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projects > interactions of mercury with dissolved organic carbon in the florida everglades > 1998 proposal


Interactions of Mercury with Dissolved Organic Carbon in the Everglades

Project Proposal for 1998

Program: FRAGILE ENVIRONMENTS

Project Title: Interactions of Mercury with Dissolved Organic Carbon in the Everglades
Location of Study Area: South Florida Ecosystem
Project Start Date: 1/95
Project End Date: 9/99
Project Number: 4386-34900

Project Chief: George Aiken; Mike Reddy
Region/Division/Team/Section: CR/WRD/BRR
E-mail: graiken@usgs.gov, mmreddy@usgs.gov
Phone: (303) 541-3036; (303) 541-3012
Fax: (303) 447-2505
Mailing Address:
U. S. Geological Survey
3215 Marine Street
Boulder, Colorado 80303

Program Element(s)/Task(s) Element 6
Task 6.8 Interactions of mercury and DOC in the Everglades

Panel:
Collaborators, Clients:
1. Other Ecosystem Initiative projects - our role will be to provide DOC data and relevant information about the nature of the DOC at key sampling locations.
2. Dr. Cynthia Gilmour - Benedict Estuarine Lab. Dr. Gilmour will be studying microbial mercury methylation rates. We will provide data and samples of isolated organic material to assess the role of DOC-Hg interactions in controlling the rate of methylmercury generation.
3. Dr. Rochell Araujo, US EPA, Athens, Georgia. Dr. Araujo is interested in chemical speciation modeling. We will provide binding constant data and will work with EPA modelers on the speciation modeling.
4. WRD South Florida NAQWA project. It is planned to co-locate sampling sites. We will share data and results from our work.
5. Larry Fink, South Florida Water Management District and Dr. Tom Atkeson, Florida Department of Environmental Protection. Data, field information, and assistance in the form of field help and space have been made available to us. will share our findings and consult with these agencies regarding issues involving the transport and reactivity of DOC.
6. Dr. Joseph Ryan, University of Colorado. Dr. Ryan and Ravi Mahalingam, Ravichandran, graduate student from the University of Colorado, are working with us to determine Hg-DOC binding constants. This part of the research is funded separately under an interagency agreement with the EPA.



BACKGROUND NARRATIVES

Project Summary: Interactions of mercury and dissolved organic matter (DOC) play an important role in controlling both the availability of mercury for uptake by living organisms, and the types of chemical reactions that can occur with mercury. The goal of our research is to provide information about the interactions of mercury and dissolved organic matter that will better define this important, albeit, poorly understood process. Effective management strategies will require a more thorough understanding of the processes that control the reactivity, bioavailability and transport of mercury in the Everglades. Ultimately, our research will lead to a more complete model of mercury behavior in the Everglades ecosystem.

Project Justification: Effective management strategies for mitigating mercury contamination of game fish in South Florida requires understanding of factors and processes resulting in the transport and controlling the reactivity and bioaccumulation of Hg in the Everglades. Our project will focus on the effect of DOC on the transport and reactivity of Hg in the Everglades. Results of this research will be used by U. S. Geological Survey, South Florida Ecosystem Initiative scientists, U. S. EPA, Florida Department of Environmental Protection, and the South Florida Water Management District. It is expected that the information provided by this project, especially with regard to the Hg-speciation model, will be used by management agencies in South Florida to implement remediation strategies. It is recognized that the chemical forms of Hg in the water column and sediments are intimately related to bioaccumulation and body burden

Project Objectives: Interactions of Hg with DOC appear to be important in controlling the transport and fate of Hg in the water column. To understand the chemistry of Hg in aquatic systems, better definition of geochemical processes as they apply to DOC is required. Our research will meet this need by focusing on the interactions of the cationic forms of Hg with DOC in a combined field/laboratory study. The characterization of Hg binding resulting from this study will help quantify DOC facilitated transport of Hg in the Everglades. The specific objectives of this research are:

1. To determine the nature and amount of DOC in the Florida Everglades. This work will lead to a more detailed understanding of the influence of hydrologic and seasonal factors on the nature and reactivity of DOC at the field study locations.
2. To measure distribution coefficients for Hg with DOC and aquatic humic substances isolated from the Everglades and elsewhere.
3. To incorporate the distribution coefficient data into speciation models to better describe the geochemistry of Hg in aquatic systems containing DOC.
4. To identify analytical parameters to predict potential organic matter-Hg interactions.

Overall Strategy, Study Design, and Planned Major Products: Our project will use a combined field/laboratory approach to assess the significance and strength of DOC-Hg interactions in the Everglades. Temporal variations in DOC concentrations will be measured at appropriate sampling locations to provide a measure of DOC loadings in the system. Major fractions of the DOC will be isolated from the water and characterized by determining chemical composition, molecular weight, and structural characteristics. Whole water samples and the isolated fractions of the DOC will then be used to study interactions of DOC with mercury in laboratory experiments. The goal of these measurements will be to increase our understanding of how mercury interacts with DOC. These measurements will also provide binding constants, which will be used to model the geochernical behavior of mercury in the Everglades. This model will allow us to synthesize the overall effects of the DOC-Hg associations and how they change as the qualitative and quantitative character of the DOC varies in our study systems. The major products of this research will be water quality data published in the form of a USGS Open-file report, journal articles, and a PhD thesis.

WORK PLAN

Overall: Our project will use a combined field/laboratory approach to assess the significance and strength of DOC-Hg interactions in the Everglades. Both the inorganic composition of, and the DOC associated with, surface water, pore waters, and ground water from the Everglades will be characterized. Temporal variations in DOC concentrations will be measured at appropriate sampling locations to provide a measure of DOC loadings in the system. These measurements will be coupled with determinations of the nature of the DOC under different hydrologic conditions (low and high flow conditions). Major fractions of the DOC will be isolated from the water samples for further analysis. These fractions are composed of a variety of organic compounds, each interacting differently with mercury. The fractions will be characterized by determining chemical composition, molecular weight, and structural characteristics.

Whole water samples and the isolated fractions of the DOC will then be used to study interactions of DOC with mercury in laboratory experiments under a range of pH and concentration conditions. In addition, these measurements will also be made with previously isolated samples from other locations that vary significantly in structural composition. The goal of these measurements will be to increase our understanding of how mercury interacts with DOC. These measurements will also provide binding constants. which are a measure of the strength of the mercury-DOC interactions, that will be correlated with the structural properties of the organic matter to provide inexpensive analytical parameters to be used to estimate the strength of DOC-mercury interactions in the Everglades.

Finally, using the binding constants determined in the laboratory studies, a computer program will be used to model the geochemical behavior of mercury in the Everglades. This model will allow us to synthesize the overall effects of the DOC-Hg associations and how they change as the qualitative and quantitative character of the DOC varies in our study systems

Timeline:

                         FY 1997         FY 1998         FY 1999
     Activities           1997            1998            1999
                      1  2  3  4      1  2  3  4      1  2  3  4
Equipment Purchase          X  X
Data Collection       X  X  X  X      X  X  X  X
Data Analysis         X  X  X  X      X  X  X  X      X  X
Interim Products      X     X         X               X
Write First Drafts             X      X               X  X  X
Mtg With Clients            X  X            X  X               X
Directors Approval          X	      X                        X

Planned Deliverables/Products:
1.) USGS Open File report series of water quality data. The first installment of this continuing series has been published. Additions to this series will become available approximately annually.
2.) Journal articles detailing the spatial, seasonal and hydrologic variability in DOC. It is anticipated that a draft of the first paper describing DOC in the Everglades suitable for review will be available 10/97. Anticipated publication 3/98.
3.) PhD thesis describing DOC-Hg binding constant research. Anticipated 6/98.
4.) Journal articles describing DOC-Hg binding constant research. Anticipated 1/99.

Planned Outreach Activities: The results of this research will be presented in overall project reviews (Florida DEP, SFWMD), information meetings (USGS), and scientific meetings (ACS, ASLO). Data and results are shared freely with other Ecosystem Initiative projects working in South Florida through project meetings, USGS Open-file report, and upon request.

Prior Accomplishments in Proposed Area of Work: N/A

New Directions, Expansion of Continuing Project (if applicable): It is anticipated that field related studies will continue through FY 1998 in support of the mercury geochemistry work being done as part of the South Florida Ecosystem Initiative. More attention will be given to the ENR, a site that is receiving more attention by the project overall, and sites within WCA2B and WCA3A that were identified in FY 96 as being active with respect to methylmercury. Our field effort will be extended to any new sites to the south of WCA2 that will be potentially added to the study in FY 97.

Increased attention will be given to the role of DOC in the photochemical activity of mercury in the system. This is an important process in the cycling of mercury that is thought to be intimately tied to the reactivity of the DOC. In addition, this process is important for understanding carbon cycling in the Everglades. Preliminary experiments have indicated that the DOC in the surface waters of the Everglades is photochemically active. This work is being done in conjunction with Dave Krabbenhoft (USGS) and Jim Hurley (DNR, Wis.).

Additional research will be done to understand the distribution of Hg among various fractions of the DOC by developing "clean" DOC fractionation techniques, and by combining the DOC fractionation approach with ultrafiltration.

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH

Accomplishments and Outcomes, Including Outreach: FY 97 has been devoted primarily to the collection and characterization of field samples. Three major field trips were undertaken in FY 97 to determine the temporal and spatial variability of (DOC) and water chemistyr at select sites in WCA2 and WCA3. Characterization of these samples is an ongoing task. The preliminary results are rather exciting in that the differences in both the quantity and quality of the DOC in the zones where mercury is most active are different from that noted in other areas under study. In addition, large differences in porewater profiles were noted between wet and dry periods. Prior to the past two spring field seasons the Everglades were uncharacteristically wet preventing the collection of dry-period samples

Jim Hurley of Wisconsin DNR spent 3 months working in Aiken's laboratory during the spring of 1997. This time was spent collaborating on the development of 11 clean" procedures for DOC fractionation, designing studies to understand differences in Hg fractionation by ultrafiltration, and designing both field and laboratory experiments to better define the photochemical behavior of both Hg and DOC. These experiments are scheduled to be carried out during the summer of 1997 and into FY 98.

A collaboration was developed with Carol Kendall to determine the stable isotopic composition of isolates and plant materials in the Everglades. This work is being done in conjunction with a series of plant extractions to help define the sources of DOC in the Everglades. This research will be tied into Carol's efforts to use isotopic analyses to define food-web dynamics and will be an important part of the carbon cycling story.

Also in FY 97, Mahalingam Ravichandran, a graduate student at the University of Colorado, continued his work to determine the mercury-DOC binding constants. This work is funded separately under an agreement with the EPA, however, it is an important element of our mercury-DOC work in the Everglades. This research has focused on the application of an ion-exchange distribution method for the measurement of binding constants and cinnabar dissolution experiments to directly assess the ability of organic matter to compete with sulfide for Hg. Preliminary results indicate that Hg interacts strongly with organic matter isolated from the Everglades.

Deliverables, Products Completed:
1. Factsheet entitled: "Interactions of Mercury with Dissolved Organic Carbon in the Florida Everglades" by George Aiken and Mike Reddy published in late FY 96
2. Data report entitled: "Summary of Data from On site and Laboratory Analyses of Surface Water and Marsh Porewater from South Florida Water Management District Water Conservation Areas, the Everglades, South Florida, March, 1995" by Michael Reddy, George Aiken, Paul Schuster, Charmaine Gunther, Scott Charlton, and Jason Tregellas approved FY97
3. Abstract entitled "Dissolved organic matter in the Everglades, Florida" by G. R. Aiken and M. M. Reddy was published as part of the August 1996 ACS meeting, Orlando, Florida
4. Abstract entitled "Dissolved organic carbon/fulvic acid ionic mercury interactions in the Everglades water conservation areas. Surface and sediment porewater DOC concentrations and fulvic acid mercury binding potentials" by M. M. Reddy and G. R. Aiken was published as part of the August 1996 ACS meeting, Orlando, Florida
5. Abstract entitled "Dissolved organic matter in the Everglades, Florida" by G. R. Aiken and M. M. Reddy was published as part of the February 1997 ASLO meeting, Santa Fe, New Mexico
6. Manuscript entitled "System Controls on Aqueous Mercury Distribution in the Northern Everglades" by J.P. Hurley, D.P. Krabbenhoft, L.B. Cleckner, M.L. Olson, G. Aiken and P.J. Rawlick has been submitted for publication by the journal Biogeochemistry
7. Seminar entitled "Interactions of mercury with dissolved organic carbon in natural waters" presented by M. Ravichandran, April 1997, University o Colorado, Boulder, CO.
8. Presentation of findings by G. Aiken at meeting of researchers for Mercury Project (South Florida Ecosystem Initiative) October 1996, Madison, Wis.
9. Abstract and presentation of talk entitled "Dissolved organic matter in the Everglades, Florida" by G. Aiken and M. Reddy at the Annual Workshop - South Florida Mercury Science Program (Florida DEP, SFWMD) May, 1997
10. Abstract and presentation of talk entitled "Speciation and fractionation modeling studies - DOC-Mercury Interaction" by M. Reddy and G. Aiken at the Annual Workshop - South Florida Mercury Science Program (Florida DEP. SFWMD) May 1997
11. Abstract entitled "Dissolved organic matter in the Everglades, Florida" by G. Aiken and M. Reddy to be presented at the Annual South Florida Symposium (USGS) August, 1998
12. Abstract entitled "Speciation and fractionation modeling studies - DOC-Mercury Interaction" by M. Reddy and G. Aiken to be presented at the Annual South Florida Symposium (USGS) August, 1998

NEEDS

Required Expertise:
FY 98
Chemists
Technicians
Field Assistance
Modelers

FY 99
Chemists
Technicians
Modelers

Names of Key Project Staff:
FY 98
George Aiken (Project chief)
Mike Reddy (Project chief)
Paul Schuster
Jason Tregellas
Janece Koleis

FY 99
George Aiken (Project chief)
Mike Reddy (Project chief)
Paul Schuster

Major Equipment/Facility Needs:
FY 98
Laboratory space for organic, inorganic and mercury analysis

FY 99
Laboratory space for organic, inorganic and mercury analysis


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