Landscape-level

(Eddy Covariance)

Measurement of CO2

and Other Fluxes

Measuring Componentsof Solar Radiation

Close-up ofEddy Covariance

Flux Sensors

Tower Flux Measurement and Analysis

Verma/IndoFlux/IndoFlux_July 2006

Outline• Background information/

methodology

• Flux magnitudes: seasonal/ interannual variations

• Controlling variables

• Comments

Objectives• Quantify CO2 exchange in major

ecosystems: seasonal and interannual variability

• Improve our basic understanding of biophysical processes that govern CO2 exchange in these ecosystems

• Test and improve terrestrial biosphere models of CO2, water, and energy exchange

Landscape Level Carbon Dioxide Flux(uptake and release)

Plant photosynthesis

Above ground productivity

Root and rhizosphererespiration

Partitioning of Carbon in Agroecosystems

Soil respiration

Plant respiration

Microbialrespiration

Root exudates

Root productivity

Organicmatter

decomposition

Methodology: Eddy Covariance

Fluxes of CO2, Water Vapor, and Energy:

• Continuous Measurements

• Long-term

• Ecosystem scale/landscape level

ppm

m /s

1.5

15

3qc

w

5

1200

Instantaneous F lux = ws M ean H ourly F lux = Tim e average of

1201 1202 1203 1204 1205

Td

g/kg

Eddy Covariance

instantaneous flux = wsfor C Ofor w ater vaporfor sensib le heat

2for C Ofor w ater vaporfor sensib le heat

2

Mead, Nebraska

• Primary Measurements- Fluxes of CO2, water vapor, sensible heat & momentum- Mean wind speed, air temperature, humidity and CO2

concentration- Wind direction- Soil heat flux & soil temperature- Radiation:

Net radiation Short wave radiation (incoming & reflected) PAR (incoming & reflected)

- Light interception- Atmospheric pressure- Precipitation

• Supporting Measurements- Soil moisture- Leaf area index, canopy height, biomass- Leaf nitrogen content

Measurements

Data Submission

Tower Eddy Covariance CO2 Flux Measurements: Net Ecosystem Exchange (NEE)

Mead, Nebraska

-10

-5

0

5

10

15

20

25

5/1/01 8/29/01 12/27/01 4/26/02 8/24/02 12/22/02 4/21/03 8/19/03 12/17/03 4/15/04 8/13/04 12/11/04 4/10/05

Dai

ly N

EE

(g

C m

-2 d

-1)

Site 1

P HHH PP

maize maize maize

Irrigated Continuous

Maize

maize

P H

-10

-5

0

5

10

15

20

25

5/1/01 8/29/01 12/27/01 4/26/02 8/24/02 12/22/02 4/21/03 8/19/03 12/17/03 4/15/04 8/13/04 12/11/04 4/10/05

Dai

ly N

EE

(g

C m

-2 d

-1)

Site 2

P P P HHH

maize maizesoybean

IrrigatedMaize-Soybean

Rotation

soybean

P

H

-10

-5

0

5

10

15

20

25

5/1/01 8/29/01 12/27/01 4/26/02 8/24/02 12/22/02 4/21/03 8/19/03 12/17/03 4/15/04 8/13/04 12/11/04 4/10/05

Dai

ly N

EE

(g

C m

-2 d

-1)

Site 3

P P PH H H

maizemaize soybean

RainfedMaize-Soybean

Rotation

soybean

P

H

Daytime CO2 Uptake and Night Emissions

Ecosystem

Peak daytime

CO2 uptake

(mg m-2s-1)

Peak night

CO2 emission

(mg m-2s-1)

Leaf Area Index

(LAI)

Irrigated maize 2.8 – 3.0 0.6 – 0.7 5.6 – 6.0

Rainfed maize 2.6 0.4 – 0.5 4.0

Irrigated soybean 1.7 0.7 5.7

Rainfed soybean 1.5 0.4 3.0

Grassland (tallgrass prairie)

1.2 0.4 – 0.5 3.0

Temperate forest 0.9 0.2 – 0.3 4.9

Reday = NEEnight * Q 10 (Ta,day - Ta,night)/10

GPP = NEE - Re

Ecosystem Respiration (Re) and Gross Primary Productivity (GPP)

Annually Integrated NEE

(g C m-2 y-1)Maize, NE 300 to 500 (Verma et al., 2005)

Harvard Forest, MA 200 (Barford et al., 2003)

Howland Forest, ME 174 (Hollinger et al., 2004)

Univ. of Michigan Biological St 80 to 170 (Schmid et al., 2003)

Wind River, WA -50 to 200 (Pers. Comm.)

Douglas Fir, B.C. 270 to 420 (Morgenstern et al., 2004)

Tallgrass Prairie, OK 50 to 275 (Suyker et al., 2003)

Northern Temperate Grassland, Alberta

-18 to 20 (Flanagan et al., 2002)

Mediterranean, Annual Grassland, CA

-30 to 130 (Xu and Baldocchi, 2003)

Soybean, NE -10 to -75 (Verma et al., 2005)

4.0

-1.0

0.0

1.0

2.0

3.0

0 500 1000 1500 2000

Incoming PAR (mol m-2 s-1)

NE

E (

mg

m-2

s-1

)

June 13-19: V6-V7: 0.4<LAI<1.3

July 4-10: V11-V12: 4.4<LAI<5.6

July 18-24: V19-VT: 6.2<LAI<6.3

Aug 29-Sept 4: R5: 3.7<LAI<4.3

Daytime CO2 Flux Irrigated Maize

Night CO2 Flux

Tallgrass Prairie, Manhattan, KS, 1987

Energy Partitioning

Daytime

Energy Partitioning

Tallgrass Prairie7/31/97

-500

-250

0

250

500

750

0 600 1200 1800 2400

Local Time, Hrs

Flu

x, W

m-2

RnGHLE

Shidler, Oklahoma

Tallgrass Prairie, Manhattan, KS, 1987

Checks and Balances• Data Quality Control

– Foken and Wichura, 1996, Agric. For. Meteorol., 78, 83-105

– Aubinet et al., 2000, Advances in Ecol. Res., 30, 113-175

• Energy Budget Closure: LE + H vs. Rn + G

• NEE – Biomass Relationship

Day Night

NEEday NEEnight

Rg Rr Rc

Daily net gain of CO2 by crop

Rg Rr

Rc

Gain of CO2 by cropduring day

= NEEday – RgdayD

D

=Net canopy photosynthesis

in 24 hours

= ( NEEday + NEEnight ) – ( Rgday + Rg night ) D

N

= Daily NEE + Daily Rg

Loss of CO2 by cropat night

= Rc + Rr

= NEEnight – Rg night N

N

N

D

N

=( NEEday – Rgday) + ( NEEnight – Rg night )

DD

N

N

N Rc + Rr + Rg = NEEnight

(Biscoe et al; 1975. J. Applied Ecology, 12, 269-291)

NEE-Biomass Relationship

Daily net gain of CO2 by crop = Daily NEE + Daily Rg

(Biscoe et al., 1975, J. Applied Ecology, 12, 269-291)

NEE = Net ecosystem CO2 exchangeRg = Respiration by soil organisms

Estimating Microbial Respiration (Rg)

• Soil surface CO2 flux measurements (Fs)– Two different kinds of chambers:

Model LI-6200, Li-Cor, Lincoln, NEHutchinson & Mosier (1981) type chamber

– Used data from field measurements of maize soil respiration in root excluded and non-root excluded soil to estimate Rg

• Night NEE data– Adjusted for plant respiration based on leaf gas

exchange measurements– Adjusted for night/day temperatures– Applied measurements of root-excluded vs. non-root

excluded soil to estimate Rg as mentioned above

Challenges• Insufficient mixing at night

• Filling in data gaps

• Complex terrain

N2O and CH4 Fluxes