Grantee Research Project Results
Final Report: Ecohab: Florida; Hydrography/Physical Oceanography Component
EPA Grant Number: R826792Title: Ecohab: Florida; Hydrography/Physical Oceanography Component
Investigators: Vargo, Gabriel A.
Institution: University of South Florida
EPA Project Officer: Packard, Benjamin H
Project Period: June 1, 1998 through May 31, 2001
Project Amount: $360,000
RFA: Ecology and Oceanography of Harmful Algal Blooms (1998) RFA Text | Recipients Lists
Research Category: Water Quality , Harmful Algal Blooms , Water , Aquatic Ecosystems
Objective:
The objectives of the combined U.S. National Oceanic and Atmospheric Association (NOAA) and U.S. Environmental Protection Agency (EPA) ECOHAB Florida program were to: (1) model the initiation, maintenance, and export of Gymnodinium breve red tides on the West Florida Shelf at different time and space scales to predict landfall; (2) describe the physical habitat that affects the transport and concentration of Gymnodinium breve; (3) determine the interactions of cellular, behavioral, life cycle, and community regulation processes with environmental forcing factors during stages of bloom development; (4) determine the sources of inorganic and organic nutrients that allow growth and persistence of large Gymnodinium breve populations in coastal waters; and (5) determine the production, occurrence, fate, and effects of brevetoxins in the environment during and after G. breve blooms. The specific objectives of the U.S. EPA subsection of the ECOHAB:Florida program were to provide: (1) basic current meter and meteorological measurements on the northern West Florida Shelf off Cedar Key; (2) monthly near-synoptic surveys of the physical, chemical, and biological fields within the ECOHAB:Florida control volume; and (3) chlorophyll a and biomass indicators at selected locations within the ECOHAB:Florida control volume.
Summary/Accomplishments (Outputs/Outcomes):
Objective 1. Drs. Sturges and Weatherly of Florida State University were funded through a subcontract to provide basic current meter and meteorological measurements on the northern West Florida Shelf off Cedar Key. The location of the current meters and the data available from the moorings that was provided to the University of South Florida (USF) can be found on the Florida State University Web Site. The data are used as far-field input for the physical oceanographic model that was developed by Dr. Robert Weisberg of USF, which is coupled with the ecological model developed by Dr. John Walsh. They are funded by our NOAA ECOHAB Florida partner.
Objective 2. Over the past 3 years, we have collected water column samples from less than 70 locations during monthly quasi-synoptic cruises for: hydrographic information, phytoplankton biomass as chlorophyll a and particulate carbon, nitrogen and phosphorus, live G. breve counts from surface samples and near bottom samples from selected locations, preserved samples for total phytoplankton abundance and species composition (analyzed by others), total dissolved organic nitrogen and phosphorus, inorganic nutrients samples (analyzed by others), and water column samples for the abundance of Trichodesmium spp. (a nitrogen-fixing cyanobacterium). As of December 2001, we had completed 40 monthly synoptic cruises on the Florida Institute of Oceanography (FIO) research vessel R/V Suncoaster, and 26 cruises to sample the alongshore transect from Tampa Bay to Charlotte Harbor aboard the FIO vessel R/V Bellows. Bellows cruises were coincident with the synoptic cruises to the extent possible, and are funded by the State of Florida via the Florida Marine Research Institute (FMRI). Our cruise tracks and locations of the stations occupied by the Suncoaster and Bellows are illustrated in Figure 1. A total of 113 different students, interns, and scientists from various federal and state laboratories and agencies that are engaged in harmful algal bloom research have taken advantage of the cruise opportunities to participate in this program.
We have two monthly near-synoptic surveys remaining, and approximately 10 additional months of Bellows cruises. The data collected will be part of the overall ECOHAB Florida dataset and will be processed with support from fourth year funds from the U.S. EPA and the U.S. NOAA.
All other analyses are complete, with the exception of total dissolved nitrogen samples. The data have been checked for quality control (see Table 1). We estimate that another 3 to 4 months are required for completion of data entry, calculations, and a final quality check before posting the data on the ECOHAB Florida Web Site.
Table 1. Summary of ECOHAB Measurement Status
Measurement | Status* |
Inorganic Nutrients (NO3, NO2, SiO4, PO4, NH3) | current |
Organic Nutrients | TDP: current |
DON: analyzed through March, 2000 | |
Particulate Nutrients | CHN: current |
Particulate P: current | |
Chlorophyll a | Completed through current survey |
G. breve Cell Concentration | Completed through current survey |
Phytoplankton Community Composition | Archived for future; analysis underway |
Underway Data (Fluorescence, Temperature, Salinity, Turbidity)** | Processed through current survey |
* Status indicated as completed, includes chemical analysis, data entry, calculation.
**Processing of data underway, consists of manual inspection of data for recording errors prior to bin averaging (30 second) and combining approximately 35 files to facilitate data analysis and graphing.
Objective 3. Four major toxic Karenia brevis (also known as Gymnodinium breve) blooms occurred on the West Florida Shelf between October 1998 and January 2002. Population levels in each bloom were considerably different and ranged from 1,000 to 5.4 million cells per liter. The spatial extent of each bloom also varied considerably; from hundreds to thousands of square kilometers. Despite these differences, we noted several common features in the hydrographic and nutrient regime and several indicators of nutrient status. We examined these indicators to assess potential initiation and maintenance mechanisms.
All blooms appeared after breakdown of vertical stratification; they also were associated with nearshore thermal or salinity fronts as indicated, underway temperature, salinity monitoring, and by silicate distributions (as an indicator of riverine water). However, no one hydrographic feature characterized the early stages of each bloom. Water column dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphorus (DIP) molar ratios (DIN:DIP) were generally less than 1, suggesting N-limitation paralleling P-enrichment from nearby rivers, which drain commercially-exploited phosphate deposits.
Elevated dissolved silicate concentrations, in association with high cell abundance, occurred during all four blooms. This suggests estuarine export of N and P into coastal waters for bloom maintenance. Although estuaries in the Tampa Bay and Charlotte Harbor areas are depleted in DIN due to phosphate enrichment, dissolved organic nitrogen (DON) concentrations range from 5 to >15 µM, and may serve as a source of N to support growth and elevated biomass.
Estimates of DIN, DIN + DON, and DIP fluxes from Tampa Bay based on the WASP4 model, indicate that advective transport could supply approximately 7 percent, 24 percent, and 100 percent, respectively, of the N and P required for daily growth needs of a moderate population (3 x 105 cells/L) of Karenia brevis. Our results suggest that estuarine fluxes of N and P are sufficient to support moderate to high populations when they occur in nearshore waters.
Most blooms, however, have population levels greater than 3 x 105 cells/L. The dilemma is how the meager nutrient supply can contribute to the maintenance of such high populations for weeks or months. Vertical migratory activity allows dense surface populations to form during the light period (>106 cells/L). These dense populations disperse throughout the water column during darkness. We speculate that this dispersal would allow cells to utilize available nutrients from the entire water column and achieve nutrient sufficiency.
The blooms, however, cannot be characterized by a single physiological indicator. Particulate C:N, C:P, and N:P molar ratios ranged from values suggesting N limitation to P limitation. Particulate C:N molar ratios for two of the blooms ranged from 5 to 7, near Redfield, to values less than 1 for populations greater than 5 million cells per liter during the 1999-2000 bloom. Prior to bloom termination, C:N ratios ranged from 14 to 35, which suggests limitation; however, particulate molar C:P and N:P ratios and weight ratios of P:Chl for all blooms were high, suggesting P limitation.
In addition to estuarine nutrient flux as a potential source of N and P that is required to support these blooms, other sources also have been examined.
All of the blooms were associated with vertically well-mixed water columns. Breakdown of stratification is most likely due to a combination of windmixing and onshore transport of water as a result of upwelling favorable winds. Upwelled water has a midshelf origin, and can form a thermal front seaward of the 10 m isobath but is not enriched with nitrate. Therefore, other sources of nutrients, primarily nitrogen, are required to support elevated biomass and maintenance of that biomass.
Centric diatom populations with high biomass (> 5 µg Chl/L) develop in near-bottom water during summer stratification seaward of the 20 m isobath. These populations are potentially fueled by nitrate originating from offshore intrusions of shelfbreak water associated with Loop Current movement. This upwelled water does not, however, reach the surface, and it has not been associated with elevated K. brevis populations. One possible source of the required N for bloom development and growth may be the decay and remineralization of the nearbottom diatom populations, combined with the breakdown of the summer thermal stratification by vertical mixing during the fall. Measurements of elevated DON in offshore waters coincide with the timing of increased vertical mixing and resuspension.
Mid- to late-summer blooms of the diazotroph, Trichodesmium erythraeum, which often precede G. breve blooms, appear to be stimulated by iron input from Saharan dust events, and also may act as a source of organic N via excretion of amino acids or inorganic N after bacterial breakdown of the excretory products and particulate matter. Elevated populations of Trichodesmium sp. coincide with elevated DON concentrations and nondetectable DIP and DOP concentrations.
Measurements of δ15 particulate organic nitrogen (PON) from locations throughout the study area, including G. breve populations, strongly suggest that N from several sources is used by G. breve. The range of δ15N values indicate that N derived from T. erythraeum remineralization, estuarine-derived and seagrass-derived material may contribute to the N requirement for bloom populations. Ongoing studies are aimed at distinguishing between offshore and coastal sources of utilizable DON.
Finally, wind direction, coastal currents, temperature, and salinity fronts are key to bloom movement and bloom development. Wind-induced upwelling appears to transport populations shoreward (1998-1999 bloom), where they may be trapped behind thermal and salinity fronts that result from the outwelling of estuarine water. Based on acoustic doppler current profiler (ADCP) records from moorings located along the 10 m isobath, transport of the 1998-1999 bloom from the Charlotte Harbor area to Tampa Bay within a 1-month time period was due to a northerly flowing current. Similarly, ADCP and meteorological records from our moorings confirm that the nearly stationary position of the 1999-2000 Charlotte Harbor bloom coincided with a period of low and variable winds, which yielded reduced current speeds in coastal waters.
We conclude the following:
· K. brevis blooms within the ECOHAB Florida control volume were associated with temperature/salinity fronts in nearshore and offshore environments.
· We suggest that the fronts act as accumulation mechanisms, possibly by restricting downward swimming movements, due to thermal discontinuities (Heil, 1986) or salinity gradients. Measured nearshore current speeds and direction can account for the observed northward movement of the 1998 bloom.
· Particulate stochiometery, both molar and weight ratios, indicates N-sufficiency and P-limitation, whereas dissolved DIN:DIP ratios indicate P availability relative to N.
· Adding ammonia and available DON (either remineralized or excreted by T. erythraeum) to the equation would account for N-sufficiency relative to P.
· Based on our measured bloom stochiometery, we hypothesize that available P and/or its turnover rate sets the upper limit of K. brevis (and other phytoplankton) biomass in the ECOHAB Florida region, despite the fact that nearby estuaries are P-enriched.
Figure 1. Station Locations Occupied During the Monthly ECOHAB Florida Synoptic Cruises.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 31 publications | 5 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Del Castillo CE, Coble PG, Conmy RN, Muller-Karger FE, Vanderbloemen L, Vargo GA. Multispectral in situ measurements of organic matter and chlorophyll fluorescence in seawater: Documenting the intrusion of the Mississippi River plume in the West Florida Shelf. Limnology and Oceanography 2001;46(7):1836-1843. |
R826792 (2000) R826792 (Final) |
not available |
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Heil CA, Glibert PM, Al-Sarawl MA, Faraj M, Behbehani M, Husain M. First record of a fish-killing Gymnodinium sp bloom in Kuwait Bay, Arabian Sea: chronology and potential causes. Marine Ecology-Progress Series 2001;214():15-23 |
R826792 (2000) R826792 (Final) |
not available |
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Walsh JJ, Weisberg RH, Dieterle DA, He R, Darrow BP, Jolliff JK, Lester KM, Vargo GA, Kirkpatrick GJ, Fanning KA, Sutton TT, Jochens AE, Biggs DC, Nababan B, Hu C, Muller-Karger FE. Phytoplankton response to intrusions of slope water on the West Florida shelf: models and observations. Journal of Geophysical Research 2003;108(C6):3190. |
R826792 (Final) |
not available |
Supplemental Keywords:
harmful algal blooms, ecosystem, habitat, marine science, ecology, oceanography, monitoring, satellite, Gulf of Mexico, tourist industry., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, State, Oceanography, algal blooms, Biochemistry, remote sensing, bloom dynamics, coastal resources, hydrography, marine biotoxins, brevetoxins, phytoplankton, remote sensing techniques, bioindicator development, transport and concentration, ECOHAB, Florida, FLAProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.