Géologie urbaine

International audienceEn milieu urbain et péri-urbain, les usages du proche sous-sol se densifient, se diversifient et s'intensifient du fait de l'accroissement des populations citadines et de leurs besoins. Dans un contexte de changement climatique, ces usages doivent s'inscrire également dans une logique de développement durable tout en répondant aux défis sociétaux (sécurité, ressources, ...). Ceci impose de s'appuyer sur une connaissance plus précise des formations en place, qu'elles soient d'origine naturelle (allochtone ou autochtone) ou anthropique, sur le 0-100m. Cette session ouverte vise à accueillir des contributions présentant les recherches récentes concernant les développements méthodologiques et la valorisation des données géologiques en zones urbaines ou péri-urbaines avec des finalités variées : connaissance géologique (modélisation et visualisation), risques naturels (microzonage sismique, simulation numérique en 3D de la propagation des ondes sismiques, cavités, subsidence), ressources en eau souterraine (modélisation hydrogéologique, remontée de nappe, qualité, surveillance...), ressources en énergie (géothermie, stockage...), ressources en sols (construction/refonctionnalisation, fond géochimique...), aménagement et urbanisme (propriétés géotechnique, géochimie/pollutions, BIM, GeoCim...), etc

Emergent properties of microbial activity in heterogeneous soil microenvironments:Different research approaches are slowly converging, yet major challenges remain

Over the last 60 years, soil microbiologists have accumulated a wealth of experimental data showing that the usual bulk, macroscopic parameters used to characterize soils (e.g., granulometry, pH, soil organic matter and biomass contents) provide insufficient information to describe quantitatively the activity of soil microorganisms and some of its outcomes, like the emission of greenhouse gases. Clearly, new, more appropriate macroscopic parameters are needed, which reflect better the spatial heterogeneity of soils at the microscale (i.e., the pore scale). For a long time, spectroscopic and microscopic tools were lacking to quantify processes at that scale, but major technological advances over the last 15 years have made suitable equipment available to researchers. In this context, the objective of the present article is to review progress achieved to date in the significant research program that has ensued. This program can be rationalized as a sequence of steps, namely the quantification and modeling of the physical-, (bio)chemical-, and microbiological properties of soils, the integration of these different perspectives into a unified theory, its upscaling to the macroscopic scale, and, eventually, the development of new approaches to measure macroscopic soil characteristics. At this stage, significant progress has been achieved on the physical front, and to a lesser extent on the (bio)chemical one as well, both in terms of experiments and modeling. In terms of microbial aspects, whereas a lot of work has been devoted to the modeling of bacterial and fungal activity in soils at the pore scale, the appropriateness of model assumptions cannot be readily assessed because relevant experimental data are extremely scarce. For the overall research to move forward, it will be crucial to make sure that research on the microbial components of soil systems does not keep lagging behind the work on the physical and (bio)chemical characteristics. Concerning the subsequent steps in the program, very little integration of the various disciplinary perspectives has occurred so far, and, as a result, researchers have not yet been able to tackle the scaling up to the macroscopic level. Many challenges, some of them daunting, remain on the path ahead

Development and analysis of the Soil Water Infiltration Global database

In this paper, we present and analyze a novel global database of soil infiltration measurements, the Soil Water Infiltration Global (SWIG) database. In total, 5023 infiltration curves were collected across all continents in the SWIG database. These data were either provided and quality checked by the scientists who performed the experiments or they were digitized from published articles. Data from 54 different countries were included in the database with major contributions from Iran, China, and the USA. In addition to its extensive geographical coverage, the collected infiltration curves cover research from 1976 to late 2017. Basic information on measurement location and method, soil properties, and land use was gathered along with the infiltration data, making the database valuable for the development of pedotransfer functions (PTFs) for estimating soil hydraulic properties, for the evaluation of infiltration measurement methods, and for developing and validating infiltration models. Soil textural information (clay, silt, and sand content) is available for 3842 out of 5023 infiltration measurements ( ∼ 76%) covering nearly all soil USDA textural classes except for the sandy clay and silt classes. Information on land use is available for 76% of the experimental sites with agricultural land use as the dominant type ( ∼ 40%). We are convinced that the SWIG database will allow for a better parameterization of the infiltration process in land surface models and for testing infiltration models. All collected data and related soil characteristics are provided online in *.xlsx and *.csv formats for reference, and we add a disclaimer that the database is for public domain use only and can be copied freely by referencing it. Supplementary data are available at https://doi.org/10.1594/PANGAEA.885492 (Rahmati et al., 2018). Data quality assessment is strongly advised prior to any use of this database. Finally, we would like to encourage scientists to extend and update the SWIG database by uploading new data to it

Effet de l'apport de composts sur la dynamique hydrique du sol, la disponibilité de l'azote pour la plante et le lessivage du nitrate : cas d'un sol limoneux cultivé du bassin parisien

This research aimed at evaluating the effect of repeated application of different types of urban composts on the dynamics of water and nitrogen (N) in a cultivated loamy soil. We conducted a field study to quantify the impact of compost on soil water dynamics, solute transport and nitrogen leaching. In addition to the monitoring of soil water potential and water content using tensiometers and TDRs, a tracer study was carried out to evaluate the effect of compost application on the transport of non-sorbing conservative solutes in soil. The dynamics of nitrogen was evaluated by sampling destructively the soil to measure its mineral nitrogen content. The deterministic soil-crop model PASTIS was used to simulate the observed water and N dynamics. Compost application affected the soil water properties only in the upper tilled horizon by increasing its water holding capacity and reducing cumulative evaporation under high evaporative demand. This could be explained by the increase in soil organic matter content after 10 years of compost application. Simulated N fluxes showed that the application of urban composts increased nitrogen availability for plants. Compost with high biodegradability presented higher nitrogen release the year following its application, while composts with low biodegradability allowed long term availability of N after several years of compost applicationL'objectif de la thèse est d'étudier l'impact d'apports répétés de composts urbains sur la dynamique de l'eau et de l'azote dans le système sol-plante, en sol cultivé. La dynamique de l'eau a été suivie en sol nu et en sol cultivé avec du maïs à l'aide de sondes TDR et de tensiomètres, entre 20 et 160 cm de profondeur. Un suivi de la dynamique d'un traceur de l'eau (anion bromure) et de l'azote minéral du sol a été réalisé par des prélèvements destructifs. Les données mesurées ont été utilisées pour simuler la dynamique de l'eau et de l'azote dans le sol suite aux apports de composts à l'aide du modèle PASTIS. L'apport de composts a affecté les propriétés hydriques de l'horizon de surface du sol, en augmentant la rétention en eau et en diminuant les flux d'évaporation par rapport au témoin. Cet effet peut être relié à l'augmentation de la teneur en matière organique du sol après 10 ans d'apports des composts. La modélisation de la dynamique de carbone et de l'azote dans le sol a permis de montrer l'importance des arrières effets des apports précédents sur la fourniture en azote minéral du sol et un effet positif de l'apport de PRO sur la disponibilité de l'azote pour la plante. L'apport d'un compost à forte biodégradabilité, comme amendement organique, présente plus d'intérêt durant l'année qui suit son apport, alors que les composts à faible biodégradabilité représentent l'avantage d'avoir une minéralisation plus importante à long terme (après des apports répétés)

Is the focus on “ecosystems” a liability in the research on nature’s services?

For the last 20 years, the concept of ecosystem has constituted one of the key pillars on which the study of “ecosystem services”, i.e., the benefits that human populations derive from nature, has been based. Yet, at this stage, one could argue that, in general and especially in fields related to agriculture, the ecosystem framework tends to limit unnecessarily the range of benefits to humans that are considered in practice, to hinder the necessary measurement of services, and to make it challenging to convince individuals to take nature’s services into account in their decision making. In the present Perspective piece, we analyze these 3 arguments in detail, conclude that the current focus on ecosystems is more a liability than an asset in the field, and suggest a return to the less constraining notions of “nature’s functions and services”, without a necessary tie to ecosystems

Effet de l'apport de composts sur la dynamique hydrique du sol, la disponibilité de l'azote pour la culture et le lessivage du nitrate (cas d'un sol limoneux cultivé du Bassin parisien)

L'objectif de la thèse est d'étudier l'impact d'apports répétés de composts urbains sur la dynamique de l'eau et de l'azote dans le système sol-plante, en sol cultivé. La dynamique de l'eau a été suivie en sol nu et en sol cultivé avee du maÏs à l'aide de sondes TDR et de tensiomètres, entre 20 et 160 cm de profondeur. Un suivi de la dynamique d'un traceur de l'eau (anion bromure) et de l'azote minéral du sol a été réalisé par des prélèvements destructifs. Les données mesurées ont été utilisées pour simuler la dynamique de l'eau et de l'azote dans le sol suite aux apports de composts à l'aide du modèle PASTIS. L'apport de composts a affecté les propriétés hydriques de l'horizon de surface du sol, en augmentant la rétention en eau et en diminuant les flux d'évaporation par rapport au témoin. Cet effet peut être relié à l'augmentation de la teneur en matière organique du sol après 10 ans d'apports des composts. La modélisation de la dynamique de carbone et de l'azote dans le sol a permis de montrer l'importance des arrières effets des apports précédents sur la fourniture en azote minéral du sol et un effet positif de l'apport de PRO sur la disponibilité de l'azote pour la plante. L'apport d'un compost à forte biodégradabilité, comme amendement organique, présente plus d'intérêt durant l'année qui suit son apport, alors que les composts à faible biodégradabilité représentent l'avantage d'avoir une minéralisation plus importante à long terme (après des apports répétés).ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

A Field Experiment to Assess the Influence of Heat and Mass Transfer at the Soil Surface on Shallow Ground Heat Exchanger Performances

International audiencePrediction of soil thermal regime is still a difficult task for design of ground-coupled heat pump system units (GCHP). A Field experiment was carried out to study the near-surface and moisture transport effects on soil temperature distribution. Energy balance components at the soil surface was monitored using a meteorological station, that included a pyrgeometer and a pyranometer to measure short and far infrared radiation, and using two heat flux plates installed in the soil at a depth of 0.08 m to measure ground heat fluxes. A 2.5 m deep trench has been dug in order to (i) characterize soil hydraulic and thermal properties at different depths and (ii) install tensiometers and thermocouples allowing continuous measurements of soil water tension and soil temperature. We observed that variations of soil properties along the profile as well as compaction influenced soil thermal properties. Results showed that temporal variations of soil heat flux at 8 cm depth closely followed those of available energy (net radiation), vertical turbulent heat fluxes (latent and sensible fluxes) near the soil's surface

Water and Bromide Dynamics in a Soil Amended with Different Urban Composts

International audienceUrban waste compost additions to soil can increase soil organic matter content and improve soil physical conditions, leading to agronomic and environmental benefits. The need for information still exists to evaluate more precisely the effects of urban waste compost on soil physical properties. Three types of urban waste composts, a biowaste compost (BIO), a municipal solid waste compost (MSW), and a co-compost of green waste and sewage sludge (GWS), were applied once every 2 yr on a loamy soil for 10 yr. The effects of the three composts on soil water and solute transport dynamics were tested. Soil water matric head and water content were monitored using tensiometers and time domain reflectometry probes, respectively. A Br− tracer experiment was also conducted to evaluate the effect of compost application on nonsorbing solute transport. Water content measurements showed that the application of composts significantly (P < 0.05) affected soil water content in the plow layer, with average increases of 0.03 cm3 cm−3 for the GWS and MSW compost, and 0.015 cm3 cm−3 for the BIO compost compared with a control without organic amendment. Bromide tracing during the wetting period showed that the application of urban waste composts did not affect the soil's potential for leaching. The application of composts did reduce soil evaporation during the spring, however, which in turn favored downward Br− migration in the soil

A simple heat and moisture transfer model to predict ground temperature for shallow ground heat exchangers

International audienceA simple model is proposed to describe transient heat and moisture transfer in the soil under moderate climates to predict near surface ground temperatures using a minimum set of variables and easily accessible weather data. The model is computationally efficient enough to allow for multi-year simulations of shallow ground heat exchangers. It uses a realistic representation of the interactions between the main processes occurring at the soil surface and the heat and moisture dynamics in the soil including the influence of water content on soil thermal properties. The model has been tested against soil temperature measurements taken at different depths (from 0.06 to 1.5 m) on a grass-covered site. Measurements, including meteorological data, were recorded with a time step of 10 min for one year. It is shown that the agreement between soil temperatures predicted by the proposed model and measurements is relatively good for either dry or rainy conditions. Average errors are between +0.47 and + 1.63 °C. Furthermore, this study shows that a proper account of the soil surface cover and site-specific soil properties is necessary to obtain accurate soil temperature predictions

Increased nitrogen availability in soil after repeated compost applications: Use of the PASTIS model to separate short and long-term effects

Yves Coquet : UMR7327 Present address on sept. 2012International audienceRegular application of composts on cropped soils has been shown to restore soil organic matter contents. The effect of repeated applications of three urban composts on the nitrogen (N) dynamics in a cropped loamy soil was compared to farmyard manure application and a control receiving no amendment. Each amendment application brought on average 250-400 kg ha−1 of total N. After five applications, total organic N increased in amended soils from 9 to 27% compared to control and the increase of soil organic N corresponded to 32-79% of total N brought by the amendments. The PASTIS model was used to describe the N balance in the soil-plant system during the 2 years after a sixth amendment application and provided correct predictions of N dynamics in cropped plots. The N availability increased in all treatments receiving organic amendments. The N availability in the soils amended with urban composts or manure was predominantly driven by the biodegradability of the organic amendments, their mineral N content and by the cropping conditions. Composts with high biodegradability exhibited higher proportion of N recovery by plants (21% for the municipal solid waste compost) during the year following their application, while more stabilised composts (biowaste compost, co-compost of sludge and green wastes) increased the N availability mainly through the increase of soil organic N content and mineralisation after several compost applications (6-8% of the soil organic N increase). Mature composts behaved comparably to FYM, except that for FYM very little N from the last application was available. Regular compost applications equivalent to 200 kg N ha−1 every other year could increase N availability for crops of 50-70 kg N ha−1 over the 2 years of the crop rotation. However, the most stabilised composts led to a higher crop N recovery but also to potential higher amounts of leached N compared to less mature composts