caa a22 4500 475777255 CHVBK 20180406123634.0 cr unu---uuuuu 170329e20000801xx s 000 0 eng 10.1023/A:1002497616547 doi (NATIONALLICENCE)springer-10.1023/A:1002497616547 On Measuring Net Ecosystem Carbon Exchange Over Tall Vegetation on Complex Terrain [Elektronische Daten] [Dennis Baldocchi, John Finnigan, Kell Wilson, K. Paw U, Eva Falge] To assess annual budgets of CO2 exchange betweenthe biosphere and atmosphere over representativeecosystems, long-term measurements must be made overecosystems that do not exist on ideal terrain. How tointerpret eddy covariance measurements correctlyremains a major task. At present, net ecosystemCO2 exchange is assessed, by members of themicrometeorological community, as the sum of eddycovariance measurements and the storage of CO2 inthe underlying air. This approach, however, seemsunsatisfactory as numerous investigators are reportingthat it may be causing nocturnal respiration fluxdensities to be underestimated. A new theory was recently published by Lee (1998, Agricultural and Forest Meteorology 91: 39-50) for assessing net ecosystem-atmosphere CO2 exchange(Ne) over non-ideal terrain. Itincludes a vertical advection term. We apply thisequation over a temperate broadleaved forest growingin undulating terrain. Inclusion of the verticaladvection term yields hourly, daily and annual sums ofnet ecosystem CO2 exchange that are moreecologically correct during the growing season.During the winter dormant period, on the other hand,corrected CO2 flux density measurements of anactively respiring forest were near zero. Thisobservation is unrealistic compared to chambermeasurements and model calculations. Only duringmidday, when the atmosphere is well-mixed, domeasurements of Ne match estimatesbased on model calculations and chamber measurements. On an annual basis, sums of Newithout the advection correction were 40% too large,as compared with computations derived from a validatedand process-based model. With the inclusion of theadvection correction term, we observe convergencebetween measured and calculated values ofNe on hourly, daily and yearly time scales. We cannot, however, conclude that inclusion of aone-dimensional, vertical advection term into thecontinuity equation is sufficient for evaluatingCO2 exchange over tall forests in complexterrain. There is an indication that the neglected term,ū(∂ c¯/∂ x), isnon-zero and that CO2 may be leakingfrom the sides of the control volume during the winter. In this circumstance, forest floor CO2 effluxdensities exceed effluxes measured above the canopy. Kluwer Academic Publishers, 2000 AmeriFlux nationallicence FLUXNET nationallicence Carbon balance nationallicence Micrometeorology nationallicence Deciduous forest nationallicence Eddy covariance nationallicence Ecophysiology nationallicence Baldocchi Dennis Ecosystem Science Division, Department of Environmental Science, Policy and Management, University of California, 151 Hilgard Hall, Berkeley aut Finnigan John CSIRO Land and Water, GPO Box 821, 2601, Canberra, ACT, Australia aut Wilson Kell Atmospheric Turbulence and Diffusion Division, NOAA, PO Box 2456, 37831-2456, Oak Ridge, TN, U.S.A. aut Paw U K. Department of Land, Air and Water Resources, University of California, 95616, Davis, CA, U.S.A. aut Falge Eva Ecosystem Science Division, Department of Environmental Science, Policy and Management, University of California, 151 Hilgard Hall, Berkeley aut Boundary-Layer Meteorology Kluwer Academic Publishers 96/1-2(2000-08-01), 257-291 0006-8314 96:1-2<257 2000 96 10546 https://doi.org/10.1023/A:1002497616547 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1023/A:1002497616547 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Baldocchi Dennis Ecosystem Science Division, Department of Environmental Science, Policy and Management, University of California, 151 Hilgard Hall, Berkeley aut NATIONALLICENCE 700 1- Finnigan John CSIRO Land and Water, GPO Box 821, 2601, Canberra, ACT, Australia aut NATIONALLICENCE 700 1- Wilson Kell Atmospheric Turbulence and Diffusion Division, NOAA, PO Box 2456, 37831-2456, Oak Ridge, TN, U.S.A aut NATIONALLICENCE 700 1- Paw U K. Department of Land, Air and Water Resources, University of California, 95616, Davis, CA, U.S.A aut NATIONALLICENCE 700 1- Falge Eva Ecosystem Science Division, Department of Environmental Science, Policy and Management, University of California, 151 Hilgard Hall, Berkeley aut NATIONALLICENCE 773 0- Boundary-Layer Meteorology Kluwer Academic Publishers 96/1-2(2000-08-01), 257-291 0006-8314 96:1-2<257 2000 96 10546 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer