>Various metabolic processes in some organisms "discriminate" against N15,
>because each atom weighs slightly more than an atom of N14; more work to
>move the N15 around. So, as a result of this continuous discrimination,
>some organic residues will be "lighter"; they'll contain relatively more
>N14. On the other hand, other metabolic processes in other organisms don't
>discriminate against N15, so that they'll contain relatively more N15 and
>be considered "heavy" or enriched in N15. The isotopic ratio can be
>considered a signature, and gives you important clues to both the origin
>of organic material and an idea of how trophic webs work (who eats who).
Thanks! I wonder at what trophic level(s) this is most important. Using
the salmon example, are marine salmon metabolic systems less discriminatory
because these fish have to grow large fast? Or is it because that
discrimination occurred with their food, or their food's food? Or none or
all, or is it not that simple?
-- Jay DeLong Olympia, WA
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