Measuring and Modeling Transpiration, or What the Flux is Hydrology? ChEAS Workshop

Ecosystem Hydrology Modeling Group email: [email protected]://ra.forest.wisc.edu/ehmg

ChEAS WorkshopKemp StationAugust 20, 2002

Measuring and Modeling Transpiration,or What the Flux is Hydrology?

ChEAS Workshop

Scott Mackay

UW-Madison



Outline

(A) Basic Hydrologic ConceptsA.1 Water Resources and Global Terrestrial EcosystemsA.2 Hydrologic budgets and conservationA.3 Evapotranspiration as a residual: the traditional hydrologic

approach

(B) TranspirationB.1 Direct measurements of transpirationB.2 Indirect measurements of transpirationB.3 Sapflux instrumentation and flux measurements in N. Wisconsin

(C) Water Flux ModelingC.4 Groundwater / surface water interactionsC.2 Incorporating spatial variation in water fluxesC.3 Incorporating physiologyC.4 Results from N. Wisconsin

(D) Future Directions?



• Suggested question:– How does landscape fragmentation affect transpiration

and carbon flux rates?

• Your mission:– Develop a 1 (2 max) page micro proposal that

addresses the above question or one of your choosing;

– Your proposal should state questions or hypotheses, objectives, how you would conduct the work, and what the anticipated results would be.

Future Directions?



Outline


approach






Water and Global Vegetation

Precipitation (mm)

500 4500

Deserts



Outline


approach






a – evaporation, non-vegetation

b – evapotranspiration

c – lateral transport

d – precipitation

e – runoff

f – ground water recharge

Hydrologic Cycle



Streamflow Discharge



tantTtq

Groundwater Flow



Sand and Gravel AquiferPrice County



Outline


approach






First

Stream Orders

Stream

Stream junction

Divide

Watershed Boundary

NestedWatershed

Second

Third

Hillslope

WatershedOutlet

Evapotranspiration as a Residual

P + GIN - (Q + E + GOUT) = 0

E = P - Q

AssumesGIN = GOUT



Hillslope Profile (or Catena)

Evapotranspiration

Precipitation

Runoff

Streamflow

Infiltration

Drainage

Throughfalland stemflow

Groundwater flow

Hillslope Hydrology



Outline


approach






1) leaf level gas exchange

a) direct measurement

b) interrupts ambient environment

c) large number of samples needed to scale up

Direct Transpiration Measurements

Pearcy et al. (1989); Schulze et al. (1982)



2) tree level xylem sap flow

a) large number of measurements

b) does not interrupt ambient environment

c) requires appropriate scaling in time and space


Cermak and Kucera (1973);Granier (1987);Schulze and Fichtner (1988)



3) lysimeters

a) most accurate method

b) large disturbance to soil environment

c) difficult to measure large trees

d) difficult to field replicate


van Bevel and Meyers (1962);Fritschen et al. (1973)




4) micrometeorological techniques

a) direct ecosystem level measurement

b) requires appropriate site conditions

c) can not separate ecosystem components directly

Campbell and Unsworth (1979);Kaimal (1979);Wyngaard (1981)



Outline


approach






Indirect Evapotranspiration Estimation

1. Temperature-Baseda. Cannot resolve time intervals less than monthlyb. Ignore processes

2. Energy Balancea. Simpleb. Relies on differences between uncertain quantitiesc. Unreliable for large vapor pressure gradients

3. Mass Transfera. Uses reliable micrometeorological measurementsb. Data collection difficult for multiple measurement sites

4. Combination Methodsa. Combines benefits of energy balance and mass transferb. Data intensive



Thornthwaite (1949)Temperature-Based

a

I

tdE

10

6.1










Energy Balance Method

B = 0.1 (tropical oceans), 0.4 to 0.8 (temperate forests), 10.0 (deserts)

as

asa

ee

TTPc

LE

HB

622.0

EBLEBH w

B

GRE

w

n

1

w

n GHRE

Rn

G

H LE










constant2

OHaT

e

aa eT Sate VPD

(Ideal Gas Law)

Mass Transfer

aaSatOH

a eTeP

E 2

622.0



Frictional Drag

Eddy Currents

Z

M

M = momentum

HLE

H = sensible heatLE = latent heat of evaporation

HLE

HLE

HLEVapor

PressureGradient

TemperatureGradient

Wind Speed

Mass Transfer: Vertical Transport



EvKE 2

0

2

ln

622.0

2

2

z

zzPD

DK

dOH

a

M

OHE

Mass Transfer: Vertical Transport










aaSat eTeE

OH

aaSatOHEn eTevKRE

2

2

Combination Formula (Penman, 1948)

Energy Mass TransferVertical Transport

2

0

2

ln

622.0

2

2

z

zzPD

DK

dOH

a

M

OHE

w

n GHRE



OH

aaSatOHEn eTevKRE

2

2

Penman-Monteith (Monteith,1965)

2

0

2

ln

622.0

2

2

z

zzPD

DK

dOH

a

M

OHE

aaSatE eTevKE

c

aOH

aaSataaanC

g

g

eTegcRE

12

2

0

2

ln

1

z

zz

v

rg

da

a



Priestley and Taylor (1972)

OH

nTPTP

RE

2

asoilvw

assatpaS RR

eTecE

])([

Deardorff (1978); Maufouf and Noilhan (1991)

- works best for low VPD;

- crude for low canopy conductance (<20mm/s)

- sensitive to stability; -soil resistance not easyto calculate;

- numerous variants areavailable



Outline


approach






Types of Tree Level Xylem Sap Flow

Xylem flow velocity with heat pulses V=D/T Hard to determine true distances due to wall friction, anastomising

flow paths and other problems

Measurement of xylem sap mass flow (Cermak and Kucera-type sensors)

1) Null balance method maintains a constant pre-selected temperature (4 C) between temperature measurement points

a) power requirements minimal because power is proportional to flowb) little empiricismc) can not determine within tree flow paths

2) Constant heating method (Granier-type sensors)



Granier-Type Sap Flux Measurements



231.1M6

S 10119

T

TTJ





1) Appropriate thermal protection (Ewers and Oren 2000)a) minimize thermal gradients b) do not overinsulate

2) Sapwood estimation (Waring, et al. 1982. Whitehead et al. 1984, Ewers et al. 1999, Oren et al. 1999, Schafer et al. 2000)a) use stem cores or cross sectionsb) computer tomography

3) Spatial scaling within trees (Phillips et al. 1996, Ewers and Oren 2000, Oren et al. 1999, Clearwater et al. 1999, Lu et al. 2000, Ewers et al. 2002, James et al. 2002)a) need to measure both circumferential and radial trendsb) appropriate use of tree allometric relations

4) Environmental measurements

5) Time lags (Kostner et al. 1992, Martin et al. 1997, Phillips et al. 1997, Ewers and Oren 2000)













Inner extent of sapwood

Sapwood Estimation











3

1

3

1

ii

iSii

S

W

JW

J

Circumferential Trends



G

SSC AA

JE

Allometric Relations











Canopy Environmental Measurements

Environmental measurements (VPD)











Diurnal Time Lags and Daily Fluxes





Canopy Transpiration – N. Wisconsin

Notes: All species show exponential EC

rise to a maximum with respect to vapor pressure deficit;

Stomatal control exhibits similar function across species;

Maximum stomatal conductance varies 2-3 fold among species



Outline


approach






tantTtq

Recall: Groundwater Flow



fazz /))tan/ln(( area

a )tan/ln(

Topography-Based Groundwater-Surface Water Interactions



Groundwater Flow

Samanta and Mackay, 2002, WRR in press



Outline


approach






Effect of reduced stomatal regulation of leaf water potential is to lower Bowen ratios, increase pre-dawn water potentials and reduce water use efficiency

Soil or VPD ControlledTranspiration?

Mackay, 2001



Outline


approach






Physiology of Water FluxLeaf Water Potential

Pre-Dawn: Stomata Closed Midday: Stomata Open



ghΨΨDKG wLSLS

DmGG lnSrefS SrefS 6.0lndd GDGm

Monteith, 1995; Sperry et al., 1998; Oren et al., 1999; Ewers et al., 2000

Hydraulic Limits to Transpiration

0

20

40

60

80

100

120

140

160

180

0 1 2

lnD [ln(kPa)]

GS

(mm

ol

m-2

s-1) bDmGs ln

0

20

40

60

80

100

120

140

160

180

0 1 2

lnD [ln(kPa)]

GS

(mm

ol

m-2

s-1) bDmGs ln

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

GSref (mmol m-2 s-1)

-dGS

/ dl nDS

[mm

ol

m-2

s-1l n

(kP

a)-1

]

SrefGb

DG

m S

lndd

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

GSref (mmol m-2 s-1)

-dGS

/ dl nDS

[mm

ol

m-2

s-1l n

(kP

a)-1

]

SrefGb

DG

m S

lndd



f f f min321SmaxS Q g = g

DgG 1SmaxSref

D

Dgm

lnd

ddˆ Smax

DmQGG lnˆ, minSrefS

Replacing Boundary Line Analysis with Modeling

Model gSmax, , Qmin with automated parameter evaluation

Qmin

Jarvis (1976)

Mackay et al (2002)Advances in Water Resources



Universal Relationship

0

0.4

0.8

1.2

0 0.5 1 1.5 2

G Sref (mm s-1)

-dGS

/dlnD

[m

m s

-1 ln

(kP

a)-1

]

red pine

aspen

sugar maple

alder

cedar

m ~ -0.6 GSref y = 0.601x - 0.022

R2 = 0.96

0

0.4

0.8

1.2

0 0.5 1 1.5 2

G Sref (mm s-1)

-dGS/d

lnD

[m

ms

-1 ln

(kP

a)-1

]

Stomata are regulatingleaf water potential

Mackay et al (2002) - Advances in Water Resources





Outline


approach






Mackay et al., 2002 GCB



Effect of Spatial Aggregation



Effect of Taxonomic Aggregation





Outline


approach






• Suggested question:– How does landscape fragmentation affect transpiration

and carbon flux rates?

• Your mission:– Develop a 1 (2 max) page micro proposal that

addresses the above question or one of your choosing;

– Your proposal should state questions or hypotheses, objectives, how you would conduct the work, and what the anticipated results would be.

Future Directions?

Documents

Measuring and Modeling Transpiration, or What the Flux is Hydrology? ChEAS Workshop