EPA
United States
Environmental
Protection Agency
Region 4 Science & Ecosystem
Support Division, Water Manage-
ment Division and Office of
Research and Development
EPA 904-R-01-002
September 2001
South Florida Ecosystem Assessment:
Phase l/ll (Summary) -
Everglades Stressor Interactions:
Hydropatterns, Eutrophication, Habitat
Alteration, and Mercury Contamination
Monitoring for Adaptive Management:
Implications for Ecosystem Restoration
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South Florida Ecosystem Assessment Project
The South Florida Ecosystem Assessment Project is being conducted by the United States
Environmental Protection Agency Region 4 in partnership with the Florida International Univer-
sity Southeast Environmental Research Center, FTN Associates Ltd., and Battelle Marine Sci-
ences 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 Environmental 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.
L'1SH& WlLlJMI
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South Florida Ecosystem Assessment Project
EPA904-R-01-002
September 2001
SOUTH FLORIDA
ECOSYSTEM ASSESSMENT:
Phase l/ll - Everglades Stressor Interactions:
Hydropatterns, Eutrophication, Habitat
Alteration, and Mercury Contamination
(Summary)
by
Q. J. Stober1, K. Thornton2, R. Jones3, J. Richards4,
C. Ivey3, R. Welch5, M. Madden5, J. Trexler4, E. Gaiser3,
D. Scheldt6 and S. Rathbun7
1Project Manager, U.S. Environmental Protection Agency, Region 4, Science and
Ecosystem Support Division, Athens, GA; 2FTN Associates, Ltd., Little Rock, AR;
3Florida International University, Southeast Environmental Research Center, Miami, FL;
4Florida International University, Department of Biological Sciences, Miami, FL; Univer-
sity of Georgia, Department of Geography, Center for Remote Sensing and Mapping
Science (CRMS), Athens, GA; 6U.S. Environmental Protection Agency, Region 4, Water
Management Division, South Florida Office, West Palm Beach, FL; 7University of Geor-
gia, Department of Statistics, Athens, GA
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South Florida Ecosystem Assessment Project
ACKNOWLEDGEMENTS
Participants in USEPA Region 4
Everglades Assessment Project
USEPA Region 4
Program Offices
APTMD
J. Ackerman
L. Anderson-Carnahan
D. Dubose
L. Page
ORC
P. Mancusi-Ungaro
SESD
A. Auwarter
G. Bennett
B. Berrang
M. Birch
J. Bricker
G. Collins
D. Colquitt
J. Davee
C. Halbrook
R. Howes
P. Kalla
D. Kamens
B. Lewis
P. Mann
W. McDaniel
P. Meyer
D. Norris
M. Parsons
B. Noakes
B. Pruitt
J. Scifres
S. Sims
T. Slagle
T. Stiber
D. Smith
M. Wasko
WMD
M. Flexner
H. Johnson
J. Negron
D. Powell
E. Sommerville
USEPA - Office of Research
and Development
NHEERL
K. Summers
T. Olsen
NERL-RTP
R. Linthurst
J. Messer
R. Stevens
R. Bullock
J. Pinto
NERL-ATHENS
R. Araujo
C. Barber
L. Burns
N. Loux
Florida International
University-SERC
A. Alii
M. Bascoy
N. Black
Y. Cai
D. Diaz
A. Edwards
C. Ivey
R. Jaffe
A. Jelensky
W. Loftus
J. Lopez
P. Lorenzo
I. MacFarlane
L. Scinto
R. Taylor
J. Thomas
C. Ugarte
University of Georgia
S. Rathbun
A. Homsey
University of Florida
P. Frederick
Florida Department of
Environmental Protection
T. Atkeson
Florida Fish & Wildlife
Conservation Commission
T. Lange
South Florida Water
Management District
L.Fink
D. Rumbold
Contractors
J. Maudsley, Mantech
B. Heinish, Mantech
L. Dorn, Mantech
M. Weirich,Mantech
D. Stevens, Mantech
S. Ponder, ILS
B. Simpson, ILS
K. Simmons, ILS
S. Pilcher, ILS
J. Benton, FTN Assoc, Ltd.
B. Frank, FTN Assoc, Ltd.
L. Gandy, FTN Assoc, Ltd.
C. Laurin, FTN Assoc, Ltd.
L. Lewis, FTN Assoc, Ltd.
D. Lincicome, FTN Assoc, Ltd.
J. Malcolm, FTN Assoc, Ltd.
S. Phillips, FTN Assoc, Ltd.
M. Ruppel, FTN Assoc, Ltd.
N. Siria, FTN Assoc, Ltd.
K. Thornton, FTN Assoc., Ltd.
E. Crecelius, Battelle Marine
Sciences
B. Lasorsa, Battelle Marine Sciences
Funding for this Regional Environ-
mental Monitoring & Assessment
(REMAP) Project 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,
National Park Service.
IV
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United States
Environmental
Protection Agency
Region 4 Science & Ecosystem
Support Division and Water
Management Division
Office of Research and Development
South Florida Ecosystem Assessment Report
EXECUTIVE SUMMARY
South Florida Ecosystem Assessment
What Did We Learn?
Things Are Changing; But The Issues Are The Same!
What does this mean?
Over the past 8 years, the US Environmental Protection Agency (EPA) Region 4 has been
conducting an ecosystem assessment of the South Florida Everglades ecosystem in
conjunction with the Florida Department of Environmental Protection, US Geological
Survey, South Florida Water Management District, Florida International University, other
universities, and the private sector. Over this time period, there has been a significant
decrease in nutrient concentrations and mercury contamination throughout the ecosystem.
Change, however, is not a trend. Continued monitoring will be required to determine if these
concentrations continue to decrease through time. What was clear at the beginning of the
study, and is still clear, is the need for integrated management of the ecosystem.
Hydropattern modifications, nutrient loadings and
eutrophication, habitat alteration, and mercury
contamination are all interrelated. These problems
cannot be managed independently!
EPA Region 4 initiated the South Florida Ecosystem
Assessment Project in 1993. The Project used a
statistical survey design to sample the South Florida
ecosystem from Lake Okeechobee in the north to
Florida Bay in the south, from the Miami urban area
on the east to Big Cypress on the west (Figure 1).
Wthin this 2.5 million acre area, a variety of
measurements were made on samples taken from
water, soil, sediment, plants (both the algae and the
standing plants like sawgrass and cattails), floe
(organic debris on the soil) and mosquitofish. These
samples were taken in canals (1993-1995) and
throughout the marsh (1995-1996,1999) in both wet
(rainy) and dry seasons. Because the marsh was
sampled in 1995-96 and again in 1999, it was
possible to detect changes that had occurred in
some marsh constituents during this period. The
South Florida Ecosystem Assessment has been an
innovative research, monitoring, and assessment Figure 1. uses satellite image of south Florida:
Project that has produced a number Of Significant light areas on the east indicate urban areas; dark
1 ' - areas in the center are the remnant Everglades; the
findings With management implications. red area at the top is the Everglades Agricultural
Area and the western part of the image is Big
Cypress National Preserve.
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South Florida EocBystanAssessrrent Report
FINDINGS
Some of the significant findings from the Project are that:
Hydropattern modifications and the water requirements
to cover different marsh areas can be estimated with
a simple surface area-volume relationship. Long and
short hydropattern areas can also be determined us-
ing this relationship. The plant species distributions
observed in the study reinforced and supported these
hydropatterns. Water changes from dry to completely
flooded are necessary to sustain a pulsed ecosystem
like the Everglades.
There are significant north to south gradients, from
Lake Okeechobee to Florida Bay, in total phosphorus,
total organic carbon, and sulfate (Figure 2) in the eco-
system. These gradients affect eutrophication and mer-
cury contamination throughout the Everglades. These
gradients also are affected by hydropattern modifica-
tions. These factors are all interrelated.
SURFACE WATER
SULFATE
SEPTEMBER 1995-1996
Figure 2. Under the right conditions,
sulfate can stimulate sulfate-reducing
bacteria to convert inorganic mercury to the
toxic organic form of mercury. Note the
strong north to south gradients in sulfate
concentrations during a wet season.
1 2D.O-
I
Cluster Data
1999
D
Spikerush Cluste
LONGITUDE, de
.al degn
Figure 3. Spikerush community distributions
showing areas of the marsh with low total
phosphorus concentrations in soil and
intermediate to long hydroperiod. Spikerush
distributions might be good indicators for
assessing the success of restoration.
Total phosphorus (nutrient) concentrations were
significantly lower throughout the marsh in 1999
compared to 1995-96. Continued monitoring will
be needed to determine if this change represents
a decreasing trend in total phosphorus concen-
trations.
The distribution of different aquatic plant species
(i.e., macrophytes) throughout the marsh provide
good indicators of:
hydropattern - water lily (Nymphaea odorata)/
purple bladderwort (Utricularia purpurea) indicate
stable waterslough habitat (i.e., long hydroperiod).
low soil phosphorus - spikerush (Eleocharis
cellulosa) (Figure 3) is found in soils with low phos-
phorus concentrations and intermediate to long
hydroperiod.
high soil phosphorus - cattail (Typha
domingensis) is found in soils with high phos-
phorus concentrations.
VI
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South Florida Ecosystan Assessment Report
In addition, the change in some plant
characteristics also were associated with
variations in soil phosphorus
concentrations. Broad leaves and short
petioles in arrowhead (Sagittaria lancifolia)
were associated with high soil phosphorus
concentrations. Narrow leaves and long
petioles in arrowhead were associated
with low soil phosphorus concentrations.
There is a "hot spot" of mercury contamina-
tion in mosquitofish located in the southwest-
ern part of Water Conservation Area 3 be-
low Alligator Alley (Figure 4). The area north
of Alligator Alley has high methylmercury
concentrations in the water and soil, but low
mercury concentrations in the mosquitofish.
The area south of Tamiami Trail in Ever-
glades National Park has low methylmercury
concentrations in the water and soil, but rela-
tively high mercury concentrations in the
mosquitofish.
.i 26.0-
LU
Q
ALL CYCLES, 1995 &1996
Hg in Chick
Feathers (ppm)
A 9.40 to 10.50
10.50 to 20.00
20.00to 55.71
-01.0 Jin.B -Bn.fi -8D.4
LONGITUDE, decimal degrees
Mercury concentrations in the water and in Figure 4. The hot spot is the same for total mercury in
mOSquitOfiSh Were Significantly lOWer both mosquitofish and great egret chick feathers.
. . . . . _ _ _ . Largemouth bass and algae mercury concentrations are
throughout the marsh in 1999 compared to aiso high in this hot spot.
1995-96 (Table 1). Water and mosquitofish
mercury concentrations corresponded with
changes in atmospheric wet deposition.
Both top-down and bottom-up controls in the ecosystem explain the observed effects of
nutrient loading, and mercury contamination. High chemical (nutrient, TOC, SO4, S2~)
concentrations exert a bottom-up control on ecosystem responses in the northern area.
Biological interactions exert a top-down control on ecosystem responses in the low
nutrient southern area. The mercury "hot spot" is in the transition zone between these
two areas where both bottom-up and top-down interactions occur.
Table 1. Change in total mercury mass (kg) in different media from 1995 to 1999 over the study area. Merci
contamination appears to be decreasing in the ecosystem during the wet season.
Media 1995 1996 199J
Atmospheric Wet Deposition 153 116 14
Water 6.0 4.7 3.£
Mosquitofish 0.64 0.41 0.3J
VII
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South Florida EocBystanAssessrrent Report
A reasonable question to ask, given these findings, is "So What?" Why are these findings
important and what are the implications for management?
MANAGEMENT IMPLICATIONS
Wetlands, by definition, are water driven systems and the water regime drives all
other interactions in the wetland. Modifying the water regime will affect everything
else in the Everglades ecosystem. Fluctuating water levels are an integral part of the
pulsed Everglades ecosystem. These fluctuations need to be maintained and man-
aged.
Distributions of plant species, such as water lily, spikerush, and cattail, and plant char-
acteristics, such as arrowhead leaf widths, are cost effective indicators for assessing
the success of the restoration effort because they reflect hydropattern modifications
and changes in soil phosphorus concentrations.
Mosquitofish are good indicators for assessing change in mercury contamination be-
cause they are found throughout the marsh, have a short life span, and respond
quickly to changes in mercury concentrations. The change in atmospheric deposition
might correspond with decreased mercury emissions, but it also relates to less rainfall
in 1996 and 1999 compared to 1995.
Restoration efforts related to managing the water regime, controlling nutrient loading,
minimizing habitat alteration, and reducing mercury contamination must proceed to-
gether. These factors are all interrelated and must not be managed independently.
Consistent, long-term monitoring is the only way of evaluating the success of the
restoration effort. It appears the nutrient management practices and mercury emis-
sion reductions have contributed to a decrease in phosphorus concentrations and
mercury contamination. However, only continued monitoring will tell if these changes
represent a real decreasing sustainable trend and whether management practices
are influencing the trend. Statistical survey monitoring networks complement on-go-
ing monitoring programs and should be integrated into the Comprehensive Everglades
Restoration Plan.
FOR MORE INFORMATION, PLEASE CONTACT
Dr. Jerry Stober
US EPA Region 4 SESD
980 College Station Road
Athens, GA 30605-2700
(706) 355-8705
Additional reports and information can be obtained by visiting
the Region 4 Website at www.epa.gov
VIM
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South Florida Ecosystem Assessment Project
CONTENTS
US EPA REGION 4
SOUTH FLORIDA ECOSYSTEM ASSESSMENT
EXECUTIVE SUMMARY v
INTRODUCTION 1
South Florida Everglades 2
A Troubled River 2
Issues 3
US EPA REGION 4 SOUTH FLORIDA ECOSYSTEM ASSESSMENT PROJECT 6
HIGHLIGHTS 10
Hydropatterns 10
Habitat Alteration 14
Eutrophi cation 17
Mercury Contamination 20
Mercury Patterns 21
Other Water Quality Patterns 23
Causes of Mercury Contamination 27
Mercury Sources 27
Explaining the Environmental Patterns 30
North of Alligator Alley 31
Alligator Alley to Tamiami Trail 33
South of Tamiami Trail 35
Top Down vs Bottom Up 35
Changes in Mercury Contamination 38
Risk Assessment 44
Synthesis 46
POLICY AND MANAGEMENT IMPLICATIONS 47
THE FUTURE 48
REFERENCES 50
LIST OF APPENDICES
APPENDIX A Findings and Management Implications 56
IX
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South Florida Ecosystem Assessment Project
LIST OF ABBREVIATIONS
ac-ft = acre feet
ug/m2 = microgram per meter squared
% OM = percent organic matter
cm = centimeter
ft = foot
km = kilometer
mi = mile
kg/yr = kilogram per year
ppm = parts per million (mg/L)
ppb = parts per billion (ug/L)
ppt = parts per trillion (ng/L)
mg/kg = milligram per kilogram (ppm)
ug/kg = micrograms per kilogram (ppb)
uMol/hr = micromoles per hour
kg = kilogram
m = meter
Hg = mercury
HgO = elemental mercury
Hgll = inorganic mercury
MeHg = methylmercury
ACME = Aquatic Cycling of Mercury in the
Florida Everglades
AFDW = Ash Free Dry Weight
APTMD = Air, Pesticides, and Toxics Manage-
mentDivision
B AF = Bioaccumulation Factor
BMPs = Best Management Practices
CERP = Comprehensive Everglades
Restoration Program
culm = the stem of a grass-like plant
EAA = Everglades Agricultural Area
EMAP = Environmental Monitoring and Assess-
ment Program
ENP = Everglades National Park
FDEP = Florida Department of Environmental
Protection
FIU SERC = Florida International University
Southeastern Environmental Research Center
GIS = Geographic Information System
LOX=Loxahatchee National Wildlife Refuge
NAWQ A = National Water Quality Assessment
Program
NERL - Athens = National Exposure Research
Laboratory - Athens, GA
NHEERL - RTF = National Health and Environ-
mental Exposure Research Laboratory -
Research Triangle Park, NC
NFS = National Park Service
ORC = Office of Regional Counsel
peri=Periphyton
PS = Periphyton(soil)
PU = Periphyton (utricularia)
REMAP = Regional Environmental Monitoring
and Assessment Program
S2 = Sulfide
SESD = Science and Ecosystem Support Divi-
sion
SFWMD = South Florida Water Management
District
SFWMM = South Florida Water Management
Model
SRB = Sulfate Reducing Bacteria
STAs = Stormwater Treatment Areas
TP = Total Phosphorus
US EPA = United States Environmental Protec-
tion Agency
USGS = United States Geological Survey
WCA = Water Conservation Area
WMD = Water Management Division
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South Florida Ecosystem Assessment Report |y\
[tl
INTRODUCTION
The United States Environmental Protection Agency (US EPA) Region 4 South Florida
Ecosystem Assessment Project is an innovative, long-term research, monitoring, and assessment
project. Its ultimate goal is to inject sound scientific information into management decisions on
the Everglades ecosystem and its restoration.
The South Florida Ecosystem Assessment Project has a five-fold purpose:
1) Contribute to the South Florida Everglades Restoration Program by monitoring the condition
and trends in the Everglades ecosystem.
2) Assess the effects and potential risks due to mercury contamination in the South Florida
ecosystem, specifically on fish, wading birds, and other biota, as part of the South Florida
Mercury Science Program.
3) Assess the effects and potential risks from other
environmental stresses such as hydropatt
modification, habitat alteration, phospho
rus loading, and eutrophication on the
Everglades ecosystem (Figure 1).
4) Improve monitoring design and eco-
logical assessments for evaluating the
relative risks of environmental stressors
acting on the Everglades ecosystem.
5) Provide scientifically credible informa- _. ra , M . , ,. ,. , ,. ,.
' \ Figure 1. Numerous environmental issues threaten the South
tion on a regular basis that Contributes to Florida Everglades "River of Grass," including mercury
management decisions on Everglades contamination.
restoration issues.
Working in partnership with Florida International University, Southeast Environmental
Research Center; the State of Florida Department of Environmental Protection; Florida Fish and
Wildlife Conservation Commission; South Florida Water Management District; United States
Geological Survey; United States National Park Service; industry; and other organizations;
United States EPA Region 4 Science and Ecosystem Support Division has been monitoring the
condition of the South Florida ecosystem since 1993.
This is the fifth assessment report on the issues affecting the Everglades ecosystem. This
report expands on the US EPA report series (Stober et al. 1995, Stober et al. 1996, Stober et al.
1998, Scheldt et al. 2000, and Stober et al. 2001). Data are presented for the entire freshwater
Everglades marsh system.
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South Florida Ecosystem Assessment Report
This report summarizes the results of the comprehensive Phase I (1995-96) and Phase II
(1999) marsh sampling efforts which included assessing:
hydropattern modifications in the system and
responses during dry and wet seasons, based
on six sampling events,
plant community responses, including both
periphyton and macrophytes, and habitat al-
terations associated with nutrient loading and
hydropattern changes,
changes in nutrient concentrations in water
and soil over time,
current status of mercury contamination,
identification of mercury sources,
mechanisms controlling mercury contamina-
tion,
biological availability and uptake of meth-
ylmercury through the food chain,
the relative risks from these stressors, and
the management implications and the inter-
actions of these issues.
South Florida Everglades
The Florida Everglades is one of the largest freshwa-
ter marshes in the world. The marsh is a rich mosaic of
sawgrass, wet prairies, sloughs, and tree islands (Fig-
ure 2). 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 Carib-
bean flora created habitat for a variety of fauna, includ-
ing Florida panthers, alligators, and hundreds of thou-
sands of wading birds. The unique and timeless nature
of the Everglades was described by Marjory Stoneman
Douglas (1947) in her classic work, The Everglades:
River of Grass.
A Troubled River
During the last century, however, the "River of
Grass" has become a troubled river. The Everglades
ecosystem has been altered by extensive agricultural
and urban development (Figure 3). Today, 50% of the
historic Everglades wetland has been drained. South
Florida's expanding human population of nearly 6 mil-
lion continues to encroach on this ecosystem's water
and land. This human population is projected to in-
crease to 20 million people in just a little over 20 years.
Figure 2. Numerous environmental issues threaten
the Everglades "River of Grass," such as water
management, soil loss, water quality degradation, and
habitat alteration.
Figure 3. Residential development on former
Everglades wetlands.
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South Florida Ecosystem Assessment Report
Issues
The Everglades changed dramatically
as drainage canals were dug and agricul-
tural and urban development increased in
the 20th century. Most of the remaining
Everglades are in Loxahatchee National
Wildlife Refuge, Everglades National
Park, or the Water Conservation Areas
(WCAs) (Figure 4). Today, Everglades
National Park includes only one-fifth of
the original river of grass that once
spread over more than 2 million acres.
One-fourth of the historic Everglades is
now in agricultural production within the
1,000-square-mile Everglades Agricul-
tural Area (EAA) (Figure 4), where sugar
cane and vegetables are grown on fertile
peat soils. Big Cypress National Preserve
protects forested swamp resources within
the Everglades watershed (Figure 4).
Although half of the 16,000-square-mile
Everglades watershed is in public owner-
ship, there are a number of environmen-
tal issues that must be resolved to restore
and protect the Everglades ecosystem,
Figure 5. Eutrophication promotes cattail
expansion. Cattails are an invasive species.
Figure 4. USGS satellite image of South Florida: light areas on
the east indicate urban areas; dark areas in the center are the
remnant Everglades; the red area at the top is the Everglades
Agricultural Area and the western part of the image is Big Cypress
National Preserve.
including eutrophication
(Figure 5); mercury
contamination of
gamefish, wading
birds, the endan-
gered Florida
panther (Figure 6),
and other top
predators; habitat
alteration and loss;
hydropattern
modification' Figure 6. A Florida panther, which is an
endangered species, might have died from
water Supply mercury toxicity in 1989.
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South Florida Ecosystem Assessment Report
conflicts; protection of endangered species; and introduction and spread of nuisance exotic
species (McPherson et al., 2000). Many of these problems were discussed in previous EPA
Region 4 publications, South Florida Ecosystem Assessment: Interim Report (Stober et al. 1996)
and South Florida Ecosystem Assessment: Phase I Final Technical Report (Stober et al. 1998,
2 volumes), South Florida
Ecosystem Assessment: Ever-
glades Water Management,
Soil Loss, Eutrophication and
Habitat (Scheldt et al. 2000)
and South Florida Ecosystem
Assessment: Phase I/II
Everglades Hydropattern,
Eutrophication, Habitat and
Mercury Contamination Final
Technical Report (Stober et al.
2001, 2 volumes), of which
this report is a summary.
These problems are interre-
lated. In fact, the problems
may have been aggravated
because each problem was
managed independently.
Figure 7. Historic flow pattern (left) and present flow patterns (right) through the
South Florida system. Water movement is highly managed through the canals and
water control structures.
HYDROPATTERNS
Clearly, the greatest change that occurred in the Everglades ecosystem was "draining the
swamp"; changing the natural hydropattern, or the depth, timing and distribution of surface water
(Figure 7). Wetland systems, by definition, are driven by water. Canal drainage systems, levees,
flood control structures, and water supply diversions have collectively contributed to large-scale
changes in the Everglades ecosystem. The US Army Corps of Engineers and the South Florida
Water Management District in their comprehensive review study of the Central and Southern
Florida Project (1999) are evaluating the modification of canals and levees to return the hydro-
pattern to a more natural regime. Determining
the natural flow regime and hydropattern and
subsequently implementing the required flows in
the Everglades is a major restoration activity.
Hydropattern modification represents one of the
greatest issues facing the Everglades ecosystem.
HABITAT ALTERATION
Over 1 million acres of the original "River of
Grass" have been drained and altered for other
uses since the turn of the 20th century (Figure 8).
In addition to the habitat lost, much of the re-
maining habitat has been altered because of
unnatural flooding and drying, ground water
Figure 8. Extensive canal systems and water manage-
ment have modified the natural hydropattern.
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South Florida Ecosystem Assessment Report
removal, or similar perturbations. This habitat alteration is still ongoing as the population of
South Florida continues to expand. Unlike eutrophication and mercury contamination, habitat
loss is irreversible with certain land uses. In addition, habitat alteration aggravates other environ-
mental problems, and these interactions are poorly understood.
EUTROPHICATION
Nutrient loading from the Everglades Agricultural Area and urban areas has significantly
increased nutrient concentrations, particularly phosphorus, in the downstream Water Conserva-
tion Areas and the Everglades National Park. This has resulted in major eutrophic impacts on
these wetland systems (Figure 5). Among the progressive Everglades eutrophic impacts are
increased water and soil phosphorus content, changed periphyton communities, increased mass
of oxygen-demanding organic matter, loss of dissolved oxygen in water, loss of native sawgrass
plant communities, loss of important wading bird foraging habitat, and conversion of wet prairie
plant communities to cattails. These collective changes are systemic and impact the structure and
function of the aquatic system. The Florida Department of Environmental Protection (FDEP) has
concluded that eutrophi cation of the Everglades results in the violation of four Florida water
quality standards to protect fish and wildlife and creates an imbalance in the natural population
of aquatic flora and fauna, with a resulting loss in biological integrity. Some eutrophic impacts,
such as periphyton community changes, are thought to be short-term (day-months) and reversible
if nutrient additions can be significantly decreased. Other impacts are considered longer-term
(years-decades), such as loading peat soil with excess phosphorus that triggers the loss of native
plant communities and foraging habitat. There are still many marsh areas where natural water
phosphorus concentrations are less than 10 parts per billion (ppb). A combination of agricultural
best management practices and construction of over 47,000 acres of wetlands (Stormwater
Treatment Areas) are being implemented in an attempt to control phosphorus loadings. The
effectiveness of these controls in reducing nutrient concentrations to near historic levels, how-
ever, is not yet known.
MERCURY CONTAMINATION
One of the more insidious problems facing the Everglades is mercury
contamination. Over 2 million acres in South Florida are under fish
consumption advisories or bans because of mercury contamination in
top predator fish such as largemouth bass, bowfm, and oscar. These
fish consumption advisories are for human consumption offish. The
human population can change its eating preferences and choose other
species offish or other food to eat. Unfortunately, fish and wildlife
that have a diet of mercury contaminated fish do not change their diets
because offish consumption advisories. Mercury concentrations in an
endangered Florida panther within Everglades National Park were high
enough to either have killed or contributed to its death in 1989. Wading
bird populations are about one-fifth of their abundance in the 1930s.
Wading bird (Figure 9) mercury concentrations in certain Everglades
areas in the early 1990s were at or above levels generally considered
to be toxic. Mercury contamination might have been a factor in their
decline.
Figure 9. Everglades
wading bird populations
significantly declined during
the 1900s.
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South Florida Ecosystem Assessment Report
Many of the other ecological issues in South Floridanutrient loading, hydropattern modifi-
cation (Figure 8), habitat alterationcontribute to the mercury problem, and all these issues are
embedded in the South Florida Ecosystem Restoration effort. This report discusses the mercury
contamination problem in South Florida in relation to these other issues. Specifically, the discus-
sion focuses on
Where and why the mercury problem exists,
Mercury sources to the Everglades ecosystem,
Changes in mercury contamination levels over time,
Mercury uptake through the food web, and
Management implications of mercury contamination in South Florida.
INTERACTIONS AMONG ISSUES
None of the issues discussed previously are independent of the others. They are all inter-
twined, each problem affecting the others. Addressing these issues requires a large-scale perspec-
tive. Integrated and holistic studies of the multiple issues impacting the Everglades need to
compare the risks associated with all impacts and their interactions. The US EPA South Florida
Ecosystem Assessment effort is a project that provides a foundation for addressing these issues
and contributes to the Comprehensive Everglades Restoration Plan (CERP, or the Plan).
ECOSYSTEM RESTORATION
Among the federal and state Everglades restoration efforts in progress are the EAA phospho-
rus control program and projects to restore water delivery (and ecology) throughout the Ever-
glades. The present US EPA South Florida Ecosystem Assessment effort evaluates the integral
impacts of several important restoration issues and provides a critical, science-based foundation
for future ecosystem assessment and restoration design. Long-term monitoring will provide
critical baseline information to evaluate the progress of ecosystem restoration. More importantly,
continued monitoring is the only way to evaluate the effectiveness of management strategies
undertaken to improve ecological conditions.
US EPA REGION 4 SOUTH FLORIDA
ECOSYSTEM ASSESSMENT PROJECT
The Region 4 South Florida Ecosystem Assessment Project uses the US EPA (1998) ecologi-
cal risk assessment framework as a foundation for injecting scientifically sound information into
the decision-making process (Figure 10). The mercury contamination issue is guided by seven
policy-relevant questions.
1. What is the magnitude of the problem?
2. What is the extent of the problem?
3. Is it getting better, worse, or staying the same over time?
4. What is causing the problem?
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South Florida Ecosystem Assessment Report
Ecological Risk Assessment
PROBLEM FORMULATION
A
n
a
1
y
s
i
s
Characterization of
._ ^ w Ecological
Exposure ^ w- a
K Effects
*
RISKC
***
H
ARACTERIZ
v*
A"
f
noN
Figure 10. Ecological Risk Assessment Framework. Ecological
risk assessment is a way of determining the likelihood of adverse
ecological effects from a pollutant such as mercury.
5. What are the sources of the problem?
6. What is the risk to the ecological resources?
7. What can we do about it?
These seven questions are equally applicable for all the
environmental problems in the Everglades. These problems
include eutrophication, hydropattern modification, habitat
alteration, mercury contamination and exotic species intro-
ductions.
To begin answering these seven questions, the Region 4
project used a statistical, probability-based sampling (see
sidebar) strategy to select sites for sampling. A key advantage
of probability-based sampling 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 re-
sources (Thornton et al. 1994, Stevens 1997). Also, indicators
of pollutant exposure and habitat condition can be used to
identify associations between human-induced stressors and
ecological condition. This design has been reviewed by the
National Academy of Sciences, and the US EPA has applied it
to lakes, rivers, streams, wetlands, estuaries, forests, arid
ecosystems, and agro-ecosystems throughout the United
States (Olsen et al. 1999, US EPA 1995).
Probability Samples:
Foundation For Regional
Risk Assessment
Probability samples are
samples where every member
of the statistical population has
a known chance of being
selected and where the samples
are drawn at random. The
project used a statistical survey
design in selecting its probability
samples so that the samples
were drawn in direct propor-
tion to their occurrence in the
population, whether it was EAA
or WCA canals, sawgrassor
cattail marshes, or soil type.
Consequently, the measure-
ments can be used to estimate
the proportion (extent) and
condition of that resource in
South Florida. As important,
each site is selected so it
represents that resource in an
unbiased manner. 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 was easier,
or selecting a canal because it
looked good or bad). The risk
to any of the ecological re-
sources from the multiple
environmental threats in South
Florida is a direct function of
the extent and magnitude of
both the threat and the ecologi-
cal effects. Probability samples
permit us to estimate both
magnitude and extent of
problems for the entire marsh
and canal ecosystems. Probabil-
ity samples, therefore, provide
the foundation for ecological
risk assessment in South
Florida.
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South Florida Ecosystem Assessment Report
Samples were collected from south of Lake Okeechobee to the mangrove fringe on Florida
Bay and from the ridge along the urban, eastern coast into Big Cypress National Preserve on the
west. The distribution of 200 canal stations is shown in Figure 11 while the distribution of
750 marsh stations is shown in Figure 12. The stations represent the ecological condition in over
750 miles of canals and over 3,000 square miles of marsh. Canals were sampled in September
1993 and 1994, and May 1994 and 1995. Some of these results have been reported in previous
documents. Marshes were sampled in April 1995, May 1996 and 1999, and September 1995,
1996 and 1999. This corresponds to three dry (April and May) and three wet (September) seasons
for the marsh system over a five-year period. Big Cypress National Preserve was not sampled in
1999 in order to place all the effort on the central flow-way of the Everglades marsh, which is the
focus of this report. The sample collection included surface water (Figure 13), marsh soil (Fig-
ure 14), fish (Figure 15), and algae at each site during each sampling period. Porewater, floe,
periphyton species composition, sawgrass and cattail tissue, macrophyte species, and plant
community composition from ground sampling and aerial photo interpretation for each site were
added in 1999. The comprehensive multimedia design of this project included over 60 laboratory
analytical procedures. In addition to the canal and marsh sampling, mercury was also sampled
biweekly at 7 canal flow control structures to estimate mercury loading from runoff into the
Everglades during a 3-year period from 1994-96.
26.6-
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in
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D
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STATION LOCATIONS
0 4. * +
.****: *, . J.?i
;- ..- v. **- *
* : ** :Vi
LOX
WCA2
WCA3-N
WCA3-SW
WCA3-SE
SHARK
TAYLOR
-81.0 -80S -80.6 -80.4
LONGITUDE, decimal degrees
Figure 11. 200 sampling sites are
located on over 750 canal miles.
Figure 12. 750 sampling sites are located in over
2 million marsh acres.
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South Florida Ecosystem Assessment Report
J-
Figure 13. Helicopters and air boats were used
for sampling the marsh.
Figure 14. Soil cores were collected at
each of the marsh sites and analyzed for
mercury, nutrients, and other constituents.
This study permits a synoptic look at the ecological
condition in all of the freshwater Everglades marsh and
most of the freshwater canal system in South Florida
from Lake Okeechobee to the mangrove system. This
large-scale perspective is critical in predicting the
impacts of different factors, such as mercury and
phosphorus 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 South Florida can give
a distorted perspective. The statistical sampling ap-
proach permits quantitative estimates, with known
confidence, about population characteristics, such as
acres of marsh in cattails, percent of the marsh with
fish mercury concentrations greater than a proposed
predator protection level, or percent of canal miles with
total phosphorus concentrations greater than the initial
control target concentration of 50 ppb.
Parameters measured at each site can be used to
answer questions on multiple issues including
Mercury contamination (e.g., mercury in water, soil,
algae, and fish).
Eutrophication (e.g., total phosphorus concentra-
tions, cattail, other macrophyte species, and per-
iphyton distributions).
Habitat alteration (e.g., plant community distribu-
tion throughout the Everglades).
Hydropattern modification (e.g., water depth at all
sites).
Study information is contributing to decisions not
only on mercury contamination, but also on the other
major problems facing ecosystem restoration in South
Florida.
The study provides information critical to the South
Florida Ecosystem Restoration design and evaluation
of whether its precursor and ecological success criteria
are being achieved (Table 1).
Figure 15. Mosquitofish were sampled
because they are common in both the canals and
the marsh.
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South Florida Ecosystem Assessment Report
Table 1. Example Everglades Ecosystem Restoration success indicators (Science Subgroup, 1997).
Problem Success Indicators
Water Management Reinstate system-wide natural hydropatterns and sheetflow
Habitat Alteration Increased spatial extent of habitat and wildlife corridors
Eutrophi cation Reduced phosphorus loading
Mercury Contamination Reduce top carnivore mercury body burden
Endangered Species Recovery of threatened/endangered species
Soil Loss Restore natural soil formation processes and rates
The next sections assess hydropattern modification, habitat alteration, eutrophication and
mercury contamination based on the sampling program in canals and marshes from 1993 to 1999.
A weight-of-evidence approach was used in this assessment. Not all the information needed to
provide definitive answers for each of the seven policy-relevant questions is known, but provid-
ing information on an interim basis and incrementally increasing our knowledge permits this
information to be used in upcoming and future decisions concerning Everglades restoration.
For the sake of clarity in understanding the interaction of these issues, this report describes
the ecosystem by dividing the central north to south flow-way into seven subareas. These subar-
eas (Figure 4) are from north to south: The Arthur R. Marshall Loxahatchee National Wildlife
Refuge or Water Conservation Area 1 (WCA1 or Lox); Everglades Water Conservation Area 2
(WCA2); Everglades Water Conservation Area 3 north of Alligator Alley (WCA3-N); Everglades
Water Conservation Area 3 Southeast of Alligator Alley (WCA3-SE); Everglades Water Conser-
vation Area 3 Southwest of Alligator Alley (WCA3-SW); WCA3-SE and WCA3-SW indicate an
east- west gradient in the central part of this system; Everglades National Park south of Tamiami
Trail is divided into Shark River Slough (SRS) and Taylor Slough (TS) by striking a line from
northeast to southwest along the leading edge of a low geological ridge of cap rock in the system.
The interaction of the issues among these seven subareas is the substance of this report.
HIGHLIGHTS
Hydropatterns
The "River of Grass" was so named because the original Everglades was a slowly moving
river, flowing from Lake Okeechobee in the north to Florida Bay in the south. Urban expansion
on the east and the construction of canals and levees to store and drain water have significantly
altered the natural hydrologic regime of the Everglades. The original Everglades, however, was
not always inundated. Understanding the hydrometeorology patterns is important to understand-
ing nutrient and mercury loading and transport in the system. The term hydropattern refers to the
depth, duration of flooding, timing, and distribution of freshwater flows. It includes the concept
of hydroperiod, which is the amount of time each year that the ground is covered with water, as
well as the spatial distribution of water.
10
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South Florida Ecosystem Assessment Report
There are distinct seasonal patterns of
precipitation and inundation in the sub-
tropical Everglades. Precipitation follows a
cyclic pattern with May-October being the
rainy wet season and November-April being
the dry season (Figure 16). This pattern is
opposite that in most temperate areas where
the wet seasons are during the winter and the
dry seasons are during the summer. The
sampling events in this study were near the
end of the dry (April, May) season and the
wet (September) season. Stormwater dis-
charge patterns lag the rainfall, but also
indicate the seasonal swing from wet to dry
periods (Figure 17). Even though the hydrol-
ogy of the Everglades is highly managed, there
are still characteristic hydropatterns that follow
the precipitation patterns.
Water depth, and the wet-dry areas of the
Everglades, vary significantly throughout the
year and among years. Geographically distrib-
uted probability samples of water depth taken
during each systematic survey found surface
water coverage ranged from 44% to 100% of
the 5,500 km2 area of Everglades marsh (Fig-
ure 18). Spatial plots of these data for each
cycle illustrate a progression of surface water
volume increasing from May 1999 <
May 1996 < April 1995 < September
1996 < September 1999 < September
1995 which was a record wet season
(Figure 19). Long-term, period of
record, mean monthly marsh water
depths measured at four fixed loca-
tions indicate the same seasonal
fluctuations, with minimum water
levels in April-May and maximum
water levels generally in October-
November similar to those measured
during the 1995, 1996, and 1999
sampling years (Figure 20). During
100
1993
1994
1995 1996 1997
1988
1999
Figure 16. Monthly rainfall (inches) from 1993 to 1999 at
pumping station S-8. Months when samples were collected are
indicated by a dot.
500
Figure 17. Monthly discharge at S-8, a pumping station
that provides flood control for part of the EAA by discharging
into the Everglades. Discharge varies from zero to several
thousand cfs in response to rain events.
Marsh Water Depth
All Cycles
ro
0)
20
0.8 1.0 1.2
Depth, m
Figure 18. Cumulative distributions of water depths during sampling.
W = wet season, D = dry season, No = Year.
11
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South Florida Ecosystem Assessment Report
WATER DEPTHS
SEPTEMBER 1995
CYCLE 1
APRIL 1995
CYCLE 0
SEPTEMBER 1996/ XX
CYCLE 3 i
MAY 1996
CYCLE 2
MAY 1999
CYCLE 4
SEPTEMBER 1999
CYCLE 5
25.4-
Depth (meters)
>0.90
0.60
0.30
0.15
0.03
0.00
DRY
-81.0 -80.8 -80.6 -80.4 -81.0 -80.8 -80.6 -80.4
LONGITUDE, decimal degrees
12
Figure 19. Water depth in the marsh system during the six sampling events. Colored squares
indicate the location of water depth gauges used for Figure 20.
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South Florida Ecosystem Assessment Report
April 1999, maj or areas in the northern part of
the system (e.g., WCA-3N) became dry enough
that wildfires occurred, burning much of this area.
Wildfires are a natural phenomenon in the Ever-
glades during drought years.
Because the sampling design was based on
a systematic, probability sample, there was a
relatively uniform distribution of sites
throughout the system. Surface contouring
with spatial statistical software such as
SURFER (Golden Software 1999) or
ARCVIEW (1996) is compatible with a
systematic distribution of points. In addition,
the probability samples permit estimates of the surface area associated with each sampling site.
Therefore, it is possible to use the measurements taken at sites to characterize conditions, includ-
ing water depth, for the entire 5500 km2 area. Using the mean depth computed for the areas
inundated during the dry seasons in 1995 - 1999 and the wet season in September 1996, it was
possible to estimate the volume of water that was on the marsh at these times because volume is
equal to the mean depth multiplied by surface area.
Figure 20. Average monthly water depths measured at
gages 3A-NE, 3A-4, 3A-28, and P-33. Dots indicate the water
depths at the sampling times in 1995, 1996, and 1999.
386,1
3i
772.2
Area (mi2)
1158.3 1544.4
1930.5
05
2
I I I
m3 = 1,69@8 * exp(0.00052*(sq km))
ac-fl = 1.37e5 * exp(0.0013*(sq mi))
(# = 0.994
2316.6
2.43
1.62
Examination of stage duration curves for gages located in southern WCA3 and northern Shark
Slough indicated about 5 inches of water were ponded behind (i.e., north of) Tamiami Trail during the
1999 dry season. A surface water volume to surface area curve for the ecosystem was developed
(Figure 21) using Geographic Information
System (GIS) techniques for the four driest
sampling cycles. The lowest point on the
curve is an estimate of the loss of ponding in
the system and was determined by subtract-
ing 5 inches from the dry 1999 water levels.
The curve illustrates the very large surface
area to volume ratio characteristic of this
ecosystem. It also indicates that the
5,500 km2 ecosystem becomes completely
inundated with a surface water volume of
about 2.9 x 109 m3. Under extreme drought
conditions, such as May 1999, the surface
water volume in the marsh declined to about
0.5 x 109 m3. Elimination of ponding in the
system would result in an additional dry area
of about 400 km2 of present slough habitat.
The long and intermediate hydropattern area
of the marsh occupies about 4200 km2 with
an associated water volume of 1.5 x 109 m3.
0
1000 2000
0.81
0.00
5000
6000
3000 4000
Area (km2)
Figure 21. The surface area to volume curve, in both English & metric
units, shows how much water (volume) is presently needed to flood given
areas of the marsh ecosystem. The area of long hydroperiod marsh is
left of the vertical dashed line.
13
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South Florida Ecosystem Assessment Report
To inundate the additional 1,300 km2 of marsh required an equivalent volume of water even though the
surface area is only about one-third of the longer hydropattern marsh.
Water management to sustain ecological resources will require substantial quantities of water
to maintain even minimum habitat coverage during the dry seasons. The short hydropattern
portion of the marsh beyond 4,200 km2 will most likely remain dependent on the wet season
rainfall. Due to the present system of levees and canals, ponding in the system occurs primarily
in WCA3-SW and WCA3-SE with smaller areas along the southern reaches of Loxahatchee and
WCA2 (Figure 22). The surface areas of inundation illustrated show the area without ponding
< dry 1999 water level <4,200 km2< remaining 1,300 km2 describing the long, intermediate,
short and extremely short hydropatterns, respectively (Figure 22). Drought prone areas are the
northern tip of Loxahatchee, WCA3-N and Taylor Slough (See Figure 19, Cycle 4 dry areas). A
loss of peat soils occurred in WCA3-N (Davis, 1946, Stober et al. 1998, Scheldt et al. 2000). Water
management to establish minimum surface flow in extremely short hydroperiod marshes like WC A3 -N
will be a considerable challenge. Alternatively, maintenance of ponded slough habitat during drought
conditions is critical because the most stable aquatic habitats with a rich flora and fauna occur in these
areas. Odum (1971) cites the Everglades as a "fluctuating water ecosystem" or pulsed ecosystem where
recurrent drought maintains the system in an early successional stage. He stresses the importance of the
seasonal change in water level in maintaining
the natural system.
This study provided a synoptic look at
the water regime over the entire system
during both dry and wet seasons. It spans
the range of hydrologic conditions that
typically occur in the system and provides
a sound baseline for evaluating desired
future changes in hydropattern during
restoration. It also provided a general
surface area to volume relationship
(Figure 21) that can be used to quickly
evaluate volume requirements for differ-
ent inundation regimes.
Habitat Alteration
One of the greatest human impacts in
South Florida has been to the natural
habitat. Over 50% of the historic Ever-
glades wetlands have been converted to
urban and agricultural uses. The original
habitat was described as a "River of Grass"
because of the vast expanses of sawgrass
communities. One approach for assessing
Everglades Ecosystem
Area of Surface Water Inundation
/\/ Canals
B
Extremely Short Hydropattern 495 mi.
Short Hydropattern 473 mi.:
Intermediate Hydropattern 423 mi.*
Long Hydropattern 746 mi.*
Total Area: 2137 mi.'
WCA3-N
WCA1
WCA2
WCA3-SE
Shark Slough
Taylor Slough
Figure 22. Based on water depths measured during the study,
plant community distributions, and comparisons with SFWMM
output, the area and contours of long to short hydropattern were
estimated with CIS.
14
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South Florida Ecosystem Assessment Report
current habitat condition, then, would be to characterize the existing plant communities. Three macro-
phyte studies were completed during 1999 in the Everglades ecosystem, including an aerial photo
vegetation assessment, a presence/absence macrophyte community census study, and a macrophyte
morphometric/landscape abiotic parameter analysis.
The first study utilized remote sensing and GIS techniques to successfully assess vegetation patterns
over the Everglades ecosystem. Analysis of areal summary statistics for 1994-95 indicated general
trends such as the diminishing coverage of cattail from north to south ranging from 12 to 17% in the
north to 0.4% in the south. It also provided insight into other habitat characteristics. Wet prairie vegeta-
tion was found to cover greater percentages of the WC As than the ENP, while the ENP contained the
highest percentage of sawgrass. Randomly selected 1 km2 plots around each sampling site adequately
represented vegetation cover in the Everglades. The average difference in percent cover for vegetation
types for the 1 km2 samples at 250 probability sites compared to full coverage maps of the marsh was
1.5% in ENP Shark Slough (Welch and Madden 1999) and 0.4% in WCA3-N (Rutchey and Vilchek
1999). This effort established a baseline of conditions existing in 1994/1995 when the photographic
series was made and a quantitative methodology for efficiently monitoring future vegetation patterns and
assessing changes in the Everglades ecosystem over space and time. Capturing this baseline for the
entire ecosystem will be important for comparison with future monitoring efforts because a comparable
systematic baseline prior to this did not exist. It also allowed characterization of the habitat at the
beginning of the 1995 marsh sampling events.
In the second study, a total of 161 taxa were collected during the macrophyte census. One
hundred twenty-eight of these taxa were identified to the species level and eight to the genus
level, for a total of 136 identified taxa from 250 marsh sites. This second study provided a quan-
titative evaluation of marsh macrophyte community types and their distributions across the
Everglades ecosystem. This quantitative evaluation established a baseline against which to
evaluate community change during restoration. Cluster analysis indicated that four major plant
community types were found to occur across the entire ecosystem: sawgrass (Cladium
jamaicense); waterlily (Nymphaea odorata)-purp\Q bladderwort (Utriculariapurpurea);
spikerush (Eleocharis cellulosa); and cattail (Typha domingensis). These communities differ in
their hydroperiod, water depth, soil type and nutrient level requirements. The dominant species
within each community have different tolerances for soil TP
Sawgrass is the only community that occurs across the entire ecosystem (Figure 23); the other
communities are more localized in their distributions. The sawgrass community type is domi-
nated by Cladium jamaicense, with the next most common species present approximately 25% of
the time. Thus, although specialized for survival in an oligotrophic environment, sawgrass is a
generalist in this ecosystem, occurring across a broad range of hydroperiods, soil types, and soil
nutrient levels. A plot of Cladium jamaicense culm densities shows not only the ubiquitous
distribution across the ecosystem but areas around the EAA and in Taylor Slough where densities
are highest in the system (Figure 24).
15
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South Florida Ecosystem Assessment Report
«
£ 2l.t-
Cluster Data
1999
D
Sawgiass Cluslti
a
E 26.0-
1- 25.8-
Sawgrass Culm Density
1999
0
r of Culms
-tut tt.t -11.4
LOKGITUDE. decimal degfin
Figure 23. Sawgrass occurs almost everywhere
throughout the marsh as indicated by its spatial
distribution shown above.
-81.0 -80.8 -80.6 -80.4
LONGITUDE, decimal degrees
Figure 24. Sawgrass culm densities across the
ecosystem.
Although different parts of the ecosystem and different water management subareas share many
plant species, these areas do not have equal representation of the maj or plant communities identified
here. The frequency and abundance of these communities differ across the system, indicating that water
conditions or ecosystem processes, such as nutrient cycling, vary among the subareas. The water lily-
purple bladderwort community (Figure 25) is a very good indicator of stable water slough habitat (i.e.,
long hydroperiod) in this system, along with its associated communities of aquatic invertebrates and
fishes. The distribution of the cattail cluster is also illustrated in Figure 25 where it is largely associated
with WCA2, WC A3 -N, and the undeveloped part of the EAA. The spikerush community is found in
areas of the marsh with low total phosphorus concentrations and intermediate to long hydroperiod
(Figure 26). Some communities, for example beakrush (Rhynchospora tracyi\ which have been noted
to be prominent historically in previous work (Loveless 1959, Gunderson 1994), did not appear as
distinct communities in our analysis. These differences could represent a historical change in community
composition in the ecosystem and/or could be a result of the unbiased quantitative nature of a random
survey.
The third 1999 macrophyte study investigated plant morphological changes in relation to
abiotic spatial changes across the ecosystem. Sagittaria lancifolia (Arrowhead) was found across
a broad range of soil TP and soil organic content in the Everglades. We have shown in a parallel
study that S. lancifolia leaf morphology provides an indication of soil nutrient level and water
depth. Plants with broader laminae and shorter petioles are found in sites with higher nutrients,
while plants with longer petioles are found in deeper sites with lower nutrients. Although sawgrass was
16
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South Florida Ecosystem Assessment Report
Cluster Data
-81. 0 -80.8 -80.6 -80.4
LONGITUDE, decimal degrees
Figure 25. Water lily distributions showing long
hydroperiod areas of the marsh and cattail cluster
distributions associated with high soil phosphorus.
re
E 26.0-
Cluster Data
1999
-81.0 -80.8 -80.6 -80.4
LONGITUDE, decimal degrees
Figure 26. Spikerush community distributions
showing areas of the marsh with low total
phosphorus concentrations in soil and intermediate
to long hydroperiod.
present throughout the Everglades, sawgrass morphology and density varied across the environment,
which correlated with changes in soil type, nutrients, and hydroperiod. Controls on variations in density
and morphology, as well as patchiness, represent areas for future research.
These data, in conjunction with future monitoring, can be used to predict changes in the distribution
of the maj or macrophyte communities as a result of restoration actions that change water depth. It has
also identified potential indicators of low and high phosphorus regimes and long versus short hydropat-
tern areas.
Eutrophication
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 reduced to 50 ppb 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 27) and agricultural Best Management Practices (BMPs). The first
STA (about 10% of the Phase I treatment acreage) began discharging in 1994, and the BMPs were
required to be fully implemented by 1995. Comparing 1999 with 1995-96 baseline phosphorus con-
centrations presents an opportunity to look for early changes in total phosphorus concentrations in water
and soil. McCafferty and Baker (2000) report a 55% reduction in EAA basin phosphorus load for
17
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South Florida Ecosystem Assessment Report
WY2000 and a 3 year trend showing a 48%
reduction as compared to what would have
been expected without BMPs. A clear trend in
phosphorus load reductions has resulted
following implementation of the BMPs.
The median wet season water total phos-
phorus concentrations with associated 95%
confidence intervals are presented by subarea
along the flow path (Figure 28) with the com-
bined 1995-96 data compared with the 1999
data. The 1999 water total phosphorus con-
centrations indicated that all subareas were
about equal to or less than the 1995-96 con-
centrations with a statistically significant de-
crease (confidence limits do not overlap) in
Taylor Slough. A total phosphorus gradient in
water persists in the system with maximum
concentrations occurring in WCA3-N. How-
ever, even in WCA3-N, the medians declined
from 16 to 11.4 ppb over the intervening three
year period. Nutrient loading might have
increased across the northwestern portions of
WCA3-N and WCA3-SW in 1999 (Fig-
ure 29), but decreased in other areas. The high
concentrations of TP in water observed in WCA3-
SE and WCA3-SW during the 1999 dry season
might have been from phosphorus mobilization during
the wildfire, which burned WCA3-N two weeks
prior to sampling. There has been consistent im-
provement in the spatial extent of wet season TP
concentrations in marsh water since 1995. The extent
of the marsh area less than 10 ppb in the 1999 wet
season had increased to 87% from 41% in 1995
(Table 2).
The median wet and dry season soil concen-
trations with associated 95% confidence intervals
are presented by subarea along the flow path
(Figure 30) with the combined 1995-96 data com-
pared with 1999. The floe and layer of periphyton
mat, if present on the soil surface, was removed and
analyzed separately leaving only the soil material
minus large roots, rocks and coarse debris. Some
Stormwater
Treatment
Areas
Everglades
Agricultural
Area
Figure 27. 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 (from
SFWMD).
Wet Seasons
25
en
20
S 15
_c
CL
10
1995-1996
1999
Figure 28. Median wet season water total phosphorus
concentrations were lower in the high loading areas of
WCA2 and WCA3N during 1999 compared to 1995-96.
18
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South Florida Ecosystem Assessment Report
SURFACE WATER
TOTAL PHOSPHORUS
APRIL 1995 AND MAY 13961
SURFACE WATER
TOTAL PHOSPHORUS
SEPTEMBER 1995-1996
SURFACE WATER
TOTAL PHOSPHORUS
SEPTEMBER 1999
Figure 29. Surface plots of TP measured in surface water
during dry (left) and wet (right) seasons in Phases 1 (1995-96)
and 2 (1999) showing north-south gradients.
Table 2. Spatial extent (%) of TP in water (wet
seasons marsh).
Year
1995
%<10ppb 41
%<15ppb 65
% >50 ppb 3
1996
78
87
2
1999
87
93
2
investigations analyze the periphyton mat as
part of the soil. Periphyton was analyzed
separately to investigate uptake and bioac-
cumulation of mercury and subsequent
transfer to other parts of the food web.
The 1999 data indicate a significant
decline in TP soil concentrations in
Loxahatchee, WCA3-N, WCA3-SE,
WCA3-SW, and Shark Slough. Lowest
concentrations were consistently found in
Taylor Slough, however, the 1999 decline
was not significant. No significant change
in soil TP concentration was found in
WCA2, the most impacted part of the
system. The median soil TP concentra-
tions ranged from 350 to 400 mg/kg,
which contributes to a significant increase
in the proliferation of cattails in the
northern subareas (Figure 31) where most
of the stormwater runoff enters the public
Everglades from the EAA. The location of
the decrease in soil TP observed from
1995-96 to 1999 in the downstream
subareas is consistent with expectations.
The initial subareas to indicate a response
will be those with lower soil concentra-
tions, while the last subareas to show
change with reduced TP loading to the
system will be the most highly contami-
nated northern subareas. Figure 31 also
shows total phosphorus concentrations in
soil for 1995-96 and 1999, indicating the
hot spots greater than 600 mg/kg in
subareas WCA2 and WCA3-N along with
the decline observed in 1999.
Changes in the total mass of phosphorus,
by media, from 1995 to 1999 are shown in
Table 3. There was a significant decrease in
the phosphorus mass in water from 1995 to
1996. Water total phosphorus mass was
comparable between 1996 and 1999. There
has been a progressive decline in the total
mass of phosphorus in the 0-10 cm of soil
19
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South Florida Ecosystem Assessment Report
from 1995 to 1999. The mass of phosphorus in
floe, although only measured during 1999, was
over 50 times the mass of phosphorus in the
water. The floe is a microbially active media that
likely plays an important role in phosphorus
cycling in the marsh. Little is known about the
dynamics in the floe layer.
The changes observed in water and soil TP
mass and concentrations from 1995-96 to 1999
require verification by future large scale monitor-
ing due to the dynamic nature of this ecosystem.
However, the baseline and tools needed for
assessments of system responses have been
developed.
Mercury
Contamination
The Regional Environmental Monitor-
ing and Assessment Program (REMAP)
was initially designed to address mercury
contamination in South Florida.
Assessing the extent and magnitude of
mercury contamination and associated
factors provides insight into where the
contamination might be occurring. The
first step was selecting appropriate indica-
tors. Largemouth bass would appear to be a
good indicator for mercury contamination.
They are a popular sport fish and have high
mercury concentrations because they are at
the top of the aquatic food chain. Unfortu-
nately, largemouth bass are not found at
every sampling site, they live several years and
may move over large areas so it is hard to
determine exactly where their mercury con-
tamination occurred. They are also harder to
sample in the marsh. Largemouth bass moni-
toring was the responsibility of Florida Fish &
Wildlife Conservation Commission.
uuu
'55
^.
= 400
"Q
c
b. 200
2
"o
n
i
-
i
.1
<
fs.
--s.
1
:v
i i
V
/k
1
1995-1996
1999
-
\I
"
V :
"N^
'
i
Figure 30. Median soil concentrations of TP (ug/kg dry weight)
for wet and dry seasons combined by subarea along the
Everglades flow path.
Total Phosphorus in Soil
and Cattail Locations
PTTI Big Cypress
Cattail Li] National Preserve
_j_ * mg/kg
100 200 300 400 500 >600
81.0 -80.3 -80.6 -30.4 -81.0 -80.8 -80.6 -80.4
LONGITUDE,decimal degrees LONGITUDE, decimal degrees
Figure 31. Spatial plots of total phosphorus in soil measured
during phases 1 and 2 indicating sites where cattails occurred.
20
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South Florida Ecosystem Assessment Report
Table 3. Metric tons of total phosphorus, by media and year, in
the South Florida ecosystem.
1995
75.2
Mosquitofish were selected
as the indicator fish species
because they are common
throughout the marsh and
canals, can be easily collected
at all sampling sites, and are in
the food chain for wading birds
and sport fish. In addition, a
predator protection level of
100 ppb mercury in prey fish
has been proposed by the US
Fish and Wildlife Service (Eisler,
1987). Since mosquitofish are
prey for the largemouth bass,
this predator protection level can be used as a criterion to determine potential exposure of largemouth
bass and other fish-eating animals to mercury.
Media
Water
Floe*
Soil
1996
23.5
39,489
46,833
Macrophytes
* Assumed floe thickness = 0.1 water depth
1999
24.3
1,549
21,281
MERCURY PATTERNS
The highest baseline Phase I (1995-96) mercury concentrations in fish were found in the
marsh (Figure 32). Over half the area in the marsh (62% or over 1 million acres) had
mosquitofish with mercury concentrations that exceeded 100 ppb (Figure 32). Only 17% of the
canal miles (about 130 miles) had mosquitofish with mercury concentrations that exceeded
100 ppb (Figure 32). There also was a "hot spot" of mercury in mosquitofish and wading birds
(Frederick et al. 1997) between Alligator Alley and Tamiami Trail (Figure 33) in subarea
WCA3-SW Alligator Alley and Tamiami Trail are two highways that divide the Everglades into 3 gen-
eral areas and provide a frame of reference for looking at these spatial patterns. The highest mercury
concentration in mosquitofish occurred between Alligator Alley and Tamiami Trail in both the canal and
marsh habitats (Figure 34). However, mosquitofish also had high mercury contamination in the marsh
south of Tamiami Trail in Shark Slough (Figure 34). The marshes, then, were the primary areas of
mercury contamination. Methylmercury was
found to exceed 95% of the total mercury in
mosquitofish. ^^| "\
Fish Hg >100 ppb (62%) Fish Hg >100 ppb (17%)
/ \
The highest concentrations of methylmercury
(the form of mercury concentrated in the food
chain) in algae, which are plants at the base of
the food chain, were also found in the marsh
between Alligator Alley and Tamiami Trail.
Fish Hg<100ppb(38%)
Marsh
Fish Hg<100 ppb (83%)
Canals
Figure 32. About 62% of the marsh area, compared to 17%
of the canal miles, have mosquitofish with mercury
concentrations exceeding the proposed predator protection
level of 100 ppb.
21
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South Florida Ecosystem Assessment Report
Similar mercury patterns and their
general location were also observed in the
monitoring of largemouth bass conducted
by Florida Fish & Wildlife Conservation
Commission since 1989 (Lange and Rich-
ard 2001).
The highest methylmercury concentra-
tions in water, however, were found north
of Alligator Alley (Lox, WCA2, and
WCA3-N). The methylmercury water
concentrations found between Alligator
Alley and Tamiami Trail (AA-TT included
WCA3-SE and WCA3-SW) were only
slightly lower than concentrations north of
Alligator Alley (Figure 35). Methylmercury
concentrations in water south of Tamiami
Trail (TT-S) in Shark Slough were 50 to
60% lower than concentrations found in the
other areas to the North.
OTHER WATER QUALITY
PATTERNS
There were also patterns from north to
south in the system for constituents besides
mercury. Total phosphorus (Figure 29),
total organic carbon (Figure 36), and sulfate
(Figure 37), for example, all had steep,
26.6-
ALL CYCLES, 1995 & 1996
ALLIGATOR
ALLEY
Hi) in Chick
Feathers (ppm)
A 940 to 10.50
10.50 to 20.00
20.00 to 55.71
-81.0 -80.8 -80.6 -80.4
LONGITUDE, decimal degrees
Figure 33. The hot spot is the same for total mercury in both
mosquitofish and great egret chick feathers. Largemouth bass
and algae mercury concentrations are also high in this hot spot.
Marsh
Median Mosquitofish Mercury Concentrations, ppb
0 100 200
Canals
Median Mosquitofish Mercury Concentrations, ppb
0 100 200
Above Alligator Alley
Alligator Alley to Tamiami Trail
Below Tamiami Trail I
Wl
ii'/i
29
80
i
42
Figure 34. Comparison of marsh and canal mosquitofish mercury distribution from north to south in the Everglades. Note:
100 ppb is proposed predator protection level and the average mosquitofish mercury concentration exceeds this level in all
three marsh areas.
22
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South Florida Ecosystem Assessment Report
AA-N
AA-TT
TT-S
decreasing gradients from north to south
(Figure 35). Loxahatchee (WCA1) at the top
of this system is a rainfall-driven bog with
very deep peat soil. There is some transport
of EAA discharges into Loxahatchee from
the surrounding peripheral canals, but the
effects are significantly less than the main
stormwater diversion into the flow-way
occurring in WCA2. Taylor Slough is a sub-
basin at the far south end of this system,
which also has very different characteristics
than the other Everglades subareas. Gener-
ally, it has an extremely short hydroperiod
and shallow marl soils.
North to south gradients in the system
due to stormwater from the EAA are
common, with peak concentrations in
WCA2 extending through WCA3-N,
WCA3-SE, WCA3-SW and Shark Slough
(Figure 35). Sulfide in surface water and
porewater was measured during the 1999
sampling seasons (Figure 38), which also
showed a steep decreasing gradient from
north to south. The spatial footprint of
porewater sulfide concentrations showed
WCA2 and WCA3-SE were the most
impacted subareas with predominant reduc-
ing conditions, while sulfide was at back-
ground concentrations in WCA3-SW, Shark
Slough and Taylor Slough. Differences in
porewater sulfide clearly defined the east-
west gradient between WCA3-SE and
WCA3-SW Sulfide has important implications in the bioaccumulation of mercury.
Why do we see these gradients and hot spots of methylmercury in water and mercury in fish
and birds? Why are mercury concentrations in biota highest between Alligator Alley and
Tamiami Trail while the gradients in other constituents are higher north of Alligator Alley?
CAUSES OF MERCURY CONTAMINATION
For mercury contamination to occur in fish and wildlife, four factors must be present:
1) There must be a source(s) of mercury,
Figure 35. Mean wet season (+-95 C.I.) methylmercury, TP,
TOC, and sulfate in surface water and sulfide in soil porewater
for phase 1 and 2 by subarea.
23
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South Florida Ecosystem Assessment Report
-81
-80.8 -80,6
-80.4
-81
-SOS
-304
266
264
26.2
SURFACE WATER
TOTAL ORGANIC CARBON
APRIL 1995 AND MAY 1996
SURFACE WATER
TOTAL ORGANIC CARBON
SEPTEMBER 1995-1996
SURFACE WATER
TOTAL ORGANIC CARBON
SURFACE WATER
TOTAL ORGANIC CARBON
SEPTEMBER 1999
258
256
254
266
26.4
26.2
258
256
254
Figure 36. Surface plots of TOC measured in surface water during wet and dry seasons in phases 1
and 2 showing north-south gradients.
24
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South Florida Ecosystem Assessment Report
-81 -808 -806 -80.4
-81.0
-80.8 -806
-804
26.6
26.4
26.2
25.8
25.6
254
SURFACE WATER
SURFACE WATER
SULFATE
SEPTEMBER 1995-1996
SULFATE
APRIL 1995 AND MAY 1996
SURFACE WATER
SULFATE
SURFACE WATER
SULFATE
SEPTEMBER 1999
26.6
26.4
26.2
25.8
25.6
25.4
m
Figure 37. Surface plots of sulfate measured in surface water during wet and dry seasons in phases 1
and 2 showing north-south gradients.
25
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South Florida Ecosystem Assessment Report
-81
-80.8 -806
-804
808 -806
-80.4
266
264
262
258
256
254
SURFACE WATER
SULFIDE
SEPTEMBER 1999
SURFACE WATER
SULFIDE
PORE WATER
SULFIDE
SEPTEMBER 1999
PORE WATER
SULFIDE
266
26.4
26.2
258
256
25.4
Figure 38. Surface plots of sulfide in surface and porewater during phase 2 wet and dry seasons
showing north-south gradients.
26
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South Florida Ecosystem Assessment Report
2) The right combination of environmental conditions must exist for inorganic mercury to be converted to
organic or methylmercury,
3) Methylmercury, the mercury form readily taken up by biological organisms, must be available (un-
bound) at the base of the food web, and
4) There must be biological uptake and accumulation of methylmercury through the food chain to higher
trophic levels.
Once mercury enters the food chain, it increases in concentration or biomagnifies at each
higher step or level in the food chain (Figure 39). The highest mercury concentrations are usually
found in top predator fish (e.g., largemouth bass), birds, reptiles, and mammals that eat fish or
fish-eating animals (e.g., raccoon, Florida panther, respectively).
Given the mercury contamination fish consumption advisories throughout the Everglades ecosystem,
obviously all four factors must be present. But, how does this contamination occur in the Everglades?
MERCURY SOURCES
Mercury Bioaccumulation
r~~**\ Plankton Eaters »f Top Predators -4Bottom Feeders] I Aquatic Rants
Figure 39. Bioaccumulation of mercury up the food chain from the water to wading birds and the Florida
panther. Mercury concentrations in largemouth bass are over 1,000,000 times higher than methylmercury
concentrations in water.
There are multiple possible sources contributing mercury to the Everglades ecosystem, including
those external to the system:
1) Atmospheric deposition (wet and dry fall) from local and regional sources;
2) Global background, which contributes mercury to the Everglades from international sources primarily
via wet deposit!on;
3) Loading from the Everglades Agricultural Area stormwater; and those internal to the system:
4) Peat decomposition and decay and fires releasing mercury stored in the plant tissue;
m
27
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South Florida Ecosystem Assessment Report
5) Weathering and erosion of mercury in rocks (e.g., limestone) in the Everglades ecosystem.
Currently, the magnitude of only three of these sources has been estimated - atmospheric deposition
(Figure 40), EAA loading (Figure 41), and global background. Monthly-weighted average atmospheric
mercury deposition monitoring data were collected at 10 locations throughout South Florida, including a
site to estimate global background (Figure 42) (Guentzel et al., 2001). US EPA and the South Florida
Water Management District monitored total mercury concentrations biweekly at the pumps located on
the canals surrounding the EAA to
estimate the mercury load from the EAA
(Stober et al., 1998). Data from these
two sources (atmospheric and canals)
were used to estimate the annual total
mercury loading to the Everglades
ecosystem (Table 4). Atmospheric
deposition in precipitation contributed
from 35 to 70 times the mercury loading
to the freshwater Everglades compared
to mercury coming from EAA stormwa-
ter loadings. The global background site
provided one estimate of the amount of
the atmospheric total mercury load that
was derived from distant or global
background sources. Some analyses indicated that global contributions account for between 25 and
40% of the atmospheric load to South Florida. Mercury emission source studies, being conducted by
US EPA, indicated that medical and municipal incinerators are major atmospheric mercury emission
sources in South Florida (Figure 43). The portion of atmospheric total mercury that is derived from all
local and regional sources, estimated from these separate EPA studies, ranged from 60 to 75%, which
is consistent with estimates of the global background contributions (Dvonch et al., 1999). These studies
are on-going, so more accurate estimates of atmospheric mercury loadings will be available in future
reports.
Figure 40. Fate and transport of mercury emissions from the source to
the atmosphere with deposition over the marsh.
Table 4. Comparison of atmospheric vs.
surface water mercury loading.
Atmospheric EAA
Deposition Water
Year (kg/yr) (kg/yr)
1994 140 2
1995 155 3-4
28
Figure 41. EAA stormwater discharge contributes nutrients and
mercury to the public Everglades.
-------
South Florida Ecosystem Assessment Report
West Palm
Beach
LOXAHATCHEE
NATIONAL
WILDLIFE REFUGE
Ft. Lauderdale
Stormwater Treatment Area
Everglades Agricultural Area
Water Conservation Area
Everglades National Park
Big Cypress National Preserve
Wildlife Management Area
Figure 42. Deposition monitoring locations in the Everglades.
Figure 43. Waste incinerators are one of the sources of
atmospheric mercury.
All plants and rocks
contain small concentra-
tions of mercury. When
the plants decompose or
decay and when rocks
erode and weather, this
mercury re-enters the
mercury cycle in the
system. There are no
precise estimates of the
amount of mercury
derived from these two
sources. However,
Scheldt etal. (2000)
estimated up to 3 feet of
peat loss in the public
Everglades over the past
50 years (Figure 44).
One of the questions that
arises is "where did this
mercury go?" The answer
to this question is un-
known. However, be-
cause mercury is a volatile
element, it could have
entered the atmosphere
and become part of the
global background, or
perhaps redeposited in
marsh water or sediment
and again taken up by
plants. Better estimates of
mercury source contributions will be available in the
future. For now, it is clear that atmospheric emissions
from human activities (e.g., incinerators) are an
important source of mercury in the Everglades
ecosystem.
Simply having a mercury source, however, does
not mean that mercury will become a concentrated
contaminant in the ecosystem. The right combination
of conditions also must exist for mercury to be
converted to a form that can be bioaccumulated and
biomagnified through the food chain.
Fakahatchee Strand
ENP - Beard Research Center
ENP - Tamiami Trail Ranger Station
Little Crawl Key
Andytown, Broward County
Everglades Nutrient Removal Project Site
29
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South Florida Ecosystem Assessment Report
Explaining
the
Environmental
Patterns
CHANGE IN
PEAT
CHANGE IN
PEAT
LONGITUDE, decimal degrees
Figure 44. Subsidence estimates (1945-1996) indicate that peat has been lost in
portions of the public Everglades. Minimum estimates of peat change are shown on
the left with maximum estimates shown on the right. The answer to the question
"Where did the mercury tied up in this peat go?' is unknown.
For mercury to be
converted from an inor-
ganic to an organic form
that can contaminate
biological organisms, the
right combination of envi-
ronmental conditions must
occur. The seven subareas
of the Everglades that have
been identified have differ-
ent environmental condi-
tions and characteristics.
These different environmental conditions affect both the methylation (conversion from inorganic to
organic mercury) and the mercury bioaccumulation processes. These differences probably contribute to
the development of the mercury hot spot between Alligator Alley and Tamiami Trail in WCA3-SW.
Comparing the differences among environmental conditions in these areas can help explain why there
are differences in mercury contamination across the ecosystem. A conceptual model which consolidated
the seven subareas into three larger areas can help explain the interactions among different constituents
(Figure 45). It is these interactions that result in the mercury responses and patterns that were observed
and are discussed with broad general statements for each subarea.
NORTH OF ALLIGATOR ALLEY
Discharge from the EAA controls most constituent concentrations in WCA2, WCA3-N and
WCA3-SE (Figure 45). Total organic carbon, total phosphorus, and sulfate concentrations in
water are high in these subareas (Table 5). Dissolved oxygen concentrations, however, can be
low or zero in both the water and soil in this area. This is important because sulfate reducing
bacteria (SRB), an important type of bacteria that methylates or converts inorganic mercury to
organic mercury, only live in environments without oxygen. There is a lot of sulfate available in
30
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South Florida Ecosystem Assessment Report
so, /]
THg 1 //
\\\/,J
TWeH/
* MeHg-MatPert
.. ' , _ . £ (Other Organ )
MeHg-SosI Pe*f *
MeHg ^ S
V /\
4-~THg
AFDW-C SO.
Above Alligator Alley
Note: Arrow size proportional
importance of interaction.
TP
so, / /
: n.h THg I / /
f\l^T
1 * /
c* "*^ _ /
.JL/
MiH9^ ~~--~
f * MeH9-9«j»Perl
'
MeHg -4 S'
\ \
. THg
\
AFDW-C SO,
Between Alligator Alley
and Tamiami Trail
to
Mercury Interactions:
Conceptual Models
N so. TP
\ THg ,
Fish '\, TOC
*
* Small tna«cfe*
, \JS""»*«"^ Ur^"""B
MeHg-StM) Peri "~"F Shrimp : ^ pjg^|
1
MeHg S*
. THg
AFDW-C SO,
Below Tamiami Trail
Figure 45. Above Alligator Alley, chemical concentrations (TOC, SO4, S2~) are high and bind inorganic and methylmercury
making it less biologically available. Below Tamiami Trail, chemical concentrations are low, methylmercury is readily
bioavailable, and food web complexity magnifies mercury through the food chain. Between the Alley and the Trail, there are
dynamic chemical and biological interactions resulting in the "hot spot" of mercury contamination. SRB = sulfate reducing
bacteria.
these areas for these bacteria to use in their growth. In addition, there is a lot of organic carbon that also
serves as an energy source for these and other bacteria. The spatial pattern of high sulfide concentra-
tions in soil porewater validates the presence of reducing conditions prevalent in WCA2 and WCA3-
SE. An important interaction between marsh drying and sulfate in soil was found (Figure 37) by obser-
vation of a large increase in sulfate in 1999. As water depth declines and soil is exposed to drying,
sulfide is oxidized to sulfate that is available upon refl coding to stimulate the growth of sulfate reducing
bacteria and methylmercury production. The highest methylmercury concentrations in water were found
in Lox, WC A2, and WC A3 -N (Table 5). Higher total phosphorus concentrations cause the plants to
grow and also produce a lot of organic matter. Bacterial decay and decomposition of the organic matter
from the EAA take the oxygen out of the water. With high concentrations of organic carbon and sulfate
as food, there is a lot of production of methylmercury by the sulfate-reducing bacteria which results in
high methylmercury concentrations in water north of Alligator Alley. The complex interactions of sulfate/
sulfide on control of microbial methylation hot spots in the Everglades have also been reported by Orem
et al. (1999), Bates et al. (1998), Bates et al. (1999), Orem et al. (2000), andKrabbenhoft et al. (2000
and 2001).
Mosquitofish mercury concentrations were lower in LOX, WCA2, WCA3-N and WCA3-SE
than in WCA3-SW and Shark Slough even though surface water methylmercury concentrations
were higher (Figure 49). There are several possible explanations for why the fish mercury con-
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South Florida Ecosystem Assessment Report
Table
5. Median marsh and canal water quality in three Everglades zones.
North of
Alligator Alley
Marsh
Constituents
Total Phosphorus,
ppb (ug/L)
Total Organic Carbon,
ppm (mg/L)
Sulfate, ppm (mg/L)
Methylmercury,
ppt (ng/L)
1995-
1996
18
29
15
0.4
Marsh
1999
10
28
11
0.4
Canal
1995-
1996
83
25
34
0.2
Alligator Alley to
Tamiami Trail
Marsh
1995- Marsh
1996 1999
11 7.4
20 18
<2 1.4
0.4 0.3
Canal
1995-
1996
26
21
5
0.2
Marsh
1995-
1996
10
16
<2
0.2
South of
Tamiami Trail
Marsh
1999
5.3
11
0.7
0.1
Canal
1995-
1996
14
10
9
0.1
centrations were lower in the northern subareas.
First, although the sulfate reducing bacteria need organic carbon and sulfate as a substrate,
organic carbon and the reduced form of sulfate (sulfide) can also both bind inorganic mercury
and methylmercury (Cai et al. 1999; Cai 1999; Aiken et al. 2000; Reddy et al. 1999; Lu and Jaffe
2001). This binding can make the inorganic mercury less available to the sulfate reducing bacte-
ria and the methylmercury less available for biological uptake. The net result could be less
methylmercury in the food chain.
Another reason for lower fish mercury concentrations could be a different food chain in the
eutrophic subarea north of Alligator Alley compared with the food chain in WCA3-SW and
Shark Slough to the south (Kendall et al. 2000). For mercury contamination to occur in higher
trophic levels, there must be bioaccumulation through the food chain. The amount of organic
carbon discharged from the Everglades Agricultural Area or produced by plants because of higher
total phosphorus concentrations may overwhelm the capacity of the system to handle the volume
of organic material. Dissolved oxygen concentrations are low or zero. This condition is not
tolerated by many invertebrates and fish. The food chain, therefore, could be altered in this area so that
mercury is not efficiently accumulated to the higher trophic levels. Much of the plant matter produced
probably falls to the bottom and decays or rots. Many of the organisms living in this area might feed on
this decaying plant matter where the mercury is either bound by the organic matter, or it is demethylated
and converted back to an inorganic form. Those organisms that can tolerate these conditions, however,
might proliferate and grow faster. This increased mass and number of organisms might dilute the concen-
tration of methylmercury in any one organism, resulting in reduced bioaccumulation in the food chain.
The inorganic mercury formed by demethylation reactions could also be bound as sulfide in this high
sulfate, highly reducing environment.
32
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South Florida Ecosystem Assessment Report
Finally, much of this area dries during the dry season so there will be less habitat for aquatic organ-
isms, fish, and wildlife, including wading birds that feed on these organisms. The exact pathways and
processes that are occurring in this area are not fully known, but similar processes do occur in other
wetland ecosystems.
ALLIGATOR ALLEY TO TAMIAMI TRAIL
Total organic carbon, sulfate, and total phosphorus loadings from the EAA have been assimilated in
WCA2, WCA3-N, and WCA3-SE resulting in concentrations of these constituents that are significantly
lower in the southern subareas (WCA3-SW, Shark Slough and Taylor Slough). Water methylmercury
concentrations, however, are comparable to those north of Alligator Alley for several reasons. First,
there is an unknown amount of downstream transport of methylmercury in the water from upstream.
Second, because the organic carbon and sulfide concentrations are lower, there is less binding of total
mercury and methylmercury. However, there are relatively high porewater sulfide concentrations in
WCA3-SE establishing an additional sharp gradient from east to west in WC A3 (Figure 38). Structural
equation modeling or path analysis (Duncan 1975,Hoyle 1995, StatSoft Inc. 2000) of multiple interact-
ing variables by subarea identified the importance of TOC in WCA3-SE and sulfate in the adjoining
subarea WCA3-SW, which constitutes the highly active interface between the more heavily impacted
northern subareas and the less affected subareas to the south. More inorganic mercury is available for
the sulfate reducing bacteria and more methylmercury is available for uptake and bioaccumulation
through the food web (Figure 39). Third, there is a significant increase in periphyton mats throughout this
area (Figure 46). Although phosphorus concentrations have diminished, these concentrations can still
stimulate production of periphyton. These periphyton mats (Figure 47) become so thick that the interior
of the mat becomes anoxic or devoid of oxygen during darkness. At night, when there is no oxygen
production by the periphyton, the sulfate reducing bacteria in the thick periphyton mats (Figure 47)
methylate mercury (Cleckner et al. 1998,
Cleckner et al. 1999). The methylmercury is
then taken up by the growing periphyton. The
methylation rates measured as part of the US
Geological Survey studies were some of the
highest methylation rates that have been
observed in any aquatic ecosystem (Gilmour
etal. 1998). These higher rates probably
reflect the warmer temperatures in the Ever-
glades waters.
Because this system is not overwhelmed
by the loading of material from the EAA, the
food chain is more complete. There are
additional pathways for both the uptake of
methylmercury by plants and for the transfer
of this methylmercury to higher levels in the
food chain. The highest mercury concentra- Figure 46. Periphyton mats were found more often in 1995-1996
tons in mosquitofish are found in this area than 1999, but were more frequent south of Alligator Alley in both
periods.
PERIPHYTON
PRESENCE
1995-1996
PERIPHYTON
PRESENCE
1999
33
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South Florida Ecosystem Assessment Report
(WCA3-SW and Shark Slough). In fact, this is the
area with the mosquitofish and large mouth bass
(Lange et al. 2000) mercury hot spot (Figure 48)
(Stober et al. 1996). Periphyton concentrations were
also high in this hot spot.
A large part of this area also remains wet during
the dry season and offers significant habitat for wading
birds as feeding, roosting, and nesting sites. This is
probably why there are high mercury concentrations in
wading bird nestlings in this area (Figure 48)
(Frederick and Spalding, 2000). Unfortunately, the
exact processes controlling wading bird mercury
concentrations are not fully understood.
SOUTH OF TAMIAMI TRAIL
26.6-
26.4-
u>
01
O)
1_
01
at
26.2-
.5 26.0-
E
u
IP
a
ul
Q
25.8-
25.6-
25.4-
ALL CYCLES, 1995 &1996
lly in Chick
Feathers (ppm)
A 940 to 10.50
10.50 to 20.00
20.00 to 55.71
-81.0 -80.8 -80.6 -80.4
LONGITUDE, decimal degrees
Figure 48. The hot spot is the same for total mercury in both
mosquitofish and great egret chick feathers (Frederick et al. 1997).
Figure 47. Periphyton mats can be stimulated to grow
by total phosphorus loading and become so dense that the
mat interior becomes anaerobic and mercury methylation
occurs inside the mat.
Aside from the interior of Loxahatchee,
concentrations of all constituents are lowest
south of Tamiami Trail in Shark and Taylor
Sloughs, except for total mercury in fish
(Figure 45, Table 5). The methylmercury,
although significantly lower in
concentration, is probably more
biologically available than in the subareas to
the north. Organic carbon and sulfide
concentrations are significantly lower and
bind less of the methylmercury produced.
Therefore, the methylmercury present
should be more available for uptake and
accumulation by biological organisms.
The mosquitofish mercury concentra-
tions in Shark River Slough in the Ever-
glades National Park are almost as high as
the fish mercury concentrations found in the
WCA3-SW hot spot below Alligator Alley
(Figure 49).
The food chain is probably more
complete in this area so there is greater
accumulation and biomagnification through
multiple links in the food web (Figure 39)
(Loftus et al. 2000). This area had the
highest observed bioaccumulation factors
(B AF) for mercury of any of the three
34
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South Florida Ecosystem Assessment Report
areasone million times higher mercury concentrations in mosquitofish when compared to the water
methylmercury concentrations. Much of this area also dries during the dry season and many of the
wading bird nesting and roosting sites have been disrupted because of changes in hydropattern and
urban and agricultural development on the eastern edge of the Everglades National Park.
TOP DOWN vs BOTTOM UP
m
Wet Seasons
AA-TT
TT-S
"Top down" versus "bottom up" is a concept used to explain how control of patterns and processes
in aquatic systems changes during eutrophication or as nutrient loading to a system increases (Carpenter
etal., 1985 and 1995). Some of these
ecological attributes are compared
between oligotrophic and eutrophic
systems in Table 6. The comparison is
relevant because eutrophication, in part,
affects mercury contamination patterns
and processes; the concept is an analog
for mercury contamination; and the
Everglades ecosystem shows the entire
gradient from eutrophic in the north to
oligotrophic in the south.
Oligotrophic systems can be viewed
as "top-down" controlled ecosystems.
Nutrient cycles are tightly coupled be-
cause nutrients are limiting, biotic-abiotic
interactions control the response of the
ecosystem and the variability in biomass
production is relatively small, varying by a
factor of only 4 to 5 over a year (Table 6).
Oligotrophic systems usually have a
seasonal renewal of nutrients, such as
during the rainy season. The predictability
of the response of oligotrophic ecosys-
tems is relatively low because there are
multiple factors that control the interac-
tions among biotic and abiotic constituents
and these are not understood very well.
Eutrophic systems can be viewed as
"bottom-up" controlled ecosystems
because nutrient cycles are leaky and
decoupled from higher levels in the food
chain. Physical factors such as inflow,
hydrodynamic mixing and sedimentation
XXX*
Figure 49. Median wet season concentrations and 95% C.I. for
total and methylmercury in water and periphyton (soil, floating,
utricularia associated), total mercury in mosquitofish and the
bioaccamulation factor by subarea for phase 1 (1995-96) and phase
2(1999).
35
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South Florida Ecosystem Assessment Report
Table 6. Comparison of processes and patterns between oligotrophicand eutrophic systems.
Ecological Attribute
Controlling Factors
Nutrient Cycling
Forcing Functions
Temporal Patterns
Nutrient Requirements
Predictability
Oligotrophic Systems
"Top-down"
Tightly coupled nutrient
cycles-algae-grazers-microbes,
regenerated in water column
Biotic-abiotic interactions
Relatively small biomass
variability
Seasonal renewal
Low-multivariate relationships
among biomass and controlling
factors not well understood
Eutrophic Systems
"Bottom-up"
Loose nutrient cycling-
decoupled from higher food
chain, supplied from inflow,
sediment cycling
Physical factors-inflow,
hydrodynamic mixing
Large biomass variability
Continuous supply
High-statistical relationships
between nutrient loads and
biomass
control system responses, and there typically are large variations in biomass production, varying by over
an order of magnitude throughout a year (Table 6). Nutrients are supplied primarily through inflows and
are relatively continuous throughout the year. The predictability of the system response is relatively high.
Statistical relationships between nutrient loads and biomass can be developed (i.e., Vollenweider-type
nutrient loading models (Vollenweider 1976)).
A statistical analysis technique called structural equation modeling or path analysis was used to
evaluate some of the linkages among factors such as water depth, different chemical constituents [e.g.,
total organic carbon (TOC), total phosphorus (TP), sulfate, total mercury (THg) and methyl mercury
(MeHg)] in both water and soil, and different biological assemblages, such as soil periphyton or mat
periphyton and mosquitofish. Path analysis or structural equation modeling estimates the strength of the
associations or linkages among different constituents simultaneously, by evaluating the patterns in vari-
ability among constituents. This is a different approach than is used in standard regression analyses, but
it can be a powerful approach for looking at relationships among many variables, such as there are in the
Everglades ecosystem. If the association between two different factors or variables, such as between
TP and TOC was estimated to be 1.0, this would indicated there was a strong relationship between the
two variables. If this estimated association was 0.0, it would indicate there was no relationship between
the two variables. Estimating these path coefficients, then, provides an indication of the strength of the
relationship among variables and can indicate which pathways are statistically significant. These path-
ways and the strength of the associations and direction (positive in blue and negative in red) are shown
in Figures 50 through 52.
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South Florida Ecosystem Assessment Report
North of Alligator Alley (except for Loxahatchee), the marsh is eutrophic. Chemical constituent
concentrations are high (e.g., TP, TOC, SO4), and chemical interactions appear to control mercury
bioavailability and bioaccumulation (i.e., bottom-up) (Figure 50). The food web in this eutrophic area is
likely very different from other areas in the marsh.
Between the Alley and the Trail, the system is in transition between a eutrophic and oligotrophic
ecosystem. Productivity is still stimulated by nutrients, but chemical interactions and interferences with
methylmercury bioavailability and bioaccumulation have decreased. Methylmercury concentrations are
high, and mosquitofish mercury concentra-
tions are at their greatest values. Food
webs are likely more tightly coupled,
contributing to the elevated fish mercury
concentrations. Transition areas typically
are dynamic and have characteristics of
both eutrophic and oligotrophic ecosys-
tems (Figure 51).
South of Tamiami Trail, the marsh is
oligotrophic, chemical constituent concen-
trations are low, and biotic-abiotic interac-
tions are likely much more tightly coupled
(i.e., top-down) (Figure 52). Although
methylmercury concentrations in water are
low, more of this methylmercury is likely
biologically available and, therefore,
bioaccumulated and biomagnified through
the food web. The methylmercury BAF
(Figure 49) is significantly higher in this area
than in the north.
Understanding some of the eutrophi ca-
tion processes helps our understanding of
mercury contamination. For example, the
path analyses indicated that the area be-
tween Alligator Alley and Tamiami Trail was
dynamic, with multiple pathways and
interactions among chemical constituents
and methylmercury concentrations in water
and soil, periphyton and fish (Figure 51).
North of Alligator Alley, where the system
was eutrophic and chemical constituent
concentrations were high, the pathways
were simple (Figure 50). South of Tamiami
Trail, where the system is oligotrophic, the
TH8
0.36
Phase I - North of Alligator Alley
TP
032
TOC
029 \
H9-w -02\
MeHg-w
0.31
THg-Fish
Soi!_-Wat_e_r_
MeHg-Soil
TH9 041 032
078 AFDW TP
Interface
Figure 50. Chemical interactions dominate in the area north of
Alligator Alley. Blue lines represent positive interactions; red lines
negative interactions. The strength of the interactions is indicated by
the numbers with 1.0 being the strongest interaction and 0 being no
interaction. Simple linkages among constituents and chemically
dominated linkages are typical of eutrophic systems. (Note: AFDW =
ash free dry weight).
Phase I - Alligator Alley to Tamiami Trail
Water^ «, TP
Depth
wn ~^. f
0.13
-041
TOC
0.25
\ 065
\ ' i QM-r MeHg-PU
MeHg-w ^O63 ^
MeHg-PS 0.30
THg-Fish
Soil-Water
056
AFDW
086
MeHg-Soil
030 °23
THg TP
034
Interface
Figure 51. The system is highly dynamic between Alligator Alley
and Tamiami Trail with significant positive (blue) and negative (red)
interactions among the chemical and biological factors such as
floating periphyton (PU) and soil periphyton (PS). These interactions
are part of the reason the hot spot occurs in this area.
37
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South Florida Ecosystem Assessment Report
pathways are relatively complex, with both floe and water methylmercury concentrations associated
with fish mercury concentrations. Structural equation modeling indicated that both detrital and au-
totrophic pathways contribute to fish mercury concentrations (Figure 52). Brumbaugh et al. (2001) also
found that fish mercury concentrations were strongly correlated with water methylmercury concentra-
tions in a national study of 21 National Water Quality Assessment Program (NAWQ A) watersheds.
CHANGES IN MERCURY CONTAMINATION
Atmospheric emissions of mercury began to decline from municipal solid waste incinerators
in the late 1980s. This was followed in the early 1990s by further restrictions on medical waste
incinerators that resulted in an overall 95% decline in mercury emissions in South Florida
through 1999 (FDEP). The marsh spatial monitoring data collected in this study were generated
during the mid and late 1990 when atmospheric emission rates in South Florida were thought to
have declined from around 100 to 10 ug/m3. However, precipitation, and therefore wet
deposition, also declined from 1995 to 1996, with 1999 being a drought year. One approach for
assessing change in an atmospheric
contaminant is to consider change
across large spatial areas, or over an
entire ecosystem over long periods of
time. This approach smooths out the
noise in the signal that occurs because
Phase II - South of Tamiami Trail
Water .040
Depth THg
-0 51 / 0 32 0 49 TOC
'042
MeHg-w 04°
TP
0.78
039
°17
so4
042
034
0.28
047
THg-Fish
0.33
MeHg-Floc
Soil-Water
so,° %,
031
AFDW'
MeHg-Soil
Interface
Insufficient
Periphyton
0.76
THg
Figure 52. In the oligotrophic area south of Tamiami Trail, the food webs
are complex, and the linkages are almost all positive. A small increase in
nutrients, sulfate, or inorganic mercury will likely result in increased mercury
in fish because of the complex food webs and biological magnification of
mercury through the food chain.
of small temporal and spatial scale
variations, and helps reveal changes in
the underlying signal.
Mass estimates were calculated for
total and methylmercury by media and
by year to assess possible changes in
the distribution of mercury in the South
Florida ecosystem from 1995-96 to
1999 (Tables 7 and 8). These mercury
distributions and their change overtime
can indicate possible effective manage-
ment actions for implementation as part of the restoration efforts. The total mercury mass in wet deposi-
tion, water, floe, soil, periphyton, and fish are shown in Table 7. There has been a decrease in total
mercury wet deposition to the system from 1995 to 1999. In addition, there has been a statistically
significant decrease in soil total mercury mass between the 1995-96 period and 1999. There was a
corresponding decrease in total mercury in water and fish during this same period. Periphyton mercury
mass was highly variable among years, reflecting the relative distribution of periphyton throughout the
system.
The thickness of the floe layer was difficult to accurately measure in the field. The floe layer thick-
ness typically varied from about 0.01 to 0. 1 (i.e., 1 - 10%) of the water depth. Floe mercury mass
estimates, therefore, were estimated as a range. Even assuming the minimum thickness, total mercury
mass in floe exceeded that in the water and periphyton by at least 2-fold and might have exceeded it by
38
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South Florida Ecosystem Assessment Report
over an order of magnitude. Other studies have included the floe and soil periphyton as part of the soil
measurements so this component of the ecosystem and its role in mercury cycling has been confounded
with soil estimates and processes. Future studies might consider separating the floe from the soil and
studying the dynamics of the floe-sediment interactions and the floc-microbial-microcrustacean interac-
tions.
A methylmercury mass estimate was also calculated for the system (Table 8). Methylmercury mass
decreased during 1996 and 1999 in water, periphyton, and fish compared with the methylmercury mass
estimates for 1995. Soil methylmercury mass decreased between 1995 and 1996, but increased
significantly in 1999. Floe methyl mercury masses ranged from being comparable to the methylmercury
mass in water to having an order of magnitude more mass than water and about 5 times the methylmer-
cury mass found in periphyton. As indicated above, the thickness of the floe layer varied from 0.01 to
0.1 times the water depth. The floe layer has not been adequately studied and could be a maj or path-
way for mercury methylation, uptake and bioaccumulation in the ecosystem.
Table 7. Total mercury estimated by media on a total mass (kg) and areal basis (g/m2, in parenthe-
ses) for the three wet season monitoring years.
Media 1995 1996 1999
Wet Deposition 153.3(27.7) 116.1(21.0) 146.5(26.5)
Water 6.0(1.1) 4.7(0.8) 3.8(0.7)
Floe 658 (123)+
65.8 (10)++
Soil 11,559(2,090) 11,078(2,006) 9,232(1,665)
Periphyton (Combined) 39.2 (7) 152.3(29) 24.5(5)
Mosquitofish 0.64(10.12) 0.41(10.07) 0.39(6.07)
+ Assumes floe thickness = 0. f water depth ++ Assumes flock thickness = 0.01 water depth
Similar changes were noted in constituent concentrations over time. Wet season results collected
during the September rainy season are presented in Table 9. Wet season samples were collected during
the period of maximum atmospheric deposition and with sheetflow occurring throughout the system. The
median concentrations of total mercury in surface water showed a significant decline from 1.96 ng/L in
1995-96 to 1.43 ng/L in 1999, a 27% decrease. This decline is illustrated in Figure 49 showing that the
1999 total mercury in water was equal to or less than the 1995-96 baseline across all subareas. The
lack of change in WCA2 could be due to the input from the downstream transport of total mercury from
the EAA while the remaining subareas were responding mainly to atmospheric deposition. Over the
same time period, methylmercury in water declined from 0.275 to 0.174 ng/L, a decrease of 37%. The
methyl to total mercury ratio in water ranged from 0.145 to 0.163, showing no significant change over
the same time period.
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South Florida Ecosystem Assessment Report
Table 8. Methyl mercury, by media, expressed on a total mass (kg) and an areal basis (|jg/m2, in
parentheses) for the three wet season monitoring years.
Media
Water
Floe
1995
1.76(0.32)
Soil 62.2(11.2)
Periphyton (Combined) 3.8 (0.7)
Mosquitofish 0.64(0.12)
1996
1.02(0.18)
56.9(10.3)
2.8(0.5)
0.41 (10.07)
1999
0.79(0.14)
9.2(1.7)+
0.9(0.17)++
128.9(23.3)
1.29(0.23)
0.39 (0.07)
Subarea wet season median methylmercury concentrations in water in 1999 were equal to or less
than those measured in 1995-96 except in WCA2 which may also have been receiving an unknown
amount of methylmercury from the EAA (Figure 49). Median methylmercury concentrations in soil by
subarea increased in 1999, with higher concentrations to the north. Most of the areas with highest soil
concentrations of methylmercury were located in the WCAs closest to the EAA where the soil had been
dried during the previous season (Figure 53). Median total mercury in all periphyton types decreased
significantly in 1999 while median methylmercury concentrations remained at similar levels as those in
1995-96.
A comparison of dry season mercury concentrations is strongly influenced by the degree of dry
down in the marsh (Table 10). The 1995-96 dry seasons were relatively wet (8% and 17% dry surface
area, respectively) in comparison to the 1999 dry season in which 54% of the marsh surface area was
exposed to drying. The median total mercury concentrations in water in 1995-96 were identical in both
the dry and wet seasons at 1.96 ng/L (Table 10). Dry season surface water median total mercury
concentrations increased to 3.30 ng/L in 1999. Dry season methylmercury in surface water was found
to reach medians of 0.578 and 0.723 ng/L in 1995-96 and 1999, respectively (Table 10) followed by
declines in the subsequent wet seasons to 0.275 and 0.174 ng/L in 1995-96 and 1999, respectively
(Table 9). There was no significant change in total or methylmercury in wet season soil, however, dry
season soil concentrations of total mercury decreased 15%, while methylmercury increased 18%.
Median methylmercury concentrations in periphyton were not substantially different between seasons or
years. The water constituent concentrations, which increase with seasonal dry down of the marsh and
decrease with the onset of the rainy season, represent a pattern to which this ecosystem is exposed on
an annual basis.
The South Florida Everglades ecosystem is a pulsed system that is maintained by wetting and drying
(Odum, 1971). The fluctuating water levels are part of the regular, but acute, physical perturbations
under which the system evolved. The dry season drawdown speeds aerobic decomposition of accumu-
lated organic matter, transforms some reduced species such as sulfide back to oxidized species such as
sulfate, and concentrates aquatic species such as the mosquitofish and invertebrates in smaller areas
where they are preyed on by other fish, terrestrial mammals (e.g., raccoon), and wading birds. The
40
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South Florida Ecosystem Assessment Report
Table 9. Freshwater Everglades Ecosystem wet season median concentrations of total and methylmer-
cury by media.
Parameter 1995-96
Surface Water (ng/L)
HgT 1.96
MeHg 0.275
Ratio MeHg:HgT 0.145
Soil (ug/kg)
HgT 130
MeHg 0.40
Floe (ug/kg)
HgT
MeHg
Periphyton (ug/kg)
HgT 151
MeHg 1.21
Mosquitofish (ug/kg)
HgT (Wet + Dry) 163
(100 ppb)
(200 ppb)
BAF x 105
68
40
5.3
C.I.
N
1999
C.I.
N % Change
1.9-2.13
0.229-0.305
0.127-0.161
110-140
0.32-0.50
207
207
207
207
180
1.43
0.174
0.163
130
0.38
157
0.79
1.28-1.58
0.127-0.245
0.11-0.188
120-140
0.27-0.58
130-179
0.48-1.69
112
100
99
113
113
100
84
-27
-37
12
NS
NS
125-185 76 27.34 22.5-31.8 55 -82
1.05-1.65 130 1.145 0.74-1.82 55 NS
149-180 350 123
% Exceedance
63-73 350 60
% Exceedance
35-45 350 20
3.9-6.7 196 7.5
107-140 151 -24
52-68
151 -12
13-26 151 -50
5.9-9.4 99 43
NS = not significant, CI = 95% confidence interval, N = number, B AF = Bioaccumulation Factor
nutrients, sulfate, and other constituents released during the dry season contribute to productivity and
other processes such as mercury methylation during the wet season. The pulsed nature of the ecosys-
tem is an integral part of the life histories of many species such as the wood stork. The wood stork
breeds when the water levels are falling and small fish on which it feeds are concentrated in the pools. If
the water level remains high during the normal dry season, or fails to rise in the wet season, the wood
stork does not nest (Kahl 1964). Changing the water level fluctuations can affect both the distribution
41
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South Florida Ecosystem Assessment Report
;.Q
METHYL MERCURY
SOIL
APRIL 1996 AND MAY 1996 I
0-10 cm
METHYL MERCURY
SOIL
SEPTEMBER 1996 -1996
Figure 53. Surface plots of methylmercury measured in soil
during wet and dry seasons in phases 1 and 2 showing north-
south gradients.
and nesting of wading birds within the system
and has likely been a maj or contributor to the
decrease in wading bird populations and
concentrating the nesting and feeding areas
around the mercury hot spot in WCA3-SW
(Frederick et al. 1998, Rumbold 2000).
The mosquitofish can integrate mercury
exposure across both wet and dry season
conditions, so combined wet/dry season results
are presented. Total mercury concentrations in
trophic level 3 mosquitofish (Gambusia
holbrooki) were lower in 1999 especially in the
mercury hot spot (WCA3-SW). However,
these differences were not significant in a
subareaby subarea comparison (Figure 49).
Analysis of total mercury concentrations in
mosquitofish across the entire study area
showed a decline in median concentration of
24% from 1995-96 to 1999. A reduction of
12% in the fi sh exceeding the 100 ug/kg
concentration was evident (i.e., 68%
exceedance in 1995-96 to a 60% exceedance
in 1999), however, there was a 50% decrease
(40 to 20%) in fish exceeding 200 ppb. There
was a greater decline in the fish with higher
mercury concentrations (Table 9).
The wet season B AF in mosquitofish
across the entire ecosystem ranged from a
median of 5.3 x 105 in 1995-96 to 7.5 x 105 in 1999 indicting a 43% increase. However, analysis by
subarea showed a strong gradient from north to south ranging from 2 x 105 to 1 x 106 (Figure 49). The
dry season median BAFs were significantly lower than the wet season with 3. Ox 105in 1995-96 and
2.0 x 105 in 1999 due to the extremely high concentrations of methylmercury in water. The BAF
gradient was still apparent in the dry season but shifted to the south.
The Florida Fish and Wildlife Conservation Commission has monitored mercury in large-
mouth bass fillets since 1990 showing a 66% decline in mercury concentrations over this period
at a canal location in southern WCA3 (Lange et al. 2000). Fredrick and Spalding (2000) showed
a 50% decline in mercury concentrations in great egret nestling feathers from 1994 to 2000 in
WC A3 colonies. The area of the marsh with >100 ppb total mercury in mosquitofish has re-
mained about the same during the 1995, 1996, and 1999 wet seasons at 60, 59, and 62%, respec-
tively. Most of the decline in mosquitofish mercury concentrations has occurred in these fish with
42
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South Florida Ecosystem Assessment Report
Table 10. Ecosystem dry season median concentrations of total and methylmercury by media.
Parameter 1995-96
Surface Water (ng/L)
HgT 1.96
MeHg 0.578
Ratio MeHg:HgT 0.341
Soil (ug/kg)
HgT 130
MeHg 0.44
Floe (ug/kg)
HgT
MeHg
Periphyton (ug/kg)
HgT 54.73
MeHg 2.24
Mosquitofish (ug/kg)
HgT (Wet + Dry) 163
(100 ppb)
(200 ppb)
68
40
C.I.
N 1999
1.64-2.34 178 3.30
0.573-0.717 177 0.723
0.279-0.399 176 0.217
114-140 207 110
0.33-0.62 187 0.52
171
0.20
50.03-56.09 143 31.64
1.71-2.78 135 1.29
149-180 350 123
% Exceedance
63-73 350 60
% Exceedance
35-45 350 20
C.I.
107-140
52-68
13-26
N % Change
2.44-3.91 50 68
0.458-0.966 50 25
0.170-0.266 50 -36
93-116 112 -15
0.31-0.84 103 18
152-221 49
0.20-1.31 46
25.25-40.3 72 -42
0.884-1.72 73 -42
151 -24
151 -12
151 -50
BAFxlO5 3.0 2.5-3.6 152 2.0 1.1-2.7 39
NS = not significant, CI = 95% confidence interval, N = number, B AF = Bioaccumulation Factor
-34
above 200 ppb whole body concentration in WCA3-SW. Reduction of the maximum mercury concen-
trations in prey fish has apparently been responsible for the downward trends in top predator total
mercury concentrations in this system.
The previous data and observations indicate that wet season changes in mercury concentrations in
water, and prey fish correspond to changes in atmospheric deposition. If deposition declines due to
local emission controls, these changes can probably be detected by the large scale changes in water and
mosquitofish mercury concentrations. With continued local diligence, a management goal of approxi-
mately 100 ppb in prey fish species appears to be practically achievable. Mercury concentrations in
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South Florida Ecosystem Assessment Report
largemouth bass fillets declined to about 650 ppb in 1999 (Lange et al. 2000). It appears that if the
mosquitofish hot spot continues to decline to 100 ppb that the largemouth bass may reach the FDEP
criterion level of 500 ppb. However, to achieve the US EPA (2001) methylmercury human health water
quality criterion of 300 ppb in fish will require that the concentrations in mosquitofish must decline to
approximately 60 ppb across the marsh assuming bioaccumulation increase per trophic level of five
times. To achieve this level may not be possible in this very reactive ecosystem, and may well require
additional, significant reductions in emissions of mercury to the air at all three spatial scales: locally
(within south Florida), regionally (statewide and adj acent states), and internationally. Scientific debate
continues regarding the relative importance to mercury deposition from emissions sources at the three
scales. Currently, controls on waste combustion (important in South Florida) have been implemented,
and EPA is pursuing regulations to reduce mercury from coal fired boilers at electric utilities (important
regionally). To reach the goal of very low deposition may require voluntary efforts beyond regulations,
as well as obtaining international agreements to reduce mercury emissions which can be transported on
a global scale.
RISK ASSESSMENT
Structural equation models were used to estimate the change in fish tissue mercury that might
result from reductions in total mercury, sulfate, total organic carbon, and/or total phosphorus
inputs to the system and subsequent changes in the bioaccumulation of methylmercury within the
ecosystem. These results were then coupled with the ecological risk assessment analyses conducted by
Rumbold (2000) to evaluate any risk reductions that might occur at higher trophic levels within the
South Florida ecosystem. As indicated previously, mercury concentrations in mosquitofish decreased
from 1995 to 1999. More importantly, the greatest decline occurred in mosquitofish with mercury
concentrations exceeding 200 ppb. There was a corresponding decrease in risk to top predators
consuming mosquitofish as a maj or part of the diet of the predator or the prey that were feeding on
mosquitofish and subsequently consumed by the predator. The risk reduction was greatest when
mosquitofish were the maj or portion of the predators diet.
Several uncertainties remain in gaining a complete understanding of the spatial mercury
mass balance across the Everglades ecosystem. There is little doubt that atmospheric wet and dry
deposition accounts for a major part of the input of mercury to the ecosystem, but it is unclear
how much of the atmospheric deposition is re-volatilized. Lindberg et al. (2001) compared the
mercury flux data from open water surface to cattails and sawgrass and found the "transpiration"
of Hg°from these aquatic macrophytes the single largest flux of mercury in the ecosystem. The
summer daytime emission rates from cattails and sawgrass were 31 and 17 ng/m2/hr, respectively
and he reported that incubation studies on soil and lacunal gas both suggested that the source of
mercury flux from vegetation was the soil. If deposition and volatilization/transpiration are
approximately in balance any other source such as stormwater from the EAA or anthropogenic
air emissions could become a net addition and of much more importance than currently appreci-
ated. The relative importance of the soil as a mercury source via transpiration in contrast to the
mercury deposited from the atmosphere to the water column has not been determined.
What are the conditions that lead to mercury methylation and mobilization? Microbial
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degradation or chemical reactions within the aquatic environment have not been thoroughly worked out
to determine the relative flux of soil mercury to the water as opposed to transpiration and deposition
from the atmosphere to the water. The data seem to support that low redox conditions created by high
phosphorus enrichment combined with wet/dry cycles leads to methyl mercury mobilization, however, in
the presence of high sulfate and total organic carbon the amount of methyl mercury which is not bound
and available for bioaccumulation has not been quantified. We think this probably explains why the hot
spot for bioaccumulation is not the same as the site of maximum methyl mercury formation. Unbound
methyl mercury in the water column appears to be most available to bioaccumulation by the foodweb.
The role of sunlight in photoreduction, photooxidation and methyl mercury degradation has not been
quantitatively investigated. The abiotic formation of methyl mercury has received little attention in the
Everglades and may be significant. With the strong north-south chemical gradients much remains to be
developed before a spatial mercury flux model can be developed for the Everglades ecosystem. Im-
proved integration with the numerous process study results could provide a more comprehensive
understanding of this ecosystem.
Synthesis
Although there are differences in constituents, methylmercury concentrations and fish bioac-
cumulation factors among the subareas in the South Florida Everglades ecosystem, there are also
several unifying themes that emerge from analysis and study of the large-scale patterns measured
by the US EPA Region 4 monitoring program when considered in concert with mercury work of
other agencies and scientists:
Hydropattern modifications and the water requirements to cover different marsh areas can
be estimated with a simple surface area-volume relationship. Long and short hydropattern
areas can also be determined using this relationship. The plant species distributions
observed in the study reinforced and supported these hydropatterns. These water changes
from dry to completely flooded are necessary in sustaining a pulsed ecosystem like the
Everglades.
There are significant north to south gradients, from Lake Okeechobee to Florida Bay, in
total phosphorus, total organic carbon, and sulfate in the ecosystem. These gradients
affect eutrophication and mercury contamination throughout the Everglades. These
gradients also are affected by hydropattern modifications. These factors are all interre-
lated.
Total phosphorus (nutrient) concentrations were significantly lower throughout the marsh
in 1999 compared to 1995-96. Continued monitoring will be needed to determine if this
change represents a decreasing trend in total phosphorus concentrations.
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The distribution of different aquatic plant species (i.e., macrophytes) throughout the marsh
provide good indicators of:
hydropattern - water lily (Nymphaea odorata)/purp\e bladderwort (Utricularia
purpured) indicate stable water slough habitat (i.e., long hydroperiod).
low soil phosphorus - spikerush (Eleocharis cellulosd) is found in soils with low
phosphorus concentrations.
high soil phosphorus - cattail (Typha domingensis) is found in soils with high
phosphorus concentrations.
In addition, the change in some plant characteristics also were associated with variations
in soil phosphorus concentrations. Broad leaves and short petioles in arrowhead
(Sagittaria lancifolia) were associated with high soil phosphorus concentrations. Narrow
leaves and long petioles in arrowhead were associated with deep water and low soil
phosphorus concentrations.
There is a "hot spot" of mercury contamination in mosquitofish located in the southwestern part
of Water Conservation Area 3 south of Alligator Alley. The area north of Alligator Alley has
high methylmercury concentrations in the water and soil, but low mercury concentrations in the
mosquitofish. The area south of Tamiami Trail in Everglades National Park has low methylmer-
cury concentrations in the water and soil, but relatively high mercury concentrations in the
mosquitofish.
Mercury concentrations in the water and in mosquitofish were significantly lower
throughout the marsh in 1999 compared to 1995-96. Water and mosquitofish mercury
concentrations corresponded to changes in atmospheric wet deposition.
Both top-down and bottom-up controls in the ecosystem are needed to explain the effects
of nutrient loading and mercury contamination. High chemical (nutrient) concentrations
exert a bottom-up control on ecosystem responses in the northern area. Biological interac-
tions exert a top-down control on ecosystem responses in the low nutrient concentration
southern area. The mercury "hot spot" is in the transition zone between these two areas
where both bottom-up and top-down interactions occur.
POLICY AND MANAGEMENT IMPLICATIONS
Seven management and policy-relevant questions guided this proj ect. One of the primary obj ectives
of this proj ect was to provide scientifically sound information to answer these questions and contribute
to management decisions on the South Florida Everglades ecosystem. This is an interim assessment so
not all of these questions can be fully answered, but at least partial answers can be provided for each
question. Based on the findings noted above, the management implications are:
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Wetlands, by definition, are water driven systems and the water regime drives all other interactions in
the marsh. Modifying the water regime will affect everything else in the Everglades ecosystem. Fluc-
tuating water levels are an integral part of the pulsed Everglades ecosystem. These fluctuations need
to be maintained and managed.
Distributions of plant species such as water lily, spikerush, and cattail, and plant characteristics such
as arrowhead leaf widths are good indicators for assessing the success of the restoration effort
because they reflect hydropattern modifications and changes in soil phosphorus concentrations.
Mosquitofish are good indicators for assessing change in mercury contamination because they are
found throughout the marsh, have a short life span, and respond quickly to changes in mercury
concentrations. The change in measured atmospheric wet deposition might correspond with de-
creased mercury emissions, but it also could be a result of less rainfall in 1996 and 1999 compared
to 1995.
Restoration efforts related to managing the wa-
ter regime, controlling nutrient loading, minimiz-
ing habitat alteration, and reducing mercury con-
tamination must proceed together. These fac-
tors are all interrelated and must not be man-
aged independently (Figure 54).
Consistent, long-term monitoring is the only way
of evaluating the success of the restoration ef-
fort. It appears the nutrient management prac-
tices and mercury emission reductions have al-
ready contributed to a decrease in phosphorus
concentrations and mercury contamination. But,
only continued diagnostic monitoring will tell if
these changes represent a sustained decreasing
trend. Statistical survey monitoring networks
complement on-going monitoring programs and
should be integrated into the Comprehensive Ev-
erglades Restoration Plan.
Eutrophication
Endangered
Species
Figure 54. Restoration issues are highly interdependent
and must be addressed together.
THE FUTURE
US EPA Region 4 completed the baseline sampling cycles in canals (1993-95) and marshes from
1995 through 1996. That information was analyzed and reported in 1998 followed by adjustments in
the monitoring network to emphasize the marsh. The phase n 1999 marsh monitoring effort was carried
out during comparative dry and wet seasons to begin the trend monitoring assessment. This information
has been used not only to answer the seven policy relevant questions identified for mercury, but also to
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answer similar questions related to the other environmental problems threatening the Everglades ecosys-
tem. For example, plant communities were monitored using both remote sensing and field techniques
during Phase n to determine not only their role in mercury methylation, but also their response to total
phosphorus changes and hydroperiod. This information can be used to evaluate the effectiveness of the
BMPs and Stormwater Treatment Areas in reducing phosphorus loading to the ecosystem. The com-
prehensive sampling design of this proj ect has allowed an integration of interacting variables across the
entire ecosystem that has not been duplicated by any other proj ect. Additional monitoring is essential to
determine the variability in the seasonal and annual patterns, interactions of controlling variables and the
effect of this variability on future management decisions. Continued monitoring will increase the ability to
make statements about subareas in the Everglades ecosystem under different water management
regimes, and will minimize the time required to detect changes from adaptive management actions
because it will take advantage of the information already collected. Monitoring and iterative comparative
ecological risk assessments must continue into the future to help improve our scientific understanding of
the interactions among constituents and management actions.
This monitoring is beginning to provide information on emerging trends in environmental problems
and will permit an evaluation of the effectiveness of any policy and management strategy implemented to
fix these problems. Consistent, long-term monitoring is the only approach that can be used to assess the
success and performance of management practices.
The US EPA, a member of the South Florida Ecosystem Restoration Task Force, is contribut-
ing to other studies being conducted as part of the restoration effort including the on-going
mercury biogeochemistry and bioaccumulation process studies being conducted by the USGS.
For example, the Region 4 Ecosystem Assessment Project has identified critical study areas in
South Florida where process research is needed to better understand the interrelationships among
hydropattern modifications, nutrient additions, and mercury cycling in the Everglades ecosystem.
This project is also providing complementary monitoring information for simultaneous studies of
atmospheric mercury emissions, and subsequent mercury transport and deposition in South
Florida. In addition, the US EPA is working with the SFWMD, the US National Park Service, the
US Army Corps of Engineers, and Florida Department of Environmental Protection in order to
better understand the Everglades so it can be protected and restored.
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APPENDIX A
Findings and Management Implications
HYDROPERIOD MANAGEMENT-
FINDINGS
The surface water coverage in the Everglades during the six synoptic surveys ranged from 44 to
100% considering both dry and wet seasons.
A surface area to volume curve was calculated, which indicated the long hydroperiod marsh
covered about 4,200 km2.
Inundating the short hydroperiod marsh from 4,200 km2 to 5,500 km2 (an increase in area of
1,300 km2) requires twice the water volume to inundate this area compared to the volume of
water covering the long hydroperiod marsh.
The shortest hydroperiod marsh is located in northwestern WCA3-N and Taylor Slough.
The area of ponding estimated during the 1999 dry season indicated that if ponding of water
north of the Tamiami Trail roadway were eliminated, the wet prairie/slough habitat in the marsh
would be reduced by about 400 km2.
Total and methylmercury, total phosphorus, total organic carbon, and sulfate concentrations
increased during the dry season.
North to south gradients in this system are apparent in almost every water and soil quality
parameter. Their characteristic footprints were identified in this study.
Dry down of the soil appears to oxidize sulfide to sulfate, which then stimulates mercury methy-
lation by sulfur reducing bacteria when the area re-floods.
MANAGEMENT IMPLICATIONS
Water management changes to restore sheet flow in this system will require significant volumes
of water based on the surface area to volume curve to achieve relatively small surface water
coverage of the ecosystem in the dry season.
Annual drought cycles are a natural occurrence and some will be more severe than others. Large
volumes of water continuously supplied will be required to make ecologically significant dif-
ferences in surface water coverage when system storage capacity is low.
Ponding in the system increases the wet prairie/slough refugia where aquatic organisms remain
during droughts. Careful consideration should be given before any actions to reduce these areas
are carried out.
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There may be insufficient volume to reestablish sheet flow in chronically drought prone short
hydroperiod areas of the system. This does not mean that additional flow in central and eastern
WCA3-N would not begin reversing the soil loss which has occurred there over the last 50 years.
However, the build up of peat soil will occur most rapidly if continuous surface water coverage
is maintained over long periods of time.
The water and soil quality gradients identified in this study must be considered before plans are
implemented to divert water from contaminated areas farther downstream in this system which
could increase the area of impact across the ecosystem.
There are macrophyte and periphyton community indicators of hydropattern modifications de-
veloped in this study that can be used to assess the effectiveness of future restoration efforts
prior to and following implementation.
NUTRIENT LOADING-
FINDINGS
The median concentrations of total phosphorus in water decreased from 1995-96 to 1999, how-
ever, the change was not statistically significant across the ecosystem. The greatest change
among the subareas was found in WCA2 and WCA3-N.
Maximum water total phosphorus concentrations occurred in WCA3-N where the median TP
concentrations declined from 16 to 11.4 ppb over the intervening three year period.
Nutrient loading appeared to increase across the northwestern portions of WCA3-N and
WCA3-SW in 1999, even though it decreased in other subareas.
The increased water TP concentrations in WCA3-SE and WCA3-SW during the 1999 dry sea-
son probably resulted from phosphorus transport from WCA3-N because a wildfire that oc-
curred in WCA-3N two weeks prior to sampling transformed plants and peat into phosphorus-
rich ash.
The extent of marsh area with TP in water <10 ppb has continued to increase over time, from
41% in 1995 to 78% in 1996 and 87% in 1999.
The extent of marsh area with TP in water <15 ppb has likewise continued to improve from
65% in 1995 to 87% and 93% in 1996, and 1999, respectively.
The extent of marsh area with TP in water >50 ppb remained at 2%.
Median TP concentrations in soil decreased from 350 mg/kg in 1995-96 to 250 mg/kg in 1999.
Median wet season soil TP concentrations were lower in Loxahatchee, WCA3-N, WCA3-SE,
WCA3-SW and Shark Slough in 1999 versus 1995-96 while no change was evident in WCA2.
The lowest median wet season soil TP concentrations consistently occurred in Taylor Slough.
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Median wet season soil TP concentrations in WCA2 and WCA3-N were 350 and 400 mg/kg,
respectively. The invasion of cattails is most prevalent in these subareas.
Soil TP concentrations greater than 400 mg/kg occur along the EAA border of WCA2 and
WCA3-N.
Future changes in TP concentrations in water and soil require further monitoring to verify trends.
MANAGEMENT IMPLICATIONS
The phosphorus control program, principally the Best Management Practices which have been
in place since 1995, may be reducing the loading to the ecosystem.
The decline in soil phosphorus concentrations in the less saturated downstream subareas is the
area where an initial response to decreased loading is expected. The upstream heavily impacted
subareas would be the last subareas expected to respond to decreased phosphorus loading.
The invasion of the cattail community correlates with the high soil phosphorus in WCA2 and
WCA3-N.
Monitoring using the same methodology needs to continue in order to establish trends used to
evaluate the effectiveness of the phosphorus control program.
HABITAT MANAGEMENT-
FINDINGS
Remote Vegetation Assessment
Remote sensing and GIS techniques were successfully used to assess vegetation patterns over
the entire Everglades ecosystem.
Areal summary statistics indicated spatial trends such as decreasing cattail coverage ranging
from 12-17% in the north to 0.4% in the south.
Plant communities identified in 1 km2 plots, overlaid on the randomly selected sampling sites,
adequately represented the vegetation cover in the Everglades. Comparison of remotely sensed
estimates with existing database for ENP-Shark Slough and WCA3-N found the average differ-
ence in vegetation type percent cover estimates was 1.5% in ENP-SRS and 0.4% in WCA3-N.
This demonstrated the data compatibility among USNPS and SFWMD vegetation mapping
efforts.
This effort establishes a baseline of conditions existing in 1994/1995 and a quantitative meth-
odology for efficiently monitoring future vegetation patterns and assessing changes in the Ever-
glades ecosystem over space and time.
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Macrophyte Distributions and Morphology
Because this study provides a quantitative evaluation of marsh macrophyte community types
and their distributions across the Everglades ecosystem, it provides a background for evaluating
community change during and after restoration.
There are four maj or communities that are found across the entire ecosystem: sawgrass, waterlily-
purple bladderwort, spikerush, and cattail. These communities differ in their hydroperiod/water
depth, soil type, and nutrient requirements. The dominant species within each community have
different tolerances for soil TP.
Sawgrass is the only community that occurs across the entire ecosystem; the other communities
are more localized in their distributions.
Although sawgrass was present throughout the Everglades, sawgrass morphology and density
was correlated with changes in soil type. Controls on variations in density and morphology, as
well as patchiness, represent areas for future research.
Some communities that have been noted to be prominent historically did not appear as distinct
communities in our analysis. For example, the Rhynchospora tracyi (beakrush) community did
not form a distinct community in our clustering. These differences could represent a historical
change in community composition in the ecosystem and/or could be a result of the quantitative
nature of our analysis.
Sagittaria lancifolia is found across a broad range of soil TP and soil organic content in the
Everglades. We have shown in a parallel study that S. lancifolia leaf morphology provides an
indication of soil nutrient level and water depth. Plants with broader laminae and shorter peti-
oles are found in sites with higher nutrients, while plants with longer petioles are found in
deeper sites with lower nutrients.
The distribution of the major macrophyte communities can be used to monitor the effects of
restoration actions.
Periphyton Distributions
This study demonstrated that diatom community metrics are associated with specific environ-
mental changes and can be a useful tool in environmental monitoring. Diatom community
metrics should be integrated into Everglades assessment protocols for the following reasons:
Diatoms are ubiquitous in the Everglades yet species have non-random distributions. Baseline
distribution data is now available for use in detecting environmental change.
Diatoms are sensitive to environmental variation. Assemblage and species responses to spatial
variation in ion content, nutrient availability and hydroperiod have been identified. Temporal
models can be built from these spatially explicit data to predict community change under differ-
ent management scenarios with a measurable degree of accuracy.
Diatoms respond quickly to environmental change. Unlike many other biotic indicators, changes
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in diatom assemblage composition can happen over very short time scales (days to weeks) and,
therefore, can provide sensitive early warning signals of impending ecosystem change.
The taxonomic reference base generated from this survey will increase efficiency of future
diatom inventories. Many surveys exclude diatom analyses because of perceived technical dif-
ficulties in collection and assessment. Currently available taxonomic databases should substan-
tially reduce allocation of time and resources to identification. There are fewer species of dia-
toms in the Everglades than vascular plants. Given currently available reference materials, lack
of technical expertise in this field is no longer a viable argument against diatom assessments,
especially given their potential in environmental monitoring.
MANAGEMENT IMPLICATIONS
A baseline of vegetative conditions using remote sensing, ground transect macrophyte commu-
nity sampling, macrophyte morphology and periphyton communities has been established for
monitoring and assessing future changes of the Everglades marsh habitat.
The mosaic of plant communities across the ecosystem integrates the natural and the anthropo-
genic impacts imposed on this ecosystem.
Changes in plant community response are of critical importance in evaluating the effectiveness
of restoration practices.
Indicator macrophyte and periphyton species have been identified which respond to multiple
key interacting variables that can be used in assessing change.
Each habitat methodology applied in this study has developed a unique and cost effective data
set needed to track future habitat responses across the entire ecosystem.
MERCURY CONTAMINATION
HOW BIG IS THE PROBLEM (MAGNITUDE)?
FINDINGS
Over 60% of the marsh mosquitofish exceeded the USFWS proposed predator protection crite-
ria for mercury.
Less than 20% of the canal mosquitofish exceeded the USFWS proposed predator protection
criteria for mercury.
About 98% of the sampling sites had total mercury concentrations less than the mercury water
quality criteria of 12 ppt (parts per trillion).
Methylmercury concentrations in the water rarely exceeded 1 ppt, yet mercury concentrations
in mosquitofish and largemouth bass exceeded 500 ppb and 1 ppm, respectively. This is a
biomagnification factor of 500,000 to 1,000,000 times the methylmercury concentration in the
water.
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MANAGEMENT IMPLICATIONS
The methylmercury criteria based on mercury concentrations in fish tissue (300 ppb) is appro-
priate because it considers bioaccumulation and biomagnification through the food chain.
WHAT IS THE EXTENT OF THE PROBLEM (EXTENT)?
FINDINGS
There is a hot spot in Water Conservation Area 3 A, just below Alligator Alley, where methylm-
ercury concentrations are highest in water, algae, fish, and wading birds. This hot spot has an
area of over 200 square miles.
There is an area that extends from this hot spot below Alligator Alley down through Shark River
Slough in Everglades National Park in which fish and wading birds also have elevated mercury
concentrations.
MANAGEMENT IMPLICATIONS
By both magnitude and extent, fish, alligators, wading birds, the Florida panther, and other
organisms in the marsh have greater mercury contamination than organisms in the canals. Fo-
cus management actions on the marsh.
The mercury hot spot corresponds with an area in which wading birds breed and feed.
IS IT GETTING BETTER OR WORSE OVER TIME (TRENDS)?
FINDINGS
A solid baseline (1993-1996) has been established to evaluate future trends. The comparative
comprehensive monitoring in 1999 has provided the opportunity to begin trend assessment
which can be compared to other more frequent trend monitoring in top predators to determine
the status of mercury contamination in the Everglades ecosystem through time.
During the past 10 years there has been an estimated 95% decrease in local atmospheric emis-
sions in South Florida. There also has been a corresponding reduction in total mercury concen-
trations in surface water and declines in prey fish, largemouth bass and great egret chick feath-
ers.
Total mercury concentrations in Everglades prey fish greater than 200 ppb declined from a 40%
exceedance in 1995-96 to a 20% exceedance in 1999. This indicates an approximate reduction
of 50% in mercury in fish with the highest concentrations.
Although Everglades largemouth bass monitoring by FloridaFish and Wildlife Conservation Commis-
sion (FFWCC) indicates a 75% decline in total mercury through 2001 in fillets, these fish still exceed
the Florida fish consumption advisory of 0.5 ppm.
Monitoring of Everglades great egret chick feathers by University of Florida scientists from 1994-
2000 has shown a 75% decline in mercury through 2001.
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MANAGEMENT IMPLICATIONS
Maintain the US EPA Region 4 monitoring program with seasonal sampling, but emphasize the
marsh sites compared to the canals. Establish trend sites.
Continue monitoring the great egret check feathers, largemouth bass, and mosquitofish to as-
sess trends.
The mercury problem did not occur overnight and it will not be corrected overnight. Long-term
management practices will be required to fix the mercury problem.
Consistent long-term monitoring is the only approach for assessing the effectiveness of man-
agement and restoration practices to control eutrophication, restore natural hydropattern changes,
and eliminate mercury contamination.
WHAT IS CAUSING THE PROBLEM (CAUSATION)
FINDINGS
The exact causes of mercury contamination in the South Florida ecosystem are unknown. How-
ever, it is likely the interaction of total phosphorus, TOC, and sulfate loading from the EAA,
water depth, organic matter sources and production, food chain links and continued input of
atmospheric mercury to the ecosystem control mercury contamination.
The large scale spatial patterns of these environmental conditions have been established through
the US EPA Region 4 program, FFWCC fish sampling, and NPS/FDEP wading bird sampling
programs.
Processes responsible for these large-scale patterns are being studied through the USGS ACME
program, US EPA and FDEP atmospheric deposition studies.
MANAGEMENT IMPLICATIONS
There is no "magic bullet" that can be implemented to control one factor and eliminate mercury
contamination.
Factors controlling mercury should be determined in the hot spot and compared with factors in
other areas without extensive mercury contamination to develop effective management strate-
gies.
Controlling EAA loading of phosphorus, sulfate, and TOC concentrations might also reduce the
mercury problem by reducing constituents that are influencing mercury contamination.
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WHAT ARE THE SOURCES OF THE PROBLEM (SOURCES)?
FINDINGS
Annual atmospheric mercury loading is from 35 to 70 times greater than mercury loading from
the Everglades Agricultural Area.
An EPA ORD study indicated municipal and medical waste incineration emissions had higher
mercury concentrations than emissions from a coal-fired cement kiln.
MANAGEMENT IMPLICATIONS
Local emissions are a significant source of inorganic mercury.
Mercury emissions controls would reduce mercury loadings to the Everglades ecosystem.
However, waste disposal is a multimedia problem. Controlling mercury emissions might create
other problems such as disposal of solid waste, including not only the waste, but also the mer-
cury removed from the emissions.
WHAT IS THE RISK TO THE ECOSYSTEM (RISKS)?
FINDINGS
Mercury methylation is also controlled or influenced by hydropattern, habitat alteration, and
food web complexity.
Over 60% of the marsh area has mosquitofish with mercury concentrations that exceed the
proposed predator protection level.
Mercury concentrations during the early-1990s were high, near toxic levels in wading bird
livers and other organs but have been declining in largemouth bass and wading birds over the
past 8 years.
There is a 200 square mile hot spot where mercury contamination in biota is greatest, which
corresponds with an area of wading bird rookeries.
MANAGEMENT IMPLICATIONS
Biological species higher in the aquatic food chain are at increased risk from mercury contami-
nation, even though the effects are subtle. Because mercury bioaccumulates, the risks increase
over time. The longer management is delayed, the greater the risks.
However, the greatest threat to the Everglades ecosystem is to assume the environmental prob-
lems are independent.
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WHAT CAN WE DO ABOUT THE PROBLEM (MANAGEMENT)?
FINDINGS
The SFWMD Everglades Nutrient Removal project removes nutrients and total and methylm-
ercury from the inflow to the Project.
Atmospheric mercury loading to the Everglades is much greater than mercury loading from
EAA stormwater.
MANAGEMENT IMPLICATIONS
Controlling nutrient loading, hydropattern and habitat type should contribute to reducing the
mercury contamination problem.
Controlling local atmospheric mercury emissions has apparently reduced the mercury load to
the South Florida Everglades ecosystem and the concentration in biota. However, there has
been no apparent change in mercury deposition over the past 8 years, suggesting the greatest
change in mercury deposition occurred before monitoring began and there is a time lag in the
biological response.
Emission controls have multimedia impacts and must be assessed as a multimedia issue, not as
a single media issue.
If the nutrients, sulfate and TOC concentration gradients, were decreased further and moved
upstream, the zone of impact where fish mercury is high could be reduced and might be outside
the areas where wading birds concentrate for breeding, feeding, and with reduced emissions,
the overall fish concentrations might be lower.
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