Photocredit:SkyLovill

WaterIsotopicSignatureofTranspiration

InezFungUCBerkeley

WaterIsotopesandClimateWorkshopOct22019

ModelingEvapotranspirationforThree-dimensionalGlobalClimateModels.Dickinson(GeophysicalMonographSeries1984)

Ontimescales>decades:δDET=δDPRECIP

ModelingEvapotranspirationforThree-dimensionalGlobalClimateModels.Dickinson(GeophysicalMonographSeries1984)

1.  Leafdrip–ignoreevapofinterception

1

226

5

43

2

2.Infiltration–assumeδDsameasprecip

3.Percolation–togrdwater4.Rootuptake–assumeδDsameaswatersource,nofractionation5.Stemflow–assumexylemδDsameasroot

6.Transpiration–assumetimescale>daystoignorefractionationeffects

Elder Creek Watershed • Winter rain, summer dry • Sedimentary bedrock • Steep, no floodplain • Old growth forest

Colored digital vegetation and topography from a lidar survey

EelRiverWatershedAngeloCoastRangeReserve

Rivendell

2007-2013:KeckHydroWatchProject(PI:Fung)2013-2018:NSFCriticalZoneObservatory(PI:Dietrich)

WELLS:GROUNDWATER

Well01

Well03

Well10

Whatisunderfoot?

Well15

SoilSaprolite

WeatheredBedrock

Fresh

Bedrock

ElderCreek

Water table fluctuations at 7 wells over 6 years

Rapid rise – slow decline after storms

Drought – not very evident in water tables

Salve, Rempe, and Dietrich, WRR 2012

ModelingofflowinthevadosezoneRichard’sEquation;y = pressurehead(suction)

C(ψ )specific mositure capacity

!∂ψ∂t

=∂∂z

K(ψ )hydraulicconductivity

!∂ψ∂z

− 1$%&

'()

*

+

,,,

-

.

///+ S(z,ψ )

sink"#$

θ (ψ )soilwatercontent

! = θ reswiltingpoint

! +θ sat (z)−θ res1+ (α ψ

n( )m

Θ(z, t)saturation0≤Θ≤1

"#$ =θ (z, t)−θ resθ sat (z)−θ res

Pressureheadisrelatedtotheamountofmoisturepresentandhencetothedegreeofsaturation

AnewparameterizationofHydraulicConductivity

Vrettasa

ndFun

g(JA

MES201

6)

K(Θ)=ΘλKbkg

Kbkg(Θ;µ ,Λ2)= 1Θ 2π Λ

exp(− (lnΘ− µ)22Λ2 )lognormal

Kbkg = µ(z)~exp(−z ⋅be ); var(Kbkg)= Λ2 =η(1−Θ)

SimulationofthewellwatertablesatRivendell…

VrettasandFung(JAMES,2016)

HydraulicConductivityincreaseswithsaturation

K(Θ)=ΘλKbkg

Kbkg(Θ;µ ,Λ2)= 1Θ 2π Λ

exp(− (lnΘ− µ)22Λ2 )lognormal

Kbkg = µ(z)~exp(−z ⋅be ); var(Kbkg)= Λ2 =η(1−Θ)

Intensestormsàfasterpenetrationtodepth

Figure16-revised1-Dtimeseriescartoon.

HL

HR

“HydraulicLift(HL)orRedistribution(HR)”

ToddDawson

Photocredit:SkyLovill

Wheredotreesgettheirwater?

IsotopemeasurementsSept2012-Feb2013

Precip-wtdmean

δDgroundwater

creek

δ18O

DrySummerpro

gresses

Soilmoisture

JasperOshun

15 16

7

SapVelocitiesDrySeason(Summer)

WetSeason(Winter)

Intermediate(Spring)

Tree15DougFir(cm/hr)

Tree16Madrone(cm/hr)

Tree7LiveOak(cm/hr)

datagap

LinketalWRR2014

δ18O

δD

JasperOshun

IsotopicSignaturesinxylem

DouglasFirs

MadronesLiveOaks

δD

δ 18OδD

δ 18O J.Oshun

Douglasfirs•  Hydraulicredistribution•  Deeproots•  Maxdailytranspiration

inrainywinter

Madrones•  Deeproots•  Maxdailytranspiration

indrysummer

Summary•  Inareaswithweatheredbedrock•  Rapidmovementofwaterdown(preferentialflow)andup(hydraulicredistributionbyroots)

•  XylemδDreflectseasonalityoftranspirationandthemixtureofdeepandshallowmoistureatthetimeoftranspiration

Outlook:Needforobservations

•  Near-surfaceδDofvaporfromsatellite•  Rootarchitectureofdifferenttreespecies•  Geologicsubstrateàreservoirsofrockmoisture