Global Climate Change Affecting the Florida Everglades
Anthropogenic causes for disaster in the South Florida Ecosystem
Climate change at the local and global level is effecting the environment. One microcosm to be used as an example for this is the Florida Everglades. The Everglades are a delicate wetland system of diverse plants and animals whose health is easily changed as climate is altered. This study discusses the direct and indirect anthropogenic causes for destruction and alteration of the Everglades, including drainage, habitat loss, landscape alteration, mercury poisoning, ozone depletion and global warming, red tides, and sea level rise.
Climate change at the local and global level is effecting the environment. One microcosm to be used as an example for this is the Florida Everglades. The Everglades are a delicate wetland system of diverse plants and animals whose health is easily changed as climate is altered. This paper will discuss some documented disturbances and their effects on the Everglades ecosystem.
Many researchers have focused on particular disturbances to the Everglades ecosystem. I have attempted a comprehensive discussion of human related disturbances, including the indirect impact humans have had on the environment through the vehicle of global climate change.
Materials and Methods
I have been unfortunate in data collection by living 1000 miles from the area of research, but fortunate in being able to use the internet as a source for data. Agencies such as the Environmental Protection Agency, and National Parks Service, as well as Universities in South Florida, have posted vast amounts of data on the web that has aided me in my studies.
The Florida Everglades are one of the most unique wetland areas in North America. Historically, they used to be fifty miles wide, and extend from Lake Okeechobee southward 100 miles to the southern tip of the Florida peninsula. In 1947, the southern most portion of the Everglades was established by Congress as the Everglades National Park to help protect and preserve this unique area. The Seminole Indians called the Everglades Pahhayokee or "grassy waters," since there is an almost unnoticeable sheet flow of fresh water beneath a sea of sawgrass prairies traveling south, which empties into the Florida Bay and the Gulf waters. Only a few inches deep and supplied solely by the rain that falls on it, this natural water supply is the lifeline of the Everglades which supports rare and endangered species of plants and animals, including the American alligator and Florida panther. Everglades National Park contains 1.5 million acres and is located just to the west of the densely populated city of Miami, and within close proximity of Ft. Lauderdale, and West Palm Beach. Over the last few decades, the development of South Florida has pitted the people and the Everglades as competitors for a finite water supply which has already been reduced dramatically from extensive canal and levee systems designed for flood control and agricultural use (http://www.eng.fiu.edu/evrglads/introenp/introeve.html).
The evolution of the Everglades began about 5000 years ago, with the accumulation of peat soil in the area. From its much lower stand during the glacial period, the sea level had risen enough so that the area that was to become the Everglades could no longer drain rapidly. In addition to the rise in the sea level, the rainfall in the area had increased and the climate was more humid than earlier. The surface water affected the existing upland plants and encouraged the growth of marsh plants. Wetland soils began to accumulate under the water, and so the Everglades began (Lodge, 1994).
The Everglades came to be known after the US and Seminole Wars of 1835-42. The area started to change once Florida entered the Union in 1845 and Congress passed the Swamplands Act of 1850. This act authorized the transfer of 20 million acres to Florida for the purpose of drainage and reclamation (Light et al., 1994). By 1917, four major muck canals crossed the Everglades from Lake Okeechobee to the Atlantic Ocean. The Everglades Drainage District also constructed 47 miles of sand and muck levee around the southern rim of Lake Okeechobee (Light et al., 1994). The construction of the Tamiami Trail, which linked Miami with Naples, was the next major change in the area between 1915 and 1928. The Everglades National Park was established in 1947 to preserve and protect the southern section of the Florida Everglades. Over the next 50 years, numerous levees, pumps, canals, and hurricane gates were installed to drain land, discourage flooding, and improve agriculture in general.
Direct Human Impact
Human beings have had varying degrees of impact on the Everglades ecosystem. This first section, “Direct Human Impact,” focuses on a few major causes of Everglades destruction as a direct result of human interference.
Perhaps the most immediately devastating human impact on this region has been drainage of the freshwater marsh. Since the early 1900’s, marsh has been drained, dammed, levied, and diverted, for the purpose of agriculture in the area. This has led to a loss of millions of acres of marshland over the century.
Historically, the flow of the wide, shallow "River of Grass" began in the Kissimmee River, and Lake Okeechobee. Fifty miles (80 km) wide in places, one to three feet (0.3 to 0.9 meters) deep in the slough's center but only 6 inches (15 cm) deep elsewhere, it flowed south 100 feet (30 meters) per day across Everglades sawgrass toward mangrove estuaries of the Gulf of Mexico (Fig. 1). A six-month dry season followed.
Everglades’ plants and animals are adapted to alternating wet and dry seasons. During the dry season (December to April), water levels gradually drop. Fish migrate to deeper pools. Birds, alligators, and other predators concentrate around the pools to feed on a varied menu of fish, amphibians, and reptiles. This abundant food source is vital to many wading birds who are nesting during the dry season. In May, spring thunderstorms signal the beginning of the wet season. A winter landscape dotted with pools of water yields to a summer landscape almost completely covered with water. Wildlife disperses throughout the park. Insects, fish, and alligators repopulate the Everglades, thus replenishing the food chain. By December, the rains cease and the dry cycle begins again (http://www.nps.gov/ever/eco/ever101.html). With the advent of drainage, water cycle disruptions have ruined crucial feeding and nesting conditions, including a tremendous loss of habitat (See Appendix A).
Most lesser-known extinctions in the United States were probably caused by habitat loss. Extinct and endangered species in the United States and Canada are predominantly endemic species, suggesting that the localized habitats of these species have been usurped by human activity. Because many endemic plant species are concentrated in localized habitats, such as outcrops of rare rock types, destruction of habitat is the leading cause of biological destruction. Because more than 87% of recent wetland losses are attributable to agriculture, protecting wetland-associated species in many regions is largely a matter of reforming agricultural practices (LaRoe, et al., 1998).
Cape Sable Seaside Sparrow
This unlucky bird serves as an example for habitat loss to a species, showing a direct relationship between anthropogenic habitat loss, and species decline.
The sparrow exists almost exclusively within the boundaries of Everglades National Park and Big Cypress National Preserve. The sparrow’s preferred habitat is marl prairie, due to its dryness during the breeding season. Catastrophic events such as fires, hurricanes, floods or droughts can wipe out an entire core population. As discussed before, this bird is a species that lives in an endemic environment. 25% of the sparrow's marl prairie habitat has been lost to agriculture and urban development, and 25% more abitat has been rendered unsuitable due to changes in the dominant vegetation initiated by changes in the hydrologic regime. Excessive and untimely flooding may also interrupt sparrow nesting and lead to unsuccessful breeding seasons. Furthermore, restricted surface water inputs and over-drainage result in the invasion of woody plants and a higher incidence of fires. In short, human impact has had devastating effects on this declining bird’s populations (Fig. 2, 3), (Knight, 2000).
The main freshwater slough of the Everglades was a broad, shallow river supporting a diversity of plant communities, habitats and wildlife between Lake Ocheechobee and the Gulf Coast. Artificial drainage and intensive human settlement have profoundly altered the natural hydrological regime of the Slough. Reduction in aquatic communities, reduction of sawgrass, and loss of peat soils, are among the changes induced by this disturbance. In addition to loss due to drainage and fire, non-native species such as cattails, have invaded marshes (Armentano et al., 2000). Around 1960, cattail abundance began to increase to the highest recorded levels in the Everglades at sites that were nutrient enriched due to agricultural runoff. Studies showed a single cattail seedling grown in nutrient enriched areas expands dramatically, and a seedling grown in un-enriched areas shows little or no expansion. Cattail growth changes the gently flowing, fresh, marshy waters of sawgrass, into a sediment-filled, drying ecosystem, that does not cleanse water and hold wildlife as well (Childers et al., 2000). My own photographic evidence shows cattails in abundance in the region (Fig. 4). In addition to cattail growth, the excess nutrients from agricultural runoff may destroy mats of composite algae called periphyton. These algae are the primary producers in the Everglades food web and provide both food and oxygen for small aquatic organisms. In the dry season, these algal mats also provide the critical moisture that enables many small organisms, including some fish eggs and snails, to survive the long months until rains come again (http://www.nps.gov/ever/eco/quality.html).
Mercury pollution is a growing problem. High levels of mercury were first detected in Everglades’ freshwater fish in early 1989. Although mercury occurs naturally in the environment, it is also a dangerous pollutant. Tests show that the park's raccoons and alligators also have high levels of this toxic metal in their systems. A Florida panther found dead in December 1989 had levels of mercury that would be lethal to humans (http://www.nps.gov/ever/eco/quality.html). Gaseous mercury, poured into the atmosphere naturally and by human industry, is traveling on trade winds from as far away as Europe and Africa. Some 900 pounds a year is then "scrubbed" out of the atmosphere by Florida thunderstorms and dumped in the Everglades (CNN, 1998). Mercury may be passed along through the food chain, resulting in higher accumulations of the poison in higher species. Plankton and bacteria first absorb this element, and are consumed by plants and fish, which are consumed by bigger fish and birds, and finally by alligators, panthers, and humans. The result is fatally toxic levels in top members of the food chain (see chart, Fig. 5).
Indirect Human Impact
I consider change on the Everglades ecosystem as a result of anthropogenic climate change, to be an “Indirect Human Impact.” This section will discuss a few documented and projected effects that anthropogenic climate change may have on the Everglades.
Ozone Depletion and Global Warming
Through release into the atmosphere of CFCs and other ozone-destroying emissions, humans have succeeded in creating a seasonal, and growing hole in the ozone layer (see Fig. 6). This hole is cause for increased radiation to the earth, resulting in global warming and health hazards for earth’s biomass. Correlations between the emergence of animal diseases and changing weather patterns are common. Examples include the 3-4 year cycles in population crashes in feral sheep in the St. Kilda Archipelago, Scotland, and major epizootics of AHS over the past 10 to 15 years in South Africa (Grenfeld, 1998). There is increasing evidence that the frequency and severity of these events are influenced by anthropogenic effects on climate change. A newly discovered fungal disease, cutaneous chytridiomycosis, in the pristine populations of amphibians in Central American, and Australian rainforests, has been linked to anthropogenic effects on climate change (Ballis, et al., 1999). This evidence can be applied to the Florida Everglades.
Increased temperatures and solar radiation, coupled with the introduction of chemicals from agricultural runoff into waters, have resulted in harmful algal blooms, including the phenomenon known as “red tides.” Red tides are a harmful algae that can kill numbers of fish and marine life at each influx. A red tide is a higher-than-normal concentration of a microscopic algae. In Florida, the species that causes most red tides is Gymnodinium breve (G. breve). This organism produces a toxin that can affect the central nervous system of fish. At high concentrations, the organisms may discolor the water. However, red tides are not always red. They can appear greenish, brownish and even purple in color, or, the water can remain its normal color (http://floridamarine.org/features/view_article.asp?id=1289). Although red tides have been reported as early as 1530, increased instances of red tides have been shown and can be linked to anthropogenic cause (Fig. 7).
Sea Level Rise
As we all know, accompanying global warming will be a rise in sea levels. This will prove detrimental to the Everglades, and has been already. Two main problems exist for Florida in the event of sea level rise. One is permanent flooding of coastal areas, and the other, which accompanies this, is saline inundation of fresh water aquifers and estuaries. Due to a combination of canals and drainage already occurring in the everglades, as sea level rises, there is not enough back pressure of fresh water to stave off salt water intrusion, and massive areas of fresh water are rendered brackish and contaminated, destroying entire ecosystems (see Fig. 8 “Barnacles on Mangroves in the Everglades”). Another result of a higher sea level, and destroyed marsh vegetation, is the effect severe weather would have on the state of Florida. Historically, as sea levels became higher, the marsh had time to retreat. With the rapid rise in sea level, marsh, which is a natural barrier for the shock of severe weather (including storm surge), is being destroyed, leaving the area vulnerable to hurricanes and other severe weather (Barth, Titus, 1998).
The wetlands offer numerous benefits to us as we strive to eke out an existence in this unregulated environment. As a species support, wetlands provide important and valuable harvests and recreational fishing and hunting. As ecosystem, wetlands contribute to the stability of global levels of available nitrogen, atmospheric sulfur, carbon dioxide and methane (Internet, NPS 2001). Wetlands also influence regional water flow regimes. One way they do this is to intercept storm runoff and store storm waters, and hence change sharp runoff peaks to slower discharges over long periods of time. Coastal wetlands absorb ocean storms as they come ashore. Here salt marshes and mangrove wetlands act as giant storm buffers. The Everglades are also the primary source of recharge for fresh water aquifers in Florida, and must be conserved as a source of clean water for all. Wetlands may also act as toxic, organic, and inorganic material removers from water that flows across them, due the low velocities and a variety of aerobic and anaerobic processes. Finally, and of equal importance, is the aesthetic value of our wetlands. The Everglades are a place of beauty and heritage, and a microcosm for how the earth should function in an interrelated fashion as a whole.
Armentano, Jones, Gamble, Ross, Snyder. "What is happening to the grass in "The River of Grass? Shark Slough - Everglades National Park." U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology. Online. 2000.
Ballis, M., PC Mellor, R Meiswinkle, nature 397, 574, (1999).
Barth, Titus. "An overview of the causes and effects of Sea Level Rise,” EPA Pamphlet. Online. 1999.
Childers, Havens, McCormick, Miamo, Newman, Scinto, Steinman. "Biological Impacts of Excess Nutrient Loading on Lake Okeechobee." Florida International University. Online. 1999.
"Climate Change and Florida." EPA Publication. Online. 2000.
CNN. "Study Mercury in Everglades comes from distant sources." Online. February 13, 1998.
Cunningham, A., Peter Daszak, A. Hyatt. "Climate Change and Florida." SCIENCE Vol. 287. p. 447. January 2000.
Grenfeld, BT., et al. Nature 394, 674 (1998).
http://www.eng.fiu.edu/evrglads/introenp/introeve.html, webpage, 1998.
http://floridamarine.org/features/view_article.asp?id=1289. Website. 1999.
http://www.nps.gov/ever/eco/ever101.html, webpage, 1999.
http://www.nps.gov/ever/eco/quality.html. Online. 2000.
http://sofia.usgs.gov/sfrsf/rooms/nutrients/impacts/vegetation.html, website. 1998.
Knight, Erik. "The Cape Sable Seaside Sparrow: why does a tiny bird have a large impact?" U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology. Online. 2000.
LaRoe, Noss, Scott., "Endangered Ecosystems of the United States: A Preliminary Assessment of Loss and Degradation." Washington, D. C., 1998.
Light, S. S. and J. W. Dineen, 1994. "Water Control in the Everglades: A Historical Perspective" in Everglades: The Ecosystem and Its Restoration, S. M. Davis and J. C. Ogden (Eds.), St. Lucie Press, Delray Beach, Florida, chap. 4.
Lodge, T., 1994. The Everglades Handbook:Understanding the Ecosystem. St. Lucie Press, Delray Beach, Florida.
NOAA Site for weather data (Ozone Graph).
Habitat Loss for Florida
15% conversion of barrier island habitats (all types) on Atlantic and Gulf coasts to urban area by 1975; 300% increase in urban development from 1945 to 1975.
27% loss of total forest area in Florida from 1940 to 1980.
88% loss of longleaf pine forests in Florida from 1936 to 1987.
74.4% of xeric habitats (scrub, scrubby flatwoods, and sandhills) on southern Lake Wales ridge, Florida, lost to development or degraded.
64% loss of Florida sand pine (Pinus clausa) scrub on Lake Wales, Lake Henry, and Winter Haven ridges since settlement.
60.5% of flatwoods-swale habitats on southern Lake Wales Ridge, Florida, lost to development or degraded.
88% loss of slash pine (Pinus elliottii) forests in southwestern Florida from 1900 to 1989.
98% loss of pine rockland habitat.
60-80% loss of tropical hardwood hammock on the central Florida keys.
28% of presettlement wetlands (all types combined) in the southeastern coastal plain lost by 1986.
46% loss of wetlands in Florida between 1780's and 1980's.
50% loss of presettlement wetlands (all types) in Florida.
92% loss of mangrove swamp and salt marsh along Indian River Lagoon (Brevard, Indian River, and St. Lucie counties) between 1955 and 1974 from impoundment for mosquito control.
56% decline of marsh (herbaceous wetland) habitat in Florida from 1936 to 1987.
51% loss of freshwater marshes in southwest Florida from 1900 to 1989.
25% of bayhead wetlands on the southern Lake Wales Ridge, Florida, lost to development or degraded.
33% loss of seagrass beds that existed in Florida before World War II.
75% loss of seagrass meadows in Tampa Bay, Florida.
(LeRoe, Noss, Scott, 1988).
Climate Change Impacts
United States Environmental Protection Agency
• Precipitation changes and increased evaporation can affect:
– water supplies
– water quality and drinking water
– water uses: hydropower, irrigation, fisheries
• Floods more likely due to more intense rainfall
• Droughts likely to be more severe due to increased
evaporation and drier soils
• Climate change will add to stresses in the Great Basin,
California, Missouri, Arkansas, Texas Gulf, Rio Grande
and Lower Colorado river basins
• Along much of the U.S. coast, sea levels have risen 10-12
inches in the last century
• Sandy beaches would be eroded 100-150 feet with a 1-foot rise
in sea level in 2100
• The projected global sea level rise of 20 inches (6-38 inches)
by 2100 could:
– Inundate 5,000 square miles of dryland
– Drown 15-60 percent of our coastal wetlands
• Some states will experience greater increases in sea level (e.g.,
over 4 feet in Louisiana)
• Cumulative capital costs of defending against a 20 inch rise in
sea level are estimated at $30-40 billion (1988 $)
• Coastal wetlands are vulnerable to sea level rise and coastal
– At risk: fish, shellfish, flood and erosion control, habitat
• Inland freshwater marshes (including prairie potholes) are
vulnerable to hotter, drier conditions
– At risk: migratory bird and other species habitat
• Western riparian wetlands are vulnerable to hotter, drier
– At risk: fish and wildlife habitat, flood and erosion
control, water quality, grazing
•Each 1 o C of warming will shift temperature zones by about
100 miles northward (or 500 feet in elevation)
– Many plant and animal species will be unable to migrate
fast enough to find suitable habitats
– Natural or man-made barriers may block natural migration
• Climate change poses risks to major U.S. national parks
(e.g., Everglades National Park, Glacier National Park)
• An increase of 3 o C could threaten 7-11% of North America’s
• Northern limits of many birds strongly associated with climate
• Loss of cold-water fish habitat of 1.7-2.3 million acres by 2060
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