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Past Projects - South Florida Ecosystems Abstracts

Volume Transport and Nutrient Loading to Florida Bay through East Cape Channel

Joseph N. Boyer, Southeast Environmental Research Center, OE 148, Florida International University
Chris Sinigalliano, Southeast Environmental Research Center, OE 148, Florida International University
Evelyn Gaiser, Department of Biological Sciences and SERC, OE-148, Florida International University
Makoto Ikenaga, Southeast Environmental Research Center, OE 148, Florida International University
Serge Thomas, Southeast Environmental Research Center, OE 148, Florida International University

The Florida Bay ecosystem is the point of interaction between the waters of the southern Everglades and the Florida Keys National Marine Sanctuary. Our rationale is that exchange of water and its constituents between Florida Bay and its adjacent systems is key to understanding the interconnectedness of South Florida’s unique ecosystems. Florida Bay is directly influenced by Shark River Slough drainage from the southern Everglades through the transport of water and nutrients into the system through East Cape Channel. The objective for this study is to quantify
the exchange of water and nutrients in the northwest section of Florida Bay as baseline data in the context of proposed changes in the hydrology of the southern Everglades and its direct impact on the Florida Bay Ecosystem. The goal of this two year study is to provide a data set of water volume transport and nutrient loading taking place in the channel south of East Cape for an annual period. The research hypothesis is that the East Cape Channel is the most significant point of exchange of water and nutrients for Florida Bay. The flux estimates will be compared with existing values from other bay boundaries such as Taylor Slough inputs and exchange
through keys tidal channels and used to refine existing Florida Bay nutrient budgets. This study will be conducted using mid-channel current and depth measurements, channel calibration runs to quantify volumes imported and exported over tidal and longer time scales, and coordinated nutrient samplings at a range of temporal scales from hours to days.

Simulations of Circulation and Nutrient Transport Around Florida Bay and the Florida Keys with the South Florida Regional SoFLA-HYCOM Model

Dr. Vassiliki Kourafalou, Rosenstiel School of Marine and Atmospheric Science (RSMAS), University of Miami
Dr. George Halliwell, Rosenstiel School of Marine and Atmospheric Science (RSMAS) University of Miami
Dr. Peter Ortner, Atlantic Oceanographic & Meteorological Laboratory, NOAA

The regional South Florida Hybrid Coordinate Ocean Model (SoFLA-HYCOM) was
developed during the SFP 2004 period and has been closely linked to the Florida Bay and Florida Keys Feasibility Study, as part of the Comprehensive Everglades Restoration Plan, by providing the SFWMD developed Environmental Fluid Dynamic Code (EFDC) Florida Bay hydrodynamic model with boundary conditions of physical properties. As the EFDC model expands to water quality simulations, the proposed study will expand the SoFLA-HYCOM accordingly, to include a nutrient transport module that will allow the inclusion of biophysical properties in the EFDC boundary conditions, in support of alternative Everglades Restoration evaluation scenarios.
The scientific implications of the proposed study arise from the need to understand the processes that control the links between Florida Bay/Florida Keys and the adjacent coastal and oceanic seas and to be able to predict changes in the South Florida coastal ecosystems, as a function of potential man-made disturbances (related to the Everglades Restoration activities) and natural disturbances associated with large scale flows, climatic variability and connectivity to remote sources of nutrients and pollutants. The proximity of Florida Bay to the Florida Keys National Marine Sanctuary and its Dry Tortugas Ecological Reserve requires careful evaluation
of the impact that the Everglades Restoration activities may have on these environmentally sensitive areas. In addition, the proposed study will help other interdisciplinary efforts in the SFP, such as the study of recruitment pathways of pink shrimp and the investigation of the downstream effects of Everglades restoration on the ecologically fragile Florida Keys Marine Sanctuary, by providing water and nutrient transport pathways that can be utilized by ancillary projects. Finally, the proposed study is closely linked to SFP observational efforts, by employing data for model calibration and validation.

Benthic and Pelagic Grazing of Phyoplankton in Florida Bay

Christopher Gobler, Brad Peterson, Marine Sciences Research Center - StonyBrook University

Florida Bay represents a critical habitat and nursery for a wide range of
commercially and recreationally important fish and invertebrate species. Unfortunately, this estuarine ecosystem has experience an unprecedented series of ecological disturbances during the past decade, including decreased water clarity associated with frequent picocyanobacteria blooms. These recurrent algal blooms are a primary water quality concern in Florida Bay as high concentrations of algal biomass have been implicated in the loss of seagrasses, resource fisheries,
sponges and spiny lobsters in this system. To date, managers and scientists have focused almost exclusively on nutrients as the cause of algal blooms in Florida Bay. However, consideration of the documented dynamics of phytoplankton in this system along with our preliminary data has led us to an alternative hypothesis: algal blooms are being promoted by a substantial reduction in the two primary algal mortality processes, benthic grazing by sponges and pelagic grazing by zooplankton. Although sponges were formerly the primary benthic grazer in Florida Bay, the recent loss of sponge biomass in this system has substantially decreased the grazing loss rates for
algal cells in some regions of Florida Bay. Field-measured sponge grazing rates in Florida Bay are needed to precisely quantify this change. Although zooplankton grazing is another important source of mortality for phytoplankton populations, extreme hypersalinity, which is common during summer months in Florida Bay, and the cellular properties of dominant algae in this system are both inhibitory to the survival of these micrograzers and as such, are also likely contributing toward higher levels of algal biomass. However, the lack of a single peer-reviewed study on zooplankton grazing within Florida Bay presently prohibits this hypothesis from being
further considered. Superimposed over the radical ecological changes that have occurred in Florida Bay is the Comprehensive Everglades Restoration Plan, which seeks to restore the natural hydrological flow of freshwater in through the Everglades into Florida Bay. The regions of Florida Bay that have experienced persistent phytoplankton blooms are also the regions that will be the most impacted by increasing freshwater flow. While we hypothesize that increased
freshwater inputs may enhance zooplankton grazing rates, the effects on sponges is unclear. The primary objective of this project is to determine the grazing rates of the primary benthic (sponge) and pelagic (zooplankton) herbivores on the various groups of phytoplankton within Florida Bay. We will conduct field experiments to determine the in situ filtration and grazing rates of sponges and zooplankton within the four main regions of Florida Bay during each season. In addition, we will survey the temporal and spatial variability in zooplankton communities and quantify how
natural changes in salinity effect the growth and survival rates of the dominant sponge species in Florida Bay. Finally, we will model the net accumulation of various components of the phytoplankton community within Florida Bay as a function of phytoplankton growth, zooplankton grazing, sponge grazing and physical circulation. We will also examine how these net accumulation rates may vary with potential future changes in salinity in this system. Our results, therefore, will be directly usable for the water quality model under development by the South Florida Water Management District. Our results will also be applicable to the development of alternative management strategies and the prediction of changes in the
ecosystem due to restoration scenarios proposed.

Estuarine Wetland Control of Nitrogen Loading to Florida Bay

Victor H. Rivera-Monroy, Wetland Biogeochemistry Institute, Louisiana State University
Stephen E. Davis, III, Texas A & M University
Daniel Childers, Florida International University

Florida Bay is a critical region of an estuarine continuum that spans from freshwater and mangrove wetlands in the upper estuary linking with coral reef ecosystems along the outer edge of the Florida Keys. As a result of its position along this continuum, changes in the timing, duration and magnitude of freshwater flow at the head of the estuary have affected salinity patterns and nutrient loading into Florida Bay. These hydrologic alterations have been linked to changes in seagrass community structure and productivity, phytoplankton dynamics, and water clarity in parts of the bay, and may threaten the survival and permanence of coral reefs. To alleviate the current environmental impacts in Florida Bay, the Comprehensive Everglades Restoration Plan (CERP) will increase freshwater delivery by modifying (or eliminating) within the next 30 years water structures that currently control water delivery to creek systems of lower Taylor Slough that directly discharge into Florida Bay. One of the major concerns of the CERP is the potential effect of the re-introduction of freshwater on Florida Bay water quality. But despite the vulnerability of Florida Bay to potential increases in N loading, there is a lack of information on how N processing (e.g., denitrification, nitrogen fixation, nitrification) will be modified across Taylor Slough and how these changes will affect the exchange of N at the mangrove ecotone—
bay interface. The objective of this proposed research is to evaluate how nitrogen transformations within key vegetation units across Taylor Slough contribute to regulating the net exchange of N between a major tidal creek (Taylor River) and Florida Bay. We propose the use of the biogeochemical “hot spot” concept to evaluate nitrogen fluxes across Taylor Slough and at the boundary with Florida Bay. In the southern Everglades, well-defined “hot spots” that are sensitive
to changes in freshwater delivery (and sea level rise) are freshwater sawgrass marsh, mixed eleocharis/graminoid marsh, tree islands, and continuous scrub-mangrove forest. The research questions we plan to address in this work are: How do nitrogen transformation rates vary along the longitudinal axis of the Mangrove Salinity Transition Zone (MSTZ) in response to seasonal patterns in hydrology and water quality, 2) How does local N processing along the salinity transition zone control the net exchange of N (inorganic and organic) at the mangrove-Florida
Bay interface? and 3) What is the anticipated change in N processing and exchange from upstream to downstream locations due to changes in regional hydrologic restoration in the Everglades region. We hypothesize that rates of N transformations will vary in magnitude depending on seasonal changes in water residence time, hydroperiod, and salinity along the hydrological gradient where weekly and monthly scales bound the rates as result of the tremendous influence of climatic drivers controlling hydrological patterns. We also expect high N sequestration reflected by low denitrification rates and high nitrogen fixation rates in all landscape patches particularly in freshwater marshes, tree islands, and scrub mangrove wetlands.
We will use cross-sectional flux studies, natural and isotope enrichment techniques, and a mass balance approach to determine the role of vegetation landscape units as sink, sources or transformers of N. Our results will provide information to calibrate and validate Florida Bay water quality models and submerged aquatic vegetation simulation models.

Sediment-Water Exchange of Dissolved Organic Phosphorus in Florida Bay

Jia-Zhong Zhang, Atlantic Oceanographic and Meteorological Laboratory, NOAA

Because phosphorus (P) is a limiting nutrient to seagrasses throughout the entire Florida Bay and to phytoplankton at least in eastern bay, the supply of P is critical to the health of seagrass community and the frequency, intensity and duration of phytoplankton blooms. Our multiyear monitoring has demonstrated that seawater contains a very low concentration of dissolved reactive phosphate (10-100 nM). However, dissolved organic phosphorus (DOP) is usually an
order magnitude higher than dissolved reactive phosphate, dominating dissolved phosphorus pool in the water column. On the other hand, carbonate sediments strongly retain P and sediments have been identified as a dominant P reservoir in Florida Bay. Sediments are readily suspended by wind and tidal mixing into surface water in shallow (average water depth I m) Florida Bay. The sediment/water exchange of P through adsorption/desorption represents the most important P cycling process and plays a critical role in regulating bioavailable P to the water column. Our previous studies have shown a strong gradient of decreasing sediment exchangeable P concentration from the west to the east across the bay. The spatial pattern of
sediment exchangeable P is similar to that of dissolved phosphate concentrations in the water. As carbonate sediments function as a P buffer system, it is reasonable to hypothesize that sedimentary P, to a large extent, regulates the dissolved phosphate concentrations in the shallow water column. Our study on the fractionation of sedimentary P pools by a sequential extraction technique reveals that 60% of exchangeable sediment P is in the organic form, indicating that the dissolved organic P in bay water is reactive in adsorption/desorption processes at sediment/water
interface. However, there is little study on organic P sorption on marine sediment surface. To characterize the sediment-water exchange of DOP in Florida Bay, a systematic study is proposed to quantify the sediment characteristics with respect to sediment/water partitioning of DOP. For a given station location, individual sediment parameters for DOP exchange, such as the zero equilibrium DOP concentration, the distribution coefficient, and DOP buffering capacity of sediment will be quantified by isotherm experiments with a model organic compound AMP at
ambient temperature and salinity. Such experiments will be conducted at 40 selected sampling locations covering both different sediment characteristics and geographic region of the bay. This systematic study will provide a spatial distribution of sediment parameters relevant to DOP cycling in Florida Bay. These parameters are essential in water quality models for predicting the sediment/water exchange of DOP in Florida Bay.

Measuring and Modeling Nutrient Uptake in Florida Bay

Patricia M. Glibert, University of Maryland Center for Environmental Science
Cynthia Heil, Fish and Wildlife Research Institute, Florida Fish & Wildlife Conservation Commission

With the impending restoration of Florida Bay and the proposed return of surface flow through the Everglades, the forms, amount and delivery of dissolved nutrients to the bay are expected to change, particularly dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN). Both DON and DIN in Florida Bay are dynamic and their abundance and proportion are major factors in regulating phytoplankton composition. The major sources of DON, Taylor Slough and Shark Slough, appear to differ in composition, and in their bioavailability to the biota. A combination of terrestrial (Everglades runoff), sedimentary and internal sources may exist.
Differentiating these sources will be critical, as some sources may ultimately be controllable, such as runoff from the Everglades, while other sources, such as sedimentary or groundwater sources, will be more difficult to control. Available data to date suggest that : 1) Differences in the nature, composition, distribution, and ratio of dissolved organic and inorganic nutrients observed throughout the Florida Bay can be traced to specific, different, regional inputs from the Everglade watersheds; 2) Different components of the plankton community (e.g. cyanobacteria,
diatoms, heterotrophic bacteria) respond to different fractions of the organic and inorganic nutrients and their relative abundance; and 3) These relationships have application beyond Florida Bay, with similar responses now observed for the Western Florida Shelf. The proposed effort includes application of previously measured rates of N, P and Si uptake to models being developed by the South Florida Water Management District, further assessment of the kinetics of uptake of individual N and P compounds in natural samples and in culture studies of several dominant bloom-forming phytoplankton (e.g. Synechococcus and Cyclotella sp.), and application
of new methodology which will allow us to fully characterize the varying source DOM pools and the individual compounds which may be used by the biota. The new approach to be used is electrospray ionization mass spectrometry (ESI-MS). ESI-MS provides a window into the “black box” of DOM by providing molecular weight information of each ionizable compound, and a measure of concentration. It will be used to characterize individual components of the DOM from the source waters of Taylor Slough and Shark Slough, and the bioavailability of individual components to ambient microbiota will be traced in bioassay experiments during both wet and
dry seasons. This project thus incorporates modeling and synthesis of previous data with application of new experimentation to further our understanding of the role of DOM in plankton dynamics of Florida Bay.

Longterm monitoring of benthic habitat in the Florida Keys National Marine Sanctuary

James W. Fourqurean, Department of Biological Sciences and Southeast Environmental Research Center, Florida International University

This program was designed to addressthe following objectives: 1) Define the present distribution of benthic communities within the FKNMS, 2) Provide high-quality, quantitative data on the status of the seagrasses within the FKNMS, 3) Quantify the importance of seagrass primary production in the FKNMS, 4) Define the baseline conditions for the seagrass communities, 5) Determine relationships between water
quality & benthic community status, and 6) Detect trends in the distribution and status of the benthic communities. In this project, two sampling strategies are used: 1) semi-synoptic maps of indicator parameters are generated through sampling ca. 350 randomly-located points in a 19,000 km2 area that includes the FKNMS and the region of shallow coastal water to the north of the Sanctuary, south of Cape Romano, and west of Everglades National Park; and 2) quarterly sampling of fixed transects at 30 permanent monitoring sites in the FKNMS. Indicators of the
status of the seagrass communities assessed include: species composition, cover and abundance of macrophyte communities, elemental and stable isotopic content of seagrass leaves, seagrass morphology, and seagrass growth rate. The reasons for the selection of these indicators is given in the proposal. At the permanent sites, quarterly measures of these indicators have been made since winter of 1995. Eight of the 30 permanent monitoring sites displayed change consistent with models of eutrophication responses of tropical seagrass beds. At 4 sites, macroalgae have
become relative more abundant, and at 4 other sites the elemental content of seagrass leaves has shifted towards the “Seagrass Redfield Ratio.” The rates of change of the permanent stations have been slow, except for three sites which have been severely impacted by hurricanes in the monitoring period. The slow rates of change indicate the need for monitoring for long periods to be able to detect net change; the fact that storms have affected 10% of these randomly selected
locations indicates that all stations are needed in order to assure long-term records in the absence of storm-induced disturbance. Synoptic mapping was carried out during the years 1996-2000. In 2003, the 300 stations originally surveyed in 1996 were revisited, in 2004 the stations visited in 1997 were revisited, and in 2005 the stations visited in 1998 were revisited. This will allow for over 1000 pairwise measurements of the magnitude and direction of change in seagrass communities in the region. Lastly, statistical models describing the relationships between seagrass habitat status and water quality will be developed in conjunction with the water quality monitoring program for the FKNMS.