Introduction to Environmental Isotopes

Stefan Uhlenbrook and Jochen WenningerUNESCO-IHE, VU Amsterdam and TU Delft, Delft, Netherlands

5 November 2009, Dutch Hydrology Meeting to receive the Darcy Lecture 2009, by Dr. Peter Cook, VU Amsterdam

Outline of This Lecture

1. Introduction2. How can environmental isotopes help to

detect and quantify global change impacts on water? Evaporation Runoff generation Groundwater Precipitation

3. Concluding Remarks

2

4

3

5

6

1

0

Glo

bal

Tem

pera

ture

(°C

)

IPCC Projections2100 AD

N.H

. Tem

pera

ture

(°C)

0

0.5

1

-0.5

1000 1200 1400 1600 1800 2000

Lower Risk forInstabilities

High Riskfor Instabilities

It is Getting Warmer!

The context – ONE

'climate colonialism'

A massive land-grabbing scramble in Africa as foreign companies -some with foreign aid money support - rapidly establish enormous monoculture fields in tropical countries.Prof Seif Madoffe, SUA

Sugar Cane – Kilombera Basin, Tanzania

The context – TWO

Global Changes

Climate (temperature, precipitation, radiation …) Land use, land cover

De-forestation / re-forestation Urbanisation Etc.

Population (amount, density, structure, …) Water use in space and time Economic development Change of diet (more meat => more water) N- and P-fluxes to water bodies Pollution (new substances etc.) Change in composition of species etc. etc. etc.

…. and many interdependencies/feedbacks!

Picture from Fairless, 2007, Nature

EIEIET ETES ES

SS SS

QR QR

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QS QS

P P

P PImpacts of land use change on hydrological processes P=Q+E+dS/dt

Short-term dynamics (e.g. interception, flood generation) vs.long-term dynamics (e.g. groundwater recharge, base flow)

PQQEEQEE gg

fuTu

sss

II

dtdS

dtdS

dtdS

dtdS

II Edt

dS Interception processes

sss QEdt

dS Surface water processes

gg Qdt

dSGroundwater processes

Water Balance Equation: P=Q+E+dS/dt

Where:

Root zone moisture processes fuTu QEEdt

dS

Possible changes in all variables dueto climate and/or land changes!!

Weatherley catchment, South Africa

How can Environmental Isotopes help??

Environmental Isotope – Basics

16O

8

Mass number (= protons + neutrons)

Atomic number (= protons)

18O

8

8 protons (positive), 8 electrons (negative), 8 neutrons (neutral)

8 protons, 8 electrons, 10 neutrons

- Nuclides with same atomic number (i.e. an element) but different mass number are called isotopes

- 92 natural elements have more than 1000 stable and radioactive isotopes

- Protons and neutrons in the nucleus have approximately the sameweight

- Electrons (negative charge) are lighter and are located in electron shells

Some common environmental isotopes

Source: Kendall, 1998

Picture from Fairless, 2007, Nature

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SS SS

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QS QS

P P

P P

Investigation of different compartments of the water cycle using environmental isotopes

P=Q+E+dS/dt

Meteoric Water Line (MWL): The Concept

Source: IAEA

Observing evaporation using environmental isotopes in big systems

Agarwaal et al., 2002

Transpiration Evaporation

Soil moisturesensors

Data Logger

Soil

Balance

Percolation

Rhizon watersamplers

Better Understanding of Evaporation Fluxesusing Environmental Isotopes

Wenninger et al., in preparation

Evaporation is the driving factor in isotopic fractionation

Transpiration and Percolation do not cause fractionation

Quantification between fractionating and non-fractionating losses

Conservation of mass and isotopes

ztvpif mmmmmm

ppiizzttvvff xxxxxx

Isotope Mass Balance

p; precipitationt; transpiration

v; evaporation

z; percolation

i; ff; final WCi; initial WC

Total

jj m

mx piTotal mmm with:

(e.g. Robertson et al. 2006, J. of Hydrol.)

Isotope Depths Profiles and Evaporation Line

-70

-60

-50

-40

-30

-20

-10-10 -8 -6 -4 -2

Irrigated water Soil water percolated water MWL

y = 3.8x-18.6

R2 = 0.95

GMWL

Comparison between different evaporation estimations:(a) measured using hydrometric data and HYDRUS 1D, and(b) calculated using isotope mass balance.

(a)

(b)(a)

(b)

New way to estimate evaporation fluxes?!Lysimeter A Lysimeter B

Evaporation E (mm) 19 77

Transpiration T (mm) 99 0

T/Etotal ratio 84% 0

Picture from Fairless, 2007, Nature

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P P

P P

Investigation of different compartments of the water cycle using environmental isotopes

P=Q+E+dS/dt

Studying hillslope processes with environmental isotopes

Spring A (Zipfeldobel)Spring B (Zängerlehof II)

Investigation Period

0 , 0

0 , 4

0 , 8

1 , 2

1 , 6

2 3 . 1 0 . 9 9 2 9 . 1 0 . 9 9 0 4 . 1 1 . 9 9 1 0 . 1 1 . 9 9 1 6 . 1 1 . 9 9

Dis

char

ge [l

/s]

Z i p f e l d o b e l s p r i n g Z a e n g e r l e h o f I I s p r i n g

E v e n t 1 E v e n t 2 E v e n t 3

0

2

4

6

8

Prec

ipita

tion

[mm

]

Spring A Spring B

(Uhlenbrook, Didszun, Wenninger, 2008, Hydr. Sci. Journal)

Hydrochemical Dynamics: Dissolved SilicaSpring A

Spring B

40

60

80

100

120

140

24.10.99 26.10.99 28.10.99 30.10.99 01.11.99Sta

ndar

dize

d co

ncen

tratio

ns [%

]

0,2

0,6

1,0

1,4

Dis

char

ge [l

/s]

Silica Discharge

40

60

80

100

120

140

24.10.99 26.10.99 28.10.99 30.10.99 01.11.99Sta

ndar

dize

d co

ncen

tratio

ns [%

]

0,2

0,3

0,4

0,5

0,6

Dis

char

ge [l

/s]

Silica Discharge

Hydrochemical Dynamics: DeuteriumSpring A

Spring B-100

-90

-80

-70

-60

-50

23.10.99 25.10.99 27.10.99 29.10.99 31.10.99

δ D

v-sm

ov [‰

]

0,2

0,3

0,4

0,5

0,6

Dis

char

ge [l

/s]

Deuterium Precip. Discharge

-100

-90

-80

-70

-60

-50

23.10.99 25.10.99 27.10.99 29.10.99 31.10.99

δ D

v-sm

ov [‰

]

0,2

0,6

1,0

1,4

1,8

Dis

char

ge [l

/s]

Spring Precip. Incr. Mean Discharge

0

0,4

0,8

1,2

1,6

24.10.99 26.10.99 28.10.99 30.10.99

Dis

char

ge [l

/s]

direct Runoff

deep GW

Discharge

shallow GW

Results of Hydrograph Separation at both Springs/Hillslopes

Spring A

Spring B0,0

0,2

0,4

0,6

24.10.99 26.10.99 28.10.99 30.10.99 01.11.99

Dis

char

ge [l

/s]

direct Runoff

deep & shallow GWDischarge

Example: Interpretation of Dominant Processes at the Hillslope Scale

(Mc Donnell, 1990, WRR)

(Picture: P. Mosley)

pre-event water

event water

Event (new) and prevent (old) water!

“ … all nice, but we need measurements at catchment

scale!”

(Keith J. Beven)

0

5

10

1520

25

30

35

0 10 20 30 40 50 60Time

Stre

am D

isch

arge

Quickflow, Stormflow

Baseflow

The bench mark paper:Sklash & Farvolden, 1979: The role of ground-water in storm runoff. Water Resources Research.

Tracer-based Hydrograph Separation in the Weatherley Catchment, South Africa

Wenninger, Uhlenbrook, Lorentz, 2008, Hydr. Sci. Journal

Picture from Fairless, 2007, Nature

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P P

P P

Investigation of different compartments of the water cycle using environmental isotopes

P=Q+E+dS/dt

Estimation of Residence Times of WaterGroundwater and surface waters are a mixtureof different ages

Definition of “groundwater age”:

The “age” of a groundwater parcel is the time elapsed since this parcel had the last contact to the atmosphere (time since recharge at the groundwater surface).

(from: A. Suckow, 2004, IAEA)

Groundwater Residence Time Estimation (‘age dating’)

Which tracer is useful for which time scales?

Tritium: 1-40a(admixture only)

0.1 1 10 100 1000 10000 100000

Groundwater Age [years]

D, 18O: 0.1-4a14C: 2ka-40ka

85Kr: 1-40a

CFC/SF6: (4)10-40a

T/3He: 0.5-35a4He: 50- >100 000a (age estimates)

40Ar: >100 000a39Ar: 50-2000a

36Cl: >100 000a

Tritium, 3H

Tritium input into the water cycle

(From: IAEA, 2005)

Tritium input function: Radioactive decay

1970 1980 1990 2000Year

0

100

200

300

400Tr

itium

in P

reci

pita

tion

[TU

]

1950 1960 1970 1980 1990 2000Year

0

2000

4000

6000

Triti

um in

Pre

cipi

tatio

n [T

U]

Already verylow again!

springfor watersupply

Estimation of Residence TimesUse environmental isotopes: 18O, 2H, 3H, CFCs ….

-18

-14

-10

-6

-2

Jan 95 Jan 96 Jan 97 Jan 98 Jan 99 Jan 00 Jan 01 Jan 02

Zeit

Einzelw erte Input Sinusfunktion Input Einzelw erte Output Sinusfunktion Outputinput output

Time (months)

Example for Estimating of Residence Times at a Spring

Using environmental isotope: 18O

1.02.95 1.08.95 1.02.96 1.08.96 1.02.97

-10

-9

-818 O simulation (exponential-piston-flow model)18 O sample, storm flow18 O sample, base flow

18

O [%

o]

Exponential-piston-flow model:

t0 = 36 months, = 1.12

Mean residence time: 26-36 mon(Uhlenbrook et al. 2002, WRR)

CFCs for dating groundwater

-> confirmation of

3H results

b) F-12

48 96 144 192 240

300

400

500

600

a) F-11

48 96 144 192 240

F-11

[ppt

]

150

200

250

300

Exponential-Piston-Flow Model:

n = 1.06; t0 = 28 months

Dispersion Model:PD = 0.22; t0 = 84 months

06/82 06/9806/9406/9006/86

F-12

[ppt

]

06/82 06/9806/9406/9006/86

c) F-113

36 72 108 14440

60

80

100

Dispersion Model:PD = 0.05

t0 = 40 months

Exponential-Piston-Flow Model:

n = 1.06; t0 = 22 months

F-11

3 [p

pt]

01/90 01/9901/9601/93(Uhlenbrook etal., 2002; WRR)

Sub-basin Brugga (40 km2)Three main flow systems with different residence times and

contributions on a seasonal time scale

~ 10 %

~ 20 %

~ 70 %

(Uhlenbrook et al. 2002, Wat. Resour. Res.)

Picture from Fairless, 2007, Nature

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P P

P P

Investigation of different compartments of the water cycle using environmental isotopes

P=Q+E+dS/dt

Figure 2. Rainout effect on H and O values (based on Hoefs 1997 and http://www.sahra.arizona.edu/programs/isotopes/oxygen.html

Changes in Isotopic Composition of Precipitation

Spatial variations of isotopes in the USA

Source: Kendall and Coplen, 2001

Spatial and temporal variations of deuterium in Germany

(Source: Leibundgut et al., 2009)

(Wissmeier and Uhlenbrook 2007, J. of Hydrol.)

Validating catchment

models

(Wissmeier and Uhlenbrook 2007, J. of Hydrol.)

Validating catchment

models

(1) The world is changing – Hydrology too (‘stationary is dead’)

(2) How can environmental isotopes help us to understand changes and their impacts?

(3) Innovative ways to observe hydrological processes, in particular in combination with other methods (geophysics, model etc.)

(4) Today: Isotope Hydrology using 18O, 2H, 3H, components of the water molecule

(5) Next time: Isotope Biogeochemistry using 15N, 13C and 34S, or other dating techniques noble gases, metals, etc.

Concluding Remarks – Introduction to Environmental Isotopes