Interim Operational Plan

Project 

Evaluation 

Report

SFNRC Technical Series

2006:2

An Assessment of the

National Park Service

U.S. Department of the Interior

South Florida Natural Resources Center

Everglades National Park 
An Assessment of the

Interim Operational Plan

Project Evaluation Report

SFNRC Technical Series 2005:2

South Florida Natural Resources Center

Everglades National Park

Homestead, Florida

National Park Service

U.S. Department of the Interior

Cover photograph by Lori Oberhofer, ENP
ii South Florida Natural Resources Center Technical Series (2005:2)
An Assessment of the Interim Operational Plan iii

Table of Contents

Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

List of Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Study Area / Physiographic Regions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Structural Features for the Delivery of Water to Everglades National Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Early Water Delivery Plans for Everglades National Park. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

The Minimum Schedule of Water Deliveries Plan (1970-1983). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

The Experimental Program of Water Deliveries to Everglades National Park (1984 -1999). . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Interim Water Delivery Plans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

The Interim Structural and Operational Plan (ISOP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

The Interim Operational Plan (IOP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Toward Restoration of Everglades National Park: Implementation of the Modified Water 

Deliveries and C-111 Projects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

The Modified Water Deliveries Project. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

The C-111 Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Restoration Objectives of the Modified Water Deliveries and C-111 Projects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

An Assessment of the Interim Plans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Physical Environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Biological Environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Conclusions and Recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Positive Outcomes in the Assessment of Interim Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Sources of Concern in the Assessment of the Interim Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Supporting Documents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Literature Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
iv South Florida Natural Resources Center Technical Series (2005:2)

Acknowledgements

The authors and contributors to this report wish to thank the following for their careful and timely review of the draft document: 

Staff of the U.S. Fish and Wildlife Service, Vero Beach, Florida - Mary Ann Poole, Dan Nehler, Freddie James, Tylan Dean

Staff of the U.S. Army Corps of Engineers, Jacksonville, Florida - Barbara Cintron, Jim Riley, Robert Evans, Luis Alejandro, 

John Moulding, Mark Shafer, Susan Sylvester

Staff of the South Florida Water Management District - Paul Linton

Terrence Salt and Don Jodrey of the Department of the Interior

Contributing Authors: 

Introduction and Background

David Sikkema, Brandon Gamble, Alice Clarke, Sherry Mitchell-Bruker

Hydrology

Hosung Ahn, Robert Fennema, Kevin Kotun, Sherry Mitchell-Bruker, Sara O’Connell, Thomas Van Lent

Water Quality

Bob Kadlec, Mike Zimmerman, Nick Aumen, Bill Walker, Dan Childers

Salinity

Hosung Ahn, Dewitt Smith, Bill Nuttle, Frank Marshall

Freshwater Communities

Joel Trexler, Bill Loftus, Christina Bruno, Rick Jacobsen, Evelyn Gaiser, Jeff Kline

Vegetation

Mike Ross, Thomas Armentano

Cape Sable Seaside Sparrow

Skip Snow, Oron “Sonny” Bass, Stuart Pimm

Mangrove, Estuarine, and Marine

Jerry Lorenz, Thomas Armentano









Please reference this report as follows: 

SFNRC. 2005. An Assessment of the Interim Operational Plan. South Florida Natural Resources Center, Everglades National Park, Homestead, 

FL. Project Evaluation Report. SFNRC Technical Series 2005:2. 47 pp.
An Assessment of the Interim Operational Plan

Foreword

In September 2005, Everglades National Park issued a report to Congress on the impacts of the Interim 

Operational Plan (IOP), the water delivery plan that currently determines the quantity, timing, distribution, 

and quality of water entering the park. This technical report is equivalent to the report sent to Congress. 

It describes the effects and the significance of IOP to the hydrology and ecology of the park ecosystem, and 

analyzes the important role that this water operations plan has in defining future water operations plans for 

the Everglades. 

In February 1999, the U.S. Fish and Wildlife Service issued the Final Biological Opinion for the Modified 

Water Deliveries Project, the C-111 Project, and the Experimental Program of Water Deliveries to 

Everglades National Park. The Biological Opinion found that the hydrological impacts associated with the 

Experimental Program would likely jeopardize the Cape Sable Seaside Sparrow (Ammodramus maritimus 

mirabilis) and adversely modify its critical habitat. In response, the U.S. Army Corps of Engineers initiated 

a series of interim water management actions (IOP), which persist today and are designed to protect the 

endangered Cape Sable Seaside Sparrow until completion of the Modified Water Deliveries and C-111 

Projects. 

Since the operations associated with the IOP represented a change from prior water delivery plans, 

Congress expressed concern that the operations might pose significant threats to Everglades National Park. 

Water pollution and disruption of natural flows, as well as the links between the IOP (designed for a single 

species) and full ecosystem restoration were specific concerns, and are addressed in this report.

At the time of this writing, a new operational plan, called the Combined Structural and Operational 

Plan (CSOP) is being designed to incorporate all of the structural and operational features of the foundation 

projects for the southern portion of the south Florida ecosystem, the Modified Water Deliveries and C-111 

projects. This new plan will supersede the IOP, and should function to provide protection for the Cape Sable 

Seaside Sparrow while moving forward significantly with ecosystem restoration.

Specific recommendations regarding the completion of IOP modifications, the implementation of CSOP, 

and the implementation of the Comprehensive Everglades Restoration Plan are presented in this report. The 

Executive Summary and supporting documents containing detailed technical analyses are provided on a CD 

included with this report.

Robert Johnson

Director

South Florida Natural Resources Center

Everglades National Park

December, 2005
vi South Florida Natural Resources Center Technical Series (2005:2)

List of Abbreviations

BACI - Before-After Control Impact

BO - Biological Opinion

C&SF - Central and Southern Florida Project

CERP - Comprehensive Everglades Restoration Plan

CPUE- Catch-per-unit-effort

CSOP - Combined Structural and Operational Plan

EIS - Environmental Impact Statement

ENP - Everglades National Park

FWS - U.S. Fish and Wildlife Service

IOP - Interim Operational Plan

ISOP - Interim Structural and Operational Plan

MWD - Modified Water Deliveries Project

NESS - Northeast Shark Slough

NSM - Natural System Model

P - Phosphorus

RPA - Reasonable and Prudent Alternative

SFWMD - South Florida Water Management District

SFWMM - South Florida Water Management Model

TP - Total phosphorus

USACOE - U.S. Army Corps of Engineers

WCA - Water Conservation Area
An Assessment of the Interim Operational Plan 

Introduction

The Interim Operational Plan, or IOP, for water deliveries to 

Everglades National Park (ENP) is the most recent in a long 

series of water management plans designed to provide water 

supply to the park. The specific purpose of this operational 

plan, however, is to create more favorable hydrologic conditions within ENP for the protection of the endangered Cape 

Sable Seaside Sparrow (Ammodramus maritimus mirabilis) 

and its designated critical habitat. Control and manipulation 

of water deliveries to ENP have been practiced for approximately four decades. Throughout this long period, the often 

conflicting needs of the natural environment and the needs of 

the built environment have complicated the decision-making 

process regarding water deliveries to the park; often resulting 

in neither set of needs being fully met. IOP presents a new 

version of this challenge. It seeks to avoid jeopardizing the existence of a species endemic to a portion of the ecosystem in 

the short-term before restoration of the greater ecosystem can 

be effected in the longer-term.

The operations associated with the IOP, initiated in mid2002, are anticipated to be in place until completion of all 

structural features associated with two broader ecosystem 

restoration projects, the Modified Water Deliveries (MWD) 

and C-111 Projects. Once these projects have been completed, the operations of the combined project features will be in 

accordance with a new plan, currently under development. 

This new plan, referred to as the Combined Structural and 

Operational Plan (CSOP), is scheduled for implementation in 

2006.

This report provides a compilation of the analyses conducted in support of the congressional directive to evaluate 

the hydrologic and ecological effects of IOP. The specific objectives of the document are as follows:

1. Assess the impacts of the IOP structural and operational features on water quality in ENP.

2. Assess the impacts of the IOP structural and operational features on the preservation and restoration 

of natural ecological and hydrologic regimes.

3. Recommend any needed modifications to the IOP 

structural and operational features, including proposed plans for marsh-driven operations, based on 

hydrologic, ecological and water quality analyses. 

Marsh-driven operational criteria would reduce 

the seepage gradient between ENP and the IOP 

detention areas, which will reduce the potential for 

nutrient enrichment.

4. Recommend a monitoring program to assess the 

long-term impacts of the IOP structural and operational features.

Specific conclusions regarding the operational plan are 

provided along with recommendations for future improvements. Given the short time period for IOP data collection, 

we lack either the quantity or quality of information needed 

to draw firm conclusions for some analyses. For this reason, 

one of the more important components of this report is the 

recommendation for continued monitoring and research. It is 

the opinion of ENP that any operational plan, including IOP 

and subsequent plans for water deliveries to ENP, can only 

be properly evaluated with information of sufficient quantity, 

quality, and duration. These standards must be met in order 

to assess the impacts in a manner that provides meaningful 

recommendations for the successful management of this 

complex ecosystem.

“The Committee is concerned about recent efforts to alter significantly the Interim Operational Plan (IOP) for the protection of the Cape Sable Seaside Sparrow. The proposed new plan appears to pose significant threats to the park, in the form 

of water pollution and disruption of natural water flows, and may compromise the ability to move forward with true 

restoration. The Committee is concerned that the proposed IOP may not be operated in a way that is consistent with the 

authorized purposes of the modified water deliveries and C-111 projects. The Committee directs the Everglades National 

Park to prepare a comprehensive report concerning possible impacts of the proposed IOP on water quality in the park, 

and the preservation and restoration of natural hydrologic regimes.”

House Appropriations Committee Report 107-564, July 11, 2002

Cape Sable Seaside Sparrow with band. Photo by Lori Oberhofer, 

ENP.
 South Florida Natural Resources Center Technical Series (2005:2)

Background

Study Area / Physiographic Regions

The subtropical climate of south Florida, with its distinct wet 

and dry seasons, high rates of evapotranspiration, and extreme 

events – including floods, droughts, and hurricanes – represents a major physical driving force that shapes and sustains 

the Everglades, while creating water supply and flood control 

challenges in the agricultural and urban segments. South Florida’s climate – in combination with low topographic relief – 

delayed the development of south Florida until the Twentieth 

Century, motivated the creation of the Central and Southern 

Florida (C&SF) water management project fifty years ago, and 

continues to necessitate water management planning today.

Seasonal rainfall patterns in south Florida resemble the 

wet and dry season patterns of the humid tropics more than 

the winter and summer patterns of temperate latitudes. South 

Florida receives, on average, 53 inches of rain annually, with 75 

percent falling during the wet season months of May through 

October. Wet season rainfall follows a bimodal pattern with 

peaks during May-June and September-October. Tropical 

storms and hurricanes provide major contributions to wet 

season rainfall. Inter-annual variation in rainfall, ranging from 

37 to 106 inches, is high and unpredictable. Both flood and 

drought years occur frequently. The location of south Florida 

between temperate and subtropical latitudes, its proximity to 

the West Indies, the expansive wetland system of the greater 

Everglades, and the low levels of nutrient inputs under which 

the Everglades evolved, all combine to create a unique and 

species-rich vegetative mosaic. Today, nearly all elements of 

south Florida’s native vegetative community have been either 

altered or eliminated by development, altered hydrology, increased nutrient inputs, and spread of non-natives that have 

resulted directly or indirectly from a century of water management. This is true even in seemingly remote areas of the 

remaining Everglades found within the Water Conservation 

Areas (WCAs) and ENP. 

The problems of the Everglades extend to the mangrove 

estuary and coastal basins of Florida Bay, where the forest 

mosaics and submerged aquatic vegetation show the effects 

of diminished freshwater heads and flows upstream. The 

upland pine and hardwood hammock communities of the 

Atlantic Coastal Ridge, once interspersed with wet prairies 

and cypress domes and dissected by “finger glade” water 

courses that flowed from the Everglades to the coast, remain 

only in small and isolated patches that have been protected 

from urban development. The importance of south Florida’s 

vegetation, its unique and diverse composition, as well as its 

critical linkage to the region’s fauna, makes its current state of 

degradation a major concern and its restoration a primary objective in any water management project in this area. In-depth 

vegetative studies have focused on those wetland systems that 

are the most seriously degraded and that stand to benefit most 

from restoration efforts. Those systems include the Everglades 

peatlands, the Everglades marl prairies and Rocky Glades, and 

the mangrove estuaries and coastal basins of Florida Bay.

For purposes of this report, investigations focused on 

assessing the hydrologic, water quality, and ecological conditions within five major physiographic regions within the 

southern Everglades. These regions are WCA-3A and WCA3B, Shark Slough, Taylor Slough and the Rocky Glades, the 

Eastern Panhandle, and Florida Bay (Fig. 1). 

Water Conservation Area 3 (WCA-3A 

and WCA-3B)

Three state and federally managed WCAs serve to provide 

water to the remaining Everglades and to provide water control functions (water storage, aquifer recharge, and flood control) for the region. WCA-3, the largest of the WCAs, covers 

915 mi2. WCA-3 was historically linked to the other WCAs to 

the north and ENP, as part of the system of overland flow that 

extended from Lake Okeechobee to Florida Bay.

The Everglades peatland that remains in the WCAs consists of a mosaic of sawgrass (Cladium jamaicense) strands, 

wet prairies, sloughs, and tree islands that are oriented in the 

direction of flow patterns in the pre-drainage system. Sawgrass 

commonly forms monospecific strands throughout these areas. Cattail (Typha sp.) has replaced sawgrass in phosphorus 

(P) enriched areas, and the non-native melaleuca (Melaleuca 

quinquenervia) has invaded sawgrass in peripheral and overdrained areas. A less dense wet prairie community characterized by spikerush (Eleocharis spp.), maidencane (Panicum 

hemitomon), and other emergent macrophytes grows at 

Figure 1. Five major physiographic regions of the south Florida 

Everglades and WCA 3.
An Assessment of the Interim Operational Plan

slightly lower elevations than sawgrass. The wet prairie blends 

into a more open-water floating and aquatic community 

characterized by white water lily (Nymphaea odorata) and 

bladderwort (Utricularia spp.) in the lowest elevation water 

courses between the sawgrass ridges.

Wet prairies and sloughs support luxuriant attached algal 

communities known as periphyton, the important base of 

aquatic food webs and a diagnostic indicator of water quality 

and hydrologic conditions in the Everglades. Wet prairies and 

sloughs also provide habitat for aquatic fauna and foraging 

wading birds. Sawgrass is filling in wet prairies and sloughs 

in much of the remaining Everglades peatlands, probably as a 

result of lowered water levels. Tree islands dot the landscape 

in the form of either teardrop-shaped larger islands or round 

smaller islands. The heads of larger teardrop-shaped islands 

support swamp forest trees, such as red bay (Persea borbonia), 

in the WCAs and tropical hardwood trees, such as gumbo 

limbo (Bursera simaruba), in ENP. The tails of the islands often support willow (Salix caroliniana) and other more watertolerant species. The smaller round islands are referred to as 

battery islands, or bay heads, and support willows or swamp 

forest species. Often many hundreds of years old, tree islands 

provide essential habitat not only for their unique forest plant 

assemblages, but also for vertebrate species that depend upon 

them, particularly during high water. Tree islands have been 

destroyed or damaged both by lowered water levels that have 

resulted in tree island and underlying soil burnout, and by 

unnaturally high water levels that have killed the less watertolerant tree species. 

Shark Slough (West Shark Slough and 

Northeast Shark Slough)

Shark Slough is the main flow-way within ENP. It is immediately south and, until recently, was contiguous with the 

wetlands comprising the WCAs. The slough is a broad bedrock depression confined on the east and west by transitional 

areas of slightly higher elevations and shorter hydroperiods. 

The vegetative community in Shark Slough is similar to that 

in the WCAs but represents a more natural state. The slough 

gently arcs from northeast to southwest as a continuous 

unit composed of various plant communities well-suited to 

micro-variations within the slough. In Shark Slough, the predominant soils are comprised of Loxahatchee peat and tall 

sawgrass Everglades peat. Deeper water favors Loxahatchee 

peat formation, while shallower depths favor Everglades peat 

(the former predominates in southern Shark Slough). In areas of Northeast Shark Slough (NESS), which was formerly 

a peat-forming environment, marl forms the surface layer 

(Tropical BioIndustries 1990; Winkler et al. 1996; Loftus, U.S. 

Geological Survey, unpubl. data). Reductions of inflows from 

the north and northeast, the routing of water to the west side 

of Shark Slough, and the barrier to eastward flows by the L-67 

extension canal appear to have produced conditions leading 

to peat loss. The restoration of hydroperiods and water depths 

supporting the long-term predominance of slough vegetation 

(i.e., average annual hydroperiods of 9 months or more and 

water depths of at least 0.6 m) would promote formation of 

Loxahatchee peat throughout the main channel of the slough 

(Tropical BioIndustries 1990; Noble et al. 1996). 

Taylor Slough and the Rocky Glades

Taylor Slough is a 158-mi2 freshwater wetland located 

within ENP. The slough consists of a relatively narrow, sediment-filled channel that broadens southward and is flanked 

by areas 10-30 cm higher in elevation and is much broader 

than the slough itself. The headwaters of Taylor Slough are 

poorly defined and originate in the Rocky Glades. This slightly 

elevated area lies to the west of the Miami Rock Ridge, a low 

outcropping of oolitic limestone. Under natural conditions, 

Taylor Slough regularly channeled water drained off adjacent 

uplands and marl prairies southward to the mangrove forests 

along the north shore of Florida Bay. During wet years, additional water flowed from the much larger Shark Slough to 

the northwest across the slightly elevated Rocky Glades into 

the northern portions of the slough. The resultant sheet flow 

persisted in the early dry season, maintaining high marsh 

groundwater levels and freshwater flows to northern Florida 

Bay.

Three vascular plant species are characteristic of the 

slough and appear to have some value as indicators of hydrologic conditions. Sawgrass is the freshwater marsh species 

dominant throughout most of the Everglades including large 

portions of Taylor Slough. It occurs in marshes that range in 

hydroperiod (annual duration of surface flooding) from 2 to 9 

months. Muhly grass (Muhlenbergia filipes) is a characteristic 

species of marl prairies that annually are flooded for approximately 1 to 3 months a year, but sometimes up to 6 months 

(Olmsted et al. 1980). Spike-rush (Eleocharis cellulosa) often 

is found in wet prairies that are annually-flooded on average 

about 6 to 9 months (Gunderson and Loftus 1993; Olmsted 

and Armentano 1997). 

Muhly grass in full bloom on marl prairie in ENP. Photo by Joy 

Brunk, ENP.
 South Florida Natural Resources Center Technical Series (2005:2)

The higher elevation wetlands that flank Taylor Slough 

support the highly diverse landscape of the marl prairie and 

Rocky Glades. This mosaic of short stature sawgrass, wet 

prairie, muhly prairie, and tropical hammock tree islands 

grows on marl and exposed limestone substrate in areas 

where the marsh naturally would dry for 2 to 4 months during most years. The wet prairie community of the marl prairie 

and Rocky Glades shares some species with the wet prairies 

described in Shark Slough for Everglades peatlands, but it 

grows under drier conditions and includes the most speciesrich wetland plant assemblage in the Everglades. The wetland 

communities of the marl prairie and Rocky Glades support a 

distinct calcareous periphyton mat from which the marl substrate is formed. The muhly prairie community is particularly 

important as critical habitat for the endangered Cape Sable 

Seaside Sparrow.

The tree islands found in this landscape support a diverse 

assemblage of tropical hardwood species mixed with temperate species. Shortened annual duration of flooding in the marl 

prairie and Rocky Glades landscape presently supports a primarily terrestrial community that is flooded briefly each year 

rather than a primarily aquatic community that dries briefly 

each year. Impacts to vegetation include the loss of species 

richness in wet prairie communities, the conversion of muhly 

prairie and mixed species prairie to sawgrass, the invasion of 

woody and non-native trees and shrubs into prairie communities, and tree island burnout. 

Eastern Panhandle 

The Eastern Panhandle is a flat coastal plain that ascends 

from sea level to approximately 1 m above sea level at the base 

of the uplands. Soil substrates are mostly marls produced under freshwater conditions, or peats, or some combination of 

the two (Leighty et al. 1965). The lower half of the Eastern 

Panhandle is dissected by ephemeral creeklets, which range in 

depth from several inches in the upper reaches to several feet 

near the coast. Much of the variation in vegetation structure, 

including a profusion of tree islands, appears to be associated 

with these and smaller local undulations in topography. Water 

levels at sites in the lower panhandle respond primarily to 

fluctuations in the adjacent marine waters, while levels in the 

interior marshes are highly correlated with artificially maintained stages in the C-111 canal (see Section 2 below). 

Immediately downstream of this area is the mangrove estuary between the freshwater Everglades and Florida Bay. This 

region supports a mosaic of mangrove forests, tidal creeks, 

salt marshes, coastal lakes, tropical hardwood hammocks, and 

Florida Bay coastal basins. Red mangrove (Rhizophora mangle) 

swamp dominates the landscape along with stands of buttonwood (Conocarpus erectus), black mangrove (Avicennia germinans), and white mangrove (Laguncularia racemosa). Tidal 

creeks dissect the mangrove forests and are often bordered by 

salt marsh communities of black rush (Juncus roemarianus) 

and cord grass (Spartina spp.). Tropical hardwood hammocks 

with canopy trees such as West Indian mahogany (Swietenia 

mahogoni), Jamaica dogwood (Piscidia piscipula), and strangler fig (Ficus aurea) grow on elevated coastal embankments. 

Coastal lakes and basins support seasonally variable beds 

of submerged aquatic macrophytes that range from low-salinity to marine communities. Reduction in freshwater heads and 

flows from the Everglades, in concert with sea level rise, has 

caused community shifts in the submerged aquatic vegetation 

of the coastal lakes and basins and apparently has contributed 

to the filling in of tidal creeks. A salinity regime favoring an 

increased frequency of high salinity events and a decreased 

frequency of low salinity events in the coastal lakes and basins 

has resulted in the loss of the low-to-moderate salinity macrophyte communities that seasonal populations of migratory 

waterfowl once utilized in Florida Bay.

Florida Bay

Florida Bay is located at the southern tip of the Florida 

peninsula and covers about 850 mi2, including 700 mi2 within 

ENP. The bay is relatively shallow with average depths less than 

3 ft. The bay is bounded by ENP on the north and the Florida 

Keys on the southeast and includes over 200 small islands or 

“keys.” The shorelines of most of the keys are vegetated with 

mangroves and have interior irregularly flooded “flats” with 

calcareous algal mats. Extensive meadows of seagrass cover 

the bottom of Florida Bay and, together with the Florida Keys, 

form one of the world’s largest seagrass beds. The meadows 

are prime habitat for many fish species and for pink shrimp. 

Red mangroves (Rhizophora mangle) in south Taylor Slough. 

Photo by Frederico Mindermann, ENP.
An Assessment of the Interim Operational Plan 

Overland surface water flow across marl prairies of the 

southern Everglades, as well as creeks fed by Taylor Slough 

and the C-111 canal, provide fresh surface water inflows into 

northern Florida Bay. Surface water from the Shark Slough 

system flows into Whitewater Bay and may also move south 

around Cape Sable to western Florida Bay. 

Water discharged from Shark Slough, in the form of direct surface water contributions as well as from groundwater 

flow, also contribute significant quantities of freshwater to the 

northern portions of central Florida Bay. Water level in the 

central and eastern bay is often driven more by wind than tidal 

forces. Central Florida Bay becomes hypersaline during the 

late dry season and this physiologically stressful condition becomes more severe (approaching 70 parts per thousand) and 

widespread in times of drought or reduced freshwater input. 

Florida Bay is known as the principal inshore nursery for 

the offshore Tortugas shrimp fishery and also provides critical 

habitat for juvenile spiny lobsters, stone crabs, and many important finfish species. The bay supports numerous protected 

species including the bottle-nosed dolphin, the American 

crocodile, the West Indian manatee, and several species of sea 

turtles.

Structural Features for the Delivery of 

Water to Everglades National Park 

Water deliveries to ENP are largely determined by a series 

of water control structures constructed along the northern 

and eastern boundaries of the park. These project features 

determine the quantity, timing, and distribution of flow to 

the major drainage basins of the park: Shark Slough, Taylor 

Slough, and the Eastern Panhandle. All of the current structural components of the C&SF Project, which are used in the 

management of ENP water deliveries, are depicted in Fig. 2. A 

detailed explanation of the important features for each of the 

three major drainage basins follows.

Shark Slough. Much of the surface water delivered to the 

Shark Slough basin of ENP originates in either WCA-3A or 

WCA-3B, located immediately north of Tamiami Trail (US 

41) and ENP. The WCAs were deliberately created through 

the construction of the C&SF Project components. The most 

notable of these features are the L-67A and L-67C canals and 

associated levees, which were constructed across the natural 

surface water flow path through the area. This location of 

L-67A and C was selected to effectively isolate the western 

half of WCA-3 (WCA-3A) from the highly transmissive eastern half (WCA-3B) in order to contain these waters for water 

supply purposes for the expanding urban and agricultural 

development of Miami-Dade and Broward counties. Coupled 

with these features, four large-capacity structures (S-12 A-D) 

were constructed in the 1960s under the re-aligned Tamiami 

Trail to control discharges to the park from WCA-3A. The 

L-67 extension canal and levee was constructed during the 

extreme drought of the mid-1960s to assist in the delivery of 

water from the conservation areas to the park, but the original design purpose was to prevent the flow of surface water 

from west Shark Slough into NESS, the lands of which were in 

private ownership at the time and could not be intentionally 

flooded. The combination of the L-67A canal, L-67 extension, and the S-12 structures resulted in much of the water 

discharged to Shark Slough being confined to an area referred 

to as west Shark Slough. These same C&SF features, coupled 

with the construction of the L-29 and L-30 levees effectively 

isolated the wetlands within WCA-3B. As a result, the wetlands 

immediately south of WCA-3B in NESS were largely deprived 

of significant surface water flow upon completion of these 

features. The net result of the construction of these C&SF 

Project features and subsequent operation was to direct large 

quantities of water into west Shark Slough and relatively little 

water to NESS.

Several important downstream hydrologic monitoring 

sites within Shark Slough serve important functions in assessing the discharge of water to the basin. As will be detailed 

in subsequent sections of this report, station NP-205 is currently used to determine the dry season discharges through 

the S-12 structures for protection of the Cape Sable Seaside 

Sparrow. In a similar manner, station G-3273 and Angel’s Well 

serve important functions in determining the timing of water 

releases to NESS through structure S-333 and the protection 

of the 8.5 Square Mile Area from higher water levels in NESS 

due to these releases.

Taylor Slough. Many of the early features (Fig. 3) responsible for the delivery of water to Taylor Slough and the rest 

of south Miami-Dade County resulted from the modifications to the C&SF Project associated with the construction 

of the South Dade Conveyance System. The primary purpose 

of these features was to provide agricultural water supply to 

south Miami-Dade County and to meet the congressionallymandated minimum water deliveries to Taylor Slough. To 

achieve the latter purpose, the L-31W canal was constructed 

immediately adjacent to the park boundary, thereby providing a conduit for delivery of water from the L-31N canal to 

Panorama of Florida Bay. Bill Perry, ENP.
 South Florida Natural Resources Center Technical Series (2005:2)

pump station S-332. This pump station was constructed for 

the primary purpose of meeting the minimum quantity of water to Taylor Slough as mandated by Congress (see Minimum 

Schedule of Water Deliveries Plan below). Depending on 

the time of year and prevailing hydrologic conditions, this 

could require the transfer of water from the regional system 

down the two major South Dade Conveyance System canals 

on the east side of the park, the L-31N and C-111 canals. 

Immediately downstream of the S-332 pump station is a gravity flow spillway, S-175, which allows for the discharge of water to the southern portion of the L-31W canal that eventually 

discharges into central Taylor Slough. These operations were 

often conducted during flood events and allowed for the rapid 

routing of water from the northern portions of the basin, effectively “short-circuiting” northern Taylor Slough wetlands 

in order to remove additional water from the basin. 

Eastern Panhandle. Most of the congressionally-mandated 

minimum water deliveries to the Eastern Panhandle region of 

ENP are made through a single structure, S-18C. However, the 

actual quantity of water discharged to the Eastern Panhandle 

is dependent on the net discharge in the reach of the C-111 canal between S-18C and S-197. Since S-197 discharges directly 

into Manatee Bay, the quantity of water actually discharged to 

the Eastern Panhandle region is the amount released through 

S-18C reduced by the amount released from S-197. This net 

discharge flows from the C-111 canal through over bank flow 

along the entire reach of the southeast alignment of the C-111 

canal immediately north of the park boundary. Upon leaving 

the canal, these waters flow through the marsh and into tidal 

creeks of the mangrove communities of the Eastern Panhandle 

before ultimately discharging into Northeast Florida Bay.

Figure 2. Components of the C&SF Project that affect water deliveries to ENP and some important monitoring sites (red) for controlling 

deliveries and evaluating potential impacts.
An Assessment of the Interim Operational Plan 

Figure 3. South Dade Conveyance System (reproduced from Davis and Ogden 1994).
 South Florida Natural Resources Center Technical Series (2005:2)

Early Water Delivery Plans for 

Everglades National Park

The Minimum Schedule of Water 

Deliveries Plan (1970-1983)

In response to the drought conditions of the 1960s, Congress 

authorized a minimum allocation of water from the C&SF 

Project for Shark Slough, as well as Taylor Slough and the 

Eastern Panhandle drainage basins. This management approach – often referred to as the minimum water delivery 

schedule – was active from 1970-1983. The minimum allocations were based on average monthly flow volumes from 

1939-1960 that existed prior to the construction of the WCAs. 

However, these minimum volumes were routinely exceeded 

due to regulatory discharges designed to ensure that water 

levels in the upstream reservoirs were maintained within the 

range necessary to meet water supply and flood control requirements. Large regulatory water releases, in great excess of 

the prescribed minimum resulted and caused rapid changes 

in hydrologic conditions within the downstream park and disastrous ecological consequences, including the flooding of 

eggs within alligator nests and the abandonment of nestlings 

within wading bird colonies. It should be noted that all of 

the releases, including the large regulatory discharges, from 

WCA-3A during this period were in accordance with the prescription for water deliveries to the park in effect during this 

time. With the construction of the South Dade Conveyance 

System, the methods of water delivery to ENP evolved into 

an increasingly more complex set of rules that also served to 

highlight the increasingly divergent needs of the natural and 

built environments.

The Experimental Program of Water 

Deliveries to Everglades National Park 

(1984 -1999)

Since many of the problems associated with the management 

of water deliveries to ENP reflected the fact that the jurisdictional boundaries of the park were not coincident with the 

historic drainage patterns in south Florida, Congress authorized the establishment of an experimental water delivery 

program. Initiated in the early 1980s, the goal of the experimental program was to modify the schedule for delivery of 

water to ENP and conduct experimental deliveries for the 

purpose of determining an improved schedule of water deliveries. Much of the ecological and hydrologic information that 

existed prior to the program indicated a need to reestablish 

historic flow patterns within the entire Shark Slough drainage 

basin. However, much of the historic basin area (referred to 

as NESS) was located outside and east of the park. This area 

includes lands having undergone agricultural and residential 

development. In order to reestablish flows within this portion 

of Shark Slough, several compensatory measures were implemented that allowed for the lowering of the canals east of, 

and adjacent to, ENP in order to introduce additional water 

into NESS. These changes in water management had consequences of their own. The lowering of canals, particularly in 

the vicinity of Taylor Slough and the Rocky Glades, is thought 

to have contributed to an alteration of the landscape mosaic 

through an associated expansion of non-native vegetation 

and increased fire frequency within this area. Due to extremely porous underlying limestone, lowering water levels in the 

canals adjacent to ENP also lowers water levels throughout 

the region and may contribute to decreased discharges to the 

downstream estuary and subsequent increases in Florida Bay 

salinity.

Throughout the Experimental Program, the U.S. Fish and 

Wildlife Service (FWS) consulted with the U.S. Army Corps of 

Engineers (USACOE) on the implementation of each phase of 

the program pursuant to the requirements of the Endangered 

Species Act. One of the primary reasons for the consultation 

was concern for the endangered Cape Sable Seaside Sparrow. 

Much of the FWS concern emanated from actual census data 

collected by ENP from the period 1981 to the present. Species 

monitoring results indicate that several sub-populations exist, whose distribution, size, and importance have changed 

dramatically with time. Bass and Kushlan (1982) described 

sub-population A in Shark Slough and sub-population B in 

Taylor Slough. Studies that followed identified a total of six 

sub-populations (Curnutt and Pimm 1993). These corresponded to the original A and B sub-populations described 

in 1982 and four others (C through F). Pimm (1998) further 

suggested that three breeding sub-populations are needed 

to sustain the survival of the endemic species. The range for 

these sub-populations is depicted in Fig. 4.

Based on its review of census data, the FWS became concerned about the impacts of the Experimental Program on the 

continued existence of the sparrow and its designated critical 

habitat. The population census data from up to, and including, 1995 and other available scientific information led the 

FWS to conclude in its Biological Opinion (BO) of October 

27, 1995 that Test Iteration 7 was likely to jeopardize the continued existence of the sparrow. The BO also instructed the 

USACOE to develop a Remedial Action Plan as part of the 

Reasonable and Prudent Alternative (RPA) to avoid jeopardy. 

Due to disagreements on the content of the Remedial Action 

Plan, consultation was reinitiated in November 1997.
An Assessment of the Interim Operational Plan

Figure 4. Cape Sable Seaside Sparrow sub-populations A through F.
10 South Florida Natural Resources Center Technical Series (2005:2)

Interim Water Delivery Plans 

In February 1999, the FWS issued the Final BO for the MWD 

Project, the C-111 Project, and the Experimental Program of 

water deliveries to ENP. The FWS found that the hydrologic 

impacts associated with the Experimental Program, if continued, would likely jeopardize the continued existence of the 

Cape Sable Seaside Sparrow and adversely modify its critical 

habitat. In response to a FWS concern of imminent peril in 

December 1999, the USACOE initiated two plans designated 

Interim Structural and Operational Plan (ISOP) 2000 and 

2001, followed by the Interim Operational Plan (IOP), designed to protect the endangered Cape Sable Seaside Sparrow 

until completion of the MWD and C-111 projects, which have 

been delayed for a variety of reasons.

Both ISOP and IOP were formulated to address specifically 

the concerns for the Cape Sable Seaside Sparrow as stated in 

the original and subsequent versions of the FWS BO. The intended purpose of these plans was to implement water management actions consistent with the specific provisions of the 

RPA to avoid jeopardy to the Cape Sable Seaside Sparrow and 

not destroy or adversely modify designated critical habitat.

The Interim Structural and Operational 

Plan (ISOP)

ISOP was developed in response to concerns expressed by the 

USACOE for the potential to aggravate flooding in the east 

Everglades, particularly the 8.5 Square Mile Area, should the 

USACOE be required to introduce additional water into the 

NESS according to the 1999 RPA. To resolve the potential conflicts between the FWS RPA and these concerns, numerous 

meetings were held in 1999 to discuss RPA implementation. 

In December 1999, the President’s Council on Environmental Quality assembled representatives from the Department of 

the Interior and the USACOE to facilitate the negotiations on 

the elements of a water delivery plan agreeable to the participating agencies. This resulted in the development of the first 

generation of the Interim Structural and Operational Plan, or 

ISOP 2000. This plan was in effect from December 1999 until 

January 2001 when the plan was replaced with ISOP 2001 that 

was in effect from January 2001 until July 2002. The ISOP 2001 

plan supported the same objectives as ISOP 2000, but attempted to resolve some of the shortcomings of ISOP 2000. The major operational features of the ISOP are depicted in Fig. 5.

Figure. 5. Depiction of the structural and operational components of the ISOP and IOP. The S-332B-C connector detention area has yet 

to be completed. Problems with the acquisition of the land between the north and south segments prevent complete connection of 

these two detention areas.
An Assessment of the Interim Operational Plan 11

The most fundamental change that occurred in the implementation of ISOP was the institution of limitations on the 

quantity of water discharged through the S-12 structures. This 

action allowed for better control of water level conditions in 

the vicinity of sub-population A of the Cape Sable Seaside 

Sparrow and, thereby, created hydrologic conditions more 

favorable to sparrow nesting success. In addition, ISOP also 

allowed for the routing of water from WCA-3A through structure S-333 and S-334 and, subsequently, into south MiamiDade County through G-211 and S-331 to improve conditions 

for sub-populations C, D and F. To assist in the management 

of potentially higher water levels in WCA-3A, the ISOP operations also specified an additional management zone for 

the regulation of water levels within the conservation area. 

Referred to as Zone E1, this regulatory zone allowed for the 

lowering of water levels within WCA-3A to levels 0.5 ft lower 

than the regulations prior to the implementation of ISOP. 

Water from WCA-3A was then transferred to south MiamiDade County through S-333 and S-334 into the L-31N canal. 

These waters were then subsequently discharged through a 

new pump station (S-332B) into a newly constructed detention area of the C-111 Project. This detention area is located 

immediately east of ENP and in the vicinity of sub-population 

F of the Cape Sable Seaside Sparrow. The S-332B detention 

area also has a weir located on the west side for discharge of 

surface water under emergency conditions into ENP, including the sparrow habitat.

The net effect of these ISOP structural and operational 

modifications was to move water away from western Shark 

Slough, which was too wet for sparrow nesting, to regions 

of the Rocky Glades and Taylor Slough on the east side of 

ENP, which were too dry for maintenance of sparrow habitat. 

Collectively, these modifications would meet conditions of 

the RPA, according to the USACOE.

Detention area east of L31W canal and levee. Photo by William Perry, ENP. 

S-332D pump station in the C-111 Project area. Photo 

by Kevin Kotun, ENP.
12 South Florida Natural Resources Center Technical Series (2005:2)

The ISOP was revised in the March 2000 Environmental 

Assessment (USACOE 2000) to include flood control operations and pre-storm operations. The ISOP operations in the 

March 2000 Environmental Assessment “seek to lower canal 

levels during the wet season and allow for higher water levels 

during the dry season. These operations also take into account real-time field conditions as measured in groundwater 

wells and forecasted storm events” to lower water levels in the 

L-31N and C-111 canals in order to improve flood protection 

capability in southern Miami-Dade County. The increased 

flood protection capability is made possible by pumping additional water from the canals into the new detention area on 

the east side of ENP. The target water levels in the C-111 canal 

were adjusted downward to accommodate the higher levels 

of flood protection desired as well as the need to effect operations in advance of a major storm event.

The Interim Operational Plan (IOP)

The ISOP was discussed and adjusted throughout much of 

2001 until the USACOE issued the June 2002 Final Environmental Impact Statement for IOP “to create favorable hydroperiods in sparrow habitat in ENP while providing flood 

protection capability for developed lands east of the L-31N 

Canal”. The IOP makes use of the ISOP features as well as additional structural features from both the MWD and C-111 

projects and is intended to be only an interim plan that will be 

replaced with an operational plan for these two projects upon 

their completion.

Monitoring of conditions within the sparrow sub-populations of ENP continued and resulted in additional refinements 

to the plan of operations for the Cape Sable Seaside Sparrow. 

Through an interagency collaborative process, the following 

structural and operational components were identified as 

part of IOP (IOP-Alt 7R), in addition to the continued use of 

the features constructed as part of ISOP:

Degradation of the lower four miles of the L-67 extension canal and levee.

Raising of the western levee of the S-332B detention area 

to reduce the frequency of surface water flows from the 

detention cell into ENP. This feature is predicated on 

the completion of an additional detention area (S-332B 

north) adjacent to the original ISOP-implemented S332B west detention area.

Construction of the temporary S-332C 500 cubic ft/

second (cfs) pump station associated with the C-111 

Project.

Construction of four new reservoirs within the C-111 

Project area:

S-332B north detention area to augment storage capability of the existing ISOP S-332B west detention 

area.

S-332C detention area

Connector detention area between the S-332B and 

S-332C detention areas.

S-332D detention area including a high head cell located immediately west of the S-332D pump station 

to distribute the water discharged from the pump 

along the full width of the northern portion of this 

detention area

Construction of a temporary S-356 pump station to discharge from the L-31N canal into the L-29 canal

A marsh-driven operational plan, to be implemented 

through a collaborative interagency process, to address 

concerns expressed by ENP regarding potential impacts 

of direct surface water discharges as well as high water 

levels in the detention areas.

At the time of this writing, four of the above-mentioned 

features of the IOP remain unimplemented: (1) the S-332B 

detention area weir remains at the original crest elevation; (2) 

ENP lands have not been exchanged for similar lands from 

the South Florida Water Management District (SFWMD) to 

complete the direct north-south S-332B and C connector; (3) 

S-356 operations have not been adopted; and (4) the marshdriven operations also remain unimplemented. However, the 

land exchange legislation is pending in Congress and proposals for the S-356 and marsh-driven operations are undergoing 

interagency technical review.

Based on USACOE’s initial assessments of IOP-Alt 7R, 

the USACOE requested that the FWS amend the Final BO of 

1999 to include IOP-Alt 7R as a second RPA to address jeopardy to the Cape Sable Seaside Sparrow. In March 2002, the 

FWS amended the BO stating, “the Service has determined 

that IOP-Alt 7R represents an additional RPA for water-management actions to avoid jeopardy to the Cape Sable Seaside 

Sparrow and would not destroy or adversely modify designated critical habitat.” The USACOE subsequently released the 

Final Environmental Impact Statement in May 2002 identifying IOP-Alt 7R as the recommended plan. The structural and 

operational features of both the ISOP and IOP are depicted 

in Fig. 5.



















Degradation of the L-67 extension canal and levee. Photo by 

Elizabeth Crisfield, ENP.
An Assessment of the Interim Operational Plan 13

Toward Restoration of 

Everglades National Park: 

Implementation of the Modified 

Water Deliveries and C-111

Projects

The Modified Water Deliveries Project

While some successes were realized through iterations of the 

experimental program, it soon became apparent that only 

limited changes to the water deliveries to ENP were possible 

when much of the Shark Slough basin was outside the management jurisdiction of the National Park Service. This limitation was acknowledged in 1989 when Congress passed the 

ENP Protection and Expansion Act. The purpose of the Act 

was twofold: (1) incorporate the 109,000 acres of NESS into 

ENP and (2) implement structural modifications to the C&SF 

Project to restore the natural hydrologic conditions within the 

park. Congress also authorized the use of information from 

the experimental program as the basis for the structural and 

operational features of what would become the MWD Project.

The C-111 Project 

In 1994, Congress authorized modifications to the C&SF 

Project features within the C-111 basin (the C-111 Project) to 

address problems associated with water deliveries on the east 

side of the park. The primary purpose of the C-111 Project, 

according to the 1994 General Reevaluation Report, is restoration of the ecosystem in Taylor Slough and the Eastern Panhandle of ENP while maintaining the level of flood protection 

existing prior to construction of the features associated with 

the C-111 Project recommended plan. The concept was to 

build features in the C-111 canal and adjacent areas to contain the seepage losses from ENP in a manner that would also 

maintain the level of flood protection prior to the proposed 

modifications.

Restoration Objectives of the Modified 

Water Deliveries and C-111 Projects

Initial phases of the restoration of ENP will require the implementation of components from both the MWD and C111 Projects. The MWD components are designed to restore 

the Shark Slough basin, while the C-111 Project features are 

directed towards restoration of the Taylor Slough, Rocky 

Glades, and Eastern Panhandle regions of ENP. Unfortunately, the implementation of both of these projects has been delayed due to problems of flood control and flood mitigation, 

and land acquisition, as well as design refinements needed to 

provide the level of performance to produce the conditions 

that will result in restoration. The current implementation 

schedules for these projects will not have them both operational until late 2007. Until completion, operations must continue in a manner that is consistent with the restoration intent 

of these projects while also meeting other project purposes 

and legal mandates.

Significant restoration is anticipated through the implementation of the MWD and C-111 Projects. The authorized restoration objectives for these projects include the 

following:

Restoration Objective 1. Improve the timing of water deliveries to ENP, and change the schedule of water deliveries 

so that it fluctuates in consonance with local meteorological 

conditions, including providing for long-term and annual 

variation in hydrologic conditions in the Everglades.

Restoration Objective 2. Improve the location of water 

deliveries to ENP, and restore WCA 3B and Northeast Shark 

Slough as a functioning component of the Everglades hydrologic system.

Restoration Objective 3. Improve the quantities of water deliveries to ENP, and adjust the volumes of water discharged to 

ENP to minimize the effects of too much or too little water.

Restoration Objective 4. Restore historic hydrologic conditions in Taylor Slough, the Rocky Glades, and the Eastern 

Panhandle of ENP.

Restoration Objective 5. Protect the natural values associated with the Everglades National Park.

Restoration Objective 6. Eliminate the damaging freshwater flows to Manatee Bay/Barnes Sound and increase flows to 

northeast Florida Bay from the lower C-111.

Restoration Objective 7. Ensure that project waters delivered to ENP, an Outstanding Florida Water body, meet all 

applicable water quality criteria.

While it is not the expectation of the park to meet these 

objectives through the implementation of the ISOP or IOP, it 

is expected that the operations be consistent and compatible 

with the MWD and C-111 Project objectives. For this reason, 

each of the assessments that follow will evaluate the ISOP/IOP 

operations based on certain stated expectations. The ability 

of the ISOP/IOP operations to meet these expectations serves 

as the basis for the conclusions and recommendations. 

Shark River Slough hydrologic monitoring station. Photo by 

William Perry, ENP.
14 South Florida Natural Resources Center Technical Series (2005:2)

An Assessment of the Interim 

Plans

Biological resources are sensitive to changes in the physical 

environments upon which they depend. Assessing biological change, however, is not easy, in part because the physical 

conditions governing biological processes are often complex 

and poorly understood. Physical modeling approaches are 

not applicable in such cases. Alternatively, statistical methods 

are often used to assess change. A Before-After and Control 

and Impact (BACI) approach is one such statistical method 

for assessing change that has proven to be very powerful in 

detecting even small changes (Stewart-Oaten et al. 1986). At 

the beginning of the assessment of ISOP/IOP impacts, hydrologists and biologists working on ENP research met to 

discuss the approach to be used in evaluating IOP impacts. 

This group determined the parameters to be analyzed and selected the BACI approach as the primary analytic method to 

be employed in the IOP assessment. Therefore, the BACI approach was applied to hydrologic and biologic data whenever 

possible. Some water quality and biological data that were not 

readily fitted to the BACI approach due to limited duration 

and frequency of sampling were analyzed by alternative statistical approaches. The period of the BACI analysis extends 

from 1995 to 2002.

Physical Environment

The Department of the Interior has been monitoring the 

physical environment within and adjacent to lands now comprising ENP since before the park was authorized. The collection of discharge data under the Tamiami Trail, along the 

northern boundary of the park, was initiated in 1939 and 

continues through a collaborative effort of the ENP, the U.S. 

Geological Survey, the USACOE, and the SFWMD. Since the 

initiation of this monitoring, hundreds of additional sites have 

been added to the network for the collection of hydrologic, 

climatological, and water quality parameters. This information has proven vital to understanding the natural resource requirements of the park as well as to establishing the important 

characteristics needed for its restoration. The assessments of 

the ISOP/IOP that follow were a result of analyses of data from 

this extensive network. The purpose of these assessments was 

to provide a summary of the consequences of the alterations 

in the management of discharges to ENP as well as to provide 

complementary information needed to understand how these 

changes might affect the biological resources of the park. 

Hydrology

ISOP and IOP will have their most direct and observable 

effects in the hydrology. The purpose of ISOP and IOP was 

to use the C&SF Project structures to manipulate hydrologic 

responses of groundwater and surface water to rainfall. This is 

a summary of the major findings, grouped by location.

Rainfall. The study period includes the years 1995 to 

2002, where 1996 to 1999 define the Test 7 years while 2000 

to 2002 define the ISOP/IOP years. The ENP basin average 

rainfalls were computed by historical rainfalls measured from 

25 gauging stations in and around the park. The annual average rainfall during the study period is about 3% higher than 

the long-term average, which is about 56 inches, mainly due 

to higher wet season totals. The ISOP/IOP period is close to 

the long-term annual ENP average, but rainfall differs by approximately 8 inches annually and by about 6 inches during 

the dry period. During the study’s time period, the rainfall totals between ENP and WCA-3 differed, principally in that the 

wet season totals in WCA-3 were lower than the ENP totals. 

The most significant variation occurred during 2001 when the 

difference was 11 inches.

Water Budget Synopsis. Canal water budgets were analyzed to provide insights concerning the response of the 

managed system to the operational rules and rainfall events. 

These water budgets were constructed based on controlling 

flow at major hydrologic structures in the form of total annual 

flow volumes. The water budgets are summarized as follows. 

First, there are large changes in the magnitude of the S-12 

discharges, as the ISOP/IOP flows appear to be considerably 

reduced. Another point of interest is S-335, which is the outlet 

of L-30, the canal along the eastern side of WCA-3B and the 

western side of the Pennsuco wetlands. Flows appear to increase during ISOP/IOP when compared to prior years, even 

as rainfall decreases. Similarly, outflow at S-338 appears to 

increase significantly in the above average ISOP/IOP rainfall 

years when compared to prior operations. S-331 and G-211 

flow volumes are similar in both periods, but do exhibit interannual variability. The Test 7 and ISOP/IOP canal water budgets also show a marked difference in the operations around 

S-332D. S-332 use is minimal since ISOP implementation, 

and S-176 flows were also significantly reduced. This change 

of operations led to close scrutiny of marsh impacts in upper 

Taylor Slough. Although operations affecting upper Taylor 

Slough appear to be different after ISOP implementation, the 

structures in C-111 do not appear significantly different in 

terms of annual flow volumes. S-177 and S-18C flows seem 

very similar. This was not entirely desirable, as the hope was 

that modification of S-332D operations would result in more 

flow down lower Taylor Slough. This suggests that C-111 is 

capturing a significant amount of S-332D outflow as well as 

water from Taylor Slough. 

Water Conservation Area 3A 

According to the Environmental Impact Statement (EIS) 

(USACOE 2002), WCA 3A was predicted to increase in 

depth. This conclusion was a major factor in the “Finding of 

Significant Impact” in that EIS. This increase was expected 

because of the periodic closure of the S-12 structures, which 

release water from WCA 3A into ENP. 
An Assessment of the Interim Operational Plan 15

The analysis of hydrologic data for Conservation Area 

3A seems to indicate that the area was likely lower under 

ISOP/IOP than it would have been under Experimental 

Water Deliveries operations. The addition of Zone E1 appears to have over-compensated for the partial closures of the 

S-12 structures. Moreover, aggressive releases of flood water 

from WCA 3A during the wet season into the South Dade 

Conveyance System also had the effect of keeping water levels 

lower than anticipated. 

Water Conservation Area 3B

There is no issue related to the Cape Sable Seaside 

Sparrow directly tied to WCA 3B. For this reason, the impacts 

from ISOP/IOP were expected to be small, although the EIS 

did anticipate the possibility of higher water levels related to 

increased seepage from WCA 3A. 

An analysis of the available hydrologic record for WCA 3B 

indicates that operations associated with ISOP/IOP resulted 

in lower water levels in WCA3B. Gage 3BSE, located in the 

southeast corner of WCA3B showed the greatest reduction in 

water levels. This appears to be related to a change in the operational philosophy for S-335 and S-338, and not an explicit 

and intentional element of ISOP/IOP. The S-335 operations 

have resulted in undesirable and unintended consequences 

related to the ability of the C&SF Project to provide dry season water supply.

Central and Western Shark Slough

The primary objective in implementing the ISOP and IOP 

was to reduce damaging high water levels in the Cape Sable 

Seaside Sparrow habitat along the western flank of Shark 

Slough. The purpose was not only to provide an improved opportunity for nesting, which is directly related to water levels 

during the breeding season, but also to allow the habitat to 

recover from prolonged unnatural flooding. 

According to an analysis of the ISOP/IOP operations, the 

plan achieved the fundamental goal of reducing water levels in 

western Shark Slough and Cape Sable Seaside Sparrow habitat. However, because this was accomplished by reducing the 

total volume of water crossing Tamiami Trail, the result was 

also significant reductions in water levels and hydroperiods in 

central and lower Shark Slough. 

Northeast Shark Slough

In a restored, functional Everglades, NESS would receive 

the major portion of flow, would experience peak water 

depths exceeding 2 ft, and would dry out only during severe 

droughts. Although the RPA called for diverting water from 

western Shark Slough into NESS, this was deemed impractical under ISOP and IOP, primarily because of the potential 

effects on the 8.5 Square Mile Area. The expectation in ISOP 

was that NESS would experience no significant changes, and 

that, with the removal of the lower end of L-67 extension, 

there was a possibility of some improvements in water levels 

and hydroperiods in IOP.

In examining the available hydrologic data, there is virtually no change in NESS attributed to ISOP/IOP operations. As 

was the case prior to ISOP/IOP, NESS receives very little of 

the wet season water deliveries. Lower water levels recorded 

during the ISOP/IOP period were likely related to rainfall. The 

removal of the lower four miles of the L-67 Ext. canal and levee was expected to provide some benefit to NESS; however, 

the existing hydrologic monitoring network is inadequate to 

determine the effects of the canal/levee removal. The conclusion is that ISOP/IOP impacts were consistent with the expectation (i.e., that ISOP/ IOP would not provide the needed 

benefits to NESS). Implementation of the MWD project will 

be needed to realize any benefits in this important region.

The Rocky Glades

The major difference between ISOP and IOP was the 

construction of additional buffer reservoirs between L-31N 

and ENP. The expectation was that these reservoirs would 

compensate for the reduction in L-31N water levels, which 

had resulted in over-drainage and a general decline in habitat 

quality in the Rocky Glades. These reservoirs would serve as 

a hydraulic barrier, decreasing seepage losses from ENP. They 

also would improve water levels and hydroperiods, and make 

the response of the wetlands to rainfall more natural. 

The analysis of the effects of ISOP/IOP in the Rocky 

Glades proved very difficult. The network was not adequate 

to get a complete picture of the response. Moreover, the datasmoothing required to look at general trends did not allow for 

a quantitative investigation of the effects of pre-storm operations. However, the network that was in place was situated to 

pick up the most likely expected benefits. 

The analysis of the available information showed that 

ISOP/IOP operations did result in a slight increase in water 

depths and a small reduction in seepage losses. It does not apS-12 control structure on the Tamiami Trail. This is one of four 

structures that deliver water to western Shark Slough, ENP. 

Photo by William Perry, ENP.
16 South Florida Natural Resources Center Technical Series (2005:2)

pear that the significantly decreased water levels in the lower 

L-31N canal translated into significant reductions in marsh 

water levels, as had been the result when canal stages were 

lowered in the Experimental Water Deliveries Program. That 

is, the ISOP/IOP structures probably were sufficient to offset 

reductions in L-31N canal stages, but not sufficient to result 

in significantly improved water depths and hydroperiods, as 

anticipated in IOP. 

Upper Taylor Slough

In this report, upper Taylor Slough is considered to be the 

region just west of the Frog Pond, where the C&SF Project 

has historically delivered water to Taylor Slough. Water deliveries to Taylor Slough underwent significant changes from 

Test 7 Phase I to ISOP, and again from ISOP to IOP. In IOP, 

the USACOE constructed significant engineering works in 

the Frog Pond to improve the water deliveries from the new 

pump station, S-332D. The expectation for IOP was that 

volume, timing, and distribution of inflows to Taylor Slough 

would become more natural.

Results of IOP operations in upper Taylor Slough were 

unique in comparison to the other regions examined in this 

report. A prior analysis of the ISOP operations indicated that 

the ISOP resulted in wholly unnatural and very undesirable 

impacts in upper Taylor Slough. However, IOP appears to have 

substantially corrected those problems. The new operational 

scheme and structures represent a significant improvement. 

More natural wet season recession patterns were observed 

including a greater spatial extent of surface water during the 

wet season and a possible decrease in seepage losses. All these 

suggest that IOP resulted in more natural timing and distribution of inflows to upper Taylor Slough. 

Lower Taylor Slough and the Eastern Panhandle

The construction of S-332D made it possible to divert 

flood discharges drained from the Rocky Glades back into 

Taylor Slough rather than passing those flows down C-111 

and into the Eastern Panhandle of ENP. In both the ISOP and 

IOP, operations were designed to do exactly this. The expectation was that by putting the flows into Taylor Slough, they 

would flow down Taylor Slough and enter Florida Bay much 

farther west than if they were routed down C-111. This also 

would reduce the frequency of direct freshwater discharges 

into Barnes Sound. 

From the analysis of the hydrologic information, it is clear 

that direct surface water discharges from L-31N into C-111 

have been significantly reduced. However, this reduction in 

surface water discharges has been almost exactly offset by an 

increase in groundwater seepage into C-111. No significant 

improvement in flow characteristics into lower C-111 and the 

Eastern Panhandle was found. In addition, there was no strong 

evidence of improvements in flow into lower Taylor Slough. 

Apparently, the significant benefits observed in upper Taylor 

Slough do not propagate very far downstream. The most likely 

obstacles are the lower L-31W and Aerojet canals that capture 

groundwater and surface water and rapidly convey it back towards C-111. Moreover, low wet season operational levels in 

C-111 result in strong gradients and large seepage rates from 

Taylor Slough back toward the C-111 canal. 

Water Quality

Water quality is a major concern in the restoration of the 

Everglades. Direct impacts (e.g., nutrient loading and the 

introduction of contaminants, such as heavy metals and pesticide), as well as indirect impacts, such as elevated salinity associated with the decreases in freshwater flow, all contribute 

to factors affecting the successful restoration of the ecosystem. Evaluation of the quality of water requires an examination of the physical properties and chemical constituents of 

both surface and groundwater. The water quality at any given 

location depends on many interrelated factors. One of the 

most important factors affecting water quality in the Greater 

Everglades is the water source. The delivery and routing of 

water through the canals, pumps, and other structures of the 

C&SF Project to ENP is controlled and regulated. With the 

changes in the water deliveries imposed by the ISOP/IOP, 

Congress specifically expressed concern for how the altered 

water delivery schemes might impact the quality of water delivered to ENP.

Historically, the macronutrient, phosphorus (P) is the 

water quality variable that has drawn the most attention. 

This nutrient limits Everglades ecosystem productivity and 

biomass accumulation. The Everglades ecosystem has developed under extremely low levels of P. Excessive levels of P 

cause anthropogenic eutrophication that is characterized by 

increased productivity, reduced dissolved oxygen, changes in 

species composition, and reduced biodiversity. Stormwater 

discharges from Everglades Agriculture Area and urban areas have elevated levels of total phosphorus (TP), and when 

the stormwater is discharged into the Everglades, it impacts 

the Everglades ecosystems. The severity and extent of these 

impacts on A.R.M. Loxahatchee National Wildlife Refuge 

and ENP caused the federal government to sue the State of 

Florida in 1988 for not enforcing its water quality laws. The 

lawsuit was settled in 1991 and the resulting Consent Decree 

established TP interim and long-term limits for inflows to the 

refuge and park. Numerous sampling sites were established 

throughout south Florida and the Everglades to monitor TP in 

rainfall, in the marshes, and at water management structures 

(Fig. 6). 

ENP expectations of water quality changes during ISOP/

IOP include decreases in TP concentrations at the Shark 

Slough inflow structures (during ISOP/IOP, four Stormwater 

Treatment Areas located between the Everglades Agricultural 

Area and the WCAs began functioning), slight increases of 

total phosphorus (TP) concentrations at the L-31N/C-111 

structures (historically Shark Slough flows have had higher 

TP concentrations than L-31N/C-111 flows), uptake of TP in 
An Assessment of the Interim Operational Plan 17

soils of detention areas, and no increases of TP concentrations 

in surface water, groundwater, and soils of ENP (detention areas remove excess TP before discharging into ENP marshes).

Because of possible ecological impacts, changes in TP 

loads and concentrations at structures and sites located in 

and around ENP following implementation of ISOP/IOP 

have been evaluated. A relatively simple statistical procedure 

was applied to identify monitoring sites where changes in 

average flows, concentrations, or loads were likely to have 

occurred following ISOP/IOP implementation in late 1999. 

The procedure accounted for background variations associated with rainfall. More detailed analyses and interpretations 

of the results were performed on a regional basis (WCA-3A, 

Shark Slough, and Taylor Slough/Eastern Panhandle) to 

further describe the changes and assess the causal linkages to 

the ISOP/IOP, as opposed to other anthropogenic or natural 

factors. The performance of the C-111 detention areas is evaluated in terms of TP removal using both the actual data and 

the Dynamic Model of Stormwater Treatment Areas (Walker 

and Kadlec 2002). Monitoring of TP concentrations in soil 

and surface water in ENP marshes is reported.

Shifts in mean flow, TP concentration, or TP load, have been 

identified by comparing yearly data before and after ISOP/IOP 

using graphical and statistical techniques. Identifying water 

quality changes specifically related to ISOP/IOP is difficult in 

the presence of background variability attributed to a variety 

of natural and anthropogenic factors, as well as to sampling 

variability. Background variance in structure flows and TP 

loads is correlated with basin rainfall at most structures. A 

regression model was used as the screening procedure to 

test for shifts in the long-term mean between the two time 

periods in the presence of natural variations associated with 

rainfall and other random factors. Table 1 summarizes the 

screening results of this analysis in the three main geographic 

areas and Fig. 7 shows the changes in TP concentration (PreISOP/IOP- 1994 to 1999 vs. ISOP/IOP – 2000 to 2003 in the 

three geographic areas). The detailed technical analyses can 

be found in a series of supporting documents listed in Section 

VII of this report (also available at http://www.sfnrc.ever.nps.

gov/iop_data/).

WCA-3A 

This analysis (see Table 1 and Fig. 7) identified two significant changes in WCA-3A inflows during the ISOP/IOP time 

period. First, there were increases in TP concentrations and 

loads discharged from S-140. S-140 is a SFWMD pump station that discharges partially-treated stormwater (Stormwater 

Treatment Area-5) from the agriculture-dominated basins 

southwest of Lake Okeechobee. Flows from the L-28 canal 

and the western L-28 basin are pumped east into WCA-3A 

at S-140. Apparent increasing trends over the 1994-2003 period are not explained by rainfall or flow. It is unlikely that 

the trends were related to ISOP/IOP. They may be related to 

changes in the drainage basin and/or diversion of L-28 canal 

inflows to the northwest corner of WCA-3A. Second, there 

were increases in outflows, TP concentrations, and loads from 

S-9. S-9 is a SFWMD pump station that discharges untreated 

stormwater from urbanized central Broward County. Runoff 

from the C-11 West basin is pumped into eastern WCA-3A at 

S-9. A portion of the flow is recycled seepage from adjacent 

WCA-3A and WCA-3B. Apparent increasing trends in TP 

loads and concentrations are not explained by rainfall or flow, 

but are probably related to urban development in the western 

C-11 basin.

While apparently unrelated to ISOP/IOP, increases in TP 

load to the central portion of WCA-3A via S-140 (78%) and 

S-9 (71%) are of potential water quality concern because 

these inflows are closest to ENP inflow structures. The lower 

F WCA-3A stages required by ISOP/IOP reduce overland flow igure 6. Water quality monitoring sites.
18 South Florida Natural Resources Center Technical Series (2005:2)

of S-140 and S-9 discharges into the marshes of WCA-3A that 

would remove TP from the water column. This often results 

in direct discharge of S-140 and S-9 flows into ENP. The 

percentage of the total load to WCA-3A attributed to these 

sources increased from 9% in the pre-ISOP/IOP years to 21% 

in the ISOP/IOP years. 

Shark Slough 

This analysis revealed two significant changes due to ISOP/

IOP at Shark Slough inflow structures. First, the combined 

flow-weighted mean concentration at the S-12s and S-333 

increased by 1.9 ppb or 22%. There are numerous potential 

Table 1. Results of the Screening Analysis of flow, TP load and mean TP concentration at inflow structures (see Fig. 6, Monitoring sites) 

by region. pre-ISOP/IOP = 1994-1999 mean. Increase = ISOP/IOP (2000-2003) mean – pre-IOP mean. % Incr = Increase as percent of preISOP/IOP mean. p = significance level, two-tailed test (light shading/* p < 0.15 (significant), dark shading/ ** p < 0.05 (very significant)). 

Values adjusted to average rainfall.

Structure pre-IOP Increase % Incr p pre-IOP Increase % Incr p pre-IOP Increase % Incr p

WCA-3A Inflows

S150 52 -11 -23% 0.48 3467 -588 -17% 0.63 56.6 -1.3 -2% 0.90

S140 124 12 9% 0.50 6034 4730 78% 0.02 ** 42.5 28.1 66% 0.06 *

G155 102 -50 -61% 0.03 ** 22696 -9085 -40% 0.07 * 183.9 14.1 8% 0.77

S190 80 11 13% 0.57 11647 217 2% 0.96 112.7 -3.6 -3% 0.86

S8+G404 347 -23 -7% 0.69 39795 -1086 -3% 0.91 91.9 -3.5 -4% 0.83

S11X 574 -130 -25% 0.12 * 18443 -5784 -31% 0.02 ** 27.9 -6.0 -22% 0.21

S9 235 32 13% 0.11 * 4091 2885 71% 0.01 ** 14.3 7.4 52% 0.03 **

WCA-3A IN 1512 -160 -11% 0.20 106173 -8712 -8% 0.60 56.3 -0.3 -1% 0.97

ENP Shark River Slough

S12A 156 -11 -7% 0.78 1190 406 34% 0.24 7.0 2.8 40% 0.01 **

S12B 134 7 5% 0.81 1049 221 21% 0.47 6.6 1.1 17% 0.19

S12C 281 -21 -8% 0.56 2467 -21 -1% 0.94 7.6 0.7 10% 0.35

S12D 354 -50 -15% 0.25 3685 17 0% 0.98 9.0 1.8 20% 0.06 *

S12X 925 -76 -8% 0.54 8391 623 7% 0.63 7.9 1.5 19% 0.08 *

S333 166 20 11% 0.72 2345 748 32% 0.43 11.3 2.3 20% 0.02 **

S12X+S333 1090 -56 -5% 0.62 10736 1371 13% 0.39 8.6 1.9 22% 0.02 **

NESRS 157 -15 -10% 0.77 2127 392 18% 0.67 10.8 3.4 31% 0.01 **

SRS_ENP 1081 -91 -9% 0.46 10517 1015 10% 0.54 8.4 2.0 24% 0.02 **

ENP Taylor Slough/Eastern Panhandle

L31N_IN 63 72 79% 0.01 ** 1133 959 85% 0.05 * 13.1 -0.9 -7% 0.71

S174+S332D 87 51 48% 0.04 ** 1027 548 53% 0.31 9.1 -0.2 -2% 0.93

S332+S175 203 -104 -64% 0.12 * 1858 -947 -51% 0.26 7.2 -0.6 -8% 0.68

S176 89 -30 -39% 0.11 * 1125 -511 -45% 0.32 9.8 -1.7 -18% 0.58

S177 131 4 3% 0.86 1140 513 45% 0.25 7.2 2.6 36% 0.20

S18C 190 -10 -5% 0.69 2616 -691 -26% 0.46 10.5 -2.4 -23% 0.39

S18C-S197 158 -6 -4% 0.84 1958 -447 -23% 0.60 9.4 -1.8 -20% 0.47

Flow (kac-ft/yr) Total P Load (kg/yr) Mean Concentration (ppb)
An Assessment of the Interim Operational Plan 19

mechanisms for the observed increase in WCA-3A outflow 

TP concentrations to Shark Slough between 1994-1999 and 

2000-2003. First, there were increases in external TP loads to 

the central portion of WCA-3A via S-9 and S-140. A second 

mechanism is an increase in TP recycling from marsh soils and 

vegetation promoted by WCA-3A drawdown under ISOP/

IOP. ISOP/IOP changed the WCA-3A regulation schedule 

(ISOP/IOP Zone E1) by allowing a decrease in water levels of 

0.5 ft between February and July, relative to the pre-ISOP/IOP 

period. Further analysis (referenced in Section VII) of the data 

showed an inverse relationship between TP concentration 

and WCA-3A stage at many structure and monitoring sites in 

WCA-3A and Shark Slough. TP concentrations increase when 

the stage drops below approximately 9.5 ft at all outflow sites 

(S-12s, S-333, US41-25), flows under the Tamiami Trail into 

Big Cypress (TAMBR-105), interior sites in the central and 

southern portions of WCA-3A (CA311, CA315), and marsh 

sites in Shark Slough (P-33, P-35, P-36, NE-1, NP-201). 

Another mechanism is the increase in the proportion of the 

flow through S-333 vs. S-12s.

The final mechanism responsible for this increase in TP 

concentrations is the enhancement of TP transport from 

external sources through WCA-3A as a consequence of 

drawdown and its associated hydraulic effects. This caused 

decreases in the residence time required for assimilation of 

external loads by the WCA-3A marsh and caused increases in 

the proportion of canal flow vs. marsh sheet flow at low stage, 

particularly down the Miami Canal and along L-67A canal.

Second, there was a shift in WCA-3A outflows from the 

S-12 structures to S-333. This shift is a consequence of the diversion of dry season flows away from western Shark Slough 

through S-333 to NESS and the L-31N/C-111 basin. The 

overall pattern is consistent with the ISOP/IOP strategy. 

Taylor Slough and the Eastern Panhandle 

Screening of the L-31N/C-111 data identified no significant changes in TP concentrations after IOP implementation. 

The following factors and data limitations, most of which are 

less important in or absent from the Shark Slough data, contribute to the variability in the data from this basin and reduce 

probabilities of detecting changes. The recent data may not 

adequately reflect long-term water quality conditions likely to 

result from continuation of the ISOP/IOP, particularly with 

future evolution of the C-111 Project and potential urban 

development in the region. 

One factor is greater year-to-year variation in flow-weighted-mean TP concentration at L-31N/C-111 structures (CV = 

0.25 – 0.45), compared with Shark Slough structures (CV = 

0.15 – 0.25). This is partially attributed to lower analytical precision at the lower TP concentration range. Greater variation 

decreases the probability of detecting change in a dataset of 

fixed length (Snedecor and Cochran 1989).

A second factor is that adjustments for rainfall generally removed less variance from data at sites in this basin, as 

compared with sites in Shark Slough and WCA-3A. This may 

reflect the fact that hydrologic variability in this system is 

controlled more by seepage, canal stages, and local inflows, 

as opposed to WCA rainfall. Screening results do not change 

significantly using rainfall measured at S-18C instead of the 

WCA/Everglades Agricultural Area basin average.

The 2000-2003 ISOP/IOP period did not include wet 

years, which would be critical to evaluating long-term water 

quality impacts of operating the system (via the S-332B, C, 

and D pumps and lower canal elevations) to provide flood 

control for areas east of the canals. Wet year data are needed 

to assess critical conditions and long-term-average loads at 

S-18C, which is influenced by direct agriculture runoff via 

the C-111E canal via S-178. While flow data are insufficient 

to evaluate loading at S-178, geometric mean TP concentrations at this site increased from 21 ppb in the 1994-1999 to 32 

ppb in 2000-2003. Unlike most other sites in the ENP region, 

TP concentrations at S-18C tend to increase at high flows, a 

pattern typical of sites influenced by runoff (e.g., S-9 or S-8). 

Figure 7. Map of changes in TP concentration. Pre-IOP (1994-1999) 

vs. IOP (2000-2003) periods. Up arrow = significant increase (red 

p < 0.05, orange p < 0.15). Down arrow = significant decrease 

(dark blue p < 0.05, light blue p < 0.15). Orange circle = increase, 

not statistically significant (p > 0.15). Blue circle = decrease, not 

significant (p > 0.15).
20 South Florida Natural Resources Center Technical Series (2005:2)

For example, monthly flow-weighted TP concentrations at 

the S-12s generally decrease from approximately 15 ppb at 

low flows to approximately 6 ppb at high flows, whereas TP 

concentrations at S-18C increase from approximately 6 ppb at 

low flows to approximately 20 ppb at high flows. Canal water 

budgets indicate that under the dry-to-average rainfall conditions typical of the 2000-2003, flow and TP concentrations at 

S-18C are likely to be dominated by seepage from ENP and the 

L-31N/C-111 buffer cells, as opposed to watershed runoff.

Another possible factor is the sampling methodology. With 

the exception of S-332D, the screening analysis is based extensively upon biweekly grab samples. This type of sampling 

is generally inadequate for detecting infrequent spikes in TP 

concentration and loading associated with runoff events and 

flood-control operations. TP spikes may account for a large 

fraction of the TP load at a given site. Grab samples may be 

adequate to measure the TP loads at the S-12s, but continuous 

flow-weighted composite sampling is needed to measure TP 

loads at S-18C and other sites in this basin possibly affected by 

runoff events and flood control operations. A comparison was 

made of SFWMD grab and weekly composite samples at S332D and S-18C that showed TP levels of composite samples 

were higher than grab samples during periods when flows are 

high. Because composite sampling was not initiated at S-18C 

until 2003, the above screening analysis for S-18C was based 

exclusively upon grab samples. While it is possible that some 

of the differences between grabs and composites can be attributed to initial “shake-down” of the automatic sampling 

devices or other artifacts, there is a significant risk that grab 

samples under-estimate flow-weighted-mean TP concentrations and loads at these and other structures in the basin.

The final responsible factor is that the initial phases of the 

C-111 buffer project (including S-332B, S-332C, S-332D, and 

their associated detention areas, and other components) were 

not in full-scale operation for the entire 2000-2003 IOP period 

analyzed. Local inputs to the L-31N/C-111 canals are diluted 

by seepage losses from ENP (Walker 1997). An increase in TP 

concentration would be expected when the buffer project is 

in full operation and seepage losses are reduced, particularly 

if the system is operated to provide additional flood control 

for developed areas east of the canals. Occasional TP spikes 

(20 to 90 ppb vs. baseline of less than 10 ppb) in the C-102 

and C-103 data from 2001-2003 (Anamar Inc. et al. 2003) 

provide evidence of inputs from eastern developed areas that 

are inadequately characterized by grab sampling. TP concentrations from these areas will increase with future land use 

changes and/or system operation to provide additional flood 

protection (Harper 1994). 

Water Quality at C-111 Detention Areas

A review of the operation of the C-111 detention areas 

in terms of water quality showed little improvement in TP 

removal. Infiltration rates in the various basins ranged from 

75 cm/day at S-332B (Hendron 2000) to 30-50 cm/day at the 

S-332D detention area. These rates are in the expected range 

for this area. As a result, water detention times in the detention 

areas are very short, typically less than a day. Water quality 

modeling was conducted on flow and TP concentration data 

from the S-332B detention area using the Dynamic Model of 

Stormwater Treatment Areas (Walker and Kadlec 2002). A 

good correspondence between model and observed performance was found. Both measured and modeled removal of 

25% of the inflow TP load was being discharged as surface 

overflow, 70% was lost to seepage, and 5% was retained in the 

system. However, the TP concentration reduction achieved 

for overland discharges to ENP was less than 1 ppb, and is 

forecast to be on the order of 5-15% for incoming TP concentrations of 6-20 ppb. Because of the high infiltration rates 

and high hydraulic loadings during pumping events, water 

residence time was less than 1 day, which is insufficient to 

allow for significant biological uptake of inflowing TP loads. 

The direction and rate of TP transport to seepage and affects 

of antecedent soil TP are generally unknown. Unless specific 

and predictable removal mechanisms are identified, the detention areas should not be relied upon to provide significant 

water quality treatment. 

Everglades National Park Marshes

In upper Taylor Slough marshes during IOP, there were 

regular events in which TP concentrations exceeded 15 ppb. 

Furthermore, there were a number of times in late 2003 where 

the water entering this marsh from L-31W canal via the levee 

scrape-down area just north of S-332 had TP concentrations 

above 30 ppb. The nitrogen data are even more dramatic from 

the upper Taylor Slough marsh site. Total nitrogen concentrations during IOP have nearly always exceeded 700 ppb and 

at times have exceeded 1.4 ppm. Soil sampling west of the 

S-332B detention area in ENP revealed soil TP values under 

210 ugP/g dw (12 of 24 sites, Fig. 8). However, there was a 

southwest-northeast pattern of soil TP values above 210 ugP/

g dw that began at the south-central portion of the S-332B detention area weir (Fig. 8). This pattern appeared to follow the 

generalized slope of this area and it appeared that this was the 

primary flow path of the discharge from the S-332B detention 

area overflow weir. Most of the soil TP concentrations in this 

“flow path” were not markedly higher than the surrounding 

marsh; however, there were a few that were much higher. This 

included a value greater than 330 ugP/g dw at the site closest 

to the weir (A5) and about 400 ugP/g dw at the site furthest 

from the weir (D2). The D2 site is a deep, slough-like environment where one would expect high soil TP concentrations. 

However, the “flow path” of moderately high TP concentrations is not a kriging/statistical artifact because this pattern 

is supported by soil TP concentrations above 210 ugP/g dw 

from 10 of the 24 sites. There is evidence of periodic, even 

regular, water quality pulses in ENP wetlands associated with 

IOP water management. While this was not a chronic problem, there is evidence of water quality problems.
An Assessment of the Interim Operational Plan 21

In composite samples collected in C-111 marshes since 

1998, TP has seldom exceeded 10 ppb, and with the exception of certain events, there is some evidence of a 6-year 

downward trend of TP in the water entering C-111 marshes. 

Total nitrogen concentrations are considerably lower than 

Taylor Slough marshes (350 to 420 ppb), and the data show 

a clear downward trend in total nitrogen concentrations. At 

this time, there is no evidence of water quality impacts on 

C-111 wetlands, and since these wetlands are well north of 

ENP wetlands, there can be no evidence of IOP water quality 

problems on Eastern Panhandle wetlands. 

Summary

The resulting increases in TP concentration at the Shark 

Slough inflows as a result of ISOP/IOP were unexpected and 

are a major concern. Management changes should be made 

in the WCA-3A regulation schedule and plugs placed in the 

L-67A canal that will presumably reduce TP concentrations 

of Shark Slough inflows to ENP. The finding of no increases 

and low TP concentrations at L-31N/C-111 structures was 

a positive outcome of ISOP/IOP. However, the observation 

of pulses of nutrients in the surface waters and high soil TP 

in ENP marshes is a source of concern. The inability of the 

detention areas adjacent to ENP to provide significant water 

quality treatment should be thoroughly evaluated in future 

operational evaluations.

Salinity 

Salinity may be affected by changes in water management and may directly impact the function of downstream 

estuarine systems, making it one of the most important water 

quality variables to be considered when evaluating operational changes. Increased salinity in Florida Bay or Gulf Coast 

estuaries as a result of changes in water management is generally considered to run counter to the goals of restoration. 

The salinity expectations of the Comprehensive Everglades 

Restoration Plan (CERP), MWD, and C-111 projects are for 

decreases in the salinity concentration level and reductions in 

the occurrence of hyper-salinity conditions for the health of 

the estuarine ecosystem. Both ISOP and IOP were designed to 

influence the timing and allocation of surface water flowing 

into the park across Tamiami Trail from the north and through 

the L-31W and C-111 canals from the east. Evaluation of 

ISOP/IOP impacts on salinity regimes in downstream estuaries involved two tasks. The first was to investigate if any 

changes in salinity could be detected and the second was to 

test whether the changes were significant after accounting for 

climate differences. Smith (2003) analyzed ISOP/IOP impacts 

using historical salinity data and a Before-After-ControlImpact (BACI) approach. Marshall (2003) developed salinity prediction models, using a statistical approach. The latter 

study tested the models and then used them to investigate 

change in salinity due to ISOP/IOP implementation based on 

long-term simulations. 

Salinity BACI Analyses

ISOP/IOP salinity impacts in ENP estuaries were investigated using historical salinity data measured at 16 stations 

from November 1995 through October 2002 (Smith 2003). 

Historical data were used to look for differences in rainfall, 

0 - 30

30,00000001- 90

Soil TP ug/g Spline Method

50,00000001-150

150,0000001 - 210

210,0000001 - 070

210,0000001 - 030

300,0000001 - 090

390,0000001 - 450

210 105 0 210 Meters

Figure 8. S332-B Soil TP Spatial Interpolation. Soil bulk TP content 

(ug P/g dw) map for the S-332B sampling area. Detention area 

spillway is immediately east of the No Sample A Zone (shown 

in red).
22 South Florida Natural Resources Center Technical Series (2005:2)

flow, and salinity between the Test 7I period (1996-1999) and 

the ISOP/IOP period (2000-2002). A BACI design with controls for rainfall and wind, which are climatic factors that can 

also influence salinity, was then used to detect changes likely 

to be the result of water management operations. The following conclusions are based on this study:

Rainfall and Freshwater Inflow to Florida Bay: Annual 

average ENP rainfalls during the Test 7 Phase I and ISOP/

IOP periods are about 63 inches and 55 inches, respectively (Ahn 2003). An average dry season rainfall during 

the Test 7 Phase I period (19 inches) is much greater than 

that during the ISOP/IOP period (13 inches). Yearly, as 

well as seasonal, flows from Taylor Slough and C-111 canal were increased during the ISOP/IOP period compared to the Test 7 Phase I periods, but those of S197 

were decreased. Monthly flow differences (after minus 

before ISOP/IOP) from Taylor Slough and the C-111 canal were positive during the wet season (September and 

October) and early dry season (July-January), and negative during the late wet season (March-June). However, 

the ISOP/IOP impacts on such changes were not significant when tested with the BACI model. S197 flow differences were negative in June and from September through 

December but were positive in July and August. No water 

was released from this structure from January through 

May during either Test 7 Phase I or ISOP/IOP periods. 

Annual and Seasonal Salinity Changes: Annual and seasonal mean salinity generally increased with the change 

from Test 7 Phase I to IOP, but most of the changes were 

not significant. However, the annual change at Canepatch and the wet season changes at Taylor River and 

Canepatch were significant. Observed differences were 

small (e.g., Canepatch annual mean was 1.2 ppt higher) 

and only part of these differences was the result of water 

management. 

Monthly Salinity Changes: Monthly mean salinity decreased at most stations during the early dry season 

months (November-January), and increased at most 

stations during the late dry season and early wet season 

months (February-July). Observed changes varied from 

station to station during the late wet season months (August-October). However, ISOP/IOP impacts on these 

changes were not significant in most cases when tested 

using the BACI model with rain and wind as control variables. Exceptions are March mean salinity at both Canepatch and Broad River, for which the ISOP/IOP impacts 

were increased significantly (2.4 and 4.1 ppt, respectively). These increases are due to the reduction in discharges to Shark Slough under ISOP/IOP. March mean salinity 

at Highway Creek was also significantly higher (4.3 ppt) 

during the ISOP/IOP period. Any decrease in freshwater 

delivery to Florida Bay or the Gulf Coast estuaries, and 

resultant increase in salinity, would be counter to our efforts to restore these systems since the amount of fresh-







water flowing into the estuaries was greater before the 

water management system was built.

Salinity Analyses Using Model Simulations 

Marshall (2003) developed statistical models that predict 

daily salinity values using water level data, as well as wind and 

sea level data, as independent variables. He used these models 

to evaluate the long-term ISOP/IOP impact on salinity at eight 

sites in Florida Bay (Fig. 9). The models were developed and 

validated with the observed salinity data (Fig. 10) then used 

to simulate salinity using marsh water levels from the South 

Florida Water Management Model (SFWMM) for input. 

All SFWMM simulations used the same climate conditions, 

those for the 31-year period from 1965 through 1995. The 

salinity simulation models used historical wind and sea level 

data from the same period so that the only difference between 

model runs was the way water was managed.

Four water management scenarios were run: BS1995 represents regional hydrology under base operation rules as they 

existed in 1995, Natural Systems Model (NSM) represents 

regional hydrology under pre-development conditions, and 

ISOP and IOP represent regional hydrology under ISOP and 

IOP operation conditions, respectively. This analysis is based 

on the simulated long-term salinity values based on the simulations of different operation conditions with the same hydrometeorological condition. This method allows for control 

of climate changes over a relatively long period and focuses 

on conditions that result only from the management change. 

Table 2 shows simulated differences in salinity at eight stations 

over the 31-year period.

Based on the result of model simulations (Table 2 and others in Marshall 2003), the following conclusions were made: 

The ISOP/IOP runs predicted higher long-term mean salinity, compared to the result of BS1995 runs, at Little Madeira 

Bay, Terrapin Bay, North River, Whipray Basin, Duck Key, 

and Butternut Key. However, the changes were not significant 

statistically. 

ISOP and IOP simulations produced lower salinity in Joe 

Bay and Long Sound than the BS1995 simulation, although 

the changes were not significant statistically. In the case of Joe 

Bay, the effect of ISOP/IOP operations may not be discernable 

by this type of statistical analysis because of the large variance 

of the observed and simulated salinity values. Long Sound is 

relatively isolated from the open waters of Florida Bay, making the salinity prediction different from other sites.

The ISOP/IOP effect was somewhat more pronounced for 

monthly averages in the dry season. This finding is consistent 

with the result of the BACI analysis. For all sites except Joe 

Bay and Long Sound, there were at least four months where 

the salinity differences between Base95 and ISOP/IOP runs 

were positive and significant. For Little Madeira Bay and 

Terrapin Bay the differences were significant for all months 

of the dry season. At Whipray Basin, the differences were 

significant for all dry season months except January, and for 

the wet season months of July, September, and October. For 
An Assessment of the Interim Operational Plan 23

Figure 9. Map showing the location of salinity and water level stations used in the statistical salinity simulation models.
24 South Florida Natural Resources Center Technical Series (2005:2)

Duck and Butternut Keys, the differences were significant for 

the dry season months of January through May.

Higher monthly mean salinity was also predicted by ISOP/

IOP at some locations in the wet season. Statistically significant increases in salinity values were seen at two near shore 

stations (Little Madeira Bay and Terrapin Bay) and one open 

water station (Whipray Basin) during some of the months in 

the wet season.

The increase in monthly average salinity in the near shore 

central embayments were transferred to the salinity increase 

in open water stations of Whipray Basin, Duck Key, and 

Butternut Key, but the changes were not significant. This finding is also consistent with the result of the salinity BACI analysis. This is not unexpected, as the salinity at the three open 

water stations is a function of Little Madeira Bay and Terrapin 

Bay salinities that were increased by IOP.

Salinity was simulated at only one station downstream of 

Shark Slough, North River. ISOP/IOP was designed to reduce 

freshwater flow from the S12 structures to western Shark 

Slough during the dry season. As might be expected, ISOP/

IOP runs predicted significantly higher salinity values at North 

River for the months of October, November, December, and 

January.

0

10

20

30

40

MD HC LS JB TR LM TB BS BN WB BR CN TE GI NR CP

Salinity (ppt)

Dry Wet

0

10

20

30

40

MD HC LS JB TR LM TB BS BN WB BR CN TE GI NR CP

Salinity (ppt)

Test 7I ISOP/IOP

Figure 10. Comparison of historical salinity values: (A) between the wet and dry seasons, and (B) Test 7I and ISOP/IOP periods.

RUN Joe Bay Little Madeira Terrapin Bay North River Long Sound Whipray 

Basin

Duck Key Butternut Key

BS1995 13.08 20.76 27.19 7.35 19.93 34.89 26.26 28.01

IOP 12.48* 23.45 32.15 9.34 19.07* 37.17 28.26 29.77

ISOP 12.65 23.15 31.32 9.04 19.16 37.13 27.71 29.35

NSM 12.3 19.86 25.61 6.77 19.87 34.16 25.6 27.53

Table 2. Comparison of average daily salinity values (in ppt) produced by statistical models for the indicated operational scenario, 

where (*) indicates the salinity decrease by IOP.
An Assessment of the Interim Operational Plan 25

Summary

In summary, the above two studies lead to the following 

conclusions. Salinity at most monitoring sites in Florida Bay 

and Gulf Coast estuaries increased slightly during the ISOP/

IOP period compared to the Test 7 Phase I period, which is 

not desirable for the health of the ecosystem in Florida Bay. 

The increase was not statistically significant in most cases, but 

annual salinity at Canepatch on the Shark River and March 

salinity at Canepatch and Broad River were significantly increased. Long-term salinity simulations using multivariate 

regression models predicted higher salinity under ISOP/IOP 

than under without-IOP at Little Madeira, Terrapin Bay, North 

River, Whipray Basin, Duck Key, and Butternutt Key, but projections were lower at Joe Bay and Long Sound. However, the 

differences were not statistically significant.

Biological Environment

ENP is the first national park established solely to preserve 

biological resources. Key biological resources include ENP’s 

wading bird populations, endangered avian and mammalian 

faunas, temperate and tropical flora, and extensive wet prairie and sawgrass sloughs. Water management is at the core of 

sustaining these resources, and is the source of threats to the 

park’s stewardship of these irreplaceable treasures. It is impossible to monitor the impact of water management operations on all of the critical biota, so key indicators of ecosystem 

state and function were chosen for assessment of ISOP/IOP. 

These are aquatic communities indicative of nutrient enrichment and key food web linkages, vegetation dynamics, mangrove wetland food webs linked to Roseate Spoonbills, and 

the Cape Sable Seaside Sparrow. In sum, these indicators 

provide information on critical habitats affected by ISOP/IOP 

in WCA-3A and WCA-3B, Shark Slough and NESS, Rocky 

Glades and upper Taylor Slough, and in the C-111 and Taylor 

Slough oligohaline zone.

Our assessments focused on two types of expectations for 

freshwater communities: nutrient and hydrologic impacts. We 

also tracked non-native species in aquatic habitats.

Nutrient expectations

Periphyton TP should not exceed 200 ugP/g dry weight 

of tissues;

Relative abundance of midge species characteristic of 

ENP wetlands and known to be sensitive to nutrient enrichment should not decrease, while relative abundance 

of midges known to be tolerant to nutrient enrichment 

should not increase.

Hydrology expectations

Density of fish and macroinvertebrate species known to 

be sensitive to drying events should not decrease in nondrought years, while those benefiting from drying events 

should not increase outside of drought years;







Catch-per-unit-effort (CPUE) of long-lived fish species 

should not decrease outside of drought years.

Non-native species expectations

The range and abundance of non-native aquatic species, 

especially fishes, should not be increased in ENP by hydrologic operations.

Freshwater Communities

Nutrient Impacts

Nutrient enrichment resulting from ISOP/IOP water 

management is of primary concern for the Rocky Glades 

and the headwaters of Taylor Slough. These relatively shorthydroperiod areas are oligotrophic and even small additions 

of TP, if continued over time, could dramatically alter ecological relationships there. Evidence of elevated periphyton 

TP at S-332B and possibly at S-332D was found (Fig. 11). At 

present, enrichment was limited to the immediate vicinity of 

input, and the S-332B enrichment may result from groundwater seepage. Midge-indicator taxa also yielded evidence of 

nutrient impacts in ENP by disappearance of taxa intolerant 

of enrichment, and increases in taxa associated with enrichment downstream from S-332B (Fig. 12) and S-332C (Fig. 13). 





0 20 40 60 80 100

Approx distance from edge (m)

0

100

200

300

400

500

600

700

800

900

TP ( ug/g)

D

C

B

AREA

N = 1

0 20 40 60 80 100

Approx distance from edge (m)

0

100

200

300

400

500

600

700

800

900

TP ( ug/g)

D

C

B

AREA

N = 1

Figure 11. TP from periphyton samples taken along transects 

from each S-332 detention area or inflow point. Only the 0 to 

20 m distances at S-332B are different (P < 0.05). The dashed line 

indicates a threshold for enrichment. No data were collected at 

the inflow of water downstream from S-332D because no periphyton was present and N=1 at the 20 m site because periphyton was sparse in that area, indicative of nutrient enrichment or 

high flow.
26 South Florida Natural Resources Center Technical Series (2005:2)

A similar indication of nutrient enrichment was observed 

downstream from the C-111 canal (Fig. 14). These observations could be transient effects of the new structures and adjustments to their management, but also indicate a potential 

for problems if they continue. 

Hydrologic Impacts

An important goal for CERP is to provide longer hydroperiods in Shark and Taylor sloughs. However, many parameters 

evaluated by BACI analyses indicated drier conditions during 

the ISOP/IOP period. For example, the volume of floating 

mat (an indicator of periphyton mass) decreased following 

marsh drying events in Shark Slough and WCA-3A. Grass 

shrimp and small fishes sensitive to hydrology decreased by 

50% or more in the ISOP/IOP years, relative to the preceding 

four years (Fig. 15). A small fish species known to thrive in 

short-hydroperiod conditions increased in abundance under 

ISOP/IOP. Large fishes, including game species, decreased in 

density in WCA-3A and Shark Slough during ISOP/IOP, compared to the preceding years (Table 3). Also, the age structure 

of a relatively long-lived detritivorous fish species shifted to 

dominance of younger individuals in ISOP/IOP in WCA-3A. 

These observations suggest pervasive changes in the food web 

in WCA-3A during ISOP/IOP. These changes cannot be linked 

Sensitive species

0

20

40

60

80

100

332C

Pond

50m 300m 3km

Percent

Tolerant species

0

10

20

30

332C

Pond

50m 300m 3km

Percent

Figure 13. Proportion of nutrient-sensitive and nutrient-tolerant species 

in midge pupal exuviae samples collected in October 2002 from marshes 

near the S-332C detention area. Samples from the S-332C detention area 

and Cladium habitats 50 m, 300 m, and 3 km west of the S-332C detention 

area.

Sensitive species

0

20

40

60

80

332B 50m 1km

Percent 

Tolerant species

0

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4

6

8

10

12

332B 50m 1km

Percent 

A. October 2001 B. October 2002

Sensitive species

0

20

40

60

80

50m 300m 3km

Percent

Tolerant species

0

1

2

3

50m 300m 3km

Percent

Figure 12. Proportion of nutrient-sensitive and nutrient-tolerant species in midge pupal exuviae samples collected in or near detention 

area S-332B. (A) October 2001 from S-332B detention area, and from sites 50 m and 1000 m west of the detention area. (B) October 2002

from Cladium sites 50 m, 300 m, and 3 km west of S-332B detention area.

Figure 14. The relative abundances of nutrient-sensitive and nutrient-tolerant midge species in Cladium 

habitats close to, and approximately 1 km downstream 

from, C‐111 canal inflows to Taylor Slough, October 

2002.

Sensitive species

0

20

40

60

80

Near C111 1 km S of

C111

Tolerant species

0

1

2

3

4

5

Near C111 1 km S of

C111

Location Location Percent

Percent

Periphyton in Shark Slough. Photo by Michelle Peake, ENP.
An Assessment of the Interim Operational Plan 27

explicitly to the operational changes of 2000-2002 because 

these correspond to drier years than the pre-ISOP/IOP comparison period. Because all study areas had lower dry season 

water depths in these years, no benchmark from unaffected 

sites was available for comparison. However, operations in 

ISOP/IOP did not result in a lengthening of regional hydroperiods. At least in 2000, this appears to be the result of water 

management driven by concerns north of Lake Okeechobee, 

where a severe drought was experienced.

Non-Native Species

IOP construction/operation facilitated both the spread 

of non-native species into ENP marshes (Table 4) and range 

expansion of native species atypical for Rocky Glades habitats. The new S-332 structures provide direct access to ENP 

marshes from L-31W canal. Their completion coincided with 

the first collection of two new species of non-native fish and 

subsequent range expansion of two others, plus range expansion of two native taxa into nearby Rocky Glades and Taylor 

Slough habitats (Fig. 16). Also, two new non-native fish species were observed in marl prairies downstream from C-111. 

Fishes were not the only taxa affected. Midge species typical 

of canals were observed in ENP near S-332B and S-332D 

overflow, and near C-111 in the Eastern Panhandle region. 

This appears linked to the observation that detention areas 

and canals have a high diversity and density of non-native 

fishes and macroinvertebrate taxa and are potential sources 

for primary and secondary invasions.

Furthermore, the current configuration of the structural 

components of IOP allows for the introduction of non-native 

aquatic species into ENP through weirs on detention pond 

levees located on the eastern park boundary. Non-native 

fishes, while present, have previously not been particularly 

abundant in the freshwaters of ENP. These new routes of 

invasion appear to be permitting entry by species previously 

absent from the park, and these species are obtaining locally 

high abundance. Non-native fishes have been shown to decrease the abundance of native fishes in estuarine areas of 

ENP, including alteration of food-webs leading to wading 

birds in ways that are not predictable and inconsistent with 

park management goals. In addition, the presence of non-native species appears to be contradictory to the National Park 

Service Organic Act (16 U.S.C. l 2 3, and 4), which states the 

fundamental purpose of the Service is, “...to conserve the 

Variable Region 1996-99

Test 7

2000-02

ISOP/IOP

Diff P-adj

Predatory 

Fishes

Shark River Slough 0.435 0.360 -7.6 0.90

Taylor Slough 0.299 0.197 -9.7 0.8061

WCA-3 0.790 0.495 -25.7 0.0009

All fishes over

8 cm long

Shark River Slough 1.247 0.817 -34.9 0.0002

Taylor Slough 0.600 0.495 -10.0 0.91

WCA-3 1.133 0.795 -28.7 0.007

Table 3. Summary of BACI tests for effects of ISOP/IOP on big fishes in WCA-3A, WCA-3B, Shark Slough, and Taylor Slough. Predatory 

species are those consuming other fishes as a primary diet item and include largemouth bass, gar, and warmouth. The data reported 

are log-transformed mean number of fishes collected in a 5-minute electrofishing transect; Diff is the percentage change of CPUE from 

Test 7 to ISOP/IOP. Significant (P < 0.05) changes are indicated by a Tukey’s post-hoc test. 

Figure 15. Long-term monitoring sites examined for this assessment. Small fish density decreased at most sites in the ISOP/SOP 

period compared to the previous four years. Small fish are all 

species whose maximum size is less than 8 cm. These are the 

dominant fishes of the Everglades and are the primary food 

items of wading birds, especially smaller species such as snowy 

egrets. Predatory fishes decreased at all sites (see below), possibly influencing the increase of small fishes in southern WCA-3A, 

where predatory fishes were most abundant prior to ISOP/IOP.
28 South Florida Natural Resources Center Technical Series (2005:2)

scenery and the natural and historic objects and the wildlife 

therein and to provide for the enjoyment of the same in such 

manner and by such means as will leave them unimpaired for 

the enjoyment of future generations.”

Rocky Glades 

Annual minimum groundwater depths in the Rocky Glades 

area were too low during Test 7, and IOP operations failed to 

improve this situation. Current water level minima leave few 

solution holes inundated through the dry season to provide 

aquatic refuge for animals (Kobza et al. 2004). In addition, 

pre-storm drawdowns and related operations that increase 

the recession rate of water appear to result in additional fish 

mortalities. At times, pre-storm operations prematurely exposed the marsh surface in this area, which was subsequently 

re-flooded, only to dry again (called a “reversal”). Reversals 

in the Rocky Glades appear to diminish the fish spawning 

stock surviving the dry season because each re-flooding event 

reshuffles fishes among refuges, compounding losses with 

each event. The dry season corresponds with the winter, the 

non-breeding season for fishes. Thus, there is a concern that 

reversals exacerbate existing problems from the diminished 

availability of dry-season refuges in decreasing the breeding population of adults needed to re-populate the area in 

spring. 

Total fish biomass

0

2

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14

16

18

Near

2 miles west

Exotic fish total biomass

0

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14

16

18

Native fish total biomass

Month

0

2

4

6

8

10

12

14

16

18

July Aug Sept Oct

Biomass (g)

Figure 16. Biomass (g) of all non-native and native fishes collected by minnow traps in ENP marshes near S-332D inflow (solid 

symbols).

Common Name Species Name First observed in ENP Notes

jaguar cichlid Cichlasoma managuense Aug. 2000 First appeared in the canal system in Miami-Dade 

County in 1990s

jewel cichlid Hemichromis letourneauxi Aug. 2000 Very abundant in 2003

armored catfish Hoplosternum littorale Aug. 2002 Invaded Miami-Dade County via canals from east 

central Florida around 2000 

butterfly peacock bass Cichla ocellaris Nov. 2002 Collected in L31W prior to 2002

Table 4. Non-native fish species first noted in ENP after opening of S-332 structures, raising water levels, and lowering the berm on 

L‐31W leading to increased flows to the park.

Exotic fish in bucket in order of size jaguar guapote (Cichlasoma 

managuense), brown hoplo (Hoplosternum littorale), Mayan 

cichlid (Cichlasoma urophthalmus), two black acara (Cichlasoma 

bimaculatum), African jewelfish (Hemichromis letourneuxi). 

Rocky Glades habitat on the ENP side of the 332C Retention area. 

Photo by Jeff Kline, ENP.
An Assessment of the Interim Operational Plan 29

Summary

Unfortunately, our assessments of expectations for ISOP/

IOP provided reason for concern both for potential nutrient 

enrichment and a deterioration of ecological conditions in 

Shark River Slough and Taylor Slough. 

Nutrient expectations

Periphyton TP should not exceed 200 ugP/g dry weight 

of tissues;

Values in excess of this cut off downstream of S-332C 

and, possibly, S-332D were observed. 

Relative abundance of midge species characteristic of 

ENP wetlands and known to be sensitive to nutrient enrichment should not decrease, while relative abundance 

of midges known to be tolerant to nutrient enrichment 

should not increase.

A decrease of sensitive midges and increase of tolerant 

ones inside ENP in areas adjacent to S-332B, S-332C, 

and C-111 berm removal were observed.

Interpretation. These results raise concern about both surface 

flow and groundwater seepage from new structures and operations in the L-31W and C-111 areas. Further monitoring is 

needed and responsive actions would be prudent.

Hydrology expectations

Density of fish and macroinvertebrate species known to 

be sensitive to drying events should not decrease in nondrought years, while those benefiting by drying events 

should not increase outside of drought years.

Dry-down sensitive fish and macroinvertebrates decreased in density and a dry-down tolerant species increased during ISOP/IOP compared to Test 7 in Shark 

Slough and Taylor Slough. Similar impacts were noted 

in western and northern WCA-3A. 

CPUE of long-lived fish species should not decrease outside of drought years.

Large fishes generally decreased in CPUE during 

ISOP/IOP compared to Test 7 in WCA-3A, Shark 

Slough, and Taylor Slough.

Interpretation. The scale of drying in WCA-3A, Shark Slough, 

and Taylor Slough observed in 2000 and 2001 was not expected based on Test 7 operations and observed rainfall. This 

drying led to high mortality of long-lived fishes that require 

several years to recover population sizes following dry-down 

events.

Non-native species expectations

The range and abundance of non-native aquatic species, 

especially fishes, should not be increased in ENP by hydrologic operations.

Four species of non-native fishes were observed to 

expand their range in ENP during ISOP/IOP, two of 

which were new invasions to the park at a time corresponding to new water flows in ENP from L-31W 





















at the old S-332 pump station. Expansions were noted 

in both the Rocky Glades and C-111 areas.

Interpretation. Changes in water delivery to ENP from the 

L-31W and C-111 appear to have facilitated the movement of 

non-native fishes into ENP, including to federally-designated 

wilderness areas.

Vegetation 

Retrospective paleoecological studies and early observers 

depict the Everglades as a flowing-water system that favored 

formation of peat in sloughs and of marl in the slightly higher 

seasonal marshes that flank the sloughs. Patches of forested 

habitat were found as small inclusions on local elevated 

sites. Ecosystem restoration goals focus on recreating these 

conditions where they have been lost and maintaining them 

where they have persisted in the altered system. Taylor Slough 

expectations include a central channel where hydrologic 

conditions favor peat formation and accumulation, and marl 

formation occurs across the full range of flanking marshlands. 

Hydroperiods would be long enough to slow the spread of 

woody species into the more elevated prairies adjacent to the 

Atlantic Coastal Ridge. Expectations for Shark Slough concern mainly providing hydroperiods and water depths sufficient to support white water lily peat formation in sloughs, 

and Everglades peat and Gandy peat in tall sawgrass strands 

and wet tree islands, respectively, without compromising water quality.

Taylor Slough Marsh

The freshwater marsh communities in ENP and Big 

Cypress National Preserve are critical components in the biodiversity of the Everglades, both for the structure they provide 

in support of other biotic elements, and for the intrinsic values 

of their constituent plant species assemblages. To examine the 

changes in the marsh vegetation associated with the ISOP and 

IOP management periods, temporal and spatial co-variation 

of vegetation and hydrology in seasonally-flooded marshes 

was analyzed, focusing specifically on the upper reaches of 

Taylor Slough during the period 1979-2003.

Vegetation data were collected along five line transects 

(Fig. 17) of ca 2-km length: two representing the headwaters 

of Taylor Slough (Transects 4 and 5), two in Upper Taylor 

Slough (Transects 1 and 2), and one in middle Taylor Slough 

(Transect 3). The three lower transects were established 1979 

and were resampled in 1992 (Transect 2), 1995 (Transects 1 and 

2), and 1996 (Transect 3). Transects 4 and 5 were established 

and sampled in 1997, and all five transects were resampled 

in 1999 and 2003. In 1979, half of the plots established along 

Transects 1-3 were subjectively located in Cladium jamaicense 

(sawgrass) stands (C-plots) intersected by the lines, and half 

were in Muhlenbergia filipes (muhly) stands (M-plots). In 

contrast to Transects 1-3, the plots established in Transects 4 

and 5 in 1997 were selected not on the basis of existing cover 
30 South Florida Natural Resources Center Technical Series (2005:2)

types, but rather at 100-m intervals along the transect, adjusting distances where necessary to avoid tree islands. 

Hydrologic Changes in Taylor Slough

The water level in Taylor Slough was much higher in the 

1980s and 1990s than in the two previous decades (Fig. 18). 

From 1961 to 1980, prior to operation of the S-332 pump station, mean daily water level in the slough in both dry and wet 

seasons was significantly correlated with rainfall. In contrast, 

from 1981 to 2002, rainfall was a poor predictor of water levels, which were primarily determined by water management 

operations (Fig. 18).

Changes in Vegetation Patterns along and across 

Taylor Slough Transects

Vegetation composition along Transects 1-3 changed 

substantially over the study period (1979 – 2003). Changes 

in vegetation composition along Transect 1, 2 and 3 became 

apparent by 1995, when a substantial decrease in muhly cover 

and an increase in sawgrass cover occurred in the M-plots 

(Fig. 19). In the same year, sawgrass declined in the C-plots. 

Changes in both plot types were most dramatic on Transect 1 

where the absolute cover of muhly in the M-plots on Transect 

1 decreased by 1700% by 1995, compared to 400% and 300% 

on Transect 2 and 3, respectively (Fig. 19). Similarly, sawgrass 

decreased in C-plots. In contrast, sawgrass cover increased 

significantly in M-plots over the sampling period. Eleocharis 

cellulosa (spikerush), a dominant of wet prairies, which was 

present only in the C-plots of Transect 1 in 1979, became 

Figure 17. Location of Taylor Slough sampling transects, S-332 and S-332D water control structures, and detention area on the eastern 

boundary of ENP. 

Taylor Slough main flow way and adjacent shorter hydroperiod 

prairies. New bridges, constructed as part of the C-111 project, 

have increased the capacity for water conveyance through this 

area. Photo by William Perry, ENP.
An Assessment of the Interim Operational Plan 31

D-61/62D-63/6

4

D-65/66D-67/68D-69/70D-71/72D-73/7

4

D-75/76D-77/78D-79/80D-81/82D-83/8

4

D-85/86D-87/88D-89/90D-91/92D-93/9

4

D-95/96D-97/98D-99/00D-01/02

0

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52

0

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52 S332 Deliv ery S332D Deliv ery

Observ ed water lev el

 Predicted water lev el f rom Models dev eloped f rom pre-S332 period data

Model 1A Model 1B

 Predicted water lev el f rom Models dev eloped f rom S332-operation and ISOP period data

Model 3 Model 5

S332 & S332D Delivery (x1000 acre ft/month)

Water Level (inch)

Figure 18. Observed and predicted water level and water flow through S-332 and S-332D into Taylor Slough during the 1961-2002 dry 

seasons.

established in M-plots on Transect 1 and 3 by 1995 and later 

became one of major species in C-plots on all three transects.

The trends in vegetation between 1979 and 1995 continued through 1999, though the changes in muhly and sawgrass 

cover were smaller. During this period, the cover of spikerush 

increased in the M-plots on Transect 1 and in the C-plots on 

all three transects (Fig. 19), and spikerush was the most abundant species in M- and C-plots on Transect 1. Its average cover 

reached its highest abundance in the C-plots on Transect 2. 

Trends between 1999 and 2003 were the opposite of the 

pattern prior to 1999. Muhly and sawgrass cover increased 

in M- and C-plots, respectively (Fig. 19), while spikerush decreased. Spikerush was virtually absent (mean cover < 0.1%) 

in the M-plots of Transect 2 and 3, and the C-plots of Transect 

3. However, increasing sawgrass cover in the M-plots continued through 2003. Total cover of all species increased sharply 

in M-plots in all three transects, and in C-plots in Transects 

1 and 3, but not Transect 2. This recent change appears to 

indicate that vegetation was responding to the decrease in 

Taylor Slough water levels during ISOP. Species other than 

the dominants also underwent changes with, in some cases, 

an apparent relationship to hydrology.

Vegetation dynamics differed along Transects 4 and 5 during 1997-2003. The plots grouped by years in multivariate 

analysis, indicating a directional change in vegetation along an 

unidentified gradient. Total cover increased markedly, paralleling the trend in Transects 1-3 in 1999-2003. This increase 

was concentrated particularly among the two major species, 

sawgrass and muhly. In the six-year study period, the mean 

cover of sawgrass increased from 3.7% to 37.8% and from 

2.8% to 22.3% on Transects 4 and 5, respectively. The cover of 

muhly also increased more than 7-fold on these transects.

The proportion of total cover contributed by species other 

than sawgrass and muhly decreased significantly by 2003, 

and the change was more extreme during the ISOP/IOP period (1999-2003) than in first two years (1997-1999). Overall, 

macrophyte species richness varied during the study period. 

On Transects 1-3, species richness decreased dramatically 

between 1979 and 1995, and then remained almost stable 

through 1999. During the ISOP/IOP period, species richness 

increased in the M- and C-plots on Transect 1, and in the 

C-plots of Transects 2 and 3. An increase in species richness at 

the transect level was also observed on Transect 5 during the 

ISOP period, while on Transect 4, species richness remained 

nearly stable over the 6-year study period.
32 South Florida Natural Resources Center Technical Series (2005:2)

Figure 19. Absolute cover (%) of major species averaged across all M- and C-plots on Transects 1, 2, and 3, 1979-2003. Legend: sawgrass 

(green), spikerush (dark blue), muhly (purple), other species (aqua).

Vegetation-hydrology Relationships

Vegetation-hydrology relationships were examined using a weighted averaging regression and calibration model 

developed from vegetation cover data collected in 2003 on 

Transects 4 and 5 and from marl prairies west of Shark Slough. 

Hydroperiods were estimated from mean plot elevations and 

water level records from the 1996-2001 water years at ENP 

recorders CR-2, NTS-1, and NP-205. This model was applied 

to the historical and current vegetation data from the five 

Taylor Slough transects, and used to estimate vegetation-inferred hydroperiods for each sampling year during the S-332 

operation and ISOP periods (Fig. 20).

During the S-332 operation and ISOP periods, temporal 

changes in vegetation-inferred hydroperiods were substantial, especially on Transects 2 and 3 (Fig. 20). On Transect 1, 

inferred hydroperiods did not differ significantly between 

1995 and 1999, but in 2003 were shorter than in 1999, particularly at the two ends of the transect where muhly once 

dominated (Fig. 20A). On Transect 2, inferred hydroperiods 

were significantly longer in 1995 and 1999 than in 1992 and 

2003 (C-plots only) (Fig. 20B). Inferred hydroperiods along 

Transect 3 did not differ significantly between 1996 and 1999, 

but were shorter in 2003 than either of the previous years. The 

shorter inferred hydroperiods on all three transects in 2003 

in comparison to 1995 and 1999 (Fig. 20C) provide strong 

correlative evidence that the decrease in Taylor Slough water 

level during the ISOP period was responsible for the vegetation change in this portion of Taylor Slough.
An Assessment of the Interim Operational Plan 33

Among-year differences in inferred hydroperiods for 

Transect 4 and 5 during 1997-2003 were not significant on 

either transect. In conjunction with other results, these analyses suggest that factors other than hydrology were responsible 

for vegetation change in the headwater portions of Taylor 

Slough.

Summary

Under ISOP/IOP, hydrologic conditions in Taylor Slough 

produced marsh community responses that were broadly predictable based on prior field studies. That is, the hydroperiods 

supported a shift in dominance, particularly the decline in 

Eleocharis and the increase in Muhlenbergia, which created 

communities approaching those found in the slough in 1979 

when the marsh was much drier. Species richness increased, 

another result associated with shorter hydroperiods than 

found in the natural system and in the mid-1990s. Thus the 

slough reverted to a state that was further displaced from the 

restoration expectations of a wetter system than was the case 

under Test 7. No data were collected in Shark Slough, so the 

possibility of a changing vegetation pattern in response to 

ISOP/IOP could not be tested there.

Mangrove, Estuarine, and Marine

Previous research has identified two major effects of upstream water management practices on the mangrove ecosystem bordering the northern shoreline of eastern Florida 

Bay. First, diversion of natural flows alters the salinity regime 

in the wetlands that results in a reduction in primary production in the submerged aquatic vegetation community within 

the mangrove zone, which in turn causes lower abundance 

of prey. The decline in prey fishes likely explains declines in 

predator populations dependent on this food resource. The 

second effect of water management is dry season pulse releases of water from the canal system, which cause reversals 

of seasonal drying patterns within the mangrove ecosystem. 

Drying events are critical in that many predators take advantage of abundant fishes concentrated in the remaining small 

pools. Wading birds, including Roseate Spoonbills, generally 

time their nesting to these drying events enabling them to 

readily meet the high energetic requirements of their rapidly 

growing young. Reversals in the drying pattern allow prey 

base fishes to spread across the landscape making them relatively unavailable to wading birds, resulting in nesting failure. 

Fishes begin to move into deeper habitats (i.e., begin to concentrate) when water levels on the wetland surface within this 

area drop below 12.5 cm or 5 inches.

A productive mangrove ecosystem is dependent on lower 

salinity within the mangrove wetlands, made possible by high 

wet season water levels and relatively large flows through 

Taylor Slough. Prey fishes would be expected to respond 

by increasing numbers under these low salinity conditions. 

During the dry season, low water levels and curtailment of 

reversals are desirable. These conditions would be promoted 

by reduced flows through the system, especially through the 

C-111 canal. A relatively high availability of prey and high 

reproductive output by spoonbills would be expected. Thus, 

the restoration expectations associated with improving ecological conditions in the mangrove zone include lowering 

salinities of coastal wetlands so as to increase fish productivity and providing for dry season reduction of marsh water 

depths to critical levels for concentrating fishes into drying 

pools within the foraging grounds of Roseate Spoonbills and 

other piscivores.

To assess potential impacts to the estuarine region, three 

sampling sites were evaluated using BACI analysis: Taylor 

River (TR), Joe Bay (JB) and Highway Creek (HC) located in 

the Taylor Slough/C-111 area (Fig. 21). Two control sites, one 

for salinity at Barnes Sound (BS) on Biscayne Bay outside the 

effect of Test 7 or IOP, and one for water level analysis at Bear 

Lake (BL), were also evaluated. All sites were sampled for fishes in June, September, and monthly from November to April. 

Thus, six fish samples were collected at each site in each dry 

season and two were collected during wet seasons. Spoonbill 

nesting success data were collected at two sites (Tern and 

Sandy Keys). Tern Key is located directly downstream of the 

Taylor Slough/ Panhandle region. Birds from this colony feed 

in the coastal mangroves represented by the impact sites and, 

Figure 20. (A, B, and C, respectively). Plot-level vegetation-inferred hydroperiods estimated in Muhly and Cladium plots along 

the Transects 1, 2 and 3, 1992-2003. Open symbols = Muhly plots; 

Closed symbols = Cladium plots.
34 South Florida Natural Resources Center Technical Series (2005:2)

thus, comprise the impacted colony. Sandy Key is located on 

the western edge of Florida Bay. Birds from this colony feed in 

the Cape Sable area (as represented by the BL site), which is 

designated the control site since this is not directly impacted 

by water management practices.

Freshwater Flows to Mangrove Region

There were no significant differences in annual flow between the Test 7 and IOP periods for either C-111 discharges 

or Taylor Slough Bridge. However, during the wet season, 

there was significantly higher flow to the C-111 area than 

down Taylor Slough during IOP as compared to Test 7, an 

undesirable effect based on analyses of mangrove salinity patterns in response to basin flows. During the dry season, no 

statistically significant differences were observed between 

IOP and Test 7.

Salinity within the Mangrove Region

Statistical analysis showed no significant difference in 

rainfall or salinity at the control site between the Test 7 and 

IOP periods. In contrast at the three impact sites, salinity 

was significantly higher during IOP than during Test 7. These 

results indicate that Test 7 was better than the IOP at achieving the desired responses of reduced salinity within coastal 

wetlands. Furthermore, based on the relationships between 

Taylor Slough flow and salinity in the mangrove wetlands, 

these results suggest that Test 7 was better at forcing more 

water into the natural flow way of Taylor Slough. 

Water Level Effects within the Mangrove Region

Overall, there was no apparent effect of water management on annual water levels in the coastal wetlands. Although 

annual water levels are important determinants of ecosystem 

function, depth affects the system primarily during the dry 

season. Dry season water levels at the control site were not significantly different between Test 7 and IOP, but at the impact 

sites, water levels were significantly higher during Test 7. As 

discussed below, these results suggest that the IOP produced 

better conditions in the dry season than Test 7. 

Fish Abundance and Availability

Fish abundance is a measure of the biomass of fish present 

regardless of their role as prey for predators. Fish availability 

reflects the accessibility of the fish to predators. Overall, there 

was no significant difference in fish abundance at either the 

control or impact sites. Although not statistically significant, 

the greater reduction of abundance at the impacted sites 

than the control site (23% vs. 15%) in IOP may be biologically relevant. The lack of significance may result from having 

only eight samples from the control site. In contrast, when the 

control and impact sites are combined, the BACI analysis indicated that fish abundance during the Test 7 period exceeded 

that of the IOP period. Based on the inconclusive nature of 

the BACI interaction, however, we must assume that regional 

conditions account for the differences between the two periods rather than water management practices. 

BACI analysis showed that fish availability was significantly 

different due mostly to greater availability at the control site 

during Test 7 (Fig. 22). Given that there was little difference 

in water levels during the two periods at the control site, the 

difference is most likely attributable to higher fish abundance 

at the beginning of the dry season leading to greater concentrations of fishes under Test 7. Fish abundance was higher at 

the end of the wet season under Test 7 at the impacted sites 

but the difference was not significant.

Mean Fish Available to Wading Birds

0

2

4

6

8

10

BL HC JB TR

Concentration of Fish/m 2 

Test 7 (Before)

IOP (After)

Control* Impacted

Figure 22. Mean fish number (with standard error) available to 

wading birds during the dry season (i.e., fish concentration) from 

four sites for both operational periods. Analytical results indicate 

that the BACI interaction was significant. Least squares means 

indicate that there was no significant difference at the impacted 

sites; however, at the control site, fishes were 39% more concentrated during Test 7 than during the IOP (*P = 0.004).

Figure 21. Control and impact sites for the mangrove wetlands 

and Spoonbill study.
An Assessment of the Interim Operational Plan 35

Because lower dry season water levels concentrate fishes 

in pools, if drying conditions were the same under both operational plans, higher availability would be expected under 

Test 7 at the impacted sites as was observed at the control site. 

This was not the case. Dry season fish availability was very 

similar for the two periods at the impacted sites. The most 

likely explanation is that higher dry season water levels under Test 7 (above the critical level below which fishes become 

concentrated) masked the effect of the higher “starting” abundance at the end of the wet season (Fig. 23). In other words, 

the lower water levels under IOP resulted in fishes being as 

available to predators as under Test 7 even though Test 7 had 

significantly higher fish abundance when calculated for the 

entire landscape (Fig. 23). 

Impacts on Spoonbills in Mangrove Region

Spoonbills generally begin nesting in Florida Bay between 

November 1 and December 15. The incubation period is 

approximately 21 days. After hatching, the chicks require 

constant care and an unbroken supply of food for about 42 

days. After this period, the chicks are more self-reliant, but 

still unable to leave the colony for another 42 days. Thus, the 

critical period for spoonbills in Florida Bay is approximately 

from December 1 to March 31. Foraging spoonbills require 

water levels at or below the concentration threshold of 12.5 

cm somewhere within the coastal mangrove wetlands for the 

duration of this period.

Relative depth under Test 7 operations averaged well 

above the concentration threshold of 12.5 cm, while under 

IOP, water levels were well below this stage (Fig. 23). In short, 

the IOP resulted in better foraging conditions for spoonbills 

in the coastal wetlands than Test 7. 

Although not proven statistically because of a paucity of 

data points (three in each of the four categories), the data 

clearly indicate that Test 7 had a profound negative effect on 

spoonbill nesting success (Fig. 24). At the impacted colony, 

fewer than two chicks fledged per 10 nesting attempts under 

Test 7. Under IOP, 10 nests produced about nine chicks. At the 

control site, the production rate was almost eight chicks per 10 

nests during the Test 7 period and increased to 11 chicks per 

10 nests during the IOP. These results suggest that conditions 

throughout Florida Bay were not as good for spoonbills during Test 7 period as during IOP. Test 7 operations exacerbated 

already poor conditions causing almost complete failure in 

colonies impacted by these operations.

Summary

The big increase in spoonbill nesting success under ISOP/

IOP indicates a marked improvement over Test 7 and a trend 

moving towards restoration expectations. The more favorable 

water levels in IOP during the critical foraging period for the 

spoonbills may partially explain this improvement. However, 

because the responses in salinity patterns and in fish biomass 

and availability, which presumably govern the success of 

piscine predators in the coastal areas, were mixed or inconclusive, more data are needed to determine if the positive 

spoonbill response continues and whether it is statistically 

explainable from the fish and salinity data.

Mean Dry Season Depth

0

5

10

15

20

25

Rain BL HC JB TR

Rain (in) and Relative Depth (cm)

Test 7 (Before)

IOP (After)

Controls Impacted*

Spoonbill Productivity

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Control (Sandy Key) Impact (Tern Key)

Chicks/Nest to 21d post hatch

Test 7

IOP

Figure 24. Mean success rate of nesting spoonbills at two locations. The virtual lack of reproduction at the impact site under 

Test 7 and over 400% increase during IOP indicate a strong anthropogenic effect despite the lack of statistical significance.

Figure 23. Least squares means indicate that there was no dry 

season depth difference in the controls, but at the impacted sites 

combined depth was 34% greater during the Test 7 compared 

to IOP (*P = 0.0001). Also note that, at the impacted sites, mean 

water level was above 12.5 cm during Test 7 but below 12.5 cm 

during IOP.

Roseate Spoonbill. Photo by Rodney Cammauf, ENP volunteer.
36 South Florida Natural Resources Center Technical Series (2005:2)

0

500

1000

1500

2000

2500

3000

198119921993199419951996199719981999

2000(a)

2000(b)

20012002

Year

Number

0

200

400

600

800

1000

1200

198119921993199419951996199719981999

2000(a)

2000(b)

20012002

Year

Number

0

500

1000

1500

2000

2500

3000

3500

198119921993199419951996199719981999

2000(a)

2000(b)

20012002

Year

Number

0

20

40

60

80

100

120

198119921993199419951996199719981999

2000(a)

2000(b)

20012002

Year

Number

0

100

200

300

400

500

198119921993199419951996199719981999

2000(a)

2000(b)

20012002

Year

Number

0

100

200

300

400

500

198119921993199419951996199719981999

2000(a)

2000(b)

20012002

Year

Number

Biscayne

National Park

Figure 25. The location and population estimates for the six sub-populations of the Cape Sable Seaside Sparrow.

Cape Sable Seaside Sparrow

The Cape Sable Seaside Sparrow is a medium-sized sparrow that occurs in Miami-Dade and Monroe counties in south 

Florida. This non-migratory sparrow has the most restricted 

range of any bird in North America and occurs almost exclusively within the boundaries of ENP and Big Cypress National 

Preserve. 

Male Cape Sable Seaside Sparrows occupy and defend 

their territories during the breeding season. Breeding activity, 

particularly singing behavior by males, appears to decrease 

with increased surface water conditions. Nests are cups constructed of grasses and are on average approximately 4 inches 

above the ground. When water levels exceed about 4 inches, 

nesting activities cease.

The Cape Sable Seaside Sparrow was among the first group 

of species listed as endangered by the FWS on March 11, 

1967. The sparrow was listed because of its limited distribution and threats to its habitat posed by large-scale conversion 

of land in southern Florida to agricultural uses. Presently, the 

sub-species is restricted to six small sub-populations in ENP 

and Big Cypress National Preserve. Surveys of the sparrow, 

employing helicopters to ferry observers to its remote locations, began with Harold Werner in 1974. In 1981, the first 

range-wide survey was undertaken. This was repeated in 1992, 

and range-wide surveys have continued every year since. The 

surveys show that sparrows are found in a set of sub-populations (A through F) separated to various degrees by unsuitable 

vegetation (Fig. 25). With so many events occurring in more 

or less the same timeframe, biologists must be careful in assigning cause and effect. For a detailed discussion, the reader 

is referred to the body of work encompassed in Pimm et al. 

(2002).

One of the critical outcomes for the Cape Sable Seaside 

Sparrow is the expectation that ISOP/IOP would produce 

appropriate hydrologic conditions over a substantial amount 

of sparrow habitat west of Shark Slough sufficient to produce 

two broods (two nesting cycles) a year. It was expected that 

this condition would allow sub-population A to at least maintain their current numbers as required by the RPA.
An Assessment of the Interim Operational Plan 37

The Western Sub-Population (A): A Comparison of 

the years 1996 through 1999 with the years 2000 

to 2003: 

Given the importance of sub-population A, being the 

population most impacted by water management, the water 

levels within sub-population A will be discussed first. Water 

monitoring station NP205 provides the best record of water 

levels for this sub-population. The dynamics of NP205 have 

been discussed elsewhere (Pimm et al. 2002). 

Water-level data at NP205 are available for the period 

1975-2003 (Fig. 26). There were dry years in the late 70s to 

early 80s, when breeding season water levels were often under 6 ft (the approximate height of NP205), followed by wetter years in the mid-80s. The late 80s to 1992 were usually dry, 

while the years from 1993 to 1995 were exceptionally wet, a 

condition exacerbated by water releases from the S-12s during the sparrow breeding season. 

The period of interest compares the time from 1996 to 

1999 (pre-IOP) to the time from 2000 to 2003 (post-IOP), 

and involves the 90 days following March 15th each year (Fig. 

27a, b). The figures show the same data as in Fig. 26, though in 

more detail. Also relevant are rainfall events, for these elevate 

the water levels considerably. Generally, heavy rains (defined 

as totals of > 1-5 inches) are spread over two days. However, 

in some cases, heavy rain continued over three or four days. 

The figures also show these events and their durations.

Water levels at NP205 remained above 6 ft for all but about 

20 days of 1996, all of 1997, and about 30 days in 1998 (ending 

with a 2-day rainfall total of 2.72 inches in late May). In 1999, 

water levels were below 6 ft for the 90-day period commencing on March 15th.

In contrast, water levels in 2000 to 2003 were nearly always below 6 ft during these 90 days. Generally, water levels 

dropped at about 1 ft per 20 days. However, in most years, 

large rainfall events raised water levels dramatically during 

the breeding season. For example, a mid-April rain (3.76 

inches in 2 days) in 2002 raised water levels by over 2 ft, and 

a late April rain (2.66 inches in two days) in 2003 raised water 

levels by 1 ft. 

Habitat Availability for Sub-population A in West 

Shark Slough

NP205 water level data were translated into available 

sub-population habitat by an established method (Pimm et 

al. 2002) (Fig. 28). Approximately, 275 km2 of this area had 

water levels > 5 ft, 175 km2 had water levels > 6 ft, 75 km2 had 

water levels > 6.5 ft, and none of the areas had water levels > 

7 ft. These areas are total areas and do not all afford suitable 

habitat for the sparrow. Using a well-calibrated, satellite-image-based model of sparrow habitat that excludes areas that 

are too bushy for sparrows or too small to support sparrow 

territories, the amount of available habitat was estimated. 

Approximately 125 km2 of the areas with water levels above 5 

Cape Sable Seaside Sparrow. Photo by Lori Oberhofer, ENP.

NP 205

0

1

2

3

4

5

6

7

8

9

1/1/1975 1/1/1980 12/31/1984 12/31/1989 12/31/1994 12/31/1999

Date

Depth (in feet)

Fig. 26. Daily water levels at NP205; pink points are those during the breeding season, taken as the 90 days starting March 15th.
38 South Florida Natural Resources Center Technical Series (2005:2)

March 15 - June 15

NP205 Depths

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80 90

Number of Days for Sparrow Breeding Season

Water Depth (feet)

1996

1997

1998

1999

3/15 4/13 5/13 6/12

March 15 - June 15

NP205 Depths

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80 90

Number of Days for Sparrow Breeding Season

Water Depth (feet)

2000

2001

2002

2003

3/15 4/13 5/13 6/12

3.76 2.53

2.61

1.85

2.66

4.83 (3)

3.27(4)

2.72

Figure 27. (a) Water levels at NP205 from 1996 to 1999 and (b) from 2000 to 2003 for the 90 days starting March 15th each year. 

Numbers in boxes show 2-day rainfall totals, except when the rainfall events were distributed over longer than 2 days, when 

the duration, in days, is shown in parentheses. For further details see text. 
An Assessment of the Interim Operational Plan 39

ft were suitable sparrow habitat in one or more years, while 90 

km2 of the areas with water levels > 6 ft were suitable, and 40 

km2 of the areas with water levels > 6.5 ft were suitable. 

For a given water depth (see Fig. 27), Fig. 28 shows how 

much habitat is predicted to be suitable in one or more years. 

Perhaps three-quarters of this area is suitable in a particular 

year, but not all is available throughout the breeding season. 

The word “available” is the key. To be able to produce one 

brood, the birds must have dry habitat for about 40 days 

continuously to complete a nesting cycle (two broods require 

longer).

The heights of water at NP205 below which the water remained for about 40 continuous days in the breeding season, 

plus the estimates of potential available sparrow habitat (in 

km2) at that height are shown in Table 5. 

Pimm and Bass (2002) emphasize that estimates of potential area are best viewed as comparative, since the area the 

sparrows can occupy will be substantially less. Clearly, the 

three years following the massive flooding of 1993 to 1995 

were still not good for sparrow breeding. In 1999, low water 

levels afforded larger dry areas for the birds to breed. The following year, the breeding season was likely interrupted by a 

mid-season storm that flooded large areas. The following two 

years were relatively dry, but 2003 looks as though it might be 

a very poor year for sparrow breeding.

Sub-population A Numbers

Table 5 also shows the estimated number of sparrows in 

sub-population A. Because of the small numbers of individuals actually counted, interpretation requires care. The highest 

estimate (448) corresponds to the year after one of the best 

years for sparrow habitat (1999). Biologists expect that good 

breeding years would be apparent the following year. The 

mid-season flooding of 2000 likely had a negative affect on the 

sub-population, so that despite the next two years being relatively dry, the sub-population may have had trouble recovering. Fig. 29 shows their distribution. 

In order to improve the confidence of the estimates of the 

now small sub-population A, biologists conducted an additional survey in this area in 2003, using a 0.5 km grid, rather 

than the more generally applied 1 km grid (see Fig. 29). The 

figure shows that the remaining birds are found in two concentrations, a larger one in the north and a smaller one in the 

south. Both closely match the areas of highest ground.

Pimm et al. (2002) estimate the potential for sparrow numbers to increase from one year to the next. In brief, they find 

that when the sparrow population (as a whole) can produce 

only one clutch per year, it likely cannot increase and will 

merely hold its own. Only when the population (as a whole) 

Cummulative Amount of Land and Habitat in Various Elevation Categories for

Cape Sable Seaside Sparrow Population A (West of Shark River Slough)

0

50

100

150

200

250

300

350

Entire area

4.1

4.3

4.5

4.74.95.1

5.3

5.5

5.75.9

6.1

6.3

6.56.76.9

Altitude / Water level

Cummulative Amount of Land (km2)

Land

Sparrow Habitat

Figure 28. Shows the areas in sub-population A that are dry “land” and in habitat that is predicted to be suitable habitat in one or more 

years. Predicted habitat in any given year is likely to be no more than three-quarters of this latter area and the birds, at best, will be 

able to use only a fraction of this area (see text for details). 
40 South Florida Natural Resources Center Technical Series (2005:2)

can produce two broods per year will the population increase. 

Fig. 27 and the calculations derived from it show that only a 

small part of sub-population A nests on sufficiently high 

ground that it can produce even one brood a year consistently. 

An even smaller part of sub-population A is free from flooding for long enough to produce two broods a year. Potential 

exists for this population to export birds to areas from which 

flooding has removed them in the past. 

The Eastern Sub-Populations (C-F) 

The work of Lockwood (in Pimm et al. 2002, and in preparation) determined that sparrow nesting is delayed by at least 

two years following fires. Fires are most frequent along the 

eastern boundary of the sparrow’s range, likely a result of this 

area being simultaneously drier than it was historically and 

adjacent to areas outside the natural system subject to human 

use and abuse. 

Sub-populations C, D, and F are subject to frequent fires 

and part of sub-population C, near Taylor Slough Bridge, has 

suffered altered hydrology that has made the habitat unsuitable. The small numbers of birds counted, as illustrated by 

the population estimates in Table 6, means that it would be 

difficult to detect any improvement in the habitat since the 

implementation of IOP. Sub-population D, however, is cause 

for concern. Only two birds were counted in 2001 (for a subpopulation estimate of 32) and none since. 

Summary 

Target hydrologic conditions in western Shark Slough 

were largely attained through the implementation of IOP operations. Prior to the implementation of IOP, water levels at 

indicator site NP-205 remained above the threshold level of 

6.0 ft (NGVD) much of the time. 

Implementation of IOP resulted in water levels nearly always below this threshold, particularly during the Cape Sable 

Seaside Sparrow nesting window. Thus, overall conditions for 

sparrow nesting were generally more favorable in the years 

since the implementation of IOP than in the years prior to its 

implementation.

Although conditions were improved considerably for 

sparrows in sub-population A since the implementation of 

IOP from 2000 onwards, in most years since IOP, large rainfall 

events raised water levels dramatically during the breeding 

season. Sub-population A was almost certainly negatively affected by a mid-April 2000 rain event. It is of particular concern that the area that remains dry during the breeding season 

is still very small compared with the extent of the sparrow’s 

distribution in 1981 and 1992, when sub-population A held 

almost half of the total sparrow population.

When the sparrow population as a whole can produce only 

one clutch per year, it likely cannot increase its numbers from 

one year to the next and will merely hold its own. Only when 

the population as a whole can produce two broods a year will 

a population increase be detected. Only a small part of subpopulation A nests on sufficiently high ground that it can produce even one brood a year consistently. An even smaller part 

of sub-population A is free from flooding for long enough to 

produce two broods a year, and so have the potential to export birds to areas from which flooding has removed them in 

the past. Therefore, despite improved hydrologic conditions, 

sub-population A numbers remain low and are still at a high 

risk of extinction.

Sub-population D is cause for concern. Only two birds 

were counted in 2001 (for a population estimate of 32). No 

birds were seen in 2002 and 2003. A fire burned a large part of 

what was once sparrow habitat in 2000, the same year that this 

area was flooded during the breeding season. It seems likely 

that the flooding event of 2000 was responsible for the recent 

crash of sub-population D. 

Sub-population B, as expected, was not changed by the 

IOP and there is not enough information to assess the impacts 

of the IOP on sub-populations C, E, and F.

Year Height (ft) Area (km2) Estimated Sparrow Numbers

1996 6.2 76 384

1997 6.3 66 372

1998 6.2 76 192

1999 5.4 122 400

2000 6.1 89 448

2001 4.5 128 128

2002 4.7 128 96

2003 6.2 76 128

Table 5. Potential available sparrow habitat.

Cape Sable Seaside Sparrow eggs. Photo courtesy of Rodney 

Cammauf, ENP volunteer.
An Assessment of the Interim Operational Plan 41

Figure 29. Counts of sparrows in 2003 in sub-population A. Black dots are sites counted in others years, white dots sites counted in 

2003, but not found to hold birds. Blue dots are sites holding one (small dot) or two (larger dots) on the regular survey. Yellow dots are 

comparable, but counted on a supplemental survey (see text).

POP 81 92 93 94 95 96 97 98 99 00 01 02 03

C 432 48 0 0 48 48 80 144 112 96 112 96

D 400 112 96 0 80 48 48 176 64 32 0 0

F 112 32 0 0 16 16 16 0 32 16 32

Table 6. Population estimates for three eastern sub-populations.
42 South Florida Natural Resources Center Technical Series (2005:2)

Conclusions and 

Recommendations 

IOP modifications began as recently as mid-2002 and, thus, 

only very limited amounts of hydrologic and biological data 

were available for analysis. To increase the amount of data 

available for analysis, ISOP and IOP datasets were combined. 

This is justifiable because the operations under IOP were 

largely an extension of the ISOP protocols. As a result, many 

of the analyses conducted in this report examined an aggregate of the data from both the ISOP (December 1999-June 

2002) and IOP (July 2002-present) periods. This aggregation 

of ISOP/IOP data improved the ability to conduct statistical 

analyses, but could not completely eliminate the constraints 

of a short-term data collection period. Consequently, for 

some particular analyses, it remains difficult to make definitive statements as to the benefits and impacts associated with 

these operational changes and even more difficult to assign 

cause and effect. 

The limitations of the dataset are particularly evident when 

analyzing the ecological data. Many of the species common in 

the Everglades landscape respond relatively slowly to hydrologic changes. The communities and species examined in this 

report were chosen in light of this problem. For example, one 

would expect to be able to see more immediate response from 

species lower in the food chain and with relatively short generation times, such as the aquatic midge species which were 

used to assess water quality under ISOP/IOP, than in those 

which occupy positions higher in the food chain and with 

longer generation times, such as the Wood Stork. The report 

does attempt, however, to provide insights on longer-lived 

organisms, such as the Cape Sable Seaside Sparrow, when 

the changes in the communities were likely due to ISOP/IOP 

operational changes.

Two over-arching management recommendations result 

from the analyses included in this report. First, it is of paramount importance to continue the existing long-term monitoring programs. Second, research is required to understand 

better the complex processes operating within the Everglades 

ecosystem, including the consequences of water management decisions, in order to ensure the restoration, protection, 

and preservation of the resource within the context of the 

Everglades restoration effort. It is also the expectation of ENP 

that future structural and operational modifications associated with CSOP and CERP will be designed in a manner that 

will accentuate the observed ecosystem improvements and 

also ameliorate the issues of concern.

Positive Outcomes in the Assessment of 

Interim Operations

Physical Environment

Hydrology

Conclusion. IOP appears to have substantially corrected 

the unnatural and undesirable impacts in upper Taylor Slough 

associated with operations during ISOP. More natural wet 

season recession patterns, a greater spatial extent of surface 

water during the wet season, and a possible decrease in seepage losses were observed during IOP. All these suggest that 

IOP resulted in more natural timing and distribution of inflows to Taylor Slough.

Recommendation. Apparently, the significant benefits 

observed in upper Taylor Slough do not propagate very far 

downstream. The most likely explanation is that the lower 

L-31W and Aerojet canals capture groundwater and surface 

water and rapidly convey it back towards C-111. Modifications 

to the operational and structural configuration of the L-31W 

and lower C-111 canals could correct this problem and should 

be investigated in future operational evaluations. 

Conclusion. Target hydrologic conditions in western Shark 

Slough were largely attained through the implementation of 

IOP operations. Prior to the implementation of IOP, water 

levels at indicator site NP-205 remained above the threshold 

level of 6.0 ft-NGVD much of the time. Implementation of 

IOP resulted in water levels nearly always below this threshold, particularly during the Cape Sable Seaside Sparrow nesting window. Thus, overall conditions for sparrow nesting were 

generally more favorable in the years since the implementation of IOP than in the years prior to its implementation.

Recommendation. Continue IOP operations associated 

with the S-12 structures until completion of all features associated with the MWD and C-111 Projects, including the 

implementation of the operational plan for the combined 

projects.

Continuation of existing long-term monitoring efforts is important to assess future water management changes. Here, small 

fish and large macroinvertebrates are collected using a throw 

trap in Shark Slough. Photo by Joy Brunk, ENP.
An Assessment of the Interim Operational Plan 43

Water Quality

Conclusion. There is no evidence of a deterioration of 

water quality at structures (S-332B, S-332D, and S-18C) along 

the eastern side of ENP, associated with IOP operations in the 

L-31N and C-111 canals.

Recommendation. These analyses should be viewed with 

caution given the projected changes within the basins associated with the implementation and operation of C-111 Project 

features and land use changes. Extensive monitoring, data 

analysis, modeling, and research to ensure protection of ENP 

resources from potential, yet unrealized, water quality problems should guide future management.

Biological Environment

Mangrove, Estuarine, and Marine

Conclusion. IOP resulted in lower water levels during the 

dry season than during the Experimental Program Test 7 

within the mangrove region of the Eastern Panhandle, ENP. 

This allowed for improvements to spoonbill nesting success 

during IOP when compared to Experimental Program Test 7.

Recommendation. Several modifications would allow 

these conditions to persist during the dry season: (1) allow for 

more storage of water and better control in the L-31N and 

C-111 basins, (2) implement the MWD Project to introduce 

more water into NESS and upper Taylor Slough, (3) backfill 

the lower C-111 canal to prevent large flood releases to the 

Eastern Panhandle and Manatee Bay, and, (4) redistribute 

flows to the Taylor Slough/Eastern Panhandle to deliver a 

greater percentage of water to Taylor Slough than the Eastern 

Panhandle.

Cape Sable Seaside Sparrow

Conclusion. Sub-population B, as expected, was not 

changed by the IOP.

Recommendation. Continue to monitor sub-population B 

at the present level of effort.

Sources of Concern in the Assessment of 

the Interim Operations

Physical Environment

Hydrology

Conclusion. ISOP/IOP resulted in lower average water 

levels and shorter dry season hydroperiods in western Shark 

Slough, and WCA 3B when compared to Test 7, after accounting for rainfall.

Recommendation. Implement the structural and operational features of the MWD and C-111 projects, which will 

allow introducing more water into NESS, thereby increasing 

water depths and hydroperiods.

Water Quality

Conclusion. Available water quality data do not support reliance on the detention areas of the C-111 Project as 

mechanisms for water quality protection. Because of the high 

seepage rate of water out of the detention areas, the current 

footprint of the detention areas is not sufficient to remove 

nutrients from the incoming water.

Recommendation. Design the detention areas to minimize 

input to ENP in the form of either seepage or direct surface 

water flow. Specifically, it is recommended that the proposed culverts along the western side of the detention areas 

be eliminated. It is also recommended that these structural 

modifications to the C-111 Project be evaluated during CSOP 

for compatibility with the other authorized purposes of the 

C-111 Project.

Conclusion. There is an increase in TP concentrations 

in Shark Slough inflows after IOP implementation. There 

is strong evidence linking this increase to the change in the 

WCA-3A regulation schedule required by ISOP/IOP. The 

lower WCA-3A stages in the WCA-3A regulation schedule 

reduces the occurrence of S-140 and S-9 flows entering 

WCA-3A marshes where nutrient uptake occurs. The result is 

direct canal flow from S-140 and S-9 to Shark Slough inflow 

structures (S-12s and S-333). 

Recommendation. Several actions can be taken to address 

these problems:

1. Modification of the WCA-3A regulation schedule to 

avoid drawdown of water levels below Zone E, particularly to 

stages less than 9.5 ft.

2. Plug the L-67A canal to reduce transport of TP loads 

from the S-9 outflow to Shark Slough inflow structures along 

the Tamiami Canal.

3. Initiate further monitoring, analysis, and modeling of 

future and existing data from WCA-3A to further evaluate 

S-Gate 332B west of Shark Valley. Photo by Lori Oberhofer, ENP.
44 South Florida Natural Resources Center Technical Series (2005:2)

factors contributing to recent increases in TP concentrations 

at the S-12s and S-333.

Conclusion. Increases in TP concentrations at S-12A were 

larger than those observed at other Shark Slough inflow 

structures. 

Recommendation. Assess factors contributing to elevated 

TP concentrations at S-12A such as, the Zone E1 WCA-3A 

regulation schedule and inflows from S-140 and S-9. 

Conclusion. A sampling strategy of bi-weekly grab samples 

is generally inadequate for detecting infrequent spikes in TP 

concentration and loading associated with runoff events and 

flood-control operations. This problem was revealed when 

comparing TP data from grab samples and composite samples 

at S-332D and S-18C.

Recommendation. Use composite sampling to track TP 

concentrations and loads at monitoring sites in the L-31N/

C-111 region, including sites on the mainstream canals, sites 

on eastern canals (C-102, C-103, C-113, C-111E), pump stations, and buffer/detention area overflow points.

Conclusion. TP transport mechanisms from the detention areas, including the effects of antecedent soil TP, are 

unknown. 

Recommendation. Intensified monitoring of the L-31N/

C-111 detention areas to support development of accurate 

water and TP budgets, to assess the transport and fate of TP 

in surface and groundwater flows, and to support modeling 

of TP dynamics.

Conclusion. Evidence of nutrient enrichment is apparent 

from elevated TP in soil and periphyton samples from the 

marsh just west of the S-332B detention area, as well as from 

aquatic insects used as indicator species.

Recommendation. Eliminate the surface water discharges 

from the S-332B detention areas until the source of the 

elevated TP can be conclusively determined. Continued 

monitoring of nutrient levels in the soil, periphyton, surface 

and groundwater, along with aquatic insects in and around 

the detention areas, is recommended.

Salinity

Conclusion. Statistical tests reveal that yearly and seasonal 

salinity values in Florida Bay were increased slightly during 

the ISOP/IOP period compared to the Test 7 period. Longterm model simulations reveal that the ISOP/IOP scenario 

provides less water to Florida Bay through Taylor Slough. As 

a result, the calculated mean salinity values at the northeast 

Florida Bay area increase under ISOP/IOP compared to Test 

7 conditions. 

Recommendation. Restore the flow through Taylor Slough 

at the level of the natural condition so that favorable salinity conditions for a healthy Florida Bay ecosystem will be 

reestablished.

Biological Environment

Freshwater Communities 

Conclusion. Two new species of non-native fish have been 

detected and the range of a third non-native fish has expanded 

in the Taylor Slough, Rocky Glades, and C-111 regions due to 

the operations of structural features associated with the South 

Dade Conveyance System and ISOP/IOP.

Recommendation. Eliminate all surface water inflows from 

the L-31W, L-31N, and C-111 canals via the S-332, S-332C, 

S-332D, and their associated detention areas. Eliminate the 

L-31W canal to further prevent the introduction of other 

non-native species. It is also recommended that these structural modifications to the C-111 Project be evaluated during 

CSOP for compatibility with the other authorized purposes of 

the C-111 Project.

Conclusion. Pre-storm drawdowns and repetitious fluctuations of water level above and below the ground surface 

(reversals) may reduce the dry season survival of fishes in the 

Rocky Glades.

Recommendation. Initiate a study of Rocky Glades fishes 

with sampling frequency that is adequate to evaluate the impact of these events.

Conclusion. Lower average water levels and shorter dry 

season hydroperiods in central Shark Slough and central 

Taylor Slough when compared to Test 7 led to lower density 

of several species of native fishes and macroinvertebrates.

Recommendation. Implement the structural and operational features of the MWD and C-111 projects, which will 

allow for the introduction of more water into NESS, thereby 

increasing water depths and hydroperiods.

A hydrological monitoring station near S-333. Photo by Joy 

Brunk, ENP.
An Assessment of the Interim Operational Plan 45

Vegetation

Conclusion. During the IOP operational period, the composition of marsh vegetation, including species diversity, 

appeared to shift towards patterns observed in the drier periods of the 1960s through 1980s and away from the trends 

observed in the past decade. This trend is opposed to the 

ecosystem restoration goal of restoring the hydrology and the 

associated natural communities of Taylor Slough.

Recommendation. Increase hydroperiods and water depths 

in Taylor Slough by providing water as far north as possible in 

the drainage basin, with as much of the flows as possible originating from overland and groundwater flows coming from the 

natural system. Assure that this water is of the highest water 

quality. Implement the structural and operational features 

of the MWD and C-111 projects, which will introduce more 

water into NESS, thereby increasing water depths and flows 

into Taylor Slough.

Conclusion. Measurable changes in the dominant vegetative species were apparent within a period of two to three 

years. Evidently, the changes in marsh vegetation within 

Taylor Slough occur rapidly and in response to changes in 

water management.

Recommendation. Continue the fixed-plot monitoring 

program, adding new plots to improve the ability to detect 

effects of water management operations. In conjunction with 

related work funded by other sources, the expanded database 

will provide a more robust basis for drawing conclusions as to 

causative relationships between plot-level marsh water levels, 

water management operations, and vegetation response.

Cape Sable Seaside Sparrow

Conclusion. Despite improved hydrologic conditions, subpopulation A numbers remain low and are still at a high risk 

of extinction.

Recommendation. Continue the monitoring of Cape Sable 

Seaside Sparrow sub-population A and its habitat to determine if these operations actually result in increases in the 

population size and the recovery and protection of its habitat. 

In addition, sub-population A should be surveyed on a finer 

scale (0.5 km) each year and intensive on-the-ground surveys 

of population A should continue.

Conclusion. Sub-population D is cause for concern. Only 

two birds were counted in 2001 (for a population estimate 

of 32). No birds were seen in 2002 and 2003. A fire burned a 

large part of what was once sparrow habitat in 2000, the same 

year that this area was flooded during the breeding season. It 

seems likely that the flooding event of 2000 was responsible 

for the recent crash of sub-population D.

Recommendation. A detailed analysis of water levels in this 

sub-population before and after IOP should be undertaken. 

Continue to monitor sub-population D at the present level of 

effort. In addition, sub-population D should be surveyed on 

a finer scale (0.5 km) each year and intensive-on-the ground 

surveys should search for birds in sub-population D. 

Conclusion. There is insufficient information to assess the 

impacts of the IOP on sub-populations C, E, and F.

Recommendation. Continue to monitor sub-populations C, 

E, and F at the present levels of effort. In addition, sub-population F should be surveyed on a finer scale (0.5 km) each year. 

On-the-ground surveys of sub-population E should continue. 

In addition, intensive on-the-ground surveys should search 

for birds in sub-populations F.

Setting capture mistnet. Photo by Lori Oberhofer, ENP.

Anhinga on water gage in Taylor Slough. Photo by Joy Brunk, 

ENP.
46 South Florida Natural Resources Center Technical Series (2005:2)

Supporting Documents 

This report is based on technical documents prepared by staff 

of ENP in collaboration with scientists from other state and 

federal agencies, scientific organizations, and universities. 

These documents provide detailed technical analyses in support of the information contained in this report and are available on a cd included with this report.

Hydrology

Hosung Ahn, Robert Fennema, Kevin Kotun, Sherry 

Mitchell-Bruker, Sara O’Connell, Thomas Van Lent

Water Quality

Bob Kadlec, Mike Zimmerman, Nick Aumen, Bill Walker, 

Dan Childers

Salinity 

Hosung Ahn, Dewitt Smith, Bill Nuttle, Frank Marshall

Freshwater Communities

Joel Trexler, Bill Loftus, Christina Bruno, Rick Jacobsen, 

Evelyn Gaiser, Jeff Kline; Vegetation Communities, Mike 

Ross, Thomas Armentano

Mangrove, Estuarine, and Marine 

Jerry Lorenz, Thomas Armentano 

Cape Sable Seaside Sparrow

Skip Snow, Oron “Sonny” Bass, Stuart Pimm
An Assessment of the Interim Operational Plan 47

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South Florida Natural Resources Center

Everglades National Park

950 N. Krome Ave, 3rd Floor 

Homestead, FL 33030-4443