gles, and osprey (Boesch et al., 1993; Interagency Science Subgroup, 1993). The mosaic of estuarine habitats, created by the interplay between the relatively ...
Urban Ecosystems, 3, 279–303, 1999 c 2000 Kluwer Academic Publishers. Manufactured in The Netherlands. °
Environmental management scenarios: Ecological implications JOHN C. OGDEN∗ South Florida Water Management District, Office of the Executive Director, 3301 Gun Club Road, P.O. Box 24680, West Palm Beach, FL 33416-4680, USA JOAN A. BROWDER U.S. Dept. of Commerce, NOAA/National Marine Fisheries Service, Miami, FL 33149, USA JOHN H. GENTILE Center for Marine and Environmental Analyses, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA LANCE H. GUNDERSON Department of Zoology, University of Florida, Gainesville, FL 32611, USA ROBERT FENNEMA Everglades National Park, SFNRC, 40001 State Road 9336, Homestead, FL 33034, USA JOHN WANG Division of Applied Marine Physics, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA
Abstract. The measure of whether a management scenario is capable of establishing regional-scale ecosystem sustainability is the degree to which it recovers the historical characteristics of the regional landscape mosaic. This study examines the ability of alternate management scenarios to recover the defining ecological features of the Everglades and South Florida landscape. Five conceptual scenarios are evaluated for recovering and sustaining the ecological characteristics of the wetland systems in South Florida. First, the regional-scale physical characteristics are identified that created and supported the major organizing and driving forces in the predrainage Everglades and Big Cypress basins. Eight hypotheses are proposed to explain how human-caused modifications to these defining characteristics have been responsible for the substantial level of ecological deterioration that has been documented in South Florida wetlands during the last century. The restoration scenarios are evaluated on their proposed ability to correct the physical and biological problems identified by the hypotheses. Our assessment of the five scenarios shows that all would improve the problems addressed by the eight hypotheses, as all could more effectively move increased volumes of water across broader expanses of contiguous wetlands than do existing management programs. This would result in longer hydroperiods over larger areas, reflecting historical patterns. Two of the scenarios would be successful in increasing flows into Florida Bay and the Gulf coast estuaries because removing internal structures increases the spatial extent of the upstream areas that could be devoted to natural hydropatterns. The benefits of eastern boundary buffer zones include improved flow into the Taylor Slough basin. Using Lake Okeechobee as a site for increased water storage, followed by the addition of eastern buffer zones and portions of the Everglades Agricultural Area, would produce increased flexibility in providing the storage capacity required to meet sustainability goals. Scenarios with maximum areas of buffer not only are more successful in reducing groundwater seepage losses to the east but also are more likely to reduce the level of nutrients and other contaminants entering the natural wetlands. Keywords: scenario-consequence analysis, hydrology, landscape mosaic, ecosystem management ∗ To
whom correspondence should be addressed.
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Introduction The prevailing scientific consensus is that the current spatial extent and patterns of ecology and hydrology do not support a sustainable Everglades or South Florida ecosystem (Harwell and Long, 1992; Interagency Science Subgroup, 1993). Consequently, the defining ecological characteristics, species, and habitat heterogeneity of the historical Everglades system, combined with the supporting physical features of the system (e.g., dynamic patterns of water storage and sheet flow of oligotrophic waters), must be recovered as a prerequisite for long-term ecosystem sustainability (Harwell, 1997). Our strategy for evaluating the ecological implications of management restoration options relies on the use of the historic, predrainage Everglades as the template for defining sustainability goals. This involves describing the relationship between the physical organizing forces (e.g., climate, geology, topography, space, and hydrology) and the ecological characteristics (e.g., landscape mosaic, population dynamics and distributions) of the historical system. By using the predrainage natural system as the benchmark for defining sustainability, we can project the ecological changes likely to occur from the reestablishment of the major physical organizing forces that shaped the original landscape. As a part of the U.S. Man and the Biosphere (US MAB) Human-Dominated Systems Directorate (HDS) project, a set of plausible, regional-scale environmental management scenarios was developed to illustrate the recovery of the physical defining characteristics of the South Florida system and to examine their implications to the sustainability of both ecological and societal systems and processes (Harwell et al., 1996; M. Harwell et al., this volume). The measure of ecological sustainability, as used here, is the degree to which a scenario recovers the defining ecological characteristics of the regional landscape mosaic. The measure of societal sustainability is the degree to which the historical agricultural community of the region is maintained in the face of severe pressures from development, soil degradation, and environmental and political liabilities. This article briefly describes the structural and operational components and rationale for each of the scenarios. The potential hydrological and spatial improvements expected from each scenario, as well as from a “base” condition wherein no additional structural or operational improvements would be implemented beyond those of mid-1994, are also profiled. The hydrological and spatial improvements expected from each scenario become the basis for the projections of ecological recovery. This is done, first, by defining those regionalscale organizing and physical characteristics that are believed responsible for shaping the predrainage ecology of the Everglades and Big Cypress basins. A series of causal hypotheses are proposed to explain how human-caused modifications to these defining characteristics are responsible for the substantial level of ecological deterioration that has been documented in South Florida wetlands in the last century. It is widely believed that the extent of change in the physical characteristics of these wetlands has occurred over such extensive spatial scales and is of such magnitude that, given current management practices, the ecological character of the remaining degraded wetlands is no longer sustainable (Interagency Science Subgroup, 1993). Unfortunately, full restoration is unattainable, since more than one half of the original system has been lost and thus cannot be fully recovered. The final outcome
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will be a mosaic of sustainable states that, when taken together, will represent significant but not full recovery of the system. The final section in this paper presents an ecological assessment of the five US MAB conceptual recovery scenarios, based on the predicted ability of each to correct the physical and biological problems identified by the hypotheses. Defining physical characteristics We have selected the long-term goal of sustainability as a benchmark for assessing the ecological implications of the five management scenarios. This approach assumes that the recovery of the defining physical characteristics of the predrainage wetlands is a prerequisite for long-term ecosystem recovery and sustainability. We have set no numerical measures for sustainability because of the uncertainties associated with species and community response during the recovery of wetland systems that differ in scale and boundary from their predrainage condition. However, we assume that many of the ecological and biological patterns that occurred in these predrainage wetlands will again reappear if their defining physical characteristics can be substantially recovered. Thus the test of whether any regional management scenario is capable of both recovering and sustaining predrainage-like systems becomes a measure of the ability of that scenario to recover the defining physical characteristics of these regional wetlands. We identified the defining physical characteristics of the predrainage systems from recent syntheses of Everglades and Big Cypress basin databases presented in Browder and Ogden (this volume), Davis and Ogden (1994), Gunderson and Loftus (1993), and Interagency Science Subgroup (1993). These system-wide physical characteristics are as follows: Large spatial extent. Space was the dominant physical characteristic of the South Florida wetlands necessary for the interaction of all other physical and ecological components (Harper, 1927; Harshberger, 1914). The broad spatial extent of the predrainage wetlands, about 3.6 million ha, was essential for collecting and storing the amount of regional rainfall required to maintain the ecological vigor of these systems. The broad sawgrass marshes across the northern and east-central Everglades, the Shark and Taylor sloughs in the southern Everglades, and the numerous cypress strands crossing the Big Cypress, collectively stored enough water from wet seasons into dry seasons to support the region’s characteristic biological and ecological components in both the freshwater and estuarine portions of the systems (Davis, 1943). Expansive space was necessary for supporting robust populations of animals that required extensive feeding or hunting ranges across multiple landscape boundaries, during different seasons, and over varying hydrological patterns (Bancroft, 1989; Frederick and Collopy, 1989). Seasonally dynamic rainfall and surface-water patterns. The strong and variable patterns of seasonal and annual rainfall created the alternating high water–low water depth and distribution patterns of surface and groundwater in the wetlands that were the primary organizing and concentrating forces for biological production in these areas (Fennema et al., 1994; Powell, 1987). Multiyear high-water cycles may have been an important means by which freshwater pushed into the Florida Bay estuary and have been correlated with
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increased production of pink shrimp (Browder, 1985; Boesch et al., 1993; McIvor et al., 1994). A pattern of multiyear low-water cycles, followed by expansive reflooding, appears to have been the mechanism that was necessary to create pulses of primary and secondary production that in turn supported the larger wading bird nesting colonies that historically occurred in the Everglades (Kushlan, 1986; Robertson and Frederick, 1994). Seasonal wet–dry cycles created expanding and contracting surface-water patterns that were largely responsible for a range of habitat conditions. These cycles, characterized by varying hydroperiods on different temporal and spatial scales, permitted the dispersal and concentration of fishes and other small aquatic animals (Loftus et al., 1990). Hydrological gradients and sheet flow. The low topographical relief, characteristic of the Everglades and Big Cypress basins, created the subtle differences in average water depth on subregional scales that were responsible for the discrete (but hydrologically interconnected) landscape features of cypress forests, marl prairies, sawgrass sloughs, and mangrove estuaries (Davis et al., 1994). These landscapes have had different, but complementing, roles in ecological processes in South Florida. The relatively deeper water, longer-hydroperiod areas in the freshwater regions once served as principal production and survival zones, while the expansive, relatively more shallow areas served as major foraging sites for wading birds and were among the more important habitats for panther (Felis concolor coryi), deer (Odocoileus virginianus), and alligators (Alligator mississippiensis) (Maehr et al., 1990; Mazzotti, 1983; Schemnitz, 1974). The low topographical gradients across landscape scales created expansive areas of shallow edges adjacent to deeper pools. This topographic feature prolonged the value of the regional wetlands as wading bird foraging habitat in the interior marshes during dry seasons and in the higher-elevation portions of these wetlands during wet seasons (Allen, 1936; Bancroft et al., 1990; Hoffman et al., 1994; Kushlan et al., 1975; Kushlan, 1979). Expansive areas of low-relief terrain also were responsible for sheet flow, which was a mechanism that contributed both to the extremely low natural level of nutrients in the interior marshes and to the pulsed transfer of nutrients across landscape boundaries between wet and dry cycles (Browder et al., 1994; Swift and Nichols, 1987). The relationship between sheet flow and the low natural level of nutrients in the South Florida wetlands was a major defining ecological characteristic of these systems and therefore is essential to understanding production patterns in South Florida wetlands. An estuarine system. Since the Everglades and Big Cypress basins contain a major estuarine component, they differ from other large tropical and subtropical wetland systems such as the llanos (Venezuela) and pantanal (Brazil). The presence of the broad mangrove swamps along the Gulf coast, downstream from the Big Cypress and Shark Slough systems, and the larger Florida Bay and Biscayne Bay systems flanking the southeastern Everglades, substantially increases subregional levels of biological production, habitat complexity, and species diversity. High levels of estuarine production supported strong commercial and sportfishing industries and large coastal populations of fish predators such as pelicans, eagles, and osprey (Boesch et al., 1993; Interagency Science Subgroup, 1993). The mosaic of estuarine habitats, created by the interplay between the relatively more complex topographical features in the coastal regions and the broad, shifting salinity gradients, supported an array of estuarine specialists such as the West Indian Manatee, great white heron, reddish
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egret, roseate spoonbill, white-crowned pigeon, and American crocodile. Recent studies (Bancroft et al., 1990) have shown how wading birds nesting in the mainland mangrove swamps can quickly shift primary foraging sites between interior and mangrove subregions, depending on the effects that rainfall has on water levels within flying range of the colonies. This observation offers support for the hypothesis that the reason the larger, traditional, wading bird nesting colonies were concentrated along the mangrove-marsh ecotone in the southern Everglades region is that this area provided (in addition to higher levels of production) a wider range of choices for foraging sites under a variety of hydrological conditions than did other regions in the South Florida wetland systems (Bancroft et al., 1990; Erwin, 1983).
System-wide integration The integrating effects of the defining physical features of the Everglades and Big Cypress basins produced the predrainage ecological characteristics of these wetlands. The natural patterns of dynamic water storage and sheet flow, operating over an extensive area and long time scale, made the predrainage wetlands wetter than they are today, organized and concentrated the primary and secondary production, established the salinity gradients in the estuaries, and created the substantial network of dry-season refugia that was essential for all freshwater animals in the system. In a naturally oligotrophic ecosystem, with relatively low rates of production at the local scale, the large total area made it possible for hydrological mechanisms to organize and concentrate this production at different places and times, depending on highly variable seasonal and annual rainfall patterns (Walker, 1991). Habitat heterogeneity, in the form of extensive mosaics of plant communities and water depths, provided the spatial framework for the production and survival of animals under a wide range of seasonal and annual hydrologic conditions. In this environment of patchily distributed food, many of the characteristic large vertebrates were highly mobile species that were capable of adjusting the timing, location, and magnitude of their reproductive efforts, and the location of their feeding sites, to track the patterns of high levels of food availability (Bancroft et al., 1990, 1994). The Everglades was able to support large numbers of many animals at the top of the food web only so long as natural hydrological events occurred over a large expanse. The large spatial scale, coupled with the habitat mosaics, also contributed to the region’s biotic diversity by supporting animals and plants with relatively restricted habitat requirements [e.g., Cape Sable sparrow (Ammodiamus maritimus mirabilis), red-cockaded woodpecker (Picoides borealis), atala butterfly (Eumaeus atala)].
Societally-induced changes in ecosystem characteristics: causal hypotheses In order to evaluate the five proposed scenarios, we prepared a set of hypotheses to show the relationship between the human-caused alterations in the defining physical characteristics and the resulting losses of ecological sustainability in these wetlands (Lake Okeechobee to Florida Bay). Each scenario is evaluated on its capacity to recover the predrainage
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conditions for each of the defining physical parameters. It is assumed that each scenario will be developed with the management (operational) flexibility to allow for maximum recovery of the desired attributes, given that other spatial and physical constraints will prohibit full predrainage recovery in certain parts of the system. The following hypotheses are neither mutually exclusive nor an attempt to produce a comprehensive set of hypotheses that would address all ecological changes in the system. However, they do focus on the nature of the physical changes that have substantially altered the better understood characteristics of wildlife populations and community structure at regional and landscape scales in the predrainage Everglades system. The first three hypotheses describe causes for changes in the ecological characteristics of the regional wetland (South Florida) system. The remaining five hypotheses address ecological changes that have occurred within selected primary landscapes of the Everglades: (1) the Everglades marl prairies, (2) the Everglades freshwater sloughs, (3) the Big Cypress, (4) the mainland estuaries, and (5) Florida Bay. Empirical data and field observations that support each hypothesis are briefly summarized under each heading. Region-wide hypotheses Hypothesis 1: spatial extent The predrainage wetlands of southern Florida covered an area of 28,205 km2 , including 10,000 km2 of true Everglades (Light and Dineen,1994). This large spatial extent was essential (a) for the support of genetically and ecologically viable populations of species with narrow habitat requirements or large feeding ranges, (b) for the aquatic production necessary to support large numbers of higher vertebrates in a naturally nutrient-poor environment, and (c) to sustain habitat diversity created by natural disturbances and the regional patterns of topographical gradients and microtopography. We hypothesize that the loss of ecological sustainability, as characterized by these three factors, has been due to the reduction (∼50%) in the spatial extent of the predrainage true Everglades and the proportionally smaller losses in area in the Big Cypress subregion. Hypothesis 2: dynamic water storage The predrainage wetlands of South Florida were expansive interconnected hydrological systems characterized by an enormous capacity to collect and store water across multiyear time frames. Key components of the hydrological system were (a) the large water storage capacity in the peat soils, (b) the extremely slow flow rates associated with low topographical gradients and the density of the marsh vegetation, (c) the interconnection of flow within and across basin boundaries, (d) the strong connections between surface- and groundwater flows and levels, and (e) the large spatial extent of the combined basins (Interagency Science Subgroup, 1993; Smith, 1968; Stephens and Johnson, 1951). These components, by comparison with the managed system, created a wetter and more expansive system that maintained relatively higher, more consistent levels of estuarine production, assured the production and survival of fishes and aquatic invertebrates in the central sloughs during seasonal and interannual wet and dry cycles, and held groundwater levels sufficiently high to preserve the animal survival function of the solution hole ponds (Davis, 1943).
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The substantially reduced water storage capacity of the South Florida wetlands has occurred because of the loss of peat soils through oxidation (Stephens and Johnson, 1951), the storage limitations set by policy and structural limitations, the reduced total area of the systems, and the more rapid conveyance of water made possible by pumps and canals (Light and Dineen, 1994). This lost capacity has caused regionally drier conditions and loss of natural patterns of interannual variability in water depth and distribution. These changes, largely responsible for system-wide collapses in predrainage levels of production and survival of organisms, also affect the availability of prey to larger aquatic vertebrates in the correct locations and at the proper times of the year when compared with traditional reproductive and feeding patterns (Holling et al., 1994; Interagency Science Subgroup, 1993). Hypothesis 3: sheet flow Compartmentalization of the remaining Everglades into a series of Water Conservation Areas (WCAs) has substantially disrupted long-distance sheet flow through the marshes by impounding water and diverting it into fast-flow canal systems (Light and Dineen, 1994). The reduction in sheet flow, combined with management-induced moderations in interannual variability in hydropatterns, has been a major contributor to regional changes in natural patterns of nutrient cycling and flow. The addition of unnatural concentrations of nutrients (Walker, 1991; Waller and Earl, 1975), caused by the rapid distribution of agricultural waters by means of the internal canal systems, has altered the concentrations and biological roles of nutrients in the remaining wetlands (Urban et al., 1993; Toth, 1988). These changes in nutrient patterns are a contributing factor in the decrease of primary and secondary production and in the loss of the production pulses that supported the formation of the larger wading bird nesting colonies. Supporting studies Loss of habitat options and the reduction in regional levels of production can be inferred from the overall decrease in area of the Everglades system and the loss of significant portions (and in some cases all) of the major landscape features. Gunderson and Loftus (1993) reported that approximately half of the original Everglades has been converted to agricultural (28%) or urban (12%) uses, or to nonfunctional, drained sites (8%). Three landscape features of the original Everglades have been completely lost: (1) a swamp forest along the southern border of Lake Okeechobee, (2) a cypress forest along the eastern boundary of the Everglades, and (3) a system of wet prairies paralleling the eastern Everglades. A large part of a fourth landscape (the vast sawgrass plain across the northern Everglades) has been greatly reduced as a result of these conversions (Davis et al., 1994). Studies have shown that changes in hydrological patterns and water quality have further reduced the caliber of remaining wetlands. Over-drained marl prairies have been invaded by both native woody species and exotic plants (Egler, 1952; Ewel et al., 1982; Myers, 1983; Olmsted et al., 1980; Wade et al., 1980). Tree islands have been lost in WCA-2A (Worth, 1987), sawgrass marshes have decreased in the southern end of WCA-3A, a significant loss in area in the spikerush slough community has occurred (Davis et al., 1994), and mangrove forests have advanced landward over the past 50 years (Lorenz and Harrington, 1995). Relatively minor shifts in water quality, particularly when nutrient concentrations increase
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above natural levels, may have substantial impacts on species composition in the algal periphyton mats, which in turn may alter primary and secondary production in freshwater marshes (Browder et al., 1982). Greatly reduced annual hydroperiods have substantially decreased the production and survival of fishes and aquatic invertebrates in both slough and marl prairie habitats (Loftus et al., 1990, 1992; Loftus and Eklund, 1994). Further, Loftus and Eklund (1994) have shown how strong seasonal and annual variations in water depth provide a mechanism for collecting and concentrating fishes, and that this decrease in depth pattern results in the loss of a prey base for foraging wading birds. Craighead (1968) reported that the over-drainage of the marl prairies, coupled with higher salinities in the mainland estuaries, served to translocate the major alligator nesting habitat to the central sloughs. Mazzotti and Brandt (1994) documented how poorer habitat conditions for alligators in the managed sloughs may be responsible for overall lower growth rates, higher mortality rates, smaller clutch size, and reduced nesting frequency. Several studies have shown the adverse effects of regional changes in hydrological patterns on the quantity and quality of habitat for animals with large spatial requirements. That many of the larger vertebrates in the Everglades forage and reproduce in different locations and at different times, depending on seasonal and interannual differences in water depth and drying patterns, was demonstrated by Bancroft et al. (1994), Bennetts et al. (1994), Hoffman et al. (1994), and Kushlan (1979). The availability of suitable habitat is substantially reduced and/or disrupted by losses in natural hydropatterns. For example, Bancroft et al. (1994) and Frederick and Spalding (1994) showed that wading bird colony success rates are reduced when compartmentalized water management pools result in either unpredictable or reduced foraging site options. Ogden (1994) suggested that a major cause for the abandonment of traditional colony sites in the southern Everglades was the redistribution of long-hydroperiod pools associated with the creation of the WCAs in the central Everglades. Landscape-level hypotheses Hypothesis 4: Everglades marl prairies The relatively higher elevation, shorter hydroperiod (3–8 months) marl prairies that broadly flank the lower Everglades sloughs were characterized by high densities of shallow ponds (solution holes) and expansive areas of relatively sparse sawgrass- and muhly grass– dominated communities (Cladium jamaicense and Muhlenbergia filipes, respectively). These ponds, as habitats, were among the more important within the total Everglades system for alligators, were essential dry-season survival areas for such diverse animals as otters, turtles, frogs, and fishes, and provided important foraging tracts for wading birds during both early dry seasons and high water conditions. The wet prairies were an essential habitat for the endemic Cape Sable seaside sparrow. Collapse of alligator, otter, and other dependent populations of animals, loss of wading bird foraging habitat, and threats to the survival of the Cape Sable seaside sparrow were caused by (a) drainage and development of significant areas within the marl prairies, especially along the southeastern flanks of the southern Everglades; and (b) substantial reduction in annual hydroperiods and water depths, including the complete loss of surface water in
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some areas, across much of the remaining marl prairie landscape. These alterations in hydrological patterns caused the loss of soil due to increased intensity of fire and elevated rates of oxidation, the destruction of most solution hole systems following the abandonment of these sites by alligators, and the degradation of marsh communities from invasions by woody plants. Hypothesis 5: Everglades peat sloughs The relatively lower elevation, longer hydroperiod (9–12 month) peat sloughs, including the broad Shark River Slough, were characterized by complex marsh mosaics, dominated by sawgrass, spikerush (Eleocharis cellulosa), white water lily (Nyphaea odorata), and arrowhead/pickerel weed (Pontederia lanceolata) communities. These long-hydroperiod wetlands, which were the principal production and survival sites for freshwater fishes and aquatic invertebrates, frogs, limpkins, grebes, and snail kites, provided the most important mid– and late–dry season foraging habitats for the large nesting colonies of wading birds in the predrainage system. The deeper sawgrass marshes of the northern and central Everglades were principal water storage and nutrient collector systems in the predrainage wetlands. Substantial reduction in the species of aquatic vertebrates characteristic of the sloughs, collapse of the large wading bird nesting colonies, and alterations in patterns of primary and secondary production were caused by (a) significantly lower water storage capacity throughout the peat sloughs, (b) increased frequencies of landscape-wide droughts, (c) moderation in interannual water depth patterns, and (d) phosphorus enrichment of marsh communities. These altered hydrological patterns, both in quantity and quality, have disrupted the organizing effect of flood and drought cycles on primary and secondary production, changed the species composition of the periphyton mats, and reduced the survival of aquatic invertebrates and fishes. Hypothesis 6: Big Cypress The expansive freshwater swamps of southwestern Florida consisted of narrow sloughs (strands) of bald cypress (Taxodium ascendens) and swamp hardwood forest, separated by wet prairie and pond cypress (Taxodium ascendens) communities, with pinelands and hardwood hammocks on the more upland sites. The forested sloughs were characterized by organic soils and long hydroperiods, while the intervening prairies had marl soils and shorter hydroperiods. This subregion of the South Florida wetlands, a primary habitat for panther, deer, wild turkey (Meleagis gallopavo), and red-cockaded woodpeckers, contained the largest wood stork (Mycteria americana) nesting colonies in Florida and once was populated by small numbers of the now-extinct ivory-billed woodpecker (Campephilus principalis). Although the Big Cypress landscape is relatively less disturbed than other South Florida wetland landscapes, disruption of surface-water patterns along the Everglades–Big Cypress ecotone has adversely altered the distribution of flow across the northern and eastern cypress and reduced the volume of water into the downstream estuaries. Development (Golden Gate) on the western flank of the Big Cypress similarly disrupted flow and lowered groundwater in that area. These hydrological changes reduced stork nesting at the Corkscrew and Sadie Cypress colony sites by more than 90% and caused the collapse of wading bird nesting in estuarine colonies between Chokoloskee Bay and Lostman’s River.
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Hypothesis 7: mainland estuaries The broad, mainland estuarine swamps bordering northern Florida Bay and the southwestern Gulf coast, in the lower reaches of the Everglades and Big Cypress basins, were characterized by a complex mosaic of mangrove-dominated forests and numerous streams draining the interior Everglades and Big Cypress systems, coastal prairies, ponds, and lakes. This landscape, an essential production and nursery ground for estuarine and marine fishes and invertebrates, including pink shrimp, provided essential foraging habitat for wading birds (especially important for wood storks and roseate spoonbills) during the early and mid–dry season months and supported large numbers of nesting alligators (inland portions) and a large majority of the resident population of American crocodiles (north of Florida Bay). Decline in pink shrimp harvests and total number of alligators, collapse of all southern Everglades stork nesting colonies and several northeastern Florida Bay spoonbill colonies, and invasion of mangroves into marsh communities, ponds, and streams have been caused by substantial reductions in the total flow of freshwater into these mainland estuaries. Reduction in freshwater flow caused (a) decline in primary and secondary production in these estuaries, (b) reduction in inflow of natural nutrients, (c) compression in the spatial extent of the potentially most productive low-salinity zone, and (d) increase in the range and rate of salinity change, to the point where conditions exceed the physiological tolerances for some plant and animal species. Hypothesis 8: Florida Bay Florida Bay is a subtropical estuarine lagoon located immediately downstream from the southern Everglades system. The bay consists of a patchwork of broad shallow “lakes” separated by narrow, tidally flooded marl embankments and broad marl flats scattered with small forested islands. The bay, a primary nursery ground and foraging habitat for sportfish, spiny lobster (Panulirus argus), and sea turtles (Caretta caretta), also has provided nesting and feeding habitats for American crocodiles (Crocodylus acutus) and estuarine species of wading birds [great white heron (Ardea herodias), reddish egret (Egretta rufescens), roseate spoonbill (Ajaia ajaia)], brown pelican (Pelecanus occidentalis), bald eagle (Haliaectus leucocephalus, and osprey (Pandion haliaetus)]. Expansive areas of algal blooms, die-offs of turtle and widgeon grass beds (Thalassia testudinum and Ruppia maritima, respectively), and major declines in nesting populations of brown pelicans and osprey have been caused by significant reduction in the volume of freshwater entering the bay from the Everglades and by increased frequency of hypersaline conditions in the bay and in the upstream, mainland estuary. Supporting studies Loftus et al. (1992) and Van Lent and Johnson (1993) demonstrated that depth and duration of surface-water flooding and the level of groundwater in the eastern Everglades marl prairies have been greatly reduced as a result of water management practices in this region. These authors characterized surface-water conditions from 1962 to 1968 at three long-term gauges located in the eastern marl prairies as having changed from previous years as follows: (1) reduction in average peak wet-season levels of between 21 and 56 cm; (2) decrease in average dry-season levels ranging from 24 to 35 cm; and (3) shift in the timing of the maximum wet-season level to a month earlier than that recorded
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prior to 1962. These changes resulted in earlier and longer loss of surface waters in these prairies. Loftus et al. (1992) hypothesized that survival of aquatic invertebrates and fishes in the higher elevation marl prairies depended on sufficiently elevated groundwater levels during dry seasons to maintain water in solution and alligator holes. Craighead (1968) reported that alligators were common to abundant in the marl prairies prior to the time when this area was over-drained. When surface- and groundwater levels were higher in the prairies, waterfowl and wading birds were more widespread than they are now. Pimm (1995) suggested that woody plant invasions into the marl prairies, associated with reduced hydroperiods, caused the degradation of Cape Sable sparrow nesting habitat. Fennema et al. (1994) showed that the location of the deeper pools in the Everglades sloughs has shifted from the Shark River Slough to the WCA impoundments as a result of water management practices. Further, the Shark River Slough has experienced shortened hydroperiods and more frequent episodes of expansive drying during the recent management period. Browder et al. (1994) suggested that strong representation by species of green algae and diatoms in the periphyton mats of the freshwater sloughs is correlated with long hydroperiod and pristine water quality. The green algae/diatom communities are thought to be more important in the support of aquatic food chains in the Everglades system than are the blue-green algal communities, which are characteristic of shortened hydroperiods and areas of degraded water quality. Loftus and Eklund (1994) showed that the longer annual hydroperiods, characteristic of the predrainage Shark Slough, are necessary for interannual increases in populations of freshwater fishes and macroinvertebrates. Ogden (1994) proposed that alterations in surface-water patterns and primary and secondary production in the lower Shark Slough caused the collapse of the “super colonies” of nesting wading birds and the relocation of the smaller, remaining colonies into the WCAs. Robertson and Frederick (1994) suggested that the WCAs may be population sinks for wading birds that still nest in the Everglades. An overall effect of water management practices in the southern Everglades has been to reduce the total flow of freshwater into the mainland estuaries and Florida Bay (Fennema et al., 1994; Van Lent and Johnson, 1993). Browder (1985) showed a relationship between increases in freshwater flow into the mainland estuaries and resurgence in pink shrimp harvests on the Dry Tortugas fishing grounds. Lorenz and Harrington (1995) reported a correlation between the total flow into the mainland estuaries and the density and numbers of fish at study sites in the lower Taylor Slough and C-111 basins. They also reported a 4-km migration of the inner edge of the scrub mangrove zone inland in the area east of lower Taylor Slough since the 1970s, apparently the result of reduced freshwater flow. Craighead (1968) reported that the inner estuarine system, a region he referred to as the “freshwater mangrove swamps,” was a major alligator habitat in the predrainage Everglades system, and he hypothesized that alligator numbers are greatly reduced in this landscape because of increased salinities. Ogden (1994) suggested that the disappearance of nesting by egrets, herons, and ibis (Eudocimus albus) at numerous colony sites north of Lostman’s River, and the collapse of once large summer roosts of ibis in the same area, may result from decreased production in the estuaries downstream from the southern Big Cypress, caused by reduced freshwater flow into these estuaries.
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Bjork and Powell (1993) showed an increased level of sensitivity by nesting roseate spoonbills in northeastern Florida Bay to surface-water conditions in the mainland estuaries north of the Bay. The collapse of spoonbill nesting colonies in the northeastern Bay almost certainly has been caused by the overall effects of water management practices on the production and availability of prey in these estuaries. Ogden (1994) has proposed that the demise in wood stork nesting in the southern Everglades is largely caused by reduced levels of primary and secondary production in the mainland estuaries, a result of reduced freshwater flow. Boesch et al. (1993) identified decreased freshwater flow in the southern Everglades as one of the major factors contributing to the substantial ecological deterioration of the large Florida Bay estuary. McIvor et al. (1994) presented a hypothesis that the sudden, wide fluctuations in salinity, characteristic of a managed system, serve to inhibit development of abundant seagrasses and thus reduce the habitat quality for invertebrate and fish populations. Kushlan and Bass (1983) suggested that the rapid decline of nesting ospreys in Florida Bay has most likely been caused by food stress associated with changes in the bay. In addition, a decline in nesting brown pelicans in the bay has coincided in time and magnitude with that of ospreys (Kushlan and Frohring, 1985). Both species have shown significant increases in regional populations in almost all parts of Florida outside of the bay, which historically has been their primary feeding ground. Regional-scale management scenarios The US MAB team created a series of potential regional-scale management scenarios for recovering a sustainable ecosystem and evaluating effects on human and ecological systems (Harwell et al., 1996). The potential suitability of these scenarios is best evaluated if they differ in the spatial scale of their core and buffer areas and in their land use and water management patterns. Therefore, scenarios with different spatial scales were grouped into those that (a) required only existing publicly owned wetlands in the Everglades basin; (b) expanded existing publicly owned wetlands to include contiguous privately owned wetlands that were part of the original Everglades; and (c) added to the combination of publicly and privately owned wetlands those privately owned lands that would be required to maximize the recovery benefits for the total wetland area. All scenarios are designed with different combinations of core and buffer areas, based on the US MAB Biosphere Reserve concept of areas with different levels of protection and control (Harwell and Long, 1992). Core areas are defined as wetlands that can be managed principally to achieve full recovery of the defining ecological characteristics of the predrainage Everglades. Buffer areas can be either wetlands or nonwetlands, serving primarily as support systems to the core areas and only secondarily managed for direct ecological benefits. Uses for these areas include water storage and supply (both for the core areas and developed regions), flood protection for adjacent urban or agricultural regions, enhancement of water quality, and preservation of higher water stages in adjacent natural wetlands. To evaluate whether the existing core Biosphere Reserve (i.e., Everglades National Park) is spatially adequate for meeting the ecosystem sustainability goal, Scenarios A and B were examined at two levels. Level 1 in each of these two scenarios designates the existing
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Biosphere Reserve as the core area, while Level 2 greatly expands the core area to include much of the remaining natural wetlands in the Everglades/Big Cypress region. The following scenarios provide incremental changes in land use and water management practices starting with Scenario A1 and culminating with Scenario C3. Professional judgment is used to evaluate the hydrologic implications of these scenarios, since the modeling that provides a quantitative basis for evaluation is currently incomplete. In addition, all scenarios assume that changes in Lake Okeechobee operational criteria are needed to reduce the discharge of surplus water to the coasts and to maintain the more natural seasonal lake stages. This would increase water releases into the Everglades and result in a healthier lake littoral zone. The challenge is how to achieve these modifications without losing the current capability for flood control. Scenario A This scenario considers all publically owned existing and former wetlands that are part of the greater Everglades basin as the maximum boundary of the region. Included within this category are the Everglades National Park, Big Cypress National Preserve, Florida Keys National Marine Sanctuary, Loxahatchee National Wildlife Refuge, Lake Okeechobee, and the Water Conservation Areas, and all authorized additions to these units. The first version, Scenario A1 (figure 1), limits the core area to the existing Biosphere Reserve (Everglades National Park), and would use the remaining public wetlands as buffer areas to ensure that desired hydrological patterns are recovered in the core area to maximize ecosystem restoration and to meet other water supply requirements for the region. This scenario would remove levees, thus providing more natural overland flow in the northern core area, a benefit currently realized only during wet periods. The second version, Scenario A2 (figure 2), would expand the core area (and Biosphere Reserve boundaries) northward to include WCAs 1, 2A, 2B, 3A, and 3B. The remaining areas, primarily Lake Okeechobee, would serve as buffers. Structural changes, in addition to those in Scenario A1, include the removal of levees separating WCA 1 from 2, 2A from 2B, 2 from 3, and those along the Miami Canal alignment. The levees forming the eastern boundaries of the WCAs would remain intact to provide flood control. This scenario provides limited storage that will help extend dry-season hydroperiods and utilizes buffer areas to create a small area of transitional wetlands for water purification. However, given the limited space made available in buffer areas, tradeoffs among water storage, water treatment, and restoration of wetlands will be necessary. Easterly seepage from the eastern boundary of the Everglades must be properly controlled to derive any benefit from these scenarios. Scenario B This scenario utilizes not only existing publicly owned wetlands in the Everglades basin but also all contiguous privately owned wetlands as well (figures 1, 2). The added wetlands would include the Bird Drive Basin, Pensucco wetlands, Okaloacoochee Slough, and Golden Gate wetlands. To the extent possible, a buffer zone would be created along the eastern boundary of the WCAs connecting to the south with a second buffer area constructed as part of the C-111 project. Scenarios B1 and B2 parallel A1 and A2, respectively, in the location of core areas and in operational and structural changes.
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Figure 1. Scenario A1: Core area is limited to existing Biosphere Reserve (Everglades National Park), and remaining public lands are used as buffer areas to ensure that desired hydrological patterns are recovered. Scenario B1: expands core area (and Biosphere Reserve boundaries) to include Water Conservation Areas with Lake Okeechobee serving as a buffer area.
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Figure 2. Scenario A2: Core area is limited to existing Biosphere Reserve (Everglades National Park) and uses all publicly owned wetlands in the Everglades basin and adds all contiguous wetlands that are in private ownership as buffer. Scenario B2: expands core area (and Biosphere Reserve boundaries) to include Water Conservation Areas and includes Lake Okeechobee, the private ownership wetlands that include the 8.5-mile east coast buffer along the Bird Drive Basin, and the Pensucco wetlands, the Okaloacoochee Slough, and Golden Gate wetlands.
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The primary feature present in both variations of Scenario B is the establishment of an eastern Everglades buffer/transition area within either public or acquired private wetlands along the eastern boundary of the WCAs. The proposed linear buffer strip immediately east of the eastern boundary of the WCAs is, in effect, a northward extension of the buffer strip provided by the planned public purchase of the Model Lands, the Frog Pond, and the Rocky Glades. This area could potentially serve multiple purposes, among them the storage of storm water runoff from the eastern developed areas, thus providing water for other developed areas, the Everglades, and Florida Bay. East coast canals could be operated so that these marsh and reservoir buffer systems would receive all or part of the large amount of storm water now being diverted to the coasts during the wet seasons, retaining that water to offset dry season water needs in the core area and Lower East Coast urban and agricultural areas. Under the natural historic system, much of the area being considered for a marsh/reservoir buffer system was part of the greater Everglades and contributed surface flow to such areas as Northeast Shark Slough and Taylor Slough. The establishment of a buffer area with adequate storage and water quality treatment would permit wet-season capture of the necessary water to reestablish sheet flow and water levels in some eastern wetlands of the Everglades that are now drained primarily to facilitate water management east of the Lower East Coast protective levee. With appropriate measures, the buffer area would potentially reduce the large amount of seepage under the levee from these wetlands by reducing surface water infiltration. Another major benefit of an interconnected buffer system consisting of marshes and detention reservoirs is the operational flexibility it provides. If the interconnected system is properly designed, it potentially would permit the movement of water from south to north and vice versa, giving operational options that are not available in the current system, the base condition, or Scenario A. The East Coast Linear Buffer Strip proposed in Scenario B adds a relatively small area to this system, but it significantly increases the short-hydroperiod wetland habitat that has been disproportionately lost due to economic development and associated drainage from the eastern edge of the Everglades system. Scenario C This scenario combines all existing wetlands included in Scenarios A and B and adds areas of former wetlands currently under private ownership. As a means of transferring buffer area functions (e.g., water storage and supply) out of existing wetlands (figure 3), Scenario C strengthens the buffer area along the eastern boundary of the current WCAs and allows for a more natural hydrological pattern in Lake Okeechobee. The majority of private lands incorporated by this scenario would be in the Everglades Agricultural Area (EAA). Although it establishes the same core area and structural changes as Scenarios A2 and B2, it assumes that some portion of the EAA will be needed for water supply, water storage, flood protection, and enhancement of water quality. Reinstating the natural dynamic storage capacity at the upper end of the Everglades basin and providing an adequate volume of dynamic water storage would enable reestablishment of a pre-drainage pattern of sheet flow, producing more historical hydroperiods and hydropatterns throughout the Everglades, and a more natural volume and timing of water flow into Florida Bay and other estuaries of ENP. However, this scenario also produces the greatest potential water loss from the system caused by evapotranspiration.
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Figure 3. Scenario C: This scenario combines all existing wetlands in Scenarios A and B and adds areas of former wetlands that are currently in private ownership.
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Scenario C best recreates the natural drainage pattern and hydrological function of the undeveloped lands south of Lake Okeechobee. The addition of water storage in the EAA will allow flexibility in utilizing Lake Okeechobee to balance the conflicting demands associated with flood control and water supply, as well as in addressing the environmental concerns associated with the lake’s littoral zone and estuaries. Ancillary storage located in the immediate headwaters of the core area will also permit additional improvement of hydroperiods throughout the core area. Depending on the area of storage, a similar improvement can be expected in the WCAs. Sections of these areas are frequently dry because of existing operational rules governing them. Most importantly, the additional water that may be available from this storage component may help create more desirable hydrological flows and patterns in all downstream systems. The extent to which this can be realized needs to be investigated through simulation modeling. Synopsis The large spatial extent of wetlands, dynamic storage, and sheet flow are key hydrologic features necessary for the recovery of a sustainable Everglades ecosystem. The desired hydrological regimes should not be artificially imposed but should be compatible with the terrain and biological communities and reflect natural patterns of intra- and interannual variability. Scenarios A, B, and C represent a range of possible land additions to core and buffer areas intended to meet spatial-scale requirements and to achieve different degrees of hydrological improvement. This evaluation is based on specific hydrologic characteristics for each scenario. It should be recognized that the hydrological advantages of one over another can ultimately be negated by engineering. Thus the second-level distinction in scenarios (e.g., B1 and B2) was developed in part to illustrate the uncertainty regarding the desired level of hydrologic restoration and to present a range of restoration alternatives. While all scenarios were regarded as contributing to the reestablishment of the key hydrologic characteristics, the relative contributions of each differ considerably. For example, the removal of internal barriers in Scenario A is expected to result in a more natural pattern of water flow through the system. However, the limited addition of buffer areas provides neither storage for flood control releases from Lake Okeechobee nor optimally located buffer areas that can easily discharge water as sheet flow to the northern part of the core area. In addition, the lake itself cannot improve hydroperiods because of two factors, insufficient water stored during the wet season and water loss incurred in the conveyance system. Scenario B, in which a buffer zone is created along the eastern rim of the WCA, can be expected to improve the conveyance and dynamic storage properties of the system. With proper control of seepage, this additional storage will benefit the water supply as well as wetland hydrology. Quantity and delivery of water to the eastern Everglades can be improved considerably; however, delivery to the northern core area is still a problem. Flood control releases from Lake Okeechobee to estuaries would still have to be made. The lake storage would make only a minor contribution to prolonging overland flow conditions because of delivery difficulties. In addition, there exists a limited capacity for treatment of water quality problems.
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Scenario C best exemplifies a restoration of the prolonged overland flow in the overall system. The increased dynamic storage capacity could eliminate harmful discharges to the estuaries from Lake Okeechobee and would reinstate a more natural volume and timing of flow throughout the system without causing damage to the littoral zone of the lake. A range of different hydroperiod wetlands, created because of the historic topography and drainage patterns, collectively would contribute to reestablishment of desired spatially heterogeneous vegetation patterns. We have assumed that the drained water discharged to tide could be recaptured. However, it is an undeniable fact that for close to 50 years the coastal estuaries have been the recipient of, and, in some cases, successfully adjusted to, these altered discharges, which have been estimated to be at least 5 to 10 times the quantity of runoff and groundwater flow occurring under natural predrainage conditions (Light and Dineen, 1994). Any diversion of runoff will have to be justified as a reasonable balance between the competing needs of estuaries, coastal urban water supply, the Everglades, and Florida Bay. Many years will pass before the research community will have the understanding needed to determine how best to apportion available water. As a restoration alternative, Scenario C has the added advantage of providing the most flexible and adaptive configuration for meeting the diverse needs of South Florida and consequently has now become the prototype for the Preferred Alternative Plan developed and adopted by the Florida Governor’s Commission for a Sustainable South Florida (Governor’s Commission, 1996; Harwell, 1997). Conclusions Each of the hypotheses describes one or more of the ecological changes that have occurred as a result of alterations in the defining physical characteristics of the South Florida wetland systems, contributing to the loss of sustainability for an Everglades-type ecosystem. In summary, the causes identified by the hypotheses were (1) reduced areal extent of wetlands and flooding, (2) shortened annual hydroperiods, (3) lowered surface and groundwater levels, (4) loss of sheet flow, (5) alterations in timing and location of flow and in pre-drainage surface-water distribution patterns, (6) moderations in the amplitude and interannual variability of seasonal and annual water-depth patterns, (7) reduced flow into the estuaries, and (8) modified patterns of nutrient transport and concentration. We have evaluated the five US MAB scenarios in terms of the ability of each to recover the defining characteristics of the predrainage Everglades. Our evaluations are intentionally qualitative to reflect uncertainties associated with the exact characteristics of each scenario and with the ecological responses one would expect in a wetland ecosystem that has been so greatly reduced in area. Our assessment of the scenarios shows that all five can mitigate the problems addressed by hypotheses 1–8, in that all could more effectively move increased volumes of water across broader expanses of contiguous wetlands than do existing management programs. This results in improved capabilities for longer hydroperiods over larger areas, increasing the spatial extent of flooding (Table 1). For these particular hydrological parameters, Scenarios A2, B2, and C are superior to A1 and B1, because of the considerable increase in area available for recovery to natural hydrological patterns. The B2 and C scenarios could be
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The ability of scenarios to mitigate the causes for loss of sustainability. Scenarios
Causes
A1
A2
B1
B2
C
Reduced areal extent of flooding
+
+++
+
+++
+++
Shortened annual hydroperiods
+
+++
+
+++
+++
Lowered surface and groundwater
+
+
+
+++
+++
Loss of sheet flow
+
+
+
+++
+++
Alterations in timing and distribution of water flows
+
++
+
+++
+++
Interannual variability of seasonal and annual water depth patterns
+
++
+
+++
+++
Reduced flows to estuaries
+
++
+
+++
+++
Nutrient enrichment
+
+
+
++
+++
more successful in increasing flows into Florida Bay and the Gulf coast estuaries because of several factors: the removal of inhibiting internal structures, the increase in spatial extent of the upstream areas that could be managed for natural hydropatterns, and the benefits derived from the addition of eastern boundary buffer zones, which could improve flow into the Taylor Slough basin. Scenarios B and C are superior to Scenario A for recovering natural patterns of seasonal and interannual amplitude in water depths, because the addition of an eastern boundary buffer zone allows for more natural water-depth fluctuation in the core areas. For this reason, Scenario C is superior to Scenario B because the eastern buffer is more continuous. Scenarios A2, B2, and C are preferred to the other scenarios for recovering more natural patterns of water depth and distribution. Because these scenarios remove internal levees and canals, and thus decompartmentalize the system more extensively over a wider/greater area, they more closely reflect the predrainage topographical features. Within these three scenarios, B2 and C are favored over A2 because of the added benefits that an eastern buffer zone can provide towards the goal of recovery of natural water depth patterns. Scenarios A2, B, and C possess increased ability to improve the water-storage capacity of these wetlands and the volume and seasonal timing patterns of flows. The potential for using Lake Okeechobee as a site for additional water storage (A2 and subsequent scenarios), followed by the addition of eastern buffer zones (B and C) and portions of the Everglades Agricultural Area (C), provides increasing levels of flexibility for gaining the storage capacity required to meet sustainability goals. Scenarios with maximum areas of buffer not only will be more successful in reducing groundwater seepage losses to the east but also will be more likely to reduce the level of nutrients and other contaminants entering the natural wetlands. Of these options, Scenario C would provide the highest level of protection, because it couples the buffers created in the EAA with those along the eastern boundary of the core area. Scenarios B2 and C would provide the maximum level of improvement in nutrient patterns by shifting more of the total flow from canals to sheet flow in the marshes.
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Uncertainty At least three types of uncertainty can be recognized in the assessment of sustainability and the determination of preferred restoration scenarios. The first is quantifiable uncertainty, which addresses a fairly reasonable understanding of factors involved and the relationships among these elements. In an experiment as broad as seeking sustainability in the South Florida wetland systems, very little of the uncertainty is definable. Certain key uncertainties in both hydrologic (e.g., overland flow coefficients, evapotranspiration) and ecological models (parameterization of key coefficients) are of this type. A second type of uncertainty is knowable or imaginable, in which key factors are thought to be known but tend to interact in unpredictable ways. Among the imaginable uncertainties are the presence of time lags and unforeseen interactions among key variables. Time lags will likely exist between restoration of hydrology and any biotic response. Some of the lags are attributed to other changes in the systems that have occurred (e.g., loss of soil or loss of refugia), while other biotic factors such as rates of movement may also slow recovery. A great deal of uncertainty exists as to the response of biota to interactions among key variables. For example, the interaction between mercury releases and hydrologic regime, or sea-level changes and freshwater flow, are only speculative at this time, yet these relationships may have dramatic effects on biota. Other unforeseen interactions could include the influence of exotic organisms, linkages between water quantity and quality as greater volumes of water are sought outside of core wetlands, and the effects of key structuring processes such as hurricanes, storms, fires, and hydrologic regimes. All of these examples suggest that the targets of sustainability will not only be moving but are themselves likely to be changed. The third type of uncertainty is inherently unknowable, where the systems behave in ways never imagined or previously experienced. A great deal of uncertainty is unknowable. The above two paragraphs have proposed uncertainties in both the nature of factors and the models developed to assess how these factors are likely to interact. There undoubtedly will be changes in the conceptual models themselves, as more is learned. Therefore, the interventions (scenarios) that produce the most understanding are the ones that help us test the broadest set of hypotheses. Monitoring Ecological sustainability in the South Florida wetlands will be achieved when the physical defining characteristics of the system have been recovered and sufficient time has passed for recovery and maintenance of the ecological systems. Determining when this goal will be achieved depends on information produced by a permanent ecosystem-wide monitoring program. The goal of recovering both the predrainage patterns of habitat heterogeneity within and across landscape scales and the sustainable populations of the characteristic native wetland species of vertebrates provide the framework for designing an appropriate monitoring protocol. The hypotheses developed to explain why these and other ecological and biological components have been lost also identify the physical characteristics of the systems that have been altered to the point where ecological sustainability no longer occurs. At the ecosystem scale, both the physical components and the ecological components of
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these ecosystems must be monitored to provide a measure of the level of recovery towards sustainability. To verify information derived from the ecosystem-level monitoring program, additional measures must be implemented to assess ecological attributes at lower scales. The US MAB HDS ecology workshop (Harwell and Long, 1992) identified ecological endpoints for a sustainable ecosystem at the landscape, community, and habitat scale. A comprehensive monitoring program that would unequivocally measure ecosystem-wide responses must include a spectrum of components at each scale of the system. The most important application of the information derived from this program would be as input to the adaptive assessment process. Each phase in the implementation of the elements of a recommended recovery scenario would be evaluated and could lead to potential refinements in subsequent phases, depending on interpretations of ecological and hydrological monitoring data. These issues, a discussion of the relationships among societal goals for sustainability, endpoints to characterize ecological health, and specific measures to be monitored, are addressed at length in M. Harwell et al., this volume. Acknowledgments This article is contribution number US MAB HDS 054 of the U.S. Man and the Biosphere (US MAB) Human-Dominated Systems Directorate (HDS) Series. Funding for this study was provided, in part, by the US MAB Program (Grant #1753100110). US MAB is administered by the U.S. Department of State as a multiagency, collaborative, interdisciplinary research activity to advance the scientific understanding of human/environment interactions. Additional funding was received from the U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS (Contract #DACW 39-94-K-0032) and the U.S. Department of Commerce/National Oceanic and Atmospheric Administration (NOAA) through a UM/NOAA joint research project funded by the NOAA Coastal Ocean Program as part of the University of Miami-NOAA Cooperative Institute for Marine and Atmospheric Studies (CIMAS NA67RJ0149: Task 3 Coastal Ocean Ecosystems Processes). This article does not necessarily represent the policies of US MAB, the U.S. Department of State, any member agency of US MAB, the U.S. Army Corps of Engineers, or the U.S. Department of Commerce/NOAA. We would also like to acknowledge the support of the South Florida Water Management District (SFWMD), and in particular Cal Neidrauer and Randy Van Zee of the Hydrologic Systems Modeling Division. References Allen, R.P. (1936) The flock movements of herons, egrets and ibises. National Audubon Society, Tavernier, FL. Unpublished manuscript. Bancroft, G.T. (1989) Status and conservation of wading birds in the Everglades. American Birds 43, 1258–1265. Bancroft, G.T., Jewell, S.D. and Strong, A.M. (1990) Foraging and Nesting Ecology of Herons in the Lower Everglades Relative to Water conditions. Final report. National Audubon Society, Tavernier, FL. Bancroft, G.T., Strong, A.M., Sawicki, R.J., Hoffman, W. and Jewell, S.D. (1994) Relationships among wading bird foraging patterns, colony locations, and hydrology in the Everglades. In Everglades: The Ecosystem and Its Restoration (S.M. Davis and J.C. Ogden, eds.), pp. 615–657. St. Lucie Press, Delray Beach, FL.
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