Part I - Geology of Florida and the Everglades
Part II – Intended Change. Unintended Environmental Consequences.
Perhaps your best chance at time travel awaits you in the Florida Everglades. Mine was last April. It was an unforgettable experience. All senses on high alert. In the morning haze with the smell of salt and sawgrass in the air, a thousand birds in flight, vultures soaring overhead, and armies of alligators patiently awaiting their next meal, the marshy wilderness stood frozen in time.
|Alligator mississippiensis, apex predator and most important species of the Everglades|
But initial perceptions can be deceiving. These Everglades have been changed. What appears to be wild and untamed is in reality a highly engineered ecosystem, seized by man from Mother Nature and harnessed for his own needs: flood control, clean water, land for agriculture and habitation. Man’s success can be measured in the ecosystem’s loss, and ultimately, his own.
The Everglades contains one of the highest concentrations of species vulnerable to extinction in the U.S. The 5,000-square-kilometer wetland is home to at least 60 endangered species and retains less than 10% of its original habitat.
DECLINE OF THE INHERENT STRUCTURE OF THE EVERGLADES
My plane was seconds from touch down at Miami International Airport when I snapped this photo of the Everglades looking south into the haze along Krome Avenue and Canal, which joins the larger Miami Canal behind us to the north. Notice anything amiss about the marshy terrain?
The landscape to the east (left) of the canal consists of a green structureless, patchy sawgrass wetland, and to the west (right) it is more defined and linear as water flows south to Florida Bay fifty miles away. Self-serving, man-made structures such as roads, canals and levees haven’t exactly been eco-friendly. So evident is the ecosystem’s degradation that it can be seen from the air.
RIDGE AND SLOUGH
Two of the main systems that formed in the Everglades marsh are the sawgrass plains in the north and the “ridge and slough” landscape in the south. Ridge and slough consists of parallel arrangements of peat-based ridges and open sloughs (pronounced “slews”) oriented to the direction of sheet flow to the south and southwest. They are the deepest (over 3 feet in the rainy season) water communities that serve as the main avenues of flow through the Everglades. Flow, the steady and continuous movement of water, is THE most important aspect of ecosystem health in the Everglades.
Many of the sloughs possess tree islands at their upwater heads. Before channeling into Everglades National Park, the waters of the greater Everglades converge into two large sloughs called Taylor and Shark River that are basically low-lying, wide rivers with northeast-southwest axes.
|Notice that the limestone bedrock below the surface has no relationship to the ridge-and-slough landscape|
but may have a prominence below the head of tree islands.
From Chris McVoy, 2003
These structures evolved with the natural sheetflow of water, which likely began within the last 6,000 years (see my post Part I for Everglades geology here). The very identity of the Everglades is related to its slow movement across the vast, low gradient, wetland landscape. Drainage and compartmentalization for flood control and water supply have so interrupted the natural hydrology that this crucial habitat has suffered detrimental ecological damage.
LOSS OF HABITAT
As the ridge and slough landscape became topographically and vegetationally more uniform, amorphous sawgrass stands became associated with fewer numbers of animals and a lower diversity. Foraging and nesting of wading birds is closely tied to vegetation patterns which have been altered. The negative impact on the landscape extends throughout the ENTIRE food web of the Everglades. It's all about the water: quantity, quality, timing and distribution.
THE NEW RIVER CANAL AND LEVEE
The quick drive to the Everglades on Alligator Alley from South Florida's densely-settled east coast, where I was staying, parallels a large canal and levee called the New River, one of many that transect the wetlands. Native American canoe trails have crossed the Everglades since pre-Columbian times, but its modern successors are wider, deeper and hundreds of miles longer. Four major drainage canals were dredged through the Everglades in the early 20th century totaling 236 miles.
Constructed for water management and as a navigable connection between the two coasts, the New River canal and others impede the natural flow of water by slicing the Everglades into flood-manageable but ecologically-segregated parts. Canals draw water from the surrounding wetlands. During the dry season, this causes a complete dry-down of the habitat, a diminished aquatic habitat during the wet season, soil loss and degradation of the peat surface.
The excavation of canals through the less permeable peat into the highly permeable aquifer allows the mixing of ground and surface water, and discharging of salty water that is highly damaging to the biological communities. Florida, Congress and ultimately the taxpayers are learning the difficult and expensive lesson of what happens when you “re-engineer” a region’s natural hydrology.
The canals that drain the glades have reduced groundwater levels, which stopped the flow from natural springs. Saltwater from the sea has backfilled the freshwater “void” both to the detriment of the ecosystem and man’s water supply. Along estuaries at the sea, freshwater releases from canals abruptly changes the salinity, which few species can tolerate, including vegetation. Indigenous fish and oysters in coastal estuaries at the outlets of canals are on the decline, while nonindigenous predators are on the rise. Additional details of change can be found on my earlier post Part II here.
Alligator Alley’s four-lane highway has many bridges designed with the concept of “road ecology.” The intent is to allow water and wildlife to pass underneath, thereby reducing the environmental impact to the ecosystem. Unfortunately, the road acts as a dam and a formidable wildlife barrier by restricting flow, while the culverts are equivalent to mere leaks. The Comprehensive Everglades Restoration Project plans to elevate long sections of roadways to allow water to proceed unimpeded into the major sloughs and Everglades National Park to the south.
|Section of Alligator Alley with "eco-designed" structure between the compartments of WCA-2B and WCA-3A|
EXCURSION INTO THE EVERGLADES
Our Everglades excursion was led by Captain Randy of "Ride-The-Wind", a private charter touring company. Captain Randy was quick to assure us of our safety under his command. In addition to over thirty years of experience in the Everglades, he served for many years as a captain in the U.S. Coast Guard, as a certified 100-ton Master, and afterward as a gator handler and Certified Dive Master. Captain Randy comforted us by proudly stating, “We’ve never had an occupant eaten by an alligator or strangled by a python!”
Our Everglades-worthy vessel was an airboat, but fanboat is more descriptive. It’s a flat-bottomed craft propelled forward by a massive fan enclosed in a protective cage driven by an equally large (and loud) aircraft engine and steered by two rudders at the boat’s stern. A conventional motorboat with a keel would be useless in the shallow, propeller-clogging sawgrass of the Everglades. Speaking of sawgrass, the indigenous vegetation of this marshy habitat, those are nonindigenous cattails lining the canal, another symbol of ecosystem change.
At the launch site, a large, imposing flood control gate dominated the head of the canal, a reminder of the regulatory capabilities of WCA-2A, one of many compartmentalized water conservation area of these Everglades that I had entered. Remember, this is an engineered wilderness!
I was also surprised by the appearance of the water. I expected it to be cloudy, foul-smelling and swamp-like. Instead, it flowed clear and clean, albeit slowly, but far from stagnant. The waters of the Greater Everglades are funneled to the south and southwest of the Florida peninsula on a tilted-gradient of the Florida Platform that’s virtually imperceptible (see Post I for details here).
FROM A SINK TO A SOURCE
As mentioned, I expected to see sawgrass, the ubiquitous flora of the Everglades. Instead, the canal was bordered by dense, tall invasive Southern cattails. Once seen in localized small populations, they thrive on the high phosphorus content of the water filtering downstream from the north. Most ecosystems are nutrient-limited in composition, especially nitrogen and phosphorus, the principal components of fertilizers. Not here.
The original, un-engineered Everglades system held 4-10 ppb of phosphorus. With the establishment of the Everglades Agricultural Area upstream and below Lake Okeechobee (that contains high levels of natural phosphorus), the northern Everglades has become a nutrient "source" rather than its historic role as a nutrient “sink.”
Thus, cattails began to thrive downstream on high levels of nutrients (in excess of 500 ppb). The impact of this change may seem unimportant, but cattails could prove to be devastating for plant and animal life in the area by completely changing the ecology. Not only did the theme of anthropogenic change resonate throughout my excursion, but that the changes are not well understood, yet are a reality and a priority.
The dominant plant in the Everglades marsh and prairie is Jamaica swamp sawgrass. Preferring the wet soils of the Everglades, sawgrass is not “true grass” but a sedge, in a different plant family with sharp teeth along the edges of each blade. Grass stems are round and hollow, while sawgrass has a triangular stem. Rush stems are flat or round.
Fires in the Everglades play a vital role by limiting the colonization of woody vegetation that would eventually invade Everglades marshes and replace the sawgrass, changing the the marsh into the next successional habitat. Fire beneficially sets succession back and has the positive effect of releasing and redistributing locked-up nutrients in plant tissues during their growth. Thus, "natural" fires regenerate the marshes. The wet soil of the Everglades protects the roots of the sawgrass, which enables it to survive fires and then regenerate.
|Modified from finegardening.com|
Illustration by Allison Starcher
Sawgrass thrives on shallow water depths, whereas cattails flourish in deeper areas. Another hypothesis to the cattail’s radiation is that the fragmentation of the Everglades has altered the watershed’s natural hydrology, and in many areas, increased the water level beyond the sawgrass’s ecological preference. With over $11 billion in federal and state funds devoted to restoriation, all-out war is being waged against the cattails with controlled burns and “safe” chemical poisons.
VULTURES GALORE IN SEARCH OF GORE
As Captain Randy was readying his airboat, an inquisitive American Black Vulture dropped by to investigate the activity. Black Vultures have black plumage, a small, featherless grayish head and neck, and a short hooked-beak. The word "vulture" is derived from the Latin word vulturus meaning “tearer” of flesh. Being scavengers (and raptors), they dine on carrion (including roadkill), attracted to it by their keen vision. The vultures will circle gracefully overhead of a carcass riding thermals of rising air but often hunt from a perch in a tall tree.
Less than a minute after the Black Vulture's arrival, it was physically displaced by this characteristically more aggressive American Turkey Vulture. Unlike the Black Vulture, this scavenger has both a keen sense of sight and smell, which helps attract the Black Vulture to carcasses. These "buzzards" are easily distinguished by a bald, red head and silvery wings on the undersides best seen in flight. They resemble a turkey when seen from a distance and hiss when threatened.
Donning ear muffs for protection against the noise and latching up our seatbelts for safety, we effortlessly launched into a subdivision of the New River Canal and immediately veered off into a smaller ditch. Many of the ditches that crisscross the Everglades are remnants of Native American trails, which have persisted by the airboats frequent usage. As early as 300 A.D., many were built by the native Ortona and, later, Calusa and Tequesta people to connect villages to coastal trade routes.
I commented to Captain Randy that I was surprised to see so few insects. He responded that it depends on the time of the year. He also mentioned that if you catch one in your mouth while on the airboat, it’s considered Everglades “fast food.” Randy had a rather unique sense of humor.
FLORIDA’S OFFICIAL STATE REPTILE (ALONG WITH LOUISIANA AND MISSISSIPPI)
No other species defines the Everglades as does Alligator mississippiensis. It's the most important species in the Everglades. The American alligator is not only the "apex" predator at the top of the Everglades food chain, but it’s the "indicator" species for gauging the health and restoration of the imperiled ecosystem. It’s also a "keystone" species that affects nearly all aquatic life in the Everglades.
In the 1900's and 1960's, alligators were literally disappearing from the wetlands by poachers that sold their hides. Finally, the federal Endangered Species Act of 1973 made it illegal to deal in any alligator parts including skulls, teeth, claws, meat and hides. They have since rebounded tremendously, yet the main threat today facing the American alligator is the destruction and degradation of its wetland habitat.
Crocodiles and alligators belong to a group of reptiles called crocodilians, and uniquely, both reside within the Everglades, but alligators are far more common. Once occupying all wetland habitats in south Florida, development and water-management practices have reduced both the quantity and quality of these habitats. Today, the alligator inhabits freshwater wetlands of the southeastern United States but has declined throughout the Greater Everglades; whereas, the croc, being a tropical species, maintains its northern-most range in brackish, coastal mangrove areas of south Florida including Florida Bay.
Amongst other notable features, the alligator is distinguished by its broader snout, darker or blackish coloration and overlapping, upper jaws. Crocs have a tapered, triangular snout, are grayish-green and have a signature tooth jutting out from its lower jaw.
Alligators are pond-builders and worthy of their role as "ecological engineers." They alter the landscape by using their mouths, bodies and tails to remove vegetation from small depressions within the bedrock and push soil sediments onto the banks, thereby creating and maintaining "alligator holes." Their construction may not be intentional but a consequence of herding fish and foraging for food.
The holes contribute to an increase in habitat diversity and species richness both in and around the holes. Therefore, an increase in holes, nests and occupancy rates translates into a healthy ecosystem and a sign of successful restoration efforts.
|The small open area ringed by trees is an alligator hole|
National Park Service
In the dry season, the holes serve as an aquatic refugia for alligators and other aquatic organisms such as fish, amphibians and invertebrates, and as foraging sites for wading birds that prey upon the resident species.
Gators also construct many channels or trails (seen above) that lead to the holes. Many holes are surrounded by a low ring of trees or are near a tree island as this one. Typically, they are ringed by a sawgrass marsh. Many gator holes are centuries old and are maintained by successive generations of alligators.
Knowing the wetlands like the back of his hand, Captain Randy knew precisely where gator holes were located. He shut off the fan and glided us into a hole where a female was thermoregulating in the morning sun.
|Captain Randy has spotted a large female at the periphery of a gator hole.|
A low ring of trees, shrubs and even cattails often helps locate the holes.
|Notice how the sawgrass has been trampled by mama's movements around the hole.|
I spotted six juveniles basking on the periphery of the hole with likely more present within the tall sawgrass. The average clutch size is 32-46 eggs, which are laid in late June and early July, and hatch in late August or early September. That makes these youngsters about 8 months old. Many of the eggs succumb to predation from raccoons and otters, while juveniles face danger from wading birds and larger cannibalistic alligators. Interestingly, the temperature of the female's nest of vegetation and mud determines the sex of the hatchlings with more males produced at higher temperatures.
|I counted four more youngsters here.|
Many adult alligators, males in particular, have taken residence in larger, man-made canals throughout the Everglades. They are attracted by the large numbers of native and non-native fish and invertebrates, by the dry-season refugia and escape from saltwater incursion into their habitat.
|Everglades pre- versus post-drainage in regards to wet and dry seasons|
Source: Christopher McVoy, SFWMD
Canals are not suitable habitats to sustain a healthy alligator population. Smaller alligators are vulnerable to predation and cannibalism. Hatchlings are unlikely to survive, and nests are frequently flooded out. And most important to the ecosystem, alligators that rely on canals for sustenance no longer build and maintain alligator holes. Again, man's efforts to control flooding have adversely impacted the ecosystem.
FLORIDA GREEN WATERSNAKE
Just beyond the hole, I spotted what I thought was a Burmese Python by its size. It's an invasive snake that has been wreaking havoc with the small, indigenous mammals of the Everglades since 2,000 when it was released by pet owners. The snake turned out to be a Green Watersnake, the largest and most dominant watersnake in North America found throughout most of Florida.
They prefer heavy, wetland vegetation and quiescent waters of marshes and swamps. Overall, it is dark olive-green or brownish and has no distinctive markings such as stripes, spots or crossbands but is speckled with muted colors on each scale. Its size is intimidating, but it's totally harmless and non-venomous, although it may bite when cornered. Apparently, it's commonly mistaken for the venomous Florida Cottonmouth (aka water moccasin), which has a white lining around its mouth and vertically-slit eyes; whereas, the eyes of the watersnake are rounded. It dines on frogs and fish.
GREAT BLUE HERON
Over 400 species of birds have been identified in South Florida of which 60% are winters residents having migrated from the north. Many of those are in transit to more southerly tropical locations. Spotting this Great Blue was a majestic event. This stately bird with its subtle blue-gray plumage and wide, black stripe over the eye, in typical fashion, was alternately wading and motionless as it watched for prey. It’s the largest of the North American herons and yet weighs only 5-6 pounds. It can strike with lightning speed to grab or even impale a fish, frog or small mammal with its dagger-like bill.
|Concealed by sawgrass as we airboated down a canal, I caught this Great Blue in flight|
THE GREAT EGRET
Also called a Great White Heron, the Great Egret is slightly smaller than a Great Blue. They too hunt in classic fashion by standing immobile or wading through both fresh and saltwater, capturing fish with a lightning fast jab of their yellow bill. They were nearly hunted to extinction for their plumage for the hats of Victorian-era fashionable ladies. By 1900, more than 5 million birds were killed every year, including 95% of Florida's shore birds. Most were shot in the spring when their plumage was the most colorful.
Great Egrets nest in the trees of islands within the glades. In flight, they retract their S-curved neck and trail their black legs behind. Looking similar but larger and with yellow-gray legs, there is also a “white morph” of the Great Blue in South Florida.
THE ROSEATE SPOONBILL
The Spoonbill is a wading bird of the ibis family that feeds on crustaceans, aquatic insects, frogs and small fish. Like the American Flamingo, which it is closely-related and often mistaken, the color of its brilliant pink wings is diet-derived from pigments found in shrimp and algae. It is highly recognizable by its odd, flat bill, which it uses to strain small culinary delicacies from the water. Like so many other colorful birds of the Everglades (especially snowy-white egrets), they were hunted to the verge of extinction for their plumes.
Herons are long-legged freshwater and coastal birds. Some are called egrets and are mainly white with decorative plumes. They resemble birds in other families but fly with their necks retracted, not outstretched. This small white heron is also protected under federal law by the Migratory Bird Act Treaty of 1918. The area of the upper bill in front of the eyes is yellow to red, and its feet are yellow.
HAMMOCKS AND TREE ISLANDS
The Everglades is not all sawgrass marsh. It is blessed with a great variety of habitats and biological communities. We spotted one such habitat in the distance, a "tree island", which is actually a blanket term for a region with noticeably taller trees within the marsh and on higher ground of typically woody peat, a limestone outcrop or marl closer to the coast.
The standard jargon for them are "heads," which are characterized by the kinds of trees that dominate each of them. Thus, you have bayheads, willow heads, cypress heads, and so on. In addition to their clusters of trees, each of the various tree islands possesses distinctive shrubs and ferns. They are singular ecological entities as much as they are insular land features. In the 1940's there were 1,251 tree islands in the central Everglades; today there are 581. Scientists are racing against time to these "forgotten" islands to discover their formative dynamics and ecological secrets.
The early Everglades, beginning perhaps 6,000 years ago, didn't possess tree islands, which began to form about 3,500 years ago. Three main geological processes form tree islands: formation on a "fixed" high point of bedrock which acts as a nucleus for tree development; on a peat "pop-up" (the most common) of interwoven roots where bottom peat acquires buoyancy from the release of mostly methane gas from water lily roots and rhizomes; and elongated strand islands similar to the sawgrass ridges previously discussed.
Many tree islands have a teardrop shape with a bulbous, upland head and a downstream tail aligned with the direction of sheetflow. The head of the tree island is generally a tropical hardwood hammock, a localized mature forest of broad-leafed trees (as opposed to pines) that is rarely inundated by flooding. The tail can take 1,000 to 2,000 years to develop as peat accumulates above the marsh.
Fire and flooding are of key importance in the integrity of tree islands. Prolonged high water has a devastating effect in particular related to water management practices, but prolonged low water puts them at risk to peat-consuming soil fires. Natural fire actually has an important ecological role in sawgrass habitats by limiting the invasion of woody vegetation that would eventually change the marsh into the next successional habitat. Submerged sawgrass roots are able to rebound following a damaging fire. The ecosystem is now at the mercy of human intervention, and Everglades restoration is contingent on man's efforts at revitalization, including tree islands.
|Diagram of tree islands by origin|
U.S. Geological Survey Fact Sheet 2004-3095
Tree islands greatly enhance the ecological value of the Everglades. They are important centers of biodiversity with two to three times the plant and animal diversity of the surrounding wetlands.
|A flock of Black-necked Stilts exercising precise aerial maneuvers|
This island sported a half-dozen Turkey Vultures roosting in trees, waiting for warm morning air to develop into rising thermals. Notice the large nest down below.
Near the end of our airboat Everglades tour, Captain Randy readied us for this "money shot." A sky filled with egrets, herons, spoonbills, storks, ibises, cranes and pelicans.
Nourished by rain and defined by annual rhythms of drought and flood, fire and sunshine, the Everglades is totally unique. No other place possesses such a stunning diversity of plants and animals. "There are no other Everglades."
For private airboat charters in the Everglades, I highly recommend Captain Randy here.
With great appreciation, I thank amateur ornithologist Ian Starr for his expertise in identifying many of the Everglades birds.
VERY INFORMATIVE SOURCES
Geologic History of Florida by Albert C. Hine, 2013.
Geology of Florida by Albert C. Hine, College of Marine Science, University of South Florida (PDF available online).
Geologic Map and Text of Florida, Florida Geological Survey, Open-File Report 80 by Thomas M. Scott, 2001 (available online).
The Everglades Handbook: Understanding the Ecosystem, Third Edition, by Thomas E. Lodge, 2010.
The Geology of the Everglades and Adjacent Areas by Edward J. Petuch and Charles E. Roberts, 2007.
Roadside Geology of Florida by Jonathon R. Bryan et al, 2008.