Dave Krabbenhoft Orem, Bill
To meet these objectives, we have adopted a combined field/ laboratory approach. In conjunction with other research projects our field efforts are designed (1) to characterize DOM at a variety of field locations chosen to provide information about the influences of hydrology, seasonal factors (wetting and drying events) and source materials (e.g. vegetation, periphyton, peat) on the nature and amount of DOM in the system, and (2) to elucidate the roles of DOM in controlling the reactivity and bioavailability of Hg in the Everglades.
Aiken, G. R. Ryan, J. N.
The entire paper is available from the Environmental Science and Technology Journal web site; however, a journal subscription is required.
Mason, R. P Gilmour, C. C. Aiken, G. A.
Aiken, G. R. Ryan, J. N. Reddy, M. M.
Aiken, G. R.
Haitzer, Markus Ryan, Joseph N. Aiken, George R. Nagy, Kathlyn L.
Aiken, George R. Schuster, Paul F. Gunthers, Charmaine
Orem, W. H. Harvey, J.. W. Spiker, E. C.
Lerch, Harry E. Rawlik, Peter
Orem, William H. Harvey. Judson W. Spiker, Elliot C.
Reddy, M. M. Aiken, G. R.
Hurley, J. P. Aiken, G. R. Marvin-DiPasquale, M. Orem, W. H. Harris, R.
Aiken, G. R. Ryan, J. N. Reddy, M. M.
Aiken, George R. Ryan, Joseph N.
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.
We continued ongoing lab studies to better define interactions of Hg with Dissolved Organic Matter (DOM). These 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. 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.
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 latter 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 sulfate anion interactions with both DOM and particulate organic matter (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 sulfate during oxidation and remineralization of organic matter. We have strong evidence from Phase 1 studies that remineralization can provide significant contributions of sulfate to the porewaters.
Interactions of DOM with Hg in the Everglades
1. Continue lab-based studies on DOM-Hg binding constants. We have recently completed development of dialysis technique for measuring binding constants. This method is the only reliable method we have found for measuring binding constants. Development was carried out using hydrophobic sample from F1 field site. The method now needs to be used with other fractions of the DOM from F1 and other locations in the Everglades and the method should be extended for measuring DOM-MeHg binding constants.
2. Continue lab-based studies on the interactions of DOM with HgS. HgS is assumed to be an important species controlling Hg bioreactivity. Greater definition of DOM-HgS interactions is critical for understanding factors that control methylation of Hg. We previously demonstrated the strong influence of DOM on the chemistry of HgS complexes, although the processes are poorly defined. Efforts in FY 03 and FY 04 will provide data to better understand these processes and assess the role they play in controlling Hg bioavailability.
Effects of DOM on Hg cycling in the Florida Everglades
1. Continue work using field based mesocosms to address issues concerning partitioning and reactivity Hg in the Everglades with regard to the roles played by DOM in the system. Mesocosm experiments have been very successful demonstrating the influence of DOM on methylation and bioaccumulation of Hg. In this work organic matter isolated from areas with reactive DOM is added to mesocosms, in addition to other constituents (sulfate, Hg) to assess impacts on Hg partitioning, methylation and bioaccumulation.
2. Continue work assessing the roles of drying and wetting of peat soils on the generation of DOM and MeHg. Research is both lab and field based. DOM concentrations and changes in the reactivity of the DOM are determined as a function of wetting and drying, a common natural condition and one of great importance in managed wetlands, such as the Storm Treatment Areas (STA). DOM characterization methods established by USGS labs are used.
3. Begin study of DOM in Lake Okeechobee and Kissimmee River. This work is important for future efforts involving ASR. DOM sampling and characterization methods have been established by USGS labs.
4. Begin study of DOM in new Storm Treatment Areas ( STA’s). The STAs are critical for restoration efforts. DOM characterization methods established by USGS labs will be used.
5. Continue assessment of water quality changes in Everglades by participation in ACME Site Survey work. This is done in conjunction with Krabenhoft and Orem. This project is responsible for DOM measurements and characterization throughout the Everglades.
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U.S. Department of the Interior, U.S. Geological Survey, Center for
Coastal Geology
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