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  • Rabot , Eva  (26)
Language
Year
  • 1
    Language: French
    In: Notes de Recherche de l'Académie d'Agriculture de France , ., 2015
    Description: Soils and associated agricultural activities are estimated to account for about 2/3 of the global emissions of nitrous oxide (N2O), a potent greenhouse gas. Soil water saturation is known to be a key factor for controlling N2O emissions. The aim of this study was to understand the controls linked to the soil hydric functioning on N2O emissions. Laboratory experiments were designed to control the hydric status of soil samples during wetting and drying cycles, and to measure simultaneously N2O fluxes (Figure 1). Three treatments of stepwise drying were performed across the range 0 to ı100 cm pressure head in two wetting–drying cycles. This experiment was reproduced for one soil sample during the acquisition of three-dimensional X-ray images. After image treatment, we could characterize the air-filled pore volume (Figures 3 and 4a) and gaseous connectivity (Figure 4b). Two types of N2O emission peaks were detected (Figure 2). A peak appeared within two or three days after rewetting and was related to microbial production processes and a slow N2O transport in water saturated soils. The second type of peak was detected within the first two steps of the decreasing pressure head, and occurred during a brief period, an average of 1.6 hour after the beginning of the soil drying. These peaks were induced by diffusion processes, and their intensities were correlated with the amount of water drained. Entrapment of N2O during the wetting phase and rapid displacement during the drying phase occurred. We highlighted the need to distinguish N2O production/consumption and transport phases to explain the variability of N2O emissions which is commonly measured.
    Description: Les sols et les activités agricoles qu’ils supportent contribueraient à environ 2/3 des émissions globales de protoxyde d’azote (N2O), un puissant gaz à effet de serre. L’objectif des travaux était la compréhension de l’influence de l’histoire hydrique des sols sur les émissions de N2O. Une expérimentation de laboratoire permettant un contrôle fin de l’état hydrique d’échantillons de sol durant des cycles de saturation et désaturation, ainsi que la mesure des flux de N2O, a été menée (Figure 1). Cette expérimentation a été reproduite pour un échantillon pendant l’acquisition simultanée d’images à l’aide d’un scanner médical à rayons X, ceci afin de caractériser le volume de pores libres à l’air (Figures 3 et 4a) et la connectivité gazeuse (Figure 4b). Deux types de pics d’émission de N2O, d’origine biologique et physique, ont été observés (Figure 2). Il a ainsi été mis en évidence la nécessité de distinguer les périodes de production/consommation de N2O de celles de son transport pour expliquer la variabilité des émissions de N2O couramment observées.
    Keywords: N2o ; Tomographie Aux Rayons X ; Saturation Du Sol ; Propriété Hydrique Du Sol ; Émission D'Azote ; Gaz À Effet De Serre ; Désaturation Du Sol ; Protoxyde D'Azote ; Milieux Et Changements Globaux ; État Hydrique
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Language: French
    In: Notes de Recherche de l'Académie d'Agriculture de France , ., 2015
    Description: Soils and associated agricultural activities are estimated to account for about 2/3 of the global emissions of nitrous oxide (N2O), a potent greenhouse gas. Soil water saturation is known to be a key factor for controlling N2O emissions. The aim of this study was to understand the controls linked to the soil hydric functioning on N2O emissions. Laboratory experiments were designed to control the hydric status of soil samples during wetting and drying cycles, and to measure simultaneously N2O fluxes (Figure 1). Three treatments of stepwise drying were performed across the range 0 to ı100 cm pressure head in two wetting–drying cycles. This experiment was reproduced for one soil sample during the acquisition of three-dimensional X-ray images. After image treatment, we could characterize the air-filled pore volume (Figures 3 and 4a) and gaseous connectivity (Figure 4b). Two types of N2O emission peaks were detected (Figure 2). A peak appeared within two or three days after rewetting and was related to microbial production processes and a slow N2O transport in water saturated soils. The second type of peak was detected within the first two steps of the decreasing pressure head, and occurred during a brief period, an average of 1.6 hour after the beginning of the soil drying. These peaks were induced by diffusion processes, and their intensities were correlated with the amount of water drained. Entrapment of N2O during the wetting phase and rapid displacement during the drying phase occurred. We highlighted the need to distinguish N2O production/consumption and transport phases to explain the variability of N2O emissions which is commonly measured.
    Description: Les sols et les activités agricoles qu’ils supportent contribueraient à environ 2/3 des émissions globales de protoxyde d’azote (N2O), un puissant gaz à effet de serre. L’objectif des travaux était la compréhension de l’influence de l’histoire hydrique des sols sur les émissions de N2O. Une expérimentation de laboratoire permettant un contrôle fin de l’état hydrique d’échantillons de sol durant des cycles de saturation et désaturation, ainsi que la mesure des flux de N2O, a été menée (Figure 1). Cette expérimentation a été reproduite pour un échantillon pendant l’acquisition simultanée d’images à l’aide d’un scanner médical à rayons X, ceci afin de caractériser le volume de pores libres à l’air (Figures 3 et 4a) et la connectivité gazeuse (Figure 4b). Deux types de pics d’émission de N2O, d’origine biologique et physique, ont été observés (Figure 2). Il a ainsi été mis en évidence la nécessité de distinguer les périodes de production/consommation de N2O de celles de son transport pour expliquer la variabilité des émissions de N2O couramment observées.
    Keywords: N2o ; Tomographie Aux Rayons X ; Saturation Du Sol ; Propriété Hydrique Du Sol ; Émission D'Azote ; Gaz À Effet De Serre ; Désaturation Du Sol ; Protoxyde D'Azote ; Milieux Et Changements Globaux ; État Hydrique
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Language: French
    Description: Les sols et les activités agricoles qu’ils supportent, contribueraient à environ 2/3 des émissionsglobales de protoxyde d’azote (N2O), un puissant gaz à effet de serre. L’objectif de la thèseétait la compréhension des déterminismes des émissions de N2O liés aux propriétés hydriques dessols. Des expérimentations de laboratoire permettant le contrôle hydrique fin d’échantillons de sol,en saturation et en désaturation, et la mesure des flux de N2O ont été menées. Un couplage avecla tomographie par rayons-X a par ailleurs permis de caractériser la connectivité gazeuse. Enfin,une démarche de modélisation a permis de tester les hypothèses de fonctionnement émises, etde poursuivre la démarche de réflexion sur le lien entre les propriétés hydriques des sols et lesémissions de N2O. On a mis en évidence le rôle des propriétés hydriques des sols dans la variabilitédes émissions de N2O couramment observées, et la nécessité de distinguer des périodes deproduction/consommation de N2O et de transport. On retiendra ainsi le fort caractère dynamique desémissions de N2O, en lien avec la phase hydrique (saturation ou désaturation), le fonctionnementhydrodynamique des sols, le transport gazeux et la configuration spatiale de l’air et de l’eau dansle réseau de pores. Afin de décrire l’intensité et le timing des pics de N2O, il est apparu pertinentd’observer les paramètres potentiel matriciel, coefficient de diffusion gazeuse et connectivité gazeuse,en plus de la teneur en eau. Ces observations ont des implications sur la modélisation des flux deN2O. On recommande ainsi l’utilisation couplée de modules de transport hydrique, de transportgazeux et en solution de N2O, en plus de modules de production microbiologique, pour prédireefficacement les émissions de N2O.
    Description: Soils and associated agricultural activities are estimated to account for about 2/3 of theglobal emissions of nitrous oxide (N2O), a potent greenhouse gas. The aim of the thesis was tounderstand the controls linked to soil hydric properties on N2O emissions. Laboratory experimentswere designed to control the hydric status of soil samples during wetting and drying, and to measureN2O fluxes. Moreover, a coupling with X-ray computed tomography allowed characterizing thegaseous connectivity. Finally, a modeling approach allowed testing the hypotheses of functioning,and to further discuss the links between hydric properties and N2O emissions. We highlighted therole of soil hydric properties on the variability of N2O emissions which is often measured, and theneed to distinguish N2O production/consumption and transport phases. The highly dynamic nature ofN2O emissions was linked to the hydric phase (wetting or drying), soil hydrodynamic functioning, gastransport, and spatial configuration of water and air in the pore network, in addition to the water-filledpore space parameter. These observations have implications for N2O emission modeling. Werecommend thus the coupled use of hydric transport, and modules of gas and liquid transport of N2O,in addition to microbial production modules to efficiently predict N2O emissions.
    Keywords: Transport Gazeux ; N2o ; Hysteresis ; Earth Sciences ; Propriété Hydrique Du Sol ; Flux Hydrique ; Émission D'Azote ; Espace Poral ; Sciences De La Terre ; Flux D'Azote ; Gaz À Effet De Serre ; Fonctionnement Hydrique ; Protoxyde D'Azote ; Teneur En Eau ; Nitrous Oxide;Soil;Water-Filled Pore Space;Gas Transport;Hydric Fluxes;Soil Water Hysteresis ; Porosité Saturée En Eau
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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  • 4
    Language: French
    Description: Les sols et les activités agricoles qu’ils supportent, contribueraient à environ 2/3 des émissionsglobales de protoxyde d’azote (N2O), un puissant gaz à effet de serre. L’objectif de la thèseétait la compréhension des déterminismes des émissions de N2O liés aux propriétés hydriques dessols. Des expérimentations de laboratoire permettant le contrôle hydrique fin d’échantillons de sol,en saturation et en désaturation, et la mesure des flux de N2O ont été menées. Un couplage avecla tomographie par rayons-X a par ailleurs permis de caractériser la connectivité gazeuse. Enfin,une démarche de modélisation a permis de tester les hypothèses de fonctionnement émises, etde poursuivre la démarche de réflexion sur le lien entre les propriétés hydriques des sols et lesémissions de N2O. On a mis en évidence le rôle des propriétés hydriques des sols dans la variabilitédes émissions de N2O couramment observées, et la nécessité de distinguer des périodes deproduction/consommation de N2O et de transport. On retiendra ainsi le fort caractère dynamique desémissions de N2O, en lien avec la phase hydrique (saturation ou désaturation), le fonctionnementhydrodynamique des sols, le transport gazeux et la configuration spatiale de l’air et de l’eau dansle réseau de pores. Afin de décrire l’intensité et le timing des pics de N2O, il est apparu pertinentd’observer les paramètres potentiel matriciel, coefficient de diffusion gazeuse et connectivité gazeuse,en plus de la teneur en eau. Ces observations ont des implications sur la modélisation des flux deN2O. On recommande ainsi l’utilisation couplée de modules de transport hydrique, de transportgazeux et en solution de N2O, en plus de modules de production microbiologique, pour prédireefficacement les émissions de N2O.
    Description: Soils and associated agricultural activities are estimated to account for about 2/3 of theglobal emissions of nitrous oxide (N2O), a potent greenhouse gas. The aim of the thesis was tounderstand the controls linked to soil hydric properties on N2O emissions. Laboratory experimentswere designed to control the hydric status of soil samples during wetting and drying, and to measureN2O fluxes. Moreover, a coupling with X-ray computed tomography allowed characterizing thegaseous connectivity. Finally, a modeling approach allowed testing the hypotheses of functioning,and to further discuss the links between hydric properties and N2O emissions. We highlighted therole of soil hydric properties on the variability of N2O emissions which is often measured, and theneed to distinguish N2O production/consumption and transport phases. The highly dynamic nature ofN2O emissions was linked to the hydric phase (wetting or drying), soil hydrodynamic functioning, gastransport, and spatial configuration of water and air in the pore network, in addition to the water-filledpore space parameter. These observations have implications for N2O emission modeling. Werecommend thus the coupled use of hydric transport, and modules of gas and liquid transport of N2O,in addition to microbial production modules to efficiently predict N2O emissions.
    Keywords: Transport Gazeux ; N2o ; Hysteresis ; Earth Sciences ; Propriété Hydrique Du Sol ; Flux Hydrique ; Émission D'Azote ; Espace Poral ; Sciences De La Terre ; Flux D'Azote ; Gaz À Effet De Serre ; Fonctionnement Hydrique ; Protoxyde D'Azote ; Teneur En Eau ; Nitrous Oxide;Soil;Water-Filled Pore Space;Gas Transport;Hydric Fluxes;Soil Water Hysteresis ; Porosité Saturée En Eau
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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  • 5
    Language: French
    In: Biogeochemistry 2-3 , 395-408., 2015
    Description: Nitrous oxide (N2O) fluxes can increase significantly following small increases in soil water-filled pore space (WFPS). Thus, it is essential to improve our knowledge of this crucial relationship to better model N2O emissions by soils. We studied how much the addition of a gas transport and a gas–liquid equilibrium module to the model of N2O emissions NOE could improve simulation results. A sensitivity analysis of the modified model (NOEGTE: gas transport and equilibrium) was first performed, and then the model was tested with published data of a wetting–drying experiment. Simulated N2O fluxes plotted against WFPS appeared to be bell-shaped during the 7 days simulated, combining the effects of the low N2O production for WFPS 0.95. The WFPS generating the maximum simulated N2O fluxes shifted with time, from 0.76 after 12 h, to 0.79 after 168 h, because of an increase over time of the gas concentration gradient between the soil surface and the atmosphere. NOEGTE appeared able to capture the pattern of N2O emissions monitored in the experimental data. In particular, N2O peaks during drying were well reproduced in terms of timing, but their magnitudes were often overestimated. They were attributed to the increasing gas diffusivity and N2O exchanges from the liquid phase to the gaseous phase.
    Keywords: Modélisation ; Nitrous Oxide Emission Modeling;Water-Filled Pore Space;Gas Diffusivity;Soil ; Indice D'Eau ; Espace Poral ; Sciences De La Terre ; Earth Sciences ; Flux D'Azote ; Émission D'Azote ; Transport De L'Azote ; Protoxyde D'Azote ; Porosité Saturée En Eau
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: French
    In: Biogeochemistry 2-3 , 395-408., 2015
    Description: Nitrous oxide (N2O) fluxes can increase significantly following small increases in soil water-filled pore space (WFPS). Thus, it is essential to improve our knowledge of this crucial relationship to better model N2O emissions by soils. We studied how much the addition of a gas transport and a gas–liquid equilibrium module to the model of N2O emissions NOE could improve simulation results. A sensitivity analysis of the modified model (NOEGTE: gas transport and equilibrium) was first performed, and then the model was tested with published data of a wetting–drying experiment. Simulated N2O fluxes plotted against WFPS appeared to be bell-shaped during the 7 days simulated, combining the effects of the low N2O production for WFPS 0.95. The WFPS generating the maximum simulated N2O fluxes shifted with time, from 0.76 after 12 h, to 0.79 after 168 h, because of an increase over time of the gas concentration gradient between the soil surface and the atmosphere. NOEGTE appeared able to capture the pattern of N2O emissions monitored in the experimental data. In particular, N2O peaks during drying were well reproduced in terms of timing, but their magnitudes were often overestimated. They were attributed to the increasing gas diffusivity and N2O exchanges from the liquid phase to the gaseous phase.
    Keywords: Modélisation ; Nitrous Oxide Emission Modeling;Water-Filled Pore Space;Gas Diffusivity;Soil ; Indice D'Eau ; Espace Poral ; Sciences De La Terre ; Earth Sciences ; Flux D'Azote ; Émission D'Azote ; Transport De L'Azote ; Protoxyde D'Azote ; Porosité Saturée En Eau
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Language: English
    In: Vadose Zone Journal 8 , ., 2015
    Description: Water in soil is known to be a key factor for controlling N2O emissions because N2O is mainly produced by denitrification in anoxic environments. In this study, we proposed a methodology to image the water and soil structure of a soil sample with X-ray computed tomography while controlling the hydric state and monitoring N2O fluxes. We used a multistep outflow system to apply two wetting–drying cycles to an undisturbed soil. The soil core was scanned with coarse-resolution X-ray computed tomography, one time during wetting and several times during drying, to measure quantitative and qualitative indicators of the pore network. Nitrous oxide emissions were higher during the first (C1) than during the second (C2) wetting–drying cycle for both the wetting and the drying phases. Fluxes increased quickly after the beginning of the drying phase to reach a peak after 5 h. Differences in the intensity of N2O emissions between the two cycles were attributed to differences in the water saturation, air-phase connectivity, and relative gas diffusion coefficient, which led to more or less N2O production, consumption, and entrapment in the soil. The speed of the N2O emissions at the beginning of the drying phase depended on the rate of increase of the air-filled pore volume and connectivity, and was especially well described by the estimated relative gas diffusion coefficient. Parameters of the soil structure were not able to explain completely the intensity of N2O emissions during drying; N2O production and consumption factors were also involved.
    Keywords: N2o ; Earth Sciences ; Flux Hydrique ; Structure Du Sol ; Émission De Gaz ; Modélisation ; Eau Du Sol ; Flux De Gaz ; Tomographie Aux Rayons X ; Sciences De La Terre ; Alternance Humectation Dessication ; Protoxyde D'Azote ; Milieux Et Changements Globaux ; État Hydrique
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Language: English
    In: Vadose Zone Journal 8 , ., 2015
    Description: Water in soil is known to be a key factor for controlling N2O emissions because N2O is mainly produced by denitrification in anoxic environments. In this study, we proposed a methodology to image the water and soil structure of a soil sample with X-ray computed tomography while controlling the hydric state and monitoring N2O fluxes. We used a multistep outflow system to apply two wetting–drying cycles to an undisturbed soil. The soil core was scanned with coarse-resolution X-ray computed tomography, one time during wetting and several times during drying, to measure quantitative and qualitative indicators of the pore network. Nitrous oxide emissions were higher during the first (C1) than during the second (C2) wetting–drying cycle for both the wetting and the drying phases. Fluxes increased quickly after the beginning of the drying phase to reach a peak after 5 h. Differences in the intensity of N2O emissions between the two cycles were attributed to differences in the water saturation, air-phase connectivity, and relative gas diffusion coefficient, which led to more or less N2O production, consumption, and entrapment in the soil. The speed of the N2O emissions at the beginning of the drying phase depended on the rate of increase of the air-filled pore volume and connectivity, and was especially well described by the estimated relative gas diffusion coefficient. Parameters of the soil structure were not able to explain completely the intensity of N2O emissions during drying; N2O production and consumption factors were also involved.
    Keywords: N2o ; Earth Sciences ; Flux Hydrique ; Structure Du Sol ; Émission De Gaz ; Modélisation ; Eau Du Sol ; Flux De Gaz ; Tomographie Aux Rayons X ; Sciences De La Terre ; Alternance Humectation Dessication ; Protoxyde D'Azote ; Milieux Et Changements Globaux ; État Hydrique
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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  • 9
    Language: French
    In: J2M 2014 : Journées de la mesure et de la métrologie. 2014; 13. Journées de la Mesure et de la Métrologie, Stella Plage , FRA, 2014-10-13-2014-10-16, p.33, 2014
    Keywords: Sciences De La Terre ; Désaturation ; Propriété Hydrique Du Sol ; Saturation ; Earth Sciences ; Potentiel Matriciel ; Émission D'Azote ; Sol ; Système Dynamique Hybride ; Protoxyde D'Azote ; Teneur En Eau ; Teneur En Eau;Potentiel Matriciel;Protoxyde D'Azote;Saturation-Desaturation;Sol
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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  • 10
    Language: English
    In: 2014; Biogeochemical Processes at Air-Soil-Water Interfaces and Environmental Protection ASWEP, Imola, ITA, 2014-06-23-2014-06-26,, 2014
    Description: N2O fluxes can increase largely due to small increase of the soil water-filled pore space (WFPS). In models, the relationship between N2O fluxes and the WFPS is often described as a continuous exponential curve starting at a WFPS of about 0.62. However, some laboratory and field measurements have evidenced that this relationship could rather be described as Gaussian. To improve our knowledge of this crucial curve for N2O flux modeling, we have developed a laboratory experiment where the wetting and drying dynamics of undisturbed soil cylinders were strictly controlled during N2O flux measurements. We observed that N2O flux peaks could occur during the wetting phase, but more surprisingly we also observed brief and intense peaks during the drying phase. We then hypothesized (1) that N2O was produced and entrapped during the wetting phase, and was emitted from gas pockets and soil solution during the drying phase and, (2) that the addition of a gas transport and a gas-liquid equilibrium modules to an empirical biogeochemical model of N2O emissions could allow the description of the brief peaks observed during soil drying. We build such a model. It was first tested with the experimental data. We also studied its sensitivity to the WFPS parameter. We generated 200 realizations of hydric conditions and bulk densities to estimate the soil gas diffusivity. WFPS was set to be constant during the 7 simulated days. Simulated N2O fluxes plotted against WFPS appeared to be bell-shaped whatever the simulation time, combining the effects of the low N2O production for WFPS0.9. The WFPS generating the maximum simulated N2O fluxes shifted with time, from 0.76 after 12 h, to 0.79 after 168 h, because of an increase over time of the gas concentration gradient between the soil surface and the atmosphere. The study highlighted the role of diffusional processes in soil N2O emissions and the importance to take them into account in N2O modeling.
    Keywords: Modélisation ; Indice D'Eau ; Espace Poral ; Sciences De La Terre ; Earth Sciences ; Émission D'Azote ; Flux D'Azote ; Protoxyde D'Azote ; Porosité Saturée En Eau
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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