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Project Summary Sheet

U.S Geological Survey, South Florida Ecosystem Program: Place-Based Studies

Project: Application of stable isotope techniques to identifying foodweb structure, contaminant sources, and biogeochemical reactions in the Everglades

Web Site: Application of stable isotope techniques to identifying foodweb structure, contaminant sources, and biogeochemical reactions in the Everglades

Location: Total System; Palm Beach, Broward, Dade, Monroe, Okeechobee, Martin, Highlands, Glades, Hendry, and Collier Counties

Principal Investigator: Carol Kendall, ckendall@usgs.gov, 650.329.4576

Project Personnel: Cecily C. Chang, ccchang@usgs.gov, 650.329.4471; Steven R. Silva, srsilva@usgs.gov, 650.329.4558; Bryan E. Bemis, bebemis@usgs.gov, 650.329.5603.

Other Supporting Organizations: South Florida Water Management District, Florida Game and Fresh-water Fish Commission, US Environmental Protection Agency

Associated Projects: MAIN PROJECT: Integrated Geochemical Studies in the Everglades - A. Nutrients, Sulfur, and Organic Matter (Orem, borem@usgs.gov, 703.648.6273; Krabbenhoft, dpkrabbe@usgs.gov, 608.821.3843); Associated Project: 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 biogeochemical and isotopic 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 interactions of these contaminants, ecosystem responses to variations in contaminant loading, and how ecosystem restoration steps may affect existing contaminant pools. The approaches used will be extensions of our previous efforts, whereby we will enhance our abilities to address land management and ecosystem restoration questions. Major changes implemented for Phase II include the use of controlled mesocosm experiments to provide a more definitive means addressing specific management questions, studies of organic pollutants, and extending our foodweb studies beyond fish to bird populations.. Phase I work showed that excess nutrients and sulfur enter the Everglades from canal discharge originating in the Everglades Agricultural Area. The increased nutrient load has altered biotic assemblages within parts of the ecosystem. Unnaturally high levels of sulfate entering the Everglades have increased concentrations of toxic hydrogen sulfide, and are a key control regulating methylmercury (MeHg) production. The spatial extent of zones of active sulfate and nitrate reduction have been mapped using the N and S isotopic compositions of biota. The differences in the spatial patterns of sulfur isotope compositions of modern biota and older sediments is strong evidence for a significant increase in sulfate reduction in the marshes in the last few decades. The isotopic compositions of biota provide a useful constraint on the kinds of environments that favor MeHg production because their compositions are less easy to perturb than the more transient compositions of aqueous species. Phase I work on defining spatial changes in foodwebs has demonstrated that there are significant differences in foodwebs in impacted and unimpacted areas. Preliminary mass balance calculations comparing the results of gut-contents analyses and stable isotope data have shown inconsistencies, suggesting that there is a difference between what organisms eat and what they assimilate. The labeling of different environments by the C, N, and S isotopic compositions of biota has been used to provide constraints on the migration habits of game fish.

Needs and Products: Phase I work produced results on: (1) sources of nutrients and sulfur 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 foodweb in the ecosystem and its control on element transfer between trophic levels. Results were reported in several presentations to managers, scientists, and the public. Phase II results will produce many publications, as well as presentations for managers, scientists, and the public. Foodweb and biogeochemical results will also be incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem.

Application to Everglades Restoration: Results of these biogeochemical investigations will provide critical elements for building ecosystem models and screening-level risk assessment for contaminants in the ecosystem.

Study Milestones

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Familiarity

 

X

X

               

Design

   

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X

 

X

0

       

Field Work

 

X

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X

X

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Data Analysis

   

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Initial Reporting

       

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Credibility Assurance

       

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Results Published

           

0

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Synthesis

           

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Note: "x" indicates task completed, and "o" indicates task planned, but not completed


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Last updated: 24 April, 2014 @ 12:00 PM (KP)