Project: Integrated Geochemical Studies in the Everglades - Nutrients, Sulfur, and Organic Matter

Web Site: http://energy.er.usgs.gov

Location: Total System; Palm Beach, Broward, Miami-Dade, Monroe, Okeechobee, Martin, Highlands, Glades, Hendry, Collier Counites

Principal Investigator: William H Orem, borem@usgs.gov, 703.648.6273

Project Personnel: David P. Krabbenhoft, dpkrabbe@usgs.gov, 608.821.3843; George R. Aiken, graiken@usgs.gov, 303.541.3036; Carol Kendall, ckendall@usgs.gov, 650-329-4576; Robert A. Zielinski, rzielinski@usgs.gov, 303.236.4719; Harry E. Lerch, tlerch@usgs.gov, 703.648.6278; Anne L. Bates, abates@usgs.gov, 703.648.6279

Other Supporting Organizations: SFWMD, FlDEP, Arthur R. Marshall Loxahatchee National Wildlife Refuge, ENP

Associated Projects: Evolution of Everglades Tree Islands (Debra Willard, dwillard@usgs.gov, 703.648.5320), Groundwater Hydrology of the Everglades (Judson Harvey, jwharvey@usgs.gov, 703.648.5876), Everglades Risk Assessment (Tim Gross, tim_s_gross@usgs.gov, 352.373.8181)

Overview & Status: This project is an integration of a number of individual but interrelated tasks that address environmental impacts in the south Florida ecosystem using geochemical approaches. Externally derived nutrients, mercury and sulfur are three of the most important contaminants currently affecting this ecosystem. The scientific focus of this project is to examine the complex interactions of these contaminants (synergistic and antagonistic), ecosystem responses to variations in contaminant loading (time and space dimensions), and how imminent ecosystem restoration steps may affect existing contaminant pools. The approaches used will be extensions of previous efforts by the lead investigators. Major changes implemented for Phase II include the use of environmental chambers (controlled enclosures or mesocosums) and isotopic tracers to more definitively address specific management questions, and studies of organic pollutants in Everglades peats and surface waters. Phase I work showed that excess nutrients and sulfur which enter the Everglades from canal discharge originating in the EAA Area have altered biotic assemblages within parts of the ecosystem. The extent of sulfur contamination in the Everglades was first documented by this team. Unnaturally high levels of sulfate entering the Everglades have increased concentrations of toxic hydrogen sulfide, and are a key control regulating methylmercury (MeHg) production. Mercury (Hg) contamination of the Everglades is one of the most severe cases on record. Phase I work revealed that Hg and MeHg distributions in water, sediment and biota show complex seasonal and spatial trends and that ecosystem wide MeHg levels are controlled by in situ microbial processes (i.e sulfate reduction). Mercury loads to the Everglades are dominantly derived from atmospheric sources, but toxicity is largely controlled by the relative rates of conversion to MeHg, which in turn appears to be intimately associated with the sulfate/sulfide biogeochemical cycle.

Needs & Products: Phase I work produced results on: (1) sources of nutrients, sulfur, and Mercurv to the ecosystem, (2) biogeochemical processes in sediments and water controlling element recycling and mercury methylation, and (3) the spatial and temporal changes in the food web in the ecosystem and its control on element transfer between trophic levels. Results were reported in numerous presentations to managers, scientists, and the public, in numerous peer- reviewed scientific publications, and in general interest publications. Phase II results will produce similar types of publications and presentations for managers, scientists, and the public.

Application to Everglades Restoration: Study results will provide critical elements for building ecosystem models and screening-level risk assessment for contaminants in the ecosystem. Geochemical results will also be incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem.