Monday, May 26, 2008 - 10:15 AM
16

Isotopic fractionation and implications for stable isotope analysis of aquatic food webs

Stuart E. Bunn and Catherine Leigh. Australian Rivers Institute, Griffith University, Nathan, Australia

Stable isotope analysis has been widely adopted as a powerful tool in the study of aquatic food webs.  The instrumentation is readily available at low cost and rapid throughput, and little sample preparation is generally required.  Simple software packages are also available to assist with estimations of contributions of potential sources to consumer biomass.  Stable isotopes of carbon (and sulphur – though the latter is rarely used in freshwater systems) are considered to be conservative tracers in food webs and show little fractionation between source and consumer.  Unlike carbon and sulphur, stable nitrogen isotopes are known to show significant fractionation between source and consumer and this ‘predictable’ enrichment is routinely used to interpret trophic position in food webs.  However, reported fractionation coefficients are largely derived from laboratory feeding trials, often using terrestrial organisms.  Recent research on a range of freshwater ecosystems in Australia suggests that nitrogen isotope fractionation is not as consistent or as marked as reported in the literature.  Incorrect assumptions about isotopic fractionation coefficients can have major implications on the interpretation of aquatic food web data, especially when the difference between potential source signatures is relatively small. 


Web Page: nitrogen isotopes, trophic position, algae

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