United States Environmental Protection Agency
REPORT EPA-904-R-96-008 (PDF Format)
The purpose of this interim report is to introduce the systemwide (4000-square-mile) scope of the monitoring project in the Everglades ecosystem and to present preliminary findings on the mercury contamination, eutrophication, habitat alteration, and hydropattern modification issues. The greatest threat to the Everglades ecosystem is to assume these issues are independent. The monitoring in this project strongly supports the federal and state Everglades restoration efforts and will provide a means to evaluate present and future management actions. This project is focused on the ecological risk assessment process and guided by a set of policy relevant questions. A statistical survey design was used to select 200 canal and 500 marsh sampling stations, a quarter of which were sampled during successive wet and dry seasons over two years. These data allow quantitative estimation of the relative risk to the ecol ogi cal resources from mult i pl e environmental threats. Marsh monitoring has been conducted during two years, one of which was the wettest year on record. To determine the range of natural variance to support and validate mercury modeling, process studies, and future assessments, this monitoring should continue.
The highest mercury concentrations in algae, fish, and great egrets have been found to occur in Water Conservation Area 3 between Alligator Alley and Tamiami Trail. No single point source has been identified that contributes directly to these high mercury levels. Atmospheric mercury loading from precipitation is from 35 to 70 times greater in the publicly owned Everglades than mercury loading in canal water coming from the Everglades Agricultural Area. Incineration in the urban areas is likely the primary source of atmospheric mercury.
Several policy and management implications arose from these preliminary results including: (1) the current chronic mercury aquatic life criterion is underprotective and needs to be revised; (2) discharging phosphorus at the current initial control target of 50 ppb will continue to allow eutrophication of over 95% of the Everglades marshes; and (3) ecological restoration must consider hydropattern modification, nutrient loading, mercury cycli ng, and habitat alteration simultaneously, not independently.
Comparative ecological risk assessment is a critical element in adaptive management for ecosystem restoration. This ecosystem assessment project provides a critical framework and foundation for assessing the effectiveness of Everglades ecosystem restoration activities into the 21st century.