6. An interdisciplinary (geologic, hydrologic and biologic) investigation of the processes controlling Florida’s harmful algal blooms (HABs)
The coastal waters of Florida are highly productive and are extremely important for recreational and commercial fisheries and tourism. Recently, much public and scientific attention has been directed at the coastal waters off west-central Florida because of the occurrence of wide-spread persistent and recurring harmful algal blooms (HABs). These HABs, which date back prior to pre-anthropogenic conditions, are indicative of widespread eutrophication; that is, rapid plankton growth rates in response to high nutrient conditions lead to bottom water hypoxia, as well as widespread fish kills from phyto-toxins. HABs require a significant source of “new” nutrients. However, recent work has demonstrated that estuarine fluxes provide insufficient phosphorus and nitrogen to support these blooms (Vargo and others, 2004), and no single inorganic nutrient source is sufficient to support such large blooms (Vargo and others, in revision). While a current paradigm suggests that fallout of nutrients from continental dust particles may provide a source of nutrients to stimulate HABs, we have convincing evidence that the submarine groundwater-derived nutrients, enhanced by hurricane-induced high precipitation events, may be a much greater labile source of nutrients to these coastal waters (Hu and others, 2006). This research opportunity would tie directly into existing and pending projects on this topic that explores linkages between the “leaky” coastal aquifers of Florida and role of submarine groundwater discharge-derived nutrients and trace elements to the evolution of HABs.
The research questions are thus focused around identifying and quantifying potential source(s) (that is, submarine groundwater discharge, marine, recirculated) of new nutrients capable of initiating and supporting sustained plankton blooms that may cause extensive hypoxic conditions and eventual ecosystem degradation. We believe that the answer is the submarine discharge of nutrient-rich groundwater, which appears to be modulated by natural and hurricane-induced precipitation events on land. What we know little of at present is precise processes, driving factors (terrestrial vs. marine) and time/spatial scales. Groundwater has long been identified as a potential nutrient source to estuarine and coastal waters (for example, D’Elia and others, 1981; Krest and others, 2000; Dowling and others, 2004). Despite the presence of many first-order magnitude springs around the state (both on land and offshore) in areas where red tides do occur, the link between submarine groundwater discharge (SGD) nutrient inputs and red tides has not been addressed fully (Hu and others, 2006; Swarzenski, 2007). SGD rates and their role in the transport of “new” nutrients need to be examined given our increased awareness of enhanced benthic exchange processes across leaky coastal margins (Swarzenski and Kindinger, 2003; Dowling and others, 2004). SGD fluxes of phosphate and dissolved inorganic nitrogen far exceed the inputs to Tampa Bay from rivers (Hu and others, 2006; Swarzenski and others, 2006a,b, 2007) is also likely that this SGD continues to occur offshore, as well.
The primary objective of this postdoctoral research opportunity will be to work with a broad team of researchers to determine rates of submarine groundwater discharge and associated nutrient fluxes to the coastal waters off west-central Florida. We anticipate that the research will provide a geologic framework for the complex hydrogeology along peninsular Florida, into which we can place our SGD interpretations. The Mendenhall Fellow will enhance our existing capabilities by focusing on developing a more quantitative interpretation of streaming and time series resistivity techniques to evaluate the anisotropy of Florida’s coastal aquifers in terms of water/constituent transport.
In addition to the offshore work, where the role preferential flow paths will be elucidated using a combination of novel geochemical and geophysical techniques, it is also important to assess the shallow-water “boundary zone” close to shore. Near-shore activities of radium and radon are often elevated in these waters, which imply a combination of tidal-pumping, wave-induced flushing of the sediments, and groundwater discharge from the surficial aquifer when the water table is elevated. Access to a guided surface vehicle (GSV) capable of maneuvering in these shallow waters to sample for radon and nutrients can be arranged.
REFERENCES
D’Elia, C. F., Webb, K. L., and Porter, J. W., 1981, Nitrate-rich groundwater inputs to Discovery Bay, Jamaica: A significant source of N to local coral reefs?: Bulletin of Marine Science, v. 31, p. 903–910.
Dowling, C. B., Poreda, R.J., Hunt, A.G., and Carey, A.E., 2004, Ground water discharge and nitrate flux to the Gulf of Mexico: Ground Water, v. 42, no. 3, p. 401–417.
Hu, C., Muller-Karger, F., and Swarzenski, P.W., 2006, Hurricanes, submarine ground-water discharge and Florida’s red tides: Geophysical Research Letters, v. 33, no. L11601, doi:10.1029/2005GL025449.
Krest, J.M, Moore, W.S., Gardner, L.R. and Shaw, T.J., 2000, Radium isotope geochemistry in shallow groundwater below the North Inlet salt marsh, South Carolina: Global Biogeochemical Cycles, v. 14, no. 1, p. 167–176.
Swarzenski, P.W., 2007, U/Th series radionuclides as tracers of coastal groundwater: Chemical Reviews, v. 107, no. 2, p. 663–674, DOI: 10.1021/cr0503761.
Swarzenski, P.W., and Kindinger, J.L., 2003, Leaky coastal margins: Examples of enhanced coastal groundwater/surface water exchange from Tampa Bay and Crescent Beach Submarine Spring, Florida, USA, in Cheng., A.H.D., and Ouazar, D., eds., Coastal aquifer management, monitoring and modeling and case studies: Boca Raton, Fla., CRC Press, p. 93–112.
Swarzenski, P.W., Orem, W.G., McPherson, B.F., Baskaran, M., and Wan, Y., 2006a, Biogeochemical transport in the Loxahatchee river estuary: The role of submarine groundwater discharge: Marine Chemistry, v.101, p. 248–265.
Swarzenski, P.W., Burnett W.C., Weinstein, Y, Greenwood, W.J., Herut, B., Peterson, R., and Dimova, N., 2006b, Combined time-series resistivity and geochemical tracer techniques to examine submarine groundwater discharge at Dor Beach Israel: Geophysical Research Letters, v. 33, p. L24405, doi:10.1029/2006GL028282.
Swarzenski, P.W., Reich, C., Kroeger, K. and Baskaran, M., 2007, Ra and Rn isotopes as natural tracers of submarine groundwater discharge in Tampa Bay, FL: Marine Chemistry, v. 104, p. 69–84.
Vargo, G. A., Heil, C.A., Ault, D.N., and others, 2004, Four Karenia brevis blooms : A comparative analysis, in Steidinger, K.A., Landsberg, J.H., Tomas, C.R., and Vargo, G.A., eds., Harmful Algae 2002, Xth Hab: St. Pete Beach, Fla., 10th International Conference, October 21 -25, 2002. p. 14–16.
Vargo, G.A., Heil, C.A., Fanning, K.A., Dixon, L.K., Neely, M.B., Lester, K., Ault, D., Murasko, S., Havens, J., Walsh, J.J., and Bell, S., in revision, Nutrient availability in support of Karenia brevis blooms on the central West Florida Shelf: What keeps Karenia blooming: Continental Shelf Research.
Proposed Duty Station: St. Petersburg, FL; Menlo Park, CA; Santa Cruz, CA
Areas of Ph.D.: Chemical oceanography, marine biogeochemistry, hydrogeology
Qualifications: Applicants must meet one of the following qualifications: Research Chemist, Research Oceanographer , Research Hydrologist
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)
Research Advisor(s): Peter Swarzenski, (727) 803-8747, x 3072 , pswarzen@usgs.gov; Richard Poore, (727) 803-8747, x 3131, rpoore@usgs.gov; James Krest, University of South Florida, (727) 533-4970, krest@stpt.usf.edu; Chuanmin Hu, University of South Florida, (727) 553-3987, hu@seas.marine.usf.edu; Frank Muller-Karger, University of South Florida, (727) 553-3335, carib@marine.usf.edu; Cynthia Heil, Florida Wildlife Research Institute, (727) 896-8626, Cindy.Heil@fwc.state.fl.us
Human Resources Office contact: Kathy McDuffie, (703) 648-7408, kmcduffie@usgs.gov
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Summary of Opportunities |