www.csiro.au eva van gorsel 1, ray leuning 1, helen a. cleugh 1, heather keith 2 and tanja suni 1 1...
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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?
Nocturnal Carbon Efflux - September 06
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 […]
Nocturnal Carbon Efflux - September 06
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
Nocturnal Carbon Efflux - September 06
MEASUREMENTS (EDDY COVARIANCE)
40 m tall Eucalypt forest (evergreen, wet sclerophyll)
Lai~2.4
Forest cover and species homogenous within radius > 5 km
Nocturnal Carbon Efflux - September 06
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↑
Nocturnal Carbon Efflux - September 06
METHOD (EDDY COVARIANCE)
Graphics (Schematic tower): Andreas Christen
Nocturnal Carbon Efflux - September 06
METHOD (EDDY COVARIANCE)
Graphics (Schematic tower): Andreas Christen
Advection terms not measured?measurements in homogeneous flat terrain
good vertical mixingstrong turbulence
Nocturnal Carbon Efflux - September 06
METHOD (EDDY COVARIANCE)
Graphics (Schematic tower): Andreas Christen
Nocturnal Carbon Efflux - September 06
RESULTS Nocturnal Carbon Efflux // Participation Eddy Flux and Storage
Term
not measured fraction of NCE
cumulative frequency (u*)
Nocturnal Carbon Efflux - September 06
RESULTS Nocturnal Carbon Efflux // Storage term
graph: Aubinet et al.,(2005) Boundary Layer Meteorol., 116: 63-94
Nocturnal Carbon Efflux - September 06
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
Nocturnal Carbon Efflux - September 06
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.
Nocturnal Carbon Efflux - September 06
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.
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Thank You
CSIRO Marine and Atmospheric Research
Dr. Eva van Gorsel
Research Scientist – Land and Atmosphere
+61 (0)2 6246 5611
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