EARLY FORMATION OF THE EVERGLADES ECOSYSTEM

Geology, geography, climate and chemistry have joined in the Greater Everglades to produce a natural wonder. It is vast in area, uniquely complex ecologically and highly diverse in its combinations of species. It was created by an unusual combination of natural events. South Florida was sea floor for most of the last 150 million years, and very stable geologically. This history established its structure as a deep flat limestone base, formed from the calcium carbonate of the shells of tiny marine creatures over millions of years. During the last glacial minimum around 110,000 years ago, the sea deposited a porous limestone layer, the Biscayne Aquifer, which underlies much of the modern everglades and accounts for it’s extraordinary ability to store water. But the aquifer is now shared with millions of people. Around the same time the Atlantic Coastal Ridge was deposited, a several mile wide strip of limestone 20 feet higher than the current sea level. It formed the eastern edge of the everglades and, when sea levels subsided, kept much of its water flowing south into Florida Bay though some flowed east into Biscayne Bay. Changes in these fresh water flows have changed both bays.

Only about 5000 years ago did South Florida’s climate take on its current sub-tropical and monsoonal character of dry winters followed by hot moist summers with large amounts of rain (on average 50-60 inches per year), as seas that surround it on three sides warm and evaporate. In addition the northern part of the ecosystem includes one of the largest lakes in North America, Lake Okeechobee. Due to its geography, along with the wet season rains, tropical storms and hurricanes can drop 18 to 24 inches of rain in a single 24-hour period over thousands of square miles. Water is the lifeblood of the Everglades wetland; and its geological structure of porous limestone allowed much of this water to be retained within the aquifer, even during the dry season.

Finally, and very importantly, the Everglades is nutrient-poor, based on extraordinarily low natural nutrient input. For the most part, the ecosystem’s substrate was limestone, or former ocean bottom. The only net additions to the system’s nutrition came in very modest amounts from rainfall and plant decay, which over eons created a stratum of peat in depressed areas. In particular Phosphorus was a limiting factor. [2]

The result was that the most successful plants and other flora, from sawgrass to periphyton (a combination of a variety of algae, bacteria, microbes and detritus which is the base of many everglades food chains) were extremely well-adapted to dominate in the competition with other plants for the few nutrients available, especially Phosphorus.