Project: Integrated Geochemical Studies in the Everglades - Mercury Studies (ACME Phase II Project)

Web Sites: http://infotrek.er.usgs.gov/doc/mercury/home.html (site has moved to: http://infotrek.er.usgs.gov/mercury/)

Location: The Total System

Principal Investigators: David P. Krabbenhoft, (co project PI) dpkrabbe@usgs.gov, 608-821-3843; William H Orem (co project PI), borem@usgs.gov, 703-648-6273

Project Personnel: Mark Olson, mlolson@usgs.gov, 608-821-3878; John DeWild, jfdewild@usgs.gov, 608-821-3844; Shane Olund, sdoludn@usgs.gov, 608-821-3844

Other Supporting Organizations: SFWMD, FDEP, Loxahatchee National Wildlife Refuge, ENP, USEPA

Associated Projects: Mercury-DOC Interactions, (Aiken); Isotopes and Food Webs, (Kendall); Mercury Methylation and Demethylation, (Marvin-DiPasquale); Mercury Methylation in the Everglades, (Cindy Gilmour); Groundwater Hydrology of the Everglades, (Harvey); Risk Assessment, (Gross)

Overview & Status: Mercury contamination of the Everglades ecosystem is one of the most severe cases in the published literature. Currently, no human consumption of any Everglades' sport fish is recommended. Previous work by the Aquatic Cycling of Mercury in the Everglades (ACME) project has revealed that mercury (Hg) and methylmercury (MeHg) distributions in water, sediment and biota show complex seasonal and spatial trends, and that the cycling rates of Hg and MeHg are so rapid that many measurements need to be conducted on a diel basis. Mercury loads to the Everglades are dominantly derived from atmospheric sources, but toxicity is controlled by ecosystem-based conversion to MeHg. The link between Hg loads and exposure to wildlife (and humans) is the bioaccumulation process. A clear understanding of transfer mechanisms of Hg (and other contaminants) into the Everglade's food web(s) is essential for understanding how management decisions will affect exposure and risk. For instance, although periphyton in the eutrophied areas of the Everglades is a more efficient mercury methylation substrate than periphyton from more pristine areas, forage fishes from eutrophied areas do not consume periphyton and thus the MeHg production and exposure in the eutrophied areas are not as well linked. In this case, a complete understanding of methylation controls does not provide an adequate understanding of exposure. In addition, alterations in biota diversity caused by anthropogenic changes in nutrients and sulfur can significantly affect the entry points of MeHg by changing ecosystems from foodwebs dominated by algal productivity to ones dominated by macrophytes and associated microbial activity. These types of findings are critical for risk assessments, which are fundamentally based on knowing the exposure levels of contaminants for organisms of concern. Knowing exposure levels, however, requires knowing relative trophic positions of affected wildlife, and the bioaccumulation levels of the specific contaminants at the various trophic positions. This study will provide that critical information.

Needs & Products: Phase I work on ACME produced results on: (1) mercury cycling pathways, (2) information on bioaccumulation routes in the food web, and (3) interactions among exogenous factors such as nutrient sulfur inputs and mercury bioaccumulation. Results were reported at 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. We will employ several new research tools under Phase II studies, that will include in situ mesocosms and stable isotope of mercury to provide more direct answers of management related concerns for restoration effects on mercury toxicity.

Application to Everglades Restoration: This information will be used in evaluating Stormwater Treatment Areas (STA's) and other advanced technologies being applied in the everglades with respect to the risk of mercury contamination to aquatic biota.