George Aiken¹, David P. Krabbenhoft², William H. Orem¹ and Cynthia C. Gilmour^3
1U.S. Geological Survey, Water Resources Discipline, Boulder, CO USA
²U.S. Geological Survey, Water Resources Discipline, Middleton, WI USA
³U.S. Geological Survey, National Center, Reston, VA USA
⁴Smithsonian Environmental Research Center, Edgewater, MD USA

A number of biogeochemical processes that influence the fate, bioavailability and transport of mercury (Hg) in the Florida Everglades are mediated by the interactions of Hg with dissolved organic matter (DOM). In our research, we chemically characterized DOM from regions of the Everglades exhibiting different concentrations of methylmercury and are attempting to understand the influences of these organic matter samples on the biogeochemistry of Hg. These studies demonstrated that, in general, DOM binds mercury very strongly, exerts strong controls on Hg solubility and, in environments with active sulfate reduction, has a strong influence on Hg availability to methylating microbes. However, DOM from different areas of the Everglades exhibits different degrees of Hg reactivity. Chemical characteristics, such as differences in polarity, aromatic carbon content, reduced sulfur content, and carboxyl content are significant factors in controlling DOM reactivity with Hg. Field studies have shown that the amount and nature of DOM in the Everglades are dependent on the dominant vegetation types, biogeochemical processes, hydroperiod, interactions of surface water with peat pore waters, and amounts of canal water. Areas strongly influenced by the Everglades Agricultural Area had higher DOM concentrations, were more aromatic, and more reactive with Hg species than DOM from more pristine areas in the Everglades.

In addition to influencing Hg biogeochemistry in the Everglades, DOM also controls a number of environmental processes that are important for ecosystem function, including: the absorption of light, mineral dissolution/precipitation, transport of hydrophobic compounds (such as pesticides), and the transport and reactivity of metals (such as copper). Understanding the factors that control the amount and chemistry of DOM is relevant for the successful execution of the Comprehensive Everglades Restoration Plan. Proposed attempts to return the Everglades to more natural flow conditions will result in changes to the current transport of DOM from the Everglades Agricultural Area and the northern conservation areas to Florida Bay. In part, the restoration plan calls for increasing water flow throughout the Everglades by removing some of the man-made barriers to flow in place today. The land and water use practices associated with the plan will likely result in changes in the quality, quantity and reactivity of DOM located throughout the greater Everglades ecosystem. Our data suggest that the long-term ecological and geochemical effects of introducing reactive organic matter to pristine areas in the Everglades and, ultimately, to Florida Bay should be assessed.

Contact Information: George Aiken, U.S. Geological Survey, 3215 Marine St. Suite E-127, Boulder, CO 80303 USA. Phone: 303-541-3036, Fax: 303-447-2505, Email: graiken@usgs.gov

(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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