Characterizing water and solute transport in a bare soil subjected to repeated organic amendments : impact on nitrate leaching

Un dispositif en sol nu comprenant trois parcelles (90 m²) et six cases lysimétriques (4 m²) instrumentées a permis d’étudier l’influence d’apports répétés d’une boue de station d’épuration (BOUE) et de la même boue compostée avec des déchets verts (DVB) sur (i) les modifications des propriétés physico-chimiques et hydriques du sol ; (ii) le transport des ions bromures ; (iii) la dynamique de minéralisation du carbone et de l’azote organiques dans le sol. Finalement, le calage des paramètres hydrodynamiques et de décomposition de la matière organique dans le sol, propres à chaque horizon des profils de sols instrumentés, a permis une description satisfaisante de la dynamique hydrique et du transport des ions bromures et nitrates observés expérimentalement. Ces résultats aideront à l’adaptation de scénarios agronomiques sur le long terme pour répondre plus efficacement aux problématiques liées aux nouvelles exigences de recyclage des déchets et de protection de l’environnement.An instrumented experimental bare soil site including three plots (90 m²) and six lysimeters (4 m²) has enabled to study the influence of repeated sewage sludge (SS) applications, as well as the same sewage sludge composted with green waste (SGW), on (i) the soil physicochemical and hydric properties ; (ii) the transport of bromide ions ; (iii) the organic carbon and nitrogen mineralization dynamics in soil. Finally, fitting the governing hydraulic parameters and the organic matter decomposition parameters in each soil horizon allowed a satisfying description of the experimentally observed water and bromide and nitrate ions transport in soil. These results will help conceive long-term agronomical scenarios aimed at providing more efficient answers to the new requirements of environmental protection and waste recycling policies

Fluids transfers and hydrodynamics of the Vadose Zone of the O-ZNS platform site

International audienc

Caractérisation de la dynamique hydrique et du transport de solutés en sol nu soumis à des apports répétés de Produits Résiduaires Organiques : application au risque de lixiviation des nitrates

An instrumented experimental bare soil site including three plots (90 m²) and six lysimeters (4 m²) has enabled to study the influence of repeated sewage sludge (SS) applications, as well as the same sewage sludge composted with green waste (SGW), on (i) the soil physicochemical and hydric properties ; (ii) the transport of bromide ions ; (iii) the organic carbon and nitrogen mineralization dynamics in soil. Finally, fitting the governing hydraulic parameters and the organic matter decomposition parameters in each soil horizon allowed a satisfying description of the experimentally observed water and bromide and nitrate ions transport in soil. These results will help conceive long-term agronomical scenarios aimed at providing more efficient answers to the new requirements of environmental protection and waste recycling policies.Un dispositif en sol nu comprenant trois parcelles (90 m²) et six cases lysimétriques (4 m²) instrumentées a permis d’étudier l’influence d’apports répétés d’une boue de station d’épuration (BOUE) et de la même boue compostée avec des déchets verts (DVB) sur (i) les modifications des propriétés physico-chimiques et hydriques du sol ; (ii) le transport des ions bromures ; (iii) la dynamique de minéralisation du carbone et de l’azote organiques dans le sol. Finalement, le calage des paramètres hydrodynamiques et de décomposition de la matière organique dans le sol, propres à chaque horizon des profils de sols instrumentés, a permis une description satisfaisante de la dynamique hydrique et du transport des ions bromures et nitrates observés expérimentalement. Ces résultats aideront à l’adaptation de scénarios agronomiques sur le long terme pour répondre plus efficacement aux problématiques liées aux nouvelles exigences de recyclage des déchets et de protection de l’environnement

Observatoire des transferts dans la Zone Non Saturée

International audienceLa plateforme de recherche scientifique O-ZNS (Observatoire des transferts dans la Zone Non Saturée) a pour principal objectif la maitrise des processus de transfert réactif multiphasique à travers le continuum ZNS-ZS (Zone Non Saturée – Zone Saturée) en eau des structures carbonatées fracturées de la Beauce. L’originalité de cette plateforme réside dans les dimensions exceptionnelles du puits prévu, avec un diamètre fini ~ 4 m et une profondeur ~ 20 m, qui va permettre l’accès à l’ensemble de la zone non saturée de l’aquifère de Beauce, depuis la surface du sol jusqu’au toit de la nappe. Cette ZNS est fortement hétérogène, avec une séquence typique (de haut en bas) : sol / calcaire cryoturbé / marne calcaire / calcaire micritique fracturé. Lors de son exploitation (prévue pour plusieurs dizaines d’années), le projet permettra d’acquérir des données originales et uniques sur les transferts de matière (eau, solutés, contaminants organiques et inorganiques, gaz) et de chaleur (induits par les gradients de température, réactions microbiologiques, etc.) dans la ZNS, afin de suivre in situ et en temps réel les processus physiques, chimiques, physico-chimiques et biologiques couplés s’y déroulant sur le long terme. O-ZNS a pour objectif complémentaire l’évaluation de la performance de tout type d’instrumentation dédiée à la mesure ou à l’échantillonnage non destructif en ZNS (outils de monitoring environnemental)

Fiber Optic and Hydrogeological Sensors for the Monitoring of Mass and Heat Transfers Through the Vadose Zone of a Cenozoic Limestone Aquifer (beauce, ORLÉANS, France)

International audienceThe Vadose Zone (VZ) is commonly defined as the partially saturated area which extends from the surface down to the water table and plays a major role within the Critical Zone. As a result of increasing public concern about the need to protect groundwater reserves for drinking and agricultural purposes, a growing body of work has been focused on studying VZ processes, which are still not well understood. In order to integrate observations over a wide range of spatial (nm- to km-) and temporal (minutes to decades) scales, an Observatory of Transfers in the Vadose Zone (O-ZNS) is being carried out near Orléans (France) in an agricultural field. The O-ZNS project aims to understand and quantify mass and heat transfers thanks to a large access well (depth-20m & diameter-4m) surrounded by several secondary boreholes and equipped with environmental monitoring techniques. In order to meet the scientific objectives of the project, several complementary sensors and environmental monitoring techniques are under consideration as part of the instrumentation the O-ZNS experimental site. In this context, three distributed fiber optic sensors were installed in July 2020, in a continuous loop through three boreholes (21 to 23 m deep) surrounding the central well. These sensors will allow continuous measurements of temperature (DTS), deformations (DSS) and acoustic detection processes (DAS) throughout the entire depth of the VZ. Fiber optic technology provides functions similar to conventional sensors, while offering many advantages like small footprint, low attenuation and immunity to electromagnetic fields. Within the framework of the O-ZNS project, many other hydrogeological techniques are also being explored for the monitoring of the water flow and solute transport along the VZ. This includes innovative solutions such as new probes for the monitoring of the water content in hard and deep materials of the VZ, new solutions for the sampling of water and gas at several levels in the VZ, or even the latest generation of lysimeters which represent an excellent tool for the study of transfers at an intermediate scale between the laboratory and the field

Fiber Optic and Hydrogeological Sensors for the Monitoring of Mass and Heat Transfers Through the Vadose Zone of a Cenozoic Limestone Aquifer (beauce, ORLÉANS, France)

International audienceThe Vadose Zone (VZ) is commonly defined as the partially saturated area which extends from the surface down to the water table and plays a major role within the Critical Zone. As a result of increasing public concern about the need to protect groundwater reserves for drinking and agricultural purposes, a growing body of work has been focused on studying VZ processes, which are still not well understood. In order to integrate observations over a wide range of spatial (nm- to km-) and temporal (minutes to decades) scales, an Observatory of Transfers in the Vadose Zone (O-ZNS) is being carried out near Orléans (France) in an agricultural field. The O-ZNS project aims to understand and quantify mass and heat transfers thanks to a large access well (depth-20m & diameter-4m) surrounded by several secondary boreholes and equipped with environmental monitoring techniques. In order to meet the scientific objectives of the project, several complementary sensors and environmental monitoring techniques are under consideration as part of the instrumentation the O-ZNS experimental site. In this context, three distributed fiber optic sensors were installed in July 2020, in a continuous loop through three boreholes (21 to 23 m deep) surrounding the central well. These sensors will allow continuous measurements of temperature (DTS), deformations (DSS) and acoustic detection processes (DAS) throughout the entire depth of the VZ. Fiber optic technology provides functions similar to conventional sensors, while offering many advantages like small footprint, low attenuation and immunity to electromagnetic fields. Within the framework of the O-ZNS project, many other hydrogeological techniques are also being explored for the monitoring of the water flow and solute transport along the VZ. This includes innovative solutions such as new probes for the monitoring of the water content in hard and deep materials of the VZ, new solutions for the sampling of water and gas at several levels in the VZ, or even the latest generation of lysimeters which represent an excellent tool for the study of transfers at an intermediate scale between the laboratory and the field

Plateforme O-ZNS (Observatoire des transferts dans la Zone Non-Saturée) :pour une meilleure compréhension des processus physiques, chimiques et microbiologiques gouvernant les transferts de masse et de chaleur dans la zone non saturée des aquifères carbonatés

International audienc

Measurement of hydraulic properties of soils and rocks using an unconventional triaxial system coupled to the multistep outflow method

International audienceThe understanding of water flow and solute transport processes through the vadose zone is a cornerstone in the preservation of groundwater resources. For many years, various laboratory techniques and equipments have been designed to estimate soil hydraulic properties. We present an unconventional triaxial system adapted to 70 mm-diameter samples that is coupled to the multistep outflow method (MSOF) to measure the hydraulic properties of soils and rocks under both saturated and unsaturated conditions by means of a gas pressure-volume controller creating a three-phase unsaturated porous media. The purpose of this experiment is its versatility that allows the estimation of the hydraulic properties of all vadose zone samples using a unique assembly that runs the same specimen. This technique shows the benefits of using a triaxial cell, which allows reproducing overburden field conditions. The whole operating mode in saturated and unsaturated conditions may be successively carried out, thus avoiding sample being disturbed due to switching of the method or recoring that could impact the reproducibility of measurements. Among the advantages of the device is the high accuracy of the outflow measurement since the pressure-volume controller has a 1 mm3 resolution. Void ratio is also measured throughout the experiment in order to evaluate the volume change of the samples as a consequence of each pressure step. As a testing material a large range of samples with different textures and hardness were used such as repacked silty loam, undisturbed silty clay loam soil with plastic behavior, loamy sand sediment, as well as highly cemented limestone. After several tests, the effectiveness of the system has been evaluated according to the nature of the samples. Results show that the shape of the water retention curve and unsaturated hydraulic conductivity curves are in agreement with the information found in the literature according to the nature of the material. However, it seems that the effect of overburden decreases hydraulic properties when compared with other laboratory experiments. Void ratio measurements showed that porosity values decreased slightly in the order of 3-5% at the end of the whole experiment

Material Characteristics, Hydraulic Properties, and Water Travel Time through the Heterogeneous Vadose Zone of a Cenozoic Limestone Aquifer (Beauce, France)

International audienceWater retention and hydraulic conductivity are the most important properties governing water flow and solute transport in unsaturated porous media. However, transport processes in the vadose zone (VZ) are still not completely understood, in spite of their importance for the preservation and management of aquifers, especially in the geographic zones under intensive agriculture. This study has been carried out as part of the construction of the O-ZNS platform (Observatory of transfers in the vadose zone). This platform aims to integrate observations over a wide range of spatial and temporal scales thanks to a large access well (depth-20 m & diameter-4m) surrounded by several boreholes in order to combine broad characterization and focused monitoring techniques.Three cored boreholes have been drilled in Spring 2017. Structural and mineralogical analyses were carried out for four types of materials sampled throughout the entire VZ profile (20 m depth) including soft sediments (soil, marl and sand) and fractured limestone rock. Hydraulic properties (q(h) and K(h)) were measured on representative core samples by means of a triaxial system used by applying the multistep outflow method. Simulations were then made using HYDRUS-1D to simulate water flow and bromide (conservative tracer) transport over 50 years using meteorological and water table level data.The results brought valuable information about factors contributing to the heterogeneity of hydraulic properties within the VZ. For the applied matric heads (from 0 to -1000 cm), the water content and hydraulic conductivity of (i) the soft materials (9 samples) ranged from 0.173 to 0.485 cm3/cm3 and from 1.26.10-5 to 2.41 cm/d, respectively; (ii) the hard materials (5 samples) ranged from 0.063 to 0.340 cm3/cm3 and from 8.54.10-5 to 1.82 cm/d, respectively. The shape of the water retention and hydraulic conductivity curves obtained for the soft sediments is strongly related to the physical properties of the material but also to the proportion and the nature of clay minerals. The soil material displayed the largest average water retention capacity due to the presence of smectite and kaolinite, indicating weathering and matrix transformation. The water retention capacity of the marl and sand materials was lower due to higher content in palygorskyte and calcite. The limestone rock materials displayed an important heterogeneity in their hydraulic properties. Mineralogical analysis helped understanding water flow pathways within the limestone aquifer. The non-altered matrix, that seemed impermeable at first sight, presented few thin microfractures where water probably accumulates. The altered matrix showed microfractures where water has circulated and calcite has been replaced by phyllosilicates, thus increasing the water retention capacity. Natura macrofractures observed at dm-scale showed the presence of iron oxides which highlighted an exposure to high water flow. Simulations made using HYDRUS-1D allowed a first estimation of water and solutes travel time through this highly heterogeneous vadose zone. The results highlighted transfer time of between 25 to 35 years for the bromide to reach water table. The differences observed between the three cored boreholes were mainly due to the heterogeneity of the marl materials located between 1 and 7 m deep

A Comparative Study of Water and Bromide Transport in a Bare Loam Soil Using Lysimeters and Field Plots

International audienceThe purpose of this methodological study was to test whether similar soil hydraulic and solute transport properties could be estimated from field plots and lysimeter measurements. The transport of water and bromide (as an inert conservative solute tracer) in three bare field plots and in six bare soil lysimeters were compared. Daily readings of matric head and volumetric water content in the lysimeters showed a profile that was increasingly humid with depth. The hydrodynamic parameters optimized with HYDRUS-1D provided an accurate description of the experimental data for both the field plots and the lysimeters. However, bromide transport in the lysimeters was influenced by preferential transport, which required the use of the mobile/immobile water (MIM) model to suitably describe the experimental data. Water and solute transport observed in the field plots was not accurately described when using parameters optimized with lysimeter data (cross-simulation), and vice versa. The soil's return to atmospheric pressure at the bottom of the lysimeter and differences in tillage practices between the two setups had a strong impact on soil water dynamics. The preferential flow of bromide observed in the lysimeters prevented an accurate simulation of solute transport in field plots using the mean optimized parameters on lysimeters and vice versa