Hello everybody,

For a brief discussion on various designs for field precipitation
collectors that can be left unattended for 6 months, see

Scholl, M.A., Ingebritsen, S.E., Janik, C.J. and Kauahikaua, J.P., 1996,
Use of precipitation and groundwater isotopes to interpret regional
hydrology on a tropical volcanic island:  Kilauea volcano area, Hawaii,
Water Resources Research, v. 32, no. 12, p. 3525-3537.


We found the best design was a collector with a layer of mineral oil to
prevent evaporation, however, you need to use at least a 1-cm thick layer
of oil, or evaporation can occur through the oil layer, especially in
hot, dry climates.

Martha Scholl

***********************
U.S. Geological Survey
431 National Center
Reston, VA  20192

703-648-5890


On Tue, 29 Sep 1998 18:58:54 -0400
"Daniel H. Doctor" said:
> Hello Isabella,
>
> I believe that Carol Kendall at the USGS (in Reston, Virginia?) knows of a
> design for building a rain collection system that rests underground, such
> that the cooling effect of the soil provides natural refrigeration and
> helps reduce risks of fractionation due to evaporation.  Also, I've heard
> that a simple layer of mineral oil in the bottom of your collection vessel
> can act as a nice evaporation seal without risking fractionation via
> chemical reaction.  I don't know how rigorously this has been tested,
> though (quick publication potential?).  Either way, two other things will
> greatly help reduce the risk of fractionation: don't let your samples sit
> in the field for very long, and be sure to collect as large an amount of
> sample water as possible!
>
> Anybody else out there have a suggestion?
>
> Isabella, please keep me updated as to what you discover, as this is
> concern for me in my research as well.  Thanks!
>
> -Dan
>
> On Tue, 29 Sep 1998 08:41:23 -0400 wrote...
> >        Hello everyone!
> >
> >        I'm a graduate student at the University of Virginia beginning a
> >project on Oxygen-18 and deuterium in rain water.  I'm building a rain
> >collector that allows for collection at 5 minute increments for 12
> >hours and I am worried about the possibility of sample fractionation. I
> >read a paper suggesting the creation of a dodecane bi-layer when analyzing
> >for oxygen, but I am unsure how this would effect deuterium results.
> >Does anyone know of a reference or have an opinion of using such a
> >technique when analyzing for deuterium?  Due to field constraints,
> >refrigeration really isn't an option and I was curious if anyone
> >had ever run into this problem before or had a good solution to
> >fractionation in the field.
> >
> >        Thanks!,
> >                Isabella Angelini
> >                University of Virginia
> >                [log in to unmask]
> >
>
>
>
> *****************************************************
> Dan Doctor
> Dept. of Geology & Geophysics
> Univ. of Minnesota
> 310 Pillsbury Dr. SE
> Minneapolis, MN 55455
> (612) 624-1333
> Email: [log in to unmask]