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STABLE ISOTOPES IN ECOLOGICAL STUDIES: NEW DEVELOPMENTS IN MIXING MODELS (BRAZIL)
PHILLIPS, D. L. STABLE ISOTOPES IN ECOLOGICAL STUDIES: NEW DEVELOPMENTS IN MIXING MODELS (BRAZIL). Presented at Presentation for Federal University of Rio Grande, Brazil, Porto Alegre, BRAZIL, June 22, 2006.
Stable isotopes are increasingly being used as tracers in ecological studies. One application uses isotopic ratios to quantify the proportional contributions of multiple sources to a mixture. Examples include pollution sources for air or water bodies, food sources for animals, water sources for plants, and biogeochemical inputs to soils. Simple mixing models based on mass balance equations have been used for this purpose for several decades. A number of factors may complicate these analyses, including variability in the isotopic signatures of sources or mixtures, concentration differences among sources, and limitations on the number of sources that can be uniquely distinguished. In this presentation, the basic isotopic mixing models and their assumptions are first outlined. Then, recent extensions of mixing model analysis are described that deal with some of these complicating factors. These developments include: (1) examination of experimental design and the uncertainty in source estimates, (2) incorporation of elemental concentration differences among sources; (3) calculation of quantitative bounds on source proportions when the number of sources precludes unique solutions; and (4) methods for combining sources and considering non-isotopic constraints.
Record Details:Record Type: DOCUMENT (PRESENTATION/ABSTRACT)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL HEALTH AND ENVIRONMENTAL EFFECTS RESEARCH LAB
WESTERN ECOLOGY DIVISION
RISK CHARACTERIZATION BRANCH