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

Project Proposal for 1999

Project title: Chronology and Isotope Geochemistry of Ground Waters in the Florida Keys and Offshore Areas
Geographic area: Florida Bay, Florida Keys, and Coral Reefs
Project start date: 1996
Project end date: 1999?

Project chief: J.K. Bohlke (co-PIís-WRD: L.N. Plummer, T.B. Coplen, E. Busenberg; co-PI-GD: E.A. Shinn)
Region/Division/Team/Section: ER/WRD/NRP
Email: jkbohlke@usgs.gov
Phone: 703-648-6325
Fax: 703-648-5274
Mail address: 431 National Center, Reston, VA 20192

Program(s) (list all programs to which this work plan is being submitted):
Integrated Natural Resources Science Program

Program element(s)/task(s) (show percent distribution if more than one element/task). If submitting to more than one program, include element(s)/tasks from each program here:
Element 7: Florida Bay, Florida Keys, and the Coral Reefs
Task 7.2: Hydrogeology of Florida Bay and Florida Keys

Project summary: A brief (<100 words) summary written to be understood by a nonspecialist. State the issues to be addressed, the objectives of the project, significance to scientific questions and land-management and policy issues, and benefit to the Nation, all in terms that do not require technical translation. This paragraph will be used to describe this project in the Program and Division science plans.
    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.

Project objectives and strategy: More detailed/technical than the project summary, describing BRIEFLY the technical goals and approaches to be used over the LIFETIME of the project.
    We propose to test the use of environmental isotopes and tracers, combined with geochemical modeling, for determining the origins and ages of the various ground waters in the region of Florida Bay and the Keys, the extent and velocity of contaminant plumes, the fate of anthropogenic contaminants, and water-aquifer reactions that alter the source characteristics. The empirical approaches being tested include: (1) analyses of CFCís, carbon-14, and tritium and helium isotopes for information about the residence times of water and dissolved species in the subsurface; (2) analyses of stable isotopes of carbon, sulfur, hydrogen, oxygen, and nitrogen for information about sources of, and chemical reactions among, waters, nutrients, and other species; and (3) modeling of chemical reactions and residence time distributions. This work will complement other ongoing or proposed studies in the Keys involving deliberate tracer injection, hydraulic monitoring and modeling, and analyses of additional specific contaminants.
    The major elements of the data gathering part of the study are (1) well installation and selection, to provide regional coverage of various ground-water environments along with depth resolution at selected sites (many of these were done before the study, additional ones have been installed on the basis of the earlier rounds of sampling); (2) two intensive field sampling campaigns in which all of the constituents of interest are collected from a subset of the sites (one of these sampling episodes occurred in Winter 1996; the other was in Fall, 1997); (3) laboratory analyses of sample sets (some of these are done in-house; others are contracted out; overall time required for each set can be as much as a year). Modeling and interpretation of results take place in preliminary fashion as data become available, but comprehensive and reliable treatments rely upon multicomponent evaluations involving the whole data set. In particular, the treatment of chronological tracers will be done simultaneously in such a way that various combinations of flow, mixing, and degradation models can be compared. Inverse geochemical modeling will be done to determine reactions responsible for producing observed water quality characteristics (including nutrient concentrations) in the subsurface.

Potential impacts and major products: Describe expected outcomes, both scientific and management/policy-related. What scientific questions and land-management and policy issues does this project help answer? Why is it important to Program priorities? What products will you produce to contribute to the desired outcomes?
    This project will provide quantitative information about the origins, residence times, and nutrient chemistry of marine ground waters beneath the Florida Keys and nearby offshore areas. Chronologic and isotopic data for ground waters should be useful in assessing the extent and rate of movement of potential contamination in the subsurface; nutrient chemistry and isotopic data should be useful in distinguishing natural and anthropogenic sources of chemical constituents in ground water. These data and interpretations should aid decision-making about waste-water treatment and disposal in the region. In addition, the study includes testing some new combinations of methods and sample types that could expand the list of approaches available to the scientific community for future investigations of similar problems.

Collaborators, clients (Names, affiliation, and roles of internal and external users of information generated by project):
    The study is designed as a collaboration between researchers in the Water Resources Division and the Geologic Division in USGS. The study complements (and is coordinated with) several other studies in the same area. Those include: INRSP Tasks 1.7, 7.2, and 7.3, which deal with various aspects of hydrology, ground-water/surface-water interactions, and sediment diagenesis in Florida Bay and the Keys; EPA-funded radon tracer study; EPA-funded coral and hardbottom monitoring project; EPA-funded seagrass monitoring project; USGS aerial magnetic ground-water salinity mapping project; and other USGS and S. Florida Water Management projects being conducted in Florida Bay. Information about the movement and quality of ground water beneath Florida Bay, the Keys, and offshore reefs will be helpful in the design of efficient regulation policies for waste-water disposal by the Florida Dept. of Environmental Protection, the NOAA Florida Keys National Marine Sanctuary, and Everglades National Park.

Time line (FY 1999 to project end): List MAJOR tasks and deliverables by fiscal year and indicate key staff responsible for each.
    In FY99 (end year?), analyses and data summaries of samples collected in FY96-FY98 will be completed (all Reston PIís). 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 the Reston PIís). Results will be compiled and evaluated in terms of ground water sources, residence times, and geochemical reactions (all Reston PIís). Reports will be written on (1) origins and residence times of marine ground waters, and (2) nutrient chemistry of marine ground waters (Reston PIís plus Shinn).

FY 1999 activities: Statement of the work to be undertaken in FY 1999 and a description of the methods and procedures.
    Analyses of samples collected in FY96-FY98 will be compiled and evaluated. Simple mixing, dispersion, and 1-dimensional flow models will be used to interpret the chronological data and determine ground-water residence times; solutions will be sought that can account simultaneously for as many tracers as possible, and discrepancies will be evaluated with respect to possible degradation, contamination, or other more complex behavior. Chemical data will be evaluated with geochemical equilibrium speciation models and inverse geochemical reaction models to investigate natural processes affecting water quality and nutrient concentrations. A few new samples will be collected and analyzed for nutrients, chemistry, and stable isotopes (H, 0, and N) to characterize specific endmembers identified as minor mixing components in the marine ground water survey, including fresh ground waters from beneath recharge areas on Key Largo, water-supply samples, and waste-water samples from a selection of local treatment plants.

FY 1999 deliverables/products: Describe in more detail the specific deliverables/products that will result from this work in FY 1999.
    A comprehensive data report will be compiled with all of the analytical data, methods of analysis, etc. Topical reports will be prepared focusing on: (1) the origins and residence times of the marine ground waters; and (2) nutrient sources and isotopic characteristics.

FY 1999 outreach: Emphasizing FY 1999, describe plans to address client requirements, decisions, and deadlines.
New directions or major changes for FY 1999 (if applicable):

FY 1998 accomplishments and outcomes, including outreach:
    The major accomplishments so far 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. Analyses and some preliminary evaluations should be completed by about the end of FY98.

FY 1998 deliverables, products completed:
    Collection and analysis of samples comprising a comprehensive regional survey of marine ground waters beneath the Florida Keys, in offshore transects to the reefs, and throughout the Bay, will have been completed by the end of FY98. Data reports and interpretive reports have been started, but will not be completed until sometime in FY99.

Names and expertise (e.g. carbonate petrology) of key project staff (list by fiscal year for duration of project):

  • J.K. Bohlke (hydrologist, geochemist) FY99 to end
  • L.N. Plummer (hydrologist, geochemist) FY99 to end
  • E. Busenberg (inorganic and trace gas chemist) FY99 to end
  • T.B. Coplen (isotope chemist) FY99 to end
  • E. Shinn (geologist) FY99 to end
  • J.E. Hannon (stable isotope analysis) FY99
  • C. Reich (geologist) FY99

Other required expertise for which no individual has been identified (list by fiscal year for duration of project):

(Assistant for isotope analysis, data compilation and geochemical modeling in Reston) FY99 to end
(Assistant for limited sampling in Florida) FY99
Major equipment/facility needs (list by fiscal year for duration of project):

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Last updated: 24 April, 2014 @ 01:13 PM (KP)