Nocturnal Carbon Efflux can estimates of eddy covariance and chamber measurements be reconciled?

www.csiro.au

Eva van Gorsel1, Ray Leuning1, Helen A. Cleugh1, Heather Keith2 and Tanja Suni1

1Marine and Atmospheric Research2Forestry and Forest Products

September 06

Nocturnal Carbon Effluxcan estimates of eddy covariance and chamber measurements be reconciled?

Nocturnal Carbon Efflux - September 06

BACKGROUND // MOTIVATION

Comparisons between micrometeorological and chamber measurements almost consistently show:

Respiration is underestimated

NEE overestimated

The problem occurs due to advection (not usually measured)

What is // can be done?


MEASUREMENTS (CHAMBER)

Leaf Respiration

open-flow-through (IRGA, Licor6400)

Wood Respiration (Stems and Root)

transient (IRGA, Licor6200)

Soil Respiration

non-flow-through steady state (Soda lime chambers)

Keith H. et al. (2006): Measurement of soil CO2 efflux using soda lime absorption […] Soil Biol. and Biochem.

Keith H. et al. (in preparation): Net carbon exchange in a eucalypt forest […]


MEASUREMENTS (EDDY COVARIANCE)

EC-System (70 m)

Ultrasonic Anemometer (Gill HS)IRGA (open path Licor7500)

Profile Measurement (9 levels)

IRGA (closed path Licor6262)

Advection Experiment (50 x 50 x 6 m control volume)

IRGA (closed path Licor6262)

Leuning et al. (2005) Agric. For. Meteorol. 129, 151-173


MEASUREMENTS (EDDY COVARIANCE)

40 m tall Eucalypt forest (evergreen, wet sclerophyll)

Lai~2.4

Forest cover and species homogenous within radius > 5 km


MEASUREMENTS ( SITE // TOPOGRAPHY)

603700 603800 603900 604000 604100 604200 604300 604400 604500 604600

6053000

6053100

6053200

6053300

6053400

6053500

6053600

6053700

6053800

6053900

6054000

Tow er

1210

1220

1230

1240

1250

1260

1270

1280

1290

1300

1 x 1 km topographic m ap of Tum barum ba F ie ld s ite

Elevation (m )

Main mast

CV

N↑


METHOD (EDDY COVARIANCE)

Graphics (Schematic tower): Andreas Christen




Advection terms not measured?measurements in homogeneous flat terrain

good vertical mixingstrong turbulence





RESULTS Nocturnal Carbon Efflux // Participation Eddy Flux and Storage

Term

not measured fraction of NCE

cumulative frequency (u*)



CALM INTERMITTENT WINDY


RESULTS Nocturnal Carbon Efflux // Storage term


RESULTS Nocturnal Carbon Efflux // Storage term

graph: Aubinet et al.,(2005) Boundary Layer Meteorol., 116: 63-94


Total NCE

Chamber (Soil + Leaf + Wood)5.18 ± 0.18 mol m-2 s-1

RESULTS Nocturnal Carbon Efflux // Storage term // Advection

5.23 mol m-2 s-1

0.46 mol m-2 s-1

1.70 mol m-2 s-1

4.97 mol m-2 s-1


RESULTS Nocturnal Carbon Efflux // Storage term // Advection


SUMMARY // CONCLUSIONS

Maximum in storage term in early evening

regularly observed

observed at several stations

Nighttime decrease in storage term is not counter-balanced by eddy flux

Advection leads to (usually) unmeasured loss of CO2 from control volume.

Hypothesis:

the peak occurs because there is a time delay between the onset of radiative cooling

and the development of temperature gradients that are strong enough to initiate

thermally-driven horizontal and vertical flows that remove the stored CO2.


CONCLUSIONS

We propose taking advantage of this time delay to develop relationships between Rmax and Tsoil.

Comparison of chamber measurements and results from the developed temperature response function lead to excellent agreement.

The new parameterization leads to realistic values of nighttime respiration, and therefore improves estimates of net ecosystem exchange.

www.csiro.au

Thank You

CSIRO Marine and Atmospheric Research

Dr. Eva van Gorsel

Research Scientist – Land and Atmosphere

+61 (0)2 6246 5611

[email protected]

www.cmar.csiro.au/

OzFlux

www.dar.csiro.au/lai/ozflux/

Contact CSIRO

Phone 1300 363 400

+61 3 9545 2176

Email [email protected]

Web www.csiro.au

Documents

Nocturnal Carbon Efflux can estimates of eddy covariance and chamber measurements be reconciled?