forest ecosystems; advection; net ecosystem exchange; carbon balance; ADVEX
Abstract :
[en] Extensive field measurements have been performed at three CarboEurope-Integrated Project forest sites with different topography (Renon/Ritten, Italian Alps, Italy; Wetzstein, Thuringia, Germany; Norunda, Uppland, Sweden) to evaluate the relevant terms of the carbon balance by measuring CO2 concentrations [CO2] and the wind field in a 3D multi-tower cube setup. The same experimental setup (geometry and instrumentation) and the same methodology were applied to all the three experiments. It is shown that all sites are affected by advection in different ways and strengths. Everywhere, vertical advection (F-VA) occurred only at night. During the day, F-VA disappeared because of turbulent mixing, leading to a uniform vertical profile of [CO2]. Mean F-VA was nearly zero at the hilly site (wetzstein) and at the flat site (Norunda). However, large, momentary positive or negative contributions occurred at the flat site, whereas vertical non-turbulent fluxes were generally very small at the hilly site. At the slope site (Renon), F-VA was always positive at night because of the permanently negative mean vertical wind component resulting from downslope winds. Horizontal advection also occurred mainly at night. It was positive at the slope site and negative at the flat site in the mean diurnal course. The size of the averaged non-turbulent advective fluxes was of the same order of magnitude as the turbulent flux measured by eddy-covariance technique, but the scatter was very high. This implies that it is not advisable to use directly measured quantities of the non-turbulent advective fluxes for the estimation of net ecosystem exchange (NEE) on e.g. an hourly basis. However, situations with and without advection were closely related to local or synoptic meteorological conditions. Thus, it is possible to separate advection affected NEE estimates from fluxes which are representative of the source term. However, the development of a robust correction scheme for advection requires a more detailed site-specific analysis of single events for the identification of the relevant processes. This paper presents mean characteristics of the advective CO2 fluxes in a first site-to-site comparison and evaluates the main problems for future research. (c) 2007 Elsevier B.V. All rights reserved.
Feigenwinter, Christian; Faculté Universitaire des Sciences Agronomiques de Gembloux - FUSAGx > Sciences et Technologies de l'environnement > Physique des Bio-systèmes
Bernhofer, Christian; TU Dresden (TUD), Institute of Hydrology and Meteorology, Dresden, Germany > Meteorology
Eichelmann, Uwe; TU Dresden (TUD), Institute of Hydrology and Meteorology, Dresden, Germany > Meteorology
Heinesch, Bernard ; Université de Liège - ULiège > Gembloux Agro-Bio Tech > Gembloux Agro-Bio Tech
Hertel, Martin; Max Planck Institute for Biogeochemistry (MPI-BGC), Jena, Germany
Janous, Dalibor; Institute of System Biology and Ecology, Brno, Czech Republic > Laboratory of Plants Ecological Physiology (ILE)
Kolle, Olaf; Max Planck Institute for Biogeochemistry (MPI-BGC), Jena, Germany
Lagergren, Frederik; University of Lund, Lund, Sweden > GeoBiosphere Science Centre, Physical Geography and Ecosystems Analysis
Lindroth, Anders; University of Lund, Lund, Sweden > GeoBiosphere Science Centre, Physical Geography and Ecosystems Analysis
Minerbi, Stefano; Autonomous Province of Bolzano (APB), Bolzano, Italy > Forest Service
Moderow, Uta; TU Dresden (TUD), Institute of Hydrology and Meteorology, Dresden, Germany > Meteorology
Molder, Meelis; University of Lund, Lund, Sweden > GeoBiosphere Science Centre, Physical Geography and Ecosystems Analysis
Montagnani, Leonardo; Autonomous Province of Bolzano (APB), Bolzano, Italy > Forest Service
Queck, Ronald; TU Dresden (TUD), Institute of Hydrology and Meteorology, Dresden, Germany > Meteorology
Rebmann, Corinna; Max Planck Institute for Biogeochemistry (MPI-BGC), Jena, Germany
Vestin, Patrik; University of Lund, Lund, Sweden > GeoBiosphere Science Centre, Physical Geography and Ecosystems Analysis
Yernaux, Michel; Université de Liège - ULiège - Gembloux Agro-Bio Tech > Sciences et Technologies de l'environnement > Physique des Bio-systèmes
Zeri, Marcelo; Max Planck Institute for Biogeochemistry (MPI-BGC), Jena, Germany
Ziegler, Waldemar; Max Planck Institute for Biogeochemistry (MPI-BGC), Jena, Germany
Aubinet, Marc ; Université de Liège - ULiège > Gembloux Agro-Bio Tech > Gembloux Agro-Bio Tech
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