Isotopes in the unsaturated zone:new opportunities and challenges

Prof. Dr. Christine Stumpp

Institute for Soil Physics and Rural Water ManagementUniversity of Natural Resources and Life Sciences Vienna (BOKU)

International Symposium on Isotope Hydrology: Advancing the Understanding of Water Cycle Processes, Vienna, 20.05.-24.05.2019

Importance of unsaturated zone processes

• main part of critical zone

• water storage

• groundwater recharge

• ecosystem

• protection of aquifers

complex and heterogeneous

transient water flow and transport

water ages

(Lin, 2010, HESS)

Demographics of water in the critical zone

• wide range of different water ages

• strong influence of mixing at interfaces

• younger ages in soils and unsaturated zone

oxygen and hydrogen isotopes

tracer for age dating

hydrological processes

(Sprenger, Stumpp, Weiler et al, in press, Rev Geophys)

52 104 158 time [weeks]

δ18O

[‰]

-12

-

10

-8

-6

-4

precipitation

52 104 158 time [weeks]

δ18O

[‰]

-12

-

10

-8

-6

-4

precipitation

soil 1m

52 104 158 time [weeks]

δ18O

[‰]

-12

-

10

-8

-6

-4

precipitation

soil 1m

shallowgroundwater

Oxygen and hydrogen isotopes

• water fluxes and transit times• transport processes

analysis of isotopes in pore water extraction of water from variable saturated pores

Suction cups and lysimeter• apply „suction“

• matric potential controlled

• collect drainage

mobile water draining poresaccording waterretention function

mobile water

• interlaboratory comparison study• soils spiked with water of known isotopic composition

• 2 soils with different texture• 2 different water contents

compare different lab protocols best pratice

Cryogenic water extraction

(Orlowski et al. 2018, HESS)

• deviation from known isotope value• most pronounced for clayey loam and low water content

Cryogenic water extraction

(Orlowski et al. 2018, HESS)

all laboratories withdifferent results

procedure independent

development of protocols lab comparison test

Direct vapour equilibration method

• no extraction of pore water required

• measurement of isotopes in vapor phase

(Wassenaar et al. 2008, ES&T)

water – minutessoil – min. to days

Challenges of direct vapour equilibration method– Bag type and water loss

gree: crystal clear bagsblue: Ziploc bagsred: mylar bagsblack: black bagspurple: IsoPakspale blue: silver puches

(Hendry et al. 2015, HESS)

Challenges of direct vapour equilibration method– Bag type and water loss

gree: crystal clear bagsblue: Ziploc bigasred: mylar bagsblack: black bagspurple: IsoPakspale blue: silver puches

(Hendry et al. 2015, HESS)

Challenges of direct vapour equilibration method– Gas changes in bags

(Gralher et al., 2018, VZJ)

carrier gas changes need to be avoided correction of apparent evaporation effect

• build up of CO2 in bags

• bias of isotope readings

• different for oxygen and hydrogen

Challenges of direct vapour equilibration method– Gas changes in bags

(Gralher et al., 2018, VZJ)

carrier gas changes need to be avoided correction of apparent evaporation effect

• build up of CO2 in bags

• bias of isotope readings

• different for oxygen and hydrogen

Visit poster –Benjamin Gralher

In-situ equilibration techniques

(Rothfuss et al. 2013, WRR)

(Volkmann et al. 2014, HESS)

(Gaj et al. 2016, HESS)

(Volkmann et al. 2016, Plant Cell Environ)

• gas permeable tubings or other materials• pore water and xylem

high resolution sampling dynamic processes in soil hydrology and ecohydrology

polypropylen tubing

Examples - isotope depth profiles

(Chesnaux & Stumpp HSJ, 2018)

vegetationno vegetation

mathematical modelling for more detail information about flow and transport

• quantification of average recharge rates • identification of infiltation events

Mathematical modelling approaches

spatially explicit approach• Richards equation• convection-dispersion equation• e.g. HYDRUS

pro: - physically based- detailed information

con: - number of parameter- limitations for upscaling

spatially integrated approach• input – output relationship• unsaturated zone = black box

• transit time distribution functions• StorAge Selection funtions

pro: - reduction of complexity- upscaling

con: - reduction of complexity- uncertainty

isotopes increase informationcontent for inverse modelcalibration

isotopes are good tracer to testreliabilty of spatially integratedmodel approaches

Spatially explicit approach - inverse estimation of soil hydraulic and transport parameters

Optimization strategy

BOS1: θ + ψ

BOS2: ψ + δ

2SOS: θ + ψ; δ

MOS: θ + ψ + δ

(Groh et al. 2018, Vadose Zone J)

(picture: Pütz et al. 2018, VZJ)

• 6 lysimeter

• replicates

• HYDRUS-1D

flow and transport

informationcontent

optimizationstrategy

Spatially explicit approach - inverse estimation of soil hydraulic and transport parameters

Optimization strategy

BOS1: θ + ψ

BOS2: ψ + δ

2SOS: θ + ψ; δ

MOS: θ + ψ + δ

(Groh et al. 2018, Vadose Zone J)

• best optimization when water content, matric potential and isotopes are given

isotopes add information about water flow and transport

Application of lumped parameter modelapproach to describe transport in soils

( ) outoutiN

iieff

iiiinp

P

PNtC δδδα+−⋅

⋅⋅=

∑=1

)(

(Stumpp et al., 2009, J Hydro)• general pattern of flow and transport• not every precipitation event contributes to recharge

modify input function accounting for actual evapotranspiration

Application of lumped parameter modelapproach to describe transport in soils

(Stumpp et al., 2009c, J Hydro)(Stumpp and Maloszewski 2010, J Hydro)

PRO

BAB

ILIT

Y

• lumped model simultation similar to transient model• vegetation periods investigated separately transit time distributions are vegetation specific, tool for vulnerability assessment

Application of StoreAge selection functions todescribe transport

(Benettin, personal communication)

Application of StoreAge selection functions todescribe transport

(Benettin, personal communication)

Application of StoreAge selection functions todescribe transport in soils

(Asadollahi et al. submitted)

• 2 lysimeter

• artifical and environmental tracer

• SAS function

• HYDRUS-1D

model performance

variable mean transit times in Q and ET

Application of StoreAge selection functions todescribe transport in soils

(Asadollahi et al. submitted)• similar model performance• both lysimeter with similar SAS functions

fitting of SAS function providesphysically meaningful results

similar toADE withPe =10

Variable mean transit times and partioning ofprecipitation

(Asadollahi et al. submitted)

• similar mean transit times in drainage

Variable mean transit times and partioning ofprecipitation

(Asadollahi et al. submitted)

partioning of P in Q and ET

• similar mean transit times in drainage• different mean transit times in ET

• H1D: roots only in upper soil• SAS: entire water volume accessible

verification of ET not possible due tomissing tracer concentration

(Asadollahi et al. submitted)

transit times and partioning crucialfor ecohydrology and biogeochemistry

Current challenges

1) how can our methods for analysis of pore water isotopes getmore accurate?

• analysis of different pore water (mobile vs bulk)

• use of standard operating procedures

• reduce uncertainties

• awareness of uncertainties

(Gralher et al. 2018, VZJ)

development of protocols/SOPs lab comparison test

Current challenges

1) how can our methods for analysis of pore water isotopes getmore accurate?

2) how to upscale processes from the plot to the regional scale?

• choice of model complexity

• isotopes for model calibration and validation

mathematicl model development upscaling of uncertainties

(Asadollahi et al. submitted)

Current challenges

1) how can our methods for analysis of pore water isotopes getmore accurate?

2) how to upscale processes from the plot to the regional scale?

3) how to integrate time scales across compartments and at compartment interfaces?

• limitations of using stable isotopes for older ages

• high-resolution data

(Sprenger et al. in press, Rev Geophys)

multi-tracer approaches in-situ measurement of tracers

Future opportunities• which precipiation is really used by plants?

in-situ measurement of water isotopes in soilsand transpired water

partioning between evaporation and transpiration

improvement of root water uptake processes andsimulations

• how does climate impact hydrological, ecological andchemical processes in soils?

mutual feedback mechanisms

combination of isotopes approaches

combination of experiments and modelling

(Sprenger et al. in press, Rev Geophys) interdisiciplinary approaches and methodologies

Water ages in the hydrological cycleBlack Forest Autumn School

27.-31. October 2019Waldhotel Zollernblick, Freudenstadt, Germany

We will teach approaches, methods and models to determine water fractions, water ages and transit times throughout the hydrological cycle and we will foster inter-disciplinary discussions.

Course LecturerMarkus Weiler, University Freiburg, Germany

Christine Stumpp, BOKU Vienna, AustriaJames Kirchner, ETH Zürich, Switzerland

Matthias Sprenger, North Carolina State University, USAMarkus Hrachowitz, TU Delft, Netherlands

Paolo Benettin, EPFL Lausanne, Switzerland

Acknowledgement- Asadollahi, M., Stumpp, C., Rinaldo, A., and Benettin, P. (submitted) Transport and water age dynamics in soils: a comparative study of spatially integrated and spatially explicit

models. Water Resources Research

- Chesnaux, R., and Stumpp C. (2018) Advantages and challenges of using soil water isotopes for assessing groundwater recharge: Illustration with a field study located in Canada, Hydrological Sciences Journal 63, 679-695, doi: 10.1080/02626667.2018.1442577

- Gralher, B., Herbstritt, B., Weiler, M., Wassenaar, L.I., and Stumpp, C. (2018) Correcting for biogenic gas matrix effects on laser-based porewater-vapor stable isotope measurements. Vadose Zone Journal 17, 170157, doi:10.2136/vzj2017.08.0157

- Groh J., Stumpp C., Lücke A., Pütz T., Vanderborght J. & Vereecken H. (2018) Inverse Estimation of Soil Hydraulic and Transport Parameters of Layered Soils from Water Stable Isotope and Lysimeter Data. Vadose Zone Journal 17, 170168, DOI:10.2136/vzj2017.09.0168

- Orlowski, N., Breuer, L., Angeli, N., Boeckx, P., Brumbt, C., Cook, C. S., Dubbert, M., Dyckmans, J., Gallagher,B., Gralher, B., Herbstritt, B., Hervé-Fernández,P., Hissler, C., Koeniger, P., Legout, A., Macdonald, C. J., Oyarzún, C., Redelstein, R., Seidler, C., Siegwolf, R., Stumpp, C., Thomsen, S., Weiler, M., Werner, C. and McDonnell, J. J. (2018) Inter-laboratory comparison of cryogenic water extraction systems for stable isotope analysis of soil water. Hydrology and Earth System Sciences 22, 3619-3637, doi: 10.5194/hess-22-3619-2018

- Sprenger, M., Stumpp, C., Weiler, M., Aeschbach, W., Allen, S.T., Benettin, P., Dubbert, M., Hartmann, A., Hrachowitz, M., Kirchner, J.W., McDonnell, J.J., Orlowski, N., Penna, D., Pfahl, S., Rinderer, M., Rodriguez, N., Schmidt, M., and Werner, C. (in press) The demographics of water: A review of water ages in the critical zone. Reviews of Geophysics

- Stumpp C., Stichler W. & Maloszewski P. (2009) Application of the environmental isotope d18O to study water flow in unsaturated soils planted with different crops: Case study of a weighable lysimeter from the research field in Neuherberg, Germany. Journal of Hydrology, 368(1-4), 68-78

- Stumpp, C. and Maloszewski, P. (2010) Quantification of preferential flow and flow heterogeneities in an unsaturated soil planted with different crops using the environmental isotope d18O. Journal of Hydrology, 394, 407-415

References- Gaj, M., M. Beyer, P. Koeniger, H. Wanke, J. Hamutoko and T. Himmelsbach. 2016. In situ unsaturated zone water stable isotope (2H and 18O) measurements in semi-arid environments:

a soil water balance. Hydrol. Earth Syst. Sci. 20: 715-731. doi:10.5194/hess-20-715-2016.

- Hendry, M.J., E. Schmeling, L.I. Wassenaar, S.L. Barbour and D. Pratt. 2015. Determining the stable isotope composition of pore water from saturated and unsaturated zone core: improvements to the direct vapour equilibration laser spectrometry method. Hydrology and Earth System Sciences 19: 4427-4440. doi:10.5194/hess-19-4427-2015.

- Lin, H. (2010) Earth’s Critical Zone and hydropedology: concepts, characteristics, and advances. HESS 14, 25-45

- Rothfuss, Y., H. Vereecken and N. Brueggemann. 2013. Monitoring water stable isotopic composition in soils using gas-permeable tubing and infrared laser absorption spectroscopy. Water Resources Research 49: 3747-3755. doi:10.1002/wrcr.20311.

- Volkmann, T.H.M. and M. Weiler. 2014. Continual in situ monitoring of pore water stable isotopes in the subsurface. Hydrology and Earth System Sciences 18: 1819-1833. doi:10.5194/hess-18-1819-2014.

- Volkmann, T.H.M., K. Kühnhammer, B. Herbstritt, A. Gessler and M. Weiler. 2016. A method for in situ monitoring of the isotope composition of tree xylem water using laserspectroscopy. Plant, Cell & Environment 39: 2055-2063. doi:10.1111/pce.12725.

- Wassenaar, L.I., M.J. Hendry, V.L. Chostner and G.P. Lis. 2008. High resolution pore water d2H and d18O measurements by H2O(liquid)-H2O(vapor) equilibration laser spectroscopy. Environmental Science & Technology 42: 9262-9267.

Thank you….

Univ. Prof. Dr. Christine StumppInstitute for Soil Physics and

Rural Water Management (SoPhy)Univ. of Natural Resources and Life Sciences

Muthgasse 181190 Vienna, AUSTRIA

christine.stumpp@boku.ac.atTel: +43 1 47654/81511Fax: +43 1 47654/81509

….questions?