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projects > interactions of mercury with dissolved organic carbon in the florida everglades > 1999 proposal


Interactions of Hg with DOC in the Florida Everglades

Project Proposal for 1999

Project number: 4386-34900

Project Title: Interactions of Hg and DOC in the Everglades
Geographic Area: Florida Everglades
Project Start Date: 1/95
Project End Date: 9/99

Project chief(s):  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 SL
Boulder, CO 80303

Program(s): INATURES

Program element(s)/task(s):  Element 4/ Task 4.4
Interactions of Hg and DOC in the Everglades

BACKGROUND NARRATIVES
Project Summary: Interactions of mercury and dissolved organic matter play important roles in controlling both the availability of mercury for uptake by living organisms, and the types of chemical reactions that can occur with mercury. Our research goal 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.

Project objectives and strategy: 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 thc influences of hydrologic and seasonal factors on the nature and the 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.

Our project will use a combined field/laboratory approach to assess the significance and strength of DOC-Hg 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 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.

Potential Impacts and Major Products: 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. Results of our research will be used by US Geological Survey, South Florida INATURES scientists, US EPA, Florida DEP, and SFWMD. It is expected that the information provided by this project will be used by management agencies in South Florida to implement remediation strategies. 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 Ph.D. thesis.

Collaborators, Clients:
  1. Other INATURES 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 is 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. Dr. 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. We 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 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.

WORK PLAN
Time line:
 
Activity FY1998 FY 1999
1998 1998 1999
4 1 2 3 4
Field work          
Data collection X X      
Data analysis X X X    
Interim products X X      
First drafts   X X X  
Mtg with clients X   X   X
Director's approval       X X

Major tasks:
1. DOC analyses, characterization, data interpretation - Aiken
2. Inorganic constituent analyses, data interpretation - Reddy, Schuster
3. Publication of data - Aiken, Reddy

FY 1999 activities: FY 1999 brings to a close Phase I of our project work in the Everglades. The major activity in FY 1999 will be to complete all analyses, verify and compile data, and publish reports.

FY 1999 deliverables/products: The following products are anticipated in FY 1999:
1. Open-file report update for water quality data collected during the course of the project.
2. Journal articles covering the following general topics:
  -Biogeochemistry of DO in the Everglades
  -Geochemistry and hydrology of porewaters in the Everglades
  -Results of lab studies of Hg-DOC interactions including ion exchange and cinnabar dissolution experiments using Everglades samples
  -Interactions of Everglades organic matter with calcite
3. PhD thesis describing lab studies to define DOC-Hg interactions

FY 1999 outreach: The results of our research will be presented in overall project reviews (Florida DEP, SFWMD), information meetings (USGS), and scientific meetings (AGS, ASLO). Data and results are shared freely with other INATURES projects working in South Florida through project meetings, USGS Open-tile report, and upon request.

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH
1998 accomplishments and outcomes, including outreach: FY98 has been largely devoted zto the collection and characterization of field samples designed to determine the temporal and spatial variability of dissolved organic carbon and sulfur species at select sites in WCA 2 and WGA 3. In addition, samples were also collected further south in Taylor Slough. Notable accomplishments in this phase of the research were:

1. An improved method for sampling porewaters using a close interval sampler with a multichannel pump and microelectrodes was designed and field tested.
2. A diel study was conducted at site WCA 3A-15 wherein close Interval samplings of porewaters and surface water were conducted. Preliminary results indicate diffusion of sulfide and DOC from the porewater in the surface water. These parameters correlated closely methymercury.
3. Samples were collected to more completely define the composition of DOC in the porewaters. Samples were also collected and preserved with SAOB for "onsite" sulfide analyses.

A final field trip planned for June-July, 1998 will bring to completion the intensive field sampling phase of the project.

The stable isotopic composition of isolates and plant materials from the Everglades is being investigated in collaboration with Carol Kendall. Results of this research indicate that the isotopic link between plant materials and DOC are not straight forward, suggesting that different compound classes within the plants contribute in different ways to the DOC pool. This work will lead to better understanding of carbon cycling and food web dynamics in the Everglades.

The development of clean sampling techniques for DOC isolates continued in collaboration with Jim Hurley of Wisconsin DNR. A variety of cleaning procedures and resin types have been tested to minimize Hg contamination of the isolates and fractions. Field testing will be carried out during the summer 1998 field trip. Work continues on the distribution of Hg to the higher MW fractions of the DOC (determined by ultrafiltration). In collaboration with Hurley and Krabbenhoft, field and laboratory experiments to better define the photochemical behavior of Hg and DOC were designed.

The nature of organic sulfur in hydrophobic acid isolates of organic matter from various sites in the Everglades was investigated using XANES analysis at Brookhaven National Labs. Reduced sulfur containing functional groups, such as thiols, are assumed to play a major role in the binding of Hg by DOC, however, these functional groups are difficult to define by conventional techniques. XANES analyses indicate that approximately 50% of the sulfur associated with the isolates occurs as reduced sulfur.

Laboratory analyses designed to determine Hg-DOC binding constants continued in FY 98. Partially funded by the EPA, this research is an important element of our Hg-DOC work in the Everglades. Results of ion exchange binding measurements, and cinnabar dissolution and formation experiments indicate that Hg interacts strongly with organic matter isolated from the Everglades, with samples from the more eutrophic areas interacting more strongly than those from more pristine sites.

Finally, efforts continued to integrate Hg-DOC binding constants into chemical speciation models. Hg species distributions in the presence of fulvic acid were estimated with a discrete site-electrostatic model. These estimates agreed with published data. Species distributions calculated with this model were used to It estimate apparent binding constants at site U3 in WGA-2A. Apparent constants were incorporated into the MINTEQ database of the program PHREEQCI to evaluate fulvic acid-sulfide competition for Hg binding. Preliminary results indicate that reduced sulfur groups associated with fulvic acid compete with sulfide ion for Hg at higher sulfide concentrations, and, at low sulfide concentrations, Hg speciation will be dominated by fulvic acid complexation.

FY 1998 deliverables, products completed:
1. Data report entitled, Summary of data from onsite and laboratory analyses of surface water and marsh porewater from the 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 was expanded in 1997-98.

2. (Abstract) Aiken, G. and Reddy, M., 1997, Dissolved organic carbon in the Everglades, Florida, in U.S. Geological Survey Program on the South Florida Ecosystem-Proceedings of the Technical Symposium in Ft. Lauderdale, Florida, August 25-27, 1997, U. S. Geological Survey Open-File Report 97-385, p. 4. Poster presented at the meeting.

3. (Abstract) Reddy, M. and Aiken, G., 1997, Speciation and fractionation modeling studies - dissolved organic carbon (DOC)- mercury interaction, in U.S. Geological Survey Program on the South Florida Ecosystem-Proceedings of the Technical Symposium in Ft. Lauderdale, Florida, August 25-27, 1997, U. S. Geological Survey Open-File Report 97-385, p. 73. Poster presented at the meeting.

4. Charlton, S. R., Macklin, C. L., and Parkhurst, D. L., 1997, "PHREEQCI- A graphical user interface for the geochemical computer program PHREEQC, U. S. Geological Survey Water-Resources Investigations Report 97-4222.

5. Hurley, J. P., Krabbenhoft, D. P., Cleckner, L. B., Olson, M. L., Aiken, G, R. and Rawlic, P., 1998, Systems controls on aqueous mercury distribution in the Northern Everglades, Biogeochemistry, vol. 40, pp. 293-3 10

6. (Abstract) Aiken, G. R., Reddy. M., Tregellas, J., and Ravichandran, M., Dissolved organic carbon in the Everglades, Florida, presented during the Symposium on Refractory Organic Substances in the Environment, Oct. 6-8, 1997, University of Karlsruhe, Germany.

7. (Abstract) Aiken, G. R., Recent developments in Everglades dissolved organic carbon characterization and mercury complexation, presented by M. Reddy at South Florida Mercury Science Program Annual Workshop, West Palm Beach, May 18-20,1998

8. (Abstract) Reddy, M. M., Recent developments in modeling mercury fractionation, presented at South Florida Mercury Science Program Annual Workshop, West Palm Beach, May 18-20, 1998

9. (Abstract) Harvey, J. W., Krupa, S. L., Mooney, R. H., and Schuster, P., Are groundwater and surface water in the northern Everglades connected by vertical hydrologic fluxes through peat? 1998 AGU Spring Meeting, May 26-29. 1998, Boston, MA.

10. (Abstract) Reddy, M. M. and Aiken, G R., Speciation and fractionation modeling studies-dissolved organic carbon (DOC)- mercury interaction, presented at the 1998 AGU Spring Meeting, May 26-29, 1998, Boston, MA.

11. (Abstract) Aiken, G. and Reddy, M., 1997, Dissolved organic carbon in the Everglades, Florida, in U.S. Geological Survey Program on the South Florida Ecosystem 1998 AGU Spring Meeting, May 26-29, 1998, Boston, MA.

12. (Abstract) Ravichandran, M., Aiken, G. R., Reddy, M. M., and Ryan, N., Enhanced dissolution of cinnabar (mercuric sulfide) by dissolved organic matter from the Florida Everglades, 1998 AGU Spring Meeting, May 26-29, 1998, Boston, MA.

13. (Abstract) Hoch, A. R., Reddy, M. M., and Aiken, G. R., Inhibition of calcite growth by natural organic material from the Florida Everglades at pH = 8.5 and 250,1998 AGU Spring Meeting, May 26-29, 1998, Boston, MA.

14.(Abstract) Schuster, P.F., Reddy, M. M., Aiken, G. R., Hurley, J.. and Krabbenhoft, D.F., Diel sulfide and dissolved oxygen concentration gradients at two sites in the Everglades, 1998 AGU Spring Meeting, May 26-29, 1998, Boston, MA.

15. (Abstract) Hurley, J.P., Krabbenhoft, D.P., Schuster, P. F., Olson, M., Cleckner, L., and Aiken, G.R., Development of a conceptual model of the Everglades mercury cycle: Results from diel studies, 1998 AGU Spring Meeting, May 26-29, 1998, Boston, MA.

16.(Abstract) Krabbenboft, D.P., Hurley, J.P., Aiken, G.R., Olson, M., Dewild, J., Cleckner, L., Lindberg, S., and Grimshaw, J., The influence of photochemical processes on the Everglades mercury cycle, 1998 AGU Spring Meeting, May 26-29, 1998, Boston, MA.

17.(Extended abstract) Ravichandran, M., Aiken, G.R., Reddy, M.M., and Ryan, J.N., Enhanced dissolution of cinnabar (mercuric sulfide) by dissolved organic matter from the Florida Everglades, 216th American Chemical Society Meeting, Aug. 1998, Boston, MA.

18. (Extended abstract, invited talk) Aiken, 0., Ravichandran, M., Reddy, M. M., Ryan, J.N, and Tregellas, J., Interactions of dissolved organic carbon with mercury in the Everglades, Florida 216th American Chemical Society Meeting, Aug. 1998, Boston, MA.

19. (Extended abstract) Hoch, A.K, Reddy, M.M,, and Aiken, G.R., Inhibition of calcite growth by natural organic material from the Florida Everglades at pH=8.5 and 250C 216, American Chemical Society Meeting, Aug. 1998, Boston, MA.

20.(Journal article) Ravichandran, M., Aiken, G.R., Reddy, M.M., and Ryan, J.N., Enhanced dissolution of cinnabar (mercuric sulfide) by dissolved organic matter from the Florida Everglades, submitted for director's approval for submission to Environmental Science and Technology


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