U.S Geological Survey, South Florida Ecosystem Program: Place-Based Studies

Project: Interactions of mercury with dissolved organic carbon in the Everglades

Web Sites: http://sflwww.er.usgs.gov/exchange/aiken/methodchem.html; http://sflwww.er.usgs.gov/people/aiken.html; http://sofia.usgs.gov/sfrsf/rooms/mercury; http://sflwww.er.usgs.gov/projects/evergl_merc

Location: Central Everglades; Palm Beach, Broward and Miami-Dade County

Principal Investigator: George Aiken, graiken@usgs.gov, 303-541-3036

Project Personnel: James Weishaar, jlweisha@usgs.gov, 303-541-3058

Other Supporting Organizations: National Science Foundation

Associated Projects: Ones by (Krabbenhoft, Reddy, Hurley, Orem, Kendall)

Overview & Status: 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 (Environmental Science and Technology, 1998, Vol. 32, pp. 3305-3311; Environmental Science and Technology, 1999, Vol. 33, pp. 1418-1423). The ion-exchange results are contained in a PhD thesis (Mahalingam Ravichandran, 1999, University of Colorado) and are in the process of being converted into a journal article that should be ready for colleague review by Sept. 2000. We have attempted to include DOM-Hg binding components to geochemical models. The results of these efforts will be submitted for publication shortly. Finally, we also studied the interactions of DOM with calcite in the Everglades. The results of this work have been published as a journal article (Geochimica et Cosmochimica Acta, 2000, Vol.64, pp.61-72).

Needs & 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. Our project focuses on the effect of DOM on the transport and reactivity of Hg in the Everglades. The data gathered by our project are published primarily in the form of journal articles that contribute to the basic understanding of the how the Everglades system functions with regard to the nature and reactivity of DOM, and how the quality of the DOM controls the reactivity of Hg in the Everglades. Results of this research will be used by the U. S. Geological Survey, U.S. EPA, Florida Department of Environmental Protection, and the South Florida Water Management District.

Application to Everglades Restoration: This information is important to consider in designing remediation strategies. Factors such as vegetation and hydrology, for instance, may be found to be very important in controlling both DOM and Hg reactivity. In addition, our research efforts to study distribution of Hg between DOM and particulate organic matter, and the determination of Hg-DOM binding constants are critical for adequate modeling of Hg in the Everglades.