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 Florida—nutrient loading, hydropattern modifi-
cation (Figure 8), habitat alteration—contribute 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-
                                              26.4-
                                            in
                                            o>
                                            £
                                            DJ
                                            o>
                                            T3
                                            ~a
                                            E
                                            Q
                                            D
26.2-
                                              26.0-
                                              25.8-
                                              25.6-
                                              25.4-
                                                     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 -4—Bottom 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.

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                                                       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-
                                                                                                    31

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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
areas—one 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.
36

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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.
                                                                                               39

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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
                                                                                                43

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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

44

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                                                     South Florida Ecosystem Assessment Report
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.
                                                                                             45

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              South Florida Ecosystem Assessment Report
             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:
46

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                                                      South Florida Ecosystem Assessment Report
     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
                                                                                               47

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               South Florida Ecosystem Assessment Report
       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.
48

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                                                  South Florida Ecosystem Assessment Report
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      Odum, E.P. 1971. Fundamentals of Ecology. W.B. Saunders Company. P. 268ff.

      Olsen, A.R., J. Sedransk, D. Edwards, C.A. Gotway,  and W. Ligget. 1999. Statistical Issues for
      Monitoring Ecological and Natural Resources in the United States. Environmental Monitoring
      and Assessment, vol. 54, p. 1-45.

      Orem, W.H., A.L. Bates, H.E. Lerch, M. Corum, and A. Boylan. 1999. Sulfur Contamination in
      the Everglades and its Relation to Mercury Methylation. US Geological Survey Program on the
      South Florida Ecosystem. Proceedings of South Florida Restoration Science Forum, May 17-19,
      1999, Boca Raton, FL.

      Orem, W.H., H.E. Lerch, A.L. Bates, M. Corum, M. Chrisinger, and R.A. Zielinski. 2000.
      Nutrient and Sulfur Contamination in the South Florida Ecosystem: Synopsis of Phase I Studies
      and Plans for Phase II Studies. Greater Everglades Ecosystem Restoration Task Force and Work-
      ing Group, Naples, FL.

      Reddy, M.M.,  G.R. Aiken, and P.F. Shuster. 1999. Mercury-Dissolved Organic Carbon Interac-
      tions in the Florida Everglades: A Field and Laboratory Investigation.  (Abstract) US Geological
      Survey Program  on the South Florida Ecosystem, Proceedings of South Florida Restoration
      Science Forum, May 17-19, 1999, Boca Raton, FL.

      Rumbold, D. 2000. Assessment of Methylmercury Risk to Three Species of Wading Birds  in the
      Florida Everglades. (Abstract) Greater Everglades Ecosystem Restoration Science Conference.
      Hosted by: The Science Coordination Team: A Committee of the South Florida Ecosystem
      Restoration Task Force and Working Group. Naples, FL.

      Rutchey, K. and L. Vilchek. 1999. Air Photo Interpretation and Satellite Imagery Analysis
      Techniques for Mapping Cattail Coverage in a Northern Everglades Impoundment. Photogram-
      metric Engineering and Remote Sensing, 65(2):  185-191.

      Scheldt, D., QJ.  Stober, R. Jones, and K.W. Thornton. 2000. South Florida Ecosystem  Assess-
      ment: Water Management, Soil Loss, Eutrophication and Habitat. EPA 904-R-00-003. USEPA
      Region 4 Science and Ecosystem Support Division and Water Management Division; Office of
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                                                   South Florida Ecosystem Assessment Report
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              South Florida Ecosystem Assessment Report
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       Office of Water, US Environmental Protection Agency, Washington, DC.

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       eutrophication. Mem. 1st. Ital. Idrobiol. 33: 53-83.

       Welch, R. and M. Madden. 1999. Vegetation Map and Digital Database of South Florida Na-
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       US Dept of Interior, National Park Service, Cooperative Agreement 5280-4-9006, Center for
       Remote Sensing and Mapping Science, University of Georgia, Athens, GA. 43 pp.
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                                                South Florida Ecosystem Assessment Report
                             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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              South Florida Ecosystem Assessment Report
       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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              South Florida Ecosystem Assessment Report
      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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