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Last updated: June 10, 2003
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Can management of water quantity or quality
reduce the risks?
Poster presented May 1999, at the South Florida Restoration Science Forum
Poster presented by: Dr. Dave Krabbenhoft, USGS; Dr. Jim Hurley, WIDNR
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Almost all of mercury toxicity is
expressed as exposure to methylmercury. Thus, reducing risks to mercury
can be recast as, "Can Management of Water Quality and Quantity Methylmercury
Exposure by Reducing Methylmercury Production or by Increasing Destruction".
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How does methylmercury get produced
and destroyed in nature?
- Mercury delivery.
- Transport to methylation site (anaerobic).
- Reactions with sulfur or organic carbon.
- Uptake and conversion to methylmercury by bacteria.
- Release to food web or bacteria consumed by grazers.
- Possible methylmercury destruction by bacteria in sediments, or by sunlight.
- Cycle starts over again? Or evasion of mercury from water.
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(Click on image above for larger version.)
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Under this conceptual model what
are some likely responses of methylmercury production to possible changes
in the Everglades?
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| Change |
Response
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Explanation
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| Decrease in Hg inputs |
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Probably decrease, small change if sediment
Hg pool is the major source. |
| Decrease in sulfate inputs |
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System wide would likely see decrease
in production over time, but some areas may initially increases. |
| Increase in water depth (hydroperiod) |
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Due to greater sediment/water anoxia and
lower relative light penetration. |
| Increase in sheet flow rate |
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Greater flushing rates should decrease
observed concentrations, but would not directly affect production. |
| Decrease in carbon (color) in runoff |
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Due to increased light penetration and
subsequent increased methymercury destruction by sunlight. |
What has happened to mercury in
the Everglades, and what willhappen under reduced mercury inputs and runoff
of sulfate and phosphate?
(Click on graphs for larger version.)
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