Hi Francois,

        I met you twenty years ago in Peru when I did field work with Stuart
Hurlbert.  I am now at the U.S. Geological Survey on a stable Isotope
project.  I am working on NO3 and NH4 in snow, snowmelt, ppt where the
concentrations are low, (7-10 uMoles) and am writing a paper on how to
collect and processes samples of this type.  My method only works for dilute
waters, and wouldn't work for the highly saline waters of the Altiplano.   
        Stuart still works in the Andes.  
        I don't have an answer to your question, but thought I would say
hello.  
        I believe that there are papers that describe the situation you are
working on but I don't know about them off  hand.  Good luck.  
  

Cecily Chang  >

Dear listmembers,
>
>We are working on water chemistry of closed-basins in the Andean cordillera
>of Northern Chile. Precipitations occur mainly as snow. Our concern is
>about isotopic composition of infiltrating melt-water. The snow cover
>evaporates during the day. Under an arid climate, does the condensation
>during the night offset evaporation enrichment of 18O and 2H which occurs
>during the day? Does anyone know studies already done in such environments
>?
>Many thanks for you help.
>
>Francois Risacher
>Centre de Géochimie de la Surface-CNRS.
>Strasbourg. France
>
>
Cecily Chang
USGS MS 434
345 Middlefield
Menlo Park, CA 94025
650 329 4471
FAX  5590
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