Data from periphyton samples collected in the south Florida ecosystem in 1995 indicate that:

1. The percent nitrogen in periphyton is directly related to the concentrations of total mercury and methyl mercury found in periphytic material.
2. There is a difference between laboratory experiments, where the removal of methyl mercury from solution is related to the organic carbon content of the plant material, and natural concentrations of methyl mercury, which are related to the percent nitrogen in the periphytic material.
3. There is a gradient from larger to smaller concentrations of total mercury and methyl mercury in periphytic material that generally follows a north to south direction in the ecosystem.
4. The methyl mercury gradients for locations with a Water Conservation Area or within the Big Cypress National Preserve are influenced by water column pH with larger concentrations of methyl mercury in periphyton occurring when pH values are approximately neutral.

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