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Chronology and Isotope Geochemistry of Ground Waters in the Florida Keys and Offshore Areas

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Frequently-anticipated questions:

What does this data set describe?

Title:
Chronology and Isotope Geochemistry of Ground Waters in the Florida Keys and Offshore Areas
Abstract:
This project involves sampling surface waters and ground waters from Florida Bay, the Keys, and offshore to the barrier reef. Analyses will be done on a variety of isotopic and chemical species that have been used elsewhere to determine ground-water ages, contaminant sources, and geo- chemical reactions. Water Research Discipline researchers will coordinate ground water sampling and analytical work; Geologic Discipline researchers will provide access to wells and back- ground data, handle field logistics, etc.
Supplemental_Information:
This project ended in FY 1999. No data is available through the SOFIA Data Exchange pages.
  1. How should this data set be cited?

    J. K. Bohlke L. N. Plummer, T. B. Coplen, E. Busenberg, E. A. , Unpublished Material, Chronology and Isotope Geochemistry of Ground Waters in the Florida Keys and Offshore Areas.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -82.2
    East_Bounding_Coordinate: -79.82
    North_Bounding_Coordinate: 25.69
    South_Bounding_Coordinate: 24.27

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 1996
    Ending_Date: 1998
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

    2. What coordinate system is used to represent geographic features?

  7. How does the data set describe geographic features?

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    J. K. Bohlke
    U.S. Geological Survey
    431 National Center
    Reston, VA 20192
    USA

    703 648-6325 (voice)
    703 648-5274 (FAX)
    jkbohlke@usgs.gov

Why was the data set created?

A significant issue of concern in South Florida is the potential effect of anthropogenic pollutants from the Florida Keys or elsewhere on the water quality and health of offshore marine ecosystems. It has been suggested that certain contaminants (e.g., bacteria, excess nutrients) found in some offshore ground waters may be transported 'in the subsurface to discharge sites beneath Florida Bay or the reef tract, where they may be contributing to declining ecosystem health. But not much is known about the origins of the ground waters underlying the region, how the subsurface flow systems operate, and what is the fate of contaminants emplaced in ground water in the Keys.

Ground waters are potential sources, sinks, and carriers of nutrients and other contaminants beneath the Florida Keys and offshore regions to the north and south. This project is designed to provide new data on the sources, flow directions, exchange rates, and chemical characteristics of ground waters underlying the region of Florida Bay, the Keys, and offshore reefs. The results, to be derived in part from analyses of environmental tracers and isotopes, will provide general empirical information about subsurface transport processes and their potential impact on surface water chemistry.

How was the data set created?

  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    Date: 1998 (process 1 of 2)
    Samples for analysis are to be collected during 2 intensive field campaigns from observation wells, seepage collectors, and surface waters, to be accessed largely by boat. One of those collections occurred in 1996; another is planned for summer 1997 to complete the regional survey. The following types of analyses are to be done: 1 - Major-element water chemistry and dissolved gases. These data are essential for comparing water types and for calculating potential reaction relations among different waters (e.g., seawater reduction, mixing, etc.). 2 - Nitrogen isotopes in ammonium, nitrate, and N2 gas. Concentrations and isotope mass balances will be examined for evidence relating high ammonium in offshore ground waters to potential sources such as waste water and natural sedimentary organic matter. 3 - Chlorofluorocarbons (CFC's). Contamination levels of CFC's may indicate anthropogenic point sources; ambient levels may be useful in dating the recharge (entry into the subsurface) of the ground waters; no CFC's could indicate ages more than 50 years, or possibly degradation of CFC's. 4 - Tritium and He isotopes. Tritium-helium dating may indicate the residence times of ground waters since recharge from the ocean or the bay or the Keys; these data may be necessary as backup for the CFC's because of the possibility of CFC degradation in some of the reducing waters, or they may be used in conjunction with the CFC's to indicate ground-water mixing or dispersion phenomena. 5 - C-14 and stable carbon isotopes in carbonate, methane, and dissolved organic carbon. Isotopes and chemistry of around waters will be used for calculating reactions that might represent conversion of seawater into reduced marine ground water; information about the sources of organic constituents may be derived; very old waters may be detected. 6- Sulfur isotopes in sulfide and sulfate, plus mass balance of sulfate reduction. Sulfur derived from modern seawater (or Florida Bay) may be distinguishable from sulfur coming out with deep old ground waters; these data are also needed for reaction modeling. 7- Stable oxygen and hydrogen isotopes of water. Water isotopes are potentially useful for distinguishing water units such as evaporated, meteoric, marine, glacial/intergiacial, etc.

    The major accomplishments for FY98 were an intensive sampling effort in November, 1997 and subsequent analytical work on the samples. Approximately 1200 samples were collected from about 40 sites, mainly in Florida Bay, and including a few representatives of surface waters, water supplies, and nested piezometers. This sample set complements the one obtained in FY96 by extending the coverage of the project throughout Florida Bay, by including more vertical resolution at selected sites, and by including some shallow ground waters and seepage meters at one of the ocean-side experimental tracer sites.

    Date: 1999 (process 2 of 2)
    In FY99 analyses and data summaries of samples collected in FY96-FY98 will be completed. A small number of additional samples will be collected and analyzed for a subset of chemical and isotopic constituents, to fill specific gaps in the sets collected so far, and to provide some indication about short-term changes at selected sites over the course of the study (collections with aid from Shinn and Reich; analyses by Bohlke, Plummer, and Busenberg). Results will be compiled and evaluated in terms of ground water sources, residence times, and geochemical reactions. Reports will be written on (1) origins and residence times of marine ground waters, and (2) nutrient chemistry of marine ground waters.

    Person who carried out this activity:

    J. K. Bohlke
    U.S. Geological Survey
    431 National Center
    Reston, VA 20192
    USA

    703 648-6325 (voice)
    703 648-5274 (FAX)
    jkbohlke@usgs.gov

  3. What similar or related data should the user be aware of?

    Griggs, E. M. Krump, L. R., Bohlke, J. K., 2003, The fate of wastewater-derived nitrate in the subsurface of the Florida Keys: Key Colony Beach, Florida: Estuarine, Coastal and Shelf Science 58, Elsevier Science BV, Amsterdam, Netherlands.

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    unknown

  5. How consistent are the relationships among the observations, including topology?

    unavailable

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: none
Use_Constraints:
Any data are subject to change and are not citeable until reviewed and approved for official publication.

  1. Who distributes the data set? (Distributor 1 of 1)

    J. K. Bohlke
    U.S. Geological Survey
    431 National Center
    Reston, VA 20192
    USA

    703 648-6325 (voice)
    703 648-5274 (FAX)
    jkbohlke@usgs.gov

  2. What's the catalog number I need to order this data set?

    data from Chronology and isotope geochemistry of groundwaters in the Florida Keys and offshore areas

  3. What legal disclaimers am I supposed to read?

    No warranties are implied or explicit for the data.

  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 26-Oct-2006
Metadata author:
Heather Henkel
U.S. Geological Survey
600 Fourth Street South
St. Petersburg, FL 33701
USA

727 803-8747 ext 3028 (voice)
727 803-2030 (FAX)
sofia-metadata@usgs.gov

Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

This page is <http://sofia.usgs.gov/metadata/sflwww/chron_isotope_geochem_FL_Keys.faq.html>

U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
Comments and suggestions? Contact: Heather Henkel - Webmaster
Generated by mp version 2.8.18 on Thu Oct 26 18:19:03 2006