The Florida Everglades occupies a precarious ecological position. It is poised between fresh water flowing in from the north and the ocean pushing in from the south and west. So, sea level rise works against the fresh water, tipping the scales in favor of the sea. The saltwater incursion into the freshwater portions of the ecosystem stresses the existing plant and animal species.
History
The Everglades we see today is about half the size of its original extent, and it currently occupies about 1.5 million acres (2,300 square miles). The original Everglades hydrologic system occupied a shallow geologic basin that encompassed the entire area of South Florida, except for higher ground along the east and west coasts.
The northern portion of the system contains the Kissimmee River and Fisheating Creek watersheds, which feed into Lake Okeechobee. So, the source of the fresh water for the Everglades wetlands in the southern part of the system is Lake Okeechobee. Fresh water collects in the lake and then spills out from its south end and slowly flows as a sheet of water over the wetlands of the Everglades.
However, several hundred years of human tinkering with the Everglades has altered this original system. Large tracts of farmland and water control systems now separate the current Everglades from its lifeblood, the fresh water from Lake Okeechobee. These water control systems, instituted in 1948, choked off the Everglades from the full volume of water it needed. Because of the reduced water flow, plant and animal habitats suffered, and species populations shrank.
The saw grass that characterizes much of the classic Everglades wetlands requires a constant supply of fresh water to thrive. So, efforts at restoration to undo the damage were authorized by Congress in 2000. Wetland restoration was implemented via the Comprehensive Everglades Restoration Plan, or CERP. Accordingly, this massive hydrologic project seeks restoration of the wetlands through increased waterflow. But supplying this water requires a balancing act between the need for crop irrigation, municipal drinking water, flood control, and fresh water for the Everglades
Miscalculation
Thick organic peat deposits are one of the building blocks of healthy wetlands. Therefore, the saw grass ecosystems of the Everglades rest on top of fragile peat soils that accumulated over thousands of years. Without fresh water, the soils then dry out and cannot support the overlying saw grass. This is what happened before intervention. But, CERP fulfilled its goals in many areas, and restoration of groundwater levels now successfully supports the return of native vegetation.
CEPP incorporated the knowledge-of-the-day into its program, but there were miscalculations. Knowledge related to climate change was far more limited in the year 2000 than today. Sea level rise and saltwater intrusion below the ground were not properly accounted for in the original calculations.
Water wars
Below the ground, in the peat soils of the Everglades, a saltwater-freshwater transition zone marks the battle line between two separate water supply systems. Much of the fresh water from the north moves oceanward through the groundwater system. Likewise, salt water from the ocean moves landward in the same peat dominated soils.
This transition zone has moved inland about a kilometer over the past half-century. But the Everglades saw grass ecosystem is not compatible with salt water. The salt water induces chemical changes in the peat that lead to its collapse. As the land surface collapses, then rising seas surge inland, thus salt water attacks the saw grass from above and below. Already the increasing frequency and strength of king tides force seawater kilometers into the Everglades.
The amount of saltwater intrusion below the ground depends on the volume of fresh water flowing into the Everglades. However, the need for this extra volume of water was not originally accounted for by CERP. In theory, this is a solvable problem, but only if enough extra fresh water is available.
But, the incursion of salt water from rising sea levels is a much more difficult problem to solve. So, in the foreseeable future, the scales in a battle between the seawater and the fresh water are tipping in favor of the ocean and against the freshwater ecosystems of the Everglades.
ArcheanWeb:
Florida Everglades, not what it used to be (Source: ArcheanWeb) – https://archeanweb.com/2020/04/08/florida-everglades-not-what-it-used-to-be/ Also:
Saltwater invades Florida’s water supplies (Source: ArcheanWeb) – https://archeanweb.com/2019/12/09/saltwater-intrusion-florida-water-supplies/ Also:
Sources:
A freshwater, saltwater tug-of-war is eating away at the Everglades (By Carolyn Gramling; ScienceNews) – https://www.sciencenews.org/article/florida-everglades-freshwater-saltwater-sea-level-rise Also:
Feature Image: Aerial view of the Everglades coast, with clouds (Modified) By LBM1948 – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=80532102
