Biomes, Development, Pollution, and You human activity alters the Marsh ecosystem in the Everglades

Assignment 1 Discussion—Biomes, Development, Pollution, and You human activity alters the Marsh ecosystem in the Everglades

The Everglades and Everglades National Park are part of a vast wetland system that historically extended over 200 miles from the Kissimmee chain of lakes south through Lake Okeechobee into the freshwater marshes of the Everglades and to the mangrove estuaries. The southern end includes the United States’ only subtropical estuary, Florida Bay, and its associated mangrove estuaries, and the third largest coral reef in the world. On the west the system molds into the swamps of the Big Cypress (Robertson and Frederick, 1994). The uplands of the system include pinelands, hardwood forests, and herbaceous rocklands. The uplands contain a mixture of temperate and tropical species. The islands of the Florida Keys are dominated by plants of Caribbean and Central American origin (Tomlinson, 1984; Ross et al., 1992). These tropical plants are generally not found in the lower 48 states.

Figure 1. The historical watershed of the Everglades ecosystem

The vast spatial area of the wetland ecosystem of this nutrient-poor system supports a diverse and large community of species across huge seasonal and interannual variation in rainfall (Hollings et al., 1994). Approximately three-quarters of the annual precipitation occurs during the six-month period from mid-May through October (Thomas, 1974; MacVicar and Lin, 1984; Duever et al., 1994). Total annual rainfall varies from less than 1000 mm to almost 2000 mm over a seven- to ten-year cycle (Duever et al., 1994).

During the wet seasons, water levels within the marshes and lakes of the system gradually rose and water slowly flowed south (Fennema et al., 1994). During the dry season, evaporation exceeded rainfall and water levels receded, concentrating aquatic organisms (Fennema et al., 1994). The annual pulse of fresh water into the subtropical estuary created a highly productive interface between the freshwater system and marine waters of the Gulf of Mexico (McIvor et al., 1994).

In the past, the ecosystem supported a huge array of animal species. Large flocks of ducks and coots wintered within the system. In some years, upwards of 200,000 to 250,000 wading birds nested along the interface between the freshwater Everglades and the estuaries (Robertson and Kushlan, 1974; Frohring et al., 1988; Bancroft, 1989; Ogden, 1978, 1994). The estuaries were important nursery grounds for pink shrimp, sea turtles, gray snappers, and many other species now considered economically important. The coral reef bordering the Florida Keys continues to support an array of species found nowhere else in continental United States.

The climate of southern Florida in combination with good arable land has resulted in an excellent place for humans to live. The population there has increased from only a few tens of thousands in 1900 to over five million people in 1990. An increase of almost two million new residents over the next 20 years (SFWMD, 1994) is projected. Growth rates from 1950 through 1990 averaged about 3% per year. Much of this growth is the result of immigration from other places in the United States and from Cuba, Haiti, and Latin America.

This increase in human populations resulted in major changes to the natural landscape. Initially, extensive drainage of wetlands and clearing of uplands were done to create agricultural lands (Light et al., 1989; Light and Dineen, 1994). Water tables in the Kissimmee Valley and Lake Okeechobee were lowered by more than 5 feet. Extensive wetlands around Lake Okeechobee were drained and converted to agricultural lands for growing winter vegetables, sugar cane, rice, and sod (Light and Dineen, 1994; Aumen, 1994). The hydrologic connection between Lake Okeechobee and the Everglades was severed. Water that had flowed from Lake Okeechobee to the Everglades was shunted east and west to the St. Lucie and Caloosahatchee Canals. Uplands along the eastern side of the Everglades were cleared for human habitation and the cultivation of winter vegetables. Much of the tropical forests in the Florida Keys was cleared for growing pineapples, key limes, and tomatoes.

Hurricanes in 1947 caused extensive flooding, especially south of Lake Okeechobee (Light and Dineen, 1994). The federal government responded by creating the Central and Southern Florida Flood Control Project. Its primary function was to provide flood protection to South Florida while maintaining water supply for agriculture and human consumption (Light and Dineen, 1994). This project completed the draining of the northern quarter of the Everglades, thus forming the 550,000-acre Everglades Agricultural Area. The middle third of the Everglades was converted to a series of five pools (Water Conservation Areas) surrounded by levees and connected by pumps and gates. The flow of water through the system became highly controlled. The eastern boundary of the Water Conservation Areas was set 10-20 km west of the eastern boundary of the Everglades; a quarter of the original Everglades was drained. Approximately 13% of the original Everglades was protected in the recently established Everglades National Park.

With the development of air conditioning, effective controls for mosquitoes, and a reliable source of potable water, the coasts of South Florida and the Florida Keys have changed from an agricultural economy to a tourist-, international trade-, and retirement-based economy. Most of the more than four million inhabitants of Dade, Broward, and Palm Beach Counties currently live on land that was flooded during six months of the year around the turn of the last century.

Humans have recognized the ecological significance of South Florida for some time (Maltby and Dugan, 1994). When extensive drainage began late in the 19th century, some environmentalists began to question the drainage policy and alert people to the possible long-term consequences. The first major attempt to protect the South Florida ecosystem was in 1934 when the U.S. Congress authorized the creation of the Everglades National Park.

This park was dedicated in the same year, 1947, that Congress created the Central and Southern Florida Flood Control Project. Ironically, the Flood Control Project has altered the natural hydrology of the system, causing massive degradation to the park. The U.S. government has continued to recognize the ecological significance of the South Florida ecosystem by establishing Biscayne National Park, Big Cypress Preserve, Florida Keys National Marine Sanctuary, and many national wildlife refuges. The state of Florida and local governments have also preserved many smaller parcels.

The world community has also recognized the ecological importance of the Everglades ecosystem (Maltby and Dugan, 1994). Everglades National Park is listed as a Biosphere Reserve (1976), World Heritage site (1979), and a Wetland of International Importance in the Ramsar Convention (1987). Only two other sites in the world appear on all three lists.

In spite of the extensive protection provided to the South Florida ecosystem, the health of this system is continuing to decline. Of the original 10,000 km2 in the freshwater marshes of the Everglades, approximately half have been drained and converted to agriculture or urban development (Figure 2; Davis et al., 1994; Light and Dineen 1994). Of the six physiographic landscapes found within the Everglades, two are completely gone from South Florida and two have been reduced to small remnants. The subtropical pinelands that once covered the higher ground along the eastern border of the Everglades have been reduced to less than 10% of their original numbers. Over half the tropical deciduous forests that covered the uplands of the Florida Keys has been cleared (Strong and Bancroft, 1994). Florida Bay has experienced extensive sea grass dieoffs, and the corals along the Keys’ reef tract have decreased in abundance and health.

Figure 2. Alterations in the watershed of the Everglades ecosystem

These changes have been devastating to the wildlife dependent upon these systems. The population of wading birds nesting within the Everglades has decreased by over 90% (Bancroft, 1989; Ogden, 1994). Fifty-four plant and 51 animal species are listed or candidates for listing under the federal Endangered Species Act (Brown et al., 1994). Additional species are listed by the Florida Game and Freshwater Fish Commission, Florida Natural Areas Inventory, and Florida Committee on Rare and Endangered Biota as rare, threatened, or endangered.

Snail Kites and Wood Storks are on federal endangered species lists because of their decreased breeding populations within the Everglades system. Shrimp production and populations of many commercially important fish dependent on healthy estuarine ecosystems have decreased dramatically (Browder, 1985; Browder et al., 1989). Populations of species found within the uplands have become greatly reduced, and many are now isolated in small populations (Robertson and Frederick, 1994).


Human populations within South Florida have increased dramatically during the last one hundred years (Figure 3. SFWMD 1994). The quality of the ecosystem has decreased because of direct loss of habitat and the alteration of ecological processes of the remaining system (Davis and Ogden, 1994; Weaver and Brown, 1993). The pattern and quality of water flowing through the wetlands have been altered substantially, and water tables have been lowered under remaining upland habitats. Numerous exotic plant and animal species have invaded native habitats in Florida, altering communities and food chains (Bodle et al., 1994; Robertson and Frederick, 1994). Extensive commercial and recreational fishing has decreased populations of certain species. The impact of divers may be contributing to the decreased quality of the reef. In the following sections of this chapter, two topics will be discussed: 1) how these changes may have affected the ecosystem and the plant and animal populations within, and; 2) how future growth of the human population may affect the protection and restoration of what remains of the Everglades.

Figure 3. Growth of human populations in South Florida (Counties: Dade, Broward, Monroe, Collier, Lee, Hendry, Palm Beach)


Direct Habitat Loss

Approximately 80% of the uplands south of Lake Okeechobee have been lost since the turn of the century, and 40-50% of the wetlands have been drained (Robertson and Frederick, 1994). However, three relatively large pieces of uplands remain intact (Robertson and Frederick, 1994). One is Long Pine Key in Everglades National Park, the second is in the northern Florida Keys in Biscayne National Park and North Key Largo, and the third is in the lower Florida Keys. Outside these areas, the remaining uplands are small, highly fragmented, and widely dispersed. The uplands of South Florida have about 40 endemic plants and 20-25 endemic vertebrate subspecies or species. About ten vertebrate species have been extirpated locally.

Wetlands have been reduced by 40% to 50% from their 19th-century levels (Davis et al., 1994; Robertson and Frederick, 1994). Including the Big Cypress wetlands, almost 20,000 km2 of continuous area remains available for restoration and protection. No plant species are endemic to the wetlands of South Florida, and only two to three vertebrate subspecies appear endemic. No breeding vertebrate species have disappeared from South Florida wetlands in this century.

Loss of pinelands and hardwood forests have been extensive throughout South Florida. Management of these small, fragmented populations will be critical for maintaining many species that are dependent upon these upland habitats. Isolated populations of many species are susceptible to local extirpation because of stochastic demographic variation. Continued growth of human populations in South Florida will result in additional loss of upland habitat and further fragmentation. Maintaining the exchange of plants and animals between these isolated areas may be critical to the continued viability of some upland species in South Florida.

In this context, the following list contains questions for policy research:

How does one determine how much should be saved and where?

How does one manage a reserve network to deal with the problems of small population size, reduced interchange between protected areas, and areas that are too small to sustain certain species?

Alteration of Ecosystem Function

The ecosystems of South Florida have developed as a result of complex interactions between abiotic and biotic factors (DeAngelis, 1994). Climate, soils, hydrology, and fire have played a major role in determining what plant communities develop in a given area. Hydrologic and fire regimes have been altered dramatically by humans during the last century (Fennema et al., 1994; Gunderson and Snyder, 1994). Restoration of more natural regimes will be critical to the protection and restoration of protected areas and the ecosystems found within them (Davis and Ogden, 1994; Weaver and Brown, 1993).

The hydrology of the Everglades system was once characterized by extreme fluctuations in water patterns and levels in response to variation in rainfall (Fennema et al., 1994). The system was able to absorb huge amounts of water during rainy periods, then gradually allowing the water to flow out of the system. During drought years the system was able to maintain a pool of water further into the dry season than it does at present.

In recent years management of the system has attempted to control hydrologic conditions, that is, to dampen the extremes. During high-water years, what is perceived as “excess” water is quickly drained to tide. As a result, the natural system does not experience the high-water conditions it once did. The system also dries more quickly during the dry season and during drought conditions. Less of the system maintains water.

The volume of water flowing through natural areas has decreased. The pattern (timing and distribution) of the water that does flow through the natural areas has been significantly altered. Agricultural and urban development has decreased the quality of water within the system. In addition, the amount of nutrients – phosphorus and nitrogen – have increased (Davis, 1994; Aumen and Gray, 1994).

Water quantity has decreased for two reasons. First, the connection between Lake Okeechobee and the Everglades has been severed. Second, rainfall on the east coast’s developed area that once flowed southwest through the Everglades is now shunted east to the Atlantic Ocean (Fennema et al., 1994).

Historically, Lake Okeechobee’s water levels would fluctuate dramatically with rainfall patterns within the lake and its drainage basin. During wet years the lake would overflow the southern rim and contribute a broad sheet of water to the Everglades. The effects of this water – increasing water depths and lengthening hydroperiods – were seen at least through the top half of the Everglades. Water within the marshes was maintained for longer periods into the following dry season.

In recent decades Lake Okeechobee has been managed as a tradeoff between holding water for agricultural and human consumption and providing the flood protection necessary to maintain the integrity of the dike system around the lake. If the management scenario dictated that too much water was in the lake, that water was drained east and west out the St. Lucie and Caloosahatchee canals in a direction that it did not naturally flow. Under natural conditions Lake Okeechobee contributed more than a quarter of a million acre feet of water to the Everglades system.

In the past, land east of the Water Conservation Areas and Everglades National Park had surface water flow that went west through the Everglades and into the Gulf of Mexico (Fennema et al, 1994). At present, rain that falls on the east coast’s developed area is drained east to the Atlantic Ocean rather than west. Furthermore, because water tables must be well below ground surface in the developed area to allow human habitation and agriculture, a major hydrologic gradient is created between the remaining natural areas and the east coast. This gradient causes substantial quantities of water to seep from the natural areas to the east. This seepage is a major factor preventing restoration of more natural flows through the Everglades. Determining effective mechanisms to reduce or eliminate the seepage from natural areas and to recapture some water from east of the protected areas will be critical to the restoration of Everglades National Park.

Restoration of natural hydrology and natural environmental fluctuations is viewed as an appropriate approach to achieving ecological restoration through an adaptive process (Davis and Ogden, 1994). Large contiguous areas of wetlands in South Florida are publicly owned and could be restored to a more naturally functioning ecosystem. The success of restoration efforts will depend on effectively dealing with numerous water management issues. They include the following:

How to allocate water between agriculture, urban users, and the environment;

How to manage the flow of water through the natural system, and;

How to provide flood protection to agricultural and residential areas.

The South Florida Water Management District (SFWMD) is currently working on a water supply plan for South Florida (SFWMD, 1994). The district is attempting to project the water demands of the three principal users of water in the year 2010. Determining the water needs of the remaining natural areas is critical.

The district is currently using a computer model of South Florida hydrology (a Natural System Model) that has had the canals and levees removed. This “Natural System” model uses recent rainfall data to simulate how the Everglades may have looked if current development had not occurred. This model provides an estimate of the hydrologic patterns that may have occurred in the past. This estimate is being used by the district to provide initial targets for environmental water requirements, an approach that could be tested in the courts. The predictions of the model must be are calibrated and verified carefully; additional biological supports for the needs of the system must also be developed.

Redirecting the flow of water through the natural areas should be done in a manner that replicates the natural variation in hydrologic parameters (Davis and Ogden, 1994). Recent ecological work has suggested that variations in water levels can be extremely important in shaping the South Florida ecosystem (Davis and Ogden, 1994). Current efforts to manage the ecosystem attempt to reduce the intensity of flood and drought years and to create similar hydrologic conditions in all years. Formulas for each water control structure could be used to regulate the flow of water between adjacent areas, formulas based upon antecedent rainfall and upstream water levels.

More intensive land use is associated with the transition from open space to agriculture to residential areas, necessitating increased flood protection. These changes reduce the water available to natural areas. In order to provide increased flood protection in developed areas, water tables are lowered. This action reduces both the local storage of water in the ground and the probability that local rainfall will recharge well fields, which places greater demand on the regional system for water.

Moreover, lower water levels in the former wetlands east of the Water Conservation Areas and Everglades National Park create a hydrologic gradient from the remaining natural areas to the developed east coast. Recent hydrologic studies suggest that large volumes of water are lost from these natural areas and are directed to the east coast. These losses are a major factor inhibiting the restoration efforts occurring within Everglades National Park. Development of effective mechanisms to reduce or eliminate the seepage losses from the remaining natural areas will be essential to replicating more natural flow volumes through the Everglades.

Water Quality

Ecosystems in South Florida developed in an environment low in levels of phosphorus and nitrogen (Aumen and Gray 1994; Davis, 1994). The increased levels of both phosphorus and nitrogen now in surface waters of South Florida have resulted in shifts in the algae and plant communities found within lakes, marshes, and nearshore marine environments. Algae communities have shifted from ones dominated by various green algae to ones dominated by blue-green algaes. Lake Okeechobee has become more eutrophic; the frequency of large algae blooms dominated by blue-green algae has increased.

In the past, marshes of the Everglades were characterized by a mixture of sawgrass and slough communities. However, increased nutrients, particularly phosphorus, have resulted in a shift to a community dominated by cattails. Nearshore seagrass communities have become much denser, and the periphyton communities attached to the seagrass has changed. Due to these changes in the plant communities, food chains have been altered. Faunal communities have also been affected as a result.

Cleaning water to levels that do not cause subsequent changes in communities is a major issue affecting protected areas (Weaver and Brown, 1993; Brown et al., 1994). Additional research is needed to determine what levels of nutrients can be in the water and not cause alterations in floral and faunal communities. Using a standard for water quality, can that level be achieved before the water enters protected areas? Setting and meeting water quality standards in South Florida will require a much broader scientific understanding of nutrient cycling within the system and how those nutrients are used by various organisms than currently exists.

Heavy metals, particularly mercury, and pesticides have increased dramatically in South Florida as a result of increased human populations (Brown et al., 1994). The effects of these contaminants on protected areas remained poorly understood. Developing a better understanding of their effects on animals and how to reduce their concentration in the environment will be critical for the protection of biodiversity in South Florida.


Fire is a key component shaping the structure of plant communities in South Florida (Gunderson and Snyder, 1994). Fires used to occur most often in May and June when thunderstorm frequency increased, but the marshes were not flooded extensively. Humans have caused the timing of burns to shift into mid- to late winter. Many plant species are adapted to the summer burns and thus are adversely affected by winter burns. The intensity and size of burns have also changed from historical conditions, resulting in shifts in plant communities.

Developing more effective ways of using fire in the management of protected areas will be critical for the protection and restoration of these resources. Prescribed burning in fragmented protected areas is difficult but necessary if their maintenance is to be ensured. A comprehensive research program that examines the basic role of fire in South Florida ecosystems and how to manage for more natural fire regimes must be developed.



A large component of South Florida’s economy is based upon tourism. Local governments and the State of Florida spend a considerable amount of money annually to promote the growth of tourism throughout the area. The growth of two tourist industries in particular – recreational fishing and diving on the coral reefs – could represent a threat to the health of protected areas.

Recreational fishing is a major tourist industry, especially in the Florida Keys. Numerous regulations that limit the size and time that certain fish species can be taken have been developed. These regulations have been effective at protecting populations of these species. Recent evidence, however, has suggested that fishing over the coral reefs has dramatically changed the size structure and species composition of reef fishes. Managers and researchers have suggested establishing fishing-free zones as a mechanism of investigating the effects of fishing on overall reef ecology and for providing an area for fish to breed and recolonize. At this time, however, the political will to study effective management options for fish species along the coral reefs does not exist.

On an annual basis, millions of people visit the Florida Keys to dive on its coral reefs. Yet the coral reefs have been deteriorating over the last several decades, for reasons both numerous and controversial. Boat anchoring has caused extensive direct damage to corals in some areas. The touching of corals by divers may also be a serious problem. Careful studies of how divers may be affecting corals need to be conducted, so regulations can be developed that will help reduce the impacts of divers on this system.

Exotic Plants and Animals

Exotic plants and animals represent a serious threat to the integrity of natural systems in South Florida (Bodle et al., 1994; Robertson and Frederick, 1994). Growth of human populations in South Florida will increase the possibility of additional introductions of species. Suburban horticulture practices could be the major source of new invasive exotics. Effective screening mechanisms for new ornamental species should be developed.

In addition, a number of fish, animals, and birds have invaded natural habitats in South Florida. Many of these creatures have escaped from the pet trade (Robertson and Frederick, 1994). If natural communities are to be maintained, the spread of exotics must be controlled and further introductions prevented.

Governmental Management Problems

A major problem facing efforts to restore and protect the ecosystem of South Florida is that governmental agencies responsible for protecting the areas have different mandates under the law. Recently, most of the agencies have realized two critically important points: 1) that the health of the areas they are responsible for protecting and managing is affected by what happens outside their boundaries, and; 2) that their management decisions in turn have consequences for other areas (Weaver and Brown, 1993). In a large wetland system such as the Everglades, management decisions in the upper parts of the basin will have a domino effect all the way to and into the ocean. This realization has resulted in a call for a holistic ecosystem approach to managing South Florida ecosystems (Walters et al., 1992; Hollin et al., 1994; Davis and Ogden, 1994).

The U.S. Army Corps of Engineers has just completed a reconnaissance report on the Central and Southern Florida Flood Control Project (USCOE, 1994). They were charged with examining the entire federal drainage system of South Florida to decide if and how they could alter its management or structure to help restore the wetland ecosystem while maintaining flood protection and water supply to human users. The study concluded that the project could be improved, and the Corps has begun a feasibility study. In conjunction with this work, the U.S. Department of Interior established an Interagency Working Group for South Florida. The Science Subgroup has developed a series of objectives for the restoration of South Florida and is currently working on information and study needs for the system.


Changing land use surrounding, and especially upstream, of protected areas in South Florida is a serious threat to maintaining natural biodiversity. The fact that tourism in protected areas of South Florida is a major contributor to the area’s economy further complicates the issue.

Few studies have been done on the economic implications of a decline in the health of the environment due to continued intensification of land use, a result of increasing human populations. Increased human populations in the Florida Keys will probably increase nutrient loads into surrounding waters and could contribute to the degradation of the Florida Keys Reef Tract. Growing human populations along the east coast of South Florida will probably require increased flood protection, which could decrease the ability of well fields to be recharged by local rainfall. In turn, the demand for potable water from the remaining natural areas could increase. Substantial research needs to be conducted if we are to understand the linkages between increased human populations, land use, and changes in the health of the South Florida environment.


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