Dear list members,
        I'm working with a predatory zooplankton species.  Should I expect
different d13C values for the same species at different sites within the
same lake?  Could a different diet at each location enrich or deplete the
d13C of the species?  Are there other factors such as depth, temperature,
discharges from sewage treatment plants, or d13C of DIC that could affect
d13C?  What would a variation in sulfur isotope composition of the species
in different areas tell us?
        My other question deals with the procedural aspects of handling
the zooplankton samples after collection.  Is it as simple as freezing
then drying the samples before analysis?  And, finally, how many
milligrams of the zooplankton sample would be sufficient for isotopic
analysis?
        Any help or references would be greatly appreciated.  Thank you in
advance.

Cheers,
Ronnie