Part 1

Poster presented May 1999, at the South Florida Restoration Science Forum

ACME Project Collaborators

ACME Project Primary Investigators

Dave Krabbenhoft (Project Leader), Mark Olson, & John DeWild USGS, Madison, WI Bill Orem and Jud Harvey, USGS, Reston, VA George Aiken & Mike Reddy, USGS, Denver, CO Mark Marvin & Ron Oremland, & Carol Kendall, USGS, Menlo Park, CA Cindy Gilmour, Andrew Heyes, & Jani Benoit, Academy of Natural Sciences, Benedict, MD Jim Hurley & Paul Garrison, University of Wisconsin and Wisconsins DNR, Madison, WI Lisa Cleckner, University of Wisconsin, Madison, WI Ted Lange, Florida Game and Freshwater Fish Commission, Eustis, FL Reed Harris, Tetra Tech, Inc., Toronto, Canada

ACME Project Sampling Locations in Southeastern Florida

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The ACME Project has established a series of ten primary sites, which span most of the length of the remnant Everglades. Project members from across the United States have assembled three to four times per year since 1995 to conduct intensive sampling trips during which all of the individual researchers would make their respective measurement contemporaneously. By conducting our field work in this manner, we could eliminated the confounding effects of rapidly changing conditions in the field and any lack of comparability of our results. As the project members learned, the Everglades are such a dynamic system that for many of the measurements or process rates we quantified were extremely time of day dependent [see section titled 'A Dynamic System' ].

Within the marshes of the Everglades, where is the mercury coming from? On average, the vast majority (about 98%) of mercury entering the marshes of the Everglades is derived from frequent rainfall events that effectively strip mercury from the atmosphere. Runoff from canals that discharge to the Everglades only deliver about 2% of the mercury to the marshes.

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Rainfall scavenging mercury from the atmosphere

Controls on sulfur to the Everglades are also important

Runoff of Sulfate Sulfur from Agricultural Fields into Canals and Discharge of Sulfate-Contaminated Water into Everglades Marshes

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Additions of sulfur as sulfate to the Everglades has a profound effect on mercury cycling and toxicity [see section on Mercury Methylation]. Runoff from canals is a major source of sulfate, and those marshes that receive a greater proportion of their water from runoff have corresponding higher levels of sulfate. Although the addition of sulfate can often stimulate mercury methylation, excessive amounts of sulfate can actually poison the mercury methylation process by limiting the availability of mercury to methylating bacteria.

Sulfur Contamination in the Everglades

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Methylation and Demethylation:
The Keys to Understanding Mercury Exposure to Wildlife and Humans:

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How Does Methylation and Demethylation Vary Across the Everglades?

Project Study Site Number (Click on image for larger version.)

What controls the presence of methylmercury? Mercury methylation and demethylation rates vary widely across the Everglades Ecosystem. Both processes are mediated by microbes that naturally occur in most environments. In most anaerobic sediments, mercury methylation exceeds demethylation rates, which is why we observed the net presence of this very toxic compound. Mercury methylation generally cannot occur in aerobic environments. Mercury methylation also requires the presence of sulfate and a reactive carbon source to drive this reaction. As such, the availability of carbon and sulfur in the correct forms is just as important as availability of mercury for the production of methylmercury.