Assessing forest soil CO(2) efflux: an in situ comparison of four techniques.

A dynamic, closed-chamber infrared gas analysis (IRGA) system (DC-1: CIRAS-1, PP-Systems, Hitchin, U.K.) was compared with three other systems for measuring soil CO(2) efflux: the soda lime technique (SL), the eddy correlation technique (EC), and another dynamic, closed-chamber IRGA system (DC-2: LI-6250, Li-Cor, Inc., Lincoln, NE). Among the four systems, the DC-1 systematically gave the highest flux rates. Relative to DC-1, SL, EC and DC-2 underestimated fluxes by 10, 36 and 46%, respectively. These large and systematic differences highlight uncertainties in comparing fluxes from different sites obtained with different techniques. Although the three chamber methods gave different results, the results were well correlated. The SL technique underestimated soil CO(2) fluxes compared with the DC-1 system, but both methods agreed well when the SL data were corrected for the underestimation at higher fluxes, indicating that inter-site comparisons are possible if techniques are properly crosscalibrated. The EC was the only system that was not well correlated with DC-1. Under low light conditions, EC values were similar to DC-1 estimates, but under high light conditions the EC system seriously underestimated soil fluxes. This was probably because of interference by the photosynthetic activity of a moss layer. Although below-canopy EC fluxes are not necessarily well suited for measuring soil CO(2) efflux in natural forest ecosystems, they provide valuable information about understory gas exchange when used in tandem with soil chambers

Modelling of winter wheat carbon assimilation from sun induced fluorescence (SIF)

editorial reviewe

Turbulence effect on gas transport in three contrasting forest soils

peer reviewe

Eine in situ Methode zur Bestimmung von 2-D Mustern des Gasdiffusionskoeffizienten im Boden

Der Gasdiffusionskoeffizient im Boden (DS) ist ein wichtiger Parameter für die Belüftung des Bodens, und damit auch für das Wurzelwachstum und Gasumsatzprozesse. Bei Studien wird allgemein die horizontale Homogenität des Bodens inklusive des DS angenommen. Diese Annahme trifft allerdings selbst in scheinbar homogenen Böden nicht zu, wurde bisher aber nur mit destruktiven Methoden nachgewiesen. Da aber selbst bei einer aufwändigen destruktive Erfassung der DS Muster nur ein kleiner Ausschnitt der gesamten räumlichen Verteilung im Boden erfasst werden kann, und die Bodeneigenschaften zwischen den Probenahme-Positionen unbekannt bleiben, bleibt bei diesem Ansatz eine große Unsicherheit hinsichtlich der realen, resultierenden DS Muster. Unser Ziel war es, eine neue in situ Methode zur Bestimmung des scheinbare Diffusions-Koeffizienten im Boden zu entwickeln und damit ein Bodenprofil auf 2-dimensionalen DS-Muster hin zu untersuchen. Hierzu wird SF6 als Tracer-Gas kontinuierlich an einer Messstelle eingespeist. Die resultierende SF6 Konzentration wurde an allen anderen Messstellen des Profils erfasst, um daraus durch Modellierung mit Finiten Elementen die 2?dimensionale Verteilung des Diffusionskoeffizienten zwischen den Messpunkten durch abzuleiten

Agroécologie:utopie ou vision d'avenir?

l’heure où l’agroécologie devient un concept incontournable dans la sphère publique, elle reste encore une notion nébuleuse aux interprétations multiples. Incontour-nable, au point que nombres d’acteurs s’en emparent, empreint d’idéalisme pour certains, d’opportunité politique ou d’avidité mercantile pour d’autres. Nébuleuse, car certains aspects restent encore peu étudiés comme son rôle réel dans l’atténuation du changement climatique, sa contribution, difficile à caractériser, en terme de services à la société, comme les services écosysté-miques, le bien-être et la qualité de vie pour les citoyen·ne·s et les paysan·ne·s en particulier ou enfin son lien intrinsèque avec la lutte pour l’égalité de genre. Ce numéro nous amène ainsi à une compréhension plus profonde et une vision plus systémique de ce que recèle l’agroécologie

Eddy covariance raw data processing for CO2 and energy fluxes calculation at ICOS ecosystem stations

The eddy covariance is a powerful technique to estimate the surface-atmosphere exchange of different scalars at the ecosystem scale. The EC method is central to the ecosystem component of the Integrated Carbon Observation System, a monitoring network for greenhouse gases across the European Continent. The data processing sequence applied to the collected raw data is complex, and multiple robust options for the different steps are often available. For Integrated Carbon Observation System and similar networks, the standardisation of methods is essential to avoid methodological biases and improve comparability of the results. We introduce here the steps of the processing chain applied to the eddy covariance data of Integrated Carbon Observation System stations for the estimation of final CO2, water and energy fluxes, including the calculation of their uncertainties. The selected methods are discussed against valid alternative options in tenns of suitability and respective drawbacks and advantages. The main challenge is to warrant standardised processing for all stations in spite of the large differences in e.g. ecosystem traits and site conditions. The main achievement of the Integrated Carbon Observation System eddy covariance data processing is making CO2 and energy flux results as comparable and reliable as possible, given the current micrometeorological understanding and the generally accepted state-of-the-art processing methods.Peer reviewe

Towards a standardized processing of net ecosystem exchange measured with eddy covariance technique : algorithms and uncertainly estimation

Eddy covariance technique to measure CO2, water and energy fluxes between biosphere and atmosphere is widely spread and used in various regional networks. Currently more than 250 eddy covariance sites are active around the world measuring carbon exchange at high temporal resolution for different biomes and climatic conditions. In this paper a new standardized set of corrections is introduced and the uncertainties associated with these corrections are assessed for eight different forest sites in Europe with a total of 12 yearly datasets. The uncertainties introduced on the two components GPP (Gross Primary Production) and TER (Terrestrial Ecosystem Respiration) are also discussed and a quantitative analysis presented. Through a factorial analysis we find that generally, uncertainties by different corrections are additive without interactions and that the heuristic u(*)-correction introduces the largest uncertainty. The results show that a standardized data processing is needed for an effective comparison across biomes and for underpinning interannual variability. The methodology presented in this paper has also been integrated in the European database of the eddy covariance measurements.Eddy covariance technique to measure CO2, water and energy fluxes between biosphere and atmosphere is widely spread and used in various regional networks. Currently more than 250 eddy covariance sites are active around the world measuring carbon exchange at high temporal resolution for different biomes and climatic conditions. In this paper a new standardized set of corrections is introduced and the uncertainties associated with these corrections are assessed for eight different forest sites in Europe with a total of 12 yearly datasets. The uncertainties introduced on the two components GPP (Gross Primary Production) and TER (Terrestrial Ecosystem Respiration) are also discussed and a quantitative analysis presented. Through a factorial analysis we find that generally, uncertainties by different corrections are additive without interactions and that the heuristic u(*)-correction introduces the largest uncertainty. The results show that a standardized data processing is needed for an effective comparison across biomes and for underpinning interannual variability. The methodology presented in this paper has also been integrated in the European database of the eddy covariance measurements.Eddy covariance technique to measure CO2, water and energy fluxes between biosphere and atmosphere is widely spread and used in various regional networks. Currently more than 250 eddy covariance sites are active around the world measuring carbon exchange at high temporal resolution for different biomes and climatic conditions. In this paper a new standardized set of corrections is introduced and the uncertainties associated with these corrections are assessed for eight different forest sites in Europe with a total of 12 yearly datasets. The uncertainties introduced on the two components GPP (Gross Primary Production) and TER (Terrestrial Ecosystem Respiration) are also discussed and a quantitative analysis presented. Through a factorial analysis we find that generally, uncertainties by different corrections are additive without interactions and that the heuristic u(*)-correction introduces the largest uncertainty. The results show that a standardized data processing is needed for an effective comparison across biomes and for underpinning interannual variability. The methodology presented in this paper has also been integrated in the European database of the eddy covariance measurements.Peer reviewe