Water Isotopic Signature of Transpiration · Water Isotopes and Climate Workshop Oct 2 2019...
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Photo credit: Sky Lovill Water Isotopic Signature of Transpiration Inez Fung UC Berkeley Water Isotopes and Climate Workshop Oct 2 2019
Transcript of Water Isotopic Signature of Transpiration · Water Isotopes and Climate Workshop Oct 2 2019...
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
