Partitioning Evapotranspiration into Evaporation and Transpiration fluxes using Stable Isotopes of Oxygen and Hydrogen

1. Progress Report
Partitioning Evapotranspiration into Evaporation and Transpiration fluxes
using Stable Isotopes of Oxygen and Hydrogen
March 01, 2023
Presented
by
Pankaj Kumar Thakur
(Project Associate-I) GWHD
National Institute of Hydrology,
Roorkee (Uttarakhand)
Under the supervision
of
Dr. Gopal Krishan
(Principal Investigator)
Scientist ‘D’ GWHD
National Institute of Hydrology,
Roorkee (Uttarakhand)

2. Content
 Soil Water Extraction
 Xylem Water Extraction

3. Soil Water Extraction
To extract the water from soil for isotopic analysis, we reviewed the available soil water extraction
methods and techniques:
Centrifuge Method:
 Fast but unsuitable for low water content
(1-5)% soil samples and less precise
(Jusserand, 1980)
Vacuum Distillation Method:
 Requires complicated vacuum system
 Time consuming
 Not preferable for soil which releases
molecular and structural water at the
distillation temperature (Stewart, 1972)

4. Cryogenic Vacuum Distillation (CVD):
 Most common method for extracting water
from both (soil & plant). But,
 Involves high capital and operation cost.
 Time consuming
 Extreme pressure and temp. condition may
mobilize the both hygroscopic and
biologically bund water.
(Orlowski et al., 2016)
Direct vapour equilibration:
 Least expensive & least time consuming.
But,
 Has poor accuracy (<5% water content)
 Possibilities of Fractionation of the isotopic
signal due to evaporation and microbial
activities
(Orlowski et al., 2016)
High pressure mechanical squeezing
 High capital cost
 Time consuming and manpower intensive
 Storage stability and great care is required
 Not feasible for coarser soil with low water content
(Orlowski et al., 2016)

5. Our Method: Azeotropic Distillation
Simple, inexpensive, fast and widely usable..
• First used by R.M.
Brown and G.B. Allison
in the late 1970s and
was adapted from
Dewar and McDonald
(1961).
 Can be used for soil of almost
any type and grain size.
 Apparatus (Dean-Stark) has no
memory effect.
 Reagents (toluene/kerosene &
wax) do not affect isotopic
composition of soil water.
 Good Accuracy (±2%) for >3%
water content

6. Standard Dean-Stark Apparatus
Source: Holy Scientific
Source: Sunshine Scientific
Equipments
Tested (Revesz and Woods, 1990)
a) Different soil types
b) Variation in soil/toluene ratio
c) Variation in grain size of the soil
d) Memory effect between successive
samples
e) Variability of water content
substitution of kerosene (b.p. 175-
245°C) for toluene
f) Dependence on the isotopic
composition of the soil water

7. Xylem Water Extraction
Xylem tissue is fundamentally known as water carrier in plants. Xylem takes water from roots, bring
it to shoots and transpires it from leaves (stomata). Hence, we will extract only xylem water for
isotopic analysis.
We reviewed the following plant water
extraction techniques (Millar et al.,2018):
 Direct vapor equilibration
 Microwave extraction
 Two-versions of CVD
 Centrifugation
 High pressure mechanical squeezing
And,
Following two-methods were
found best (Zuecco et al., 2020):
A. Cryogenic Vacuum
Distillation (CVD)
B. Scholander Pressure
Chamber (SPC)

8. Scholander-type Pressure Chamber (SPC) vs.
Cryogenic Vacuum Distillation (CVD) Method
CVD
 CVD tends to retrieve all water stored in
the sampled tissue, from both living and
dead cells.
 Complex, expensive and requires
laboratory work.
 CVD extracts up to 99% of the water in a
sample (~2ml)
SPC
 SPC likely extracts only water within the
xylem (dead cell).
 SPC is simple, can be carried out in situ,
and it does not require specific laboratory
work.
 SPC, only extracts water present in the
xylem conduits, and given the much smaller
sample volumes were collected by SPC
than by CVD (~200 μl)
Our aim to quantify the relative contribution of the water sources to transpiration and it rely more on
the isotopic composition of xylem water. Hence, we’ll extract only xylem water by SPC method.
Source: Zuecco et al., 2020

9. Scholander-type Pressure Chamber (SPC)
Source: Zuecco et al., 2020
Source: https://www.indiamart.com/nu-tech-international/

10. References
 Jusserand, C., 1980. Extraction de l'eau interstitielle des sediments et des sols. Catena, 7:87 96.
 Stewart, G.L., 1972. Clay-water interaction, the behavior of 3H and 2H in absorbed water, and the isotope effect. J.
Soil Sci. Soc. Am., 36: 421-426.
 Orlowski, N., Pratt, D. L., & McDonnell, J. J. (2016). Intercomparison of soil pore water extraction methods for
stable isotope analysis. Hydrological Processes, 30(19), 3434-3449.
 Allison, G.B. and Barnes, C.J., 1983. Estimation of evaporation from non-vegetated surfaces using natural
deuterium. Nature, 301: 143-145.
 Dewar, W.A. and McDonald, P., 1961. Determination of dry matter in silage by distillation with toluene. J. Sci. Food
Agric., 12: 790-795.
 Revesz, K. and Woods, P.H., 1990. A method to extract soil water for stable isotope analysis. J. Hydrol., 115: 397-
406.
 Millar, C., Pratt, D., Schneider, D.J., and McDonnell, J.J.: A comparison of extraction systems for plant water stable
isotope analysis, Rapid Commun. Mass Spectrom., 32, 1031-1044, https://doi.org/10.1002/rcm.8136, 2018
 Zuecco, G., Amin, A., Frentress, J., Engel, M., Marchina, C., Anfodillo, T., Borga, M., Carraro, V., Scandellari, F.,
Tagliavini, M. and Zanotelli, D., 2022. A comparative study of plant water extraction methods for isotopic analyses:
Scholander-type pressure chamber vs. cryogenic vacuum distillation. Hydrology and Earth System Sciences, 26(13),
pp.3673-3689.

11. Thank you!
Thanks for your gift of time…