I am wondering if moisture content of various pore sizes in soil has different stable isotope composition. Hence I would like to trap water separately from a wide range of matrix potential without a pF pot. Any suggestions?
Thanks.
Hi Gergely and Andreas, I am not sure whether the rhizons will work. They are not specific for a particular matrix potential. You will probably need to extract soil moisture at very well known suctions.
Cheers Jetse
Hi Jetse, surely you have to test it, but since they've been used on deep sea sediment cores with over 100m length, it would be worth to give them a try. Sampling pristine pore water is struggling.
Thanks guys,
And what do you think about gradual heating and vapour precipitation?
Hi Andreas and Gergely, You are certainly right Andreas, you can sample under a wide range of conditions. We also used them to sample under fish ponds. I include the link. The problem is that you do not know the matrix potential when you are sampling. So you need to measure that separately, but you can certainly take the water samples with the rhizons.
Article Short Communication. Rhizons improved estimation of nutrient...
Hi Jetse, I agree with that. Thanks for the link, I'll read it.
Gergely, heating and precipitation will lead to an isotope fractionation.
Dear Gergely,
Why not try trapping water with a zeolite? This could be done in-situ in the field without taking the soil profile into the laboratory.
A dried zeolite can absorb capillary water in the soil, which can then be released at low temperatures and processed further in the laboratory. Care would have to taken to choose a desorption temperature, which would not shed structural water from the zeolite.
I have no idea if deltaD or deltaO is fractionated in the process of water adsorption in the soil, but perhaps it is correctable if tests with standards turn out favorable.
Good luck!
Thomas
I think the fractionation could have a somewhat high influence in a zeolite. For example Abe (2008) showed it for Oxygen Isotopes.
Which isotopes do you want to study, Gergely?
I have successfully used Rhizon samplers for sampling porewaters from a variety of soils and sediments in situ. Other alternative techniques I have used for sampling porewater from soils and sediments for chemical analysis includes ultracentrifugation and porewater extraction by squeezing in a specialised piston cell.
Hi, thanks for your comments.
Actually, Oxygen is in the focus. And the question is whether soil can change isotope composition of rainwater during percolation into a cave. I suppose some sort of exchange. Maybe, water adsorbed with different matrix potential has various isotope compositon?
Zeolite sounds good, however needs a couple of additional measurements/calibration.
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