Project Proposal for 2001

Project Title: Interactions of Mercury with Dissolved Organic Carbon in the Florida Everglades

Project Chief: George Aiken
Email: graiken@usgs.gov
Phone: (303) 541-3036
Fax: (303) 447-2505
Mailing address:
U.S. Geological Survey
3215 Marine Street
Boulder, CO 80303

Project Chief: Mike Reddy
Email: mmreddy@usgs.gov
Phone: (303) 236-5021
Fax: (303) 236-5034
Mailing address:
U.S. Geological Survey
Box 25046, Denver Federal Center
Denver, CO 80225

Workplan FY 2001

Introduction

Interactions of mercury (Hg) with dissolved organic matter (DOM) play important roles in controlling reactivity, bioavailability and transport of Hg in the Florida Everglades. Our project is designed to better define the nature and magnitude of these interactions. During Phase 1, we studied the distribution and nature of DOM in the northern Everglades. In this work we noted the importance of source materials (peat versus vegetation and periphyton), and the importance of hydrologic factors on the quality and amount of DOM in a given location. Differences in the DOM were clearly apparent in regions exhibiting different behavior with regard to the generation of methylmercury. The results of this research are being written up (2 journal articles) and are expected to be ready for colleague review by Sept. 30, 2000. We also studied the reactivity of Everglades DOM with mercury through cinnabar (HgS) dissolution and formation experiments, and an ion-exchange technique designed to yield information on Hg-DOM binding constants. The results of the cinnabar interactions have been published as 2 journal articles (ES & T). The ion-exchange results are contained in a PhD thesis and are in the process of being converted into a journal article. Finally, we have attempted to include DOM-Hg binding components to geochemical models. The results of these efforts will be submitted for publication shortly.

Progress was made in FY 2000 in both the field and laboratory experiments. In the field, mesocosms were deployed at select locations to be used in experiments designed to test hypotheses concerning Hg speciation and reactivity. Preliminary experiments were carried out in conjunction with other team members (Krabbenhoft, Orem, eg). As part of this effort, we collected water from F1 and isolated a large amount of organic matter for future mesocosm experiments and to provide organic matter for ongoing lab experiments assessing the interactions of Hg with DOM that may control bioavailability. In FY 2000, we will continued ongoing lab studies to better define interactions of Hg with DOM. These studies included:

1. Binding studies (Hg-DOM). Ion-exchange studies designed to measure the strength of interactions between Hg and DOC were continued, and, new techniques to assess factors controlling reactivity of DOM with Hg and the strength of binding interactions were investigated. This work is important for accurate modeling of these interactions.
2. Study of the interactions of the DOM with HgS continued. Experiments were designed to provide insight into ability of DOM to stabilize colloidal HgS. This is a potentially significant process effecting the bioavailability of Hg.
3. The study of the "partitioning" of Hg between dissolved and particulate phases was completed. Field based partitioning coefficients, necessary for accurately modeling Hg behavior in the Everglades, were corroborated. This work will be published in FY2001.

Reports:

We have authored a number of high quality journal articles describing our efforts in Phase 1. This effort will continue in FY 2001. In addition to submitting our contributions to the synthesis report, the following reports are anticipated this FY:

Reddy, M. M., Aiken, G. R., and Schuster, P. F., Hydroperiod driven solute transport at the peat-water interface in the Florida Everglades: Hydrophobic acid diffusion from peat. Journal article scheduled for review by Nov. 30, 2000.

Reddy, M. M., and Aiken, G. R., Fulvic acid-sulfide ion competition for mercury ion binding in the Florida Everglades. Submitted for publication to Water, Air and Soil Pollution. Publication anticipated in FY 2001.

Ravichandran, M., Aiken, G. R., Reddy, M. M., and Ryan, J. N., Complexation of mercury by dissolved organic matter isolated from the Florida Everglades. Journal article scheduled for review by March 30, 2001.

Aiken, G. R., Reddy, M. M., and Schuster, P. F., Organic geochemistry of dissolved organic carbon in the northern Everglades, Florida Journal article scheduled for review by Jan. 2001.

Hurley, J. P., Cleckner, L. B., Krabbenhoft, D. P., and Aiken, G. R., Pigment distribution in plankton and periphyton of the Florida Everglades. Journal article scheduled for review by FY 2001.

Benoit, J. M., Mason, R. P., Gilmour, C. C., and Aiken, G. R., Mercury binding constants for dissolved organic carbon isolates from the Florida Everglades, to be submitted to Limnology and Oceanography. Scheduled for publication in FY 2001.

FY 2001

In FY 2001 we plan to:

1. Continue work using field based mesocosms to address issues concerning partitioning and reactivity of Hg in the Everglades with regard to the roles played by DOM in the system. We plan to continue overall project support with regard to DOM analyses and isolate availability for experimentation.
2. Laboratory development of abiotic methods for assessing bioavailability of Hg will be completed, and we anticipate using these techniques in the field.
3. Lab based studies on DOM-Hg binding constants will likely be completed in FY 2002. This includes studies with cinnabar and ion exchange and dialysis techniques for estimating binding constants with Hg. Concerning the later techniques, we plan to employ these methods to assess interactions between CH3Hg⁺and OM in the system. These interactions could prove to be important controls on bioavailability of CH3Hg⁺ in the system.
4. In lab based studies to be carried out in conjunction with Bill Orem, we plan to investigate the interactions of OM and inorganic S in the Everglades. This work will attempt to investigate the role of S⁼ interactions with both DOM and POM. The organic-S in the DOM and the peat are of interest both in regard to binding of Hg and as a potential source of SO4⁼ during oxidation and remineralization of organic matter. We have strong evidence from Phase 1 studies that remineralization can provide significant contributions of SO4⁼ to the porewaters.
5. We plan to continue efforts to publish information gathered in this study and to present findings at appropriate scientific meetings.

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