Ecosystem Water Use: A Concept Linking Ecosystem Water Use: A Concept Linking Water and Carbon FluxesWater and Carbon Fluxes

Jiquan Chen

Landscape Ecology & Ecosystem Science (LEES) LabUniversity of Toledo

Feb. 21, 2005

Flux TowersFlux Towers

NEENEEcc & NEE & NEEH2OH2O

Average diurnal fluxes of CO2 and H2O in Jul., Aug., and Sept. in 1999 in a 20 and a 500 year-old Douglas-fir forest (WA). Only data from good fetch (200-310o) directions were used. Negative and positive values indicate uptake and loss, respectively. Chen et al. 2002

Measurement Year 1998 1999

Stand 40YR 450YR 20YR 450YR

Carbon(g C.m-2.day-1)

July -4.27 1.39 -0.56 -0.79

August -2.69 -0.79 -0.01 -1.10

September

-1.21 0.93 -0.33 -1.97

Overall -2.76 0.51 -0.30 -1.26

Water (mm.day-1)

July 1.15 0.87 1.67 2.09

August 1.20 1.43 1.36 2.98

September

0.87 1.58 1.02 1.74

Overall 1.15 1.29 1.35 2.30

Average daily net exchange of carbon and water in Jul., Aug., and Sept. of 1998 and 1999 at three Douglas-fir forests of different ages (20, 40, and 450 year-old) in S. WA.

Chen et al. 2002

WUE is traditionally used as the amount of photosynthetic product produced per unit water evaporated, but a number of other definitions have been given to this term as well, depending on the purposes of the experiment. In this study, we define WUEe as the ratio of net

ecosystem exchange of carbon (Fc) to evapotranspiration (ETor FH2O):

W U E e

FF

C

H O

2

Ecosystem Water Use Efficiency (WUEe) at Four Measuring Periods of 3 Douglas-fir Stands

OG98 40Y98 OG99 20Y990

2

4

6

8

WU

E (

mg.

g-1)

Dry year Wet year

•WUEe of the old-growth forest was significantly greater in the drier summer of 1998 (2.7 mg.g-1) than in 1999 (1.0 mg.g-1).

•WUEe of the young stand was significantly lower than that of old-growth forest.

ConclusionsConclusions

OG98 40Y98 OG99 20Y990

2

4

6

8

WU E

(mg.

g-1

)

Dry year Wet year

Scanlon and Albertson 2004

•How does WUEe change with stand age (succession)?

•How does WUEe vary among ecosystems (disturbance)?

A landscape is composed of a variety of ecosystems differing in type, age, size, shape, and spatial arrangement. Two questions are:

MethodsMethods

A combination of direct measurements, remote A combination of direct measurements, remote

sensing images, and ecosystem models.sensing images, and ecosystem models.

Pine Barrens Mature red pine Mature hardwood

Young red pineYoung red pine

Mature red pineMature red pine

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

May June July Aug. Sept. Oct.

Cum

ula

tive E

T, M

g m

-2

Cumulative seasonal evaportranspiration (ET) at five ecosystemsCumulative seasonal evaportranspiration (ET) at five ecosystems

MRP

YRP

PB

MHW

CC

0

10

20

30

40

50

60

MHW MRP PB CC YMP

May

June

July

August

September

October

W UE

, mg

CO

2 g-1

H2

O

WUEe of Five Ecosystems in the CNF of Northern WI

R

0

2

4

6

8

10

12

14

16

18

May June July Aug. Sept. Oct.

WU

E, m

g C

g

-1 H

2 O .

WUEe among 5 ecosystems

Water use efficiency and stand ageWater use efficiency and stand age

0

1

2

3

0 10 20 30 40 50 60 70

Age, years

WU

EE, u

g C

g -1 H

2 O

W U EG P P

Tr

[ ]1

At leaf level, instantaneous water use efficiency is defined as

N E E

E Tc [ ]2

In this paper, we defined ecosystem water use, ,

W U EN E E

E T

G P P R R

E Tec a h

G P P

E T

R

E T

R

E Ta h

A revisit of WUEA revisit of WUEee concept: concept:

Water use efficiency by RS community

0

2

4

6

8

10

12

0 2 4 6 8 10 12 14

Net Carbon Exchange

(g C m-2 d-1)

Het

erot

rop

hic

Res

pir

atio

n

(g C

m-2

d-1

)

YHW

IHW

MHW

NCE Influence on Rh: Hardwoods

0

1

2

3

4

5

6

7

8

9

0 2 4 6 8 10 12 14

Net Carbon Exchange

Het

erot

rop

hic

Res

pir

atio

n

YRP

IRP

MRP

NCE Influence on Rh: Red Pine

E TG P P

W U E

[ ]4

W U E

R

G P P

R

G P Pa h1 [5]

W U E

N P P

G P P

R

G P Ph [ ]7

W U E

N P P

G P P

R

G P PW U E

N E E

G P Ph [ ]6

0.00

0.25

0.50

0.75

1.00

YHW IHW MHW YRP IRP MRP

NP

P/G

EP

There seems a strong correlation with stand age and ecosystem type!

What’s next?What’s next?

Is (RIs (Raa/ET) varying with age & disturbance?/ET) varying with age & disturbance?

WUEWUEee in non-growing season equals to (R in non-growing season equals to (Raa/E)!/E)! How is Ra regulated by biomass (LAI), How is Ra regulated by biomass (LAI),

temperature, and moisture?temperature, and moisture? How does (NPP*WUE/GPP) vary with time How does (NPP*WUE/GPP) vary with time

scale (i.e., hours-years)?scale (i.e., hours-years)? How does (NPP*WUE/GPP) change with How does (NPP*WUE/GPP) change with

sucession and disturbance?sucession and disturbance?

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

(5-6) (12-14) (30-32) (65-71)

Regenerating clearcut Old forest

Gro

win

g S

easo

n N

EE

(Mg

C h

a-1

)

Age of Ecosystem (years)

Recent clearcut

Mature forest

Summary of growing season NEE for comparable pine ecosystems of various age classes. Data is from Baldocchi et al. 1997, Joiner et al. 1999, Pypker & Fredeen 2002, Griffis et al. 2003). Euskirchen et al. (in revision)

0

2

4

6

-2

-4

Low

High

Climate-dominantResistance to disturbance

Climate-controlSusceptible to disturbance

Chronological Age

NE

P

Legacy effect

Hypothesized carbon flux of forest ecosystems after a disturbance

Questions?Questions?

http://research.eeescience.utoledo.edu/lees/

Support provided by the National Science Foundation, Southern Global Change Program, and WESTGEC of DOE