Progress Toward Restoring the Everglades The Eighth Biennial Review - 2020 (2021) / Chapter Skim
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5 Estuaries and Coastal Systems
5 Estuaries and Coastal Systems
Pages 155-230
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From page 155... ...
. A key CERP goal is to return more natural patterns of flow to the northern estuaries and to send more water south through the remnant Everglades and into the southern estuaries of Florida Bay and Biscayne Bay.
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From page 156... ...
and will present a major challenge to the management of water, water quality, and estuarine biological resources of South Florida. Moreover, CERP projects are coming online among a complex matrix of non-CERP actions and legal prescriptions that can affect both the Everglades and
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From page 157... ...
In this chapter the committee sought to synthesize the following for the northern estuaries (Caloosahatchee River Estuary and the St. Lucie Estuary)
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From page 158... ...
and will challenge management of water, water quality, e and estuarine biological resources of South Florida. Sea-level rise will increase saltwater intrusion into inland aquifers, compromising drinking water supplies and complicating flood control; it may exacerbate peat loss in natural systems, leading to subsidence.
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From page 159... ...
Lucie estuaries are the most directly impacted by Lake Okeechobee water releases and numerous CERP projects. In this section, the committee describes environmental changes to the Caloosahatchee River and St.
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From page 160... ...
. Under predrainage conditions, no navigable connection existed between the Caloosahatchee River and Lake Okeechobee, although during rainy periods, some Lake Okeechobee water overflowed into the headwaters FIGURE 5-3 Caloosahatchee River watershed, including the estuary, the major watershed basins, and major water control structures.
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From page 161... ...
. More than 150 years ago, the Caloosahatchee River Estuary was home to abundant beds of brackish water seagrass (Vallisneria americana)
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From page 162... ...
These structural and hydrologic changes have modified salinity regimes and caused decline in water quality in ways that fundamentally altered suitable habitat for brackish water and marine seagrass, oysters, plankton, and fish in the Caloosahatchee River Estuary (Barnes, 2005; Chamberlain and Doering, 1998)
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From page 163... ...
. Structural, hydrologic, and land use alterations in the watershed and estuary have promoted water quality conditions that have caused low dissolved oxygen in some local tidal basins; reduced water clarity, which diminishes aesthetics and light required for seagrass growth; and, more recently, supported recurring toxic harmful algal blooms (HABs; see Box 5-2)
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From page 164... ...
and suggest that bloom events would be mitigated by nitrogen source and transport controls within the Caloosahatchee and/or Kissimmee River basins. Toxic cyanobacterial blooms have been recurring in Lake Okeechobee in recent years, with tre mendous impacts on the northern estuaries.
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From page 165... ...
with fresh water flow in the Caloosahatchee River Estuary. Under low flow, the estuary is dominated by a high volume of ocean waters that are high in salinity and low in color.
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From page 166... ...
Lucie Estuary and the nearby southern Indian River Lagoon were home to abundant marine and brackish-water seagrass meadows and oyster beds. This estuary and its adjacent marine lagoon fostered a rich and biologically diverse flora and FIGURE 5-7 St.
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From page 167... ...
Lucie watershed, exacerbating floods and drought conditions in the estuary. Operation of the Lake Okeechobee regulatory releases for flood control combined with the basin drainage system significantly altered the magnitude and timing of freshwater flow into the St.
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From page 168... ...
Water quality and ecological impacts. As with the Caloosahatchee River Estuary, wet season watershed runoff and Lake Okeechobee regulatory releases bring extreme fluctuations in St.
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From page 169... ...
(acre-feet/year) Aboveground Reservoirs Lake Okeechobee Watershed Restoration Plan 46,000a C-43 Reservoir 170,000 Indian River Lagoon-South 160,000b Central Everglades Planning Project (CEPP, 300,000c includes EAA Reservoir)
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From page 170... ...
, which emphasized reduction of high flows from Lake Okeechobee over basin flows. Planned and approved CERP projects will have a larger effect on low-flow events in the Caloosahatchee River Estuary.
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From page 171... ...
The model runs presented here may not have the exact same conditions from project to project, but the output collectively is presented for general trends. CEPP, Central Everglades Planning Project; LOWRP, Lake Okeechobee Watershed Restoration Project; PACR, Post Authorization Change Report.
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From page 172... ...
Lucie Estuary by 35 percent and nitrogen loads by 24 percent compared to the 2050 conditions without the project. Overall Effects from Planned CERP Projects on the Northern Estuaries As noted previously, the majority of flows and nutrient loads to the Caloosahatchee River and St.
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From page 173... ...
Planned C CERP projects are predicted to reduce the number of mean monthly low-volume flows for the Caloosahatchee River and St. Lucie estuaries by 70 and 20 percent, respectively.3 Thus, both the St.
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From page 174... ...
Oyster and brackish and marine seagrass restoration represent CERP goals. Climate change can alter these fundamental environ mental drivers.
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From page 175... ...
. On the flip side, water quality is inextricably linked to flow, so water quality managers must understand how water releases associated with CERP projects will impact water quality and attainment of TMDLs.
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From page 176... ...
2. How does water quality associated with freshwater flows affect CERP goals for restoration of seagrass and oyster habitat?
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loading for water quality analyses or hydrologic models that optimize design and operations at the project scale, and (3) estuarine hydrodynamic models (Figure 5-10 and Table 5-5)
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Lucie Estuary River Estuary Biological Models Biological Models Gulf of Mexico/Atlantic Ocean Hydrodynamic and Water Quality Models FIGURE 5-10 Conceptual illustration of the types of models that can be used to investigate restoration and water quality outcomes in the northern estuaries. The two estuaries share a regional-scale hydrologic basin model and Lake Okeechobee model.
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From page 179... ...
Lake Okeechobee Simulates Lake Okeechobee water budget, temperature, CBOD, dissolved inorganic and Water Quality Model organic nitrogen, phosphorus, phytoplankton biomass, cyanobacterial biomass, TSS (James, 2016) Watershed Model Hydrologic model; components are comprised of surface-water flow, groundwater flow, (WaSH)
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From page 180... ...
Lucie Estuary; TSS, total suspended solids. Watershed Loading and Estuarine Water Quality and HAB Toolkit As the CERP is implemented, CERP project and Lake Okeechobee opera tions will need to be refined to maximize CERP goals, minimize HABs, and balance trade-offs between restoration objectives and human water resources needs (see Box 5-3)
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From page 181... ...
The computed watershed loads are currently integrated with water releases from Lake Okeechobee and could be linked with detailed measurements and models on water releases from reservoirs, and STAs as they come online. Watershed loading models provide inputs to coupled estuarine hydrodynamic and water quality models (Figure 5-10)
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From page 182... ...
. In the Caloosahatchee River Estuary and watershed, the quantitative under standing of water quality drivers is more comprehensive than in the St.
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From page 183... ...
The Lake Okeechobee Water Quality Model has been developed to predict eutrophication and cyanobacterial blooms. James (2016)
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From page 184... ...
Water quality and HAB modeling is also needed for CERP projects. This is particularly true for the C-43 and C-44 reservoirs, which are expected to hold water for extended release during the dry season, when temperatures are high est and thermal stratification could expect to set up ideal conditions for cyano bacterial blooms.
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From page 185... ...
This FIGURE 5-11 Species that are used as CERP biological endpoints that are impacted by the magnitude, timing, and water quality of freshwater flows to the northern estuaries.
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From page 186... ...
The scientific priority is high, because this is a key limitation for the CERP to reach its goals and to provide clear justification for how HABs and water quality issues can be minimized, while optimizing CERP seagrass and oyster restoration goals. Ideally, estuarine biological tools to optimize seagrass and oyster habitat would be species-specific, spatially explicit mechanistic models that depict physiological responses to highly variable temporal and spatial gradients in flow and water quality parameters (e.g., salinity, temperature, turbidity, substrate, nutrients, CDOM, phytoplankton biomass)
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From page 187... ...
The Minimum Flow and Minimum Water Level 2018 update for the Caloosahatchee River Estuary is the most recent and comprehensive example of a synthesis and model development across multiple biological endpoints. Mechanistic or statistical models for 11 different estuarine biological response endpoints were developed to identify minimum flow targets.
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From page 188... ...
. These modeling efforts could take advantage of improved seagrass monitoring by the SFWMD now under way as well as recent advances in water quality modeling to develop more spatially explicit predictions of seagrass biomass and distribution.
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From page 189... ...
Watershed Can predict watershed water quality including the temporal Intermediate Early Stage and variability in water quality in releases of water from Lake Estuarine Okeechobee, CERP projects as they come online (C-43, C-44 Water reservoirs, STAs) , and local land uses as a function of external Quality and internal drivers Can predict estuarine water quality, including the ability to Intermediate Early Stage estimate/model patterns in concentrations and mass balances of nutrients and organic carbon, production of algae and partitioning among major taxonomic groups, and the factors limiting light to seagrass.
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From page 190... ...
In this section, the committee describes the hydrologic and water quality changes to these ecosystems, their ecological impacts, and restoration goals for Florida Bay and Biscayne Bay. In light of continued project planning and adaptive management in this region, key decisions for water management are discussed along with the adequacy of science to support these decisions.
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Estuaries and Coastal Systems 191 FIGURE 5-12 Map of Biscayne Bay showing the boundary of Biscayne National Park. SOURCE: Google Maps.
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From page 192... ...
. Recent declines in water quality in North and Central Biscayne Bay have caused massive seagrass die-offs (Millette et al., 2019; RECOVER, 2019)
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Water quality. Nutrient enrichment in Biscayne Bay compounds the effects of altered hydrology.
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From page 194... ...
Note that the scale on the top graph is 2.5 times greater than the lower plots. Red horizontal lines represent chlorophyll a water quality criteria established for the Bay; the two lines in panels (a)
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From page 195... ...
The ecological conditions of Biscayne Bay are increasingly affected by human activities that may limit the ability of the CERP to reach its goals. For example, seagrass communities in the North and Central Bay were relatively stable until 2005 when hypersalinity and increasing chlorophyll a concentration, associated with a series of algal blooms, led to extensive seagrass losses.
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From page 196... ...
SOURCE: Gimenez, 2019. Biscayne Bay.
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From page 197... ...
considers the future of Biscayne Bay's seagrass meadows as "bleak." Increasing salinity associated with sea-level rise and a lack of freshwater inflows affects not only seagrass but also animals who depend on mesohaline conditions, including the oyster (Crassostria virginica) , American crocodile (Crocodylus acutus)
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From page 198... ...
198 Progress Toward Restoring the Everglades FIGURE 5-16 Abundance of key indicator fish relative to salinity. Note open circles are con centration of juvenile fish (per 1,000 m2)
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From page 199... ...
The lack of baseline information on predrainage conditions has limited the development of CERP freshwater flow targets for Biscayne Bay (McManus et al., 2014; RECOVER, 2011a)
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From page 200... ...
. The planned diversions of canal water through the existing coastal wetlands are also anticipated to provide water quality benefits such as a reduction of 50 percent of the projected future nitrate load to Biscayne Bay (162 metric tons per year)
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From page 201... ...
Key Questions for Decision Makers on Restoration of Biscayne Bay As with the other South Florida estuaries, there are key management questions that must be answered to make sound decisions on Biscayne Bay restoration. For example, what is the timing, magnitude, and spatial distribution of freshwater inflows needed to meet restoration goals?
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• What are the effects of increased CERP flows on Biscayne Bay water quality?
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From page 203... ...
represent capabilities that have not yet been developed. TABLE 5-7 Examples of Hydrologic, Hydrodynamic, Water Quality, and Ecological Models Applicable to Florida Bay and Biscayne Bay Name Domain Description Hydrologic models Regional Simulation Everglades The RSM simulates surface- and groundwater hydrology for Model (RSM)
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From page 204... ...
, marine, and weather data to predicted salinity at 37 estuarine index areas of Everglades National Park (Marshall et al., 2011) Biscayne Bay Box Model Biscayne Bay Water quality box model that estimates the long-term average N&P concentrations and loads in the Bay based on total phosphorus and dissolved in organic nitrogen loads from canals, ungauged surface water, groundwater, atmospheric, and Atlantic Ocean contributions Ecological models Seagrass Ecosystem Florida Bay SEACOM is a mechanistic, physiological unit model that predicts Assessment and seagrass community type response to salinity and water quality, Community Organization climate and climate change on seagrass distribution, species Model (SEACOM)
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From page 205... ...
, and these impacts need to be understood in order to inform restoration investments that will provide long-term benefits. Freshwater flows to Biscayne Bay include groundwater discharge from the Biscayne aquifer, which extends westward into Everglades National Park, and surface-water inflows from canals supplied with water released from the Everglades ecosystem as well as inputs from local watersheds.
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From page 206... ...
Understanding the linkages between water quality and ecological response. Many of the current ecological issues facing Biscayne Bay, particularly in the North and Central Bay, are a result of increasing nutrient concentrations (phos phorus and nitrogen)
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From page 207... ...
In addition to the limitations of hydrodynamic models to predict spatially explicit salinities (discussed in the previous section) , the lack of water quality models, both in the watershed and in the estuary, is a key gap in advancing restoration in Biscayne Bay.
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From page 208... ...
For example, both Biscayne Bay and Florida Bay need additional freshwater flows, but plans to send water south will have differential benefits for each ecosystem. Modeling tools that weigh differ ential benefits can provide information that will make clear the consequences of possible management decisions.
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From page 209... ...
Each modeling group performed their own analysis (hydrodynamics, water quality, ecology, etc.)
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From page 210... ...
and six zones of similarity (Briceño and Boyer, 2010) in Florida Bay based on water quality characteristics (outlined in purple)
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From page 211... ...
Current freshwater flows into the Bay are primarily from Taylor Slough (see Figure 4-2) ; flows from Shark River Slough that travel via currents into Central and East Central Florida Bay are minimal, typically occur only in the wet season, and have limited spatial influence (SFWMD, 2016b)
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From page 212... ...
Water quality. Plant communities in most of Florida Bay are phosphorus limited because of very high nitrogen-to-phosphorus ratios in freshwater runoff, a long residence time for water, high rates of primary production, and carbon ate sediments that sequester phosphorus (Figure 5-20; Fourqurean and Zieman, 2002; Fourqurean et al., 1992, 1993)
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From page 213... ...
Following the 1987-1994 event, more than a decade of research ultimately uncovered a suite of interconnected contributing factors: hypersalinity caused by low freshwater inflows combined with high temperatures in areas with dense seagrass beds (Carlson et al., 2018; Fourqurean and Roblee, 1999; Johnson et al., 2018; McIvor et al., 1994; Zieman et al., 1999)
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From page 214... ...
The process is outlined in more detail in Figure 5-22. This series of events represents a collapse at the base of the food web, and the consequences included unstable sediments, algal blooms, and increased turbidity (Deis, 2011; Hall et al., 1999)
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Estuaries and Coastal Systems 215 followed similar conditions as that in the 1980s -- localized drought, high temperatures, and hypersalinity. Ecological implications.
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, the CERP aimed to increase overland flow into Everglades National Park and Florida Bay to improve salinity conditions. The broad CERP goals related to Florida Bay are captured in the 2007 Interim Goals Agreement (USACE et al., 2007)
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From page 217... ...
grid size used by the South Florida Water Management Model and the difficulty of accurately simulating flows near the coasts. Since the CERP was launched, extensive research has led to a broad scientific consensus that wetter conditions prevailed in the historic system than previously thought (McVoy et al., 2011; NASEM, 2016)
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From page 218... ...
Southern Everglades is a future CERP planning initiative that will include several project components from the Yellow Book that could benefit Florida Bay if implemented, including Everglades National Park (ENP) Seepage Management, Lake Belt Storage, and Lake Okeechobee ASR.
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From page 219... ...
is projected to increase freshwater flows into Florida Bay by 36,000 AF per year, which is greater than that projected from the CEPP and the EAA Reservoir. The greatest increases in overland flow occur through the Eastern Panhandle to East Florida Bay.
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From page 220... ...
Key Questions to Inform Management Decisions in Florida Bay Much research has been done to investigate the role of freshwater flow in the environmental problems of Florida Bay and to utilize a combination of monitoring and modeling to quantify how CERP projects will impact freshwater delivery relative to flow and salinity targets. However, Florida Bay is influenced not only by this freshwater inflow and its inherent water quality but also by the Gulf of Mexico; both hydrologic drivers will change in the future as a function of global land use and climate change.
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From page 221... ...
• What are the implications for Florida Bay if the CERP Lake Belt storage projects are never implemented? • What are the larger-scale trade-offs between increasing flow to western Taylor Slough from Shark River Slough (assuming this is feasible)
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From page 222... ...
and a statistical discriminant function model that assigns a probability of eight seagrass community types occurring for a given combination of water quality variables (Fourqurean et al., 2003; Herbert et al., 2011)
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From page 223... ...
(2011) used salinity climates from the hydrodynamic model FATHOM as input to a statistical discriminant function model that associates eight seagrass community types with water quality variables including salinity, salinity vari ability, total organic carbon, total phosphorus, nitrate, and ammonium, as well as sediment depth and light reaching the benthos.
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From page 224... ...
Salinity is affected by upstream flows, evapotranspiration, precipitation, and circulation, and, therefore, spatially explicit salinity predictions require accurate models of surface- and groundwater inflows and bay hydrodynamics. Especially challenging is the ability to simulate surface-and groundwater flows at the coastal boundary and their effects on the salinity of the North and northern Central Bay, where the CERP is expected to have the greatest potential impact.
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From page 225... ...
to assess surface water, ground water and surficial water flows and volumes from ENP into the Bay." In addition, there is a need for comprehensive scenario assessment modeling to support operational actions that could increase freshwater flow, especially into northern Central Florida Bay, where algal blooms have historically originated. For example, questions exist regarding the ability to increase surface-water flow and seepage through Buttonwood Ridge into northern portions of Central Florida Bay, which may require operations to convey water to western Taylor Slough, potentially when Shark Slough stages are high enough to overcome barriers to flow.
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From page 226... ...
. Circulation and nutrient supply from the Gulf will change with sea-level rise, requiring new or improved models for salinity and water quality prediction and cascading effects.
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From page 227... ...
CONCLUSIONS AND RECOMMENDATIONS The CERP will help address freshwater inflow concerns in all of the estuaries but it is only part of the solution. CERP ecological restoration goals, particularly in the northern estuaries and Biscayne Bay, cannot be met if water quality and associated algal blooms, which are outside of the direct purview
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From page 228... ...
Requirements for compli ance with the Clean Water Act to address pollution and water quality fall to the state and not to the CERP. Public expectations for improved estuarine condi tions, such as healthy seagrass meadows, improved oyster habitat, and control of harmful algal blooms, extend beyond what the CERP alone can achieve and require both CERP actions and water quality and habitat improvements through non-CERP efforts.
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From page 229... ...
High-priority science and modeling needs include • Spatially explicit water quality models and a sustained program of observation and research to build toward a predictive harmful algal bloom modeling toolkit for the northern estuaries; • Watershed loading and water quality models to predict effects of salinity, water quality, and light limitation on the viability of seagrass in Biscayne Bay; • Spatially explicit and mechanistic biological models (e.g., seagrass, oyster) , developed from appropriately scaled and sustained monitoring programs for the northern estuaries that can capture the quantitative basis for relationships between freshwater flows, water quality drivers, and biological outcomes of interest; • Predictive tools to identify thresholds and tipping points in all the estuaries, such as the complex factors associated with algal blooms and seagrass die-off; • A southern Everglades transition-zone observational and modeling program that supports project planning and can couple regional hydrologic models, including groundwater–surface water exchange, with spatially explicit estuarine hydrodynamic and salinity models; and • Integration of modeling and observations across the entire southern inland and coastal system to evaluate cross-project synergies and ecological responses (e.g., the ecological response of Biscayne Bay and Florida Bay to enhanced seepage management)
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From page 230... ...
To ready the toolkit for this exercise, investments recommended above to make water quality and biological models increasingly mechanistic and spatially explicit will also serve to credibly predict impacts from climate change stressors. This information can then be used to examine the long-term performance of projects and identify possible adaptive management strategies or design alterations to increase eco system resilience.
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