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Savannas make up about 20% of the global land-surface and are dependent on fires to maintain a balanced ecosystem. Fires in other fire-driven landscapes, particularly wildfires, were found to have negative effects on various soil properties. However, there is a lack of studies confirming the effect of fires on soil hydrology in African savanna soils. A long-term fire experiment in a South African savanna provided an opportunity to investigate the effect of different prescribed fire frequencies on soil properties in situ across coarse-grained granitic and fine-textured basalt-derived soils. Soil properties were compared between soils exposed to annual fires, fires every 2–4 years and where fires have been excluded for approximately 60 years. Across all three fire treatments, unsaturated hydraulic conductivity (Kunsat) was measured using a Tension Disc Infiltrometer to infer infiltration rates, saturated hydraulic conductivity (Ksat) measured with a Guelph Permeameter, soil water potential calculated using a Decagon WP4-T Dewpoint Potentiometer to infer soil water retention and soil total C and N measured using a LECO CNS TruMac Series Analyser. Our study found that Kunsat is not affected by frequent annual fires which have infiltration rates similar to soils where fires have been excluded for nearly 6 decades. However, recently burnt granitic soils, i.e. three months prior, have significantly slower Kunsat which were as low as

Real-time in-situ measurements are increasingly used to improve the estimations of simulation models via data assimilation techniques such as particle filter. However, models that describe complex processes such as water flow contain a large number of parameters while the data available is typically very limited. In such situations, applying particle filter to a large, fixed set of parameters chosen a priori can lead to unstable behavior, i.e. inconsistent adjustment of some of the parameters that have only limited impact on the states that are being measured. To prevent this, in this study correlation-based variable selection is embedded in the particle filter, so that at each data assimilation step only a subset of the parameters is adjusted. More specifically, whenever measurements become available, the most influential (i.e., the most highly correlated) parameters are determined by correlation analysis, and only these are updated by particle filter. The proposed method was applied to a water flow model (Hydrus-1D) in which states (soil water contents) and parameters (soil hydraulic parameters) were updated via data assimilation. Two simulation case studies were conducted in order to demonstrate the performance of the proposed method. Overall, the proposed method yielded parameters and states estimates that were more accurate and more consistent than those obtained when adjusting all the parameters.

Improved mechanistic understanding of soil methane (CH4) exchange responses to shifts in soil moisture and temperature in forest ecosystems is pivotal to reducing uncertainty in estimates of the soil-atmospheric CH4 budget under climate change. We investigated the mechanism behind the effects of soil moisture and temperature shifts on soil CH4 fluxes under laboratory conditions. Soils from the Huai River Basin in China, an area that experiences frequent hydrological shifts, were sampled from two consecutive depths (0–20 and 20–50 cm) and incubated for 2 weeks under different combinations of soil moisture and temperature. Soils from both depths showed an increase in soil moisture and temperature-dependent cumulative CH4 fluxes. CH4 production rates incubated in different moisture and temperature in surface soil ranged from 1.27 to 2.18 ng g−1 d−1, and that of subsurface soil ranged from 1.18 to 2.34 ng g−1 d−1. The Q10 range for soil CH4 efflux rates was 1.04–1.37. For surface soils, the relative abundance and diversity of methanotrophs decreased with moisture increase when incubated at 5 °C, while it increased with moisture increase when incubated at 15 and 30 °C. For subsurface soils, the relative abundance and diversity of methanotrophs in all samples decreased with moisture increase. However, there was no significant difference in the diversity of methanogens between the two soil depths, while the relative abundance of methanogens in both depths soils increased with temperature increase when incubated at 150% water-filled pore space (WFPS). Microbial community composition exhibited large variations in post incubation samples except for one treatment based on the surface soils incubated at 15 °C, which showed a decrease in the total and unique species number of methanotrophs with moisture increase. In contrast, the unique species number of methanogens in surface soils increased with moisture increase. The analysis of distance-based redundancy analysis (db-RDA) showed that soil pH, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial biomass carbon (MBC), NO3−-N, and NH4+-N mainly performed a significant effect on methanotrophs community composition when incubated at 60% WFPS, while they performed a significant effect on methanogens community composition when incubated at 150% WFPS. Overall, our findings emphasized the vital function of soil hydrology in triggering CH4 efflux from subtropical plantation forest soils under future climate change.

Benfratello's Contribution to the study of the water balance of an agricultural soil (Contributo allo studio del bilancio idrologico del terreno agrario) was firstly published sixty years ago, in 1961. The paper provides a practical conceptual and lumped method to determine the irrigation deficit in agricultural disctricts. Since then, it has been used in many areas in Southern Italy.According to the method, percolation and capillary rise from the groundwater table are absent, and surface runoff happens only when the soil capability of storing water is exceeded. The method is therefore suitable for semiarid (and eventually arid) climates. Dry and wet seasons are defined on a climatic basis, as the season during which potential evapotranspiration is greater than precipitations (and the stored soil--water decreases), and that during which precipitations exceed potential evapotranspiration (and the stored soil--water inccreases).With these hypotheses, Benfratello proposed to adopt a power--relationship (with power m greater or equal to 0) to assess the ratio between the actual and the potential soil--water loss, as a function of the ratio between the stored soil--water and the maximum available storage. The solution provides, in a simple closed form, the actual soil--water loss as a function of the potential loss (which is a climatic characteristic), and generalizes previous approaches, viz Thorthwaite (1948) and Thornthwaite and Mather (1955) ones, for which m = 0 and m = 1, respectively.In this contribution we present a GIS based application of Benfratello's method to assess the soil water balance and the irrigation deficit of the semiarid Capitanata plane (4550 km2, Southern Italy), one of the most important agricultural districts in Italy. A comparison between the method and previous results for the same region will be provided as well. Due to its simplicity and to the small number of needed parameters, Benfratello's method might be regarded to as an effective tool to assess the effects of climatic, landuse and anthropogenic change scenarios on the soil water balance and on the irrigation deficit.

High resolution, dynamic forest site classification is an innovative tool for decision making in forest management, in particular under the scope of climate change. For a high share of the Austrian forest area, forest soil/site maps are lacking, and, if available, they do not account for the fact that water, energy and nutrient supply may change over a forest rotation cycle. The project FORSITE aims at providing a dynamic site classification system for the Austrian province of Styria, covering 1 mio. hectares of forest area. High resolution maps of chemical and physical soil properties are a key requirement for describing water and nutrient supply, and for modelling scenarios of changing climatic conditions or the effects of management interventions. In order to provide the database for the creation of such maps, a stratified site description and soil sampling design was based on high resolution digital terrain models and lithological maps. The sampling included a detailed description of 1,800 soil pits down to a minimum of 80 cm depth or solid bedrock. Chemical and physical soil parameters (e.g. carbon content, grain size, bulk density, stone content) were determined for samples of the forest floor and up to five geometric horizons of 400 soil profiles. In addition, geologists developed a subsolum geological substrate (SGS) map describing the parent material for soil formation down to a depth of 150 cm. In the current presentation, we describe the steps of modelling maps which support the estimation of the water balance of forest sites. A first step was the development of pedotransfer-functions (PTFs) in order to upscale soil parameters like soil organic carbon content, bulk density, grain size distribution and plant available water storage capacity determined in the laboratory a. to the 1800 field sites and b. to a 10*10 m resolution grid for the whole of Styria. Subsequently, a number of published PTFs for Mualem van Genuchten values based on soil texture, bulk density and organic carbon content were compared to 100 water retention curves which were determined on a subset of the FORSITE soil profiles. These values are required for the parametrization of the lumped parameter hydrological model (Brook 90) which is used to characterize the water supply under present and future climatic conditions. The regionalisation of the single point measurements from the profiles was performed with a Neural Network. Spatial maps SGSs and derivatives of the Digital Elevation Model such as slope, elevation and curvature served as predictors. Information on SGS improves the predictions of soil properties in comparison to standard standard geological maps, because it describes in more detail the relevant layer between soil and bedrock. As Neural Networks were insufficient for describing waterlogging and groundwater influence, random forest models were applied to a dataset comprised of the ForSite profiles and 4,000 soil profiles from agricultural soil surveys in the region. The resulting high resolution maps of soil properties form the base for the hydrological characterisation of the sites and for the calculation of climate change scenarios.

In the context of climate change, strong precipitation events tend to increase in intensity and frequency. Such extreme events are associated with the genesis of fast infiltration into the soil, which can generate a very dynamic contribution of the groundwater, as it was observed during the June 2016 flood event in the Paris basin. An issue is that these events are poorly simulated, limiting the ability to monitor and forecast such event. Even with a physically based model such as the Interaction between Soil Biosphere Atmosphere soil multilayer diffusion scheme (ISBADF) the hydrodynamic of the simulated groundwater recharge at the basin scale was poor. Various hypotheses can explain these gaps like 1) a lack of physical processes such as preferential flows or double porosity 2) an inadapted characterization of soil properties and soil hydraulic properties 3) a bad representation of the vegetation properties; 4) or a too coarse spatial and temporal distributions of precipitation.To answer these questions, four lysimeters of the experimental station of the French Scientific Interest Group for Industrial Wasteland (GISFI, http://gisfi.univ-lorraine.fr/) in Homécourt, France are used. Between 2009 and 2016, the total weight, the drained flow at the base of the lysimeter, and suction/moisture content/temperature were measured of each soil column every hour at 50cm, 100cm and 150cm depth. Ten intense rainfall events were selected by the daily rainfall quantile 99. These lysimeters are cylinders (2m depth*1m diameter) and contain monoliths industrialized soils with a silty-sandy texture. Lysimeters 1 and 2 have no vegetation, contrary to the lysimeter 3 with alfalfa cover, and lysimeter 4 with Noccaea caerulescens cover. In this study, ISBADF was used to simulate each lysimeter. The local scale and high frequency evolution of soil moisture, temperature profile, drainage rate and water storage were assessed, based on soil-water retention and conductivity curves from the Brooks and Corey model. For each lysimeter, hydrodynamic parameters were determined based on the observations. The values found for these particular soils are very different from the values expected by the literature.With the fitted soil parameters, ISBADF shows a high performance in reproducing temperature profiles (R² & NSE>0,9) and has good scores for other parameters (R² & NSE>0,6). During intense precipitation, we can reproduce the drained flow at 2m depth; nevertheless, differences on the drainage period and the maximum intensity of drainage were noticed: drainage duration is generally longer for simulations with vegetation and maximum intensity seems too important for the simulations.Finally, this multi-parameter analysis at a local scale and high frequency demonstrates the good infiltration and vegetation processes of the ISBADF model, even during intense rainfall. This study seems to show that there is no need to modify the physics of the model processes, but that efforts should focus on the characterization of soil properties.

Direct measurement of unsaturated hydraulic parameters is costly and time-consuming. Pedotransfer functions (PTFs) are typically developed to estimate soil hydraulic properties from readily available soil attributes. For the first time, in this study, we developed PTFs to estimate the soil hydraulic conductivity (log(K)) directly from measured data. We adopted the pseudo continuous neural network PTF (PCNN-PTF) approach and assessed its accuracy and reliability using two independent data sets with hydraulic conductivity measured via the evaporation method. The primary data set contained 150 international soils (6963 measured data pairs), and the second dataset consisted of 79 repacked Turkish soil samples (1340 measured data pairs). Four models with different combinations of the input attributes, including soil texture (sand, silt, clay), bulk density (BD), and organic matter content (SOM), were developed. The best performing international (root mean square error, RMSE = 0.520) and local (RMSE = 0.317) PTFs only had soil texture information as inputs when developed and tested using the same data set to estimate log(K). However, adding BD and SOM as input parameters increased the reliability of the international PCNN-PTFs when the Turkish data set was used as the test data set. We observed an overall improvement in the performance of PTFs with the increasing number of data points per soil textural class. The PCNN-PTFs consistently performed high across tension ranges when developed and tested using the international data set. Incorporating the Turkish data set into PTF development substantially improved the accuracy of the PTFs (on average close to 60% reduction in RMSE). Consequently, we recommend integrating local HYPROPTM (Hydraulic Property Analyzer, Meter Group Inc., USA) data sets into the international data set used in this study and retraining the PCNN-PTFs to enhance their performance for that specific region.

Cyanobacteria and algae are photosynthetic organisms and thus dependent on light for growth. Because light penetrates only a few millimeters into most soils, these organisms are naturally constrained to a very thin layer close to the soil surface. Nevertheless, they can become important in soil stabilization, soil hydrology, biogeochemical cycling, and fertility, particularly in climates or times restrictive to the extensive development of higher plants. This chapter reviews the basic biological characteristics of cyanobacteria and algae, as well as some of their ecological roles, with special emphasis on their importance for soils.

The vadose zone links atmosphere and hydrosphere within Earth’s Critical Zone. Soils form the upper vadose zone thus crucially influencing mass exchange between the two spheres, in particular the exchange of water and the contaminants it contains. To advance the understanding of water and related contaminant fluxes in the vadose zone requires an integrated consideration of biological, physical, and hydrological soil processes whose influence on temporal and spatial scales varies relative to each other. This dissertation aims to improve the hydrological exploration of soils in order to advance the understanding of the transport processes of soil water and contaminants. For this purpose, I will introduce innovative measurement techniques, field experiments, and modelling experiments applied within two study areas of contrasting usage as well as very different soil textural and hydrological properties. The new methodologies presented in this thesis focused on two specific points: (i) To develop a method coordinating soil water extraction with predefined soil moisture states to restrict soil water sampling to drainage periods thus enabling a reliable analysis of diffusive contaminant transport. (ii) To find a method to easily and reliably binarise huge stacks of infiltration profile images derived from dye-tracer experiments using Brilliant Blue to assess the potential of preferential contaminant transport. The first method employs suction cups with soil water sampling automatically triggered when the soil moisture registered exceeds field capacity. The second method employs an algorithm, widely used in image processing for background subtraction, to classify images of dye profiles into stained and unstained pixels. During their application, both methods demonstrated a robust and reliable performance. The field experiments include: (i) seepage water quality analysis covering a 20-month period accompanied by geostatistical analysis of spatial solid phase contamination patterns; and (ii) the analysis of plot-scale irrigation to investigate spatiotemporal patterns in preferential flow and to deduce the potential risk of a preferential contaminant transport. In terms of the urban site soils, I found that field-effluent metal concentrations were mainly affected by antecedent moisture and temperature whereas rainfall characteristics hardly influenced metals’ concentrations in the investigated soils at all. Infiltration profiles of the natural soil sites were best characterised using two relatively simply image metrics. The subsequent clustering revealed five distinct groups of infiltration profiles with differing manifestations of preferential flow in terms of flow path, macropore-matrix interaction, and advective flow strength. The modelling experiments clearly supplement the field experiments in terms of: (i) unravelling the water balance to calculate contaminant migration loads for the urban soil sites as well as (ii) shedding light on the temporal evolution and degree of macropore flow during specific boundary conditions for the natural soil sites. In summary, the results of this thesis demonstrate that hydropedological investigations must inevitably take biological, chemical, and physical soil characteristics into account in order to advance our understanding of soil water and contaminant transport processes. Altogether, this thesis provides a step forward to better integrate these complex hydropedological interrelations in field investigations. It concludes with suggestions of how to improve the presented investigation tools as well as with an outline of open questions requiring further investigations., Die vadose Zone verbindet Atmos- und Hydrosphäre unserer Erde. Böden grenzen sie zur Erdoberfläche ab und beeinflussen damit maßgeblich den Massenaustausch zwischen beiden Sphären, insbesondere den Austausch von Wasser und darin enthaltenen Verunreinigungen. Ein verbessertes Verständnis von Wasser- und Schadstofftransportprozessen in dieser vadosen Zone erfordert jedoch die gleichzeitige Berücksichtigung chemischer, biologischer und physikalischer Bodenprozesse, die jeweils auf unterschiedlichen raumzeitlichen Skalen von Relevanz sind. Diese Dissertation will dazu beitragen, die hydrologische Erforschung des Bodens zu verbessern, um Transportprozesse von Bodenwasser und Schadstoffen effektiver zu verstehen. Dazu stelle ich innovative Messmethoden, Feldversuche und Modellierungsexperimente vor, die in zwei Forschungsgebieten mit gegensätzlicher Nutzung sowie unterschiedlicher Bodentextur und hydrologischen Gegebenheiten durchgeführt wurden. Die methodischen Weiterentwicklungen in dieser Promotionsschrift behandeln zwei Schwerpunkte: (i) wird eine Methode aufgezeigt, die das Sammeln von Bodenwasser mit definierten Bodenwasserzuständen abstimmt, um eine Probengewinnung ausschließlich auf Zeiträume mit Grundwasserneubildung zu beschränken. (ii) wird eine Methode präsentiert, um einfach und zuverlässig große Mengen an Bildern von Infiltrationsprofilen, als Resultat von Tracerexperimenten mit dem Lebensmittelfarbstoff Brillantblau, zu binarisieren. Für die erste Methode benutze ich Saugkerzen, wobei die Bodenwasserextraktion automatisch ausgelöst wird, sobald die gemessene Bodenfeuchte die Feldkapazität überschreitet. Für die zweite Methode verwende ich einen Algorithmus, der häufig in der Bildverarbeitung für Hintergrundsubtraktionen eingesetzt wird, um die Tracerprofile in gefärbte und ungefärbte Pixel zu klassifizieren. Beide Methoden erwiesen sich bei ihrer Anwendung als robust und zuverlässig. Die Feldversuche bestehen (i) aus einer zwanzigmonatigen Messreihe von Sickerwasserqualitäten, begleitet von geostatischen Untersuchungen der räumlichen Belastungsmuster, und (ii) der Analyse von Infiltrationsprofilen aus Bewässerungsversuchen mit Brillantblau. Bezüglich der Schadstoffverlagerung in Böden im urbanen Kontext erwiesen sich Temperatur und Vorfeuchte als Haupteinflussgrößen bezüglich der Sickerwasserkonzentration von Spurenmetallen im Bodensystem, während Niederschlagscharakteristika nahezu keinen Einfluss auf deren Konzentrationen in den untersuchten Böden zeigten. Zur Charakterisierung der Infiltrationsprofile in Böden im ruralen Kontext eigneten sich zwei relativ einfache Metriken. Die anschließende Clusterbildung ergab fünf unterschiedliche Gruppen von Infiltrationsprofilen mit differierender Ausprägung des präferenziellen Wasserflusses in Bezug auf die Fließwege, der Makroporen-Matrix-Interaktion und der Stärke des präferenziellen Fließens. Die Modellexperimente ergänzen die Feldmessung (i) hinsichtlich der Bilanzierung des Bodenwasserhaushalts zur Berechnung von Schadstofffrachten in den urbanen Böden sowie (ii) um die zeitliche Entwicklung und Ausgeprägtheit des Makroporenflusses unter bestimmten Randbedingungen für die Standorte mit natürlichen Böden. Zusammengefasst zeigen die Ergebnisse dieser Arbeit, dass eine hydropedologische Untersuchung zwangsläufig biologische, chemische und hydrologische Bodencharakteristika berücksichtigen muss, um unser Verständnis von Bodenwasser- und Schadstofftransport in der vadosen Zone zu verbessern. Die Dissertation liefert wichtige Ansätze, wie diese komplexen, hydropedologischen Zusammenhänge besser in Felduntersuchungen berücksichtigt werden können, ehe sie sich am Ende mit Optimierungsvorschlägen der dargelegten Untersuchungsmethoden sowie offenen Fragen zur weiteren Untersuchung auseinandersetzt.

[EN] The effects of a thinning treatment on soil respiration (Rs) were analysed in two dryland forest types with a Mediterranean climate in east Spain: a dry subhumid holm oak forest (Quercus ilex subsp. ballota) in La Hunde (HU); a semiarid postfire regenerated Aleppo pine (Pinus halepensis) forest in Sierra Calderona (CA). Two twin plots were established at each site: one was thinned (T) and the other was the control (C). Rs, soil humidity and temperature were measured regularly in the field at nine points per plot distributed into three blocks along the slope for 3 years at HU and for 2 years at CA after forest treatment. Soil heterotrophic activity was measured in laboratory on soil samples obtained bimonthly from December 2012 to June 2013 at the HU site. Seasonal Rs distribution gave low values in winter, began to increase in spring before lowering as soil dried in summer. This scenario indicates that with a semiarid climate, soil respiration is controlled by both soil humidity and soil temperature. Throughout the study period, the mean Rs value in the HU C plot was 13% higher than at HU T, and was 26% higher at CA C than the corresponding CA T plot value, being the differences significantly higher in control plots during active growing periods. Soil microclimatic variables explain the biggest proportion of variability for Rs: soil temperature explained 24.1% of total variability for Rs in the dry subhumid forest; soil humidity accounted for 24.6% of total variability for Rs in the semiarid forest. As Mediterranean climates are characterised by wide interannual variability, Rs showed considerable variability over the years, which can mask the effect caused by thinning treatment., This study was supported by research projects Hydrological characterisation of forest structures on a plot scale for adaptive management (CGL2011-28776-C02-02) and SILWAMED (CGL2014-58127-C3-2) funded by the Spanish Ministry of Science and Innovation and FEDER funds. CEHYRFO-MED (CGL201786839-C3-2-R), RESILIENT-FORESTS (LIFE17 CCA/ES/000063) and SilvAdapt. net (RED2018-102719-T) are also acknowledged. The authors are grateful to the Valencia Regional Government, VAERSA, ACCIONA and the "Sierra Calderona" Natural Park for their support in allowing us to use experimental forests and for their assistance in fieldwork. We also thank Rafael Herrera from the Centro de Ecologia, Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela, and the anonymous reviewers for critically reviewing the manuscript.

Soil plays a major role in the hydrological processes at the land surface. Water movement in the soil, evaporation, and transpiration processes are all strongly controlled by soil hydraulic properties. These properties are therefore important in estimating soil water fluxes.The objective of this thesis is to improve the representation of soil hydraulic properties in the ORCHIDEE (ORganizing Carbon and Hydrology in Dynamic EcosystEms) model, which describes land surface processes in the IPSL (Institut Pierre Simon Laplace) climate model, and is therefore a land surface model (LSM).Soil hydraulic properties are defined by both texture, which is the size-class sorting of the soil particles, and the structure, which is the arrangement of soil particles and pores. However, in ORCHIDEE, as in many other LSMs, these properties are inferred from a soil texture map, through pedotransfer functions. In the first part of this thesis, we investigate the impact of soil texture on the simulated soil water fluxes and storage at different scales, using several soil texture maps, to evaluate the model response to the different texture classes. This part shows that although the model exhibits a physically based response to soil texture, the choice of the soil texture map is not crucial in simulating water budgets at the global scale (Tafasca et al., 2020, HESS).Due to its important role in determining soil properties, the impact of the soil structure on hydrological processes is explored. Soils of the same texture can have different structures, leading to different hydrological behaviors. This is particularly conspicuous for clay soils, which can show a large variability in structure due to swelling clays and non-swelling clays, and which are usually put together in the same soil class despite their contrasted hydrological behavior. In the second part of this thesis, we suggest a soil mapping and pedotransfer functions which differentiate these two clay types. Moreover, one of the major controls of soil structure is organic matter, which highly influences soil porosity and all the soil hydraulic properties. Different global scale approaches are tested to account for the influence of organic matter in the ORCHIDEE model. Introducing the effect of soil structure in ORCHIDEE results in a more realistic representation of soils as well as an improvement of the simulated evapotranspiration flux.; Les sols jouent un rôle important dans le fonctionnement des processus hydrologiques à la surface de la Terre. La dynamique de l’eau dans le sol, l’évaporation ainsi que la transpiration des plantes sont tous des processus fortement contrôlés par les propriétés hydrauliques des sols. Ces dernières sont donc essentielles dans l’estimation des flux hydrologiques de surface. L’objectif de cette thèse est d’améliorer la représentation des propriétés hydrologiques des sols dans le modèle ORCHIDEE (ORganizing Carbon and Hydrology in Dynamic EcosystEms), qui décrit les surfaces continentales dans le modèle de climat de l’IPSL (Institut Pierre Simon Laplace), et qui fait donc partie des modèles de surface continentales (land surface models, ou LSMs). Les propriétés du sol sont déterminées par la granulométrie de la terre fine, dite texture, et par sa structure, qui caractérise l’assemblage de ses constituants et des pores. Mais dans ORCHIDEE comme dans beaucoup des LSMs, la représentation des sols est simplifiée : les propriétés du sol sont déduites à partir d’une carte de texture par des fonctions de pedo-transfert. La première partie de cette thèse présente l’effet de différentes cartes de textures sur les flux hydrologiques simulés, à différentes échelles, pour évaluer la réponse du modèle aux différentes textures. Cette partie démontre que, si l’influence de la texture sur les flux simulés est bien rendue par le modèle, le choix de la carte de texture joue peu sur les bilans d’eau simulés à grande échelle (Tafasca et al., 2020, HESS). Du fait de son rôle avéré dans le fonctionnement hydrologique des sols, l’influence de la structure sur les processus hydrologiques est explorée en deuxième partie. La variabilité de la structure au sein d’une même texture de sol amène à des comportements hydrologiques différents. C’est particulièrement le cas des argiles, qui sont habituellement regroupées dans une même classe texturale, malgré une structure et des comportements hydrologiques contrastés entre les argiles gonflantes (Vertisols des zones tempérées) et non gonflantes (Oxisols des zones tropicales). Cette thèse propose ainsi une cartographie et des fonctions de pédo-transfert enrichies pour distinguer ces deux types d’argiles. Par ailleurs, un contrôle majeur de la structure est la teneur en matière organique du sol, qui influence fortement la porosité et l’ensemble des propriétés hydrauliques du sol. Plusieurs approches plus globales ont été testées pour tenir compte de cette influence dans le modèle ORCHIDEE. Une conclusion majeure de cette thèse est que la prise en compte de la structure permet une représentation plus réaliste des sols ainsi qu’une amélioration de l’évapotranspiration simulée dans le modèle ORCHIDEE.

Expansive soils exhibit swell-shrink behaviour in wet-dry periods resulting in distresses on light-weight structures founded on/in them. Therefore, it is essential to investigate the climate-ground interaction when designing structures on expansive soils. Laboratory-based models are preferred to investigate the climatic-ground interaction of expansive soils due to the uncontrollability of the boundary conditions and expenses associated with field monitoring. More flexibility in analysing the climatic-induced hydraulic responses in expansive soils can be achieved by finite element modelling of data from physical model tests. However, these laboratory-based models regularly encounter the effects of boundary flaw, preferential flow paths and entrapped air that needs to be accounted for when numerically simulated. In this study, the authors aim to numerically model the hydraulic responses in an instrumented Vertosol soil column (ISC) under controlled laboratory conditions. The effects of the preferential flow paths and boundary flaws were incorporated into a modified hydraulic conductivity as a practical approach to model the hydraulic responses in ISC. Influence of the entrapped air was rectified by a suitable correction factor. These findings present a practical method for geotechnical practitioners to accurately estimate the suction and volumetric water content profiles in laboratory-based expansive soil model tests., Civil engineering; Earth sciences; Environmental science; Geotechnical engineering; Construction engineering; Soil composition; Soil hydrology; Environmental engineering; Unsaturated soil; Expansive soil; Numerical simulation; Climate-ground interaction; Mechanical properties; Sensors; Wetting

The effects of soil data sources on the performance of hydrologic model simulations remain poorly understood compared to the effects of other data inputs. This paper investigated the effects of different soil datasets in simulating streamflow and sediment yield using the Soil and Water Assessment Tool (SWAT). Furthermore, potential improvements in watershed simulations were evaluated by integrating field measured soil parameters (user soil) with global soil datasets. Five soil datasets, namely user soil, AfSIS (Africa Soil Information Service), Food and Agriculture Organization (FAO), and two integrated soils (User-AfSIS and User-FAO) produced by assimilating the user soil with the latter two, were evaluated. The benefits of the user soil in improving streamflow simulations to better replicate observed flow were greater at daily time steps than monthly. Compared to the individual AfSIS and FAO soils, their integration with the user soil improved the daily Nash-Sutcliffe Efficiency (NSE) by 0.19 and 0.17 during model calibration, respectively. Overall, all soils performed relatively similar with monthly sediment yield simulations, which were improved when it was integrated with the user soil. Based on selected rainfall events, the watershed response time was less than 1 h, which suggests that the watershed has a quick runoff response time. This paper showed that streamflow and sediment yield simulation performances of freely available global soil datasets can be improved through integration with locally measured soil information. This study demonstrated that the availability of local soil information is critical for daily hydrologic model simulations, which is critical for planning effective soil and water management practices at plot and field scales.

The Brazilian savanna, regionally known as Cerrado is an important water source due to its spatial position in the highlands known as Planalto Central of Brazil. Yet, the hydrological functioning of such complex ecosystems and its many variations is poorly understood. In this paper, we characterized the soil surface permeability to water under in one of the most common vegetation types: the Cerrado típico which is a type of savanna. In doing so, we measured infiltration capacity using the Mini-Disk infiltrometer (n = 15) and soil resistance to penetration using the Stolf penetrometer (n = 7) in a Latossolo (oxisol) under Cerrado típico located in Brasília (Planaltina), Distrito Federal, Brazil. Our results indicated a high infiltration capacity under Cerrado típico which is potentially associated with a low penetration resistance. This fact might highlight the importance of the natural undisturbed ecosystems, in this case Cerrado típico, as a land-cover which favors hydrological processes which, in turn, promotes soil-groundwater recharge that are inportant to maintain water bodies and reservoirs in the region., A savana brasileira, regionalmente conhecida como Cerrado é uma importante fonte de água devido à sua posição espacial na região de terras de alta altitude conhecida como Planalto Central do Brasil. No entanto, o funcionamento hidrológico desse complexo conjunto de ecossistemas e duas inúmeras variações são pouco compreendidos. O objetivo do presente estudo foi caracterizar a permeabilidade da superfície do solo à água em um dos mais comuns tipos de vegetação do Cerrado: o Cerrado típico que é um tipo de savana. Foram medidas a capacidade de infiltração usando o infiltrômetro Mini-Disk (n = 15) e a resistência do solo à penetração usando o penetrômetro Stolf (n = 7) em um Latossolo sob Cerrado típico localizado em Brasília (Planaltina), Distrito Federal, Brasil. Os resultados indicaram uma alta capacidade de infiltração sob Cerrado típico que pode estar associada à uma baixa resistência do solo à penetração. Este fato destaca a importância dos ecossistemas naturais sem distúrbio, no presente caso o Cerrado típico, como uma cobertura da terra que favorce processos hidrológicos que promovem a recarga do solo e a da água subterrânea que mantém a água nos corpos d´água e reservatórios da região.

The transportation load of oil palm (Elaeis guineensis Jacq.) seedlings from the nursery to planting sites is a crucial problem facing the extension of smallholder plantations in Cameroon. This load can be considerably reduced by removing soil from the roots, which in turn exposes the plants to water and nutrients stresses. A greenhouse pot experiment was carried out to evaluate the recovery performance of such soil-stripped seedlings as a function of watering frequency and soil texture. Plant recovery potential was monitored on 360 nursery seedlings aged 4 months, under two soil types (sandy clay soil with 46% fine particles and sandy loam soil with 19% fine particles) and two watering frequencies (daily and two-days). Three monthly measurements were taken on morphological plant growth parameters including Plant height, Foliar surface, Collar diameter, Root length and Plant weight. Within and between groups analyses of variance and means separation showed the greatest variability for collar diameter, foliar surface and plant weight. All the parameters showed a greater variability and an almost-constant growth from one month to another, except for plant weight that did show a highly significant (p = 0.000) increase between the first measurement and the second. Soil type, watering and their interaction explained 97–99.5% of the variations of all parameters. Except for root length, all other parameters were more sensitive to the effect of soil texture, explaining 83–95% of the total variation. Only plant weight and root length showed slightly greater values under daily watering, other parameters did not show any sensibility to the two watering frequencies proposed in this experiment. Our results showed a low response of plant growth recovery on the low clay sandy loam soil, revealing that a careful selection of a soil texture is crucial for the survival of seedlings and further establishment of the plants following drought stress. It is therefore strongly recommended to many tropical countries where oil palm is an economically important crop, to take this into account during the selection of soil type for oil palm seedlings nursery., Oil palm; Plant seedlings; Pot plant recovery; Soil-stripped seedlings; Soil texture impact; Watering impact;Agricultural soil science; Crop biomass; Soil science; Soil hydrology; Plant growth.

International audience; Simulations of 21st century climate change for Great Britain predict increased seasonal precipitation that may lead to widespread soil loss by increasing surface runoff. Land use and different vegetation cover can respond differently to this scenario, mitigating or enhancing soil erosion. Here, by means of a sensitivity analysis of the PESERA soil erosion model, we test the potential for climate and vegetation to impact soil loss by surface-runoff to three differentiated British catchments. First, to understand general behaviours, we modelled soil erosion adopting regular increments for rainfall and temperature from the baseline values (1961–1990). Then, we tested future climate scenarios adopting projections from UKCP09 (UK Climate Projections) under the IPCC (Intergovernmental Panel on Climate Change) on a defined medium CO2 emissions scenario, SRES-A1B (Nakicenovic et al., 2000), at the horizons 2010–39, 2040–69 and 2070–99. Our results indicate that the model reacts to the changes of the climatic parameters and the three catchments respond differently depending on their land use arrangement. Increases in rainfall produce a rise in soil erosion while higher temperatures tend to lower the process because of the mitigating action of the vegetation. Even under a significantly wetter climate, warmer air temperatures can limit soil erosion by enhancing primary productivity and in turn improving leaf interception, infiltration-capacity, and reducing soil erodibility. Consequently, for specific land uses, the increase in air temperature associated with climate change can modify the rainfall thresholds to generate soil loss, and soil erosion rates could decline by up to about 33% from 2070 to 2099. We deduce that enhanced primary productivity due to climate change can introduce a negative-feedback mechanism limiting soil loss by surface runoff as vegetation-induced impacts on soil hydrology and erodibility offset the effects of increased precipitation. The expansion of permanent vegetation cover could provide an adaptation strategy to reduce climate-driven soil loss

Soil hydrology is a key control for the functioning of the terrestrial environment. Many environmental issues that we need to tackle today are directly linked to soil water dynamics. This includes agricultural production and food security, nutrient cycling and carbon storage, prevention of soil degradation and erosion, and last but not least, clean water resources and flood protection. However, these problems need to be addressed at the scales of fields, regions, and landscapes, while soil water dynamics and soil hydraulic properties are well understood and typically measured at much smaller scales—the comfort zone of soil physics. An obvious problem is how to link these vastly different scales and how to profit from small-scale understanding to improve our capability to predict what is going on at the large scale. In this update, this problem is discussed based on insights gained during the last decades. As a synthesis, a two-step scaling approach is proposed for modeling soil water dynamics from local to landscape scales where the scale of the soil profile is the stepping stone.

The distribution of forest patches in the foreststeppe of central Mongolia reflects the interplay of several environmental factors that together control the vegetation pattern of the landscape. Since the mean annual precipitation of this semiarid area rarely exceeds 300 mm, the existence of forest strongly depends on the hydrological properties of the system. Only north-facing slopes provide suitable conditions for the growth of larch trees (Larix sibirica Ledeb.) due to their reduced evapotranspiration. Plains and south-facing slopes are covered by open steppe.However, after disturbance of the forest patches by fire, the regrowth of larch trees does not proceed equally in all areas. During fieldworkat the northern edge of the Khangai Mountains, we identified areas that seemed to havesimilar site conditions but neverthelessshowed different regrowth of larch trees after fire, ranging from intensive regrowth to no regrowth at all.Thisobservation stimulated us to carry out a comprehensive study of soils, vegetation and landscape development in field campaigns in 2017 and 2018, followed by laboratory analyses of soil samples.Through this work, we aimed at identifying the role of soil hydrology for forest succession in this sensitive ecotone.We described and sampled 57 soil profiles, including sites (i) under forest, (ii) under steppe, (iii) on sites with succession after forest fire, (iv) on sites without succession after forest fire. In the field, we carried out measurements of water conductivity (by use of a compact constant head permeameter). In the laboratory, we analyzed particle size distribution and carried outkfand pF measurements.These analyses showed that the dominant grain size of the soils was sand, whereby soils with forest regrowth had slightly loamier texture than those without regrowth. We concluded that already slightly loamier texture may be important for water storage during dry periods and thus for forest regrowth.Soils with forest regrowth had higher hydraulic conductivity in the first 25 cm and lower conductivity below.Soils without forest regrowth showeda reverse depth pattern of hydraulic conductivity. We concluded that quick drainage through the upper horizons supports forest regrowth, as it reduces competition for water with grass roots in the upper part of the soil.Soils with forest regrowth hadgreater plant-available water capacity than those without regrowth. We conclude that under the given climatic conditions, storage of plant-available water is a key factor for regrowth / no regrowth of forest after disturbance.

As most hydrological processes are highly nonlinear and controlled by time-varying boundary conditions, numerical models are required for their comprehensive representation. However, one of the major difficulties in vadose zone processes modeling is due to the fact that soils are heterogeneous at all spatial scales. The identification and accurate representation of such heterogeneity can be crucial for quantifying the subsurface hydrological states and water fluxes but it is still a challenge in soil hydrology.We present an integrated approach for process-based modeling of the vadose zone for a typical hillslope. The approach builds on the integration of classical soil mapping, on accurate monitoring of soil water content as well as on geophysical measurements for characterizing the subsurface heterogeneity. It finally integrates the gathered information into a physical model for simulating the vadose-zone processes with high spatial and temporal resolution.Starting with a simple soil representation, we present the modeling results for different scenarios of increasing complexity with focus on the discretization and corresponding hydrological parameterization of the soil structures in three dimensions. We highlight and discuss the key challenges that need to be addressed when continuous information about the subsurface heterogeneity is to be mapped in the field and represented in a numerical model.We argue that linking state-of-the-art experimental methods to advanced numerical tools, and bridging the gap between different disciplines such as pedology, hydrology and geophysics can be the key for improving our ability to measure, predict and better understand the vadose-zone processes. This will provide important knowledge needed for transferring this approach to larger scales where the accurate quantification of the soil water fluxes is required for a more efficient water management in the context of sustainable food production and climate change.

A high-resolution soil water retention data set (81 repacked soil samples with 7729 observations) measured by the HYPROP system was used to develop and evaluate the performance of regression parametric pedotransfer functions (PTFs). A total of sixteen soil hydraulic models were evaluated including five unimodal water retention expressions of Brooks and Corey (BC model), Fredlund and Xing (FX model), Kosugi (K model), van Genuchten with four free parameters (VG model) and van Genuchten with five free parameters (VGm model). In addition, eleven bimodal, Peters&ndash, Durner&ndash, Iden (PDI) and bimodal-PDI variants of the original expressions were studied. Six modeling scenarios (S1 to S6) were examined with different combinations of the following input predictors: soil texture (percentages of sand, silt and clay), soil bulk density, organic matter content, percent of stable aggregates and saturated water content (&theta, s). Although a majority of the model parameters showed low correlations with basic soil properties, most of the parametric PTFs provided reasonable water content estimations. The VGm parametric PTF with an RMSE of 0.034 cm3 cm&minus, 3 was the best PTF when all input predictors were considered. When averaged across modeling scenarios, the PDI variant of the K model with an RMSE of 0.045 cm3 cm&minus, 3 showed the highest performance. The best performance of all models occurred at S6 when &theta, s was considered as an additional input predictor. The second-best performance for 11 out of the 16 models belonged to S1 with soil textural components as the only inputs. Our results do not recommend the development of parametric PTFs using bimodal variants because of their poor performance, which is attributed to their high number of free parameters.

International audience; In terrestrial ecosystem studies, water drainage and nutrient leaching in the soil profile are estimated with hydrological models. Comparing modeled results to empirical data or comparing data from different models is, however, difficult because the uncertainty of input–output budget predictions is often unknown. In this study, we developed a procedure combining a Generalized Likelihood Uncertainty Estimation and a Monte-Carlo modeling approach to estimate uncertainty in model parameter estimates and model outputs water drainage and nutrient leaching fluxes for the WatFor water balance model. This procedure was then applied to compare different model optimization strategies (daily soil moisture measurements, monthly measurements of chloride concentrations in soil solution, and the elution of a concentrated chloride) at the same experimental site in a 90-year-old European beech (Fagus sylvatica L.) forest in Brittany (France). We show that the monitoring data of natural variations of chloride concentrations in soil solution were the most efficient dataset to calibrate the WatFor model compared to the soil moisture and chloride tracing experimental data. We also show that water tracing experimental data are the most efficient data to estimate the preferential flow generation model parameters. The optimization strategy had little influence on the predicted water drainage flux and nutrient leaching flux at the root zone boundary on a yearly time scale but influenced water and nutrient fluxes in the topsoil layers.

The characterisation of soil pores has a prime importance in soil hydrology particularly for soil water management in both irrigated and dryland agriculture. Hence, this study describes the soil po...

Vegetation-induced changes of soil hydrology (i.e., infiltration rate and soil matric suction) has important implication to the stability of earthen infrastructure. Predicting the plant hydrological effects is challenging when multiple species are present. Most existing models consider only single-species due to lack of reliable and relevant experimental data and difficulty to partition solar radiant energy into individual species in a mixed-species condition. This paper aims to develop an improved hydrological model that can determine the water infiltration rate and suction responses under both single- and mixed-species (one tree and one grass species) condition. The model is verified by double-ring infiltration tests and field monitoring conducted in bare, grass-only, tree-only and mixed tree-grass plots. The model was subsequently used for parametric analyses. The mixed species plot had the lowest infiltration rate and preserved the greatest suctions because the tree-grass competition for water created high soil moisture deficit. Parametric study identifies a threshold ratio of tree and grass leaf area index of 2.0, beyond which the effects of grass root-water uptake on water competition with the adjacent tree were negligible. Induced suction in the mixed tree-grass plot was close to that in a tree-only plot. Contribution of tree root-water uptake to induced suction in a mixed species plot did not increase further when the leaf area index ratio exceeds 5.0.

We thank Audrey Innes for isotope analysis at University of Aberdeen for Bruntland Burn and Krycklan sites, Johannes Tiwari (SLU) for isotope sampling in Krycklan, Pernilla Lofvenius (SLU) for providing PET data for Krycklan (via SITES), and Jeff McDonnell and Kim Janzen (University of Saskatchewan) for soil water isotope analysis for the Dorset and Wolf Creek sites. The Krycklan part was funded by the KAW Branch-Point project. We acknowledge the funding from the European Research Council (ERC, project GA 335910 VeWa). We thank the Editor and three anonymous reviewers for their critical comments during the peer-review process.