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

Eva van Gorsel 1 , Ray Leuning 1 , Helen A. Cleugh 1 , Heather Keith 2 and Tanja Suni 1 1 Marine and Atmospheric Research 2 Forestry and Forest Products September 06. Nocturnal Carbon Efflux can estimates of eddy covariance and chamber measurements be reconciled?. B ACKGROUND // M OTIVATION.

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

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  1. 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?

  2. BACKGROUND // MOTIVATION • Comparisons between micrometeorological and chamber measurements almost consistently show: • Respiration isunderestimated • NEEoverestimated • The problem occurs due to advection (not usually measured) • What is // can be done? Nocturnal Carbon Efflux - September 06

  3. 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) Nocturnal Carbon Efflux - September 06 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 […]

  4. 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) Nocturnal Carbon Efflux - September 06 Leuning et al. (2005) Agric. For. Meteorol. 129, 151-173

  5. 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

  6. MEASUREMENTS ( SITE // TOPOGRAPHY) ↑ N Main mast CV Nocturnal Carbon Efflux - September 06

  7. METHOD (EDDY COVARIANCE) Nocturnal Carbon Efflux - September 06 Graphics (Schematic tower): Andreas Christen

  8. METHOD (EDDY COVARIANCE) Advection terms not measured?measurements in homogeneous flat terrain good vertical mixingstrong turbulence Nocturnal Carbon Efflux - September 06 Graphics (Schematic tower): Andreas Christen

  9. METHOD (EDDY COVARIANCE) Nocturnal Carbon Efflux - September 06 Graphics (Schematic tower): Andreas Christen

  10. cumulative frequency (u*) not measured fraction of NCE RESULTS Nocturnal Carbon Efflux // Participation Eddy Flux and Storage Term Nocturnal Carbon Efflux - September 06

  11. INTERMITTENT WINDY METHOD (EDDY COVARIANCE) CALM Nocturnal Carbon Efflux - September 06

  12. RESULTS Nocturnal Carbon Efflux // Storage term Nocturnal Carbon Efflux - September 06

  13. RESULTS Nocturnal Carbon Efflux // Storage term Nocturnal Carbon Efflux - September 06 graph: Aubinet et al.,(2005) Boundary Layer Meteorol., 116: 63-94

  14. RESULTS Nocturnal Carbon Efflux // Storage term // Advection Total NCE Chamber (Soil + Leaf + Wood) 5.18 ± 0.18 mmol m-2 s-1 4.97 mmol m-2 s-1 5.23 mmol m-2 s-1 1.70 mmol m-2 s-1 0.46 mmol m-2 s-1 Nocturnal Carbon Efflux - September 06

  15. RESULTS Nocturnal Carbon Efflux // Storage term // Advection Nocturnal Carbon Efflux - September 06

  16. 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

  17. 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. Nocturnal Carbon Efflux - September 06

  18. Thank You CSIRO Marine and Atmospheric Research Dr. Eva van Gorsel Research Scientist – Land and Atmosphere +61 (0)2 6246 5611 eva.vangorsel@csiro.au www.cmar.csiro.au/ OzFlux www.dar.csiro.au/lai/ozflux/ Contact CSIRO Phone 1300 363 400 +61 3 9545 2176 Email enquiries@csiro.au Web www.csiro.au

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