United States
Environmental Protection
Agency
Region 4 Science & Ecosystem
Support Division and Water
Management Division;
Office of Research and Development
EPA904-R-00-003
September 2000
EPA
South Florida Ecosystem Assessment:
Everglades Water Management, Soil
Loss, Eutrophication and Habitat
Monitoring for Adaptive Management:
Implications for Ecosystem Restoration
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The South Florida Ecosystem Assessment Project is being conducted by the
United States Environmental Protection Agency Region 4 in partnership with the
Florida International University Southeast Environmental Research Center, FTN
Associates Ltd., and Battelle Marine Sciences Laboratory. Additional cooperating
agencies include the United States Fish and Wildlife Service, the National Park
Service, the United States Geological Survey, the Florida Department of Environ-
mental Protection, the South Florida Water Management District, and the Florida
Fish and Wildlife Conservation Commission. The Miccosukee Tribe of Indians of
Florida and the Seminole Tribe of Indians allowed sampling to take place on their
federal reservations within the Everglades.
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EPA 904-R-00-003
September 2000
SOUTH FLORIDA
ECOSYSTEM ASSESSMENT
Everglades Water Management,
Soil Loss, Eutrophication and Habitat
Daniel Scheldt
U.S. Environmental Protection Agency Region 4
Water Management Division
South Florida Office
West Palm Beach, Florida
Jerry Stober, Project Manager
U.S. Environmental Protection Agency Region 4
Science and Ecosystem Support Division
Athens, Georgia
Ronald Jones
Florida International University
Southeast Environmental Research Center
Miami, Florida
Kent Thornton
FTN Associates, Ltd.
Little Rock, Arkansas
This document is available on the Internet for browsing or download at:
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
EXECUTIVE SUMMARY
The United States Environmental Protection Agency South Florida
Ecosystem Assessment Project is an innovative, long-term research,
monitoring and assessment effort. Its goal is to provide timely scientific
information that is critical for management decisions on the Everglades
ecosystem and its restoration. The purpose of this report is to document
1993 to 1996 baseline conditions in the Everglades and Big Cypress prior to
ecosystem restoration efforts. The project is unique to South Florida in two
aspects: (1) its probability-based sampling approach permits quantitative
statements about ecosystem health; and (2) its extensive spatial coverage
and sampling intensity are unprecedented.
This project:
• contributes to the Comprehensive Everglades Restoration Plan by
quantifying pre-restoration conditions in three physiographic regions:
Everglades ridge and slough; marl prairie/rocky glades; and Big Cypress
Swamp.
• provides information on four groups of Everglades restoration success
indicators: water column, soils and sediments, vegetation, and fishes.
• provides a baseline against which future conditions can be compared
and the effectiveness of restoration efforts can be gauged.
• assesses the effects and potential risks of multiple environmental
stresses on the Everglades ecosystem such as water management, soil
loss, water quality degradation, habitat loss, and mercury contamination.
• provides unbiased estimates of ecosystem health with known confidence
limits, while allowing one to differentiate between seasonality and inter-
annual variability versus the effects of restoration efforts.
• provides data with multiple applications: updating and calibrating surface
water management models; updating models that predict periphyton or
vegetation changes in response to phosphorus enrichment or
phosphorus control; developing empirical models in order to better
understand interrelationships among mercury, sulfur, phosphorus, and
carbon; developing water quality standards to protect fish and wildlife.
Samples were collected from the freshwater portion of the Everglades and
Big Cypress. From 1993 to 1996 surface water, soil or sediment, periphyton,
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
and mosquitofish were sampled from about 200 canal locations and over 500
marsh locations. These samples represent the ecological condition in over
750 miles of canals and over 3,000 square miles of freshwater marsh. A
second phase of sampling, conducted in 1999 at about 250 marsh locations,
is summarized in companion reports.
Key findings:
• Pronounced water quality gradients: Water discharged from
Everglades Agricultural Area canals is loading the public Everglades with
excess phosphorus, carbon, and sulfur. Concentrations progressively
decrease downstream.
• Canals are a conduit for pollutant transport: The canal system is an
effective conduit for the transport of degraded water into and through the
Everglades marsh system. Water management affects water quality.
Downstream water quality would be improved if delivery canals were
eliminated or if they were operated to maximize surface water sheetflow
and the diluting influence of rainfall and cleaner marsh water.
• Varying water quality: Surface water conductivity, phosphorus, carbon,
nitrogen, and sulfur vary greatly throughout Big Cypress and the
Everglades and are dependent upon location, time of year, and water
management practices.
• Phosphorus enrichment: As of 1995 to 1996, about 44% of the
Everglades canal system and 4% of the marsh area had total
phosphorus concentrations exceeding the 50 part per billion Phase I
control target. As phosphorus control programs continue to advance,
this probability-based sampling can be repeated to determine whether
the Everglades' condition is improving.
• So/7 loss in the public Everglades: From 1946 to 1996, about one-half
of the peat soil was lost from about 200,000 acres of the public
Everglades. Water management must be improved to maintain the
remaining marsh soils if the plant communities and wildlife habitat of
these wetlands are to be preserved.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
• Marsh habitat a mosaic: Wet prairie and sawgrass marsh were the two
dominant plant communities in the Everglades, representing 44% and
47% of the sites sampled. Water quantity and water quality must be
managed to maintain these important habitats. Cattail was present at
10% of these sites, and was associated with elevated soil phosphorus or
proximity to canals.
• Periphyton conspicuous: Well-defined periphyton mats, a defining
characteristic of the Everglades marsh complex, were found at 67% of
the sample sites.
• Ecological condition varies by location and time: The condition of
the Everglades varied greatly with location. Rainfall-driven portions of
the system that are distant from the influence of canal water, such as the
interior of Arthur R. Marshall Loxahatchee National Wildlife Refuge and
the southwest portion of Water Conservation Area 3A, were found to
have good water quality and low soil phosphorus. The interior of
Loxahatchee National Wildlife Refuge tended to have the most pristine
water quality and the lowest phosphorus concentrations in peat soils. In
contrast, northern Water Conservation Area 3A had poorer water quality,
soil loss due to water management, elevated soil phosphorus, and cattail
encroachment. Water Conservation Area 2A had evidence of
phosphorus enrichment and cattail encroachment, along with high water
sulfate and conductivity. Big Cypress had good water quality and no
obvious indications of phosphorus enrichment. Water quantity conditions
at a given location vary with season and year.
• Environmental threats interrelated: Ecological stressors such as
water management, soil loss, water quality degradation, cattail
expansion, and mercury contamination are often interrelated.
Management actions must be holistic.
This project provides a critical benchmark for assessing ecosystem health
and the effectiveness of Everglades restoration activities into the twenty-first
century. As Everglades protection efforts proceed, this probability-based
sampling can be repeated to document the effectiveness of these actions.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
ABBREVIATIONS
cm = centimeter
cc = cubic centimeter
cfs = cubic feet per second
3 = grams
hr = hour
ppb = parts per billion (ug/L)
ppm = parts per million (mg/L) or (mg/ks)
mg/kg = milligrams per kilogram (ppm)
mgA = milligrams per liter (ppm)
ug/cc = micrograms per cubic centimeter
uMol/hr = micromoles per hour
AA = Alligator Alley (Interstate 75)
APA = Alkaline Phosphatase Activity
APTMD = Air, Pesticides, and Toxics Management Division
BCNP = Big Cypress National Preserve
BMPs = Best Management Practices
CERP = Comprehensive Everglades Restoration Plan
EAA = Everglades Agricultural Area
ENP = Everglades National Park
EMAP = Environmental Monitoring and Assessment Program
EPA = Everglades Protection Area
FIU = Florida International University
LNWR = Arthur R. Marshall Loxahatchee National Wildlife Refuge
NERL - ERD = National Exposure Research Laboratory, Ecosystem Research Division. Athens,
Georgia
NERL - AMD = National Exposure Research Laboratory, Atmospheric Modeling Division. Research
Triangle Park, North Carolina
ORC = Office of Regional Counsel
SESD = Science and Ecosystem Support Division
SERC = Southeast Environmental Research Center
SFWMD = South Florida Water Management District
TT = Tamiami Trail
USEPA = United States Environmental Protection Agency
WCA = Everglades Water Conservation Area
WCA3N = Water Conservation Area 3A north of Alligator Alley
WCA3S = Water Conservation Areas 3A and 3B south of Alligator Alley
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
US EPA REGION 4
SOUTH FLORIDA
ECOSYSTEM ASSESSMENT
INTRODUCTION AND PURPOSE 1
BACKGROUND 3
THE COMPREHENSIVE EVERGLADES
RESTORATION PLAN 7
US EPA REGION 4 SOUTH FLORIDA
ECOSYSTEM ASSESSMENT
PROJECT 10
WATER MANAGEMENT 16
WATER QUALITY PATTERNS 18
SOIL SUBSIDENCE 22
EUTROPHICATION AND HABITAT 26
MANAGEMENT IMPLICATIONS 34
REFERENCES ............................................36
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
ACKNOWLEDGEMENTS
PARTICIPANTS IN THE US EPA REGION 4
EVERGLADES ASSESSMENT PROJECT
US EPA Region 4
Program Offices
APTMD
L. Anderson-Carnahan
D. Dubose
L. Page
ORC
P. Mancusi-Ungaro
SESD
B. Berrang
P. Meyer
C. Halbrook
M. Parsons
D. Smith
W. McDaniel
M. Wasko
J. Scifres
M. Birch
P. Mann
I Slagle
I Stiber
J. Davee
D. Colquitt
D. Kamens
R. Howes
G. Collins
J. Bricker
B. Noakes
US EPA - Office of
Research and Development
EMAP
R. Linthurst
K. Summers
I Olsen
NERL-RTP
R. Stevens
R. Bullock
J. Pinto
NERL-ATHENS
R. Araujo
C. Barber
N. Loux
L. Burns
FIU-SERC
R. Jaffe
J. Trexler
Y. Cai
A. Alii
N. Black
I. MacFarlane
W. Loftus
J. Thomas
University of Georgia
S. Rathbun
Florida Department of
Environmental Protection
I Atkeson
South Florida Water
Management District
L Fink
Contractors
J. Maudsley, Mantech
B. Lewis, Mantech
M. Weirich, Mantech
D. Stevens, Mantech
M. McDowell, Mantech
C. Laurin, FTN Associates, Ltd.
J. Benton, FTN Associates, Ltd.
R. Remington, FTN Associates, Ltd.
B. Frank, FTN Associates, Ltd.
S. Ponder, Integrated Laboratory
Systems
K. Simmons, Integrated
Laboratory
Systems
S. Pilcher, Integrated Laboratory
Systems
E. Crecelius, Battelle Marine
Sciences
B. Lasorsa, Battelle Marine
Sciences
Funding for this study was provided by the United States Environmental Protection Agency
Region 4 South Florida Office, West Palm Beach; the Office of Water; the Office of Research and
Development; and the United States Department of Interior.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
INTRODUCTION AND PURPOSE
The United States Environmental Protection Agency (USEPA) South Florida Ecosystem
Assessment Project is an innovative, long-term research, monitoring, and assessment effort.
Its goal is to provide timely scientific information that is needed for management decisions on
the Everglades ecosystem and its restoration. The purpose of this report is to document
1993 to 1996 baseline conditions in the Everglades and Big Cypress prior to ecosystem
restoration efforts. This project is unique to South Florida in two aspects:
• its probability-based sampling approach permits quantitative statements about
ecosystem condition; and
• its extensive spatial coverage is unprecedented.
The South Florida Ecosystem Assessment Project:
• contributes to the Comprehensive Everglades Restoration Plan by quantifying
pre-restoration conditions in three physiographic regions: Everglades ridge and
slough; marl prairie/rocky glades; and Big Cypress Swamp.
• provides information on four groups of Everglades restoration success
indicators: water column, soil and sediment, vegetation, and fish.
FIGURE 1 . Numerous environmental issues threaten the Everglades "River of Grass," such as water
management, soil loss, water quality degradation, and habitat alteration.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
r
en
GOAL: Provide timely ecological information that contributes to
environmental management decisions on the Everglades and its restoration.
• provides a baseline against which future conditions can be compared and the
effectiveness of restoration efforts can be gauged.
• assesses the effects and potential risks of multiple environmental stresses on
the Everglades ecosystem such as water management, soil loss, water quality
degradation, habitat loss, and mercury contamination.
• provides unbiased estimates of ecosystem health with known levels of
uncertainty, while allowing one to differentiate between seasonality and inter-
annual variability versus the effects of restoration efforts.
• permits spatial analyses and identifies associations that provide insight into
relationships among environmental stresses and observed ecological responses.
• provides data with multiple applications: updating and calibrating surface water
management models; updating models that predict periphyton or vegetation
changes in response to phosphorus enrichment or phosphorus control;
developing empirical models in order to better understand interrelationships
among mercury, sulfur, carbon, and phosphorus; developing water quality
standards to protect fish and wildlife.
USEPA Region 4 and the Florida International University Southeast Environmental
Research Center began this project in 1993 to monitor the condition of the South
Florida ecosystem. This project has been carried out in cooperation with the:
Miccosukee Tribe of Indians of Florida, Seminole Tribe of Indians, United States Fish
and Wildlife Service, National Park Service, United States Geological Survey, Florida
Department of Environmental Protection, Florida Fish and Wildlife Conservation
Commission, and South Florida Water Management District.
This report describes the ecological condition of the Everglades and Big Cypress
as documented in the intensive 1993 to 1996 Phase I sampling effort. A more
technical presentation of the Phase I sampling can be found in Stober et al., 1998.
Companion reports summarize the 1999 Phase II project sampling, mercury
contamination, and the comparative risk assessment. All reports and data for the
study are available on the internet at .
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 2. The Everglades wet prairie - sawgrass marsh mosaic.
BACKGROUND
THE EVERGLADES
"Here are no lofty peaks seeking the sky, no mighty glaciers or rushing streams
wearing away the uplifted land. Here is land, tranquil in its quiet beauty, serving not
as a source of water but as a last receiver of it."
"The Everglades were not really set aside for any kind of geological wonders or
scenic features. It's the first national park set aside simply for its wildlife and the
plants and trees - for its biological diversity."
President Harry Truman, Everglades National Park dedication, 1947.
The Florida Everglades is one of the largest freshwater marshes in the world. The
marsh is a unique mosaic of sawgrass, wet prairies, sloughs, and tree islands. Just
over 100 years ago, this vast wilderness encompassed over 4,000 square miles,
extending 100 miles from the shores of Lake Okeechobee south to Florida Bay. The
intermingling of temperate and Caribbean flora created habitat for a variety of fauna,
including Florida panthers, alligators, and hundreds of thousands of wading birds.
The Everglades of the past were defined by several major characteristics:
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
How the water flowed. Water connected the system, from top to bottom. Surface
water flowed so slowly down the flat and level landscape that rainfall during one
season was still available during another. The enormous amount of water storage
capacity and the slow flow made wetlands and coastal systems less vulnerable to
South Florida's variable and often intense rainfall'1'.
Vastness. The large ecosystem area provided a variety of wildlife habitats.
Millions of acres of wetlands provided large feeding ranges and diverse habitat needs
for wildlife. The vastness produced abundant aquatic life while facilitating recovery
from hurricanes, fires, and other natural disturbances'1'.
Diverse mosaic of landscapes. The Everglades was a complex system of plant
and animal life dictated in part by water regime - minimum, average, and maximum
water depths, along with the duration of surface water inundation. This resulted in
expansive areas of sawgrass marshes, wet prairies, cypress swamps, mangrove
swamps, and coastal lagoons and bays'1'.
Natural water quality conditions. There were no external sources of pollutants to
the ecosystem. There was no urban development or agriculture. Nutrients, ions,
and metals all occurred at natural concentrations. Surface water flowed slowly
across the landscape, providing ample opportunity for cleansing by extensive
wetlands. The sawgrass marshes and wet prairies of the Everglades developed
under extremely low phosphorus conditions.
The mosaic of habitats, their vastness and the variety of water patterns supported
the long-term survival of wildlife under a range of seasonal and annual water
conditions.
A TROUBLED RIVER
One century ago, the greatest threat to wading bird populations was hunting
(Figure 3). During the last century, however, the Everglades has become a troubled
system. In response to periods of drought in the 1930s and 1940s, and severe
flooding with loss of human life in the 1920s and 1940s, the Central and Southern
Florida Flood Control Project (the Project) was created in 1948 by federal legislation.
Project purposes include flood control, water level control, water conservation,
prevention of salt water intrusion, and preservation offish and wildlife. The Project is
one of the world's most extensive public water management systems, consisting of
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 3. Decorating women's
hats with wading bird plumage led
to the near decimation of
Everglades wading bird populations
around 1900.
over 1,800 miles of levees and
canals, 25 major pumping
stations, and over 200 larger and
2,000 smaller water control gates
or structures. When the Project
was designed in the 1950s,
about 500,000 people lived in the
region and it was estimated that
there might be two million people
by 2000(1). The Project has
effectively provided flood control
and water supply to facilitate
urban and agricultural growth.
Today, 50% of the historic
Everglades wetland has been
drained. The Everglades ecosystem has been altered by
extensive agricultural and urban development (Figures 4
to 8). South Florida's human population of about six
million continues to increase and encroach on the
ecosystem's land and compete for its water. This human
population is projected to increase to 15 million within a
few decades'1' (Figure 4).
The Everglades changed dramatically during the
twentieth century as drainage canals were dug to
facilitate urban and agricultural development. Most of
the remaining Everglades are in the Everglades
Protection Area (EPA): Arthur R. Marshall Loxahatchee
National Wildlife Refuge (LNWR), Everglades National
Park (ENP), and the Water Conservation Areas (WCAs)
(Figure 8). Everglades National Park, which was
established in 1947, includes only one-fifth of the
original "River of Grass" that once spread over more
than 4,000 square miles (2 million acres)'3'. One-fourth
of the historic Everglades is now in agricultural
production within the 1,000 square mile Everglades
Agricultural Area (EAA), where sugar cane and
1900 1930
1990 2020 2050
FIGURE 4. South Florida population
from 1900-2050 (projected). Flood control
provided by the Central and Southern
Florida Project has made urban expansion
possible'1-2).
FIGURE 5. Urban expansion into
drained Everglades wetlands within west
Broward County, 1995. Note the black peat
soil.
FIGURE 6. Urban expansion into
Everglades wetlands in western Broward
County, 1995.
FIGURE 7. Residential development
on former Everglades wetlands.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
Lake
Okeechoobee
Cypress
LNWR
WCA2
WCA3N
Alligator Alley (1-75)
WCA3S
Tamiami Trail
FIGURE 8. Satellite image of South Florida, circa 1995, with the areas sampled outlined in yellow:
Everglades Agricultural Area (EAA); Arthur R. Marshall Loxahatchee National Wildlife Refuge (LNWR);
Everglades Water Conservation Area 2 (WCA2); Everglades Water Conservation Area 3 north of
Alligator Alley (WCA3N); Everglades Water Conservation Area 3 south of Alligator Alley (WCA3S); the
eastern portion of Big Cypress National Preserve (BCNP), and the freshwater portion of Everglades
National Park (ENP). Light areas on the east indicate urban development.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
During the last century, the Everglades has become subjected to
multiple, often interrelated, environmental threats. Effective ecosystem
protection and restoration requires addressing these threats holistically.
vegetables are grown on the peat soils of drained sawgrass marshes. Big Cypress
National Preserve protects forested swamp resources along the western portion of
the Everglades watershed.
Although one-third of the 16,000 square mile Everglades watershed is in public
ownership, there are many environmental issues, often interrelated, that must be
resolved to restore and protect the Everglades ecosystem. These include: water
management; water supply conflicts; soil loss; water quality degradation and
eutrophication; mercury contamination of gamefish, wading birds, and Florida
panthers; habitat alteration and loss; protection of endangered species; and
introduction and spread of nuisance exotic species.
THE COMPREHENSIVE EVERGLADES
RESTORATION PLAN
The Central and Southern Florida Project has provided
flood protection and water supply to people and agricultural
lands, as intended. However, the Project has
simultaneously altered the Everglades and the south
Florida ecosystem. The Everglades no longer receives the
proper quality or quantity of water at the right place or the
right time. The remnant Everglades no longer exhibits the
water regimes, vast area, and mosaic of habitats that
defined the pre-drainage natural ecosystem. Wildlife
habitat has been lost or changed, and the number of
nesting wading birds (wood stork, great egret, snowy egret,
tricolored heron, and white ibis) has decreased markedly
during the twentieth century'4' (Figure 9). Historically, most
water slowly flowed across or soaked into the region's vast
wetlands. Today, over one-half of the region's wetlands
FIGURE 9. Everglades
wading bird populations
significantly declined during the
1900s.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 1 O. Historic (left) Everglades water flow
patterns and present flow patterns (right)(adaptedfmm1'5)
FIGURE 11. An extensive system of
canals, levees, and water control structures has
modified Everglades water conditions and
provides a conduit for pollutant transport. This
pump station discharges untreated stormwater
from an urban basin into the Everglades.
have been irreversibly drained. The water storage and water quality filtration
functions that these wetlands provided is gone. The canal system quickly drains
water from developed areas and the wetlands that remain. On average, a billion
gallons of fresh water are discharged to the coast each year. Discharges to the
Everglades are frequently too much or too little, and are often at the wrong time
(Figure 10). Some areas are too wet while other areas are too dry. Overland
sheetflow is interrupted by levees and canals that crisscross the Everglades and
can provide a conduit for pollutant transport from urban and agricultural areas
(Figure 11). Nutrient enrichment has become a threat to the Everglades.
As the human population continues to increase, urban and agricultural water
shortages are expected to become more frequent and severe. Conflicts for water
between natural resources, agriculture, industry, and a growing population will
therefore intensify.
THE SOLUTION
Many of the problems with declining ecosystem health revolve around four
interrelated factors: water quantity, quality, timing, and distribution (Figure 12).
Consequently, the major goal of restoration is to deliver the right amount of water
that is clean enough to the right places and at the right time. Since water largely
defined the natural system, it is expected that the natural system will respond to
water management improvements (Figure 13). The Water Resources
Development Acts of 1992 and 1996 directed the U.S. Army Corps of Engineers to
review the Project and develop a comprehensive plan to restore and preserve
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 1 2. The right water quality,
quantity, timing, and distribution of water
are all critical to South Florida ecosys-
tem protection and restoration'1'.
FIGURE 1 3. The anticipated effect of the Comprehensive
Everglades Restoration Plan (CERP). Without the Plan (left)
restoration targets will not be met (red). With the Plan fully
implemented (right) restoration targets likely will be met (green).
Yellow indicates uncertainty in meeting restoration targets'1'.
south Florida's natural ecosystem, while providing for other water-related needs of
the region including urban and agricultural water supply and flood protection. The
result is the Comprehensive Everglades Restoration Plan (CERP, or the Plan). The
development of the Plan was led by the Army Corps of Engineers and the South
Florida Water Management District and was accomplished by a team of more than
100 ecologists, hydrologists, engineers and other professionals from over 30 federal,
state, tribal, and local agencies. The Plan includes: about 180,000 acres of surface
water storage areas; about 36,000 acres of man-made wetlands to treat urban or
agricultural runoff; wastewater reuse; extensive aquifer storage and recovery; water
management operational changes; and structural changes to improve how and when
water is delivered to the Everglades, including removal of some of the canals or
levees that prevent natural overland sheet flow. The entire Plan is projected to take
over 30 years and cost about $8 billion to implement, with the cost split equally by
Florida and the federal government. If nothing is done, the health of the Everglades
will continue to decline, water quality will degrade further, some plant and animal
populations will be stressed further, water shortages for urban and agricultural users
will become more frequent, and the ability to protect people and their property from
flooding will be compromised'1 6).
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
A series of ecological success criteria have been defined that will gauge the success
of ecosystem restoration efforts.
Example Everglades Ecosystem Restoration Success Indicators'7'
Problem
Water Management
Habitat Alteration
Eutrophication
Mercury Contamination
Endangered Species
Soil Loss
Success Indicators
Reinstate system-wide natural hydropatterns and sheet flow
Increased spatial extent of habitat and wildlife corridors
Reduced phosphorus loading
Reduced top carnivore mercury body burden
Recovery of threatened/endangered species
Restore natural soil formation processes and rates
To evaluate restoration success, we must have a
reliable pre-restoration baseline for ecosystem condition.
USEPA REGION 4 SOUTH FLORIDA
ECOSYSTEM ASSESSMENT PROJECT
The attention and funding devoted toward Everglades ecosystem restoration are
unprecedented. It is imperative that ecosystem health is assessed in a cost-
effective, quantitative manner such that baseline, pre-restoration conditions are
documented. Such an assessment identifies resource restoration needs. Continued
assessment allows one to determine the effectiveness of restoration efforts. A major
defining feature of the Everglades is its large spatial area; hence, to monitor
restoration it is essential to determine the area of the current Everglades that is
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
subject to various human impacts. This study employs a scientifically rigorous way of
accomplishing this, using a method called probability-based sampling.
Assessment information can be used to help answer seven policy-relevant questions:
1) Magnitude - What is the magnitude of the problem? How severe is it?
2) Extent- What is the extent of the problem? How large an area is affected?
3) Trend - Is the problem getting better, worse, or staying the same?
4) Cause - What factors are associated with or causing the problem?
5) Source-What are the contributions of and importance of different sources?
6) Risk - What are the risks to different ecological systems?
7) Solutions - What management alternatives are available to ameliorate or
eliminate the problem?
These seven questions are equally applicable for each environmental problem
threatening the Everglades, including water management, soil loss, eutrophication,
habitat alteration and mercury contamination.
This project uses a statistical, probability-based sampling strategy to select sites
for sampling. Samples were collected from the freshwater wetland portion of the
Everglades and Big Cypress. The study area extended from Lake Okeechobee
southward to the mangrove fringe on Florida Bay and from the ridge along the urban,
eastern coast westward into Big Cypress National Preserve (Figure 8). The
distribution of the 200 canal sample sites and the 500 marsh sample sites is shown in
Figure 14. The samples represent the ecological condition in over 750 miles of
canals and over 3,000 square miles of freshwater marsh. Canals were sampled in
September 1993 and 1994, and May 1994 and 1995 (about 50 sites per sampling
cycle). Marshes were sampled in April 1995, September 1995 and 1996, and May
1996 (about 125 sites per sampling cycle). This corresponds to two dry (April and
May) seasons and two wet (September) seasons for both systems over a two-year
period. Because the study involved sampling remote locations throughout an
extensive area, each marsh sampling event was performed by two teams using
helicopters equipped with floats. It took 8 or 9 days for the two teams to
simultaneously sample 125 sites while moving from the south upstream to the north.
A second phase of intensive sampling, performed at about 250 marsh sites during
1999, is described in companion reports. All reports and data for the study are
available on the internet at .
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
May 1995
September 1995
May 1996
September 1996
FIGURE 1 4. The 200 canal sampling stations (left) and 500 marsh sampling stations (right).
The media sampled at each site include surface water (Figure 15), canal
sediment, marsh soil (Figure 16), algae (Figure 17), and prey fish (Figure 18). The
study sampled three physiographic regions: Everglades ridge and slough; marl
prairie/rocky glades; and Big Cypress Swamp.
This study permits a consistent, synoptic look at indicators of the ecological
condition throughout the freshwater canal and marsh system. This large-scale
perspective is critical to understanding the impacts of different factors (such as
phosphorus and mercury distributions throughout the canals and marsh, habitat
alteration, or hydropattern modification) on the entire system rather than at individual
locations or in small areas. Looking only at isolated sites in any given area and
extrapolating to the larger system can give a distorted perspective. This study is
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 1 5. Water samples were collected at
each site and analyzed for nutrients, mercury, and
other constituents.
FIGURE 1 6. A typical peat soil core collected
from an Everglades wet prairie.
unique to South Florida: its extensive spatial
coverage and sampling intensity are
unprecedented; its probability-based sampling
approach permits quantitative statements about
ecosystem condition.
A key advantage to this study's probability-
based statistical sampling approach is that it
allows one to estimate, with known confidence
and without bias, the current status and extent of
indicators for the condition of ecological
resources'89'. Also, indicators of pollutant
exposure and habitat condition can be used to
identify associations between human-induced
stresses and ecological condition. This design
has been reviewed by the National Academy of
Sciences, and the USEPA has applied it to
lakes, rivers, streams, wetlands, estuaries,
forests, arid ecosystems and agro-ecosystems
throughout the United States'10'11'.
FIGURE 1 7. Well-defined periphyton mats are a
defining characteristic of the Everglades ridge and
slough complex.
FIGURE 18.
marsh.
Sampling prey fish in a sawgrass
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
PROBABILITY SAMPLES
A defining feature of the
Everglades is its large spatial scale;
hence, to monitor restoration
effectiveness it is essential to
determine the area of the
Everglades that is subject to various
human impacts. This study employs
probability-based sampling in order
to accomplish this. Probability
samples are samples where every
member of the population has a
known chance of being selected
and the samples are drawn at
random. Every location in the study
area has an equal chance of being
sampled, so the results of this
project are representative of the
spatial distribution of parameters
that are being measured.
Therefore, the sampling design is
not biased to favor one marsh type
over another (e.g., sampling only
the marshes next to a road because
it is easier, avoiding sawgrass
because it is unpleasant to sample
in, or selecting a canal location
because it looks good or bad). This
means that the results can be used
to estimate with known confidence
the proportion (extent) and
condition of that resource. The risk
to any ecological resource from the
multiple environmental threats in
South Florida is a direct function of
the extent and magnitude of both
the threat and the ecological
effects.
Parameters measured at each site can be used
to answer questions on multiple issues including:
• Water management (e.g., water depth at all
sites)
• Water quality and eutrophication (e.g.,
phosphorus concentrations in water and soil,
cattail distribution)
• Habitat alteration (e.g., wet prairie, sawgrass
marsh and cypress plant community
distribution)
• Mercury contamination (e.g., mercury in
water, soil, algae, and preyfish)
Specific questions related to Everglades
restoration goals that this study answers include:
• How much of the marsh or canal system has
a total phosphorus concentration greater than
50 parts per billion (ppb), the Phase I
phosphorus control goal, or 10 ppb, the
approximate natural marsh background
concentration?
• How much of the marsh is dominated by
sawgrass? Wet prairie? Cattail?
• How much of the marsh still has the natural
oligotrophic periphyton mat?
• How much of the marsh area is dry, and where?
• How much of the marsh soil has been lost due
to subsidence?
• How much of the marsh has prey fish with
mercury levels that present increased risk to
top predators such as wading birds?
• What water quality conditions are associated
with marsh zones of high mercury
bioaccumulation ?
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
The probability-based sampling design is an assessment approach that
provides unbiased estimates of ecosystem condition with known confidence limits.
Data from this study have been used by a variety of scientists and agencies for
many purposes:
• Input to models that predict the Everglades' response to water management
changes.
• Input to models that predict periphyton or vegetation changes in response to
phosphorus enrichment.
• Developing empirical models in order to better understand interrelationships
among mercury, phosphorus, sulfur, and carbon.
• Developing water quality standards to protect human health, fish and wildlife.
• Understanding the relative risks of phosphorus and mercury.
Monitoring is important for determining ecosystem condition, identifying threats,
and evaluating environmental restoration efforts. As portions of the Comprehensive
Everglades Restoration Plan are implemented, a system-wide monitoring program is
needed. Monitoring objectives include:
• Documenting status and trends;
• Determining baseline variability;
• Detecting responses to management actions;
• Improving the understanding of cause and effect relationships.
This South Florida Ecosystem Assessment Project provides such information system-
wide for the freshwater Everglades marsh. The next sections describe ecosystem status
based on the sampling program in canals and marshes from 1993 to 1996.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
WATER MANAGEMENT
The historic Everglades was defined in part by water: highly seasonal rainfall;
slow, unimpeded, sheetlike water flow; and a large storage capacity that prolonged
wetland flooding. These characteristics, along with subtle changes in ground surface
elevation of only a few feet, produced a variety of water depths and hydroperiods
(duration of surface water inundation). Because changes in water caused many of
the harmful changes to the historic Everglades, water is key to restoration. Rainfall
and the general patterns in water depth observed from 1993 to 1996 are described in
this section.
Rainfall is highly seasonal, with about 80% falling during the May to October wet
season (Figures 19 and 20). Rainfall during the 1993-1996 sampling period was
above average. Discharge through public water pumping stations is also highly
seasonal. For example, at S-8, a pumping station that provides flood control for part
FIGURE 19. A typical intense rain event in the
slough-wet prairie complex during the summer wet
season.
FIGURE 21. The slough-wet prairie complex
during the dry season.
1993
1994
1995
1996
FIGURE 2O. Monthly rainfall (inches) from
1993 to 1996 at S-8, a pumping station that
provides flood control for part of the EAA by
discharging into the Everglades.
1993
1994
1995
1996
FIGURE 22. Monthly discharge at S-8.
Discharge varies from zero to several thousand
cubic feet per second in response to rain events.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
of the Everglades Agricultural Area, discharge varies from zero during dry times to
several thousand cubic feet per second in response to rain events (Figure 22).
Dry season
April 1995
Marsh water depths vary greatly with time and location (Figures 21, 23 to 25).
Water depths are deepest immediately upstream of levees that impede the natural
flow of water, such as the southern portions of Arthur R. Marshall Loxahatchee
National Wildlife Refuge (the Refuge) and Water Conservation Areas 2 and 3A
(Figure 23). Although all of these long hydroperiod areas remained wet during the
study period, the unnaturally deep water depth of over five feet was observed within
Water Conservation Area 3 where the L-67 levee prevents sheetflow to the south.
Shorter hydroperiod portions of the
marsh are subjected to annual periods
of drying. During both wet seasons the
entire marsh was inundated, while in
April 1995 and May 1996 16% and 29%
of the Everglades marsh was dry.
Wet season
September 1995
Dry season
May 1996
Wet season
September 1996
-2
1994
1995
1996
FIGURE 24. Mean monthly water depth at four
marsh locations. Red circles indicate when sampling
occurred. See Figure 23 for locations.
r
FIGURE 23. Water depth in the marsh system during the
four sampling events. Colored squares indicate the location of
water depth gauges used for Figure 24.
FIGURE 25. The slough-wet prairie complex
during the wet season in Everglades National Park.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
WATER QUALITY PATTERNS
CONDUCTIVITY
Water conductivity is useful
for understanding the source of
the water and its flow path.
Precipitation in the Everglades
has very low ionic content, with
specific conductivity of volume-
weighted annual precipitation
of about 10 micromhos/cm(12).
In contrast, the conductivity of
water discharged from the EAA
during the wet season is about
100 times higher (1,000
micromhos/cm). Conductivity
exhibits pronounced seasonal
and spatial patterns in the
Everglades (Figures 26 and
27). Very low conductivity in
Big Cypress, the western
portions of Water Conservation
Area 3A and the interior of the
Refuge (less than 100
micromhos/cm) indicates that
these areas are largely rainfall-
driven. Higher conductivity
water is transported
downstream in canals draining
the EAA, and there is a
progressive decrease
southward to the Park with
dilution by rainfall and marsh
water. Water Conservation
Area 2 has the highest marsh
conductivity. Marsh
conductivity is higher in the dry
season due to less dilution by
• 0-199
• 200 - 399
400 - 599
600 - 799
800 - 2200
FIGURE 26. Surface water conductivity (micromhos/cm) in the marsh
(top) and canals (bottom) during the dry season (left) and wet season
(right).
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
rainfall, the drying of the marsh and subsequent evapoconcentration, and the
continuing influence of canal water. Pronounced conductivity gradients clearly
indicate pathways of water flow throughout the canal-marsh system and the extent to
which the water management system and its operation influences water quality.
Canal
Conductivity (micromhos/cm)
Marsh
Conductivity (micromhos/cm)
200 400 600 800 1000
Sulfate (ppm)
200 400 600 800 1000
Sulfate (ppm)
Total Organic Carbon (ppm)
Total Organic Carbon (ppm)
LNWR -
VVCAoN
VVCAoo -
CM p
BCNP -
I
1
i
i
i
0
10
20
30
FIGURE 27. Seasonal comparison of surface water conductivity (micromhos/cm), sulfate (ppm) and total
organic carbon (ppm) by latitudinal subarea for canals (left) and marsh (right). Blue bars are wet season,
orange bars are dry season. EPA north of AA is the Everglades Protection Area north of Alligator Alley.
WCA3N is WCA3A north of Alligator Alley. WCA3A S is WCA3B and WCA3A south of Alligator Alley. TT is
Tamiami Trail. The median is reported.
40
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
SULFATE
Sulfate is common in nature and is a natural ingredient of rainfall, surface water
and groundwater. Sulfur is also
a secondary nutrient required
for crops. Agricultural sulfur is
applied to EAA soils in order to
make plant nutrients more
readily available'13'14).
Marsh and canal surface
water sulfate from 1993 to 1996
exhibited strong gradients and
seasonality (Figures 27 and 28).
Rainfall sulfate concentrations
are less than 1 ppm(12). Marsh
background concentrations of
less than 2 ppm are found only
in the interior rainfall-driven
portion of the Refuge, and
portions of the marsh that are
distant from the influence of
canal water deliveries, such as
western Water Conservation
Area 3, Big Cypress, and
portions of the Park. The
highest sulfate concentrations
of over 100 ppm were observed
in canals within the EAA during
the wet season. The highest
marsh concentrations are found
in Water Conservation Area 2.
Concentrations progressively
decrease to the south and west.
The lowest concentrations are
found in the Refuge, Big
Cypress, and the marsh south
of Tamiami Trail during the wet
FIGURE 28. Surface water sulfate (ppm) in the marsh (top) and
canals (bottom) during the dry season (left) and wet season (right).
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
Pronounced spatial gradients in surface water conductivity and sulfate
throughout the canal and marsh system vividly demonstrate that the canal
system is a conduit for transport. Water management affects water quality.
Dry Season £ a^
Canal
5- 9
10 - 19
20-29
30-39
40 - 100
season (median of less than 2
ppm).
These spatial patterns
indicate that the canal system
delivers sulfate from the north
into Everglades marshes.
Sulfate is of particular
ecological concern since
slightly elevated sulfate
concentrations have been
hypothesized to affect
mercury cycling by stimulating
mercury methylation'15'.
TOTAL ORGANIC
CARBON
The highest total organic
carbon was observed in
canals within the EAA
(Figures 27 and 29). Total
organic carbon also exhibits
high seasonality with highest
values during the dry season.
Carbon is important in that it
also plays a role in mercury
cycling'15'. The specific
effects of carbon and sulfur on
mercury cycling are the
subject of ongoing research.
FIGURE 29. Surface water total organic carbon (ppm) in the marsh (top)
and canals (bottom) during the dry season (left) and wet season (right).
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
SOIL SUBSIDENCE
Soil is a key defining characteristic of an ecosystem, and soil preservation is an
important aspect of ecosystem protection. The South Florida Ecosystem Restoration
Task Force and the Comprehensive Everglades Restoration Plan have adopted
objectives and success indices in order to define restoration goals, track ecosystem
status, and measure restoration effectiveness. Among these is restoring the natural
rates of organic soil and marl soil accretion, and stopping soil subsidence'7'.
A variety of soil types are found in the Everglades. Soils to the west in Big
Cypress Swamp are primarily sandy, while the wetland soils of the central Everglades
are primarily organic peat (see Figures 5 and 16). Peat soils are formed by decaying
plant matter. Another major soil type found within Everglades wetlands is a calcitic
mud (marl), commonly found in the shallower peripheral marshes of the Everglades
subjected to shorter periods of surface water inundation (Figure 30). Marl is found
in association with thick algal mats, called periphyton, which are able to precipitate
calcium carbonate from the water column'16'.
The Everglades once contained the largest single body of organic soils in the
world, covering over 3,000 square miles, and accumulating to a thickness of up to 17
feet in what is now the EAA(17). The origin and perpetuation of peat and marl soils is
greatly dependent upon water depth and the duration of surface water inundation,
and the resulting wetland vegetative communities. Diminished surface water
inundation can cause soil loss or changes in soil composition, which may in turn
result in altered vegetative communities. These altered plant communities may
cause further changes in soil type and thickness as this different plant community
eventually decomposes and forms altered soil.
Peat soils are subject to subsidence and surface
elevation loss when drained. Oxidation, burning and
compaction are considered the dominant subsidence
forces, and from a practical standpoint are irreversible.
An inch of Everglades peat that takes a century to form
can be lost within a few years. Early in the twentieth
century the deep peat soils (mostly formed by decaying
sawgrass) of the 700,000 acre EAA were drained to
facilitate agricultural production. The process of soil
formation was reversed in 1906 when the first canals were
FIGURE 3O. An Everglades soil
core with peat overlaying marl.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
cut from Lake Okeechobee through the EAA to the coast'18'. Subsequent subsidence
within the EAA and efforts to control it on agricultural lands are well documented.
In contrast, prior to this study subsidence of peat soils during the last 50 years
within the Everglades Protection Area was poorly documented. Soil loss in the public
Everglades is largely due to water management practices during the 1900s. The
major canals draining the EAA extend southeast through the Everglades to the
Atlantic Ocean and were completed by 1917. However, unimpeded surface water
flow from the EAA south through the Everglades to the Park, Florida Bay, and the
Gulf of Mexico still occurred until the late 1950s, when levees were constructed
forming the southern boundary of the EAA. During the early 1960s additional levees
were completed that partitioned the Everglades into the Water Conservation Areas.
By the 1960s Everglades surface water depths, flow, and inundation periods had
been greatly altered'19'.
Soil thickness measured at 479 sampling
sites from 1995 to 1996 is presented in
Figures 31 and 32, along with soil
thicknesses reported by Davis in 1946(20).
Soil thicknesses throughout the study area
vary greatly from 0 feet to over 12 feet. The
deepest soils are the peat deposits within the
Refuge with a median soil thickness of over
9 feet. Median soil thicknesses for
remaining portions of the study area were
4.2 feet in Water Conservation Area 2,
1.2 feet in Water Conservation Area 3A north
of Alligator Alley, 2.8 feet in Water
Conservation Area 3 south of Alligator Alley,
1.0 feet in the Park, and 1.0 feet in Big
Cypress. About 19% of the Everglades had
a soil thickness less than one foot, while
40% had a soil thickness of over three feet.
The deepest peat in the Everglades outside
of the Refuge is within those portions of
Water Conservation Area 2 and southern
Water Conservation Area 3 which typically
stay inundated year-round.
Organic Matter (percent)
20
40
60
80
Bulk Density (glee)
Soil Thickness (feet)
100
LNWR
WCA2
WCA3N
WCA3S
ENP
BCNP
LNWR
WCA2
WCA3N .
WCA3S .
ENP
BCNP
| |
10
FIGURE 3 1. Spatial variation in soil organic matter,
bulk density, and thickness throughout the Everglades
marsh system at about 480 sampling sites. The median is
reported.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 32. Soil thickness (feet) as reported by Davis in 1946 (left) and at
479 sites in 1995 to 1996 (this study).
Figure 33 presents the
change in peat thickness
throughout the Everglades
during the last 50 years.
Soil volumes reported in
1946 and 1996 and the
difference have been
calculated bysubarea.
Since the 1946 peat
thickness was reported in
2-foot intervals, soil
volume differences from
1946 to 1996 are
presented as a range.
Calculation of soil loss
during the last 50 years
indicates that the portion of
Water Conservation Area
3 north of Alligator Alley
lost between 39% and
65% (2.0to6.0x108m3)
of its soil. This area was
reported to have 3 to 5
feet of peat in 1946, while
the present study found
only 1 to 3 feet of soil,
with less than 1 foot in
some areas. The
southeastern part of
Water Conservation Area
3 (WCA3B) and the
northeast Shark Slough
portion of the Park may
FIGURE 33. Soil loss (feet) from 1946 to 1996 for the Everglades. have lost up to 3 feet Of
soil, representing a 53%
loss of volume in Northeast Shark Slough, and a 42% loss of volume in WCA3B.
These three portions of the Everglades, which encompass about 200,000 acres, have
Minimum
Loss
No
Loss
Maximum
Loss
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
been subjected to decreased surface water inundation since completion of the Water
Conservation Areas about 40 years ago. During the last 50 years the Everglades
Protection Area has lost up to 28% of its soil (17 x 108 m3). The accretion of soil
within portions of the Park suggested by Figure 33 may be an artifact of the 1946
sampling method. Davis (1946) mentions seven areas of detailed sampling, none of
which were within what is now the Park.
Soil organic matter observed during 1995 and 1996 at 479 sites ranged from
<1 % to 97% (Figures 31 and 34). Peat soils are highly organic, while marl soils and
sandy soils are primarily mineral. The highest organic matter content was found in
the thick peat soils within the Refuge with a median of 93%. Water Conservation
Area 2A and Water Conservation Area 3 south of Alligator Alley also had soils
exceeding 75% organic matter. These highly organic zones coincide with the deeper
soil portions of the system. The area of maximum soil loss within Water
Conservation Area 3 north of Alligator Alley had a median soil organic matter content
FIGURE 34. Soil organic matter (percent, left) and bulk density (g/cc, right). Data are for the 0 to 10 cm soil
depth.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
During the last 50 years, over one-half of the soil has been lost from portions of
the Everglades. Water management must be improved to maintain marsh soils if
the plant communities and wildlife habitat of these wetlands are to be preserved.
of 63%, the lowest within the Water Conservation Areas. Soils in the Park, which
include the peat soils within the Shark Slough trough as well as the marl soils of
adjacent shorter hydroperiod areas, had a median organic content of 31 %. The
sandy soils of Big Cypress had a median organic matter content of only 11%.
Portions of the Park outside the central Shark Slough trough also had lower organic
matter content, usually in the 10% to 20% range.
Soil bulk density at 475 marsh sites in 1995 and 1996 ranged from 0.05 to 1.50 g/
cc (Figures 31 and 34). The highly organic peat soils of the Refuge had the lowest
bulk density with a median of 0.06 g/cc as compared to the mineral soils of Big
Cypress, which had a median of 0.75 g/cc. The median bulk density for Water
Conservation Area 3 north of Alligator Alley was 0.21 g/cc, the highest in the Water
Conservation Areas. Within the Water Conservation Areas, this portion of northern
Water Conservation Area 3 had the lowest organic matter content, the highest bulk
density, and the greatest soil loss.
All of these observations are suggestive of formerly deeper peat soils being
subjected to drier conditions due to water management changes over the last
50 years. Surface water inundation has been reduced, soils have subsided, and the
resulting surface soil has become less organic. This South Florida Ecosystem
Assessment Project is the first effort to consistently document soil thickness, bulk
density and organic matter throughout the Everglades system.
EUTROPHICATION AND HABITAT
Historically, the Everglades ecosystem was nutrient poor, with surface water
phosphorus concentrations less than 10 parts per billion (ppb)(21). Rainfall was the
dominant source of external phosphorus, and the hydrology of the marsh was rainfall-
driven, with slow overland sheet flow supplying water to downstream wetlands.
There were no canals in the Everglades region prior to the early part of the twentieth
century. This natural nutrient-poor condition resulted in a diversity of wildlife habitats,
such as sloughs, sawgrass marshes, and wet prairies which included well-developed
periphyton communities.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
Today, the canal system is a conduit for nutrient transport. Nutrient loading from
the EAA and urban areas has significantly increased phosphorus concentrations in
the downstream Water Conservation Areas and the Park, causing eutrophic impacts
to these wetland systems. Among the progressive eutrophic impacts are altered
periphyton communities, loss of water column dissolved oxygen, increased soil
phosphorus content, conversion of wet prairie and sawgrass plant communities to
cattail, and subsequent loss of important wading bird foraging habitat. These
collective changes impact the structure and function of the aquatic ecosystem.
A phosphorus control program was initiated in the 1990s in order to prevent the
further loss of Everglades plant communities and wildlife habitat due to nutrient
enrichment. Phase I of the program requires that discharges from the EAA into the
Everglades be at 50 ppb total phosphorus (TP) or less. Control is to be achieved by
a combination of about 47,000 acres of treatment wetlands, referred to as
Stormwater Treatment Areas (STAs) (Figure 35), and agricultural Best Management
Practices (BMPs). The first STA (about
10% of the Phase I treatment acreage)
began discharging in 1994, and BMPs
were required to be in place by 1995. The
1993 to 1996 sampling period reported
here corresponds to the phase-in period
for EAA BMPs, as during these years the
percentage of EAA farms with phosphorus
control BMPs in place went from 0 to 100.
The BMPs have resulted in about a 50%
three-year cumulative phosphorus load
reduction from the EAA basin to the
Everglades Protection Area, as compared
to the load that would have been expected
without BMPs(22). This report documents
the 1993 to 1996 phosphorus conditions
and habitat during the initiation of
Stormwater
Treatment
Areas
Everglades
Agricultural
Area
phosphorus control efforts.
FIGURE 35. Location of Phase I phosphorus control
program Stormwater treatment wetlands. In combination
with agricultural best management practices they are to
decrease phosphorus to 50 ppb or less prior to discharge
into the Everglades (adapted from SFWMD).
Water and soil samples were analyzed
for phosphorus and other indicators of nutrient enrichment, such as nitrogen,
chlorophyll a, and alkaline phosphatase activity. Relationships between phosphorus
concentrations in water and soils, plant communities, and periphyton presence were
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
noted to identify correlations between nutrient enrichment and habitat in the
Everglades ecosystem.
Canal TP concentrations exhibit strong north to south gradients. Concentrations
in EAA canals were significantly higher than those in any other area sampled
(Figures 36 and 37), with a wet season median of 149 ppb (as compared to 13 ppb in
canals near the Park). About 80% of
the canal miles in the EAA had TP
concentrations greater than the
^ _ Phase I STA design target of 50 ppb.
{-*|~ ' x \ ' f~~V\r ^> This drops to 15% for canals in the
\ \ \ ' V \ /I " area between Alligator Alley and
Tamiami Trail, and to only 1% for
canals in the area south of Tamiami
Trail. North of Alligator Alley wet
season concentrations tend to be
higher, while to the south dry season
concentrations tend to be higher.
Overall, 44% of canal miles had
water TP concentrations greater than
50 ppb.
Marsh sites also exhibit spatial
gradients. Marsh TP concentrations
were notably higher in the dry
season, with the highest
concentrations most consistently
occurring in northeast Water
Conservation Area 2A. The interior
of the Refuge tended to have very
low concentrations, indicative of its
rainfall-driven status (Figures 36
and 37). Median TP concentrations
throughout the Everglades system
ranged from less than 10 ppb in the
marsh during the wet season (Figure
38), to almost 50 ppb in the canals
during the dry season.
FIGURE 36. Surface water total phosphorus (ppb) in the
marsh (top) and canals (bottom) during the dry season (left) and
wet season (right).
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
Canal
Total Phosphorus
0 50 100 150
Alkaline Phosphatase Activity
Marsh
Total Phosphorus
0 10 20 30 40 50
Alkaline Phosphatase Activity
LNVVR-
WCA2 -
WCA3N -
WCA3S "
ENP-
BCNP-
I
EEP
i
i
b
^m
01234
FIGURE 37. Seasonal comparison of surface water total phosphorus (ppb) and alkaline phosphatase activity
(micromoles/hr) by latitudinal subarea for canals (left) and marsh (right). Blue bars are wet season, orange bars are dry
season. Alkaline phosphatase is an enzyme that makes phosphorus available for biological uptake. Lower activity is
indicative of higher phosphorus availability. EPA north of AA is the Everglades Protection Area north of Alligator Alley.
WCA3 N is WCA3A north of Alligator Alley (AA). WCA3 S is WC3B and WCA 3A south of Alligator Alley. TT is Tamiami
Trail. The median is reported.
Similar patterns existed for
alkaline phosphatase activity
(APA) (Figures 37 and 39).
Alkaline phosphatase is an
enzyme that makes
phosphorus available for
biological uptake. Higher
activity indicates low
phosphorus concentration. In
general, APA throughout the
marsh and canals exhibited
strong gradients and the
expected inverse relationship
with TP in water. The lowest
enzyme activities (median of
100
Canal Wet
Canal Dry
Marsh Dry
Marsh Wet
50
Total Phosphorus (ppb)
100
FIGURE 38. Cumulative distribution of frequency for total phospho-
rus by season in the marsh and canal systems. The y-axis indicates
percent of canal miles or percent of marsh area. The 50% line is the
median.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 39. Surface water alkaline phosphatase activity (micromoles per hour) in the marsh (left, September
1995) and canals. Canal data are for dry season (middle) and wet season (right).
about 0.1 micromoles/hr) were observed in EAA canals where water TP
concentrations were highest. The highest enzyme activities were found during the
wet season in the Refuge (median of 4.2 micromoles/hr) and interior portions of the
Park (median of 2.5 micromoles/hr).
Phosphorus in marsh soils can be an indicator of enrichment. Soil type varies
greatly throughout the Everglades, as the median bulk density of soil varied from
about 0.06 g/cc in the Refuge to 0.75 g/cc in Big Cypress (Figure 34). Soil
phosphorus is expressed in Figure 40 as milligrams phosphorus per kilogram of soil,
and as micrograms phosphorus per cubic centimeter of soil in order to remove the
influence of varying soil bulk density. Depicted in this manner, Water Conservation
Area 3A north of Alligator Alley and northern Water Conservation Area 2A have the
highest soil phosphorus in the portion of the Everglades with peat soil. In contrast,
the Refuge interior has much lower soil phosphorus than any other part of the
system. Results reported here for 1995 to 1996 are similar to those obtained by
others in the early 1990s for the Refuge and Water Conservation Areas 2 and 3(21).
This study is the first to perform systematic synoptic sampling of soil phosphorus
throughout all of the Everglades Protection Area and Big Cypress.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 4O. Soil total phosphorus expressed as milligrams per kilogram (left) and as micrograms
per cubic centimeter (right). Data are for the 0 to 10 centimeter soil depth.
The natural mosaic of vegetation community types is a defining characteristic of
the Everglades. Wet prairies and open water areas void of dense emergent
macrophytes serve as preferred wading bird foraging habitat. Factors driving
vegetation community composition include hydroperiod, salinity, nutrients, and
disturbances such as fire, frosts, and hurricanes. Field crews documented the
dominant and secondary plant communities at the marsh sampling sites. A simple
vegetation classification method was used to qualitatively group marsh habitat into
several classes, including sawgrass marsh and wet prairie. Field crews also noted if
cattail (Typha domingensis) was present at a site. Cattail is a native species known
to respond to phosphorus enrichment such that it can replace wet prairies and
sawgrass.
Wet prairie and sawgrass marsh are the two dominant plant communities in the
Everglades. Sawgrass was dominant at 47% of the 479 sampling sites and the wet
prairie-slough complex was dominant at 44% of the sites (Figures 41 to 43). Wet
prairie tends to dominate in the Refuge, and in wetter portions of WCA3. Sawgrass
tends to dominate north of Alligator Alley and in Water Conservation Area 2, while the
Park contains a mix of the two communities. Cattail presence along with soil
phosphorus is shown in Figure 43. Cattail was present at 10% of the sampling sites.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
FIGURE 4 1 . Aerial view of the Everglades showing the mosaic of
sawgrass marsh and wet prairie plant communities.
FIGURE 42. Sawgrass marsh with
high plant density.
Cattail was prevalent in the northern
portions of Water Conservation Areas 3A
and 2A, and sites that were generally in
close proximity to canals. There tends to
be a strong association between cattail
presence and soil phosphorus or proximity
to canals. As soil phosphorus increases,
there is a greater likelihood that cattail will
be present'23'.
Soil TP
> 870 mg/kg
FIGURE 43. The spatial distribution of the wet prairie
(blue) and sawgrass marsh (green) vegetation
communities. Red indicates the presence of cattail. Yellow
indicates soil phosphorus greater than 870 mg/kg(23).
FIGURE 44. Everglades eutrophication promotes
cattail expansion.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
Low phosphorus conditions must be restored if natural
Everglades periphyton and plant communities are to be maintained.
Well-developed attached or floating periphyton
mats are a defining characteristic of Everglades
habitats, particularly wet prairies and deeper slough
areas (Figures 2, 17, 45 and 46). These biologic
communities serve multiple functions such as
providing oxygen to the water column for fish,
removing calcium carbonate from the water and
depositing it as soil, removing phosphorus from the
water to very low levels, and serving as a food web
base'21'. These periphyton communities are
sensitive to very slight increases in nutrient
concentration, with increases in phosphorus
condition causing mat disappearance or changes to
the periphyton assemblage, including species
composition and biomass. Consequently, periphyton
are a sensitive indicator of marsh ecosystem status.
Periphyton mats were found at 67% of the
sample sites during 1995-1996. The species
composition of these mats was not documented.
Mats were less common in the Refuge and the
northern portions of Water Conservation Areas 2A
and 3A (Figure 46). With the exception of the
Refuge, the areas where periphyton mats were not
found tend to be areas where wet prairies are
absent and sawgrass or cattail dominate. In
communities where plant density, height, and above
ground biomass are high, shading effects may
preclude the development of periphyton mats and
wet prairie communities. Elevated phosphorus may
also explain the absence of the mat community, or
a change in periphyton species composition to
species that are more nutrient tolerant'21'.
FIGURE 45. Underwater view of a wet prairie
in southern Water Conservation Area 3 with
periphyton attached to macrophytes.
Present
Absent
FIGURE 46. Presence of a periphyton mat
community. Green indicates presence while
black indicates absence.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
KEY FINDINGS AND MANAGEMENT
IMPLICATIONS
This report describes the condition of the Everglades system during the extensive
1993 to 1996 synoptic sampling effort. This represents the condition prior to initiation
of the Comprehensive Everglades Restoration Program. Study findings have various
management implications.
• Pronounced water quality gradients: Water discharged from Everglades
Agricultural Area canals is loading the public Everglades with excess
phosphorus, carbon, and sulfur. Concentrations progressively decrease
downstream.
• Canals are a conduit for pollutant transport: The canal system is an effective
conduit for the transport of degraded water into and through the Everglades
marsh system. Water management clearly affects water quality. Downstream
water quality would be improved if delivery canals were eliminated or if they were
operated to maximize the diluting influence of rainfall, cleaner marsh water and
surface water sheetflow.
• Varying water quality: Surface water conductivity, phosphorus, carbon,
nitrogen and sulfur vary greatly throughout Big Cypress and the Everglades and
are dependent upon location, time of year and water management practices.
Long-term sampling is required in order to differentiate between natural
seasonality, inter-annual variability, and the effects of specific restoration actions
taken under the adaptive assessment approach.
• Phosphorus enrichment: As of 1995 to 1996, about 44% of the Everglades
canal system and 4% of the Everglades marsh area had total phosphorus
concentrations exceeding the Phase I 50 part per billion control target. Once all
phosphorus control efforts are in place (2007), probability-based sampling can
be repeated to document the effectiveness of these efforts.
• Marsh habitat a mosaic: Wet prairie and sawgrass marsh were the two
dominant plant communities in the Everglades, representing 44% and 47% of
the sites sampled. Cattail was present at 10% of these sites, and was
associated with elevated soil phosphorus or proximity to canals. Water quantity
and water quality must be managed to maintain these important habitats, and
halt further encroachment of cattail.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
• Periphyton conspicuous: Well-defined periphyton mats, a defining
characteristic of the Everglades marsh complex, were found at 67% of the
sample sites. Water quality should be maintained such that oligotrophic
periphyton mats are perpetuated.
• Soil loss in the Everglades Protection Area: From 1946 to 1996, about one-
half of the peat soil was lost from drier portions of the Everglades. This is a
serious problem that must be addressed. Water management must be improved
to maintain remaining marsh soils if the plant communities and wildlife habitat of
these wetlands are to be preserved.
• Ecological condition varies by location and time: The ecological condition of
the Everglades varied greatly with location. Rainfall-driven portions of the
system that are distant from the influence of canal water, such as the interior of
Arthur R. Marshall Loxahatchee National Wildlife Refuge and the southwest
portion of Water Conservation Area 3A, were found to have good water quality
and low soil phosphorus. The interior of Loxahatchee National Wildlife Refuge
tended to have the most pristine water quality and the lowest phosphorus
concentrations in peat soils. In contrast, northern Water Conservation Area 3A
had poorer water quality, extensive soil loss due to water management, elevated
soil phosphorus and cattail encroachment. Water Conservation Area 2 had
evidence of phosphorus enrichment and cattail encroachment, along with high
sulfate and conductivity. Big Cypress had good water quality and no obvious
indications of phosphorus enrichment. Water quantity conditions at a given
location vary with season and year.
• Environmental threats interrelated: Ecological stressors such as water
management, soil loss, water quality degradation, eutrophication, cattail
encroachment and mercury contamination are often interrelated. Management
actions must be holistic.
This project provides a critical benchmark for assessing the ecosystem condition
and the effectiveness of Everglades restoration activities into the twenty-first century.
As Everglades protection efforts proceed, this probability-based sampling can be
repeated to document the effectiveness of these actions.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
The South Florida Ecosystem Assessment Project documents conditions in the
Everglades prior to ecosystem restoration efforts. This provides a benchmark
for determining the effectiveness of future Everglades restoration activities.
REFERENCES
REFERENCES CITED
1. United States Army Corps of Engineers and South Florida Water Management District.
July 1999. Rescuing an Endangered Ecosystem: the Plan to Restore America's
Everglades. The Central and Southern Florida Project Comprehensive Review Study
(The Restudy). 28 p.
2. United States Bureau of the Census. 1890 to 1990 United States census results.
3. Davis, Steven M. and John C. Ogden. 1993. Everglades: The Ecosystem and Its
Restoration. St. Lucie Press. Delray Beach, Florida. 826 p.
4. Ogden, John C. 1993. A Comparison of Wading Bird Nesting Colony Dynamics
(1931-1946 and 1971-1989) as an Indication of Ecosystem Conditions in the Southern
Everglades, pp. 533-570 in Everglades: The Ecosystem and Its Restoration. Davis,
Steven M. and John C. Ogden (editors). St. Lucie Press. Delray Beach, Florida.
826 p.
5. Ingebritsen, S. E., Christopher McVoy, B. Glaz, and Winfred Park. 2000. Florida
Everglades, pp. 95-106 in Land Subsidence in the United States. Devin Galloway,
David R. Jones and S. E. Ingebritzen, editors. United States Geological Survey
Circular 1182. Denver, Colorado. 177 p.
6. United States Army Corps of Engineers and South Florida Water Management District.
October 1998. Overview. The Central and Southern Florida Project Comprehensive
Review Study. 29 p.
7. Science Subgroup. 1997. Ecologic and Precursor Success Criteria for South Florida
Ecosystem Restoration. Report to the Working Group of the South Florida Ecosystem
Restoration Task Force. Planning Division. United States Army Corps of Engineers.
Jacksonville, Florida. < http://www.sfrestore.org/>
8. Thornton, K. W., Saul, G. E. and Hyatt, D. E. 1994. Environmental Monitoring and
Assessment Program Assessment Framework. United States Environmental Agency
Report EPA/620/R-94/016. Research Triangle Park, North Carolina. 47 p.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
9. Stevens, Don L, Jr. 1997. Variable Density Grid-based Sampling Designs for
Continuous Spatial Populations. Environmetrics vol. 8, p. 167-195.
10. Olsen, A. R., Sedransk, J., Edwards, D., Gotway, C. A., Liggett, W. 1999. Statistical
Issues for Monitoring Ecological and Natural Resources in the United States.
Environmental Monitoring and Assessment, vol. 54, p. 1-45.
11. United States Environmental Protection Agency. 1995. Environmental Monitoring and
Assessment Program (EMAP) Cumulative Bibliography. United States Environmental
Protection Agency, Office of Research and Development. EPA/620/R-95/006.
Resarch Triangle Park, North Carolina. 44 p.
12. National Atmospheric Deposition Program. 2000. National Atmospheric Deposition
Program data, site FL11. Accessed July 19,
2000.
13. Coale, Frank J. 1994. Sugarcane Production in the EAA. pp. 224-237 in Everglades
Agricultural Area (EAA): Water, Soil, Crop, and Environmental Management.
University Press of Florida. Gainesville, Florida. 318 p.
14. Schueneman, T. J. and C. A. Sanchez. 1994. Vegetable Production in the EAA. pp.
238-277 in Everglades Agricultural Area (EAA): Water, Soil, Crop, and Environmental
Management. University Press of Florida. Gainesville, Florida. 318 p.
15. Larry Fink and Peter Rawlik. 2000. The Everglades Mercury Problem. Chapter 7 in
Everglades Consolidated Report. January 1, 2000. South Florida Water
Management District,
16. Gleason, Patrick J. and Peter Stone. 1993. Age, Origin and Landscape Evolution of
Everglades Peatland. pp. 149-197 in Everglades: The Ecosystem and Its Restoration.
Davis, Steven M. and John C. Ogden (editors). St. Lucie Press. Delray Beach,
Florida. 826 p.
17. Stephens, John C. and Lamar Johnson. 1951. Subsidence of Peat Soils in the
Everglades Region of Florida. United States Department of Agriculture Soil
Conservation Service. 47 p.
18. Stephens, John C. 1956. Subsidence of Organic Soils in the Florida Everglades.
Soil Science Society Proceedings, pp. 77-80.
19. Light, Stephen S. and J. Walter Dineen. 1993. Water Control in the Everglades: A
Historical Perspective, pp. 47-84 in Everglades: The Ecosystem and Its Restoration.
Davis, Steven M. and John C. Ogden (editors). St. Lucie Press. Delray Beach,
Florida. 826 p.
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SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT
20. Davis, John H., Jr. 1943. The Peat Deposits of Florida: Their Occurrence,
Development and Uses. Geological Bulletin No. 30. Florida Geological Survey.
Tallahassee, Florida. 247 pp.
21. McCormick, Paul C., Susan Newman, ShiLi Miao, Ramesh Reddy, Dale Gawlik, Carl
Fitz, Tom Fontaine and Darlene Marley. 1999. Ecological Needs of the Everglades.
Chapter 3 in Everglades Consolidated Report. January 1, 1999. South Florida Water
Management District,
22. South Florida Water Management District. 1999. Everglades Best Management
Practices Program. Water Year 1999: May 1, 1998 through April 30, 1999. 5th
Annual Report,
23. William W. Walker, Jr., and Robert H. Kadlec. 1996. A Model for Simulating
Phosphorus Concentrations in Waters and Soils Downstream of Everglades
Stormwater Treatment Areas. August 16, 1996 draft. 108 p.
OTHER REFERENCES
South Florida Ecosystem Restoration Task Force. 1999. Maintaining the Momentum.
Biennial Report to the U. S. Congress, Florida Legislature, Seminole Tribe of Florida,
and Miccosukee Tribe of Indians of Florida. 24 p.
Stober, Q. J., R. D. Jones and D. J. Scheldt. 1995. Ultra Trace Level Mercury in the
Everglades Ecosystem: A Multimedia Pilot Study. Water, Air and Soil Pollution vol.
80, p. 1269-1278.
Stober, Jerry, Daniel Scheldt, Ron Jones, Kent Thornton, Robert Ambrose and Danny
France. 1996. South Florida Ecosystem Assessment: Monitoring for Ecosystem
Restoration. Interim Report. EPA 904-R-96-008. USEPA Region 4 Science and
Ecosystem Support Division and Office of Research and Development. Athens,
Georgia. 26 p.
Stober, Jerry, Daniel Scheldt, Ron Jones, Kent Thornton, Lisa Gandy, Don Stevens,
Joel Trexler and Steve Rathbun. 1998. South Florida Ecosystem Assessment:
Monitoring for Ecosystem Restoration. Final Technical Report - Phase I. EPA 904-R-
98-002. USEPA Region 4 Science and Ecosystem Support Division and Office of
Research and Development. Athens, Georgia. 285 p. plus appendices.
PHOTOGRAPHIC ACKNOWLEDGEMENTS
Table of contents water control structure and Figure 8: South Florida Water
Management District; Figure 3: Everglades National Park; All other photographs:
Daniel Scheldt.
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