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 29, 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:
Azeotropic Distillation
Simple, inexpensive, fast and widely usable..

3.  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
• First used by R.M.
Brown and G.B. Allison
in the late 1970s and
was adapted from
Dewar and McDonald
(1961).
We chose Azeotropic Distillation using Standard Dean-
Stark Apparatus for Soil Water Extraction,
Because…
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

4. Standard Dean-Stark Apparatus
Source: Sunshine Scientific
Equipments
Conical Flask
(500 ml capacity)
Soil Sampling
Condenser
>90°C
Heating mantle
Sample collection

5. 𝑯𝟐𝑶 +
Principle
Azeotropic mixture
@ 84.1°C
Completely immiscible at
ambient temperature
B.P. = 100°C
Density = 1
gm/cc
B.P. = 110°C
Density = 0.867
gm/cc
Traces of Toluene can
be separated by
adding wax

6. First, the water content of the soil is determined by weighing, drying
and reweighing a small aliquot of the soil sample.
Appropriate amount of soil sample is taken in the conical flask.
Enough toluene is added so that the soil remains covered throughout
the entire distillation process.
Procedure

7. Discussion
Test 1: Heating mantle were calibrated for different
temperature
Result: Temperature could not be fixed, so high traces of
toluene came-up with water.
Test 2: Heating mantle was replaced with digital Hot Plate.
Result: Still unable control the required temperature and
therefore high concertation of toluene received with water.
Test 3: Different proportion/ratio of toluene and soil sample
were taken for azeotropic distillation.
Result: Insignificant.
Conclusive Remark
Unable to extract water from soil, effectively using Azeotropic Distillation
and further improvement is needed…

8. Coating the condenser and the funnel with a solution of
dimethyldichlorosilane compound to change the surface from
hydrophilic to hydrophobic.
 To remove traces of toluene from collected water sample wax would
be used.
 Replacement of toluene by Kerosene/𝐶𝐶𝑙4/Ethanol/Benzine or any
other reagent.
Replacement of heating mantle or Hot plat by Sand Bath or Water
Bath to perform the distillation in controlled temperature.
 Use of Centrifuge method to extract water from soil.
To be carried out…

9. 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.

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