes and posing long-term challenges to the ecosystem’s balance.