Cw04
From Environmental Technology
Contents |
Can the everglades survive?
a)
No other place combines a subtropical climate, a broad, shallow river, and a stunning diversity of plants and animals into such a complex and fragile ecosystem. No other place is so dramatically defined by annual rhythms of drought and flood, fire and sunshine and torrential rain. Today, the Everglades is an ecosystem in danger. Canals and levees capture and divert its water for human needs, including drinking water, irrigation, and flood control. Often, too much water is withheld from the Everglades during the wet season, or too much is diverted into it during the winter drought, disrupting the natural cycles of feeding and nesting which depend on these patterns. Sometimes the water is contaminated by pollutants. One thing is certain: As the human population of south Florida continues to grow, the challenge of balancing human needs with those of the natural ecosystem will be great.
b)
The Everglades is a low, flat plain shaped by the action of water and weather. In the summer wet season it is a wide, grassy river. In the winter season the edge of the slough is a dry grassland. Though Everglades National Park is often characterized as a water marsh, several very distinct habitats exist within its boundaries.
Marine/Estuarine
Florida Bay, the largest body of water within Everglades National Park, contains over 800 square miles (2072 square km) of marine bottom, much of which is covered by seagrass. The seagrass shelters fish and shellfish and sustains the food chain that supports all higher vertebrates in the bay. The hard bottom areas are home to corals and sponges. (Additional resources for teachers are available about marine ecosystems.)
Mangroves
Mangrove forests are found in the coastal channels and winding rivers around the tip of South Florida. Red mangroves (Rhizophora mangle), identified by their stilt-like roots, and the black (Avicennia germinans) and white mangroves (Laguncularia racemosa) thrive in tidal waters, where freshwater from the Everglades mixes with saltwater. This estuary system is a valuable nursery for shrimp and fish. During the dry months, wading birds congregate here to feed. Many bird species nest in the mangrove trees.
Coastal Prairie
Located between the tidal mud flats of Florida Bay and dry land, the coastal prairie is an arid region of salt-tolerant vegetation periodically flooded by hurricane waves and buffeted by heavy winds. It is characterized by succulents and other low-growing desert plants that can withstand the harsh conditions.
Freshwater Marl Prairie
Bordering the deeper sloughs are large prairies with marl sediments, a calcareous material that settles on the limestone. The marl allows slow seepage of the water but not drainage. Though the sawgrass is not as tall and the water is not as deep, freshwater marl prairies look a lot like freshwater sloughs.
Freshwater Slough
The slough is the deeper and faster-flowing center of a broad marshy river. This "fast" flow moves at a leisurely pace of 100 feet (30 meters) per day. Dotted with tree-islands called hammocks or heads, this vast landscape channels life-giving waters from north to south. Everglades National Park contains two distinct sloughs: Shark River Slough, the "river of grass;" and Taylor Slough, a narrow, eastern branch of the "river." There are no surface connections between the two. A series of other sloughs through the Big Cypress Swamp supply freshwater to western Florida Bay and the Ten Thousand Islands.
Cypress
The cypress tree (Taxodium spp.) is a deciduous conifer that can survive in standing water. These trees often form dense clusters called cypress domes in natural water-filled depressions. The trees in the deep soil at the center grow taller than those on the outside. Stunted cypress trees, called dwarf cypress, grow thinly-distributed in poor soil on drier land.
Hardwood Hammocks
Hammocks are dense stands of hardwood trees that grow on natural rises of only a few inches in the land. They appear as teardrop-shaped islands shaped by the flow of water in the middle of the slough. Many tropical species such as mahogany (Swietenia mahogoni), gumbo limbo (Bursera simaruba), and cocoplum (Chrysobalanus icaco) grow alongside the more familiar temperate species of live oak (Quercus virginiana), red maple (Acer rubum), and hackberry (Celtis laevigata). Because of their slight elevation, hammocks rarely flood. Acids from decaying plants dissolve the limestone around each tree island, creating a natural moat that protects the hammock plants from fire. Shaded from the sun by the tall trees, ferns and airplants thrive in the moisture-laden air inside the hammock.
Pinelands
The slash pine (Pinus elliottii var. densa) is the dominant plant in this dry, rugged terrain that sits on top of a limestone ridge. The pines root in any crack or crevice where soil collects in the jagged bedrock. Fire is an essential condition for survival of the pine community, clearing out the faster-growing hardwoods that would block light to the pine seedlings. Pine bark is multi-layered, so only the outer bark is scorched during fires. The pinelands are the most diverse habitat in the Everglades, consisting of slash pine firest, an understory of saw palmettos (Serenoa repens), and over 200 varieties of tropical plants.
c)
The range of the American AlligatorLink title (Alligator mississippiensis) extends south from coastal swamps in North and South Carolina to the tip of southern Florida, then west along the Gulf Coast to the mouth of the Rio Grande. Alligators range inland throughout the southern coastal flatland. Alligators eat a wide variety of foods including insects, crabs, crayfish, fish, frogs, snails, turtles, snakes, coots, grebes, wading birds, raccoons, otters, deer, and other alligators. Alligators are also known to eat dead animals. Although alligators are carnivorous, they are occasionally seen uprooting vegetation. Evidently they do not eat the plant material, and may be catching crayfish, snails, and insects living in the mud at the bases of the plants. Alligators feed most often when temperatures are between 73-90°F (20-23°C).
d)
Their wrinkled, whiskery faces, and big paddle-like tails have led some folks to call them homely. And yet there is an endearing charm to these animals that has fascinated many people who have seen them. manatees continue to be sighted in Florida Bay and other parts of Florida.Manatees pull up and eat the abundant sea grasses and aquatic plants of the bay, consuming 10 to 15 percent of their body weight a day.most of their problems are human-related. As our cities expand, their natural habitat is decreased. Added to this problem is the establishment of automatic locks and dams which can harm or kill manatees.
But the most critical problem for manatees is boating accidents. They like to rest just below the surface of the water and are often hit by speeding boats. As a result, most manatees in the wild bear prop scars on their backs. For many, the cuts lead to infections which later prove fatal. Broken ribs and punctured lungs resulting from collisions also cause many deaths.
e)
Fire is not the end, but the beginning of new life in the Everglades; it has always been an integral part of the Everglades.
It was one of the critical influences in the evolution of south Florida habitats. Everglades National Park was established to protect the biological diversity of the area. Regular fires are needed to guarantee that protection. Without those fires much of the diversity would be lost forever and several species would face extinction. As a result, park managers consider fire an important ally rather than a foe.
Fire, in unison with other natural forces such as rain, drought, hurricanes, wind, and lightning, is a natural process. Fire gives plant communities opportunities for removal of decaying vegetation and to allow for growth that did not exist prior to the burn. Nutrients released from the burn along with new growth improves habitat, increasing the variety of food sources and living conditions necessary for wildlife. Fire management in Everglades National Park seeks to maintain fire in the natural ecosystems while adequately considering impacts upon nearby human population centers.
Research has shown that fire is not the end, but the beginning of new life in the Everglades.
F)
The landscapes we see today in South Florida are a direct result of geologic events of the past. There is no place better to see this than in South Florida's National Parks. Here the geologic record is still fairly intact. Although the activities of humans have altered the landscape somewhat, the overall picture can still be seen. The rocks beneath the Big Cypress Swamp are among the oldest in South Florida. Six million years ago a shallow sea covered this area. Sediments of silt and sand and particles of calcium deposited on the bottom of this sea gradually cemented into limestone. Today this rock is called the Tamiami Formation.
The Tamiami Formation is also found in the northwest corner of Everglades National Park. Here, fresh water flowing out of Big Cypress mixes with salt water from the Gulf of Mexico in a highly productive mangrove estuary. The resulting nutrient-rich soup supports a marine nursery for pink shrimp, snook, and snapper.
Other rocks beneath the Everglades were formed during the time of the Great Ice Age. Although no glaciers developed in Florida, their effects were felt here. As glaciers in other areas of the world expanded, much of the earth's water supply was trapped in the ice. Sea levels in South Florida lowered as much as 300 feet below present levels.
The Great Ice Age was actually four shorter ice ages with periods of warming in between. During these warmer "interglacial" stages, the ice melted and returned to the sea. The last interglacial stage occurred about 100,000 years ago. At its peak, the sea level in South Florida rose 100 feet above present levels.
The rocks beneath the southeast section of the Park were formed in this sea. Calcium carbonate settling out of the water coated tiny bits of shell or sand in layer upon layer. The resulting spherical grains of limestone are called ooids. The Atlantic Coastal Ridge which runs from Mahogany Hammock northeast to Miami was formed as long shore currents pushed the ooids up into a long ridge. The ooids later cemented into rock known as Miami Oolite. Miami Oolite also covers most of the area east of Everglades National Park and most of Florida Bay.
In quieter waters covering the central portions of the Park, tiny moss animals called Bryozoans flourished. As they died their calcium skeletons settled to the bottom. These sediments later cemented into rock known as the Miami Bryzoan Limestone.
As in most areas of South Florida, subtle changes in elevation result in dramatic changes in vegetation communities. Pine forests are found on the high ground of the Atlantic Coastal Ridge. Where fire has been excluded, pines give way to hardwood hammocks. In wetter areas near the end of the ridge, dwarf pond cypress grow. South of the ridge sawgrass prairies take over again. A narrow band of mangroves fringe the southeast coast, and the shallow waters of Florida Bay today provide an abundant food supply for great numbers of wading birds.
