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Florida Bay Research Programs and their Relation to the Comprehensive Everglades Restoration Plan Executive Summary Purpose This report evaluates scientific components of the Florida Bay studies and restoration activities that potentially affect the success of the overall Comprehensive Everglades Restoration Plan (CERP). Specifically, this report deals with scientific aspects of Florida Bay that feed back to the Everglades components of the CERP and are integral to the success of the overall restoration plan. It summarizes the science needed to determine potential long-term effects of Everglades restoration on the nature of the Bay. It is not intended to be a comprehensive review of the peer-reviewed literature on Florida Bay. The Florida Bay and Adjacent Marine Systems Science Conference (Key Largo, April 2001) was a major stimulus for this report. Many of the CROGEE members attended the conference and participated in discussions with researchers working on Bay issues. This report is based on those discussions, reviews of poster presentations and abstracts from the conference, and an independent evaluation of pertinent peer-reviewed literature. Description of the Bay Florida Bay is a large, shallow marine ecosystem immediately south of the Everglades. It may be thought of as the marine extension of the Florida peninsula, beginning where the gently sloping land surface of the southern Everglades descends below sea level. It is bounded on the east and south by the Florida Keys and on the west by the Gulf of Mexico. It covers about 850 square miles (2200 square kilometers), mostly within Everglades National Park and the Florida Keys National Marine Sanctuary. It is dotted with several hundred small, mangrove-rimmed islands. The average depth of Florida Bay is less than one meter and it is generally well mixed vertically. Shallow carbonate banks divide it into semi-isolated basins that restrict circulation, especially in the central and eastern zones. Its salinity is a function of direct rainfall and evaporation, inflow of Gulf of Mexico and Florida shelf water across its open western boundary, inflow of fresh water into the northeastern Bay by sheetflow and creeks fed by Taylor Slough and the C-111 canal (a major water conveyance canal, now intentionally blocked and the levees removed, on the southeast edge of Everglades National Park), outflow through the Keys to the southeast, and saline groundwater discharge. Cells of hypersaline water are common during the dry season. For at least several decades until the late 1980s, clear water and dense seagrass (largely Thalassia testudinum, commonly known as turtle grass) meadows characterized most of Florida Bay. However, beginning around 1987, the turtle grass beds began dying in the central and western Bay, for reasons that remain uncertain and controversial. Water in the central and western Bay, which had been clear during recent decades, has become turbid because of phytoplankton blooms (which can also cause fish kills by consuming dissolved oxygen and releasing toxins) and sediment resuspension. A decline in fishing
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Florida Bay Research Programs and their Relation to the Comprehensive Everglades Restoration Plan success for some species that use the Bay as a juvenile nursery habitat also was reported during that period. Florida Bay is linked intimately to the Everglades. Some of the water draining from the Everglades through Taylor Slough/Craighead Basin flows directly into Florida Bay, supplying it with freshwater runoff. Additional water from the Everglades appears to reach the Bay indirectly after it is discharged from Shark River Slough to the northwest and mixes with inshore shelf water. The Everglades has been altered greatly during the past century, including the construction of canals, levees, pumps and control structures, and conversion of land to cities and farms. This has led to water quality degradation, nutrient enrichment, loss of wetlands, and landscape fragmentation in various parts of the Everglades. Florida Bay is included in the CERP through the Florida Bay & Florida Keys Feasibility Study (FBFKFS), which is to be conducted to assess the current conditions of the Bay and to determine the modifications needed to restore it. Research in Florida Bay is carried out by many academic and governmental institutions. One of the most important of these is the Florida Bay and Adjacent Marine Systems Science Program, formed by state and federal agencies having regulatory and/or scientific interest in this region. Potential Effects of the CERP on Florida Bay An important assumption often made by scientists and managers associated with the CERP, and by the public, is that the increased flows of water deemed necessary to restore habitats in the Everglades also will contribute to the restoration and enhancement of Florida Bay. This is because increasing frequency, severity, and duration of hypersaline conditions in parts of the Bay, and a decrease in the spatial and temporal extent of estuarine conditions, are thought by some scientists to have been major factors leading to a dramatic die-off of turtle grass around 1987. For a number of reasons, these assumptions may not be correct. First, the evidence linking the turtle grass die-off to hypersalinity is equivocal and there is little agreement within the Florida Bay research community that this was the causative factor of the die-off. Second, direct, fresh surface water flow into northern Florida Bay (i.e., via Taylor Slough and Craighead Basin, etc.) is predicted to be about the same in 2050 relative to the current condition whether the CERP is implemented or not. If this is correct, there will be little effect on salinities in central Florida Bay and no relief to any associated ecological problems that may exist. On the other hand, recent research suggests that some percentage of the proposed significant increase in fresh surface water flow through Shark River Slough will ultimately reach the central Bay by passing across the western boundary of the Bay after mixing with shelf water. It also is not clear how, or if, the CERP will affect the magnitude of groundwater fluxes to Florida Bay. At present, the freshwater-saltwater interface in the surficial aquifer system is inland of the Bay. However, if the CERP raises overall water levels in the southern Everglades, this interface may be pushed southward over time toward Florida Bay in certain areas along the coast, and could result in fresh groundwater discharge directly to the Bay. Even if the direct discharge remains saline, changes in the quantity of groundwater inputs may be important to nutrient fluxes in some parts of the Bay. In addition to the uncertainties concerning the amount of fresh surface and groundwater that may enter Florida Bay because of the CERP, it is possible that an increase in water would also bring an increase in nutrient inputs. If this is the case, the biological and ecological effects of such an increase in nutrient loadings are unclear. While there is a broad scientific consensus that the growth of phytoplankton of eastern Florida Bay and seagrasses throughout the bay is phosphorus-limited, there is less agreement about the relative importance of nitrogen and phosphorus in limiting the growth of phytoplankton and macroalgae in the central and western Bay. Florida Bay phytoplankton blooms appear to develop where nitrogen-enriched water from the eastern Bay and from land drainage mixes with relatively phosphorus-rich water of the western/central Bay. Thus, the higher natural or anthropogenic loadings of nitrogen and, perhaps, phosphorus that may
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Florida Bay Research Programs and their Relation to the Comprehensive Everglades Restoration Plan accompany increasing freshwater fluxes from Shark River Slough could potentially increase the frequency, intensity, and duration of phytoplankton blooms in regions of the Bay where these waters mix. Once generated, such blooms may be spread over larger areas within the Bay or be carried through the Keys to the coral reefs. Complicating the analysis of such issues is the lack of a circulation model for Florida Bay to link the hydrodynamic and ecological response of Florida Bay to changes in Everglades hydrology and to provide decision support and analysis tools to restoration planners. Such a model needs reliable information on water and nutrient fluxes, and a good linkage to models of the Everglades proper. Findings and Recommendations Because the CERP is an ambitious and comprehensive enterprise, with a long time horizon, it is critical that the CERP be responsive to new information as it becomes available from the extensive ongoing research and monitoring programs throughout south Florida. The assumption of a fresher and “healthier” Florida Bay because of the CERP is a case in point that should be reexamined. Major considerations leading to this position are as follows. (1) Although it remains debatable how much new freshwater flow will enter the Bay proper because of the CERP, recent physical observations demonstrate that there is commonly a hydraulic connection, albeit with seawater mixing and a time lag, between Shark River Slough discharge and the interior of Florida Bay. (2) Some fraction of the DON (dissolved organic nitrogen) that would accompany increased freshwater flows from the Everglades will likely be available, either directly or indirectly, to support undesirable algal blooms within Florida Bay. (3) Enhanced blooms of phytoplankton and/or macroalgae may reduce seagrass cover and expose sediments to resuspension. Such resuspension will increase turbidity within the Bay and contribute to additional seagrass loss. The scientific evidence suggesting that the CERP, as proposed, will affect the marine environment in ways that are not fully understood, and that may be perceived as undesirable, is sufficiently persuasive that the issue should be the subject of a focused technical review and evaluation. This review should be carried out as an early activity within the FBFKFS so that the conclusions can have an influence on early stages of Everglades restoration planning. The results of this analysis need to be evaluated by resource managers and planners of CERP so that appropriate consideration and management actions can be taken. The importance of this issue has been recognized by some members of the Florida Bay and CERP research communities, and several projects are underway or will soon begin that will be helpful in addressing it. Research in the following areas is particularly important: Some components of the water budget for the Bay are poorly known, but understanding these fluxes is critical for evaluating the water quality in the Bay. In particular, estimates of groundwater discharge to the Bay differ by many orders of magnitude. Although this discharge is saline it may be a significant source of nutrients. Moreover, the higher water levels produced by the CERP may affect the magnitude of these fluxes and, in extreme cases, may result in direct discharge of fresh groundwater to the Bay. Also of importance to both salinity and nutrient fluxes is a full characterization and quantification of surface runoff in the Taylor Slough, Craighead, and Shark River Slough basins, including the seasonality of flow. Diffuse seepage through the Buttonwood Embankment should also be investigated. On the basis of modeling, annual freshwater flows through the Taylor Slough/Craighead Basin region to Florida Bay will be about the same in year 2050 under the expanded CERP scenario D13R4 compared to the simulated current condition. At the same time, annual freshwater flow through Shark River Slough, some of which migrates to the Bay indirectly and with a time lag, is projected to increase by almost 80%. The effects on nitrogen and phosphorus fluxes of increasing this freshwater need to be quantified.
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Florida Bay Research Programs and their Relation to the Comprehensive Everglades Restoration Plan Total loads of nitrogen and phosphorus from freshwater sources should be estimated as accurately as possible. A better understanding of the transport, bioavailability, and rates of transformation of DON and DOP (dissolved organic phosphorus) into forms that can be used by algae and macroscopic aquatic plants is needed to provide insight into the effects of increases in nutrient-bearing freshwater flows to the Bay. Quantifying the magnitude of nutrient loadings by source (e.g., organic soils oxidation, urban and agricultural runoff, and regional atmospheric deposition) also will become relevant if steps to reduce nutrient loading to the Bay become necessary. A historical characterization of the Bay’s water quality would be very useful for a perspective on restoration goals. Such a characterization would be based on anecdotal as well as any scientific information available. Currently there is no Florida Bay circulation model suitable for research and management purposes, although there are several candidates; such a model is essential to support a Bay water quality model and thus facilitate analysis of CERP effects on the Bay. The difficult and time-consuming tasks of selection, development, and application of a circulation model and water-quality model for the Bay should be key components of the FBFKFS. To evaluate the effects of CERP on Florida Bay, there must be a linkage of the output of the South Florida Water Management Model (SFWMM), which has a southern boundary of the mangrove zone, and input to the Bay models. One possibility for bridging this gap is the U.S. Geological Survey’s (USGS) Tides and Inflows in the Mangroves of the Everglades (TIME) model; another is the similarly structured South Florida Water Management District (SFWMD) South Florida Regional Simulation Model (SFRSM). Both models are still under development. The USGS, SFWMD, and Corps of Engineers have not reached consensus on how to effect the interfacing of hydrologic modeling and circulation modeling, and both the USGS and SFWMD modeling efforts are proceeding without such an agreement. An interagency agreement on which model will most usefully serve as an interface between landside hydrologic and Bay hydrodynamic modeling is needed. Estimates of the influence of the CERP on Florida Bay should also be inferred from statistical and time series analysis of existing data and/or use of simpler “box models,” such as FATHOM (Flux Accounting Tidal Hydrology Ocean Model). This is especially important given the technical difficulties involved in developing full-scale simulation models. Human factors such as population growth and economic activity; and environmental events whose drivers are distant from Florida Bay and unrelated to CERP activities, such as hurricanes, flooding of the Mississippi River, atmospheric deposition of nutrients from emission sources remote to Florida Bay or its watershed, and sea-level rise; also may influence local conditions in Florida Bay. Research is needed to better define these potential effects and to integrate the results into predictive ecosystem-response models. There is much to commend in the overall research effort on Florida Bay and in the goals of the FBFKFS. But the evidence that the CERP will cause changes in Florida Bay that may be perceived as undesirable is sufficiently persuasive that the process of more detailed evaluation should begin as an early part of the FBFKFS. The effort required for all these tasks is daunting. Sufficient time and resources should be made available as part of the FBFKFS for essential research to ensure its success and usefulness for management decisions.
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