William H. Orem¹, David P. Krabbenhoft², Cynthia C. Gilmour³, George R. Aiken⁴,
Harry E. Lerch¹, Anne L. Bates¹ and Margo D. Corum^1
1U.S. Geological Survey, National Center, Reston, VA, USA
²U.S. Geological Survey, Water Resources Discipline, Middleton, WI, USA
³Smithsonian Environmental Research Center, Edgewater, MD, USA
⁴U.S. Geological Survey, Water Resources Discipline, Boulder, CO, USA

There is extensive sulfur contamination of the Florida Everglades. Sulfate concentrations in surface water of the northern Everglades are up to 60 mg/l (more than 60x background levels). Excess sulfate enters the Everglades primarily in canal discharge, and impacts about one third of the ecosystem. Evidence suggests that sulfur used in soil amendments in the Everglades Agricultural Area (EAA) is a primary source of sulfur contamination to canals and the Everglades. The excess sulfate stimulates microbial sulfate reduction in the anoxic soils (peats) underlying the freshwater Everglades, producing toxic hydrogen sulfide as a byproduct at up to 40,000x background levels in heavily sulfate-impacted areas.

The excess sulfate entering the Everglades has numerous deleterious impacts on the ecosystem. Sulfate contamination is inextricably linked to the major methylmercury (MeHg) problem impacting the entire ecosystem (MeHg is produced via microbial sulfate reduction). Neurotoxic MeHg represents a serious health threat to both wildlife and humans through consumption of MeHg-contaminated fish. Sulfur contamination has dramatically altered redox patterns in the Everglades, with unnaturally low redox and sulfidic conditions present in large swaths of the northern Everglades. The lower redox conditions and high concentrations of toxic sulfide in soils may impact macrophytes and soil infauna. High levels of sulfide and low redox conditions may also impact trace metal cycling, and increase remobilization of phosphorus from soils.

Sulfur-MeHg contamination is the most important water quality issue facing Everglades’ restoration. Current plans of decompartmentalization and restoration of sheet flow are likely to increase sulfate loads to areas such as Loxahatchee National Wildlife Refuge (LOX), Everglades National Park (ENP), and Big Cypress National Preserve (BCNP). Recently reported declines of MeHg in fish in the central Everglades are linked to declines in sulfate concentration here. Preliminary data suggest that sulfate-contaminated water has been rerouted down the canal system from the central Everglades to ENP, where recent increases in MeHg in fish have been reported. Plans to move sulfate-contaminated water from the L-28 canal into BCNP may also trigger increases in MeHg in biota here. Other unwanted impacts of sulfate contamination may also occur in these areas. Unfortunately, stormwater treatment areas, as currently designed, do little to mitigate sulfate contamination of the ecosystem. Land and water managers need to carefully assess the cost/benefit of using sulfate-contaminated water in Everglades restoration. It will be difficult to consider restoration efforts successful if sulfidic soils and MeHg-contaminated fish persist in the ecosystem.

Contact Information: William H. Orem, U.S. Geological Survey, 956 National Center, Reston, VA 20192 USA, Phone: 703-648-6273, Fax: 703-648-6419, Email: borem@usgs.gov

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

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