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# The Use of Conceptual Ecological Landscape Models as Planning Tools for the South Florida Ecosystem Restoration

Programs

Edited by:

John C. Ogden and Steven M. Davis Senior Ecologists, Executive Office

South Florida Water Management District

West Palm Beach, Florida June 29, 1999

## EXECUTIVE SUMMARY

An Applied Science Strategy has been developed by south Florida scientists as a process for organizing current scientific understandings of wetland ecosystems into formats that can effectively support the emerging ecosystem restoration programs. A new and more structured science application strategy was needed in south Florida because of the substantially greater complexity and scales of ecological issues associated with the regional focus of the restoration goals. This science strategy is being used to direct much of the planning and evaluation of the C&SF Restudy Program.

An essential component of the science strategy is a set of conceptual ecological models developed at landscape scales for the major wetland systems in south Florida. This report explains the development and application of these models and describes eight of the models currently in use. The current set of models are for Lake Okeechobee, the Caloosahatchee and St. Lucie estuaries, the Everglades ridge and slough landscape, the southern Everglades marl prairies and rocky glades, the southern Everglades mangrove estuaries, Big Cypress basin, Biscayne Bay, and Florida Bay. A ninth conceptual model is being developed for the Total System.

The conceptual model present the consensus opinion of south Florida scientists and land managers on the causal assumptions that best explain how the wetlands have been altered by human influences. The Model also identify the ecological elements that best indicate the health of the system. The C&SF Restudy planning team is using the information in these models to define the specific ecological problems that must be resolved and to determine what changes must occur in the natural system for the Comprehensive Plan to be successful. A Set of performance measures and restoration targets based on the conceptual models will lay the foundation for the design of a regionally comprehensive monitoring program and for the institution of an adaptive assessment strategy for reaching long-term restoration goals.TABLE OF CONTENTS

I. OVERVIEW OF THE D EVELOPMENT AND APPLICATION OF THE CONCEPTUAL MODELS

................................ ................................ ............................... 1

A. INTRODUCTION

................................ ................................ ................................ ................................ ........... 1

B. METHODS

................................ ................................ ................................ ................................ ....................... 2

C. DISCUSSION

................................ ................................ ................................ ................................ ................... 4

D. CONCEPTUAL MODELS IN SOUTH FLORIDA

................................ ................................ ...................... 5

E. ADAPTIVE ASSESSMENT

................................ ................................ ................................ ........................... 7

F. FUTURE TASKS

................................ ................................ ................................ ................................ ............. 8

G. REFERENCES

................................ ................................ ................................ ................................ ............... 15

II. LAKE OKEECHOBEE CONCEPTUAL MODEL

................................ ..................... 16

A. PREPARERS

................................ ................................ ................................ ................................ ................. 16

B. INTRODUCTION

................................ ................................ ................................ ................................ ......... 16

C. MODEL STRUCTURE

................................ ................................ ................................ ................................ . 16

D. EXTERNAL DRIVERS AND STRESSORS

................................ ................................ ............................... 17

E. ECOLOGICAL ATTRIBUTES

................................ ................................ ................................ .................. 18

F. QUANTITATIVE MEASURES

................................ ................................ ................................ ................... 19

G. ECOSYSTEM EFFECTS

................................ ................................ ................................ ............................. 20

H. H YDROLOGIC PERFORMANCE MEASURES

................................ ................................ ...................... 24

I. REFERENCES

................................ ................................ ................................ ................................ ............... 29

III. ST. LUCIE AND C ALOOSAHATCHEE CONCEPTUAL MODEL

........................ 33

A. PREPARERS

................................ ................................ ................................ ................................ ................. 33

B. ABSTRACT

................................ ................................ ................................ ................................ .................... 33

C. INTRODUCTION

................................ ................................ ................................ ................................ ......... 33

D. ESTUARY MODEL STRUCTURE

................................ ................................ ................................ ............. 34

E. ECOLOGICAL & SOCIETAL ATTRIBUTES

................................ ................................ ......................... 34F. LINKS FROM STRESSORS TO ATTRIBUTES

................................ ................................ ...................... 35

G. SUMMARY

................................ ................................ ................................ ................................ .................... 37

H. REFERENCE

................................ ................................ ................................ ................................ ................. 40

IV. BIG CYPRESS REGI ONAL ECOSYSTEM CONCEPTUAL MODEL

.................. 41

A. PREPARER

................................ ................................ ................................ ................................ .................... 41

B. INTRODUCTI ON

................................ ................................ ................................ ................................ ......... 41

C. ECOLOGICAL STRESSORS

................................ ................................ ................................ ...................... 42

D. ECOLOGICAL ATTRIBUTES AND MEASURES

................................ ................................ ................... 44

E. HYDROLOGIC PERFORMANCE MEASURES FOR RESTORATION

................................ .............. 48

F. REFER ENCES

................................ ................................ ................................ ................................ ............... 52

V. EVERGLADES RIDGE AND SLOUGH CONCEPTUAL MODEL

........................... 57

A. PREPARER

................................ ................................ ................................ ................................ .................... 57

B. INTRODUCTION

................................ ................................ ................................ ................................ ......... 57

C. THE SOCIETAL DRIVERS, ECOLOGICAL STRESS ORS, AND ECOLOGICAL EFFECTS

......... 57

D. CRITICAL ECOLOGICAL PATHWAYS

................................ ................................ ................................ . 60

E. ECOLOGICAL ATTRIBUTES AND MEASURES

................................ ................................ ................... 61

F. HYDROLOGICAL PERFORMANCE MEASURES

................................ ................................ ................ 62

G. REFERENCES

................................ ................................ ................................ ................................ ............... 66

VI. MARL PRAIRIE/ROC KY GLADES CONCEPTUAL MODEL

.............................. 71

A. PREPARER

................................ ................................ ................................ ................................ .................... 71

B. INTRODUCTION

................................ ................................ ................................ ................................ ......... 71

C. EXTERNAL DRIVERS AND ECOLOGICAL STRESSORS

................................ ................................ .. 71

D. ECOLOGICAL EFFECTS OF WATER MANAGEMENT: CRITICAL LINKAGES BETWEEN STRESSORS AND ATTRIBUTES

................................ ................................ ................................ .......................... 74

E. ECOLOGICAL ATTRIBUTES AND MEASURES

................................ ................................ .................. 75

F. HYDROLOGIC PERFORMANCE MEASURES FOR RESTORATION

................................ .............. 80

G. REFERENCES

................................ ................................ ................................ ................................ ............... 84VII. MANGROVE ESTUAR Y TRANSITION CONCEPTUAL MODEL

........................ 89

A. PREPARER

................................ ................................ ................................ ................................ .................... 89

B. INTRODUCTION

................................ ................................ ................................ ................................ ......... 89

C. EXTERNAL DRIVERS AND ECOLOGICAL STRESSORS

................................ ................................ . 89

D. ECOLOGICAL EFFECTS: CRITICAL LINKAGES BETWEEN STRESSORS AND ECOLOGICAL ATTRIBUTES

................................ ................................ ................................ ................................ ............................ 90

E. ECOLOG ICAL ATTRIBUTES AND MEASURES

................................ ................................ ................... 90

F. HYDROLOGIC PERFORMANCE MEASURES FOR RESTORATION

................................ .............. 93

G. MOVING TARGET

................................ ................................ ................................ ................................ ...... 95

H. LITERATURE CITED

................................ ................................ ................................ ................................ . 99

VIII. B ISCAYNE BAY CONCEPTUAL ECOLOGICAL MODEL

................................ 103

A. PREPARERS

................................ ................................ ................................ ................................ ............... 103

B. INTRODUCTION

................................ ................................ ................................ ................................ ....... 103

C. DRIVERS AND STESSORS

................................ ................................ ................................ ....................... 104

D. ECOLOGICAL EFFECTS

................................ ................................ ................................ ......................... 105

E. ECOLOGICAL ATTRIBUTES AND MEASURES

................................ ................................ ................. 107

F. REFERENCES

................................ ................................ ................................ ................................ ............. 110

IX. FLORIDA BAY CONC EPTUAL MODEL

................................ ........................... 117

A. PREPARER

................................ ................................ ................................ ................................ .................. 117

B. INTRODUCTION

................................ ................................ ................................ ................................ ....... 117

C. EXTERNAL DRIVERS AND ECOLOGICAL STRESSORS

................................ ................................ 118

D. ESSENTIAL ECOSYSTEM ATTRIBUTES AND LINKS TO STRESSORS

................................ ....... 121

E. MEASURES

................................ ................................ ................................ ................................ ................. 125

F. REFERENCES

................................ ................................ ................................ ................................ ............. 129

### I. OVERVIEW OF THE DEVELOPMENT AND APPLICATION OF THE

CONCEPTUAL MODELS

John C. Ogden, South Florida Water Management District, West Palm Beach, Florida.

A. INTRODUCTION

The Central and South Florida “ Restudy ” Project team and the Science Coordination Team of the South Florida Ecosystem Restoration Working Group have adopted the “ Applied Science Strategy ” as a process for linking the sciences and management during the planning and evaluation of the south Florida ecosystem restoration programs (SCT 1997, Ogden et al. 1997; Figure 1). The creation of a science application strategy was motivated by the need for a better focused process for organizing and converting large amounts of existing technical information into planning and evaluation tools that would directly support the restoration programs. Some sort of organizing process is clearly required where restoration planning occurs on such large scales, where information from many disciplines is widely scattered in time and place, where focused efforts are needed in order to fill the gaps in our information base with “ best professional opinion, ” and where a large degree of consensus regarding the major cause and effect relationships is necessary. To be successful, it was felt that this strategy must, (1) lay out a scientifically reviewed sequence of steps and tasks for converting research and modeling results into planning objectives, performance measures and evaluation protocols, (2) serve as a strong catalyst for promoting consensus among scientists and managers regarding the nature of the principle resource issues, and the probable routes for resolving these issues, and (3) be a process that can contribute to the objectives and needs of both the scientific and management communities in the regional restoration programs. The Applied Science Strategy is a total systems and multi-disciplinary process for determining the most appropriate restoration targets, and the best measures for each of these targets, during and following the implementation of the restoration programs. These tasks are prerequisite to the successful application of “ adaptive assessment ” during the implementation of the restoration programs.

An essential step in the Applied Science Strategy is the creation of a set of conceptual ecological models of the major wetland physiographic regions in south Florida. These simple, non-quantitative models are an effective means for developing a consensus regarding a set of causal hypotheses, which explain the affects that the major anthropogenic stressors have on the wetland ecosystems. Each model identifies the attributes in the natural systems that are the best indicators of the changes that have occurred as a result of the stressors. Each model also delineates the ecological linkages between the stressors and the attributes and the most appropriate measures for each of the attributes. The2

development of a consensus regarding the components and linkages in the conceptual models is the first step in the process of reaching agreement on specific hydrological, ecological, and biological measures of restoration success, and for designing a regional, performance-based ecological monitoring program. Conceptual models have been widely used for similar purposes in other regions of North America (e.g., pp. 31-38 in Gentile 1996; also see Rosen et al. 1995).

This report presents the schematic and narrative descriptions for eight conceptual ecological models that have been used by the C&SF Restudy team. These eight models provide a basis for developing performance measures for evaluating alternative restoration plans, for designing a performance-based monitoring program, and for adaptive assessment of the south Florida ecosystem restoration programs. The eight models are for Lake Okeechobee, the Caloosahatchee and St. Lucie estuaries (northern estuaries), the ridge and slough Everglades, the Big Cypress basin, the southern Everglades marl prairies, the southern Shark Slough and Florida Bay mangrove estuaries (southern estuaries), Biscayne Bay, and Florida Bay. A ninth conceptual for the Total System is being developed and will be reported soon (Buckingham and Poole, in prep).

B. METHODS

The set of conceptual models was initially developed and reviewed by over 100 scientists and resource managers who participated in a concentrated program of workshops between October 1996 and July 1997. The list of participating scientists and managers and a listing of the models that each participant helped to develop are presented in Table 1. These workshops were open to all interested participants. Special efforts were made to invite the field scientists in south Florida who have had considerable hands-on research experience in these landscapes, and therefore were well qualified to bring knowledgeable professional opinions on these systems to the modeling discussions. The models were developed at landscape scales (Figure 2).

The initial steps in the development of each model were to use the informal format of the workshops to identify and discuss the causal hypotheses which best explain the major anthropogenically driven alterations in each landscape. From these discussions, the participants created lists of the appropriate stressors, ecological effects, and attributes (indicators) in each landscape. The objective was to identify the physical and biological components and linkages in each landscape which best characterized the changes explained by the hypotheses. Preparers for each model used the hypotheses and lists of components to lay out an initial draft of the model and prepare a supporting narrative document to explain the organization of the model and the supporting science for the hypotheses. The drafts and3

narratives were reviewed in subsequent workshops, resulting in revisions to the models.

A schematic diagram and a narrative description are provided for each conceptual model. The diagrams follow a top-to-bottom hierarchy of information, which identifies the drivers (external sources), the specific stressors on the natural systems, the ecological effects resulting from the stressors, and the recommended ecological attributes (indicators) and measures for each attribute. Each stresssor is linked to one or more attributes. The symbols used in the models to indicate each of these model components are as follows.

The major components of the models are defined as follows.

Drivers: The major external driving forces that have large scale influences on natural systems. Drivers can be natural forces (e.g., sea level rise) or anthrogenic (e.g., regional land-use programs).

Stressors: The physical or chemical changes that occur within natural systems that are brought about by the drivers, and which cause significant changes in the biological components, patterns and relationships in natural systems.

Ecological effects: The biological responses caused by the stressors.

Attributes: Also known as indicators or endpoints. A parsimonious subset of all potential biological elements or components of natural systems, which are representative of the overall ecological conditions of the system. Attributes typically are populations, species, guilds, communities or processes. Attributes are selected to represent the known or hypothesized effects of the stressors (e.g., numbers of nesting wading birds), and the elements of the systems that have important human values (e.g., endangered species, sports fishing).

Measures: The specific feature(s) of each attribute to be monitored to determine how well that attribute is responding to projects designed to correct the adverse effects of the stressors (i.e., to determine the success of the project). DRIVERS STRESSORS ECOLOGICAL EFFECTS ATTRIBUTES MEASURES4

Measures of responses by the stressors and attributes in all models combined, are recommended as the minimal set of components in any regionally comprehensive monitoring program for the purpose of determining the success of the restoration
programs.

Critical pathways: The known or hypothesized linkages among stressors, ecological effects and attributes, which explain a high percentage of the adverse ecological responses shown in the conceptual model (e.g., the ecologically most significant pathways leading from a stressor).

Each model narrative includes, (1) a brief introduction to the dynamics and problems of the landscape, (2) descriptions of specific stressors, ecological attributes and measures, (3) descriptions of the major ecological linkages affected by the stressors, and (4) an initial set of recommended performance measures and restoration targets for the stressors and attributes.

The conceptual models should be viewed as working tools in support of the restoration programs. The models will undergo regular review and revision as new information becomes available. Earlier drafts for the four southern Everglades models (ridge and slough, marl prairies, mangrove transition, and Florida Bay) were previously reported in Ogden et al. (1997).

The organization and content for each model and the supporting text were developed by a “ preparer ” (or preparers), based on the information collected from the workshops. Each model report in this document is a product of the preparer(s).

C. DISCUSSION

The Applied Science Strategy that is being used to link the sciences and management in the south Florida ecosystem restoration programs is derived from the “ Ecological Risk Assessment ” process of the U.S. Environmental Protection Agency (EPA 1992, Gentile 1996). Risk assessments are used by the EPA as a guideline for conducting ecological evaluations of proposed management actions in both North America and Europe. A similar approach was used by the Man and the Biosphere Human Dominated Systems program to define sustainability goals and identify ecological endpoints for a series of restoration scenarios for south Florida (Harwell and Long 1992, Harwell et al. 1996). Many of the same components and steps incorporated in the Applied Science Strategy, including conceptual models, have more recently been described in Margoluis and Salafsky (1998).

Gentile (1996) suggested that risk assessment and recovery of ecological systems “

... can be viewed as opposite sides of the same coin. ” Risk assessment “

... is the process of determining the probability (with associated uncertainty) of a5

particular event occurring as a result of the action of a specific agent or stressor

... ” Recovery of ecological systems “

... can be viewed as the process for determining the probability (with associated uncertainty) of a particular event occurring (e.g., recovery to a

... ecologically desired sustainable state) as the result of mitigating the action of a specific agent (e.g., canals, berms) or stressor (e.g., phosphorus). Gentile (1996) listed three principal functions of the risk assessment process: (1) identification of potential causal relationships between stressors and effects; (2) selection of endpoints (attributes), indicators, and success criteria; and (3)development of a scale-dependent conceptual model that describes the interrelationships between multiple stressor pathways and multiple ecological receptors.

The development and application of conceptual models provide benefits to the scientists who create the models and to the managers and public who use them to guide and implement resource policy (Gentile 1996, Ogden et al. 1997, SCT 1997). The process of creating and reviewing conceptual models aids scientific endeavors by, (1) establishing a forum for open, multi-disciplinary exchanges of ideas and information pertaining to complex ecological issues; (2) developing scientific consensus regarding current understandings of ecosystems; (3) creating working hypotheses which serve to guide both research and management; (4) better defining (and reducing) areas of scientific uncertainty; and (5) providing a framework for continuing discussions and revisions as new information becomes available. For managers and the public, the models serve to (1) de-mystify the science; (2) provide a means for converting broad policy level goals and objectives into specific, measurable targets; (3) provide a visual description of the rationale for the prevailing hypotheses and management priorities; (4) reduce the complexity and dimensionality of the problems; (5) separate essential from non-essential information; (6) provide a tool for improved communication.

Gentile (1996) summarized the importance and appropriateness of the risk assessment and conceptual model process for setting ecological targets and conducting ecological evaluations in regional ecosystem restoration and management programs. The points emphasized by Gentile were, 1) that there is a large body of peer-reviewed literature that describes these methods and processes for conducting ecological assessments; 2) this literature represents an internationally accepted framework for structuring assessments; and 3) considerable effort has been devoted during recent years to formalize the process of selecting and classifying the endpoints, indicators, and metrics used in assessments.

D. CONCEPTUAL MODELS IN SOUTH FLORIDA

The overall planning strategy for the C&SF Restudy has been to use conceptual models as a basis for developing performance measures and restoration targets for the stressors and attributes in each model. These targets, collectively, describe the physical and biological conditions that will be used to define6

successfully restored natural systems. The rationale for having performance measures and targets for each stressor is that the stressors are known or hypothesized to be the immediate causes of the ecological problems in each landscape. A successful restoration program must remove the adverse affects created by each stressor. A performance measure identifies which elements of each stressor must be corrected, how those elements should be measured, and how those elements must change (i.e., the restoration target) in order to eliminate or reduce their adverse effects.

Performance measures are also developed for each attribute in the conceptual models. The attributes have been identified as the biological or ecological elements that are the best indicators of responses in the natural systems to the adverse effects of the stressors. The hypotheses used to construct the conceptual models show how attributes are linked to the stressors which are most responsible for changes in the attributes. If the hypotheses are correct, reducing the adverse affects of the stressor will result in a predictable positive response by the attribute. The performance measure developed for each attribute identifies the element of that attribute which should respond, how that element should be measured, and how that element should respond (i.e., improve, thus setting the restoration target for that attribute) once the affects of the stressor are removed.

The attributes that are selected must provide measures of responses at appropriate temporal and spatial scales, and from different taxonomic and hierarchial levels in ecological systems. They must also be measurable, and their historical patterns, relationships, and functions well enough understood, so that responses can be correctly determined and interpreted. The model teams also considered the need for a mix of attributes that can serve either as indicators of ecological conditions (e.g., diversity and productivity) or of societal priorities (e.g., endangered species and high quality sports fishing). Finally, the model teams considered the most appropriate number of attributes for each model. The desirable trade-off was to have a sufficient number to adequately reflect the major system responses, while not having more than would be necessary for this purpose or that would contribute to an unmanageably large monitoring program.

The modeling teams also identified critical linkages in the conceptual models. Critical linkages were defined as those ecological links between one or more stressors and attributes, which seem to explain most of the ecological and biological changes in the systems. The assumption was that the stressors that are part of critical linkages should have a priority during restoration planning over other, less influencial stressors. The Restudy ’ s Alternative Evaluation Team (AET) generally placed higher priority on meeting performance targets for stressors with strong critical linkages than for other stressors in the models. For example, the Everglades ridge and slough conceptual model suggests that stresses caused by reductions in the duration of uninterrupted surface water hydroperiods and by7

compartmentalization may explain much of the adverse changes that have occurred in the long-hydroperiod slough systems. Correction of these stressors became the highest priority in evaluating the predicted affects of alternative restoration plans in the sloughs of the Everglades.

The performance measures and restoration targets from both the stressors and attributes are used for two primary purposes. Performance measures function during the planning phases of the restoration projects as assessment tools for comparisons among alternative plans. What combination of structural and operational components is most likely to achieve the desired objectives of the project, as determined by how well a plan is predicted (by modeling) to meet each of the targets set by the performance measures? In this planning role, the measures and targets not only are used to determine which plan is most likely to be successful in achieving its objectives, but also are used to influence the design of the project as efforts are made to evaluate the combination of features which can best moderate or eliminate the adverse affects of the stressors.

The second primary use of the measures and targets is in the design of a system-wide, ecological monitoring program. The purpose of system-wide monitoring is to measure how elements in the natural system actually respond following the implementation of each iteration of a restoration program. Because the design of a restoration program is determined by the features that are predicted to best meet a suite of regional performance measure targets, the monitoring program must measure the responses by the same set of performance targets. Comparisons between the predicted responses by a set of stressors and attributes and the actual

responses by the same stressors and attributes, provide a basis for making revisions to the causal hypotheses and conceptual models, and a means for structuring an adaptive assessment strategy throughout the implementation of the restoration program. The overall focus of the monitoring program must be performance-based, i.e., the elements of the natural systems to be monitored must be those that provide actual measures of the stressor and attribute targets.

E. ADAPTIVE ASSESSMENT

The key to successful implementation of a regional ecosystem restoration program, e.g., maximizing the effectiveness of the program and reducing uncertainty during its implementation, is an adaptive assessment strategy. The conceptual ecological models are an integral part of this overall process. The conceptual models should be revised as new information is collected from research and monitoring programs. These revisions in the conceptual models influence predictions of system responses, and the choice of attributes and measures, for future iterations of the restoration program. As the accuracy of the hypotheses in the conceptual models improves, the opportunities for making pre-construction improvements in project design and operations are also enhanced. Greater accuracy8

in the conceptual models leads to improvements in the choice of measures and targets used to refine the design and judge the predicted performance of each project design.

F. FUTURE TASKS

The conceptual ecological models, and the planning and evaluation tools coming from the models, still require several priority improvements. These are: (1) completion of a conceptual model technical report, and peer review of this report; (2) new workshops to complete the development of performance measures for the biological attributes identified by the models; (3) workshops to design a performance-based monitoring program for the south Florida ecosystem restoration program; and (4) the development of a consensus among the participating agencies for a system-wide adaptive assessment strategy for the ecosystem restoration program, (5) the completion of the Total System and other conceptuals model as needed.

Table 1. List of the participants and the model that each helped to develop.



## Name Affiliation Models
G. Abbott SFWMD K. Alvarez FDNR BC C. Anastasiou Univ. FL FB T. Armentano NPS/EVER R/S, MP, SE, FB A. Arrington SFWMD T. Bancroft Arch. Biol. Stat. R/S, MP, SE, BC I. Barnett FDEP O. Bass NPS/EVER R/S, MP, SE S. Bellmund NPS/EVER R/S, MP, SE, BB R. Best USGS/BRD FB R. Brock NPS/EVER FB J. Browder NOAA/NMFS R/S, MP, SE, FB, BB C. Buckingham FWS BC, G. Burzycki Dade Co. DERM R/S, MP, SE, BB D. Busch NPS/EVER R/S, MP, SE K. Cairns FWS NE E. Carlson Natl. Audubon Soc. BC P. Carlson FDEP/FMRI FB B. Chamberlain SFWMD NE E. Chipouras Univ. FL FB J. Colvocoresses FDEP/FMRI FB W. Cropper U. Miami/RSMAS FB, BB, SC K. Cummins SFWMD SC S. Davis SFWMD R/S, MP, SE, BC, FB, SC9 

## Name Affiliation Models R. Day Ind. R. Lagoon NEP NE D. DeAngelis USGS/BRD SC P. Doering SFWMD NE M. Duever The Nature Conserv. BC M. Durako FDEP/FMRI FB J. Englehardt U. Miami SC E. Estevez Mote Marine Lab NE M. Gaines U. Miami/Biology D. Gawlik SFWMD R/S, SE J. Gentile U. Miami/RSMAS SC C. Goodyear NOAA/NMFS LO G. Graves FDEP NE S. Gray SFWMD NE, FB L. Gunderson U.Florida/Zoology BC, FB D. Hanisak Harbor Branch Inst. NE C. Hanlon SFWMD LO M. Harwell U.Miami/RSMAS SC D. Haunert SFWMD NE K. Havens SFWMD LO L. Heisler FGFWFC LO, R/S, SE L. Hornung USACOE SC A. Houser USACOE BC Soon-Jin Hwang SFWMD LO B. Irlandi U.Miami/RSMAS FB, BB T. James SFWMD LO T. Janicki Coastal Environ. NE D. Jansen NPS/BICY BC Kang-Ren Jin SFWMD LO K. Kibby Lee County NE W. Kitchens USGS/BRD SC M. Koch FL Atlantic Univ. SE, SC J. Koebel SFWMD B. Kruczynski EPA FB J. Layne Arch. Biol. Station BC D. Lirman U.Miami/RSMAS BB W. Loftus USGS/BRD R/S, MP, SE J. Lorenz Natl. Audubon Soc. SE, FB L. McCarthy FDACS LO, R/S, MP, SE C. Madden SFWMD NE, R/S, MP, SE, FB L. Manners USACOE LO S. Markley Dade Co. DERM BB F. Mazzotti U.Florida/IFAS R/S, MP, SE, BC, FB J. Meeder FL.Int.Univ./SERP MP, SE10 

## Name Affiliation Models
S. Melvin SFWMD R. Montgomery Coastal Environ. NE D. Morrison Natl. Audubon Soc. R/S, MP, SE, FB J. Moulding USACOE R/S, MP, SE A. Nath SFWMD S. Newman SFWMD SC J. Obeysekera SFWMD SC J. Ogden SFWMD R/S, MP, SE, BC, FB, SC, S. Olson SFWMD FB P. Ortner NOAA/AOML FB R. Pace FWS LO, NE, R/S, MP, SE T. Pernas NPS/BICY BC S. Perry NPS/EVER R/S, MP, SE M. Poole FGFWFC R/S, MP, SE, R. Punnett USACOE SC G. Redfield SFWMD LO C. Regan NPS/EVER FB L. Richardson FWS BC J. Rippe SFWMD M. Robblee USGS/BRD R/S, MP, SE, FB B. Robertson USGS/BRD R/S, MP, SE, SC B. Rosen SFWMD LO, NE D. Rudnick SFWMD NE, MP, SE, FB P. Sime SFWMD NE F. Sklar SFWMD R/S, SE T. Smith USGS/BRD SE S. Snow NPS/EVER R/S, MP, SE J. Snyder USGS/BRD BC M. Steinkamp FWS R/S,MP,SE A. Steinman SFWMD LO P. Strayer SFWMD D. Strom FDEP NE T. Tisdale SFWMD LO S. Tosini U.Miami/RSMAS L. Toth SFWMD T. Towles FGFWFC R/S,MP,SE S. Traxler USACOE NE, SE, FB J. Van Arman SFWMD NE, BC G. Warren FGFWFC LO D. Weeks NPS/BICY BC D. Welcher NOAA/AOML FB H. Zebuth FDEP LO, NE, R/S, MP M. Ziminske USACOE LO11

* Models: Lake Okeechobee (LO); northern estuaries, Caloosahatchee & St. Lucie (NE); Everglades ridge & sloughs (R/S); southern marl prairies (MP); southern Florida Bay/Shark Slough estuaries (SE); Big Cypress basin (BC); Florida Bay (FB); Biscayne Bay (BB); model steering committee and overall review (SC).12

Figure 1 : APPLIED SCIENCE STRATEGY FOR ECOSYSTEM RESTORATION 

### Societal Values Ecological research, models, and monitoring

Stressors: Performance Measures

Comprehensive Monitoring Program

Ecological Report Cards Ecosystem Responses Restoration Plans Alternative Plans Evaluation Conceptual Ecological Models

Attributes: Performance Measures Ecosystem Restoration Targets Goals and Objectives13

Figure 2 : LOCATION MAP FOR CONCEPTUAL MODELS1415

G. REFERENCES

Environmental Protection Agency. 1992. Framework for ecological risk assessment. EPA/630/R-92/001. Washington, D.C.

Gentile, J.H. 1996. Workshop on “ south Florida ecological sustainability criteria. ” Final Report. University Miami, Center for Marine and Environmental Analysis, Rosenstiel School of Marine and Atmospheric Science, Miami, FL. 54 pp.

Harwell, M.A. and J.F. Long. 1992. U.S. M.A.B. Human-Dominated Systems Directorate workshop on ecological endpoints and sustainability goals. Univ. Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL. 115 pp.

Harwell, M., J.F. Long, A. Bartuska, J.H. Gentile, C.C. Harwell, V. Myers and J.C. Ogden. 1996. Ecosystem management to achieve ecological sustainability: the case of south Florida. Environ. Mgmt. 20: 497-521.

Margoluis, R. and N. Salafsky. 1998. Measures of success. Island Press, Washington DC. 363 pp.

Ogden, J.C., S.M. Davis, D. Rudnick and L. Gulick. 1997. Natural Systems Team report to the Southern Everglades Restoration Alliance. Final draft. July 1997. South Florida Water Management District, West Palm Beach, FL. 43
pp.

Rosen, B.H., P. Adamus and H. Lal. 1995. A conceptual model for the assessment of depressional wetlands in the prairie pothole region. Wetlands Ecology and Management 3: 195-208.

Science Coordination Team. 1997. Integrated science plan. Report to the South Florida Ecosystem Restoration Task Force and Working Group. Office of the Executive Director, SFERTF, Florida International University, Miami, FL.16



### II. LAKE OKEECHOBEE CONCEPTUAL MODEL

A. PREPARERS

Karl E. Havens and Barry H. Rosen, South Florida Water Management District, West Palm Beach, Florida.

B. INTRODUCTION

Lake Okeechobee is a large (1,730 km 2 ) freshwater lake located at the center of the interconnected south Florida aquatic ecosystem. The lake is shallow (average depth <3 m), originated about 6,000 years ago during oceanic recession, and under natural conditions probably was a slightly eutrophic and had vast marshes to the west and south. The southern marsh was contiguous with the Florida Everglades, which received water as a broad sheet flow from the lake during periods of high rainfall (Gleason 1984).

Modern-day Lake Okeechobee differs in size, range of water depths, and connections with other parts of the regional ecosystem (Havens et al. 1996a). Construction of the Herbert Hoover Dike in the early to mid-1900s reduced the size of the lake's open-water zone by nearly 30%, resulted in a considerable reduction in average water levels, and produced a new littoral zone within the dike that is only a fraction of size of the natural one (yet still it is a vast expanse, at over 400 km 2 ). The lake also has been impacted in recent decades by excessive inputs of nutrients from agricultural activities in the watershed (Flaig and Havens 1995). These nutrients have exerted the most dramatic impacts on the open-water region, where large algal blooms have occurred, along with accumulation of soft organic mud bottom sediments, which cause the lake water to become highly turbid when they are resuspended during windy periods (Maceina and Soballe 1991). The littoral zone has been invaded by 15 species of exotic plants, most notably Melaleuca quinquenervia and Panicum repens (torpedo grass), which have expanded over large areas, displacing native plants. Despite these human impacts, and a consensus that the lake ’ s overall health has been greatly degraded by human actions, Lake Okeechobee continues to be a vital aquatic resource of south Florida, with irreplaceable natural and societal values. These values and their responses to anthropogenic stressors are described in the following sections.

C. MODEL STRUCTURE

The conceptual model is comprised of a top-to-bottom hierarchy of drivers

, stressors
, ecosystem effects

, attribures , and measures (refer to figure on 27). It is a complex model that includes two distinct but highly interconnected components, the open-water and littoral zones; each zone has different ecological17

effects and attributes, and different responses to stressors. Stressors in one zone may have indirect effects that cross the boundary into the other. The Lake Okeechobee model was developed in the context of the lake's existing spatial extent, recognizing that the functioning of the modern-day system is drastically different from that of the historic lake.

D. EXTERNAL DRIVERS AND STRESSORS

Eight in-lake stressors, which exert significant impacts on the lake's natural and societal attributes, originate from six external sources. Elevated concentrations of chemical contaminants , including, chloride (Cl

- ), pesticides, and total dissolved solids (TDS), are by-products of agriculture or other human activities in the watershed. A much greater concern, in terms of ecosystem impacts, are the massive quantities of nutrients , in particular nitrogen (N) and phosphorus (P), which are discharged to the lake from agriculture. The C&SF Project, which includes deep canals that allow water to enter the lake with little interaction with natural wetlands, facilitates the delivery of these chemical stressors to Lake Okeechobee, and as such, it also is considered a source.

The open-water region experiences elevated concentrations of suspended sediments , whose source is a region of soft organic mud that covers about 50% of the lake bottom. When winds mix the shallow water column, the upper few cm of mud are resuspended. The spatial extent, depth, and nutrient content of this mud have increased rapidly in the last 100 years, coincident with agricultural development and increased nutrient inputs from the watershed (Brezonik and Engstrom, 1997). The Herbert Hoover Dike may facilitate sediment accumulation by preventing natural flushing that once may have occurred during high water
events.

The C&SF Project, along with natural variations in regional rainfall, have the potential to cause prolonged or extreme high or low water levels . Because the lake is constrained within the dike system, these two stressors can cause severe damage on the lake ecosystem. Extreme high or low lake levels of any duration, or moderate high or low lake levels of prolonged duration, are considered to cause significant harm (an adverse change in ecological values that cannot recover under natural conditions). In contrast to the harmful effects of extremes, a certain degree of natural variation in lake levels, between 13 and 15 ft NGVD, has been shown to be benefit the ecosystem (Smith et al. 1995; Smith 1997).

Lake Okeechobee has suffered in recent decades from the expansion of exotic and nuisance plants and exotic animals . Today there 15 species of exotic plants in the littoral zone. Species of greatest concern are Melaleuca and torpedo grass, both of which were purposely introduced to the region, for dike stabilization and cattle forage, respectively. Other exotic plants that have stressed the lake's values include Hydrilla sp., water hyacinth ( Eichhornia crassipes ), and water lettuce18

( Pistia stratiotes ). Exotic animals in the lake now include fish ( Tilapia aurea)

, mollusks ( Corbicula fluminea ), and microinvertebrates ( Daphnia lumholtzii ). Each of these species exerts different impacts on the ecosystem, as discussed below. The final major stressor in Lake Okeechobee is increased frequency and extent of fire , which occurs due to natural causes (e.g., lightening strikes), arson, and controlled burns conducted by the South Florida Water Management District and Florida Game and Fresh Water Fish Commission, under permit from the US Department of Forestry.

E. ECOLOGICAL ATTRIBUTES

Seven natural and societal attributes are associated with the Lake Okeechobee ecosystem. These values may be broken down into those which are intrinsic to the lake (fisheries, wildlife habitat, ecotourism) and those which are extrinsic (water supplies for urban areas, agriculture, and other ecosystems). The extrinsic values differ in that they are regional in nature, and dependant upon water supply in general, rather than on Lake Okeechobee per se. It is largely for this reason that lake hydrologic performance measures (below) are based on the lake ’ s intrinsic values, while extrinsic values are addressed separately, by performance measures ascribed to the Lake Okeechobee Service Area. Nevertheless, the conceptual model can serve as an integrating framework for these different attributes.

The lake is an important source o f water for urban and agricultural
uses, and environmental water that is discharged from the lake to other ecosystems, including the east and west coast estuaries, and the Everglades water conservation areas. For each of these extrinsic values, the quantity, timing, and quality of water are critical features. The lake is important to the regional economy, whose income depends in part on use of the ecosystem for ecotourism and recreation , including bird and wildlife observation, hiking, camping, and recreational boating. The lake also supports a commercial and recreational fishery , with an estimated "total economic value" in excess of $480 million US dollars (Furse and Fox 1994). Some of the most important intrinsic ecological values of the lake are the wading birds and waterfowl , which include numerous species and large resident or migratory populations (Smith et al. 1995), and the diverse mosaic of native vegetation that characterizes the lake's littoral marsh zone (Richardson and Harris 1995). This diverse vegetation is critical to birds, fish, and other wildlife that inhabit the zone, and it is an aesthetically pleasing region that is visited by thousands of persons each year -- thereby supporting the ecotourism, recreation, and fisheries values mentioned above. The community also is a critical habitat for the federally-endangered snail kite , whose principal food resource, the apple snail, occurs at high densities in a large pristine region of the lake's marsh known locally as Moonshine Bay.19

F. QUANTITATIVE MEASURES

To quantify the current status of Lake Okeechobee, and its predicted or realized responses to restoration efforts, a suite of measures were selected that collectively characterize the condition of each ecological value. Measures were based on the results of scientific research, or in some cases, best professional judgement that indicates a strong relationship between measures and the values being assessed. The measures for Lake Okeechobee ecological values are as follows.

(1) Urban water quality and quantity . Key measures of the quality of water for urban uses include concentrations of the various Class I numeric water quality standards (for drinking water use), as well the concentrations of Class IV numeric standards (for agriculture). Water quantity can be assessed as days per year with water use restrictions.

(2) Environmental water quality and quantity . Water discharged from Lake Okeechobee may impact downstream ecosystems, including the east and west coast estuaries, the WCAs, and the Everglades, if it contains high concentrations of P, N, toxins, or turbidity. Quantities of water depend on needs of particular ecosystems, and must include a seasonal component.

(3) Ecotourism and recreation . These ecological values may be best assessed on the basis of numbers of visitors to the lake region each year and cash flow into the local economy, associated with designated lake uses, including bird and wildlife observation, hunting, boating, and hiking.

(4) Sport and commercial fishery . Measures of fishing success may be obtained from information on catch per unit effort by anglers and commercial fishers, while more quantitative information can be obtained by FGFWFC studies of population size and age structure for selected fish (largemouth bass, black crappie, bluegill).

(5) Wading birds and migratory waterfowl . Populations of selected birds may be surveyed in order to determine population sizes and nesting success.

(6) Diverse mosaic of native vegetation . Geographic Information System (GIS) maps of the littoral zone may be used to evaluate indices of overall spatial heterogeneity - several standard ones are available. It also may be important to quantify changes over time the spatial extent of selected vegetation assemblages, especially those known to be critical wildlife habitats (e.g., Eleocharis, Scirpus, Salix ). The ratio of exotic+nuisance to native plant coverage also may be a useful metric of overall vegetation quality. The marsh community is reported to include one threatened plant species, the Okeechobee gourd, and a regular census of its population density and distribution should be undertaken.20

(7) Snail kite . Snail kites are an important endangered species in south Florida, and there needs to be a continued regular census of their population size and nesting success in Lake Okeechobee.

G. ECOSYSTEM EFFECTS

The pathways linking ecosystem stressors to the natural and societal attributes are complex, and have a solid foundation in research and modeling conducted by scientists at the SFWMD, FGFWFC, and Florida universities (e.g., Aumen and Wetzel 1995, Havens et al. 1995, James and Bierman 1995, Reddy et al. 1995, Havens et al. 1996a). As we learn more about how the system functions, it is likely that additional pathways could be added to the model, or adjustments made to existing pathways. The model is a flexible tool that at any given time, reflects the current state of our best available scientific information.

Chemical contaminants in the lake water have the potential to directly impact all seven of the ecological values. Toxic materials in drinking water are dangerous to human users, or at a minimum, costly to remove during treatment operations; toxic chemicals also can kill or harm agricultural crops and the biota residing in downstream ecosystems that receive environmental water deliveries or flood control discharges from the lake. Toxic chemicals also may kill or harm native invertebrates, fish, birds, littoral plants, and other flora and fauna in the lake ecosystem, including the endangered species. Some of the chemical contaminants, including Hg and pesticides, undergo biomagnification in the food web, and thereby indirectly harm animals near the top of the web (e.g., predator birds, fishes, and other animals such as the American alligator).

Nutrients , in particular N and P, stimulate the growth of phytoplankton, and at the extreme, can cause noxious surface blooms of blue-green algae (Paerl 1988). When these algal blooms senesce, they can cause oxygen depletion and a build-up of ammonia and potentially toxic decay products in the water. Depending on the location where this occurs, these decay products can harm components of the lake's biota, including littoral macroinvertebrates and fish. This in turn can secondarily affect the predators that utilize those food resources. To date, the only documented harm, following a large bloom in summer 1986, was to the lake's apple snail population (Jones 1987), the primary food item for the endangered snail kite. The products of algal bloom decay also are detrimental to water quality for urban and environmental deliveries, and to the ecotourism & recreational uses of a lake (Heiskary and Walker 1988). The high nutrient inputs that have impacted Lake Okeechobee since human development began pre-1900 also have left their mark on the lake sediments (Reddy et al. 1995), which now contain large quantities of N and especially P. While there is a natural loss of N from the lake, by microbial degradation in a process called denitrification, there is no such loss for P, except by gradual burial in deeper sediment layers. High concentrations of P and organic21

material promote rapid growth of bacteria, which in turn deplete the oxygen from surface sediments (Hutchinson 1957). Only a small subset of benthic macroinvertebrates can tolerate low oxygen levels, and it is for this reason that the Lake Okeechobee community, once dominated by a diverse array of species, now is strongly dominated by a few species of pollution-tolerant oligochaete worms (Warren et al. 1995). This change radiates upward through the food web, affecting fishes and other animals that ultimately depend on the benthic invertebrates as a food source (Havens et al. 1996b).

Suspended sediments in the water column can cause increased P concentrations if soluble P is released from the sediment particles. This is a complex situation that is largely controlled by the concentrations of P on the particles and in the water column (Reddy et al. 1995). Under most circumstances, the particles adsorb P, and therefore sediment suspension (followed by sediment settling to the lake bottom) is a net sink for P. Suspended sediments exert another important impact. If they are present in the water column at high concentrations, they greatly reduce the amount of light that reaches the lake bottom. It the sediments are circulated to shallow near-littoral regions of the lake (this circulation appears to be enhanced by high water levels), then they may suppress the growth of submerged plants and algae that naturally occur on the lake bottom. Those plants and algae are important because they provide food and habitat for macroinvertebrates and fish (and ultimately wading birds and other animals), and they help to stabilize the sediments. If the plants are reduced or eliminated, these functions are lost. One particularly troubling result is a "positive feedback loop" that may occur, making it very difficult for the lake to recover from a highly turbid condition: turbid water reduces benthic plants, less benthic plants means more resuspension, this makes more turbid water, even less plants........etc. This situation may be occurring today at the south end of Lake Okeechobee, where turbid, P-rich water and declines in benthic algae ( Chara ) coincided with the prolonged high lake stages in 1995 and 1996 (Steinman et al. 1997). Research results also have documented that benthic algae compete for nutrients with phytoplankton (Havens et al. 1996c). Thus, when benthic algae are reduced, there is a greater potential for phytoplankton blooms. Finally, there also is a complex relationship between light penetration in the water column and phytoplankton biomass. While sediment resuspension may indirectly promote phytoplankton growth by suppressing benthic algae, at the extreme, it may be so severe as to cause light limitation of the phytoplankton too. In this case, which is typical of the mid-lake region during winter (Phlips et al. 1997), there may be little growth of any algae in the water column or on the lake bottom. At other times, when a high biomass of phytoplankton does occur (e.g., during calm mid-summer periods), phytoplankton cells may bring about a reduction in light penetration, and also contribute to the decline in benthic algae.22

Prolonged or extreme high lake levels cause substantial harm to the ecosystem. When sustained high lake levels (>15 ft for nearly 2 yrs, and exceeding 17 ft at the extreme) occurred in 1995 and 1996, wind and erosion caused emergent plants to be torn loose from their habitats, resulting in a loss of important fish and wildlife habitat (e.g., bulrush, a critical spawning habitat for largemouth bass). These "islands" of dislodged plant material also interfered with recreational uses of the lake, as they blocked canals and boat trails. During the two years of high lake levels, District scientists also documented the loss of submerged vegetation at the lake ’ s south end, likely due to light limitation caused by the deep, turbid water (Steinman et al. 1997).

High lake levels also bring about changes in the nature and extent of mixing within the lake. A Lake Okeechobee hydrodynamic model indicates that when water levels are high, nutrient and sediment-rich water from mid-lake is mixed throughout the basin, including into the littoral zone (Sheng and Lee 1991). At low water levels, the nutrient and sediment-rich water circulation is constrained towards mid-lake because an extensive rock reef along with south and west edges of the open-water region restricts water movement into the near-littoral region (Maceina 1993). When high water levels promote nutrient transport into the marsh via greater horizontal mixing, those nutrients have the potential to cause changes in the biomass and composition of both marsh plants and algae, as has been documented in the Everglades Water Conservation Areas (WCA) by Koch and Reddy (1992) and McCormick et al. (1996).

High lake levels also may affect vertical mixing in the mid-lake region. During summer calm periods, the water column may become thermally stratified for one to two week-long periods (Jin et al. 1997). When this occurs, bottom waters may become anoxic, and this in turn allows diffusion of soluble P from lake sediments. These events may be a precursor to development of mid-lake blooms of blue-green algae (Havens et al. 1997). Because it takes a greater amount of wind energy to break down the stratification and mix a deeper water column than a shallow one, high lake levels might promote longer-lasting mid-summer stratification, anoxia, and algal blooms (Havens 1996). High lake levels also may threaten the endangered Okeechobee gourd, which cannot tolerate prolonged flooding.

Prolonged or extreme low lake levels also cause significant harm to the ecosystem and its values. Low water levels expose large areas of the marsh (including native plant communities such as Scirpus and Eleocharis ) to desiccation, and render them useless as habitats for fish and waterfowl. Low water levels also may promote the expansion of exotic plants. The large Eleocharis habitat found in Moonshine Bay is an important habitat because it is a primary foraging area for largemouth bass and other recreational fish, and it supports a thriving population of snail kites. This habitat now is encircled by torpedo grass, which may readily23

overtake the region if low water levels suppress the growth and survival of the native Eleocharis . Torpedo grass grows most rapidly when water levels are at or near the soil surface, and displays considerable growth suppression when submerged under >30 cm of water (Thayer and Haller 1990). Eleocharis , on the other hand, thrives when submersed, even when water depths are near 1 m. There also is evidence that germination of Melaleuca seeds is inhibited by standing water (Lockhart 1995). Hence, if large areas of the marsh become dry for long periods of time, there could be increased expansion of this exotic plant. Indeed, one of the most rapid Melaleuca increases occurred shortly after the 1990 drought, when lake levels declined below 11 ft NGVD for just 150 days. Low lake levels also impact ecotourism and recreation, by making it difficult or impossible to access large regions of the marsh (many former boat trails become dry land at 11 ft NGVD). Finally, there is evidence that low water levels directly impact the snail kite, which requires standing water beneath the macrophytes upon which it constructs its nest.

While it is clearly the case that prolonged or extreme high and low water levels have negative impacts, these conditions alone do not describe the hydrologic variation that is required to maintain a healthy ecosystem. There is considerable evidence that the "optimal" situation would also include a certain degree of variation. In particular, a January to May recession in lake levels from near 15 ft NGVD to below 13 ft NGVD has been shown to be beneficial to wading bird and fish populations. Infrequent (every 5 to 7 years) spring recessions to below 12 ft NGVD may benefit the entire community, by exposing prey-rich submersed macrophyte beds to predators, invigorating willow ( Salix ) stands, and by allowing fires to burn
away Panicum and Typha wrack (Smith et al. 1995). These points must be taken into account when evaluating the impacts of regional restoration programs or lake regulation schedules, although they are not readily portrayed as stressors in a conceptual model of this format.

Exotic and nuisance plants have been discussed in the context of water levels and other stressors. These plants, which now cover a large portion of the marsh, exert a variety of direct and indirect impacts on the lake's ecological values. As they spread and displace native vegetation, they directly alter the vegetation mosaic. Because of their growth characteristics, they may provide poor habitat for fish and other wildlife. Torpedo grass, for example, grows in large monocultures resembling “ hayfields, ” with little or no standing water. Fish simply cannot swim through such a habitat, and any wildlife that depend upon those fish as a food resource are indirectly affected when torpedo grass becomes dominant in a region of the lake. Hydrilla and other exotic submerged plants have negative impacts on human uses of the system, by blocking canals and waterways, and often requiring repeated herbicide treatments. These plants are secondarily responsible for any adverse impacts that the herbicides have on natural vegetation in the lake or downstream ecosystems. One of the troubling patterns observed in the lake's marsh is expansion of cattail ( Typha ). This plant is a native, but once occurred at24

considerably lower densities and over a smaller spatial area (Richardson and Harris 1995). Its spread may be related to water level regimes and/or eutrophication of the lake. In either case, it displaces other native plants and impacts the value of the marsh as a wildlife habitat. There is some concern that cattail expansion in to valuable bulrush habitat may be facilitated by low lake levels (particularly those < 11 ft NGVD). Following the drought in 1989, when the lake declined to nearly 10.5 ft NGVD, large areas of bulrush became infested. These events may degrade the value of the habitat for fish and other wildlife that utilize bulrush for nesting or foraging.

Exotic animals in Lake Okeechobee can directly displace native animals through competition and predation, and they also can exert other direct and indirect effects. Tilapia aurea , for example, is an exotic fish that feeds and burrows at the benthos, and destroys submerged vegetation stands. It also transforms particulate nutrients, from sediments, macroinvertebrates, and plants, into soluble nutrients that are excreted into the water column where they may stimulate localized algal blooms. Not all impacts of exotic animals are negative, however. The mollusk Corbicula fluminea is a major food source for diving ducks and shell crackers, and the microinvertebrate Daphnia lumholtzii grazes phytoplankton, and could suppress algal blooms if its densities become very high. It also may be a good food source for plankton-feeding forage fish.

Fire is a natural forcing function in Lake Okeechobee, as well as in other south Florida ecosystems, often occurring due to natural causes, such as lightening strikes. However, in recent years, fires have been set in the lake's littoral zone by humans -- both in acts of arson, and as part of controlled burn management efforts. Arson fires are reportedly set by hunters and others who desire to visit the littoral zone for recreational purposes. The focus is most often on regions of dense torpedo grass, where plant growth has restricted access to the marsh. Interestingly, the controlled burn programs target similar regions, but for a different reason -- to burn away the exotic plant material, in order to give native plants a chance to recolonize the area from a rich buried seed bank that is known to occur in the marsh soil. In either case, fires impact the vegetation mosaic, as well as the animals that occur therein.

H. HYDROLOGIC PERFORMANCE MEASURES

A significant feature of the Lake Okeechobee conceptual model is the high degree of interconnectedness; any given stressor may impact ecological values directly, or impact those same values indirectly, by exacerbating the effects of other stressors. Two stressors that display particularly strong effects (direct and indirect) on the values are high and low water levels. Taken together, they have the potential to affect the rate of lake eutrophication, the spatial extent and overall health of25

submerged and emergent plant communities, fisheries, birds, other wildlife, and the quality of water taken from the lake from human uses.

Water inputs and lake levels also are the variables most directly impacted by the various Alternatives considered in the C&SF Restudy. Therefore, a suite of hydrologic performance measures were developed based on water depth (and seasonal variations in those depths). These measures serve as integrative predictors of overall lake ecosystem health.

The hydrologic performance indicators and measures for Lake Okeechobee are concerned with: extreme high lake levels (> 17 ft NGVD) of any duration; moderate high lake levels (> 15 ft NGVD) of prolonged duration; extreme low lake levels (< 11 ft NGVD) of any duration; and moderate low lake levels (< 12 ft NGVD) of prolonged duration; as well as the degree of variability in lake levels, within what is considered to be an “ optimal ” window for the lake ’ s biota (13 to 15 ft NGVD).

Performance Indicator – Daily Stage Hydrographs

Visual inspection of daily stage hydrographs, for the period from January 1965 to 1995, can provide information regarding the frequency of extreme high and low lake levels. One simply draws horizontal lines across these plots at 17 ft and 11 ft NGVD water levels, and counts the number of cases wherein the hydrograph goes above or below the lines. The fewer the events, the “ better ” the result, in terms of protecting the lake ’ s values. The restoration goal for the lake is to have no such
events.

Performance Indicator – Stage Duration Curves

Visual inspection of stage duration curves for various alternatives and base conditions can provide additional information that is directly related to the lake ’ s values. By drawing horizontal lines across the plot at 17 ft and 11 ft NGVD, one can quantify the percent of times that lake stage exceeded or fell below these critical values. Lower percentages in a given scenario equate to a “ better ” result. The restoration goal for the lake is to have zero % for each extreme type of event.

Performance Measure – Similarity in Duration of Stage Events > 15 ft

This performance measure consists of box and whisker plots, which indicate median, maximum, minimum, and 25 th / 75 th percentiles, for duration of moderate high lake stage events. As indicated above, prolonged lake levels above 15 ft NGVD cause significant harm to the lake ’ s ecological values, and should be avoided. For this measure, lower median values and extremes are better. The restoration goal for the lake is to have a median duration near zero, and a maximal duration no greater than 1 year.26

Performance Measure – Similarity in Duration of Stage Events < 12 ft

This performance measure is analogous to the preceding one, except that it is concerned with the duration of moderate low lake levels. Lower median and extreme values are better. The restoration goal for the lake is to have a median duration near zero, and a maximal duration no greater than 1 year.

Performance Measure – Similarity in Duration of Stage Events > 11 ft

When lake stage falls below 11 ft NGVD, significant harm ensues, even if the duration is short. Nevertheless, during regional droughts, lake levels have declined to as low as 9.6 ft NGVD. Alternatives that increase the duration of < 11 ft events are considered especially harmful to the ecosystem. This performance measure uses box and whisker plots, as in the previous item. Lower medians and extremes are better. The restoration goal for the lake is to have no such events (i.e., duration median and extreme = zero).

Performance Measure – Similarity in Duration of Stage Events > 17 ft

This performance measure is analogous to the preceeding one, except that it is concerned with the duration of extreme high lake levels. Lower median and extreme values are better. The restoration goal for the lake is to have no such events (i.e., duration median and extreme = zero).

Performance Measure – Daily Stage Hydrographs with Spring Recession Windows

In an effort to evaluate the degree to which intra-year variations in lake levels match the optimal pattern described by Smith et al. (1995), that is, a January to May recession, without reversal, from near 15 ft to below 13 ft NGVD, “ windows ” were drawn over the daily hydrograph plots. Years in which the lake levels recede smoothly from the upper left to lower right corners of the box are considered “ good ” for wading birds and other wildlife in the lake. Years in which lake levels remain far above or below the box, or those with water levels passing through the box with no trend or an increasing trend in lake levels are considered “ bad. ” A greater number of years with “ good ” scores is considered a better result. More elaborate methods may be utilized to score the results, however, it is unclear whether this is called for, given existing uncertainties about the true relationship between spring lake level recession and fish / wildlife health. Furthermore, it is uncertain whether the goal for this measure is to have the designated recession every year, or at a return frequency corresponding to some selected reference period.29

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Phlips, E.J., M. Cichra, K.E. Havens, C. Hanlon, S. Badylak, B. Rueter, M. Randall and P. Hansen. 1997. Relationships between phytoplankton dynamics and the availability of light and nutrients in a shallow subtropical lake. Journal of Plankton Research 19: 319-342.

Reddy, K.R., Y.P. Sheng and B.L. Jones. 1995. Lake Okeechobee phosphorus dynamics study volume I. Summary. Report, South Florida Water Management District, West Palm Beach, FL.

Richardson, J.R. and T.T. Harris. 1995. Vegetation mapping and change detection in the Lake Okeechobee marsh ecosystem. Archiv fur Hydrobiologie, Advances in Limnology 45: 17-39.

Sheng, Y.P. and H.K. Lee. 1991. Computation of the phosphorus flux between the vegetation area and the open water in Lake Okeechobee. Report, South Florida Water Management District, West Palm Beach, FL.

Smith, J.P. 1997. Nesting season food habits of four species of Herons and Egrets and Lake Okeechobee, Florida. Colonial Waterbirds 20: 198-220.

Smith, J.P., J.R. Richardson and M.W. Callopy. 1995. Foraging habitat selection among wading birds (Ciconiiformes) at Lake Okeechobee, Florida, in relation to hydrology and vegetative cover. Archiv fur Hydrobiologie, Advances in Limnology 45: 247-285.

Steinman, A.D., R.H. Meeker, A.J. Rodusky, W.P. Davis and S-J. Hwang. 1997. Ecological properties of Charophytes in a large subtropical lake. Journal of the North American Benthological Society, in press.

Sutton, D.L. 1996. Growth of torpedo grass from rhizomes planted under flooded conditions. Journal of Aquatic Plant Management 34: 50-53.

Thayer, P.L. and W.T. Haller. 1990. Fungal pathogens, Phoma and Fusarium
, associated with declining populations of torpedograss growing under high water stress. Proceedings of European Weed Research Society, 8 th Symposium on Aquatic Weeds, pp. 209-214.

Warren, G.L., M.J. Vogel and D.D. Fox. 1995. Trophic and distributional dynamics of Lake Okeechobee sublittoral benthic invertebrate communities. Archiv fur Hydrobiologie, Advances in Limnology 45: 317-332.3233



### III. ST. LUCIE AND CALOOSAHATCHEE CONCEPTUAL MODEL

A. PREPARERS

Susan Gray and Daniel E. Haunert, South Florida Water Management District, West Palm Beach, Florida.

B. ABSTRACT

A conceptual model of the St. Lucie and Caloosahatchee Estuaries was developed by scientists working in these systems to identify major stressors, measurable attributes of the ecosystem that are sensitive to the stressors, and linkages between the two. Both estuaries have been highly modified. The St. Lucie Estuary, located on the southeast coast of Florida, discharges into the Indian River Lagoon and Atlantic Ocean through the St. Lucie Inlet. The Caloosahatchee Estuary, located on the southwest coast of Florida, discharges into Charlotte Harbor, and then into the Gulf of Mexico. Due to extensive urban and/or agricultural drainage projects in both watersheds, the historic watershed area has been greatly expanded. In addition, both estuaries are linked to Lake Okeechobee via canals that provide both navigation and releases of floodwaters. In the Caloosahatchee, the construction of a water control structure downstream of Lake Okeechobee has also decreased the tidally influenced portion of the Caloosahatchee Estuary. The major effects of anthropogenic changes in both watersheds are significant alterations in the timing, distribution, quality, and volume of freshwater entering the estuaries. Understanding how these systems respond to stress will provide a basis for well-informed management decisions on restoration activities.

C. INTRODUCTION

The St. Lucie Estuary is located on the southeast coast of Florida, and discharges into the Indian River Lagoon and Atlantic Ocean at the St. Lucie Inlet. The estuary encompasses about eight square miles, and the historic watershed was estimated to be about 1/3 the size of its present configuration. Due to extensive agricultural and urban drainage projects beginning in the 1910s, the present day watershed area has been expanded to almost 775 square miles. Major canals in the watershed include the C-23 and C-24 canals, part of the Central and South Florida Flood Control Project. In addition, the estuary is linked to Lake Okeechobee by the C-44 canal that is utilized for both navigation and the release of floodwaters from the lake.

The Caloosahatchee Estuary is located on the southwest coast of Florida, and34

discharges into Charlotte Harbor, and then into the Gulf of Mexico. The Caloosahatchee Estuary is also connected to Lake Okeechobee through the C-43 canal (Caloosahatchee River), and there are a series of smaller drainage works in association with substantial agricultural development in the watershed. The construction of a water control structure (Franklin Lock and Dam) downstream of Lake Okeechobee has decreased the tidally influenced portion of the estuary, allowing for the convenient use of the C-43 as a potable water supply.

The major effects of anthropogenic changes in both watersheds are significant alterations in the timing (excess wet season flows, insufficient dry season flows), distribution, quality, and volume of freshwater entering the estuaries. In addition, alterations within the estuaries through dredging of navigation channels, filling of marshes, and construction of bridges and causeways has also contributed to a number of documented declines in some mollusc species and submerged aquatic vegetation. Restoration of these important species is considered critical to the overall health of these systems. Despite these impacts, the estuaries continue to be an important resource, with significant environmental and economic values.

D. ESTUARY MODEL STRUCTURE

The conceptual model for the St. Lucie and Caloosahatchee Estuaries follows the format used for other south Florida ecosystem models, with a top-to-bottom hierarchy of drivers

, stressors
, ecosystem effects

, attributes and measures

. Refer to figure on page 39. The model is similar to those developed for other ecosystems, including Florida Bay and Lake Okeechobee. One significant difference is that a single model diagram is proposed for both estuaries. During the development of this model, it became apparent that one design would serve both systems, but that the emphasis or relative importance of each segment could vary between the systems.

E. ECOLOGICAL & SOCIETAL ATTRIBUTES

Nine ecological and societal attributes associated with a healthy estuarine ecosystem were identified, along with measures that will provide information on current ecological status, as well as long-term trends. These include the following:

4 Mollusc abundance & distribution – Oysters, clams and scallops are natural components of southern estuaries, and have been documented in the past to be abundant in these systems. Oyster reefs provide several important functions, including habitat and food for other species. Scallops, clams and oysters may be a commercial and/or recreational resource.

4 Sediment quality directly affects the occurrence and abundance of benthic and sessile species. Sediments are a sink for nutrients and other materials, such as35

pesticides and metals.

4 Water quality is a major determinate of the health and condition of aquatic systems, and changes in water quality are often the linkage between the stressor and the ecosystem value.

4 Submerged aquatic vegetation (SAV) distribution and abundance - Seagrasses are considered to be a key feature of estuaries due to the functions that they perform. These functions include sediment stabilization, primary productivity, and nursery and refugia habitat.

4 Habitat structure and function , as considered on a landscape scale, integrates many of the other values. An example of a landscape-scale attribute is defining a preferred salinity regime for the estuary. Work on the St. Lucie and Caloosahatchee Estuaries has identified preliminary salinity ranges and seasonal and spatial distributions, termed “ salinity envelopes ” to meet the physiological requirements for the establishment and productivity of key estuarine species, including seagrasses and oysters.

4 Benthic invertebrate community structure - The composition of invertebrate species in the benthos serves as an indicator of the nutrient and contaminant loading to the system. Changes in species diversity and abundance have been documented in the presence of increased pollutant loadings.

4 Manatee population dynamics - Manatees are a very visible and popular feature of the estuary, and impacted by changes to the ecosystem. Their status as an endangered species adds considerable importance to their protection and stabilization of their populations.

4 Fisheries population dynamics - Fishes are an integral component of the estuary food web. In addition, they have a significant societal value for recreation and commercial harvesting.

4 Fish-eating birds population dynamics - Fish eating birds are one of the more visible keystone species in the estuarine ecosystem. Their dependence on fish for food serves as an indicator of the health and status of their prey populations.

F. LINKS FROM STRESSORS TO ATTRIBUTES

Seven stressors that exert significant impacts on the estuary ’ s ecological and societal attributes were identified for these systems. However, the linkages between ecosystem stressors to the environmental and societal values are complex, and considerable uncertainties remain. As more is learned about how these systems function, these linkages may be changed or new ones included. One aspect36

of the model is that it is flexible and can be adjusted as new information is available.

4 Altered hydrology is one of the predominant stressors on the system. This stress is the result of managing the runoff of the watershed to accommodate agricultural and urban development, along with flood control releases from Lake Okeechobee. Accompanying these hydrologic changes are increased sediment transport, transport of floating freshwater vegetation ( Hyacinth and Pistia ) into the estuarine portion of the ecosystem, and alterations in water residence time and biological flushing of the estuary. Salinity, a key organizing parameter for the estuary, is directly affected by changes in inflows and tidal exchange. All of these factors combined have been shown to impact indicator species of estuarine health, namely seagrasses and oysters.

4 Physical alterations to the ecosystem have also had a significant effect on the presence and abundance of species normally found within these systems. These alterations have occurred through a variety of activities, including shoreline hardening, inlet dredging and stabilization, removal of oyster shell for road bed material, snagging of navigation hazards, decrease in spatial extent of the estuary through construction of barriers [S-79], and the impoundment of salt marshes for mosquito control (on the east coast). Changes in the physical dimensions of the estuaries, most notably in the Caloosahatchee, have significantly reduced the euryhaline portion of the estuary, an important nursery area, feeding area and refugia for juvenile stages of desirable sport and commercial fishes. Construction and operation of the water control structures have interfered with the migration patterns of many estuarine species, and have also resulted in the death of manatees attempting to pass through these structures.

4 Nutrients and dissolved organics enter the system as a result of anthropogenic activities in the watershed, primarily agricultural and water management, although urban use of fertilizers is also a contributor. In addition, atmospheric deposition contributes to the nitrogen loading of the system. These constituents interact with alterations in salinities and sediment loading to reduce light penetration which, in turn, leads to declines in seagrasses. The shift in the species composition of benthic invertebrates to more pollution-tolerant organisms is also linked to increases in nutrients.

4 Toxics , which include pesticides, fungicides, herbicides, brine from reverse osmosis plants, coliforms from sewage treatment plants (STPs), oils, greases, and mercury are introduced into these systems from urban development, agricultural practices, and boating. Direct toxic effects have been noted on some zooplankton and fish. Indirect effects occur through the process of bioaccumulation or biomagnification through the food web, increasing the toxic load to top predators. The problem of eggshell thinning in pelicans and osprey was the result of37

bioaccumulation of DDT.

4 Temperature extremes are the result of both rare natural events, such as freezes, and human activities due to discharges from nuclear power plants and STPs. Severe freezes have resulted in the direct decline of mangroves and manatees. In addition, the unnatural congregation of manatees in waters warmed by plant discharges is thought to contribute to the spread of disease and exposure to red tide.

4 Boating pressure is a significant stress to the estuaries through direct impacts such as scouring, wake erosion, and construction of boating channels. In addition, boat collisions are the leading anthropogenic cause of manatee deaths.

4 Resource harvesting of sport and commercial fisheries has impacted the standing stocks of many species where over -fishing has occurred. This in turn impacts those species that depend on fish as their primary food source.

G. SUMMARY

A conceptual model was developed for the St. Lucie and Caloosahatchee Estuaries. The model illustrates major linkages between stressors on the system and ecological and societal values. The purpose of the model is to provide a basis for management decisions on proposed restoration activities and to assist in the development of an integrated ecological monitoring program.40

H. REFERENCE

Havens, K.E. and B.H. Rosen. 1995. Plan for quantifying long-term ecological trends in Lake Okeechobee. Report, South Florida Water Management District, West Palm Beach, Florida.41



### IV. BIG CYPRESS REGIONAL ECOSYSTEM CONCEPTUAL MODEL

A. PREPARER

Michael Duever, The Nature Conservancy, Kissimmee, Florida.

B. INTRODUCTION

The Big Cypress region covered by this conceptual model includes the freshwater portions of the area extending from the southern edge of the Caloosahatchee River watershed boundary in Lee, Hendry, and northern Collier Counties, and west of the Everglades, as delimited approximately by L-28 in the north and a diagonal line running from Forty-Mile Bend on Tamiami Trail southwest to the coast. In this region historic water flows were primarily south to the Gulf of Mexico, with minor flows in small creeks that pass through the west coast ridge to the Gulf and somewhat more significant flows east into the Everglades (Klein et al. 1970).

There are three distinct subregions within the Big Cypress Region, based on the kind and degree of development present in each (Lehman 1976). The most pristine area, because the hydrology is largely rainfall-driven, is located within the Big Cypress National Preserve in the southeastern portion of the region (Duever et al. 1986). The Preserve, along with a portion of the adjacent Seminole Indian Reservation to the north, is the Big Cypress subregion that was included in the Restudy Alternatives analyses, although only the eastern portion of this area was affected by components included in the various restoration alternatives. The most developed portion of the area, including both urban and agricultural development, is located on and just east of the coastal ridge from Naples north to Ft. Myers. The rest of the area is a mixture of agricultural lands, suburban and rural communities, and small-to-large natural areas that have been altered to varying degrees by upstream and/or adjacent development. Despite the very different degrees of development in the three subregions, the kinds of stressors and their effects on ecosystem attributes are similar throughout the Big Cypress Region and they differ only in the severity of their impacts.

The Big Cypress region is comparable to the freshwater Everglades in terms of natural community diversity, although the communities tend to form more of a mosaic as opposed to vast expenses of a single community type. The most extensive natural communities in the Big Cypress are distributed throughout the region along very gentle topographic gradients from short-hydroperiod pinelands on the uplands through marshes to long-hydroperiod cypress forests on lower elevations (Craighead 1971, Davis 1943, Duever 1984, Klein et al. 1970). Small open-water ponds are found in scattered deeper depressions, and small islands of hardwood forest occur on elevated sites among or along the edges of deeper herbaceous and forested42

wetlands. While the Big Cypress is dominated by temperate species, there is a small but unique tropical component that is most prevalent in forested upland and swamp communities (Duever et al. 1986). This component is most abundant and diverse close to the coast, but occurs further inland in association with larger and deeper wetlands, where it is protected from cold winter weather by their canopy and/or the moderating effects of standing water. Under natural conditions, the range of annual fluctuation in water levels above and below ground and the duration of inundation are the primary factors influencing the distribution of these communities, although frequent fires exert a secondary influence by controlling the kinds and structure of their dominant plant species (Craighead 1971, Duever 1984, Harper 1927, Klein et al. 1970). Cypress and marsh communities tend to be more common towards the south as elevations approach sea level, while pinelands are more common in the higher and deeper-sand substrates to the north and on the west coast ridge along the Gulf of Mexico.

C. ECOLOGICAL STRESSORS

The ultimate source of all ecological stressors in the Big Cypress ecosystem is development for agriculture and residential use (refer to figure on page 51). The

area ’ s seasonally high water table required the construction of an extensive system of small ditches connected to larger and larger canals to assure that water levels remain below ground throughout the year, in order to make the land suitable for crops and housing (Lehman 1976). The drainage systems produce lowered water tables and shortened hydroperiods for considerable distances in otherwise unaltered lands around and downstream of them (Carter et al. 1973, Klein et al. 1970, Swayze and McPherson 1977). These drier conditions can facilitate upgradient shifts in the characteristics of affected plant communities and an associated increased fire severity (Robertson 1953, Wade et al. 1980). In addition, the water in canals draining these lands normally has a different chemistry than that found in natural Big Cypress waters. This is particularly true in terms of undesirably higher concentrations of nutrients and dissolved minerals (Duever et al. 1986), which can encourage the spread and potential dominance of sites by nuisance native and exotic vegetation. The human response to South Florida ’ s dry season produces an additional hydrologic stress on natural systems in the Big Cypress in terms of lowered water tables and shortened hydroperiods . When weather conditions are dry for extended periods, water use for crops, lawns, etc. goes up substantially, which results in lower than normal water levels in and for considerable distances around the wells that provide this water (Lehman 1976, Rochow 1985). Excessive drawdowns associated with canals and wellfields can produce very significant impacts on native amphibian, fish, and crayfish populations that depend on the presence of at least some inundated wetlands for their survival through the dry season. These drawdowns can also eliminate the standing water that normally protects tropical components from winter freezes (Duever et al. 1978).43

Changes in land use associated with agricultural and residential development not only cause habitat loss on the affected lands, but fragmentation of the habitat mosaic . Habitat loss directly impacts the availability of resources required by organisms that utilize these areas. However, the distribution of these habitats across the landscape is even more important because few organisms utilize only one habitat type, particularly in a landscape that can fluctuate seasonally from inundated to completely dry and that may be affected by widespread and sometimes severe fires. Thus, when wetland connections to adjacent uplands are severed, innumerable biologically important flows are interrupted and ecosystem diversity and viability are severely compromised (Forman and Godron 1986, Harris 1984). Fragmentation and habitat loss also affects populations by reducing the spatial extent of their resource base to the point where it is no longer able to support viable populations. Exposure to hazards associated with development also increases dramatically as habitats become smaller and are more and more fragmented.

As development increases in an area, the seasonality and frequency of fire in natural communities becomes increasingly unnatural (Wade et al. 1980). Natural fires were normally most common during the summer wet season as a result of the high frequency of lightning (Duever 1984). However, they were most widespread at the end of the dry season, when the region was at its driest and lightning storms were just beginning to occur. Early in this century, cattlemen greatly increased the frequency of dormant season fires to provide more forage for their cattle during the winter months (Ackerman 1976, Alvarez no date, Kennard 1915). More recently, fire has been suppressed over much of the more developed portions of the area, which has caused unusually severe fires when they finally occur, as they always do eventually (Hofstetter 1984). The lack of fire has allowed succession to proceed in many areas, so that herbaceous communities are being invaded by dense shrub thickets and pine and cypress forests are being invaded by shrubs and hardwoods (Hofstetter 1984).

Exotic plants and animals produce drastic alterations in the composition and structure of natural communities, although many of these changes are poorly documented, such as the impacts resulting from the spread of feral hogs and exotic fish (Crowder 1974, Dineen 1984, Duever et al. 1986, Layne 1984). Some that are well documented include the spread of melaleuca and other exotic plants (Duever et al. 1986, Myers 1975). Some species, such as melaleuca and feral hogs, can readily utilize undisturbed natural communities. However, development has facilitated the invasion of exotics by creating an abundance of disturbed sites that normally would have been recolonized by native species, but these species are now being outcompeted by more rapidly invading exotics (Elton 1958, Odum 1971). In addition, farms and residential areas create new habitats that are more suitable to new species, which then invade adjacent natural areas and impact native populations either directly by predation or indirectly through competition for

resources.44

Bioaccumulation of mercury and other toxins pose a threat to fauna at all trophic levels in all South Florida ecosystems, including the Big Cypress Region, as discussed under generic issues.

D. ECOLOGICAL ATTRIBUTES AND MEASURES

Vegetation community and habitat mosaic . This attribute is affected by all of the stressors except mercury and other toxins, which tend to be more impacting on animal populations than on plant communities. Hydrologic and fire regimes control the character and distribution of the major types of Big Cypress plant communities (Craighead 1971, Davis 1943). The most frequent and widespread hydrologic alterations typically result in reduced depth and duration of inundation, which shifts the affected plant communities upgradient towards shallower wetland types, or with sufficient drainage to upland types (Alexander and Crook 1973, Duever 1984). Fires are more frequent and severe in these drier environments, in some areas resulting in dense stands of fire-tolerant cabbage palms and woody exotics (Gunderson and Loope 1982, Tabb et al. 1976). Drainage can also impact tropical components of the communities by eliminating the moderating effect of standing water on cold winter temperatures (Duever et al. 1978). Less frequent alterations involve increasing depths and/or duration of inundation, which can convert uplands to wetlands and wetlands to aquatic habitats. In some situations, altered hydrology can produce unnatural permanently disturbed habitats that are at times too deeply flooded to support upland vegetation, but for too short a period to produce wetland communities.

Natural communities in South Florida are adapted to surface waters with a chemical composition that contains very low concentrations of dissolved minerals and nutrients. Changes in surface water quality typically involve increased nutrient and mineral concentrations coming from ditch and canal outflows into natural wetlands (Drew and Schomer 1984). These increased concentrations can produce dramatic shifts from diverse herbaceous communities to communities dominated by a few native and exotic nuisance species adapted to high nutrient and dissolved mineral concentrations, such as cattails and primrose willow (Duever pers. comm.).

Dormant season fires and reduced fire frequencies can result in shifts from herbaceous to shrubby communities and from open pinelands and cypress forests to shrub and hardwood dominated forests (Alexander and Crook 1971, Duever 1984). As fuels build up in these sites, the inevitable severe wildfire will eventually occur (Hofstetter 1984), and the sites will most likely be converted to early successional communities dominated by weedy herbaceous, vine and shrub species, a large proportion of which are much less abundant, if even present, in natural communities.45

Land use changes reduce the area of affected communities and often eliminate the transitions from one to another, particularly along upland to aquatic hydrologic gradients. Since wetlands have more legal protection and are more difficult to develop than uplands, habitat loss is greatest in historical uplands, although this may not be obvious because new upland habitat is being created by the drainage occurring throughout much of the area. Upland development is also resulting in wetlands becoming more and more isolated from each other as well as from other natural parts of the system, which is in turn affecting their faunal populations and fire regimes.

All of the ecosystem alterations associated with development are facilitating the increasingly rapid spread of nuisance and exotic species throughout the Big Cypress Region landscape (Drew and Schomer 1984, Duever et al. 1986). In many areas, exotic woody vegetation such as melaleuca, Brazilian pepper, or downy rosemyrtle completely dominates what were previously herbaceous communities or open pinelands. Cattails and primrose willow have replaced marsh communities that once supported diverse herbaceous species assemblages. Feral hogs annually

“ plow ” thousands of acres, with unknown impacts on what they are foraging on, but quite visible soil disturbance effects that further exacerbate the spread of exotic plants (Duever et al. 1986, Layne 1984).

Measurements of changes in the vegetation mosaic in terms of community distribution, composition, and acreages would provide a basis for assessing habitat gains and losses in the Big Cypress Region. The above discussion is not meant to be exhaustive, but provides examples of the kinds of changes that would be useful to monitor, particularly in any areas that are established as major restoration sites or are set aside for preservation. Rates of change in these communities in response to increased or decreased levels of stressors will vary from three to twenty or more years depending on community type and the management required to accomplish restoration. Early succession communities tend to respond more rapidly to changes than do later successional communities. Management that directly affects vegetation, such as herbiciding or prescribed fire, will produce more rapid responses than will management actions that indirectly affect it, such as changes in hydrology or a reduction in fire frequency.

Logging of old growth pines, which occurred in the Big Cypress through the 1950s, has removed many of the prime red-cockaded woodpecker nesting trees throughout its range (Ligon 1971, Patterson and Robertson 1981). In addition, conversion to agriculture and housing is eliminating their habitat, and the current altered fire regime is resulting in the invasion of native and exotic woody vegetation into remaining pinelands, which is eliminating the open character of these pinelands that is needed to support this species (Patterson and Robertson 1981, Jackson 1971). Red-cockaded woodpecker nesting and nesting success is46

recommended as a measure of pineland condition, since this species is dependent upon mature, open pinelands. Suitable habitat should be extensive enough so that it would burn regularly, while having a hydrology that would prevent excessively severe fires. Sites should not support nuisance exotics that would tend to grow up and both eliminate the site ’ s open character and produce fuel loads that would result in excessively severe fires. Response to restoration that increases the suitability of habitat would like be expected within five to ten years, where reestablishing the open character of a pineland is involved, but could be twenty or more years, where young pine stands need to reach large enough sizes to provide suitable nest sites.

Native fish, crayfish, and amphibians . These species are affected primarily by altered hydrology and land use changes, both of which are resulting in habitat loss and fragmentation over large areas of the Big Cypress. Abundance of marsh fishes has been correlated with duration of flooding in the Everglades (Loftus and Eklund 1994), suggesting a decline in fish populations in remaining Big Cypress wetlands where water tables have been lowered and hydroperiods shortened. Habitat fragmentation is particularly damaging to these species, which in more natural settings take advantage of the wet season expansion of surface waters into the surrounding uplands by increasing their numbers and biomass, which then becomes available to wading birds and other predators during the surface water ’ s subsequent retreat during the dry season (Carlson and Duever 1979, Kolopinski and Higer 1969, Kushlan et al. 1975). A poorly known influence on them are exotic fish and amphibian species that have invaded the area, which are both preying on native species and competing with them for resources (Dineen 1984, Duever et al. 1986). Documenting the abundance, distribution, and diversity of these taxa will provide useful measures of how the stressors affecting them are being minimized in protected areas and are being ameliorated in areas being restored. Since these populations show a dramatic annual cycle in their numbers and biomass, responses to increasing or decreasing levels of stressors should be detectable within three to five years.

Wood Stork . The Big Cypress region supported the two largest nesting colonies of wood stork in North America between 1900 and 1965 (Ogden Pers comm.). During that period, 6,000-10,000 pairs nested annually in the Corkscrew colony, the Sadie Cypress colony of Okaloacoochee Slough, and smaller subsidiary colonies. Since 1965, wood stork nesting in Big Cypress has declined and has ranged from less than 500 to 1500 pairs since 1990 (Ogden pers. comm.). The subsidiary colonies have been largely lost. Accompanying the decline in numbers of nesting pairs has been a reduction in nesting success in the remaining colonies. The decline in success is attributed to a change in the timing of the initiation of nesting from November to February (Kushlan et al. 1975, Ogden et al. 1987, Ogden 1994). Delay in nesting until February puts nesting out of sync with seasonal rainfall patterns. With the onset of the wet season, rising water levels decrease food availability before the47

young storks fledge, causing nestling mortality due to starvation. The reduction in numbers of nesting pairs and nesting success is attributed to the loss of early dry season foraging habitat of the higher elevation wetlands of the Big Cypress region that have been drained and developed. Recovery of fish production in the higher elevation wetlands by raising water tables in preserved areas in the western and northern portions of the Big Cypress basin is expected to halt the decline in wood stork nesting in Big Cypress. A trend of increasing numbers of nesting pairs and nesting success and reestablishment of subsidiary colonies should be evident over a decade time scale after water table recovery.

Florida Panther . The Big Cypress Region supports the only viable population of Florida panthers (Logan 1993). The downward spiral of habitat loss and fragmentation leading to isolation and inbreeding has resulted in a single population struggling to survive in the largest remaining contiguous block of land within its historic range. Seventeen years of monitoring indicate a stable but saturated population in the northern portion of its current range, which encompasses public lands north of I-75 and adjacent private lands (Jansen pers. comm.). Habitat vacancies in southern Big Cypress National Preserve and Everglades National Park have not been filled due to the difficulty of population increase when there are few individuals, at times only a single sex, and infrequent ingress. Panther require dry areas for daytime resting but readily travel through inundated habitats (Jansen 1987). Deer, a preferred prey species, benefit from a hydroperiod that promotes nutritious wetland vegetation (Loveless 1959), and prescribed fire improves the nutritional quality of food used by panther prey species. Stressors for the panther include continued habitat loss, inbreeding, and mercury toxicosis. Whether the panther can survive on only existing public lands is unknown, but further habitat reduction will likely increase its vulnerability to catastrophic events. Efforts to improve genetic diversity have been initiated through the introduction of another cougar subspecies. The sources of methyl mercury, reported as the cause of death of at least one panther and known to compromise normal biological functions, have yet to be confirmed and remedied (Roelke et al. 1991). Habitat protection and restoration of natural hydroperiods with clean water would benefit the panther by providing suitable land for population expansion, as well as an uncontaminated and abundant prey base (Jansen, pers. comm.). Improvements in population size, reproductive success, and mercury body burden would likely take decades to document, given the current small population size, low reproductive rate, and the slow turnover of mercury in the body, although improvements in the prey base could be apparent in less than a decade.

Health of Aquatic Fauna . Potential inputs of mercury and other toxins in agricultural and urban runoff water, which may be needed for hydropattern restoration in the Big Cypress, could result in reduced health, behavioral and physical abnormalities, and loss of reproductive vigor unless measures are taken to48

restrict loads of these toxins in waters flowing into natural areas. Measures of aquatic faunal health that reflect responses to the mercury and pesticide inputs include body burdens of mercury and other toxins in representative species

.

E. HYDROLOGIC PERFORMANCE MEASURES FOR RESTORATION

Successful protection of undisturbed areas and restoration of disturbed areas require the establishment of hydrologic targets that define the desired characteristics of a site ’ s hydrologic regime, and hydrologic measures that evaluate the current status of the site relative to the target. In the portions of the Big Cypress that are included in both the Natural System Model (version NSM4.5F) and the South Florida Water Management Model (SFWMM), NSM conditions were defined as the hydrologic target. The following performance measures were used to evaluate the hydrologic condition of various distinct portions of the area as they were shown to be affected by proposed restoration Alternatives included in a modified version of the SFWMM. Plans are underway to create an expanded version of the SFWMM that will include all of the Big Cypress Region. At the moment there are no plans to create a NSM for the area, although this would be more feasible after the SFWMM is available, since the original NSM was created by modifying the existing SFWMM. Until this model is available, it will be difficult to accurately utilize the following performance measures for the remaining portion of the Big Cypress. Information on the hydrologic regimes of the major Big Cypress freshwater plant community types are described in Duever (1984), and these could be used as interim hydrologic targets for particular communities.

All aspects of a plant community ’ s hydrologic regime are significant in determining its taxonomic and structural characteristics, as well as its distribution across the Big Cypress landscape. The annual duration of inundation, or hydroperiod, is the most important aspect of the hydrologic regime (Duever 1984), largely because of South Florida ’ s minimal topographic relief and its distinct wet and dry seasons. Short hydroperiods eliminate wetland species that are intolerant of the more frequent and severe fires on sites that are dry most of the year, while long hydroperiods eliminate upland species intolerant of extended inundation in low areas (Duever et al. 1978). Maximum and minimum water levels are also important. Wet season water depths can eliminate emergent species that cannot tolerate extended periods of being submerged. The extent of dry season water level declines can influence the frequency and severity of fires entering wetlands, particularly those with organic soils, which maintain a relatively moist substrate and microclimate as long as they are in contact with the water table (Coultas and Duever 1984). During the wet season, water naturally moved as sheet flow across the Big Cypress (Klein et al. 1970). The fact that the water is moving is important, particularly in terms of the resulting water column mixing, which produces a very different water quality than is found in ponded water.49

Duration of inundation was evaluated using a number of performance measures. One that provided a spatial perspective of hydroperiod was the percentage of acres within a defined area with a mean hydroperiod for the 31 year simulation that was within 30 days (longer or shorter) of NSM conditions. Another compared average hydroperiod for the 31 year simulation in a specified area in terms of the absolute difference between NSM and current or proposed conditions, which is divided by 100 and then subtracted from 1. This deviation was almost always a reduction in hydroperiod, but any deviation is documented by using the absolute value for the deviation. Another perspective is provided by determining the absolute difference in the average duration of individual flooding events for NSM compared to current or proposed conditions in a defined area, dividing this difference by the NSM duration, and subtracting this value from 1.

Deviations from NSM water levels above and below ground were evaluated by examining the normalized weekly stage-duration curve from a 31 year simulation for a defined area. The performance measure involved examining the current or proposed condition stage-duration curve and determining its maximum vertical deviation from the NSM curve, and dividing this value by the maximum vertical range of NSM water level fluctuation at the site. The reason for dividing the absolute deviation by the maximum NSM water level fluctuation is that a certain degree of deviation in an area with a large natural fluctuation would be less significant than the same degree of deviation in an area with a small natural fluctuation. Typically, the greatest deviation occurred when the water table was declining through the first foot or two below the ground surface, it was smallest at its lowest point on the hydrograph, and it was relatively small when the water table was above ground.

Documenting total flows during the wet and dry season provides a measure of water movement across a defined boundary and how it changes in response to proposed hydrologic alterations in a particular portion of the Big Cypress. The absolute deviation between NSM and current or proposed condition flows was determined first, this value was divided by NSM flows, and the resulting value subtracted from 1. Initially flows were evaluated separately for the wet and dry season, so that the greater volumes of water moving during the wet season wouldn ’ t overshadow the smaller dry season flow volumes. Simple additive equations were then developed for a flow cross-section to combine the wet and dry season information.

In the final analyses, all of the performance measures for a defined area were combined in a simple additive equation. Since there could be three measures for flooding duration and only one each for water level and flows, this automatically weighted flood duration more strongly than either of the other two components of the hydrologic regime.50

It is important to be aware that the above performance measures are based on long-term averages, and there is a great deal of natural year-to-year variability in these values. In addition, the same types of communities vary substantially from one place to another, because of differences in their setting and site history. Even though extreme environmental events can have major affects in shaping natural communities, they don ’ t normally produce shifts from one community type to another because the overall ecosystem has evolved in the context of these events.52

F. REFERENCES

Ackerman, J.A., Jr. 1976. Florida cowman, a history of Florida cattle raising. Florida Cattleman ’ s Association, Kissimmee. 287 pp.

Alexander, T.R. and A.G. Crook. 1973. Recent and long term vegetation changes and patterns in South Florida. Appendix G, Part I. South Florida ecological study. University of Miami, Coral Gables, Florida. 215 pp.

Alvarez, K.C. no date. A brief history of Florida cattle ranching (1521-1900). Unpublished report. 68 pp.

Carlson, J.E. and M.J. Duever. 1979. Seasonal fish population fluctuations in south Florida swamp. Proceedings of Annual Conference of Southeastern Association of Fish and Wildlife Agencies 31: 603-611.

Carter, M.R., L.A. Burns, T.R. Cavinder, K.R. Dugger, P.L. Fore, D.B. Hicks, H.L. Revells, and T.W. Schmidt. 1973. Ecosystem analysis of the Big Cypress Swamp and estuaries. United States Environmental Protection Agency. EPA 904/9-74-002. 375 pp.

Coultas, C.L. and M.J. Duever. 1984. Soils of cypress swamps. Pages 51-59 in H.T. Odum and K.C. Ewel, eds. Cypress swamps. University of Florida Press, Gainesville.

Craighead, F.C., Sr. 1971. The trees of South Florida. Volume 1. The natural environments and their succession. University of Miami Press, Miami, Florida. 212 pp.

Crowder, J.P. 1974. The exotic vertebrates of South Florida. United States Department of the Interior, Bureau of Sport Fisheries and Wildlife, Ecological Report DI-SFEP-74-30. 43 pp.

Davis, J.H., Jr. 1943. The natural features of Southern Florida. Florida Geological Survey Bulletin 25. 311 pp.

Dineen, J.W. 1984. The fishes of the Everglades. Pages 258-268 in P.J. Gleason, ed.Environments of South Florida: past and present II. Miami Geological Society, Miami, Florida.

Drew, R.D. and N.S. Schomer. 1984. An ecological characterization of the Caloosahatchee River/Big Cypress watershed. United States Department of the Interior Minerals Management Service and Fish and Wildlife Service. FWS/OBS-82/58.2. 225 pp.53

Duever, M.J., J.E. Carlson, L.A. Riopelle, and L.C. Duever. 1978. Ecosystem analyses at Corkscrew Swamp. Pages 534-570 in H.T. Odum and K.C. Ewel, eds. Cypress wetlands for water management, recycling, and conservation. Fourth annual report to National Science Foundation and Rockefeller Foundation. Center for Wetlands, University of Florida, Gainesville.

Duever, M.J. 1984. Environmental factors controlling plant communities of the Big Cypress Swamp. Pages 127-137 in P.J. Gleason, ed. Environments of South Florida: past and present II. Miami Geological Society, Miami, Florida.

Duever, M.J., J.E. Carlson, J.F. Meeder, L.C. Duever, L.H. Gunderson, L.A. Riopelle, T.R. Alexander, R.L. Myers, and D.P. Spangler. 1986. The Big Cypress National Preserve. National Audubon Society Research Report No. 8, New York. 455 pp.

Elton, C.S. 1958. The ecology of invasions by animals and plants. John Wiley, New York. 199 pp.

Forman, R.T.T., and M. Godron. 1986. Landscape Ecology. John Wiley and Sons, New York.619 pp.

Gunderson, L.H. and L.L. Loope. 1982. A survey and inventory of the plant communities in the Raccoon Point area, Big Cypress National Preserve. South Florida Research Center, National Park Service, Everglades National Park, Homestead, Florida. Report T-665. 36 pp.

Harper, R.M. 1927. Natural resources of southern Florida. 18 th Annual Report of Florida Geological Survey, Tallahassee. 25-206.

Harris, L.D. 1984. The fragmented forest: island biogeography theory and the preservation of biotic diversity. University of Chicago Press, Chicago, Illinois. 211 pp.

Hofstetter, R.H. 1984. The effect of fire on the pineland and sawgrass communities of southern Florida. Pages 465-476 in P.J. Gleason, ed. Environments of South Florida: past and present II. Miami Geological Society, Miami, Florida.

Jackson, J.A. 1971. The evolution, taxonomy, distribution, past populations and current status of the red-cockaded woodpecker. Pages 4-29 in R.L. Thompson, ed. Proceedings of a Symposium on the Red- cockaded Woodpecker, Okefenokee National Wildlife Refuge, Folkston, Georgia.54

Jansen, D.K. 1987. Big Cypress use study. Florida Game and Freshwater Fish Commission, Tallahassee. 240 pp.

Kennard, F.H. 1915. The Okaloacoochee Slough. Auk 32: 154-166.

Klein, H., W.J. Schneider, B.F. McPherson, and T.J. Buchanan. 1970. Some hydrologic and biologic aspects of the Big Cypress Swamp drainage area. United States Geological Survey Open File Report 70003. 94 pp.

Kolopinski, M.C. and A.L. Higer. 1969. Some aspects of the effects of the quantity and quality of water on biological communities in the Everglades National Park. United States Geological Survey, Open File Report 69007. 97 pp.

Kushlan, J.A., J.C. Ogden, and A.L. Higer. 1975. Relation of water level and fish availability to wood stork reproduction in the southern Everglades, Florida. United States Department of the Interior, Geological Survey, Open File Report 75-434. 56 pp.

Layne, J.N. 1984. The land mammals of South Florida. Pages 269-296 in P.J. Gleason, ed. Environments of South Florida: past and present II. Miami Geological Society, Miami, Florida.

Lehman, M.E. 1976. Collier County: growth pressure in a wetlands wilderness. Florida Bureau of Comprehensive Planning. Tallahassee. 59 pp.

Ligon, J.D. 1971. Some factors influencing numbers of the red-cockaded woodpecker. Pages 30-43 in R.L. Thompson, ed. Proceedings of a Symposium on the Red- cockaded Woodpecker, Okefenokee National Wildlife Refuge, Folkston, Georgia.

Loftus, W.F. and A. Eklund. 1994. Long-term dynamics of an Everglades smallfish assemblage. Pages 461-483 in S.M. Davis and J.C. Ogden, eds. Everglades: the ecosystem and its restoration. St. Lucie Press, Delray Beach, Florida.

Logan, T., A.C. Eller, Jr., R. Morrell, D. Ruffner, J. Sewell. 1993. Florida panther habitat preservation plan: south Florida population. Florida Panther Interagency Committee. 105 pp.

Loveless, C.M. 1959. The Everglades deer herd, life history and management. Florida Game and Freshwater Fish Commission Technical Bulletin 6. 104 pp.55

Myers, R.L. 1975. The relationship of site conditions to the invading capability of Melaleuca quinquenervia in southwest Florida. Master ’ s Thesis, University of Florida, Gainesville. 151 pp.

Odum, H.T. 1971. Environment, power, and society. John Wiley, New York. 331 pp.

Ogden, J.C., D.A. McCrimmon, Jr., G.T. Bancroft, and B.W. Patty. 1987. Breeding populations of the wood stork in the southeastern United States. The Condor 89: 752-759.

Ogden, J.C. 1994. A comparison of wading bird nesting colony dynamics (1931- 1946 and 1974- 1989) as an indication of ecosystem conditions in the southern Everglades. Pages 533-570 in S.M. Davis and J.C. Ogden, eds. Everglades: the ecosystem and its restoration. St. Lucie Press, Delray Beach, Florida.

Patterson, G.A., and W.B. Robertson, Jr. 1981. Distribution and habitat of the redcockaded woodpecker in the Big Cypress National Preserve. South Florida Research Center, National Park Service, Homestead, Florida. 137 pp.

Robertson, W.B., Jr. 1953. A survey of the effects of fire in Everglades National Park. Unpublished Report. United States Department of the Interior, National Park Service, Homestead, Florida. 169 pp.

Rochow, T.F. 1985. Hydrologic and vegetational changes resulting from underground pumping at the Cypress Creek well field, Pasco County, Florida. Florida Scientist 48: 65-80.

Roelke, M.E., D.P. Schultz, C.F. Facemire, S.F. Sundlof, and H.E Royals. 1991. Mercury contamination in Florida panthers. Florida Panther Technical Subcommittee. 55 pp.

Swayze, L.J. and B.F. McPherson. 1977. The effect of the Faka Union canal system on water levels in the Fakahatchee Strand, Collier County, Florida. United States Geological Survey Water Resources Investigation. 77-61.

Tabb, D.C., E.J. Heald, T.R. Alexander, M.A. Roessler, and G.L. Beardsley. 1976. An ecological and hydrological assessment of the Golden Gate Estates drainage basin, with recommendations for future land use and water management strategies. Tropical Bioindustries Development Company. Miami, Florida. 178 pp.56

Wade, D., J. Ewel, R. Hofstetter. 1980. Fire in south Florida ecosystems. United States Department of Agriculture, Forest Service General Technical Report SE-17. 125 pp.57



### V. EVERGLADES RIDGE AND SLOUGH CONCEPTUAL MODEL

A. PREPARER

John C. Ogden, South Florida Water Management District, West Palm Beach, Florida.

B. INTRODUCTION

As natural systems, the Ridge and Slough landscape feature s of the Everglades were extensive, long-hydroperiod, freshwater marshes, characterized by low-velocity "sheet flow", moderate to deep organic soils and sawgrass “ ridges (Davis et al. 1994, Gunderson 1994, Gunderson and Loftus 1993, McVoy, Park & Obeysekera in prep.) ” . The ridge and slough systems were dominated by sawgrass strand (Cladium), water lily, and wet prairie (Eleocharis) communities. A spatially variable mosaic of discreet tree islands occurred throughout, ranging from widely spaced in the central Everglades to more densely distributed islands in the Loxahatchee basin and Shark Slough. The Ridge and Slough systems modeled here are defined by the portion of the Everglades basin where there were Loxahatchee Peat soils (McVoy, Park and Obeysekera, in prep.; the combined “ wet prairie/slough, tree island, sawgrass mosaic ” and “ sawgrass dominated mosaic ” in Davis et al. 1994). These sloughs made up the deeper central portions of the total Everglades basin, and occurred to a more limited extent in a series of much smaller scale flow systems located on both the eastern and western flanks of the Shark Slough in the southern Everglades (Taylor, East, Middle, Lostman's sloughs). The ridge andsloughs were principal centers for primary and secondary production and interannual survival of aquatic organisms in the freshwater wetlands of southern Florida.

The major, known alterations in the ridge and slough systems have been caused by changes in land use, drainage and water management practices in south Florida (Davis and Ogden 1994, Science Subgroup 1993). The effects from these regional “ drivers ” include compartmentalization and reduced spatial extent of the natural system, loss of organic soils, altered water depth, distribution and flow patterns, altered water chemistry, and the introduction of exotic species. It is the effects from these “ stressors ” which are modeled in the conceptual ecological model for the ridge and slough systems, which is presented here.

C. THE SOCIETAL DRIVERS, ECOLOGICAL STRESSORS, AND ECOLOGICAL EFFECTS

The workshops of the SERA Natural Systems Team and the C&SF Restudy Alternative Evaluation Team have identified four major categories of external societal influence (drivers) on the Everglades Ridge and Slough systems, leading to58

five major ecological stressors. The combined effects from these stressors explain much of the ecological changes which have occurred in the ridge and slough systems (refer to figure on page 65). The four societal drivers and their respective stressors, and the ecological effects resulting from the stressors, are as follows.

Urban and Agricultural Expansion . Drainage of wetlands, and the subsequent conversion of slough habitat into agricultural and urban uses has reduced the total spatial extent of the ridge and slough system in the main Everglades from 490,000 ha in the pre-drainage system to 365,000 ha in the current system (Davis et al. 1994). The biological and physical effects from this 26% loss in spatial extent include, (a) a substantial reduction in habitat options for wildlife, and (b) a reduction in the system-wide levels of primary and secondary production.

Space was the one physical characteristic of the south Florida wetlands that was necessary for all other physical and ecological components of these systems to be in place. The broad spatial extent of the pre-drainage sloughs was essential for collecting and storing the amount of regional rainfall that was required to maintain the ecological vigor of these systems. Large spatial scale provided the foundation for the processes that created and maintained a mosaic of habitats in a low profile terrain (Craighead 1971, DeAngelis & White 1994). Disturbances, such as fire,freezes, tropical storms, and animal related impacts (e.g., an abundance of alligatorcreated ponds and trails) served to increase the complexity of habitats, as well as the range of habitat choices for species of wildlife with both small and large home ranges (Craighead 1968, DeAngelis 1994, Duever et al. 1994, Gunderson & Snyder 1994, Davis & Ogden 1994). Extensive space was necessary for supporting robust numbers of animals requiring extensive feeding or hunting ranges throughout different seasons and a range of hydrological conditions For example, the location of feeding and nesting sites for white ibis and other wading birds, snail kites, and other common aquatic birds shifted across large spatial scales and across seasons and years, in response to variability in hydrological patterns (Kushlan 1979, Bennetts et al. 1994, Hoffman et al. 1994, Ogden 1994). The large number of ponds and depressions occurring over an extensive region allowed for comparatively sedentary species such as the alligator to maintain very large, regional numbers (Craighead 1968). Greater space enabled the system-wide aquatic production in a nutrient-poor ecosystem necessary to support large numbers of wading birds and alligators (Browder 1976, Mazzotti and Brandt 1994).

(2.) Influences from Industrial and Agricultural Practices . Increased loads of Phosphorus (P) and Mercury (Hg), originating as bi-products from an array of agricultural and urban industrial practices, were identified as the two alterations in water quality which have been demonstrated or hypothesized, respectively, to have had the greatest ecological significance in the slough systems (Roelke et al. 1991, Spalding & Forrester 1991, Lange et al. 1994, Browder et al. 1994, Davis 1994, Frederick et al. 1997). Increased phosphorus loading in a low-nutrient system59

has, (a) caused a substantial expansion of "nutrient-loving" plants (monocultures of cattail) into other communities, (b) contributed to shifts in the species composition in periphyton mats, from communities dominated by green algae/diatoms to communities dominated by blue-green algae, and (c) contributed to reductions or alterations in primary and secondary production patterns. Increased levels of environmental mercury, and the conversion to the toxic methyl mercury form, has considerable potential to substantially reduce survival rates, and alter behavior patterns, for omnivorous and carnivorous animals dependent on wetland food chains.

(3.) Water Management Practices . All five of the major ecological stressors acting on the slough systems (reduced spatial extent, the introduction and spread of degraded water, reduced water storage capacity, compartmentalization , and the introduction and spread of exotic species) have had part or all of their origins in water management practices. Major objectives of water management have included water supply and flood control, which have been achieved by means of a complex system of structural and operational modifications to the natural system. These modifications have, (a) contributed to the substantial reduction in spatial extent, (b) provided a network of canals and levees which have accelerated the spread of degraded water and exotic species, (c) greatly reduced the water storage capacity within the remaining natural system, (d) altered sheet flow velocities and directions, and (e) created an unnatural mosaic of impounded and over-drained marshes in the Water Conservation Areas (Science subgroup 1993, Davis and Ogden 1994, Light and Dineen 1994, Fennema et al. 1994).

Ecological effects from (a) and (b) are summa rized in (1) and (2) above. The combined effects from reduced water storage capacity, altered sheet flow patterns and compartmentalization have, paradoxically, included both a reduction in the duration of annual and multi-year hydroperiods and an increase in the frequency of unnatural high water events.

Shortened hydroperiods (i.e., an increase in the frequency and duration of surface water dryouts) have resulted in a substantial increase in the frequency and extent of over-drained marshes, primarily during dry season months. Over-drained marshes have contributed to a broad array of adverse ecological impacts, including the spread of woody species of plants into marshes, reduced alligator nesting effort, reduced levels of aquatic production, reduced survival by aquatic organisms over multi-year periods, and considerable loss of peat soils due to increased frequencies and intensities of fire and increased levels of soil oxidation (e.g., Craighead 1971, Davis and Ogden 1994, Fleming 1991, Gunderson and Loftus 1993, Loftus et al. 1990, Loftus et al. 1992, Loftus and Eklund 1994, Mazzotti and Brandt 1994, Myers 1983, Stober et al. 1996 ).60

The unnaturally distributed mosaics of impounded water in the southern portions of the WCAs, caused by compartmentalization, have contributed to the flooding of tree islands, have altered marsh community structure, and have caused an artificial re-distribution of the centers of aquatic production and animal survival throughout the WCA portion of the ridge and slough system (Armentano 1996, Bancroft et al. 1994, Davis et al. 1994, Fennema et al. 1994, Frederick and Spalding 1994). The break-up of the large, traditional wading bird nesting colonies and relocation of smaller, less successful colonies to the WCAs, are hypothesized to be responses by wading birds to the combined affects of marsh drainage and the relocation and fragmentation of the region's aquatic production and survival centers (Ogden 1994).

Societal influences on the species composition of regional floras/faunas

. The introduction, both intended and unintended, of large numbers of non-native species of plants and animals that have been brought into south Florida because they have been considered to be desirable additions to the region, from the perspective of a wide range of human values, has resulted in substantial alterations to the Everglades sloughs. The most blatant examples affecting the sloughs have been, (a) the invasions by Melaleuca, and the conversion of extensive marshes into woody swamps (Bodle et al. 1994, Laroche and Ferriter 1992), and (b) the spread by 15-20 species of introduced fishes throughout much of the region of the ridge and slough systems (Courtenay 1994, Robertson and Frederick 1994). Although the ecological consequences of these fishes has been largely unmeasured, it must be assumed that their presence has substantially altered the characteristics of marsh fish communities.

D. CRITICAL ECOLOGICAL PATHWAYS

The principal, broad-scale ecological responses from the combined affe cts of the five major ecological stressors acting on the ridge and slough systems have been, (a) a substantial alteration and degradation in the natural patterns of plant community composition and structure, and (b) substantial changes in the distribution, and reductions in abundance, among many of the native animals that are dependant on aquatic habitats and food chains. The relative contribution made by each of the stressors, along the different pathways shown in the model, to these two primary responses is not well known. For example, the presence of physical and biological thresholds, some of which may have been crossed as a result of the affects of the stressors, have yet to be demonstrated for most functions andrelationships in the sloughs (an exception might be the 10 ppb value for Ph). Neverthe-less, current understandings of the ridge and slough systems, as expressed by the NST and AET workshop participants, suggest that four ecological pathways have been most important for explaining how these two principle, broad-scale, ecological responses have been linked to the stressors. These four pathways are:61

(1.) The pathway that links the reduction in water storage capacity and the substantial increase in the extent and frequency of over-drained marshes (shortened hydroperiods), with an array of ecological effects characterized by a spread in woody vegetation, reduced numbers of nesting alligators, reduced marsh production, reduced dry season survival by aquatic organisms, and the loss of peat soils.

(2.) The pathway that links compartmentalization, and the adverse affects that levees have on water depth/distribution patterns and sheet flow, with altered patterns of nutrient cycling and reduced marsh production, and relocated animal distribution, production and survival centers.

(3.) The pathway that links the reduction in water storage capacity, compartmentalization and the adverse affects of regulatory releases, with flooded tree islands and flooded alligator nests.

(4.) The duel pathways that link degraded water quality and the affects of canals with increased phosphorus loading, resulting in the spread of cattail monocultures, degraded periphyton communities, and reduced marsh production.

E. ECOLOGICAL ATTRIBUTES AND MEASURES

The NST and AET workshops recommended seven ecological attributes of the Everglades ridge and slough systems, which, collectively, will provide the best measure of system responses to restoration projects (refer to figure on page 65). The model shows how each attribute is linked to one or more stressor. The recommended measures for each attribute should be treated as priority components for a comprehensive ecological monitoring program.

(1.) Peat Soils. A recovery of more natural patterns in the duration of uninterrupted surface flooding, and in water depths, should result in the return of pre-drainage rates of accretion for peat soils. Conversely, unnatural rates of loss of organic soil due to oxidation and excessive fires should be curtailed.

(2.) Community of Marsh Fishes, Invertebrates & Herps. Improved water quality, longer hydroperiods, improved patterns of nutrient cycling and primary production, and reductions in the influences of exotic fishes, should be reflected by measures of the composition, size structure and abundance of these animals.

(3.) Tree Islands. Reductions in the adverse affects of flooding, fire, and exotic plants should be reflected by measures of tree island distribution, and by the species composition and structure of woody plants on the islands.62

(4.) Marsh Plant Communities. Elimination of the adverse impacts due to excessive fire, soil oxidation, shortened hydroperiods, unnaturally deep impoundments, overdrained marshes, the spread of exotic plants, and degraded water quality should be reflected by measures of the distribution, composition and structure of the dominant marsh communities in the sloughs.

(5.) Alligators. An increase in the abundance and density of alligator nests and active alligator ponds is an expected response from lengthened hydroperiods, increased marsh production rates, and reductions in wet season regulatory releases and the unnatural affects of impoundments.

(6.) Periphyton. Improvements in water quality and in the depth and duration of flooding should be reflected by shifts in species composition and production rates in the periphyton communities.

(7.) Wading Birds. The size, timing and location of wading bird nesting colonies, as well as the occurrence and frequency of "super colonies", should reflect improvements in foraging habitat options under a range of climatological conditions, in marsh production rates, survival rates of marsh organisms during dry periods, and in the location of the major production and survival centers in the slough systems.

F. HYDROLOGICAL PERFORMANCE MEASURES

The four critical pathways (above) suggested by the Everglades ridge and slough model are driven by hydrological stressors (over-drained marshes due to reduced storage capacity; unnatural depth-distribution patterns due to levees; wet season flooding due to regulatory releases and the affects of canals and levees; increased phosphorus levels due to agricultural practices and canals). These pathways suggest that the most important hydrological targets for meeting the ecological objectives of the SERA and Restudy projects are, (a) reduction in the frequency, duration, extent and magnitude of marsh dryouts during dry seasons, (b) reduction in the unnatural spatial mosaics of deep impoundments and over-drained marshes, reductions in the duration and unseasonable timing of unnatural high water events during wet seasons, and (d) reductions in the input and rapid distribution of phosphorus. The shortened dry-season hydroperiods characteristic of the managed system are a response to substantially reduced water storage capacity in the system, coupled with the affects of compartmentalization. The unnatural mosaics of deep and shallow water are caused by compartmentalization; more specifically, by the network of levees and the operational schedules associated with the WCAs. The unnatural wet season depth patterns have been due to the combined affects of water storage in WCA-3A, and regulatory releases through the S-12s. These three stressors working in concert have caused a loss of natural patterns of inter-seasonal and inter-annual water depth distribution and depth,63

which is thought to have substantially disrupted the pulses in marsh production that once characterized the natural system. The increased phosphorus loading has been due to the rapid transport of water with elevated phosphorus levels into much of the Everglades ridge and slough system.

Of these four priority hydrological targets, three are characterized by measures of water depth, and the duration and timing of surface and ground water flooding. For these three, hydrological performance measure targets can be established, based on regional hydrological patterns predicted by the Natural Systems Model. These performance targets, and a suggested order of priority relative to the magnitude of the ecological issues associated with each, are as follows.

Priority 1. The highest priority for ecological restoration of the Everglades ridge and slough systems is the establishment of annual and interannual patterns in the duration of uninterrupted surface flooding, which are generally consistent with predictions of the NSM, in Everglades National Park and the WCAs. Included in this priority is the increase in duration of flooding in the overdrained, northern ends of the WCAs without an increase in flooding in the southern WCAs, and a recovery of the pre-drainage patterns of multi-year hydroperiods in Shark Slough.

Priority 1 Measure. For the 30 year period of record, compare patterns of uninterrupted surface water flooding for cells at key indicator regions. The performance criterion is the difference between the duration patterns shown by the NSM and the 2X2 simulations for each plan alternative. The target is a mean difference of zero. Examine annual hydrographs to insure trends are correct and that the annual drydown in any given year does not occur before the time indicated by the NSM.

Priority 2. Elimination of compartmentalization effects, characterized by unnatural mosaics of deep and shallow water across levee alignments, and by loss of sheet flow.

Priority 2 Measure. Compare monthly surface and ground water depth patterns for selected sets of cells representing opposite sides of levees, for all major structural divides within the WCAs, and between WCA 3 and Everglades National Park. The performance criterion is for water depths between paired sets of cells to not differ more than 0.2 foot during any given month, and for these depth patterns to be consistent with NSM predictions. For sheet flow, compare numbers of miles of levees and canals internal to the ridge and slough systems, and separating the ridge and sloughs from adjacent wetlands (i.e., sawgrass plain; Big Cypress).

Priority 3. A third priority in the ecological restoration of the Ev erglades sloughs is the elimination of regulatory schedules and other operational practices,64

and internal levees, which cause unnaturally deep water patterns, primarily during
wet seasons.

Priority 3 Measure. For the 30 year period of record, compare mo nthly patterns of surface water depth for cells at key indicator regions. The performance criterion is the difference between the depth patterns shown by the NSM and the 2X2 simulations for each plan alternative. The target is a mean difference of zero. Examine monthly depth pattern graphs to insure trends are correct for timing and location, relative to NSM patterns.66

G. REFERENCES

Armentano, T.V (ed.). 1996. Proceedings of the conference: Ecological assessment of the 1994-1995 high water conditions in the southern Everglades. Everglades National Park, Homestead, Fl. 210 pp.

Bancroft, G.T., A.M. Strong, R.J. Sawicki, W. Hoffman and S.D. Jewell. 1994. Relationships among wading bird foraging patterns, colony locations, and hydrology in the Everglades. Pp. 615-657 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Bennetts, R.E., M.C. Collopy and J.A. Rodgers, Jr. 1994. The snail kite in the Florida Everglades: a food specialist. Pp. 507-532 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Bodle, M.J., A.P. Ferriter and D.D. Thayer. 1994. The biology, distribution, and ecological consequences of Melaleuca quinquenervia in the Everglades. Pp. 341-355 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Browder, J.A. 1976. Water, wetlands, and Wood Storks in southwest Florida. Ph.D. dissertation, Univ. Florida. Gainesville, FL. 406 pp.

Browder, J.A., P.J. Gleason, and D.R. Swift. 1994. Periphyton in the Everglades: spatial variation, environmental correlates, and ecological implications. Pp. 379-416 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Courtenay, W.R., Jr. 1994. Non-indigenous fishes in Florida. Pp. 57-63 in, An assessment of invasive non-indigenous species in Florida ’ s public lands (D.C. Schmidt and T.C. Brown, eds.). Tech. Report TSS-94-100, Bureau of Aquatic Plant Management, FDEP, Tallahassee, FL

Craighead, F.C., Sr. 1968. The role of the alligator in shaping plant communities and maintaining wildlife in the southern Everglades. Florida Naturalist 41: 2-7, 69-74, 94.

Craighead, F.C., Sr. 1971. The trees of south Florida. Vol. 1. The natural environments and their succession. Univ. Miami Press, Coral Gables, FL67

Davis, S.M. 1994. Phosphorus inputs and vegetation sensitivity in the Everglades. Pp. 357-378 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Davis, S.M. and J.C. Ogden. 1994. Towards ecosystem restoration. Pp. 769-796 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Davis, S.M., L.H. Gunderson, W.A. Park, J. Richardson, and J. Mattson. 1994. Landscape dimension, composition, and function in a changing Everglades ecosystem. Pp. 419-444 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

DeAngelis, D.L. 1994. Synthesis: Spatial and temporal characteristics of the environment. Pp. 307-320 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

DeAngelis, D.L. and P.S. White. 1994. Ecosystems as products of spatially and temporally varying driving forces, ecological processes, and landscapes. Pp. 9-27 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, rds.). St. Lucie Press, Delray Beach, FL.

Duever, M.J., J.F. Meeder, L.C. Meeder and J.M. McCollom. 1994. The climate of south Florida and its role in shaping the Everglades ecosystem. Pp. 225-248 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Fennema, R.J., C.J. Neidrauer, R.A. Johnson, W.A. Perkins, and T.K. MacVicar. 1994. A computer model to simulate natural south Florida hydrology. In: S.M. Davis and J.C. Ogden (eds.), Everglades. The ecosystem and its restoration. St. Lucie Press, Delray Beach, FL.

Fleming, D.M. 1991. Wildlife ecology studies. 1991 annual reports. South Florida Research Center, Everglades National Park, Homestead, FL. Vol. 1, sect. 5.

Frederick, P.C. and M.G. Spalding. 1994. Factors affecting reproductive success of wading birds (Ciconiiformes) in the Everglades ecosystem. Pp. 659-691 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Frederick, P.C., M.G. Spalding, M.S. Sepulveda, G. Williams, S. Bouton, H. Lynch, J. Arrecis, S. Loerzel and D. Hoffman. 1997. Effects of environmental mercury exposure on reproduction, health and survival of wading birds in the68

Florida Everglades. Final Report. Department Wildlife Ecology and Conservation. Univ. Florida, Gainesville, FL 126 pp.

Gunderson, L.H. 1994. Vegetation of the Everglades: determinants of community composition. Pp. 323-340 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL

Gunderson, L.H. and W.F. Loftus. 1993. The Everglades. Pp. 199-255 in, Biotic communities of the southeastern United States (W.H. Martin, S.G. Boyce and A.C. Echternacht, eds.). John Wiley & Sons, New York, NY.

Gunderson, L.H. and J.R. Snyder. 1994. Fire patterns in the southern Everglades. Pp. 291-305 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Hoffman, W., G.T. Bancroft and R. J. Sawicki. 1994. Foraging habitat of wading birds in the water conservation areas of the Everglades. Pp. 585-614 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Kushlan, J.A. 1979. Feeding ecology and prey selection in the white ibis. Condor 81: 376-389.

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LaRoche, F.B. and A.P. Ferriter. 1992. The rate of expansion of melaleuca in south Florida. Jour. Aquatic Plant Management 30: 62-65.

Light, S.S. and J.W. Dineen. 1994. Water control in the Everglades: a historical perspective. Pp. 47-84 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Loftus, W.F. and A. Eklund. 1994. Long-term dynamics of an Everglades smallfish assemblage. Pp. 461-483 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Loftus, W.F., J.D. Chapman and R. Conrow. 1990. Hydrological effects on Everglades marsh food webs, with relation to marsh restoration efforts. Pp. 1-22 in, Fisheries and coastal wetlands research (G.Larson and M. Soukup, eds.). Proceedings of a 1986 conference on science in National Parks. Ft. Collins, CO.69

Loftus, W.F., R.A. Johnson and G. Anderson. 1992. Ecological impacts of the reduction of groundwater levels in the rocklands. Pp. 199-208 in, Proceedings of the First International Conference of Groundwater Ecology (J.A. Stafford and J.J. Simon, eds.). American Water Resources Association, Bethesda, MD.

McVoy, C., W. Park and J. Obeysekera. In Prep.

Mazzotti, F.J. and L. A. Brandt. 1994. Ecology of the American Alligator in a seasonally fluctuating environment. Pp. 485-505 in Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL.

Myers, R.L. 1983. Site susceptibility to invasion by the exotic tree Melaleuca quinquenerva in south Florida. Jour. Applied Ecology, 20: 645-658.

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Robertson, W.B., Jr. and P.C. Frederick. 1994. The faunal chapters: context, synthesis, and departures. Pp. 709-737 in, Everglades. The ecosystem and its restoration (S.M. Davis and J.C. Ogden, eds.). St. Lucie Press, Delray Beach, FL

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Science Sub-group. 1993. Federal objectives for the south Florida restoration. The Science Sub-group of The South Florida Management and Coordination Working Group.

Spalding, M.G. and D.J. Forrester. 1991. Effects of parasitism and disease on the nesting success of colonial wading birds (Ciconiiformes) in southern Florida. Florida Game and Fresh Water Fish Commission, Nongame Wildlife Program. Report NG88-008. Tallahassee, FL. 106 pp.

Stober, J., D. Scheidt, R. Jones, K. Thornton, R. Ambrose and D. France. 1996. South Florida ecosystem assessment. Monitoring for adaptive management: Implications for ecosystem restoration. Interim report. Environmental Protection Agency EPA 904-R-96-008.71



### VI. MARL PRAIRIE/ROCKY GLADES CONCEPTUAL MODEL

A. PREPARER

Steven M. Davis, South Florida Water Management District, West Palm Beach, Florida.

B. INTRODUCTION

In 190,000 ha of higher-elevation, freshwater marshes on either side of Shark River Slough, water levels typically drop below the ground surface each year (Davis et al., 1994). Consequently peat accretion is inhibited, and substrates consist either of marl produced by periphyton mats, or exposed limestone bedrock with solution holes (Gleason, 1972). The landscape consists of a mosaic of wet prairie, sawgrass, tree island, and tropical hammock communities that support a high diversity of plant species (Olmstead and Loope, 1984). The ephemeral characteristics of the hydrology of marl prairies and rocky glades pose stresses to the wetland animal communities regarding survival through the dry season when standing water is usually absent (Loftus and Eklund, 1994; Loftus et al., 1990). In that respect, the American alligator represents a keystone species in the marl prairie/rocky glades because alligator holes provide important refugia for aquatic fauna during dry periods (Craighead, 1968).

C. EXTERNAL DRIVERS AND ECOLOGICAL STRESSORS

The dominant sources of stressors on the marl prairie/rocky glades ecosystem are water management practices and agricultural and urban development (refer to the figures on pages 82 and 83). The water management system has altered hydropatterns of remaining wetlands primarily through the lowering of water tables and through the unseasonable regulatory release of water from upstream (Van Lent et al., 1993). A network of canals and levees, particularly the C-111 system, has resulted in the compartmentalization of the remaining marl prairie/rocky glades wetland system. The canals and pump stations are conduits for inputs of nutrients, mercury, other toxins, and exotic fishes into the remaining wetland system

Agricultural and urban development represents a direct loss of spatial extent of the marl prairie/rocky glades wetland system through conversion of marshes to farmland and housing (Davis et al., 1994). Development provides potential sources of nutrients, mercury and other toxins to the natural system via runoff water that may need to be captured and stored for hydropattern restoration.

Shortened hydroperiod (duration of uninterrupted flooding) . Much of the marl prairie/rocky glades remains dry most of an average year under present conditions,72

compared to a duration of uninterrupted flooding averaging nine months predrainage as indicated by the Natural System Model (Van Lent et al., 1993; Fennema et al., 1994; VanZee, in preparation). Shortened hydroperiod directly affects ecosystem food webs through the 1) decrease in diatoms, desmids, and other green algae associated with the periphyton mat and the related reduction of the primary production food base (Browder et al., 1994), 2) reduced secondary production and altered species composition of fish based on comparisons of long and short hydroperiod sites in Shark River Slough (Loftus and Eklund, 1994; Loftus et al., 1990; Turner et al., 1999 in press) and possibly crayfish, 3) reduced pupolation density and altered species composition of small herpetofauna, based on abundance in short-hydroperiod habitats in relation to rainfall and water levels on Big Pine Key (Diffendorfer et al., in preparation; Dalrymple, 1987; Dalrymple, personal communication), 4) loss of the potential for hypothetical wading bird and wood stork foraging during the early dry season (Fleming, personal communication in Ogden, 1994), and 5) decline in the American alligator population in the landscape where it was once abundant (Craighead, 1968; Mazzotti and Brandt, 1994). Shortened hydroperiod directly affects plant community and habitat structure, in addition to the already noted alteration of the periphyton mat and filling in of alligator holes, by enabling the invasion of woody plants such as willow and exotics such as Brazilian pepper and melaleuca in a naturally herbaceous landscape (Armentano et al., 1995; Jones and Doren, 1997), and by altering the plant species composition of macrophyte vegetation toward more terrestrial plant species (Hofstetter and Hilsenbeck, 1980; Hilsenbeck et al., 1979). Shortened hydroperiod indirectly affects plant community and habitat structure through altered fire regime: hotter and more severe fires due to the prolonged dry season (Gunderson and Snyder, 1994) further alter herbaceous plant species composition and reduce plant community heterogeneity by burning out hardwood hammock tree islands (Loope and Urban, 1980). Shortened hydroperiod, in combination with increased drought severity, threatens Cape Sable sparrow reproductive success and survival in the marl prairies to the east of Shark River Slough by increasing the frequency and severity of nest-destroying fires, or by enabling the invasion of woody plants in the absence of fire (Pimm, 1995)

Increase in drought severity . In a system where water levels typically fall below the ground surface each year, remnant pools of standing water in solution holes and alligator holes during the dry season are critical to the survival of aquatic and amphibious fauna such as fish, crayfish, herpetofauna, and alligators (Loftus et al., 1992; Mazzotti and Brandt, 1994; Diffendorfer et al., in prep.; Dalrymple, 1987; Dalrymple, personal communication). When dry conditions are prolonged, and minimum water levels during a dry season fall below the bottoms of the solution holes and alligator holes, the function of these dry season refugia is diminished or eliminated.73

Wet season water level reversals . Field observations indicate that when water depth drops to less than 0.2 feet during a period of flooding, aquatic fauna population densities decline, survivors retreat to refugia in solution holes or alligator holes, and population recovery is slowed (Loftus and Eklund, 1994; Loftus, personal communication).

Drying pattern reversals due to upstream regulatory releases . Reversals in the seasonal timing of water level recessions due to regulatory releases from WCA3A detrimentally affect nesting density and success of the endangered Cape Sable sparrow (Pimm, 1995). Drying pattern reversals have been particularly detrimental to sparrow nesting in the marl prairies to the west of Shark River Slough, in an area that is affected by water releases from the S-10 A and B outflow gates from Water conservation Area 3A. Unnaturally high flow volumes to the west of Shark River Slough, rather than via Northeast Shark River Slough under NSM conditions, exacerbates the problem of the sparrow. The Cape Sable sparrow depends on predictably dry conditions during its spring nesting period which corresponds to the late dry season (Pimm, 1995). Drying pattern reversals and their effects on the sparrow are analyzed as an endangered species issue.

Increased nutrient inputs . Agricultural and urban runoff water from the lower east coast that may be needed for hydropattern restoration is anticipated to bring with it increased inputs of phosphorus, nitrogen and other nutrients. Cattail has already dominated portions of Taylor Slough downstream of the Park road since pump station S332 commenced to deliver canal water to Taylor Slough (Davis, personal observation). A probable effect of nutrient additions to the marl prairie/rocky glades would be the loss in the periphyton mat and the dominance of blue-green algae, with resulting reductions in the primary production food base and reductions in marl substrate accretion (Browder, 1994).

Compartmentalization . The levees that bound and dissect the marl prairie/rocky glades on the east side of the Everglades, and the C-111 system in particular, may create barriers that genetically isolate populations of aquatic fauna, as demonstrated by the genetic structure of mosquitofish and grass shrimp in the Water Conservation Areas compared to Everglades National Park (Trexler et al., in review). Canals adjacent to the levees provide corridors of permanently flooded, deep-water habitat that would not otherwise occur in the marl prairie/rocky glades. These corridors allow the expansion of exotic and higher trophic level fishes into areas where they could not survive naturally (Howard et al., 1995). The prevalence of higher trophic fishes in the canals diminishes the value that this habitat might otherwise serve as a dry season refugium for aquatic and amphibious fauna.

Loss of spatial extent . The conversion of eastern portions of the marl prairie/rocky glades to agriculture and housing has reduced the spatial extent of primary production that provides the base of the food webs of fish, crayfish, herpetofauna,74

alligators, and wood storks and wading birds. The spatial loss of the aquatic habitat has also directly reduced populations of these organisms. The extent of loss in production and aquatic habitat is directly proportional to the spatial extent of the area that has literally been taken out of production as wetland (Davis et al., 1994). Loss of spatial extent may have reduced the range of habitat options that are available at any given time for faunal populations (DeAngelis and White, 1994), including nesting by the Cape Sable sparrow nesting (Pimm, 1995) and potential foraging by wood storks and wading birds (Fleming, personal communication in Ogden, 1994).

Introduction of exotic plants . Melaleuca, Brazilian pepper and Australian pine are the three most widespread exotic plant species that have spread into native plant communities of the marl prairie/rocky glades, due to their introduction combined with shortened hydroperiod which allows their expansion (Olmstead and Loope, 1984; Armentano et al., 1995; Jones and Doren, 1997).

Burning practices . Burning practices, particularly from illegally set fires, have shifted the seasonal timing of fires from the May-June early wet season, due to lightning strikes, to the winter-spring dry (Gunderson and Snyder, 1994). Fire severity has been exacerbated by shortened hydroperiod and increased drought severity. The road access provided by levees contributes to fire ignition by humans by allowing arsonists access to the marshes and by creating a source of ignition from vehicle sparks (Burzycki, personal communication). Intense, dry season fires have burned out hardwood hammock tree islands in the marl prairies and rocky glades to the east of Shark River Slough. Fire hazard due to over-drainage also poses a threat to Cape Sable sparrow nesting success and survival in the marl prairies to the east of Shark River Slough.

D. ECOLOGICAL EFFECTS OF WATER MANAGEMENT: CRITICAL LINKAGES BETWEEN STRESSORS AND ATTRIBUTES

Four major causal pathways appear to account for the decline in the ecologicalattributes of the marl prairies and rocky glades as a result of water managementinduced stressors. Each pathway, other than that of the Cape Sable sparrow, has been most severely impacted in the marl prairies and rocky glades to the east of Shark River Slough.

1) The periphyton mat has been altered in ways that reduce its contribution to aquatic food chains and marl formation. Diatom, desmid and other green algal components of the periphyton mat have decreased as a result of severelyshortened hydroperiod. The mat is lost entirely and replaced by non-matforming bluegreen algae as a result of nutrient additions in pumped inflow
water.75

2) The American alligator has been mostly eliminated, due to severely shortened hydroperiod and lowered water table, from the landscape where it was once most abundant. Alligator holes in depressions in the limestone bedrock have silted in with organic debris and no longer function as dry season refugia for aquatic fauna. Their loss has decreased the heterogeneity of vegetation habitat and micro-topography.

3) The marsh fishes, herpetofauna and probably other aquatic fauna of the marl prairies and rocky glades can maintain only diminished population density and secondary production given the shortened hydroperiod and lowered water table, the altered periphyton mat, the loss of dry season refugia in alligator and solution holes, and the physiological stress due to wet season water level reversals.

4) The vegetation community mosaic has lost heterogeneity and changed in species composition due to community shift due to shortened hydroperiod and lowered water table, the loss of alligator holes, tropical hammock tree island burn-out due to altered fire regime, woody plant invasion, and the spread of exotic plants.

5) The Cape Sable sparrow is limited in reproductive success and population size by drying pattern reversals from upstream water releases to the west of Shark River Slough. To the east of the Slough, the sparrow is threatened by shortened hydroperiod and lowered water table, which result either in increased fire frequency and severity, or in woody plant invasion in the absence of fire.

E. ECOLOGICAL ATTRIBUTES AND MEASURES

Periphyton mat . The periphyton mat of attached algae plays a key role as a food chain base (Browder et al., 1994), as habitat structure (Loftus, personal communication), and as the source of marl sediments (Gleason, 1972) in the marl prairies and rocky glades. Species composition of the periphyton is a sensitive indicator of both hydrologic conditions and water quality (Browder et al., 1994). Severely reduced hydroperiod in the marl prairies and rocky glades results in a decrease in the diatom, desmid and other green algal species in the periphyton mat, leaving mostly mat-forming blue-green algae that are less valuable as food sources for consumers (Browder et al., 1994). Nutrient enrichment, that may accompany the inflow of canal water, results in the loss of mat-forming species altogether and replacement by non-mat-forming blue-green algae (Browder et al., 1994). Measures of periphyton communities that indicate recovery due to lengthened hydroperiod and potential impacts of nutrient enrichment include aerial coverage, species composition, biomass, and primary productivity rates of periphyton mats of the marl prairies and rocky glades.76

Marl substrate . Mat-forming calcitic algae deposit the marl substrate that is characteristic of the marl prairies (Gleason, 1972; Browder et al., 1994), where hydroperiod is too short for the accretion of peat soils. Most of the plant communities described by Olmstead and Loope (1984) and Gunderson (1994) for this region are supported by the marl soils. The dependence of marl deposition on the productivity of the calcitic periphyton mat indicates that the negative impacts of shortened hydroperiod and nutrient enrichment that are noted above for the periphyton mat would also adversely affect the rate of marl accretion. Measures of the marl substrate that should reflect responses to hydroperiod, and nutrients and restoration efforts include marl distribution and depth and marl accretion rate

. Vegetation mosaic and diversity . A unique feature of the marl prairies and rocky glades is the extremely high species richness of their flora. Within the mosaic of low-stature graminoid communities, sawgrass and muhly grass dominate, although more than 100 species of mostly herbaceous plants have been reported (Olmstead and Loope, 1984). The higher-elevation tropical hammock and pine forests that occur as islands within the prairie landscape support flora of West Indian origin that are unique to south Florida, other than the Keys, and that contain the highest number of rare and threatened plant species in south Florida (Gunderson, 1994). The plant communities of the marl prairies and rocky glades have been impacted by man through drainage, exotic invasion and burning practices. Tree island burn-out (Loope and Urban, 1980), shifts to more terrestrial plant associations in the graminoid communities (Hofstetter and Hilsenbeck, 1980; Hilsenbeck et al., 1979), loss of the vegetation heterogeneity associated with the micro-topography of alligator holes (Craighead, 1968), and woody plant invasion of the graminoid communities (Armentano, et al., 1995) have accompanied shortened hydroperiods and lowered water tables. These effects are exacerbated by the spread of exotic trees (Olmstead and Loope, 1984; Armentano et al., 1995; Jones and Doren, 1997) and by dry season burning practices (Gunderson and Snyder, 1994), particularly from illegally-set fires. Measures of vegetation responses to stressors and restoration efforts in the marl prairies and rocky glades include the spatial cover and species composition of graminoid and tree island communities

. Cape Sable sparrow . The Cape Sable seaside sparrow is endemic to the marl marshes of the southern Everglades, where it is listed as an endangered species.The three major breeding colonies of the sparrow include the western subpopulation in marl marshes to the west of Shark River Slough, the eastern subpopulation to the east of mid Shark River Slough, and the central sub-population to the east of the southwest Slough (Pimm, 1995). The sparrow nests during the dry season months, mostly during April –June, in sites free of standing shrubs or trees. The construction of nests approximately 10 cm above the ground at the bases of tussocks of muhly grass and other marsh graminoids makes the sparrow vulnerable both to spring wildfires and unseasonable water depth increases (dry season water level reversals). Successful nesting requires approximately 45 days of nearly dry77

conditions without fire. Dry season water level reversals have been a particular problem to the nesting success of the western sub-population, where regulatory water releases through the S-12 A and B outflow gates of Water Conservation Area 3A contribute to the reversals and subsequent nest drowning (Pimm, 1995). The eastern sub-population occupies an over-drained region of marl prairie subject to spring wildfires or to invasion of woody vegetation. The central population is the most stable because of its remote location, although it is vulnerable to infrequent, naturally-occurring dry season fires. Measures of sparrow populations that reflect responses to stressors and restoration measures include nesting distribution, density and success

. Aquatic fauna . The aquatic fauna of freshwater Everglades marshes include the myriad of small fishes, amphibians, reptiles, crayfish, grass shrimp, snails, amphipods and other invertebrates that must play enormously important roles in food webs, nutrient cycles and energy transfers from primary consumers to the highest trophic levels in the ecosystem. Considering their prevalence, little is known about the life histories, population dynamics and ecosystem roles of the aquatic fauna, particularly regarding their ecology in the marl prairies and rocky glades.

Population density of small marsh fishes in the Everglades is directly related to the duration of uninterrupted flooding, and maximum densities are reached only after several years of continual surface water (Loftus and Eklund, 1994; Loftus et al., 1990; Turner et al., 1999 in press). The herpetofauna of the short-hydroperiod wetlands reach higher abundance in habitats with longer hydroperiods and higher water tables (Diffendorfer et al., in preparation.;Dalrymple, 1987; Dalrymple, personal communication). These studies provide evidence that the marl prairies and rocky glades represent stressful environments for aquatic fauna. Thesemarshes typically dried for an average of three months each year under predrainage conditions, and extensive areas of this landscape are only wet for an average of three months each year under present conditions (Van Lent et al., 1993; Fennema et al., 1994; VanZee, in preparation). Survival of aquatic fauna during dry periods in the marl marshes and rocky glades depends in the availability of refugia in solution holes, alligator holes, and under periphyton mats which may retain aquatic or moist environments during times when surface water is absent (Loftus et al., 1990; Loftus et al., 1992; Dalrymple, 1987; Diffendorfer et al., in preparation; Loftus, personnal communication; Dalrymple, personal communication).

The small marsh fishes provide the major prey base for the wading birds, wood storks and roseate spoonbills that forage and nest in the Everglades (Ogden, 1994; Bjork and Powell, 1994). Crayfish are particularly important in the diets of white ibis. The marl marshes may provide foraging opportunities for wading birds early in the dry season when deeper water depths in the lower-elevation sloughs are78

unsuitable for efficient feeding (Fleming, personal communication in Ogden, 1994). However, the relationship of such foraging opportunities to the advent of nesting and the subsequent reproductive success of wading birds is still hypothetical.

Reduced production and altered species composition of fishes and herpetofauna in the marl prairies and rocky glades result from 1) the direct impact of shortened hydroperiod (Loftus and Eklund, 1994; Turner et al., 1999 in press; Diffendorfer et al., in preparation; Dalrymple, 1987; Dalrymple, personnal communication), 2) indirect impacts of shortened hydroperiod via the loss of the periphyton mat and a reduced primary production food base (Browder et al., 1994), 3) the prolongation of dry conditions and reduction in dry season minimum water levels via the diminished dry season refugium function of solution holes, alligator holes and periphyton mats (Loftus et al., 1992; Diffendorfer et al, in preparation; Dalrymple, 1987; Loftus, personal communication; Dalrymple, personal communication), 4) reduction in spatial extent of wetland habitat (Davis et al. 1994), 5) increased nutrient inputs via the loss of the periphyton mat and a resulting reduction in the primary production food base (Browder et al., 1994), and 6) compartmentalization via levees as potential genetic barriers (Trexler et al., in review) and via canals as corridors for the spread of exotic and higher trophic level fishes (Howard et al., 1995). Measures of aquatic fauna populations that reflect responses to the above stressors include density and species composition of fishes and density of representative herpetofauna and invertebrate species

. American alligator . Prior to drainage, the American alligator was more abundant in the marl marshes and rocky glades than in the deeper central marshes of the Everglades(Craighead, 1968; Mazzotti and Brandt, 1994). By excavating sediments from large solution holes in the limestone bedrock, the alligator created aquatic habitats in which it, and many other groups of aquatic fauna, survived the few months of dry conditions that occurred most years (Craighead, 1968). In theexcavation of holes and the creation of nest mounds, the alligator created a microtopography that supported aquatic as well as terrestrial flora and fauna (Craighead, 1971; Kushlan, 1974). The mounds provided nesting sites not only for the alligator, but also for other marsh reptiles (Deitz and Jackson, 1979; Kushlan and Kushlan, 1980). In these ways, the alligator was a keystone species in the marl prairies and rocky glades because of the aquatic habitats and dry season refugia it created. The high abundance of alligators in the marl marshes and rocky glades, in comparison to lower densities in Shark River Slough, was attributed to high water depths in the Slough that would have been less suitable for alligators prior to drainage (Ogden, 1976; Mazzotti and Brandt, 1994). Given the shortened hydroperiods and lowered water tables in the Everglades due to drainage (Van Lent et al., 1993;Fennema et al., 1994; VanZee, in preparation), the alligator has mostly abandoned the marl marshes and rocky glades, and today the distribution of the alligator in the southern Everglades has shifted to Shark River Slough (Craighead, 1968; Mazzotti and Brandt, 1994). With the loss of alligators from the marl prairies and rocky79

glades, the habitats and dry season refugia that were provided by its holes and nest mounds have also diminished.

Abandonment by the alligator of the marl prairie/rocky glades has resulted from shortened hydroperiod and increased drought duration and severity, in that the alligator does not occupy habitat that is predominantly dry. Cumulative effects leading to the reduced production of aquatic fauna at all trophic levels probably have also contributed to the demise of the alligator in the mark prairies, since the alligator depends upon these organisms for food during various stages of its life history. The reduced population of alligators has in turn allowed depressions that were previously alligator holes to fill in, further diminishing the populations of aquatic fauna upon which upon which the alligator fed. The restoration of hydroperiods and water tables to those approaching pre-drainage conditions in the marl prairies and rocky glades is anticipated to allow the alligator to re-colonize this region, as measured by density and distribution by age class and density and distribution of alligator holes

. Wading bird and wood stork early dry season foraging . Prior to drainage, the marl prairie/rocky glades may have provided shallow-water foraging opportunities for wading birds and wood storks early in the dry season, at a time when water was too deep to allow successful foraging in Shark River Slough (Fleming, personal communication in Ogden, 1994). The early dry season foraging opportunities may have contributed to the early formation of nesting colonies, and thereby the nesting success of the birds, but this would have been dependent upon an adequate prey base of aquatic fauna in the marl prairie/rocky glades. The relationship of such foraging opportunities to the advent of nesting and subsequent reporductive success of wading birds and wood storks is hypothetical. Under present conditions, both shortened hydroperiod (Van Lent et al.,1993; Fennema et al., 1994; VanZee, in preparation)and loss of spatial extent Davis et al., 1994) have directly reduced the area of feeding habitat and the range of feeding options available to the wading birds and wood storks in the marl prairie/rocky glades (Ogden 1994). Cumulative effects leading to the reduced production of fish and other aquatic fauna, as noted above, have further reduced the prey base for wading birds and wood storks. As a result, the value of the marl prairies and rocky glades for wading bird and wood stork foraging appears to be very limited today in comparison to pre-drainage conditions (Fleming, personal communication in Ogden, 1994). Measures of wading bird and wood stork utilization of the marl prairie/rocky glades that reflect responses to the above stressors include the seasonal distribution and abundance of foraging birds

.80

F. HYDROLOGIC PERFORMANCE MEASURES FOR RESTORATION

Recovery of the ecological values of the marl prairie/rocky glades is dependent upon the reversal of the cumulative effects of decades of drainage, detrimental fire regimes, and exotic plant invasion. The key role of the C&SF Comprehensive plan in the restoration of the marl prairie/rocky glades ecosystem is to provide for the quantity, timing, and distribution of water deliveries that contain low levels of nutrients and toxins. Three priority hydrologic performance measures for the ecological restoration of the marl prairie/rocky glades, in order of priority, are the duration of uninterrupted flooding, drought severity as measured by the duration of dry conditions, and the number of wet season depth reversals.

The duration of a uninterrupted flood events is the highest priority hydrologic performance measure for ecological restoration in the marl prairie/rocky glades. It is identified as the single hydrologic parameter that affects all the ecological values of that region. Only flood events when the mean water depth equals or exceeds 0.2 feet are measured because depths less than 0.2 feet have been observed to impair the establishment of populations of aquatic organisms. The mean duration of all such flood events during the 31-year period of record is the performance measure. The target is the mean duration of flooding indicated by NSM45F. Duration of uninterrupted flooding given a weighting of 3 when averaged with the other performance measures.

Drought severity is the second most important hydrologic variable for ecological restoration in the marl prairie/rocky glades. Drought severity is most clearly indicated by 2X2 model output as the duration of dry conditions. Dry events are defined as times when the water level drops either to zero or a negative value below the ground surface. Two dry events that are separated by a flood event when the water level rises to less than 0.2 feet above the ground surface are grouped as one dry event because such a minor flood event has been observed to not support the establishment of populations of aquatic organisms. In that case, the duration of the dry event is calculated as the sum of the two dry events and the intermittent flood event. The performance measure is the mean duration of all dry events during the 31-year period of record. The target is the mean duration of dry events indicated by NSM45F. The mean duration of dry events is given a weighting of two when averaged with the other performance measures.

Wet season water level reversal is the third most important hydrologic variable for ecological restoration in the marl prairie/rocky glades. A wet season water level reversal is defined as an incident during a period of flooding when water depth recedes to less than 0.2 feet, but then rebounds to greater than 0.2 feet, without the marsh drying completely. A reversal is distinguished from a dry period in that during a reversal, water depth does not drop to or below the ground surface. The performance measure is the total number of reversals during the 31-year period81

of record. The target is not to exceed the number of reversals indicated by NSM45F. The number of wet season reversals is given a weighting of one when averaged with the other performance measures.

Ecological attributes and indicators of restoration success in the rockland marl marsh that are linked to the above hydrologic performance measures in the conceptual model include 1) re-colonization and population resurgence by American alligators and a subsequent increase in the number of occupied alligator holes to serve as dry season refugia for aquatic fauna and to increase habitat heterogeneity, 2) increased population density of aquatic fauna, 3) increased seasonal abundance and foraging activity of wading birds and wood storks, 4) enhanced production and community composition of periphyton, 5) accelerated accretion of marl substrate, 6) increased nesting success and population size of Cape Sable seaside sparrows, and 7) persistence and resilience of highly diverse macrophyte and tree island plant communities.

A performance measure that is generic to the conceptual models of all physiographic regions of south Florida is the input and bio-accumulation of mercury and other toxins. Potential inputs of mercury and pesticides in agricultural and urban runoff water that may be needed for hydropattern restoration in the marl prairie/rocky glades might result in reduced health, behavioral and physical abnormalities, and loss of reproductive vigor of the fauna unless measures are taken to restrict loads of these toxins in inflow water. Measures of faunal health that reflect responses to the mercury and pesticide inputs include body burdens of mercury and other toxins in representative species of fauna and the incidence of physical and behavioral abnormalities in fauna.84

G. REFERENCES

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Bjork, R.D. and G.V.N. Powell. 1994. Relations between hydrologic conditions and quality and quantity of foraging habitat for roseate spoonbills and other wading birds in the C-111 basin. National Audubon Society Final Report to South Florida Research Center, Everglades National Park.

Browder, J.A., P.J. Gleason and D.R. Swift. 1994. Periphyton in the Everglades: Spatial variation, environmental correlates, and ecological implications. In: S.M. Davis and J.C. Ogden, eds . Everglades: The Ecosystem and Its Restoration , St. Lucie Press, Delray Beach FL: 379-418.

Burzycki, G. Personal communication, Dade County Department of Environmental Resource Management, Miami FL.

Busch, David E., William F. Loftus, and Oron L. Bass, Jr. 1998. Long-term hydrologic effects on marsh plant community structure in the southern Everglades. Wetlands 18: 230-241.

Craighead, F.C. 1968. The role of the alligator in shaping plant communities and maintaining wildlife in the southern Everglades. Florida Naturalist 41: 2-7, 69-74, 94.

Craighead, F.C. 1971. The Trees of South Florida , Volume 1. University of Miami Press, Coral Gables FL: 212pp.

Dalrymple, G.H. 1987. The herpetofauna of Long Pine Key in relation to vegetation and hydrology. In: C. Szaro et al., tech. coordinators. Management of Amphibians, Reptiles, and Small Mammals in North America, USDA Forest Service General Technical Report RM-166R, Ft. Collins, CO.

Dalrymple, G. Personal communication, Everglades Research Group, Inc., Homestead, FL.

Davis, S.M., L.H. Gunderson, W.A. Park, J.R. Richardson and J.E. Mattson. 1994. Landscape dimension, composition, and function in a changing Everglades ecosystem. In: S.M. Davis and J.C. Ogden, eds . Everglades: The Ecosystem and Its Restoration , St. Lucie Press, Delray Beach FL: 419-444.85

Davis, S.M. personal observation, South Florida Water Management District, West Palm Beach FL.

DeAngelis, D.L., and P.S. White. 1994. Ecosystems as products of spatially and temporally varying driving forces, ecological processes, and landscapes: A theoretical perspective. In: S.M. Davis and J.C. Ogden, eds. Everglades: The Ecosystem and Its Restoration , St. Lucie Press, Delray Beach FL: 9-27.

Deitz, D.C. and D.R. Jackson. 1979. Use of alligator nests by nesting turtles. Journal of Herpetology 13: 510-512.

Diffendorfer, J.E., P.M. Richards, G.H. Dalrymple and D.L. DeAngelis. In preparation. Using ecosystem and food webs in conservation; an example from the herpetological assemblage.

Fennema, R.J., C.J. Neidrauer, R.A. Johnson, T.K. MacVicar and W.A. Perkins. A computer model to simulate natural Everglades hydrology. In: Davis, S.M. and J.C Ogden, eds. Everglades: The Ecosystem and Its Restora tion, St. Lucie Press, Delray FL: 249-289.

Gleason, 1972. The origin, sedimentation, and stratigraphy of a calcitic mud located in the southern fresh-water Everglades. Ph.D. thesis, The Pennsylvania State University, University Park PA.

Gunderson, L.H. 1994. Vegetation of the Everglades: Determinants of community composition. In: S.M. Davis and J.C. Ogden, eds. Everglades: The Ecosystem and Its Restoration , St.Lucie Press, Delray Beach FL: 323-340.

Gunderson, L.H. and J.R. Snyder. 1994. Fire patterns in the southern Everglades. In: S.M. Davis and J.C. Ogden, eds. Everglades: The Ecosystem and Its Restoration , St. Lucie Press, Delray Beach FL: 291-305.

Hilsenbeck, C.E., R.H. Hofstetter and T.R. Alexander. 1979. Preliminary synopsis of major plant communities in the east Everglades area, vegetational maps supplement, University of Miami Report, University of Miami, Miami FL: 36pp.

Hofstetter, R.H. and C.E. Hilsenbeck. 1980. Vegetational studies of the east Everglades. Final Report to Dade County Planning Department, East Everglades Resources Planning Project: 109pp.

Howard, K. S., W. F. Loftus, and J. C. Trexler. 1995. Seasonal dynamics of fishes in artificial culvert pools in the C-111 basin, Dade County, Florida. Final86

Report to the U. S Army Corps of Engineers as Everglades N. P. Cooperative Agreement #CA5280- 2-9024.

Jones, D.B. and R.F. Doren. 1997. Distribution, biology and control of Schinus terebinthifolius in southern Florida with special reference to Everglades National Park. In: J.H. Brock, M.Wade, P. Tysek and D. Green, eds. Plant Invasions: Studies From North America and Europe , Backhuys Publishers, Lyden, Netherlands: 81-93.

Kushlan, J.A. 1974. Observations on the role of the American alligator ( Alligator mississippiensis ) in the southern Florida wetlands. Copeia 1974: 993-996.

Kushlan, J.A. and M.S. Kushlan. 1980. Everglades alligator nests: Nesting sites for marsh reptiles. Copeia 1980: 930-932.

Loftus, W.F. Personal communication.

Loftus, W. F. and A. M. Eklund. 1994. Long-term dynamics of an Everglades fish community. In: S.M. Davis and J.C. Ogden, eds. Everglades: The Ecosystem and Its Restoration , St. Lucie Press, Delray Beach, FL: 461-483.

Loftus, W. F. and James A. Kushlan. 1987. Freshwater Fishes of Southern Florida. Bulletin of the Florida State Museum, Biological Sciences 31: 147-344.

Loftus, W.F., J.D. Chapman and R. Conrow. 1990. Hydroperiod effects on Everglades marsh food webs, with relation to marsh restoration efforts. In: G. Larson and M. Soukup, eds. Proceedings of the Conference on Science in The National Parks, July 13-18, 1986, U.S. National Park Service and the George Wright Society: 1-22.

Loftus, W.F., R.A. Johnson, and G.H. Anderson. 1992. Ecological impacts of the reduction of ground water levels in short-hydroperiod marshes of the Everglades. In: J.A. Stanford and J.J. Simons eds. Proceedings of the First International Conference on Ground Water Ecology. American Water Resources Association, Bethesda, MA: 199-207.

Loope, L.L. and N.H. Urban. 1980. A survey of fire history and impact in tropical hardwood hammocks in the east Everglades and adjacent portions of Everglades National Park. Report T-592, South Florida Research Center, Everglades National Park: 48pp.

Mazzotti, F.J. and L.A. Brandt. 1994. Ecology of the American alligator in a seasonally fluctuating environment. In: S. M. Davis and J.C. Ogden, eds.87

Everglades: The Ecosystem and Its Restoration, St. Lucie Press, Delray Beach FL: 485-505.

Ogden, J.C. 1976. Crocodilian ecology in southern Florida. In: Research in the Parks: Transactions of the National Park Centennial Symposium, 1971. National Park Service Symposium Series Number 1, U.S. Department of the Interior, Washington D.C.

Ogden, J.C. 1994. A comparison of wading bird nesting colony dynamics (1931- 1946 and 1974-1989) as an indication of ecosystem conditions in the southern Everglades. In: S.M. Davis and J.C. Ogden, eds. Everglades: The Ecosystem and Its Restoration, St. Lucie Press, Delray Beach FL: 533-570.

Olmstead, I.C. and L.L. Loope. 1984. Plant communities of Everglades National Park. In: P.J. Gleason, ed. Environments of South Florida: Past and Present II

, Miami Geological Society, Coral Gables FL.

Pimm, S.L. 1995. Population ecology of the Cape Sable Sparrow ( Ammodramus maritima mirabilis ). Annual report 1995. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville TN: 57pp + 35 figures.

Trexler, J.C., W. F. Loftus, and O. L. Bass. 1996. Documenting the effects of Hurricane Andrew on Everglades aquatic communities, Part I. In: J. C. Trexler, L. Richardson, and K. Spitze eds. Effects of Hurricane Andrew on the structure and function of Everglades aquatic communities. Final Contract Report CA5280-3-9014 to Everglades National Park, Homestead, FL: 6-136.

Trexler, J. C., W. F. Loftus, C. F. Jordan, J. Lorenz, and J. Chick. In Prep. Empirical assessment of fish introductions in southern Florida: an evaluation of contrasting views. Biological Invasions.

Trexler, J. C., K. L. Kand, and C. F. Jordan. In review. Metapopulations or patchy populations: population structure of three species of aquatic animals from the Everglades. Evolution.

Turner, A., J. C. Trexler, F. Jordan, S. J. Slack, P. Geddes, J. Chick, and W. F. Loftus. In Press. Conservation of an ecological feature of the Florida Everglades: pattern of standing crops. Conservation Biology.

Van Lent, T.A., R.A. Johnson and R.J. Fennema. 1993. Water management in Taylor Slough and effects on Florida Bay. South florida Natural resources Center Technical report 93-3: 97pp.88

VanZee, R. In preparation. Natural system model version 4.5 documentation report. Draft report, South Florida Water Management District, West Palm Beach FL.89



### VII. MANGROVE ESTUARY TRANSITION CONCEPTUAL MODEL

A. PREPARER

Steven M. Davis, South Florida Water Management District, West Palm Beach, Fl.

B. INTRODUCTION

A brackish water ecotone of coastal bays and lakes, mangrove and buttonwood forests, salt marshes, and tidal creeks separates Florida Bay from the freshwater Everglades. The 24 km-wide ecotone adjoins the north shoreline of Florida Bay between Highway Creek (US1) and Whitewater Bay, which delineate the eastern and western boundaries of the mangrove estuary transition model. Whitewater Bay is included in the model because it is influenced by the Shark River drainage basin originating in the Everglades. The mangrove estuary transition is characterized by a salinity gradient and mosaic that vary spatially with topography and that vary seasonally and inter-annually with rainfall and freshwater flow from the Everglades. Because of its location at the lower end of the Everglades drainage basin, the mangrove estuary transition zone is potentially affected by upstream water management practices that alter the freshwater heads and flows that drive salinity gradients.

C. EXTERNAL DRIVERS AND ECOLOGICAL STRESSORS

Stressors on the mangrove estuary transition ecosystem and the drivers that create them fall into five categories (refer to figures on pages 97 and 98). Sea level rise is an important non-societal driver (Wanless et al., 1994) that is causing the inland movement of marine conditions into the estuary transition zone (Meeder et al., 1996). The inland movement of marine conditions due to sea level rise is happening independent from other societal-driven stressors. The societal-driven water management operations of the C&SF Project stress the transition zone through reductions in the volume and duration of freshwater flow entering the zone(McIvor et al., 1994) The introductions of exotic fishes and plants are other societaldriven drivers that have resulted in the dominance of the Mayan cichlid east of Taylor Slough (Trexler et al., in prep.) and the invasion of Schinus and Colubrina into mangrove forests (Armentano et al., 1995). The societal input and bioaccumulation of mercury and other toxins pose a threat to faunal health at all trophic levels in all south Florida ecosystems, including the mangrove estuary transition, as discussed under generic issues.90

D. ECOLOGICAL EFFECTS: CRITICAL LINKAGES BETWEEN STRESSORS AND ECOLOGICAL ATTRIBUTES

The inland movement of marine conditions due to sea level rise and the reduced input of freshwater due to water management work together to alter and compress the salinity gradient of the mangrove estuary transition (Browder and Moore, 1981). They both result in the landward movement of salinity, the loss of a seasonal shift from moderate saline to oligohaline conditions, and occurrence of hypersalinity within the transition zone during dry years. Both directly change habitat structure by contributing to the siltation and mangrove encroachment of tidal creeks (Meeder et al., 1996), to the extent that open water courses that were described earlier this century are no longer recognizable (Glen Simmons, personal communication).

The alteration and compression of the salinity gradient results in the loss of the spatial overlap of salinity zones with shoreline habitat and nursery grounds (Browder and Moore, 1981). Ecological values of the mangrove estuary transition that depend on the overlap of salinity and habitat include the mangrove/salt marsh vegetation mosaic, the resident mangrove fish assemblage, the wood stork and roseate spoonbill, the American crocodile, spotted seatrout nursery grounds, pink shrimp nursery grounds, and coastal lake vegetation and waterfowl.

E. ECOLOGICAL ATTRIBUTES AND MEASURES

Mangrove/salt marsh vegetation mosaic . The alteration and compression of the salinity gradient potentially can affect the community cover, distribution, and production of the mangrove forests ( Rhizophora

, Avicennia
, Laguncularia , and Conocarpus ), salt marshes and tidal creeks of the mangrove estuary transition that are documented by Welsh et al. (1995). Some mangrove forests in the transition zone have experienced invasion by the exotic trees Schinus and Colubrina (Armentano et al., 199 5) . Tidal creeks and adjacent salt marshes have been encroached by red mangrove as described above. The invasion of the freshwater marl marshes at the upstream end of the salinity gradient by red mangrove (Meeder et al., 1996) corresponds to an accelerated rate of sea level rise. The vegetation mosaic defines the habitats of the mangrove estuary transition zone. The spatial distribution of those habitats, in combination with the salinity gradient that overlays them, may determine the suitability of this region to sustain its ecological attributes (Browder and Moore, 1981). The importance of this habitat mosaic warrants the monitoring of the distribution and cover of vegetation communities and tidal creeks in the mangrove estuary transition zone as efforts proceed to restore freshwater inputs and salinity regimes.

Resident mangrove fish community . The resident fish community of sheepshead, sailfin mollies, topminnows, rainwater killifish, and sunfish thrives under low91

salinity, decreasing in production and increasing in mortality when salinity exceeds 5-8 ppt (Lorenz, 1997 and in press). The exotic Mayan cichlid has become established in this fish community to the extent that it presently is the dominant species from Taylor River east to Highway Creek (Trexler et al., in prep.). Lowered salinity regimes due to increased freshwater inputs are expected to result in community recovery as measured by increased production and abundance of resident mangrove fishes. The dependence of wood storks on larger resident mangrove fishes above approximately 10 cm in length (Ogden et al., 1978) provides an additional measure of increased survival of topminnows and sunfish to year class

one (into their second year of life). Consistently lower salinities at the upstream end of the salinity zonation are expected to reduce mortality and allow survivorship of these species to the larger size classes that are available to wood storks.

Wood stork and roseate spoonbill . The collapse of the coastal nesting colonies of wood storks and great egrets is attributed largely to a decline in the production and density of the resident mangrove fishes (Ogden, 1994), particularly topminnows and sunfish that survive past their first year to a size that wood storks can capture (Ogden et al., 1978). The decline in roseate spoonbill nesting and the shift of nesting distribution from eastern to western Florida Bay (Powell et al., 1989) are also attributed to the reduction in populations of resident mangrove fishes upon which they feed (Bjork and Powell, 1994). Small fishes have been reported to be the primary part of the diet of roseate spoonbills in Florida Bay (Allen, 1942; Powell and Bjork, 1990). Increased density of resident mangrove fishes and increased fish survival to year class one, as a result of consistently lower salinity patterns at the upstream end of the gradient, are expected to contribute to the re-establishment of wood stork coastal nesting colonies, the re-establishment of roseate spoonbill Florida Bay nesting colonies east of Seven Palm Lake, and an increase in number of nesting pairs and nesting success of both species

.

American crocodile . The American crocodile dwells in the ponds and creeks of the mangrove estuaries of Florida Bay (Ogden, 1976; Mazzotti, 1983). American crocodiles are tolerant of a wide salinity range as adults because of their ability to osmoregulate (Mazzotti, 1989). Juvenile crocodiles lack this ability, however, (Mazzotti, 1989) and their growth and survival decline at salinities exceeding 20 ppt (Mazzotti et al., 1988; Mazzotti and Dunson, 1984; Moler, 1991). Juvenile crocodiles tend to seek freshwater pockets such as black mangrove stands when those choices are available. Re-establishment of a salinity gradient with levels below 20 ppt in shoreline and tidal creek habitats, which would indicate a gradient and mosaic of lower salinities upstream, is expected to benefit the crocodile as measured by increased growth and survival of juveniles

. Spotted sea trout nursery grounds . Post larval spotted sea trout utilize the coastal basins of the Florida Bay mangrove estuary as nursery grounds from Terrapin Bay west to Whitewater Bay. Densities of post larvae in those basins are highest at an92

intermediate salinity range of 20-30 ppt, and densities drop when salinity exceeds that of seawater (35 ppt) (Thayer et al., 1998; Schmidt, 1993). Restoration of a salinity gradient with a persistent zone of <35 ppt in the coastal basins, as a result of freshwater input from upstream, is expected to result in an increase in the post larval density and thereby an enhancement of the nursery ground value for spotted sea trout and possibly other sport fish species in the coastal basins.

Pink shrimp . Mangrove estuaries in Everglades National Park, along with Florida Bay, are nursery grounds for pink shrimp, an ecologically and economically important species in south Florida. Pink shrimp are harvested commercially on the Tortugas grounds, and the pink shrimp fishery is one of south Florida ’ s most valuable fisheries in terms of ex-vessel value. Pink shrimp are also a food source for many recreationally and commercially important estuarine and marine species such as mangrove snapper and spotted seatrout (Higher Trophic Levels Working Group, 1998).

Pink Shrimp spawning occurs in the Dry Tortugas area, and eggs and larvae are carried inshore by currents and tides (Jones et al., 1970; Hughes, 1969). Browder (1985) and Sheridan (1996) have found positive relationships between indices of freshwater inflow to the coast and Tortugas pink shrimp landings. Sheridan ’ s annually updated statistical model based on various freshwater inflow indices has successfully predicted annual pink shrimp landings in most of the past decade (Sheridan 1996 and unpublished). The salinity gradient associated with coastal runoff may provide navigational directions to immigrating young pink shrimp (Hughes, 1969). Survival rates of juvenile pink shrimp are sensitive to salinity and decrease markedly under extreme hypersaline conditions (Browder, in press). Optimal salinities for survival are not fully determined, but probably are somewhat below that of seawater (35 ppt). Tabb et al. (1962), Rice (1997), and others have documented that the mangrove estuaries in the Whitewater Bay system of Everglades National Park are pink shrimp nursery grounds.

Coastal lake vegetation and waterfowl . Compression of the salinity gradient has changed the coastal lakes and basins of the mangrove ecotone from estuarine to predominantly marine systems. Coastal lakes such as Seven Palm Lake, Cuthburt Lake, Long Lake, West Lake, Lake Monroe and the Taylor River ponds are contained within the mangrove forest and are connected to Florida Bay only by tidal creeks. Coastal basins such as Joe Bay, Little Madeira Bay, Terrapin Bay, Garfield Bight, and Whitewater Bay open directly to Florida Bay or the Gulf of Mexico. The coastal lake and basin estuary ecosystems require seasonal salinity variations from oligohaline (wet season) to mesohaline (dry season) conditions, in contrast to the mesohaline to marine conditions that presently occur during most years. Prolonged periods of salinity concentrations near that of seawater (35 ppt) in the coastal lakes and basins appear to have contributed to the near-elimination the once-abundant beds of the submerged aquatic plants Ruppia
, Chara , and Utricularia (Ogden,93

personnal communication) which require oligohaline to mesohaline conditions (Morrison and Bean, 1997). Utricularia tolerates only oligohaline salinities with an upper limit of 5-8 ppt. Chara also thrives under freshwater conditions but tolerates mesohaline salinities up to 15-20 ppt. Ruppia grows under a mesohaline salinity range of 10-25 ppt. Waterfowl species including coot, scaup, widgeon and pintail feed on the Ruppia
, Chara , and Utricularia . The reduction in beds of these plants apparently has contributed to the precipitous decline in numbers of seasonally abundant waterfowl that formerly utilized the coastal lakes and basins (Kushlan et al., 1982). Recent high-rainfall years have witnessed an increase in coot numbers on the West Lake to approximately 2000 during winter 96-97 (Bass, personalcommunication), but not to the population size of approximately 50,000 that overwintered there until the 1960's (Kushlan et al., 1982). Re-establishment of a salinity gradient that restores seasonal variation from oligohaline to mesohaline conditions in the coastal lakes and basins is expected to result in an increase in the aerial cover of Ruppia
, Chara , and Utricularia and the return of winter waterfowl populations of coot, scaup, widgeon and pintail to the lakes and basins.

F. HYDROLOGIC PERFORMANCE MEASURES FOR RESTORATION

Ecological restoration of the mangrove estuary transition requires a reduction in the frequency of high salinity events that have been identified for each coastal basin through the conceptual model process. Another restoration measure is to increase the frequency of low salinity events that have been identified for each coastal basin. The high and low salinity levels represent the best professional judgement of those scientists working in the mangrove estuary, based on the existing information on the biological requirements and distributions of the estuarine organisms that are described above, available salinity data, and field observation.

Table 1 displays the lower and upper salinity levels identified for coastal basins. It is desirable to decrease the frequency that salinity exceeds upper levels, and to increase the frequency that salinity drops below lower levels.

Table 1 Salinity Values
Basin Lower Level Upper Level Joe bay 5 ppt 15 ppt Little Madeira Bay 15 ppt 25 ppt Terrapin Bay 25 ppt 35 ppt Garfield Bight 25 ppt 35 ppt North River Mouth 5 ppt 15 ppt

The strategy for ecological restoration of the mangrove estuary transition is to maintain freshwater heads and flows in the Everglades at the upstream end of the salinity gradient in order to achieve desirable salinity regimes in the Florida94

Bay coastal basins at the downstream end of the salinity gradient. Regression analyses demonstrated inverse relationships of salinity in the coastal basins to water level upstream in the Everglades (Davis, 1997). The regressions indicated that stages of 7.3 and 6.3 feet msl at the P33 gage in central Shark River Slough produce the lower and upper salinity levels for Joe Bay, Little Madeira Bay, Terrapin Bay, Garfield Bight, and North River Mouth. Four performance measures for the ecological restoration of the Florida Bay mangrove estuary and coastal basins are derived from the simulated stages at the P33 gage and salinity levels in the coastal basins.

The frequency of stages of 6.3+ at P33 is applied as a performance measure for the Florida Bay coastal basins. The performance measure is the number of months during the 31-year period of record when stages at P33 rose to, or above, 6.3. The target is the number of months that NSM45F provided stages of 6.3 or above. A reduced frequency of high salinity events is given a high priority in the ecological restoration of the coastal basins, thus the frequency of 6.3+ stages is given a weighting of two when averaged with the other performance measures.

The frequency of stages of 7.3+ at P33 is applied as a performance measure to the Florida Bay coastal basins. The performance measure is the number of months during the 31-year period of record when stages at P33 rose to, or above, 7.3. The target is the number of months that NSM45F provided stages of 7.3 or above. An increased frequency of low salinity events is given a lower priority than a reduced frequency of high events, thus the frequency of 7.3+ stages is given a weighting of one when averaged with the other performance measures for the coastal basins.

The transition from the late dry season to the early wet season during March through June is a critical period to estuarine organisms in the Florida Bay coastal basins regarding the frequency and duration of high salinity events. Salinity is estimated based on relationships between mean monthly salinity in the coastal basins and water stage at the P33 gage in mid Shark River Slough. The cumulative salinity difference (ppt) from the high salinity levels that have been identified for Florida Bay coastal basins is summed during the dry/wet season transition months of March-June. Differences are summed over five coastal basins (Joe Bay, Little Madeira Bay, Terrapin Bay, Garfield Bight and North River Mouth) and over the 31-year period of record. Differences above the specified high salinity levels are given a positive value, and differences below the high salinity levels are given a negative value. The target is to reduce the cumulative salinity difference to a value that does not exceed the cumulative difference produced by NSM45F. The cumulative March-June salinity difference from high levels is given a weighting of one when averaged with the other performance measures for the coastal basins

During the August-October transition from the late wet season to the early dry season, it is important to achieve low salinity levels in the Florida Bay coastal95

basins to provide the seasonal environment for low-salinity estuarine organisms and to postpone the onset of high salinity events further into the dry season. Salinity is estimated based on relationships between mean monthly salinity in the coastal basins and water stage at the P33 gage in mid Shark River Slough. The cumulative salinity difference (ppt) from the low salinity levels that have been identified for the Florida Bay coastal basins is summed during the wet/dry season transition months of August-October. Differences are summed over the five coastal basins and over the 31-year period of record. Differences above the specified low salinity levels are given a positive value, and differences below the low salinity levels are given a negative value. The target is to reduce the cumulative salinity difference to a value that does not exceed the cumulative difference produced by NSM45F. The cumulative August-October salinity difference is given a weighting of one when averaged with the other performance measures for the coastal basins.

Ecological attributes and indicators of restoration success in the Florida Bay mangrove estuary and coastal basins that are linked to the above hydrology/salinity performance measures in the conceptual model include 1) increased production of low-salinity mangrove fishes, 2) re-establishment of coastal nesting colonies of wood storks/great egrets and eastern Florida Bay colonies of roseate spoonbill, 3) earlier timing of coastal colony formation by wood storks/great egrets and of Florida Bay colony formation by roseate spoonbills, 4) increased growth and survival of juvenile American crocodiles, 5) increased cover of low-to-moderate salinity aquatic macrophyte communities in coastal lakes and basins, 6) return of seasonal waterfowl aggregations to coastal lakes and basins, 7) enhanced nursery ground value for spotted seatrout and pink shrimp in coastal basins, and 8) persistence and resilience of the mangrove, salt marsh and tidal creek vegetation mosaic.

A performance measure that is generic to the conceptual models of all physiographic regions of south Florida is the input and bio-accumulation of mercury and other toxins. Potential inputs of mercury and pesticides in agricultural and urban runoff water that may be needed for freshwater input into the mangrove estuary transition might result in reduced health, behavioral and physical abnormalities, and loss of reproductive vigor of the fauna unless measures are taken to restrict loads of these toxins in inflow water. Measures of faunal health that reflect responses to mercury and pesticide inputs include body burdens and the incidence of physical and behavioral abnormalities in representative species.

G. MOVING TARGET

Predicted rises in sea level require re-evaluation of relationships between Everglades stage and mangrove estuary transition salinity during the next century. However, the strategy for the maintenance of salinity at the lower end of the gradient by adjusting upstream water stage at key Everglades gages will continue96

to apply. Maintaining Everglades stages based on presently derived stage/salinity relationships provides one potential strategy to support a salinity gradient, but with a landward shift in response to rising sea level. Raising Everglades stages based upon revised stage/salinity relationships provides another potential strategy to offset sea level rise and maintain the mangrove estuary transition in its present location. Regardless of rising sea level, however, a salinity gradient supportive of an ecologically functional mangrove estuary transition zone will be required to maintain the integrity of the south Florida ecosystem.99

H. LITERATURE CITED

Allen, R.P. 1942. The Roseate Spoonbill. Dover Publications, New York: 142pp.

Armentano, T.V., R.F. Doren, W.J. Platt and T. Mullins. 1995. Effects of Hurricane Andrew on coastal and interior forests of southern Florida: Overview and synthesis. Journal of Coastal Research Special Issue 2: 111-114.

Bass, O.L., Jr. Personal communication. Everglades National Park, Homestead FL.

Bjork, R.D. and G.V.N. Powell. 1994. Relations between hydrologic conditions and quality and quantity of foraging habitat for roseate spoonbills and other wading bird in the C-111 basin. National Audubon Society Final Report to South Florida Research Center, Everglades National Park.

Browder, J.A. 1985. Relationship between pink shrimp production on the Tortugas grounds and water flow patterns in the Florida Everglades. Bulletin of Marine Science 37: 830-856.

Browder, J.A. In press. Environmental influences on potential recruitment of pink shrimp, Penaeus duorarum , from Florida Bay nursery grounds. Estuaries 1999.

Browder, J.A. and D. Moore. 1981. A new approach to determining the quantitative relationship between fishery production and the flow of fresh water to estuaries. In: R. Cross and D. Williams, eds. Proceedings of the National Symposium on Freshwater Inflow To Estuaries,Volume 1, FWS/OBS-81/04, Office of Biological Services, U.S. Fish and Wildlife Service, Washington D.C.: 403-430.

Davis, S.M. 1997. Salinity in coastal basins estimated from upstream water stages. In: Central and Southern Florida Project Comprehensive review Study, http://www.restudy.org , Comprehensive Plan Evaluation, Evaluation of Alternative Plans, About the P.M. ’ s.

Higher Trophic Level Working Group. 1998. Draft Report of Higher Trophic Level Working Group of Florida Bay Program Management Committee, South Florida Ecosystem restoration Task Force.

Hughes, D.A.. 1969. Responses to salinity changes as a tidal transport mechanism of pink shrimp Penaeus duorarum . Biological Bulletin 136: 43-53.100

Jones, A.C., D.E. Di itriou, J.J. Ewald and J.H. Tweedy. 1970. Distribution of early developmental stages of pink shrimp, Penaeus duorarum , in Florida waters. Bulletin of Marine Science 20: 634-661.

Kushlan, J.D., O.L. Bass Jr. and L.C. McEwan. 1982. Wintering waterfowl in Everglades National Park. South Florida Research Center Report T-670, Everglades National Park, Homestead FL: 26pp.

Lorenz, J.J. 1997. The effects of hydrology on resident fishes of the Everglades mangrove zone. National Audubon Society Final Report to South Florida Research Center, Everglades National Park, Homestead FL: 193pp.

Lorenz, J.J. In press. The response of fishes to physical-chemical changes in the mangroves of northeast Florida Bay. Estuaries 1999.

Mazzotti, F.J. 1983. The ecology of Crocodylus acutus in Florida. Ph.D. dissertation, The Pennsylvania State University, University Park PA: 161pp.

Mazzotti, F.J. and W.A. Dunson. 1984. Adaptations of Crocodylus acutus and Alligator

for life in saline water. Comp. Biochem. Physiol. 79A: 641-646.

Mazzotti, F.J. and W.A. Dunson. 1989. Osmoregulation in crocodilians. Am. Zool. 29: 903-920.

Mazzotti, F.J., A. Dunbar-Cooper and J.A. Kushlan. 1988. Desiccation and cryptic nest flooding as probable causes of embryonic mortality in the American crocodile, Crocodylus acutus , in Everglades National Park, Florida. Florida Scientist 52: 65-72.

McIvor, C.C., J.A. Ley and R.D. Bjork. 1994. Changes in freshwater inflow from the Everglades to Florida Bay including effects on biota and biotic processes. In: S.M. Davis and J.C. Ogden, eds . Everglades: The Ecosystem and Its Restoration , St. Lucie Press, Delray Beach FL: 117-146.

Meeder, J.F., M.S. Ross, G. Telesnicki, P.L. Ruiz and J.P. Sah. 1996. Vegetation analysis in the C-111/Taylor Slough Basin. Document 1: The Southeast Saline Everglades revisited: a half-century of coastal vegetation change. Document 2: Marine transgression in the Southeast Saline Everglades, Florida: rates, causes and plant sediment responses. Final Report. Contract C-4244. Southeast Environmental Research Program. Florida International University, Miami FL

Moler, P.E. 1991. American crocodile population dynamics. Final report, Florida Game and Freshwater Fish Commission, Tallahassee FL: 23pp.101

Morrison, D. and D.L. Bean. 1997. Benthic macrophyte and invertebrate distribution and seasonality in the Everglades-Florida Bay ecotone. National Audubon Society Final Report to South Florida Research Center, Everglades National Park, Homestead FL: 25pp+figures and tables.

Ogden, J.C. Personal communication. South Florida Water Management District, West Palm Beach FL.

Ogden, J.C. 1976. Crocodilian ecology in southern Florida. In: Research in the Parks: Transactions of the National Park Centennial Symposium, 1971, National Park Service Symposium Series No. 1, U.S. Department of the Interior, Washington D.C.

Ogden, J.C. 1994. A comparison of wading bird nesting colony dynamics (1931- 1946 and 1974-1989) as an indication of ecosystem conditions in the southern Everglades. In: S.M. Davis and J.C. Ogden, eds. Everglades: The Ecosystem and Its Restoration. St. Lucie Press, Delray Beach Fl: 533-570.

Ogden, J.C., J.A. Kushlan and J.A. Tilmont. 1978. The Food Habits and Nesting Success of Wood Storks in the Everglades National Park in 1974. Natural Resources Report 16, U.S. National Park Service, Washington D.C.: 25pp.

Powell, G.V.N. and R.D. Bjork. 1990. Relationships between hydrologic conditions and quality and quantity of foraging habitat for roseate spoonbills and other wading birds in the C-111 basin. National Audubon Society Second Annual Report to South Florida Research Center, Everglades National Park, September 1990.

Powell, G.V.N., R.D. Bjork, J.C. Ogden, R.T. Paul, A.H. Powell and W.B. Robertson, Jr. 1989. Population trends of some south Florida wading birds. Wilson Bulletin 101: 436-457.

Rice, J.K. 1997. An analysis of environmental factors influencing juvenile pink shrimp ( Penaeus duorarum ) abundance in southwest Florida. Masters Thesis. University of Miami, Coral Gables FL.

Schmidt, T.W. 1993. Community characteristics of dominant forage fishes and decapods in the Whitewater Bay-Shark River Estuary, Everglades National Park. Technical Report NPS/SEREVER/NRTR-93/12.

Sheridan, P.F. 1996. Forecasting the fishery for pink shrimp, Penaeus duorarum

, on the Tortugas grounds, Florida. Fishery Bulletin 94: 743-755.102

Simmons, Glen. Personal communication. Homestead FL.

Tabb, D.C., D.L. Dubrow and A.E. Jones. 1962. Studies on the biology of the pink shrimp Penaeus duorarum Burkenroad, in Everglades National Park, Florida. Technical Series 37: 1-30, Florida State Board of Conservation, University of Miami, Miami Laboratory, Miami Florida.

Thayer, G.W., A.B. Powell, and D.E. Hess. 1998. Response of larval, juvenile and small adult fishes to changes in environmental conditions in Florida Bay: A decadal comparison. Proceedings of the 1998 Florida Bay Science Conference, May 12-14, 1998.

Trexler, J.C., W.F. Loftus, F. Jordan, J.J. Lorenz and J. Chick. In prep. Empirical assessment of fish introductions in southern Florida: An evaluation of contrasting views.

Wanless, H.R., R.W. Parkinson and L.P. Tedesco. 1994. Sea level control on stability of Everglades wetlands. In: S.M. Davis and J.C. Ogden, eds. Everglades: The Ecosystem and Its Restoration . St. Lucie Press, Delray Beach FL: 199-223.

Welsh, R., M. Remillard and R.F. Doren. 1995. GIS data base development for south Florida ’ s national parks and preserves. Photogrammetric Engineering and Remote Sensing 61(1): 1371-1381.103



### VIII. BISCAYNE BAY CONCEPTUAL ECOLOGICAL MODEL

A. PREPARERS

Diego Lirman, Elizabeth A. Irlandi, and Wendell P. Cropper, Jr., Center for Marine and Environmental Analyses, University of Miami, Miami, Florida.

B. INTRODUCTION

Biscayne Bay is a subtropical lagoon located on the southeast coast of Florida. The Bay is generally subdivided into three sections with unique biological and physical characteristics: a) North Bay, north of the Rickenbacker Causeway, b) Central Bay, from the Rickenbacker Causeway to Card Sound, and 3) South Bay, an area that includes Card Sound and Barnes Sound (VanArman et al., 1989).

The North Bay, an area heavily influenced by urban development activities, has reduced water clarity, high concentrations of toxicants and nutrients, and chronic sewage pollution (e.g., Wanless, 1976; Harlem, 1979; Judge et al., 1979; Wanless et al., 1984; Corcoran et al., 1987). The main sources of pollution for this heavily urbanized watershed are the Miami River, the Port of Miami, and various canals (e.g., Buck, 1976; Corcoran et al., 1984; Dade County , 1987; Markley et al., 1990). High levels of toxic metals, organic contaminants and pesticides have been found in the water and sediments of discharge sites. Altered salinity regimes, increased nutrient and contaminant loadings, and high water turbidity have all contributed to the decreased health and extent of biological communities within the northern section of Biscayne Bay.

The central portion of the Bay is better flushed than the North Bay and has extensive, healthy seagrass beds and other benthic communities. Nevertheless, industrial and agricultural discharges, as well as leachete from the South Dade landfill, are important sources of pollution to this area (McKenzie, 1983; Shinn and Corcoran, 1987). A salinity gradient is found in the Central Bay, with lower, variable salinity occurring on the western margin of the Bay due to freshwater inflow from canal discharge and runoff, and higher, more stable salinities in the eastern margin, where oceanic influences prevail (Wang et al., 1978; Chin Fatt and Wang, 1987).

The southern portion of the Bay (Card Sound and Barnes Sound) is influenced primarily by agricultural development. Freshwater inflow into the area is mostly through canal discharge, and flushing is limited as there are no direct connections to the ocean. Accordingly, salinity can vary from relatively low values during the wet season (10-20 ppt) to potentially hypersaline values (40-45 ppt.) during the dry season (Lee and Rooth, 1975). Southern Biscayne Bay has extensive, healthy seagrass beds,104

and is critical habitat for a number of threatened species such as the Cape Sable seaside sparrow, roseate spoonbills, as well as crocodiles, manatees, and snail kites (Kushlan and White, 1977; Kushlan and Mazzotti, 1989).

The benthi c habitats of Biscayne Bay are dominated by extensive beds of seagrass that cover most of the Bay bottom (Thorhaug, 1976). Thalassia testudinum is the dominant seagrass species, but Halodule wrightii and Syringodium filiforme are also present and may dominate locally. The seagrass beds also have associated rhizophytic (e.g., Halimeda spp., Penicillus spp., and Udotea spp.) and drift-algal (e.g., Laurencia spp., Polysiphonia spp.) components. Hardbottom areas with sponges, soft corals, hard corals, and macroalgae are less extensive and occur primarily in the eastern and central portions of the Bay (DiResta et al., 1995; Cropper and DiResta, 1999).

Both commercial and recreational fishing are important activities within Biscayne Bay (Berkeley et al., 1985). Sport-fishing activities are concentrated mainly on fish species such as tarpon, snook, bonefish, and permit (deSylva, 1969). The groups of organisms harvested commercially within the Bay include: spotted seatrout, the snapper-grouper fish complex, bait fish, bait shrimp, stone and blue crabs, lobsters and sponges (Ault et al., 1997).

C. DRIVERS AND STESSORS

The anthropogenic and natural drivers creating potential stressors to the Biscayne Bay ecosystem include urban, industrial, and agricultural development, water management (C&SF project), commercial and recreational fishing and boating activities, and natural disturbances such as storms (refer to figure on page 109).

Prior to the extensive human development in the area, inputs of fresh water int o Biscayne Bay were mainly from the Miami River, Little River, Arch Creek, and Snapper Creek. Sheet flow from the adjacent Everglades system, artesian flow from the underlying limestone bedrock, and runoff after storms or heavy rains were important additional sources of fresh water before development (Harlem, 1979; Wanless et al., 1984).

However, since the early 1900s, the hydrology of the Bay has been significantly modified due to coastal construction and the development of the extensive water management system now in place (Wanless et al., 1984). Fresh water input patterns have been highly modified from pre-development patterns, limiting both surface and groundwater inflow into the Bay. At present, the main sources of fresh water are local rainfall and runoff, as well as canal discharges (Wanless et al., 1984).105

During the rainy season, tremendous volumes of water can be released through flood control structures creating large and rapid fluctuations in salinity in the vicinity of canal mouths and over-all reduced salinity on the western fringe of the Bay (Wang et al., 1978). Increases in freshwater inflow from runoff as well as from point sources have also contributed to a significant decrease in water quality within Biscayne Bay. Major issues of concern include increased sedimentation and turbidity as well as increased nutrient loading and chemical pollution (VanArman et al., 1989).

Both commercial and recreational boating activities can cause significant physical damage to seagrass beds, hardbottom communities, and manatees (O'Shea et al., 1985; Sargent et al., 1995; Ault et al., 1997). Major storms can also have significant effects on water quality and benthic habitats. After Hurricane Andrew, high turbidity, increased nutrient and pollutant loading, high dissolved organic carbon, and persistent plankton blooms were observed within Biscayne Bay (Tilmant et al., 1994). Benthic communities also experienced high erosion, and burial and removal of organisms during Andrew and previous hurricanes (Thomas et al., 1962; Tilmant et al., 1994).

D. ECOLOGICAL EFFECTS

Salinity : Alterations in salinity can impact species composition and productivity of seagrass communities. Of the three most abundant seagrass species that occur in the Bay, Halodule is the most tolerant of low-salinities, and tends to be dominant in areas adjacent to canal discharge sites. Thalassia and Syringodium are also found near canals, but growth and productivity of these species is reduced at sites influenced by freshwater discharge (Conover, 1964; Lewis et al., 1985; Montague, 1989). Salinity also affects other benthic primary producers associated with seagrass communities. Pulses of reduced-salinity water can have negative effects on the growth of the drift alga Laurencia and rhizophytic algae such as Penicillus spp., Udotea spp., and Halimeda spp. (Conover, 1964; Irlandi et al., unpublished data).

Similarly, salinity fluctuations can affect faunal composition and abundance as some species are more tolerant to low salinity than others (Serafy et al., 1997). Salinity effects on the distribution of grazers (both fish and invertebrate) may influence the abundance of phytoplankton, epiphytes and macroalgae that can potentially shade seagrasses (Irlandi et al., 1997). Negative effects of low salinity have also been detected in sponges (Smith, 1973; Storr, 1976).

Pollution : Urban and agricultural development, as well as boating activities in the Bay, contribute to the introduction of contaminants and toxins into the environment. The use of herbicides in farming may potentially influence seagrass growth and production while heavy metals, mercury, and other toxic materials can be detrimental to the health and survival of fish populations and higher trophic levels that feed on them (e.g. bioaccumulation of toxins). Several studies have detected a high number of106

abnormalities in several fish species within Biscayne Bay, specially around heavily polluted areas such as marinas and canal outflows (e.g., Browder et al., 1993; Gassman et al., 1994)

Nutrients : Agricultural runoff, urban runoff, and stormwater release can result in an increase in both water-column and sediment nutrients, promoting growth of phytoplankton, seagrass epiphytes, and macroalgae (e.g., Lapointe and Clark, 1992; Frankovich and Fourqurean, 1997). Phytoplankton blooms, epiphyte growth, and growth of attached and drift macroalgae can reduce light availability to seagrasses and reduce their growth and production. Similarly, high concentrations of phytoplankton may be deleterious to filter-feeding sponges in hardbottom habitats due to a potential clogging effect.

Nutrient gradients caused by point sources may have a major influence on the abundance, composition, and distribution of benthic communities. Mats of drift algae are common along the western boundary of the Bay where several canals drain agricultural fields, and their growth and distribution may be the direct result of the increased nutrients. Changes in nutrient levels can also affect the community composition of seagrass meadows by influencing the competitive interactions among the dominant seagrass species (Williams, 1987; Harwell and Fong, 1994; Fong et al., 1997), producing shifts in dominance from Thalassia to Halodule (Fourqurean et al., 1995) as well as influencing competitive interactions between seagrasses and algae (Williams, 1990; Holmquist, 1992).

Sedimentation : Increased sediment loads associated with canal discharge, runoff, and resuspension due to storms and boating activities can increase water turbidity, shading benthic plants and decreasing productivity (Hall et al., 1991; Onuf, 1991; Tilmant et al., 1994; Sargent et al., 1995). If sediment concentrations are high, there is also the potential for burial and smothering of benthic-communities components.

Harvesting and Poaching: Commercial and recreational fishing can influence the biotic communities of Biscayne Bay. Fishing pressure, species targeted, and size of fish captured can alter the species composition and trophic structure of fish communities. For example, the removal of omnivorous bait fish in large quantities (e.g., pinfish) may result in decreased grazing rates that may facilitate algal and epiphyte overgrowth of seagrasses and hardbottom-community components.

Poach ing can also have significant impacts on the populations targeted. The removal of undersized lobsters as well as the removal of large, reproductive sponges can have significant long-term effects on the survival of these populations (Cropper and DiResta, 1999).

Many of the commercially and recreationally important fish and macroinvertebrates found in the Bay rely on seagrass and hardbottom habitats for food107

and/or shelter, therefore, factors influencing the distribution, productivity, and abundance of these benthic habitats will have an effect on the distribution and abundance of fishery resources in the Bay.

Physical Damage : Direct physical damage to the biotic communities of Biscayne Bay can be caused by boating and harvesting activities as well as by intense storms. Shrimp trawlers actively target seagrass habitats but may venture into hardbottom areas removing and damaging sponges and gorgonians with their gear. Ault et al. (1997) found that considerable damage to both seagrass and hardbottom communities can result from trawl and trap fishing practices. Significant by-catch of juvenile fish that suffer physical damage and/or mortality can also occur.

Most of the seagrass beds within Biscayne bay show some signs of boat scarring. Boat scars result in the loss of essential habitat for associated fauna, sediment erosion, and increased water turbidity (Sargent et al., 1995). Furthermore, several studies have shown that the recovery of deep scars by seagrasses can be a slow process taking anywhere from a few months to several years to recuperate original seagrass shoot densities (Zieman, 1976; Durako et al., 1992). Lastly, the scouring effects of sediments suspended during intense storms may cause significant mortality of benthic organisms and affect their distribution within the Bay (Tedesco et al., 1995).

E. ECOLOGICAL ATTRIBUTES AND MEASURES

A set of endpoints or attributes can serve as indicators of the health of the Biscayne Bay ecosystem. Most of these attributes are biological components of the system such as the health of birds, macroinvertebrates (e.g., lobsters, shrimp, scallops), fishes, manatees, and seagrass and hardbottom communities.

Faunal Communities : This endpoint considers the abundance, size, and health of Bay species or species groups that are of commercial or recreational importance such as bait shrimp, crabs, lobsters, tarpons, bonefish, snappers and groupers, birds, dolphins, crocodiles and manatees. Measurements and indicators for this endpoint include distribution, abundance, growth, recruitment, and population size structure of these organisms, nest distribution, as well as incidence of disease and abnormalities. Information about the health of commercial stocks could be obtained from landings and fishing effort statistics.

Seagrass Communities: Seagrasses compose a keystone community within Biscayne Bay; they not only dominate spatially but also serve as essential habitat (e.g., food and refuge) for a productive food web. Their presence also plays a role in maintaining water quality (e.g., sediment stabilization, nutrient uptake), another major endpoint for the Bay. The spatial extent, density, and productivity of seagrass beds are key attributes of these communities and can be estimated directly.108

Hardbottom Communities: Hardbottom communities within Biscayne Bay contain high densities of sponges, soft corals, and macroalgae. Hard corals can also be important components locally. Just like seagrass communities, hardbottom communities provide essential habitat for a large number of organisms. Juvenile lobsters are often found within sponges (Butler et al., 1994) and large stands of the attached alga Sargassum provide both food and shelter to juvenile fishes seasonally.

Also, water and sediment quality are impo rtant attributes of the system as the health of the biological components is often tightly linked to them. Direct indicators and measurements of water and sediment quality include turbidity, salinity, dissolved oxygen, bacterial counts, chlorophyll concentrations, and the concentration of nutrients and pollutants. Secondary indicators of reduced water and sediment quality may be the distribution and composition of invertebrate communities (e.g., meiofauna) that respond differently to different environmental conditions.110

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### IX. FLORIDA BAY CONCEPTUAL MODEL

A. PREPARER

David T. Rudnick, South Florida Water Management District, West Palm Beach Florida.

B. INTRODUCTION

A simple conceptual model of the Florida Bay ecosystem is presented here. This model is consistent with our effort to assess the current understanding of south Florida ’ s ecosystems, identify the most important human effects on these ecosystems, identify restoration goals and success criteria, and identify the minimum measurements required to determine whether these criteria are being met. The structure of the model is largely based on the expert opinions of scientists who have focused their attention on Florida Bay during the past several years. During this time, detailed reviews of our understanding of the Florida Bay have been presented (Boesch et al. 1993, Boesch et al. 1995, Boesch et al. 1997, Fourqurean and Robblee 1999). Detailed plans that identify quantitative information needs for environmental management decision making, as well as strategies to provide this information, have also been presented (Armentano et al. 1994, Armentano et al. 1997). While the conceptual model presented here is largely consistent with the body of knowledge described in the reviews and plans noted above, some details or omissions of this model may not be consistent will the opinions of every contributor listed above or every contributor to the larger Florida Bay research effort.

Florida Bay primer. Florida Bay is a triangularly shaped estuary, with an area of about 850 square miles, that lies between the southern tip of the Florida mainland and the Florida Keys. About 80% of this estuary is within the boundaries of Everglades National Park. A defining feature of the bay is it ’ s shallow depth, with a mean depth of about 1 meter (Schomer and Drew 1981). This shallowness allows light to penetrate through the water to the sediment surface in almost all areas of the bay and results in the potential for the bay to sustain seagrass beds as a dominant habitat and source of productivity. The shallowness of the bay also affects the circulation and salinity regime of the bay; with a complex network of shallow mud banks, water exchange among the bay ’ s basins and between these basins and the Gulf of Mexico is restricted (Smith 1994, Wang et al. 1994). With a long residence time and shallow depth, the salinity of Florida Bay water can rapidly rise during drought periods. Salinity levels as high as twice that of seawater have been measured (McIvor et al. 1994). Another defining feature of the bay is that the sediments are primarily composed of carbonate mud, which can scavenge inorganic phosphorus from bay waters (DeKanel and Morse 1978).118

Until the 1980s, Florida Bay was perceived by the public and environmental managers as being a healthy estuary, with clear water, lush seagrass beds, and productive fish and shrimp populations. By the mid 1980s, however, catches of pink shrimp had declined dramatically (Browder et al. 1999) and in 1987, the mass mortality of turtle grass ( Thalassia ) beds began (Robblee et al. 1991). By 1992, the ecosystem appeared to shift from a clear water system, dominated by primary production on the sediment (benthic production) to a turbid water system, dominated by algae blooms in the water column and resuspended sediment. The conceptual model focuses on these changes in seagrasses and water quality as the central issues to be considered by environmental managers.

Reality check. The simple model presented below does not address the spatial complexity of Florida Bay. Florida Bay is, indeed, not so much a singular estuary, but a complex array of basins, banks, and islands that differ across a set of regions. The mosaic of seagrass habitat and mangrove habitat, as well as water quality and ecosystem processes, vary distinctly with this spatial variation. Nevertheless, only a single, generic model is described and this model is intended to summarize the main characteristics and trends of the bay. While the structure of this model is appropriate for most areas of the bay, the relative importance of the model ’ s components differ considerably among the bay ’ s sub-regions. Any application of this model (for example, recommendations for a specific set of monitoring parameters and guidelines) must take the spatial variability of the bay into account.

C. EXTERNAL DRIVERS AND ECOLOGICAL STRESSORS

It has often been assumed that a direct cause of Florida Bay ’ s ecological changes is a long-term increase in the Bay ’ s salinity that resulted from the diversion of freshwater away from Florida Bay via SFWMD canals. However, recent research has indicated that the Bay ’ s changes are not attributable to a single cause - while decreased freshwater inflow and resultant increased salinity have been part of the problem, it appears that other human activities, as well as natural forces, have also contributed to the problem (Armentano et al. 1997, Boesch et al. 1993, Boesch et al. 1995, Boesch et al. 1997, Fourqurean and Robblee 1999). The conceptual model thus includes both natural and human derived sources of stress (refer to figure on page 127).

Altered salinity regime. The salinity regime of an estuary is a primary determinant of the species composition of communities, as well as strongly influencing functions of these communities (Sklar and Browder 1998). Salinity is a direct stress on biota; all estuarine biota have adapted to a given salinity range and a given degree of salinity variability. For a given organism, changing salinity beyond this range or too quickly within this range can result in poor health or119

death. Thus long-term changes in salinity level or variability are detrimental to some species, but favorable for other species.

Florida Bay ’ s salinity regime varies greatly over time and space. This variation ranges from coastal areas that can be nearly fresh during the wet season, to large areas of the central bay that can have salinity levels near 70 ppt during prolonged droughts, to nearly stable marine conditions (about 35 ppt) on the western boundary of the bay. The main forces that determine salinity regime in the bay are the inflow of freshwater from the Everglades, rainfall over the bay, evaporation from the bay, and exchange with seawater from the Gulf of Mexico and the Atlantic Ocean. Both freshwater inflow and seawater exchange have changed drastically in the past hundred years, resulting in an alteration of the bay ’ s salinity regime.

Freshwater inflow to Florida Bay decreased in volume and changed in timing and distribution during this century because of water management . Hydrologic alteration began in the late 1800s, but accelerated with the construction of drainage canals by 1920, the Tamiami Trail by 1930, and the C&SF Project and South Dade Conveyance System from the early 1950s through 1980 (Light and Dineen 1994). With the diversion of freshwater to the Atlantic coast and Gulf of Mexico coast, the bay ’ s mean salinity inevitably increased. The extent of this increase and how the variability of salinity changed is not known, but is the subject of current research.

Results from this research indicate that another important development that altered the salinity regime of Florida Bay was construction of the Flagler railway across the Keys from 1905 to 1912 (Swart et al. 1996, Swart et al. 1999). It appears that in the last century, prior to railway construction and water management, Florida Bay had a lower mean salinity and more frequent periods of low (10 ppt - 20 ppt) salinity than during this century. The extent and frequency of high salinity events does not appear to have changed between centuries. The bay ’ s salinity regime changed abruptly around 1910 because passes between the Keys were filled to support the railway. Thus, water exchange between Florida Bay and the Atlantic Ocean was decreased and water circulation throughout the bay was probably altered.

Two important natural controls of salinity, sea level rise and the frequency of major hurricanes must also be considered. Florida Bay is a very young estuary, the product of sea level rising over the shallow slope of the Everglades during the past 4000 years. With rising sea level, the bay not only became larger but also became deeper. With greater depth, exchange of water between the sea and the bay probably increased, resulting in a more stable salinity regime with salinity levels increasingly similar to the sea. However, a factor that has counteracted the rising sea is the accumulation of sediment, which makes the bay more shallow. Most sediment that accumulates in Florida Bay is carbonate that is precipitated from120

water by organisms that live in the Bay. The extent to which these sediments accumulate is a function of the biology of these organisms, the chemistry of the water, and the physical energy available to transport these sediments from the Bay

. Major hurricanes are thought to be important high energy events that can flush the bay of these sediments. However, since 1965, no major hurricane has directly affected Florida Bay. Florida Bay ’ s ecological changes during the past decade may thus be indirectly influenced by changing circulation patterns and resultant changing salinity regimes because of changing water depth in the bay.

Nitrogen and phosphorus inputs. The productivity and food web structure of all ecosystems is strongly influenced by patterns of nutrient cycling and the import and export of these nutrients. Throughout the world, estuarine ecosystems have undergone dramatic ecological changes because they have been enriched by nutrients derived from human activity. These changes have often been catastrophic, with the loss of seagrasses and the occurrence of algal blooms and lethal low oxygen or anoxic events. The input of nitrogen and phosphorus (N and P) to estuaries is thus a potentially important stressor of estuaries.

The importance of N and P as stressors in Florida Bay is unclear. In general, the bay is rich in N and poor in P, especially towards the eastern region of the bay (Boyer et al. 1997). There is little evidence that nutrient inputs to the bay have increased during this century, but with expanding agriculture and residential development in south Florida through this century, and particularly development of the Keys, nutrient enrichment almost certainly has occurred (Lapointe and Clark 1992, Orem et al. 1998). Anthropogenic nutrients that enter Florida Bay are derived not only from such local sources (fertilizer and wastes from agriculture and residential areas), but also from remote sources. It is likely that remote contributions to the Gulf of Mexico, such as from the phosphate fertilizer industry of the Tampa-Port Charlotte area and residential development from Tampa to Naples, are the most important external sources of nutients (Rudnick et al. 1999). This enrichment from external sources, however, may not less important to the bay ’ s ecology than it ’ s own internal sources and cycling. It is, nevertheless, a reasonable hypothesis that a chronic increase in nutrient inputs has occurred in Florida Bay in this century and this increase has contributed to ecological changes. Ongoing research will provide information to test this hypothesis. Development of a water quality model will also help us understand the effects of past nutrient inputs and predict the effects of future management scenarios.

In the conceptual model, water management is listed as a source of stress because the canal system can transport nutrients through the wetlands toward the bay, decreasing nutrient retention by the wetlands and possibly increasing nutrient inputs to the bay. Nutrient inputs from the Everglades and the Gulf of Mexico are affected not only by changes of freshwater flowing from Taylor Slough and Shark River Slough, but also by changes in bay circulation. Nutrient retention within the121

Bay is certainly sensitive to these changes in circulation, which have been caused by Flagler railway construction and the balance of sea level rise and sedimentation or sediment removal by major hurricanes . The influence of hurricanes may be particularly important, as nutrients (particularly P) accumulate in the bay ’ s carbonate sediment and the absence of major hurricanes may have resulted in an accumulation of nutrients during the past few decades.

Pesticides and mercury. With the widespread agriculture and residential development of south Florida, the application and release of pesticides and other toxic materials has increased. Mercury is of particular concern because of high concentrations of methylmercury in upper trophic level species. However, it is unclear whether anthropogenic mercury inputs to the Everglades or Florida Bay have increased or whether mercury cycling and methylation rates have changed. Pesticides and mercury are of concern because they can affect human health after the consumption of fish or other biota with high concentrations of these toxins, and because other species may be adversely affected by these compounds. To date, there is no evidence the main ecological changes in Florida Bay are in any way linked to inputs of toxic compounds. Water management affects the distribution of these toxic materials and potentially their transport to Florida Bay. Controlling water levels in wetlands may also influence the decomposition of pesticides and mercury methylation rates because both of these processes are sensitive to the presence of oxygen in soils, which is affected by water levels.

Fishing pressure. For any species that is the target of recreational or commercial fisherman, fishing pressure directly affects population dynamics and community structure. Within Everglades National Park, commercial fishing has been prohibited since 1985, but populations that live outside of ENP boundaries for at least part of their life cycle, which includes most of Florida Bay ’ s sport fish species, are nevertheless affected by fisheries (Tilmant 1989).

D. ESSENTIAL ECOSYSTEM ATTRIBUTES AND LINKS TO STRESSORS

A set of Florida Bay ’ s attributes that are either indicators of the health of the ecosystem or intrinsically important to society are given in the conceptual model. These attributes in most cases are biological components of the ecosystem, including seagrass, molluscs, shrimp, fish and birds, but also an aggregated attribute of the chemical and physical condition of the bay, termed “ water quality condition. ” While the list of biological components is broad, it is clear from the links to stressors that are presented that these attributes are not equally weighted within the model; the central attribute of this conceptual model of Florida Bay is the seagrass community. Details of each attribute and linkage are given below.122

Seagrass community . The keystone of the Florida Bay ecosystem is its seagrasses (Zieman et al. 1989, Fourqurean and Robblee 1999). These plants are not only a highly productive foundation of the food web, but are also the main habitat of higher trophic levels and a controller of the bay ’ s water quality. Understanding how seagrasses affect water quality is essential for understanding the current status and fate of the bay.

Seagrasses affect water quality by three mechanisms: nutrient uptake and storage, binding of sediments by their roots, and trapping of particles within their leaf canopy. With the growth of lush seagrass beds, these mechanisms drive the bay towards a condition of clear water, with low nutrients for algae growth in the water and low concentrations of suspended sediment in the water. During the 1970s through the mid-1980s, lush Thalassia beds grew throughout central and western Florida Bay and the water was reported to be crystal clear. We hypothesize that with the onset of a Thalassia mass-mortality event in 1987 (Robblee et al. 1991), these mechanisms reversed, initiating a cycle that causes continued seagrass habitat loss and propagates persistent turbid water with algae blooms (Stumpf et al. 1999).

The cause of the 1987 mass-mortality event is not known, but thought to be related to earlier changes in two stressors, the salinity regime and nutrient availability. These changes caused Thalassia beds to grow to an unsustainable density by the mid 1980s. It is also likely that a decrease in shoal grass and widgeon grass ( Halodule and Ruppia ) occurred with the Thalassia increase. Thalassia “ overgrowth ” may have occurred because the species thrived when the salinity regime of the bay was stabilized, with few periods of low salinity. Nutrient enrichment also may have played a role, with a chronic accumulation of nutrients caused by increased inputs over decades or decreased outputs because of the absence of major hurricanes or closure of Keys ’ passes. The factors that conspired to initiate the mass-mortality event in 1987 are also unknown, but thought to be related to the high respiratory demands of the dense grass beds and accumulated organic matter. During the summer of 1987, with high temperatures, sulfide levels may risen to lethal concentrations.

Regardless of the cause of the mass-mortality event, once this event was initiated, the ecology of Florida Bay changed. The cycle causing continued seagrass habitat loss, which characterizes the present Florida Bay, is illustrated in the model. Continued seagrass mortality results in increased sediment suspension and increased nutrient release from the sediments (>N & P), stimulating the growth of algae in the water column. The presence of both these algae and suspended sediment result in decreased light penetration to the seagrass bed. In this cycle, it is this decreased light that stresses the seagrasses and sustains the feedback loop. Light penetration is thus an essential aspect of the attribute, water quality.123

The dynamics of this feedback loop are probably not independent of the salinity regime. A disease of seagrass, caused by a slime mold infection, seems to be more common at salinities near or greater than seawater ( = 35 ppt) than at low (15 to 20 ppt) salinities (Landsberg et al. 1996). This may have played a role in either the initial seagrass mass mortality event, but more likely has served to continue seagrass mortality since that event. The incidence of this disease may be directly affected by water management actions.

If the state of the seagrass community is to be used as a criterion to decide the success of environmental restoration efforts, environmental managers must specify the desirability of alternative states. The consensus among scientists is that the Florida Bay of the 1970s and early 1980s, with lush Thalassia and clear water, was probably a temporary and atypical condition. From an ecological perspective, restoration should probably strive for a more diverse seagrass community, less dominated by Thalassia than during that period.

Water quality condition. Water quality condition reflects not only obvious characteristics, such as salinity, but also the light field, algae in the water column, and the availability of nutrients in the ecosystem. All of these characteristics are closely related to the condition of seagrasses and the food web structure and dynamics of the bay. While these characteristics have been monitored and researched since the early 1990s, earlier information is scarce for salinity and even less available for other characteristics. Thus, at the present time, we do not know whether nutrient inputs to the bay have actually increased in recent decades or whether periods with sustained algal blooms and high turbidity occurred in the past.

Salinity has frequently been suggested as a primary restoration target. However, establishing salinity success criteria, such as those used in the Restudy ’ s evaluation of the effects of hydrological alternatives on coastal salinity, depends on the development of a model of the “ natural ” salinity distribution of Florida Bay in time and space. This requires a both a water budget for the bay (monitoring rainfall, evaporation, and freshwater flow, water level, and salinity) and a hydrodynamic model, which is now under development. With modeled salinity variability for a wide variety of target sites in the bay, the fit of observed salinity fields to modeled fields could serve as the basis of deciding levels of success.

The magnitude of nutrient inputs to the bay, and their relationship to freshwater inputs is under investigation. Success criteria based on water column nutrient concentrations are probably less meaningful than criteria based on nutrient loading. Preliminary results indicate that phosphorus loads to the bay do not greatly increase with increased freshwater inputs (Rudnick et al. 1999), but Florida Bay is probably very sensitive to any increase in P availability. Unlike phosphorus, nitrogen loads probably do increase with more freshwater flow and124

algae blooms in western and central Florida Bay appear to be stimulated by increased N (Tomas 1996).

Finally, as emphasized earlier, the penetration of light through Florida Bay waters is a key to the health of seagrasses. An important success criterion should be light penetration, which is largely a function of turbidity from algae and suspended sediment. Light penetration should be sufficient to support a viable seagrass habitat. Such light-based criteria have been used successfully in other estuaries.

Molluscs. Because of our ability to assess historical community structure, molluscs are a good indicators for the entire ecosystem. The composition and activity of the molluscan community is a function of salinity, seagrass and other habitat availability, and food supply. Studies of long-term changes in the composition of this community (by analyzing shells in the sediment) have indeed found changes that reflect the large-scale changes of the bay ’ s salinity regime. Furthermore, molluscs are likely to be important as grazers of algae in bay waters; the trophic status of the bay is reflected by molluscan community composition.

Pink shrimp. Pink shrimp are intrinsically important to society as an economic asset. They are also ecologically important, serving as a major component of the diet of game fish and wading birds; pink shrimp are an indicator of the bay ’ s productivity. Florida Bay and nearby coastal areas are a primary nursery ground for pink shrimp - a nursery that supports the shrimp fishery of the Tortugas Grounds (Costello and Allen 1966). Hydrological and ecological changes in the Everglades and Florida Bay may have impacted this fishery, which experienced a decline in annual harvest from about 10 million pounds per year in the 1960s and 1970s to as little as 2 million pounds per year in the late 1980s (Ehrhardt and Legault 1999). This decline may have been associated with seagrass habitat loss or high salinity (50 to 70 ppt) during the 1989-1990 drought; experiments have shown that pink shrimp mortality rates increase with salinities above 40 ppt (Browder et al. 1999). Shrimp harvest statistics indicate that shrimp productivity increases with increasing freshwater flow from the Everglades (Browder 1985).

Fish populations. The health of Florida Bay ’ s fish populations is of great importance to the public; the sport fishing is a major economic asset to the region. It is clear from recent studies that seagrass beds and the mangrove zone are important habitats for fish, but no dramatic bay-wide decreases in total fish abundance have been observed along with seagrass mass-mortality (Thayer et al. 1999). Rather, a shift in the species composition of this upper trophic level has occurred as a result of the cycle of seagrass habitat loss and sustained algae blooms. While some fish species have declined, fish that eat algae in the water, such as the bay anchovy, are thriving. Thus the stressors, such as altered salinity, not only125

affect upper trophic level animals directly, but also affect them indirectly through food web changes.

Another important stressor that needs to be considered with regard to fish populations is the impact of pesticides and mercury. As concentrations of mercury and some pesticides greatly increase in upper trophic level animals, such as sport fish, (via the process of bioaccumulation), and people eat such fish, a human health issue potentially exists. Pesticides and mercury can also have ecological impacts by physiologically stressing organisms (particularly reproductive functions). The extent of any existing problem with these toxic compounds in Florida Bay is being investigated, but they currently do not appear to significantly impact human health or ecological health in the bay. The possible impact of future restoration efforts on these issues, however, must still be considered.

Among the many fish species that could be used as indicators of the health of the ecosystem ’ s upper trophic level, there is consensus among scientists that spotted sea trout is a key species. This is the only major sport fish species that spends its entire life-span in the bay. Population changes and toxic residues in this species thus reflect the specific problems of the bay and should also reflect the restoration actions that we take. For northeastern Florida Bay, the abundance of snook, tarpon, and crevalle jack should also be considered.

Water Birds. Florida Bay and its mangrove coastline is an important feeding ground and breeding ground for water fowl and wading birds. Conceptual models for other regions of the Everglades, particularly the mangrove - estuarine transition zone conceptual model, present more detailed descriptions of the use of bird populations as ecological indicators and consider a wide variety of birds. For the Florida Bay conceptual model, we consider only fish-eating birds, such as osprey, brown pelicans, and cormorants. These birds are important predators of fish in the bay and are potentially impacted by any stressors that affect their prey base, including salinity changes, nutrient inputs, toxic compounds, and fishing pressure. As with other top predators, these bird species are the most vulnerable members of the ecosystem with regard to pesticide and mercury effects.

E. MEASURES

A list of fundamental measures associated with each of the model ’ s ecosystem attributes is given. This list should be considered minimal; interpretation of many of these measures requires a set of associated measures. The list includes not only

“ structural ” variables (for example, pink shrimp abundance), but also dynamic, process variables (for example nutrient fluxes). Note that this list does not reflect the temporal or spatial time scale at which measurements are necessary, but temporal patterns, such as seasonality and interannual variability, and spatial126

patterns are a central aspect of ecological dynamics. Also note that the power to predict the fate of any ecosystem requires more than monitoring; research and modeling are also essential components of sound environmental management.128129

F. REFERENCES

Armentano, T., M. Robblee, P. Ortner, N. Thompson, D. Rudnick, and J. Hunt. 1994. Science Plan for Florida Bay. 43 pp.

Armentano, T., R. Brock, J. Hunt, W. Kruzynski, D. Rudnick, S. Traxler, N. Thompson, P. Ortner, K. Cairnes, M. Robblee, and R. Halley. 1997. Strategic Plan for the Interagency Florida Bay Science Program. Florida Bay Program Management Committee, unpublished, 42 pp.

Boesch, D., N. Armstrong, C. D ’ Elia, N. Maynard, H. Paerl, and S. Williams. 1993. Deterioration of the Florida Bay Ecosystem: An Evaluation of the Scientific Evidence. Report to the Interagency Working Group on Florida Bay.

Boesch, D., N. Armstrong, J. Cloern, L. Deegan, R. Perkins, and S. Williams. 1995. Report of the Florida Bay Science Review Panel on Florida Bay Science Conference: Report by Principal Investigators, October 17-18, 1995.

Boesch, D., N. Armstrong, J. Cloern, L. Deegan, S. McCutcheon, R. Perkins, and S. Williams. 1997. Annual Report of the Florida Bay Science Oversight Panel: Perspectives from the 1996 Florida Bay Science Conference and Review of the Strategic Plan.

Boyer, J.N., J.W. Fourqurean, and R.D. Jones. 1997. Spatial characterization of water quality in Florida Bay and Whitewater Bay by multivariate analysis: zones of similar influence (ZSI). Estuaries 20:743-758.

Browder, J.A. 1985. Relationship between pink shrimp production on theTortugas grounds and water flow patterns in the Florida Everglades. Bull. Mar. Sci. 37:839-856.

Browder, J.A. V.R. Restrepo, J.K. Rice, M.B. Robblee, and Z. Zein-Eldin. 1999. Environmental influences on potential recruitment of pink shrimp, Penaeus duorarum , from Florida Bay nursery grounds. Estuaries (in press).

Costello, T. J., and D. M. Allen. 1966. Migrations and geographic distribution of pink shrimp, Penaeus duorarum, of the Tortugas and Sanibel grounds, Florida. U.S. Fish Wildl. Serv., Fish. Bull. 65:449-459.

DeKanel, J. and J.W. Morse. 1978. The chemistry of orthophosphate uptake from seawater on to calcite and aragonite. Geochem. Cosmochem. Acta. 42:1335- 1340.130

Ehrhardt, N.M. and C.M. Legault. 1999. Pink shrimp recruitment variability as an indicator of Florida Bay dynamics. Estuaries (in press).

Fourqurean, J.W. and M.B. Robblee. 1999. Florida Bay: a history of recent ecological changes. Estuaries (in press).

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