Hi Laura:  For a less pessimistic perspective of the uses of N and O
isotopes in groundwater and surface water studies, you might want to look
at two other recent reviews of the subject:

Kendall, C., 1998. Tracing nitrogen sources and cycling in catchments,
Chapter 16, In: C. Kendall and J.J. McDonnell (Eds.), Isotope Tracers in
Catchment Hydrology, Elsevier, Amsterdam, p. 519-576.

Kendall, C., and Aravena, R., 2000. Nitrate isotopes in groundwater
systems, Chapter 9, In: P. Cook and Herczeg, A.L. (Eds.), Environmental
Tracers in Subsurface Hydrology, Kluwer Academic Publishers, p. 261-297.

--Carol

*******************************************************************************

Carol Kendall                                                        tel:
1-650-329-4576
USGS, 345 Middlefield Road, MS 434           fax: 1-650-329-5590
Menlo Park, CA 94025 USA                    email:[log in to unmask]












                    "L.Handley"
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                    Sent by: Stable          Subject:     Re: 15N - Linda
                    Isotope                  Handley
                    Geochemistry
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                    03/24/00 07:21 AM
                    Please respond to
                    Stable Isotope
                    Geochemistry








Laura Vitoria wrote:
      Linda: Thanks for your explanations and the time you consecrate to
     answer my mails. I like also your sincerity in your answers but there
     are things I don't understand or I don't agree. I am going to work
     with polluted groundwaters with a lot of nitrate (in the ppm range).
     My first objective is to choose two restricted and separated areas
     with different origins of contamination. I'll make a chemical
     characterization, with general chemistry and isotopic chemistry: 34S
     of SO4, 15N of NO3 and NH4 andsurely 18O of SO4 and NO3.The first area
     will be one of the polluted areas that we have in Catalonia
     contaminated by farm's residues, specifically by pig's farms. It would
     have to be an area only with this source of contamination.The other
     one would have to be only contamianted by commercial fertilizers.We
     are going to characterize these contaminations sources, and
     groundwaters, and then try to understand the fractionations they take
     place.Afterwards, we would like to do the same study in a mix area, I
     mean, where there are both sources of contamination together.
     ------------------------



     The key problem with the delta15N is that the isotopic value of the
     samples you measure probably have no relationship with the source
     signature.  delta 15N is not a tracer.  You may or may not find out
     that the delta 15N of the nitrate in the pig area is larger than the
     delta 15N of the nitrate in the fertiliser area, but the values you
     measure will reflect the microbial and physical processes acting on
     the N before you sample it; it will not have much or anything to do
     anymore with the original source signature; even if you find samples
     that look like values similar to the source signature, you cannot
     assume that it is not just a coincidence. In other words, you may find
     differences, but you won't know what they mean, and you can't apply
     them to a mixing model and the processes acting on the N in a third
     area won't necessarily be the same as in the other two areas, and you
     won't have any basis for assuming that they are.  Using 18O won't help
     sort this out.  there is not enough known about the process-related
     changes of 18O to make any sense out of it. 18O is a whole new
     research area, even less well understood, at this point, than 15N.
     Neither isotope pair is understood well enough to use in secondary
     applications to problems like you describe.
     -------------------------
       I know that the method of cation/anion exchange columns are one of
     the most common, but we found that the diffusion method of Khan, S.A.
     (1997), is cheaper and seems to be faster.
     ---------------
     If nitrate is the only major form of N, then it may work fine.
     ------------------------------------
     Also, it seems that it will work for our tipe of samples (have you
     read the article?).If it won't, we will change the method.Even so, I
     looked for the article of Cecily Chang which seems interesting, and
     yours, which I couldn't found. I would be very gratefull if you could
     send me a copy as you said, because I would like to read it also. If
     you could send it to me in the adress below...
     ----------------------------------
     I sent you a copy some days ago and also a copy of a major review I
     wrote on this subject ; they should be with you soon.
     All the best, and good luck!
     Linda



      And also, I think that your invitation to go to learn your method is
     very nice from you and I will keep it in mind. cheers,Laura Vitoria i
     Codina Grup Consolidat de Mineralogia Aplicada i Medi AmbientDpt.
     Cristal.lografia, Mineralogia i Dipòsits MineralsFacultat de
     GeologiaUniversitat de BarcelonaC/ Martí i Franqués s/n08028
     Barcelona, SpainTel.34-93-4021345; Fax. 34-93-4021340e-mail:
     [log in to unmask]