Document Detail


Combining sources in stable isotope mixing models: alternative methods.
MedLine Citation:
PMID:  15711995     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Stable isotope mixing models are often used to quantify source contributions to a mixture. Examples include pollution source identification; trophic web studies; analysis of water sources for soils, plants; or water bodies, and many others. A common problem is having too many sources to allow a unique solution. We discuss two alternative procedures for addressing this problem. One option is a priori to combine sources with similar signatures so the number of sources is small enough to provide a unique solution. Aggregation should be considered only when isotopic signatures of clustered sources are not significantly different, and sources are related so the combined source group has some functional significance. For example, in a food web analysis, lumping several species within a trophic guild allows more interpretable results than lumping disparate food sources, even if they have similar isotopic signatures. One result of combining mixing model sources is increased uncertainty of the combined end-member isotopic signatures and consequently the source contribution estimates; this effect can be quantified using the IsoError model (http://www.epa.gov/wed/pages/models/isotopes/isoerror1_04.htm). As an alternative to lumping sources before a mixing analysis, the IsoSource mixing model (http://www.epa.gov/wed/pages/models/isosource/isosource.htm) can be used to find all feasible solutions of source contributions consistent with isotopic mass balance. While ranges of feasible contributions for each individual source can often be quite broad, contributions from functionally related groups of sources can be summed a posteriori, producing a range of solutions for the aggregate source that may be considerably narrower. A paleo-human dietary analysis example illustrates this method, which involves a terrestrial meat food source, a combination of three terrestrial plant foods, and a combination of three marine foods. In this case, a posteriori aggregation of sources allowed strong conclusions about temporal shifts in marine versus terrestrial diets that would not have otherwise been discerned.
Authors:
Donald L Phillips; Seth D Newsome; Jillian W Gregg
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2005-02-16
Journal Detail:
Title:  Oecologia     Volume:  144     ISSN:  0029-8549     ISO Abbreviation:  Oecologia     Publication Date:  2005 Aug 
Date Detail:
Created Date:  2005-08-31     Completed Date:  2005-09-27     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0150372     Medline TA:  Oecologia     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  520-7     Citation Subset:  IM    
Affiliation:
US Environmental Protection Agency, Office of Research & Development, Western Ecology Division, National Health & Environmental Effects Research Laboratory, 200 SW 35th St., Corvallis, OR, 97333, USA. Phillips.Donald@epa.gov
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MeSH Terms
Descriptor/Qualifier:
Algorithms
Animals
Biomass
Ecology / methods*
Ecosystem
Environmental Monitoring / methods
Evolution
Food Chain
Humans
Isotopes / analysis,  metabolism*
Models, Theoretical
Plants / metabolism
Reproducibility of Results
Chemical
Reg. No./Substance:
0/Isotopes

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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