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• Multiple machine-learning algorithms were used to develop new PTFs for SHP prediction. • 1-km resolution maps of 0–2 m SHPs were generated for China's arid region. • The new PTFs had a higher accuracy than other commonly used PTFs. • Regional terrestrial biosphere modeling by using global SHP datasets should be endorsed with caution. Accurately quantifying the mass (water, nutrients, and carbon) and energy exchange processes between the Earth's atmosphere, biosphere, and lithosphere requires the accurate parameterization of soil hydraulic properties (SHPs) and their spatial heterogeneity. Because direct measurements of SHPs are difficult, time-consuming, and impossible at larger spatial scales, various pedotransfer functions (PTFs) have been developed in the last few decades, providing divergent estimates of SHPs from readily measurable variables. However, existing PTFs are mostly developed for specific regions and may not be suitable for other pedoclimatic conditions. Here, PTFs were developed using multiple machine-learning algorithms to estimate SHPs and examined the weaknesses and strengths of each method in estimating the average and variability of SHPs across China's arid region. The optimal PTFs were applied to a 1 × 1 km2 regional map of texture and bulk density, thus producing maps of the saturated hydraulic conductivity (K s), the parameters of the van Genuchten (VG) formulation, field capacity (θ fc), wilting point (θ wp), plant available water (θ pa), and soil macroporosity (ϕ m) in the 0–2 m soil profile throughout the region. The results indicate that the ensemble model with the averaging method (EMA) is the most robust for estimating all SHPs. The EMA-PTFs for K s yielded the best performance for sand textures, followed by sandy loam, loam, silty loam, silty clay loam, loamy sand, and clay loam textures. There were no significant differences in estimating soil water retention curve parameters among the different soil texture classes. Using the same observed data set, we demonstrated that the new EMA-PTFs outperformed those of existing PTFs, such as Rosetta and HYPRES, with RMSE values decreasing by 25–83 % depending on the SHPs. Furthermore, our SHP datasets exhibited significantly deeper soil profiles and higher accuracy than other available regional and global SHP products. The VG retention parameter α shows the greatest variation vertically throughout the 0–2 m soil profile, followed by ln(K s), θ r , θ pa , θ fc , θ wp , ϕ m , θ s and n. All SHPs exhibit much lower variability in the desert than in other areas, likely due to the homogeneous particle size distribution of desert areas. This study provides more accurate SHP estimates in China's arid region than the existing SHP products by developing advanced PTFs and highlights the inconsistency in SHPs among different global or regional products; the uncertainties induced by PTFs should thus be considered in future terrestrial biosphere modeling. [ABSTRACT FROM AUTHOR]

• Development of reference curves to describe temporal variation in soil properties. • Two-step model is proposed to obtain soil hydraulic properties at any time step. • Reduce need for extensive field measurements and numerical computations. • The developed model is validated with numerical and experimental data. Accurate knowledge of temporal variability in soil hydraulic properties (SHPs) can improve the prediction capability of flow and transport models. Lab and field measurements for determining SHPs at multiple timescales are expensive and time-consuming. Further, the existing Fokker-Plank equation (FPE) based numerical and analytical models for describing temporal variation in SHPs require parameterization. In this study, a scaling model is proposed to describe temporal variation in SHPs of four different soils. As field studies related to temporal variation in SHPs are limited, first synthetic temporally varying SHPs, soil water characteristic curves and hydraulic conductivity curves are generated using the analytical solution of FPE. Functional normalization approach is then used to develop reference curves and to obtain scale factors at different time-steps. The time-varying scale factors and the initial SHPs are related by two-step regression equations. The reference curves and the regression equations together can be used to estimate SHPs at any time given the initial SHPs. The developed model is validated using a 5-fold cross validation method and with experimental data at two study sites. The average percentage error in predicted van Genuchten parameters (θ s , n and K sat) except for α are mostly less than 10 %. The performance of the proposed model is comparable to that of FPE analytical model for experimental data. The proposed method holds promise for describing temporal variation in SHPs using only the initial SHPs. [ABSTRACT FROM AUTHOR]

Laboratory tests were conducted to investigate the properties of a bentonite slurry enhanced by the biomass derived from wheat straw. The bentonite concentration of the basic slurry varied from 40 kg/m3 to 60 kg/m3. The biomass contents of the enhanced slurry were between 37.5 kg/m3 and 87.5 kg/m3. Compared to the pure bentonite slurry, the viscosity of the biomass-enhanced bentonite slurry did not show significant increase. Moreover, the density of the biomass-enhanced bentonite slurry did not significantly increase. It appeared that the stability of suspended particles was slightly weakened by the added biomass. The minimal content of biomass needed for filter cake formation in the coarse sand decreases with the bentonite concentration. With a proper biomass content, the slurry pressure could be fully transferred to the effective support pressure within 120 s. Generally, the hydraulic conductivity value of the filter cake was less than 10-7 m/s, meeting the requirement for safe construction. Furthermore, as the biomass was gained from wheat straw, the enhanced slurry showed a high possible application in slurry-shield tunnelling. [ABSTRACT FROM AUTHOR]

• Van Genuchten-Mualem soil's steady flux analyzed; analytical solutions developed. • First solution for flow equation without prior assumptions on pressure head's form. • Solution derived using double Maclaurin series and multinomial theorem. • Analytically identify hydraulic parameters, avoiding numerical inverse procedures. Various analytical solutions for steady-state vertical flux through unsaturated soils exist in the literature. These solutions often assume specific hydraulic conductivity forms such as exponential form, rational power form, or power-law form such as the Brooks-Corey model. The van Genuchten-Mualem model is widely used in practical applications of flow through unsaturated soils. It is among the most complicated hydraulic conductivity forms for which no analytical solutions are available. This paper deals with the development of an analytical solution for steady-state vertical flux using van Genuchten-Mualem model. The analytical solution is obtained using Maclaurin series expansions and the multinomial theorem. The general form expresses the depth as a function of pressure head. The analytical solution can be used to model both infiltration (positive flux rate) and evaporation (negative flux rate). The derived analytical solution is compared with numerical results and shows excellent agreement. It can also be used to identify the hydraulic parameters analytically, eliminating the need of a numerical inverse procedure. As far as the author's knowledge, the proposed solution is the first analytical solution dealing with van Genuchten-Mualem model, which is directly derived from the flow equation without any predefined mathematical form of the pressure head. [ABSTRACT FROM AUTHOR]

• Performances of 45 pedotransfer functions of K sat were evaluated using soil databases from U.S.A. • Pedotransfer functions were classified into four groups according to its input requirements. • Best performing PTFs were identified for each group at different texture classes. • Results of the study were compared to the results of five recent studies evaluated the same PTFs. Direct measurements of saturated hydraulic conductivity (K sat) are costly and time-consuming. Alternatively, pedotransfer functions (PTFs) have been developed to estimate K sat in terms of readily available soil properties. The goal of this study is to evaluate forty-five PTFs of K sat. The functions were divided into four groups according to their input requirements: EP-K sat group (F1.1-F1.9) require the effective porosity as inputs; SSC-K sat group (F2.1-F2.12) require (sand, silt, clay contents); SSCBD-K sat group (F3.1-F3.8) require (sand, silt, clay contents), bulk density; and SSCBDOM-K sat group (F4.1-F4.16) require (sand, silt, clay contents), bulk density, and organic matter content. The results showed that the best PTFs were F1.9 and F1.5 in EP-K sat group. For the SSC-K sat group, the PTFs F2.1, F2.11. For the SSCBD-K sat group, the PTFs F3.5, F3.6. For SSCBDOM-K sat group, the PTFs F4.13 and F4.8. Results of this study are helpful for predicting K sat inputs required for large scale hydrologic models with reliability. [ABSTRACT FROM AUTHOR]

• Particle batch smoother can identify the variations of soil hydraulic parameters. • Variations of soil hydraulic parameters correlated with soil organic matter. • Soil organic matter was replenished by litterfall and consumed by respiration. Soil hydraulic parameters are influenced by various inherent soil properties, such as pore structure and organic matter content, which can vary with changes in the ecosystem. However, identifying the temporal variations of soil hydraulic parameters in a co-evolving soil-vegetation system remains a challenge. This study focused on a tropical forest with significant seasonal variations in vegetation attributes, evaporation, and carbon fluxes over a five-year monitoring period. The particle batch smoother algorithm was integrated with an unsaturated flow model to identify the seasonally varied soil hydraulic parameters through assimilation of in-situ measured soil moisture. As a benchmark, the Generalized Likelihood Uncertainty Estimation method was applied to optimize soil hydraulic parameters without considering temporal variation. The results indicated that the temporally varying soil hydraulic parameters exhibited regular seasonal patterns and outperformed the unvaried soil hydraulic parameters in terms of reducing the errors in modeling of soil moisture and evaporation. Moreover, the seasonal variations in soil hydraulic parameters were closely linked to changes in the litterfall and terrestrial carbon fluxes over time. Specifically, due to the hysteresis of the transformation from litterfall to soil organic matter, the accumulated litterfall in Hot-dry season can replenish the soil organic matter, resulting in an increase in field capacity and saturated hydraulic conductivity in the Hot-rainy season. However, the intense decomposition of soil organic matter under high temperature in Hot-dry season led to a decrease in field capacity and saturated hydraulic conductivity. This study emphasizes the value of the particle batch smoother algorithm in detecting temporal variations in soil hydraulic parameters within a coevolving soil-vegetation system, thereby contributing to a more comprehensive understanding of the intricate dynamics within the ecohydrological system under a changing environment. [ABSTRACT FROM AUTHOR]

A multi-exponential function (ME) is proposed to depict the highly nonlinear soil water retention curve and hydraulic conductivity function. Then, semi-analytical solution of pore-water pressure in an unsaturated infinite slope at steady state is derived using ME to depict soil hydraulic properties. The solution is verified with experimental and numerical results. It is found that ME can better describe the highly nonlinear hydraulic properties of soil than the single exponential function (SE), which is commonly-used previously. At steady state, the adoption of SE results in overestimating negative pore-water pressure (PWP; i.e., matric suction) by about 25 kPa and slope's factor of safety (FOS) by 100% under rainfall, but underestimating negative PWP by about 50 kPa under evaporation. The difference between PWP and FOS calculated by using SE and ME becomes more significant for soil with bimodal hydraulic conductivity function than that with unimodal one. This difference reduces at a larger slope angle and deeper depth. Moreover, this difference generally increases at a lower S ME /S SE , where S ME and S SE represent the suction at which the unsaturated hydraulic conductivity expressed by ME and SE equals the applied rainfall intensity or evaporation rate, respectively. When S ME /S SE is greater than 0.1, the difference basically diminishes. [ABSTRACT FROM AUTHOR]

• Analytical solutions for steady vertical flux with generalized hydraulic conductivity. • The solutions generalize existing solutions based on Brooks-Corey and rational models. • The proposed model provides better estimate of drying fronts for evaporation problems. • The analytical solutions allow a better fitting of experimental data. In this paper, analytical solutions for one-dimensional nonlinear steady-state vertical flux through unsaturated soils are presented. The analytical solutions are applicable for homogeneous soils for which the hydraulic conductivity function is a generalized form of the well-known Brooks-Corey and rational models. The adopted generalized soil–water retention model involves two additional parameters which reflect the curvature of hydraulic functions near saturation. The main advantage of the used generalized hydraulic conductivity function is that it fits better experimental data. The soil domain is a finite-depth medium overlying a fixed groundwater level. The derived analytical solutions are obtained using the Maclaurin series expansion technique. Analytical solutions for both infiltration and evaporation are developed. For evaporation from a fixed groundwater level, the derived solutions can be used to predict the existence of a vaporization plane below the soil surface. For this case, analytical expression of the position of drying front separating liquid and gas regions is derived. The analytical results are compared to numerical ones for various infiltration and evaporation examples and excellent agreements are obtained. The generalized model is also used to fit experimental data obtained for two soils. The results show that the use of the standard Brooks-Corey model may lead to an overestimation of the position of the drying front. [ABSTRACT FROM AUTHOR]

The settlement has been reported to regularly be a fundamental factor in controlling the stability of geotechnical structures. Because the theory of elasto-plasticity is widely employed to predict the settlement, the elastic modulus is a vital parameter that is regularly utilized for theoretical calculation. Moreover, thermomechanical behaviour of unsaturated soils has recently received considerable attention because its importance in various energy geostructures applications, as well as in relation to climate change. This paper presents a coupled thermo-hydro-mechanical model of the elastic modulus characteristic curve (EMCC) that was developed based on the effective stress theories of unsaturated soils. The proposed model uses the soil–water characteristic curve (SWCC) and the modulus of elasticity under saturated conditions to predict the variation of modulus of elasticity with matric suction for unsaturated soils. The successful prediction performance of the proposed model is demonstrated by the comparison of measured and predicted outcomes for various published data sets in the literature related to different soil types. The proposed method was then used to present a parametric study considering the coupled impact of some important parameters on SWCC and EMCC. The analysis results indicated that the normalized elastic modulus rate increases with increasing matric suction, hydraulic conductivity, soil density, and with decreasing flow rates, temperatures, and normal stresses. [ABSTRACT FROM AUTHOR]

The bimodal characteristic of water retention curves of dual-porosity soils has been fully recognized, however, the excessive number of fitted parameters in the existing models limits their application. This study develops a simple water retention model for dual-porosity soils that considers the self-similar characteristics of the pore size distribution (PSD) between macropore and micropore regions. In the model, we simulate the macropore PSD by differential VG model, which is then shifted and scaled to capture micropore PSD. It is hypothesized that the bimodal PSD can be obtained by superimposing the PSDs of macropore and micropore regions to derive the bimodal water retention curve (BWRC). The mercury intrusion porosimetry (MIP) tests and water retention tests are conducted on Nanyang clay with three different dry densities to evaluate the proposed BWRC. The results show that the new parameter can be determined by the MIP dataset and then used to predict the water retention behavior of dual-porosity soils well. Finally, we also explore the application of the proposed BWRC in predicting the hydraulic conductivity of dual-porosity soils without adding any extra parameters. [ABSTRACT FROM AUTHOR]

Crop management practices such as rotation, as well as climatic and edaphic factors, modulate soil physical health. However, the overall magnitude of crop rotation benefits on soil physical health properties across a broad range of different conditions remains uncertain. To address this, we conducted a meta-analysis on 865 paired comparisons from 148 rotation studies to examine i) how crop diversity affected soil physical health properties: bulk density, aggregate stability, porosity, infiltration rate, and saturated hydraulic conductivity, and ii) how management practices, climatic, and edaphic factors influenced crop diversity effects. Overall, increased crop diversity (i.e., number of crop species in the rotation) significantly reduced bulk density (−1.6 ± 1.3%), enhanced soil aggregation (15.9 ± 12.7%), improved porosity (3.1 ± 2.0%), and saturated hydraulic conductivity (112.8 ± 57.9%), but did not significantly change infiltration rate (92.2 ± 98.7%) compared to less diverse systems. Compared to using conventional tillage and cereals-only rotations, diverse rotations combined with conservation tillage or including grain legumes performed even better in enhancing both soil aggregation and porosity. Diverse crop rotations managed for 5–10 yr showed greater benefits in regions experiencing mean annual precipitation > 900 mm, and in medium- and fine-textured soils. Among soil physical health properties, saturated hydraulic conductivity was the most responsive to management practices. Based on this meta-analysis, we conclude that rotations including diverse crop species and grain legumes, managed under conservation tillage are best for improving soil physical health, and thus should be considered when designing and developing sustainable cropping systems that promote soil health, system resilience, and crop productivity. • Increasing crop diversity improved most soil physical health properties. • Grain legumes in cereal-based rotations improved soil physical health properties. • Diversity with conservation tillage enhanced soil aggregation, porosity, and saturated hydraulic conductivity. • Crop diversity improved soil hydrologic properties in regions with mean annual precipitation > 900 mm yr-1. • Rotational diversity over long periods had greater benefits in medium- and fine-textured soils. [ABSTRACT FROM AUTHOR]

[Display omitted] • Saturated hydraulic conductivity decreased in all microplastics (MP) treatments (types, sizes, and concentrations). • Soil water retention reduced in all MP-treatments. • Contact angle increased at a concentration of 2 % MP. • Smallest size fraction (S) had the most substantial effect on saturated hydraulic conductivity reduction. Environmental contamination with microplastics (MP, 0.1 µm – 5 mm diameter) potentially threatens various soil functions and agricultural production. In this study we evaluated the effects of MP on physical soil parameters (saturated hydraulic conductivity, water retention and water repellency) at MP concentrations (0.5 to 2 % w/w) that have been reported for farmland soils. Polyethylene terephthalate (PET) and polystyrene (PS) of three sizes ranging between 0.5 and 3 mm diameter, were mixed with loess topsoil material from an agriculturally used Luvisol. Results show that increasing MP concentration decreased the saturated hydraulic conductivity (k sat) compared to the control soil (without MP), irrespective of MP type. The highest reduction of k sat was found for the highest concentration (2 %) and the largest size MP (approx. 3 mm diameter). Compared to the control, MP addition significantly decreased soil water retention with increasing concentration. In contrast, air capacity was increased with MP addition where strongest effect was found for largest PET particles at the highest concentration. Soil water repellency (measured as Wilhelmy Plate contact angles) was increased at a concentration of 2 % and for MP sizes > 1 mm, while no effect was observed for lower concentrations and smaller MP. In conclusion, MP type, size, and concentration did affect key soil physical parameters, likely to negatively influence plant growth in contaminated soils. [ABSTRACT FROM AUTHOR]

• Capillary-based Weibull distribution hydraulic models are extended to oven-dry. • Peters-Durner-Iden (PDI) and Brunswick (BW) models are improved and compared. • Improved PDI and BW models can predict the saturated noncapillary conductivity well. Accurate descriptions of soil hydraulic properties over the entire matric suction range require the consideration of both capillary and noncapillary processes. This study extended the Weibull distribution models of hydraulic properties to complete dryness by the modular frameworks of Peters-Durner-Iden (PDI) and Brunswick (BW). Model-data comparison results showed that the original Weibull distribution models, accounting solely for capillary phenomena, provided inadequate descriptions of measurements in the dry range of water retention curve and hydraulic conductivity curve. The improved models of PDI and BW, accounting for both capillary and noncapillary processes, effectively described the hydraulic properties data from saturation to complete dryness, although the BW model violated the linearity requirement for water retention in dry soils with wide pore-size distributions. The PDI model overall performed better than the BW model in terms of their capability to fit the retention data and predict the conductivity data. Adopting the physically-based approach developed recently, the improved PDI and BW models can reliably predict the hydraulic conductivity along the complete matric suction range from water retention only, without use of fitted conductivity parameters. Thus, the improved PDI and BW models are applicable to cases where measured conductivity data (particularly noncapillary-dominated range) are not available. [ABSTRACT FROM AUTHOR]

Discrepancies in time-space representation of indata and calibration/validation data obstructs analysis of hydrological processes thatlink natural and anthropogenic water infrastructure in catchments and landscapes. To improve indata for hydrological- and modelling of the soil-plant-atmosphere-continuum, this paper presents a high-resolution dataset of hydrological functions in the agricultural landscape of Tidan, Sw Sweden. We firstly address spatial representation of soil physical parameters, describing soil water flows and storage. Secondly, we derive tile drainage datasets from historical maps. Lastly, we explore delineation and spatial location of streams, ditches and waterbodies to improve description of water connectivity. The new soil datasets with top- and subsoil descriptions varied in depicting the sensitivity of saturated hydraulic conductivity and water holding capacity. The most representative soil map showed moderate (34%) - to very rapid (21%) saturated hydraulic conductivity, water holding capacity below 40 mm 10 cm−1 (94%) and a dry bulk density ranging between 1.2 and 1.8 g cm−3 (71%). The digitalization of drained fields suggests that 69% of the arable fields are under tile drainage, dominated by sandy loam, loam and clay loam. The combined stream network resulted in 5350 km of streams and ditches, + 14% km and + 129%, respectively, compared to available best resolution datasets. Landscape surface water storage increased with a small addition (+ 6439 m3 storage potential) compared to previously available datasets. The improved descriptors of natural and anthropogenic flow and storage can potentially serve to improve water quantity and quality modelling under current and future climate- and hydrological changes. [ABSTRACT FROM AUTHOR]

Saturated hydraulic conductivity (K s a t) and other soil (hydraulic) properties are fundamental for applications that depend on modeling hydrological processes, such as the quantification of future groundwater recharge rates. Yet, for most areas in the world, local soil information is lacking. Additionally, access to local soil surveys is often restricted or costly. Available global and regional digital soil mapping (DSM) products differ in scale and degree of data aggregation, as well as in spatial coverage. K s a t – and soil properties in general – are also characterized by a high spatial variability at all scales. Most often, there is no single data product available that covers the whole study area and still displays the variability of local soil observations. Thus, it is often a challenge to combine and predict soil data from different sources and resolutions while preserving the characteristically high spatial variability of soil properties. This study develops and compares two approaches for producing spatially distributed K s a t maps. First, an indirect approach based on two machine learning (ML) models – eXtreme Gradient Boosting (XGBoost) and feed-forward neural network (FNN) – that are trained with available local soil data sources and environmental raster datasets to predict the soil parameters sand, silt, clay, and organic matter content. K s a t is then determined by applying existing pedotransfer-functions (PTFs) on these regionalized soil parameters. Second, a direct approach in which ML models are directly trained with available soil hydraulic datasets to predict K s a t. Both approaches are applied to predict K s a t for Austria. While the resulting soil property maps of the indirect approach are able to largely reproduce the original data variability, the prediction of K s a t includes high levels of uncertainties and the predicted vertical distribution of K s a t is not plausible. The spatial distribution of K s a t in the direct approach resembles available global K s a t maps. In the existing global K s a t maps as well as in the results of the direct approach the small-scale variability of K s a t is reduced. In both approaches XGBoost outperforms FNN. The derived soil property maps help to reduce current gaps in soil data availability for Austria, but also highlight the need for additional K s a t field data acquisition. • Large-scale 3D modeling of soil properties at a resolution of 1 km² over Austria. • Comparing two Machine Learning based approaches for K s a t prediction. • Evaluation of generated maps with globally available digital soil mapping products. • Identification of limitations related to scale, soil variability, and data scarcity. • Open source modeling code and generated soil maps. [ABSTRACT FROM AUTHOR]

Salinization is a global threat to the sustainability of farmland in arid areas. However, the mechanisms by which soil physicochemical and microbial properties affect soil nutrients in salinized farmlands are not completely understood. Here, the direct and indirect responses of edaphic properties (bulk density [BD], saturated hydraulic conductivity [SC], field capacity [FC], alkalinity[pH], microbial biomass carbon [MBC], and microbial biomass nitrogen [MBN]) and soil microbial properties (denitrifying genes [ nirS ], nitrogen-fixing genes [ nifH ], catalase [ CAT ] and urease [ UR ] activities, and species richness [ Chao1 ]) to the total soil N content (TN), soil organic carbon (SOC), alkali hydrolyzable N (AN), potassium (K+), and calcium (Ca2+) ions at low-salinity (2–4 dS m−1), mid-salinity (4–8 dS m−1), high-salinity (8–15 dS m−1) sites, and non-salinity (Control, 0–2 dS m−1) farmland in arid areas of northwest China were examined. Soil UR activity (range: 703.5–956.6 U UR L-1) and nifH , AN, SOC, and MBN content were higher at the low-salinity than at the medium- and high-salinity sites. Furthermore, FC was indirectly affected by the soil nutrients due to their effects on nifH and CAT activities. The relative contribution of soil TN, SOC, and AN content on the direct responses of the microbial attributes (52–70%) was higher than that of the soil physicochemical properties (27–45%) in different reclamation types. The reclamation process on abandoned salinized farmland promoted the activity of microorganisms, further improving the soil's physical properties and nutrient status. This study has found that improving microbial metabolic activity in combined with reclamation measures will be crucial for future salinity management. [Display omitted] • Reclamation measures most significantly increased alkali-hydrolyzable nitrogen in arid areas. • Field capacity (FC) indirect affects soil nutrients by directly promoting denitrifying genes (nirS). • The contribution of soil nutrients to the physical properties was lower than soil chemicals. • A differential response between soil physical and chemical existed with reclamation. • The differential response led to the elevation of soil nutrients acquiring urease activities. [ABSTRACT FROM AUTHOR]

• Comparison of laboratory results with the properties of the material obtained by in-situ mixing. • Little impact of soil clay content on the compressive strength of laboratory specimens. • The dynamic modulus is both impacted by soil's nature and cement dosage. • In situ, higher water content is needed to achieve homogeneous mix materials. • Relationship between W/C ratio and strength less obvious than in conventional concrete. Soil mix material is a soil–cement material mixed in place. The process results in the formation of "concrete" in which the soil is being used as aggregate. The objective of this paper is to compare laboratory-proportioning tests with results obtained on three different construction sites (CS_1, CS_2, CS_3) using deep soil mixing method, establishing relationships between physico-mechanical properties of laboratory and construction site materials. In CS_1, Deep Soil Mixing was used to make a temporary retaining wall. Two soil-mixing columns of 80 cm diameter and 3 m depth were realized. After curing, 230 cylindrical specimens of Φ 10 × 20 cm and 130 samples of Φ 5 × 10 cm were drilled. In CS_2 and CS_3, Trench mix method was used for cut-off walls construction. In these sites, 48 specimens and 22 specimens of Φ 11 × 22 cm of fresh mixed-soil were collected, respectively. Two types of soils, from 1 and 3 m depth, were collected from CS_1 to prepare soil–cement laboratory specimens. Soil-cement mixtures contain different cement contents (100, 150, 200, 250 and 300 kg/m3), and 50 % water content. Compressive strength, dynamic modulus, porosity and hydraulic permeability are investigated. The influence of cement dosage and soil type is discussed. There is a close fit between the laboratory results and the site results for soils with low clay content. The difficulty of uniformly mixing the clay results in a lower performance of the mixed in place material compared to the laboratory material. [ABSTRACT FROM AUTHOR]

• The presence of biocrusts significantly changed soil hydraulic properties. • Biocrusts enhanced soil water holding capacity by increased soil fine particles. • Soil hydrophobicity and unsaturated hydraulic conductivity had opposite effect on soil water redistribution. • Consideration of biocrusts could precisely evaluate the water cycle in dryland. Water redistribution profoundly affects the dryland ecosystem's function. Biological soil crusts (BSCs or biocrusts), which cover a large part of soil surface in arid land, significantly affect the water redistribution, but the results are conflicting at regional scale. In this study, the effects of different biocrusts on soil hydraulic properties, including soil water retention curve, soil water sorptivity, soil hydrophobicity and unsaturated hydraulic conductivity, were clarified in Tengger Desert. The results showed that the presence of BSCs significantly changed soil hydraulic properties. Compared to sand, BSCs increased water holding capacity and soil hydrophobicity, and decreased soil water sorptivity and unsaturated hydraulic conductivity. The enrichment of fine particles during the change from the less to the more developed BSCs contributed to the enhancement of water holding capacity, but this effect was mainly limited at 3-cm layer of soil underneath the ground surface. Soil hydrophobicity decreased with crust development, which contributed to the increase of soil water sorptivity. Unsaturated hydraulic conductivity decreased during the change from the less to the more developed BSCs, which exerted some negative effect on water infiltration. Our results highlight the important role of BSCs in hydraulic properties, and consideration of biocrusts and its hydrological behavior could help us better understand the distribution, movement and retention of soil water in this area. [ABSTRACT FROM AUTHOR]

Tropical country such as Malaysia experienced high intensity and long period of rainfall, which is the main factor of slope failure. The increasing of seepage subjected by rainfall not only distress suction distribution, but also affects hydraulic properties of soil lead to the decreasing of soil strength. This also leads to soil slope failure. The main hydraulic properties for soils are Soil-water characteristic curve (SWCC) and hydraulic conductivity, k. The relationship of these parameters is highly influenced by tropical soil, thus contributes to soil instability phenomenon. The main objective of this paper is to study the relationship between soils' hydraulic properties and particle size distribution (PSD). Four types of soils investigated in this research include one sample taken from Universiti Kebangsaan Malaysia (UKM)'s reserved forest, and three samples were commercially obtained. Other than soil basic properties, pressure plate extractor and permeability tests were conducted for SWCC and permeability, respectively. Tests show that different types of soils demonstrate different characteristic of SWCC and hydraulic conductivity. Result also shows that PSD has the influence and affect the result of hydraulic properties of soils. This study is expected to enhance the understanding of complex phenomenon of residual soil instability. • Infiltration of rainwater into soil is a main cause of slope instability. • Tackle this issue by studying relationship of hydraulic properties of soils. • Result shows that PSD has the influence and effect to hydraulic properties of soils. [ABSTRACT FROM AUTHOR]

• Hydraulic properties of soils with rock fragments were indirectly determined. • Measurements from field drainage experiments and undisturbed soil samples were used. • Parameter optimization was accomplished with the Hydrus-1D "Inverse solution". • Bimodal hydraulic functions showed more suitable for soils with rock fragments. • Using a sequential optimization, hydraulic functions could be parameterized. The application of inverse modeling to determine the hydraulic properties of layered soils with rock fragments (RF > 2 mm) is associated with complex challenges such as selecting suitable hydraulic functions and defining a strategy to optimize many parameters. These two issues were addressed in this study by performing field drainage experiments in layered soil profiles (three layers) with different particle size distributions and different percentages of RF. Water contents (θ) and pressure heads (h) were monitored at different soil depths during drainage experiments (h ≥ −200 cm). Data of θ and h for a drier range (h < −5000 cm) were determined with a dew point potentiometer on disturbed soil samples. The unimodal and bimodal van Genuchten-Mualem functions were evaluated, and their parameters were optimized using the Hydrus-1D "Inverse solution". The RETC curve fitting software was used to estimate the second set of parameters of the bimodal function. The parameters for the uni- and bimodal models (15 and 27 parameters, respectively) were repeatedly optimized by fixing some parameters while estimating others. The unimodal van Genuchten-Mualem function provided a satisfactory fit of θ and h measurements only when either drainage or dew point potentiometer measurements were used. On the other hand, the bimodal van Genuchten-Mualem function provided a satisfactory fit of θ and h measurements when both sets of data (drainage and dew point potentiometer measurements) were used simultaneously. Furthermore, the optimized parameters were physically consistent except for a few high saturated hydraulic conductivity values. Therefore, bimodal functions should be considered to represent the hydraulic properties of soils with RF. The problem of many calibrated parameters when using bimodal functions can be managed using sequential optimization, which allowed us to estimate 27 parameters for layered soils with RF successfully. [ABSTRACT FROM AUTHOR]

• Soil-pipes caused a several order-of-magnitude increase in nitrate bypass of riparian zones. • Soil-pipes impact riparian bypass most in soils with low hydraulic conductivity and gradients. • The amount of nitrate bypassing the riparian zone was most sensitive to soil pipe length. • We created a nondimensional parameter (bypass potential) that explains variation in bypass. Streams are vital landscape ecosystems, and urbanization and modern agriculture have introduced pollutants (including excess nitrate) which threaten these waterways. Riparian zones have been shown to attenuate pollutants, and riparian buffers are commonly implemented to capture these benefits. Nevertheless, preferential flowpaths such as soil pipes have potential to bypass such attenuation. We used a MODFLOW groundwater model with the conduit flow package (CFP), along with the groundwater transport code MT3D-USGS, to simulate flow of water and nitrate through riparian groundwater to a gaining stream. We conducted a numerical sensitivity analysis to examine the impact of soil pipe presence and characteristics, as wells as soil matrix characteristics, on nitrate transport and uptake by denitrification within the saturated zone. We found that in systems with 2.0-m-long soil pipes, low head gradient (∇h less than 0.0035), low hydraulic conductivity (K < 10−4.75 m/s), and high reaction-constant (k > 4 day−1), soil pipes increased riparian bypass of nitrate by several orders of magnitude. Yet soil pipes increased the volumetric flowrate of water across the riparian zone only by up to 3.9 times. This comparatively greater effect on transport occurred because the accelerated advection of nitrate through the soil pipes decreased the residence time available for denitrification. We created two non-dimensional parameters that show when bypass will be important, the riparian bypass potential (ψ) that accounts for key governing factors such as volumetric flowrate and Damköhler number, and riparian predictive index (ζ), which is calculated from easily measurable parameters. Nitrate bypass starts to increase by orders of magnitude above ψ ≈ 2.75 and ζ ≈ 3.4. Our results emphasize the importance of accounting for soil pipes when constructing riparian buffers and predicting their effects on dissolved pollutant transport. [ABSTRACT FROM AUTHOR]

[Display omitted] • Average hydraulic properties were obtained for thirty-six soil texture classes. • Static hydraulic properties were calculated for 368 Dutch soil profiles. • Soil profiles were clustered to obtain a map with 79 soil physical units. • Dynamically simulated transpiration reduction was well predicted within units. • This approach can be used for other locations and applications as well. Soils and their properties play an important role in land evaluation studies. Often such studies focus on larger scales ranging from watersheds up to the national scale or even larger. Soil properties are often known at smaller scales, sometimes at the level of individual soil samples. The aim of this study is to show how point information on soil hydraulic properties, i.e. , water retention and hydraulic conductivity characteristics, can be upscaled via soil textural classes to a soil physical units map of a region or nation. Base information is the Dutch soil map (1:50,000) and the hydraulic properties of individual soil samples. All individual soil samples for which hydraulic properties were measured were divided based on their texture into eighteen top-soils and eighteen sub-soils. For each of these thirty-six groups geometric average water retention and hydraulic conductivity characteristics were derived. In total 368 derived soil profiles are distinguished in the Dutch soil map consisting of soil layers that are linked to the thirty-six texture groups. For each soil profile eight static hydraulic properties were calculated. The soil profiles were then clustered based on these properties into seventy-nine clusters or units, which then make up a soil physical units map for the Netherlands. It has been demonstrated that dynamically simulated transpiration reduction for the clustered situation is similar to obtained for all individual soil profiles. At the Dutch national scale, the difference in simulated transpiration reduction between runs using all 368 soil profiles or the 79 soil physical units was less than 2.5 % percentage-points in 96 % of all plots or less than 5 % percentage-points in 99 % of all plots. Similar good correspondence was obtained for other water balance terms as well, including actual transpiration, actual evaporation at the soil surface, degree of saturation at 15 and 30 cm depth, the integrated water flux at 100 cm depth and surface runoff. [ABSTRACT FROM AUTHOR]

The iron-reducing bacterium (IRB) Shewanella oneidensis MR-1 and a sulfate-reducing bacterium (SRB) Desulfovibrio vlugaris miyazaki , were used in varying sequences for batch and column arsenic extraction experiments to assess their use in alleviating arsenic pollution from arsenic-containing ferrihydrite in soil. Both batch (four conditions) and column experiments show variations in biological sequence affect the arsenic release and species. The results of arsenic release from batch conditions are: IRB-SRB (2.28 mg/g) > SRB-IRB (1.72 mg/g) > SRB+IRB (0.55 mg/g) > Control group (pure water, 0.04 mg/g). Further cycle operations from batch experiments showed that IRB-SRB operation always obtained the best performance of releasing arsenic. The column experiments achieved greater arsenic release: SRB+IRB (10.87 mg/g) > IRB-SRB (7.54 mg/g) > SRB-IRB (6.48 mg/g) relative to arsenic in the pristine samples (36.6 mg/g). Flow methods could obtain more releasing performance than batch experiment. The hydraulic conductivity in the column experiments was best in the SRB-IRB operation (average water difference: 0.39 psi for SRB-IRB, 0.86 psi for IRB-SRB and 1.07 psi for SRB+IRB). After the biological operation, chemical treatment (0.5 M, (NH 4) 2 HPO 4) only desorbed 11.14–39.81% of the total arsenic quantity of each operation. Reductive dissolution is the main driving reason for arsenic release, though the formation of FeS was found to hinder arsenic release. Analysis of the solids showed that the SRB+IRB operation results in 58.07% arsenic released. These results suggest that microbially-assisted reduction using iron- and sulfate-reducing bacteria may be an effective technology for remediating arsenic-bearing soil e.g. paddy soil using systems such as an in-situ injection and pump. [Display omitted] • Biological reduction operation could effectively sequestrate arsenic from arsenic-containing ferrihydrite. • Different Injecting sequence results in variation in performance. • SRB+IRB operation obtained the best release ratio of arsenic (58.07%). • Microbially-assisted reduction technology could be effective clean technology. [ABSTRACT FROM AUTHOR]

• The drying effect makes the connected macropores become poor, the wetting effect the macropore space and porosity increase after wetting. • The variation of connected pore porosity is larger than that of the porosities of the total and isolated pores. • The connectivity of pores decreases with an increasing number of wetting and drying cycles. • The connected macropores play a decisive role on the saturated hydraulic conductivity of granite residual soil. Soil usually experiences multiple wetting and drying cycles due to changes in climate conditions, which directly lead to changes in the soil pore structure, especially macropores, thus affecting the mechanical properties and permeability. In this paper, the macropore structure of granite residual soil during three wetting and drying cycles is examined by X-ray computed tomography (CT). The pore spatial distribution (including connected pores and isolated pores), pore number, pore porosity and hydraulic conductivity are analysed and quantified. The results show that the variation in the 2D porosity distribution curve continuously decreases in size and reaches the smallest size in the third cycle. Interestingly, the variation in the connected pore porosity is greater than that of the porosity obtained based on all pores as well as isolated pores. The cycles make the soil shrink, the drying effect reduces the connectivity of the pore space, and the number of isolated pores increases; the wetting effect contributes to the recovery of the lost pores and connections, and the pore space and porosity increase after wetting. In addition, the hydraulic conductivity decreases due to the connected porosity, the pore/throat radius decreases, and the connected macropores play a decisive role in the saturated hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Inverse modeling of in-situ experiments is already a standardized approach for identifying various types of material parameters. In this contribution we are focused on the single ring (hereafter SR) infiltration experiment, which is a standard and robust dynamic field experiment. The steady state part of this experiment is traditionally used for the identification of saturated hydraulic conductivity. We explore here the possibility of extending the applicability of this experiment for evaluating the hydraulic parameters for unsaturated conditions from an unsteady part of this experiment for the top soil layer using inverse analyses of the governing flow motion equation. The problem of SR infiltration is governed by the quasilinear Richards equation. We present a new scanning methodology to avoid convergence issues with the nonlinear operator, originating from difficult combinations of input parameters, which can be hard to avoid when automatically analyzing a broad parameter space. We validated our methodology with virtual infiltration problems for clay and sand, and applied it on real-world SR infiltration data. To evaluate non-uniqueness, local optima were identified and mapped using a modified genetic algorithm with niching. Our results show the existence of multimodality in, both, the benchmark problems and the real-world problem. This is an important finding as local optima can be identified, which are not necessarily physical and also for systems that do not exhibit multimodal grain size distributions. The identified local optima were distinct and showed different retention and hydraulic conductivity curves. The most physical set of SHP could be identified with the knowledge of the saturated water content. [ABSTRACT FROM AUTHOR]

• The effects of slope position on soil erodibility were quantified by multi-indicators. • Different trends were detected in nine erodibility indicators with slope position. • CSEI increased from upper to middle and then decreased quickly to lower position. • SOM and PC th were the dominant factors influencing the variation in CSEI. The position of the rolling hill slope has considerable effects on soil properties and crop growth via the spatial heterogeneity of erosion intensity, which in turn probably impacts soil erodibility. However, few studies have been carried out to quantify the potential effects of slope position on soil erodibility indicators on long gentle slope. This study aimed to quantify the spatial variations in soil erodibility indicators of soil cohesion (Coh), saturated hydraulic conductivity (K s), mean weigh diameter (MWD), mean number of drop impact (MND), soil penetration resistance (PR), soil structural stability index (SSI), soil erodibility of K factor, slaking rate (SR), organic matter content (SOC) and a comprehensive soil erodibility index (CSEI) on two typical rolling hill slopes in northeast China. Soil properties, root mass density (RMD) and litter mass density (LMD) were determined to explain the spatial change of soil erodibility indicators with slope position. The results showed that Coh, MWD, MND, PR and SOC declined from upper to middle, and then increased continuously until to lower position. The distinctly opposite changes were found in K s and SR with slope position. No distinct variation was observed in K factor and SSI with slope position. For both two slopes, CSEI increased from upper to middle, and then decreased quickly to lower position. Compared to middle position, the mean reduces of two tested hillslopes were 51.72%, 14.74%, 24.28% and 72.52% for upper to lower positions, respectively. The results of Path analysis showed that SOM was the main factors contributing to the variation of CSEI with slope position. This study confirmed that the middle position is the most susceptible area to erosion on long gentle rolling hillslope. The results are helpful to understand the spatial variation in soil erosion intensity and design soil conservation measures on long gentle slopes. [ABSTRACT FROM AUTHOR]

Efficient simulation of water-flow processes in the vadose zone is crucial to increase agricultural productivity within environmental limits. This requires deriving detailed soil hydraulic parameters of the soil profile that is highly challenging, particularly for heterogeneous soils. We therefore developed an alternative indirect methodology to calibrate the hydraulic parameters from soil water content time series measured at multiple depths by using the new physically based hydrological model HyPix. We propose a novel, efficient, multistep optimization algorithm for layered soils that derives an optimal set of hydraulic parameters for a desired number of soil layers. For each selected soil layer, HyPix derives five physical, bimodal, Kosugi hydraulic parameters that describe the soil water retention and hydraulic conductivity by using a novel algorithm that reduces the degree of sensitivity and freedom of the parameters. The optimization algorithm upscales the soil hydraulic parameters by gradually incorporating the soil heterogeneity. This method overcomes the problems associated with optimization of the hydraulic parameters of each layer individually, which leads to poor results because it does not represent the cohesive soil water dynamics across the unsaturated zone. We tested the method using soil water content measurements at different depths at five heterogeneous experimental sites in New Zealand. We show how the accuracy of the simulated water balance components increases with the number of soil layers. The multistep optimization upscales a detailed, layered profile of soil hydraulic parameters into a model with fewer layers. The methodology developed provides an estimate of the uncertainty of using a reduced number of soil layers. We also show that a pedological description can provide an indication of the minimum soil layers of vertical discretization required to accurately compute the soil water balance components. • A hydrological model that solves the Richardson–Richards' equation allowing vertical scaling of hydraulic properties. • Vertical multistep optimization of bimodal Kosugi hydrological parameters for layered soils. • Accuracy of simulated water balance components and soil water content with different number of soil layers. • Soil description informs the vertical discretization required to compute water balance components. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Graphene is tested as soil improver and compared with classical ones. • Graphene changes dispersivity and specific retention in sandy soils. • Graphene did not alter hydraulic conductivity, total and effective porosity. • Graphene allowed a faster heat transfer in the soil. In this study, for the first time, the changes in relevant hydraulic parameters (e.g., hydraulic conductivity, effective porosity, and dispersivity) induced by the introduction of graphene in a calcareous sandy soil and a siliciclastic riverine soil were monitored and modelled via leaching column experiments. Column experiments were also run with traditional soil improvers (compost, biochar, and zeolite) to compare the changes induced by graphene versus well-studied soil improvers. Constant pressure head tests were used to calculate the hydraulic conductivity of each column, while leaching experiments were run to estimate porosity and specific retention, and for each treatment three replicates were done. Columns were then run in saturated conditions via a low flow peristaltic pump and monitored for electrical conductivity, temperature, and chloride. CXTFIT 2.0 was employed to inversely model the column experiments and retrieve parameters like effective porosity, longitudinal dispersivity, bulk thermal diffusivity, and thermal retardation factor. Results highlighted small changes of hydraulic conductivity, porosity, and effective porosity induced by graphene addition (as well as by the other soil improvers) for both soils. A marked increase (nearly 20 %) of specific retention values was instead recorded in the amended columns with respect to control ones. Chloride breakthrough curves modelling showed that graphene doubled dispersivity in the calcareous sandy soil (5.82 ± 1.4 cm) compared to the control (2.6 ± 0.29 cm), while it halved dispersivity in the siliciclastic riverine soil (0.31 ± 0.05 cm) with respect to the control (0.65 ± 0.06 cm). Thermal retardation factors were decreased by graphene by approximately 20 % for both soils. The model fitting via TDS (derived from the electrical conductivity monitoring) produced unreliable dispersivity values in most of the experiments due to the nonconservative nature of this parameter compared to chloride. The results highlight that graphene affected dispersivity but did not significantly alter other physical parameters relevant for solutes transport in sandy soils in comparison to classical improvers, thus future studies should focus on the graphene's effects on nutrients and agrochemicals leaching in unsaturated flow conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A paired site study to explore land use effects on soil hydraulic properties (SHPs). • Maize cropping degraded SHPs relative to pasture grazing in two contrasting soils. • Interaction effect on SHPs existed between land use and soil depth but not soil order. • Maize cropping in Gley soils had greatest SHP degradation. Soil hydraulic properties (SHPs), including available water content and near-saturated hydraulic conductivity (K ns), affect hydrological and biochemical processes. The SHPs information is crucial to agricultural water management. The objective of this study using paired sites was to investigate the effects of land use on SHPs in two contrasting soil orders. Soil water retention curves and K ns at three soil depths (0–10, 10–20 and 20–30 cm) were measured under two land uses (pasture, consisting of a rye grass [ Lolium perenne L.] and white clover [ Trifolium repens L.] mix, and maize [ Zea mays L. ] cropping > 10 years) in Waikato, New Zealand. For each land use, two soil orders with contrasting soil structural vulnerability were selected: less vulnerable Allophanic soil and more vulnerable Gley soil. Compared with pasture, maize cropping reduced macroporosity, readily available water capacity and K ns of 0–30 cm, and the effect was greater in the deep layer (20–30 cm). This indicated that maize cropping practices result in greater structural degradation to soils compared with pasture, which include the potential for greater subsoil compaction. There was no land use by soil order interaction effect on SHPs, suggesting that the relative SHP degradation under maize cropping compared with pasture grazing was not associated with soil structural vulnerability. Our study emphasised that long-term continuous cropping with maize on the more vulnerable soil (i.e. Gley soil) resulted in the poorest soil physical health. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microplastics reduced the infiltration and retention of clay and sand soil water. • Microplastics impacted clay soil with higher organic content more. • Microplastics caused soil pore size and number to decline. • Residual plastics in agricultural soils need to be managed to maintain soil quality. Microplastic pollution and changes to soil hydraulic characteristics affect the physical properties and functions of soil; however, knowledge remains limited on how microplastics influence soil hydraulic properties. Nonetheless, it is important to understand these relationships to maintain soil health and ensure sustainable land use, especially in the current "plastic age." This case study explored how different particle sizes (20, 200, and 500 μm) and concentrations (up to 6%) of polypropylene microplastics affect the hydraulic properties of three soil textures (loam, clay, and sand). The results show that addition of microplastic reduced the saturated hydraulic conductivity (Ks) of the three soils by 69.79%, 77.11%, and 95.79%, respectively. These observed adverse effects of microplastics on the infiltration properties of the three studied soils were influenced by particle size, with larger particles having the weakest effect. Furthermore, microplastic addition reduced the water retention capacity of the clay to a greater extent than that of the loam and sand. In the case of clay, the slope of the water characteristic curve (SWRC) increased significantly, whereas the saturated water content (θs) and residual water content (θr) curves decreased significantly. Importantly, the interaction between microplastics and soil alters the soil pore-size distribution and reduces pore availability. Overall, this case study demonstrates the impact of microplastic on the hydraulic properties of different soil textures, which can inform management strategies to minimize the adverse effects of microplastic accumulation on yields where plastics are used in agricultural production. [ABSTRACT FROM AUTHOR]

• Loess admixture to sandy subsoils increases their water retention. • Loess admixture to sandy subsoils decreases their K sat. • SOM content of sandy soils enhances their water retention and porosity. The admixture of loess in soils formed in sandy parent materials has considerable impact on pedogenesis and soil ecological functions. This study aimed to evaluate these effects on soil hydrology by quantifying the relationships between loess content and soil hydrological properties in a sandstone landscape covered by Pleistocene periglacial slope deposits in central Europe. Studied properties were saturated soil water capacity, field capacity, permanent wilting point, available water capacity, macro-porosity, matrix porosity and saturated hydraulic conductivity. The effect of loess addition on soil hydrological properties differed between topsoil (pedogenic A horizons) and subsoil (pedogenic B and C horizons). In the subsoil, the studied soil hydrological properties were mainly controlled by loess content. By contrast, in the topsoil the effects of loess content on soil hydrological properties were largely masked by the effects of soil organic matter (reflected by soil organic carbon, SOC). The enhancing effect of SOC on soil hydrological properties was most prominent for saturated soil water capacity and was also significant for all other parameters except permanent wilting point. After the effects of SOC were accounted for, the residual effects of loess on soil hydrological properties were the same in both topsoils and subsoils, with one exception: Saturated hydraulic conductivity decreased with increasing loess content for subsoils, but not for topsoils. This study highlighted the ecohydrological significance of loess admixture in coarse-textured soils, especially for subsoils with low SOC contents. However, for coarse-textured topsoils, SOC content plays the dominant role in affecting soil hydrological properties. [ABSTRACT FROM AUTHOR]

• Novel workflow for coupled full waveform inversion (CFWI) was proposed. • CFWI outperforms coupled inversion of travel times to invert hydraulic properties. • A range of challenges remain for the application of CFWI to real GPR data. Coupled inversion is a promising technique for determining soil hydraulic properties from time-lapse geophysical measurements. In this inversion approach, a hydrological model is coupled with ground penetrating radar (GPR) forward modelling to avoid interpretation errors from data processing. In this study, a workflow for coupled GPR full-waveform inversion (CFWI) is proposed that combines the benefits of coupled inversion and full-waveform inversion (FWI) to estimate soil hydraulic properties from time-lapse horizontal borehole GPR measurements. In particular, a synthetic modelling study is presented that compares the performance of coupled inversion of full waveforms and first arrival time data from zero-offset profile (ZOP) borehole measurements obtained during an infiltration event for estimating hydraulic parameters and the thickness of the first layer for a 2-layer soil profile. It was found that the thickness of the first layer could be more accurately estimated by CFWI because of the additional information contained in reflected and refracted waves from the air–soil layer boundary. Furthermore, the hydraulic parameters estimated by the coupled inversion of GPR travel times slightly deviated from true values and showed a relatively large uncertainty, whereas the results of CFWI precisely matched the known water retention and hydraulic conductivity functions. Despite these promising results, several challenges should be solved before CFWI can be applied to experimental GPR data. First, conducting CFWI needs accurate conceptual setups for the hydro(geo-)logical model. Furthermore, a robust approach should be developed to accurately estimate an effective source wavelet from the experimental ZOP data, and a more sophisticated hydrological modelling approach has to be considered to better estimate the distribution of soil electrical conductivity during the infiltration event. Finally, the accuracy and efficiency of current GPR modelling methods may need to be improved. [ABSTRACT FROM AUTHOR]

Nature-based solutions to engineering challenges are essential to limit climate change impacts on the urban environment. Quantitative understanding of multiple "engineering functions" provided by soil-plant interactions of different species is needed for species selection and re-establishing natural processes affected by urbanisation. Contrasting herbaceous species (legumes, grasses, and forbs) were selected and grown as monoculture or species mix in soil columns for a five-month growing season. Saturated hydraulic conductivity was initially tested for each column, and then the columns were monitored for three-weeks of evapotranspiration. Water loss, matric suction, and penetrometer resistance were measured. Finally, soil was tested for aggregate stability and water retention. Saturated hydraulic conductivity of vegetated soil was generally larger than that of fallow soil (6.9e−6 ± 1.4e−6 m/s in fallow soil). Saturated hydraulic conductivity was significantly different between species (e.g., from 9.9e−6 ± 1.3e−6 m/s in Festuca ovina to 3.9e−5 ± 1.2e−6 m/s in Lotus corniculatus) and was negatively correlated with specific root length. The water stored in the soil was efficiently removed by plant transpiration (> 60% of evapotranspiration). Large changes in soil structure were observed in vegetated soil, with significant increases in soil strength, aggregate stability, and alteration of water retention properties. Multiple soil-plant interactions influence species selection for optimising nature-based solutions (e.g., bioretention barriers). Substantial scope exists to choose species mixes to manipulate soil hydro-mechanical properties. Enhanced biodiversity did not compromise the engineering services of nature-based solutions (e.g., water removal), and may have multiple benefits. • Contrasting herbaceous species were investigated for multiple soil-plant interactions. • Saturated hydraulic conductivity of soil significantly differed between species. • Plants significantly affected aggregate stability and water retention properties. • We can enhance biodiversity without compromising the engineering services. • There is a substantial scope to choose species to manipulate soil properties. [ABSTRACT FROM AUTHOR]

• Soil hydrological properties are improved after 20 years of vegetation restoration. • Shrubland and forest have higher K S than grassland and cropland in the Loess Plateau. • Soil porosity and bulk density explain 93.8% of soil hydrological properties variation. • Locally-developed PTF of K S using bulk density, Clay and Silt shows good performance. Soil hydrological properties play a key role in soil hydrological processes. However, the effect of long-term vegetation restoration on soil hydrological properties and the corresponding influencing mechanisms remains poorly understood. Here, three soil hydrological properties including saturated water-holding capacity (SWHC), field capacity (FC) and saturated hydraulic conductivity (Ks), as well as several basic soil properties in the Zhifanggou watershed of the Loess plateau were investigated. The variations in SWHC, FC and Ks under different vegetation restoration types and their dominant influencing factors were analyzed. Moreover, we collected available Ks data from peer-reviewed publications to determine the land use with the largest Ks across the entire Loess Plateau. The results showed that SWHC FC and Ks were increased after 20 years of vegetation restoration. The higher Ks was found in shrubland and forest in the whole Loess Plateau. Compared with cropland, Ks in shrubland was increased by 87.10% at 0–20 cm, 48.89% at 20–40 cm, and 18.37% at 40–100 cm, respectively, indicating that the impact of revegetation on Ks were most obvious in the upper soil layer. Bulk density (BD), total porosity (TP), capillary porosity (CP), noncapillary porosity (NCP) and soil organic matter (SOM) had a significant effect on SWHC, FC and Ks for different land-use types (P < 0.01). Soil porosity (i.e., TP, CP and NCP) and BD, soil chemical properties (i.e., SOM and pH), and soil particle composition explained 93.8%, 59.2%, and 13.4% of the total variance in soil hydrological properties (i.e., SWHC, FC and Ks), respectively. This indicates that soil porosity and BD are the dominant factors affecting soil hydrological properties. Moreover, soil particle composition played an important role in regulating Ks, with the contribution of 38.6%. The established pedotransfer function (PTF) of Ks using BD, clay and silt content had a better performance than two existing PTFs. This research provides a more systematic and comprehensive understanding of the soil hydrological effect of vegetation restoration in the Loess Plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • The HS and MS fires significantly affected the forest soil and vegetation. • The soil properties altered by HS and MS fires had not returned to normal 19MAF. • The fire-affected soil properties had returned to normal within 10 years. • The first three years were a crucial period for post-fire revegetation. • Complete recovery of the vegetation needs a longer period than a decade. The Hengduan Mountains are frequently disturbed by high-risk wildfires. However, insufficient information is available on post-fire temporal trends in soil properties and revegetation of areas with various fire severities. To address this gap, two adjacent wildfires that occurred in 2010 and 2018 were selected. The study areas were divided into low (LS), moderate (MS), high (HS) severity fire burned areas and unburned (as control, UB) areas. Temporal trends in soil properties (0–5 cm): soil water repellency, saturated hydraulic conductivity, bulk density, soil moisture content (SMC), and soil organic matter content (SOM) were measured by in-situ and laboratory tests at 1, 7, 19 months (1MAF, 7MAF, 19MAF), and 10 years after the fires (10YAF), respectively. Temporal trends in post-fire revegetation were evaluated via on-ground surveys and remote sensing images. The statistical analysis results showed that the HS and MS fires significantly altered the soil properties and resulted in a remarkable decrease in vegetation coverage, leading to substantial bare soil 1MAF. The soil properties of the HS and MS fire burned areas had not recovered to normal due to the significantly decreased SOM and SMC 7MAF and 19MAF, and they had recovered to the pre-fire level 10YAF. The first three years following the fires were a crucial period for revegetation, during which the shrubs and bryophytes rapidly recovered, causing a rapid increase in vegetation coverage, and a corresponding sharp decrease in the coverage of bare soil. The incompletely recovered pines of the HS and MS areas provisionally resulted in a degeneration of the forest stand within a decade after the fire. We conclude that the fire-affected soil properties can return to normal within 10 years, and complete recovery of the vegetation requires a longer period than a decade. These results may provide scientific guidance for post-fire management of the burned area. [ABSTRACT FROM AUTHOR]

The environmental impact of subsurface drainage and agricultural activities has been widely studied in the literature. Agricultural subsurface drainage modifies the hydrological behavior and accelerates the transfer of pollutants of agricultural origin into surface water during the drain flow period, which is often limited to winter. The main objective of this study is to present a modeling approach allowing an accurate modeling of subsurface drainage discharge and prediction of drain flow start times, by integrating a new conceptual soil reservoir, managing the water flow in the unsaturated zone, to the SIDRA model. A comparison of the model results with field measurements of drainage discharge at the "La Jaillière" site (France) shows that such a model can efficiently simulate drainage discharge (KGE values >0.75) and predict, with good accuracy, the drain flow start time (with a median value of 5 days and a standard deviation of 10 days). The split simple test conducted for the model calibration and validation shows that the model is temporally robust. A sensitivity analysis conducted using the Sobol method on the five model parameters reveals that the drainage discharge simulation is mainly sensitive to the hydraulic conductivity and drainable porosity parameters. On the other hand, the date delimiting drain flow start is sensitive to the soil reservoir parameters. The model's ability to accurately predict the start of drain flow serves to avoid the application of farm inputs (pesticides or fertilizers) during this critical period in order to limit their transfer to surface waters. • Drain flow start is a critical period for fertilizer and pesticide losses in an SD network. • A model has been developed to simulate SD discharge and drain flow start time. • This model requires limited input data and four calibration parameters. • Field observations have confirmed the accuracy of this model. • The model can be used as a farm input management tool in order to prevent losses to surface water. [ABSTRACT FROM AUTHOR]

• Gibbsite, hematite/goethite ratio and biological activity influence the degree of microaggregation. • The microgranular structure promotes a better-connected pore system. • A better-connected pore system improves saturated hydraulic conductivity - K sat. • The 2D and 3D analyses are complementary in the study of the porous system. Structure and porous geometry are dynamic soil parameters that control several soil processes and functions. This study details the differences in the structure of typical Oxisols regarding the clay amount, biological activity, and mineralogy. Combining 2D and 3D image analysis can provide detailed information about the soil structure and porous system. The objectives of this study were: (i) to describe the soil microstructure and degree of microaggregation; (ii) to quantify porosity, soil pore types, and soil pore size distribution using 2D and 3D techniques; and (iii) to better understand the relationship between the porous system and the biological, chemical, mineralogical, and physical properties of the soil. The study considered four Oxisols: Xantic Kandiustox (P1), Rhodic Haplustox (P2), Anionic Acrustox (P3), and Typic Hapludox (P4). The results showed that all Oxisols have some degree of microaggregation. The Rhodic Haplustox (P2) had the most pronounced degree of microaggregation, which reflects the greater biological activity and gibbsite/kaolinite ratio, and lower hematite/(hematite + goethite) ratio compared to the other Oxisols. The pore types found by 2D analysis were complex pores in P1 and P2 and rounded pores in P3 and P4. The 3D analysis showed that P2 and P3 have a more connected porous system compared to the other Oxisols, evidenced by the lower value of the Euler number. The best connectivity values of the porous system were congruent to improved saturated hydraulic conductivity measured in a separate sample set. [ABSTRACT FROM AUTHOR]

• Pore fluid concentration strongly affect the geotechnical properties of marl soils. • High retention ability of lead contaminants by marl soil is due to their high carbonate content. • Marl soils can retain lead contaminant up to 200 cmol/kg soil. Most of the industries in the south of Iran and north of the Persian Gulf are built on marl bedrocks and these industries are major sources of heavy metal pollutants. Therefore, the engineering properties of marl soils contaminated with heavy metals (particularly lead ions) are worthy of thorough investigation. This was accomplished by artificial contamination of marl soil with varying lead concentrations and measurment of some geotechnical (granularity, Atterberg limits, compressive strength, and permeability) and geo-environmental (CEC, pH, and contaminant retention) characteristics. In addition, with the aid of X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images the changes in mineralogy and microstructural behavior of lead-contaminated soil were investigated. According to the findings of the present study, marl soil can hold about 200 cmol/kg-soil of lead concentration. As seen by SEM images, the lead precipitation changed the soil's geotechnical properties by altering the structure and texture of soil (notably flocculation). At 100 cmol/kg-soil lead concentration, the compressive strength was reduced by about 85%, while the hydraulic conductivity increased up to 170 times. Adding lead to the marl soil decreased the intensity of X-ray diffraction peaks for the main clay minerals and created new peaks associated with precipitated cerussite, shannonite, and leadhillite. [ABSTRACT FROM AUTHOR]

[Display omitted] • X-ray CT was used for soil cores pore network determination. • Model allowed for permeability estimation for non-percolating macroporous cores. • Soil core to soil matrix Ksat ratio is correlated to macroporosity for non-percolated cores. • Only 2% of sample volume handles 82% of the total flux of percolated and 34% of non-percolated samples. The saturated water flow phenomenon is determined by the soil pore transport processes occurring at a micro-scale. In this study, saturated water flow was modeled using two different approaches, depending on the existence of the percolating macropore network. The soil material comprised 26 undisturbed soil cores. Soil samples were scanned using an X-ray micro-CT scanner, and saturated hydraulic conductivity (Ksat), bulk density and particle size distribution were measured. The voxel size for X-ray CT scans of soil cores was 23.6 µm, which allowed soil macropore network discrimination. The macropore network was percolating in 11 samples, while the remaining cores were not. A typical approach based on Navier–Stokes (NS) equations was used for saturated water flow modeling in the case of a percolating samples. In the case of cores with a non-percolating macropore network, the NS modeling approach could not be used. An alternative method of modeling (NS/Darcy) was used in this case, blending: regular NS flow in the well-defined macropores with the Darcy–Forchheimer flow in the remaining part – the soil matrix. Soil matrix is treated by the NS/Darcy model as a pore medium without well-defined pore geometry but with some intrinsic permeability incorporated in the model using the Darcy–Forchheimer equation. Unlike the NS approach, the NS/Darcy model allowed for the simulation of water flow for all soil samples, including those where the macropore network was not percolating. Based on simulations, the Ksat was estimated used for model validation. The analysis of results leads to the proposal of a new hybrid modeling approach, mixing the NS and NS/Darcy modeling approaches. A good estimation of the Ksat was obtained using the proposed model (R2 = 0.61). The NS/Darcy modeling approach was used for the analysis of the macropore flow in the soil media. The simulations show that water permeates through the core, but macropores are a favorable flow path if they exist, even if they are not directly connected to each other. The areas of the soil cores taking part in the preferential, macropore flow were quantified, showing that only a small fraction of the macropores take part in water flow both for percolating and non-percolating cores. But generally, for most of the analyzed flow-related indices, apparent differences in results between percolating and non-percolating samples were observed. Effective flow area (EFA), i.e., the sample area used for water flow with a velocity higher than the threshold velocity (U tr) was analyzed. Considering the macropore flow, only ∼2% of sample volume is responsible for: 82% of the total flux in case of percolated and 34% in case of non-percolated samples. Also, for non-percolated samples, the dependence (R2 = 0.44) between relative flux participation and the effective flow area is observed. The simulation results for the non-percolating samples revealed the relationship between the simulated saturated conductivity of the whole soil sample and the saturated conductivity of the soil matrix and macroporosity. This allowed for developing a simple multiple linear regression model (R2 = 0.98) of the soil core's hydraulic conductivity. [ABSTRACT FROM AUTHOR]

This research develops a framework for determining cyclic and transient volume changes in unsaturated expansive clays using suction-based modeling. A governing equation along with a coefficient of swell-shrink was developed with soil suction as the driving state variable. This soil property function was determined from laboratory tests using new sigmoidal formulations for the e -based water retention curve and the S-shaped swell-shrink curve along with the hydraulic conductivity curve. The model comprises of two components (soil-atmosphere and volume change) and couples material properties with climate data. Daily suction values were applied at the top boundary whereas transient swell-shrink, hydraulic conductivity curve, and time-dependent suction difference were used to obtain the velocity of an automatically refined moving mesh. Vertical deformations due to variation in soil suction were obtained from the governing equation using the coefficient of swell-shrink. Results indicated that the model adequately captures seasonal weather variations with respect to time and corroborates well with field monitoring data. This means that the model is useful in estimating total, cyclic, and transient heave and settlement in expansive clays. • A framework for cyclic and transient volume change in unsaturated expansive clays is proposed • Suction-based governing formulation along with a coefficient of swell-shrink is developed • Sigmoidal equations for water retention and swell-shrink along with hydraulic conductivity determine material property function • A coupled model is developed to capture the effect of seasonal weather on volume changes in a typical expansive clay [ABSTRACT FROM AUTHOR]

• Biochar affects the unsaturated hydraulic conductivity (K unsat) of compacted soils. • Biochar amendment improved the water retention capacity of the compacted soils. • The K unsat of soils is found to be decreased significantly after biochar amendment. • Biochar-amended soil could promote vegetation growth in bioengineered structures. This study investigates the influence of biochar amendment on the water retention and unsaturated hydraulic conductivity (K unsat) of compacted soils focusing on its potential application in bioengineered structures. Physical properties, water retention characteristics and K unsat of two different soils, such as silty sand and pure sand and amended with 5% and 10% (w/w) biochar made from mesquite were measured with the help of instantaneous profile method (IPM). The water retention capacity of the biochar-amended soil was characterised by plotting soil water retention curve (SWRC) and estimating the saturated volumetric water content (θ s), residual water content (θ r), shape parameter ' n ' and plant available water content (PAWC). The results revealed that the amendment of biochar in the soils increased the θ s (by 20–30%), θ r (60–370%) and PAWC (7–60%), and decreased the n (by 5–18%) and K unsat (one-two order). The microstructural observation showed that the hydrophilic surface functional groups and intra-pores in biochar contributed to the improved water retention, while the altered pore size distribution and porosity of the soils due to biochar amendment increased the tortuosity of the water flow path and hence reduced the K unsat. Based on the findings, biochar-amended soil is proposed to be used in bioengineered structures that could promote the growth of vegetation and improve the performance. [ABSTRACT FROM AUTHOR]

• Soil hydraulic properties vary with depth and between species of Sphagnum moss. • Tall (15 cm) samples have experimental limitations; short (5 cm) samples are better. • Soil hydraulic properties are consistent with landscape positional needs of mosses. • Must consider the ecohydrological setting of the mosses when modelling fluxes. The ecohydrological and biochemical processes responsible for the globally significant stores of carbon in northern peatlands are largely controlled by the soil's hydrophysical properties, in particular the relationship that soil water tension (ψ) has with soil water content (θ) and hydraulic conductivity (K). Despite the importance, little is known about how these relationships vary between species in different physiological Sphagnum microforms, such a hummock and hollow, as well as with depth within a profile. Complicating matters is that laboratory experiments to determine these relationships are almost always completed with 5 cm high samples, despite no real scientific evidence supporting this height. To address these shortcomings, we sampled 8 replicates/samples (moss surface to 15 cm depth) each from a S. magellanicum hollow and a S. fuscum hummock. We determined the K (ψ) and θ (ψ) relationships at various pressure heads (0 to –32 cm) and then sub-sectioned the 15-cm samples into 3x5-cm (top, middle, bottom) samples and repeated the tests. There were important differences in both K (ψ) and θ (ψ) relationships between the top, middle and bottom samples. Additionally, comparison of the average of the 3x5-cm samples versus the 15-cm samples suggested that the 15-cm samples were not a good representation due to not being fully compatible with the methodology, and that 3x5-cm samples were preferred. Using Hydrus-1D to simulate a 30-day drought period with local hydroclimatological data, we assessed whether the statistically significant differences were ecohydrologically significant when accounting for the different topographic niches of the two species. The different moss species responded differently, with S. fuscum becoming more water stressed than S. magellanicum , yet S. fuscum lost less water from soil water storage than S. magellanicum. This highlighted the critically important need to replicate the species' niche in the landscape, and not give two distinct species the same hydrological modelling boundary conditions to compare results. [ABSTRACT FROM AUTHOR]

• BEST-WR allows to determine the soil hydraulic characteristic curves. • BEST-WR works on both hydrophilic and water-repellent soils. • We validated BEST-WR using both analytical and field data. • We assessed soil water repellency in a Mediterranean wooded grassland. Water-repellent soils usually experience water flow impedance during the early stage of a wetting process followed by progressive increase of infiltration rate. Current infiltration models are not formulated to describe this peculiar process. Similarly, simplified methods of soil hydraulic characterization (e.g., BEST) are not equipped to handle water-repellent soils. Here, we present an adaptation of the BEST method, named BEST-WR, for the hydraulic characterization of soils at any stage of water-repellency. We modified the Haverkamp explicit transient infiltration model, included in BEST for modeling infiltration data, by embedding a scaling factor describing the rate of attenuation of infiltration rate due to water repellency. The new model was validated using analytically generated data, involving soils with different texture and a dataset that included data from 60 single-ring infiltration tests. The scaling factor was used as a new index to assess soil water repellency in a Mediterranean wooded grassland, where the scattered evergreen oak trees induced more noticeable water repellency under the canopies as compared to the open spaces. The new index produced results in line with those obtained using the water drop penetration time test, which is one of the most widely test applied for quantifying soil water repellency persistence. Finally, we used BEST-WR to determine the hydraulic characteristic curves under both hydrophilic and hydrophobic conditions. [ABSTRACT FROM AUTHOR]

• The saturated hydraulic conductivity differed between sub and top layer soils. • The aggregate bulk density is greater in sublayer than in top layer soil. • Greater mechanical strength of sublayer aggregates increased their K s. Soils are turned over during agronomic and environmental activities, such that the sublayer becomes the topsoil. Because subsoils have been subjected to high pressures over long periods in the field, their activities and functionality can be changed when they are shifted to the top layer. The present work objective was to investigated the mechanisms and processes affecting the structural stability, and consequently saturated hydraulic conductivity (K s), of a semi-arid soils, which were taken from < 0.3 m depth (top soils) and > 0.3 m depth (sublayers soils). Disturbed soil samples, with similar aggregate-size distribution and bulk densities, were packed in columns, prewetted with saline solution (SS), and then their K s values were determined during consecutive leaching with SS and deionized water (DI). The K s values of the various soils under SS leaching differed due to slaking and swelling processes that changed the soil structure. The effect of the slaking process on K s reduction was more significant in the top- than sublayer soils. Soil swelling under SS wetting and leaching caused mainly by penetration of water molecules into capillary pores in the soil that increases the pores volumes, and enlarges the aggregate swelling (matrix-type swelling). The average bulk density, and consequently the structural strength, of the aggregates in the sublayer soils were significantly higher than that of the top soils. This suggested that, under matrix-type swelling, less aggregates would be broken in the sublayer than in the top-layer soils. During leaching of the top and the sublayer soils with DI, the aggregates breakdown and K s reduction were caused mainly by dispersion and osmotic swelling of the clay fractions in the soil. In this case, a negative relationship between the K s and SAR values was obtained, regardless of the soil depths. [ABSTRACT FROM AUTHOR]

• NeuroFX PTFs estimate soil water retention and hydraulic conductivity curves in full moisture ranges. • NeuroFX provide uncertainty estimates of hydraulic parameters. • NeuroFX perform better than ROSETTA and BW PTFs in the same test samples. • Parameters of the hydraulic models were mapped for the whole contiguous USA. • NeuroFX is available as R codes and can be used in simulation models. Current pedotransfer functions (PTFs) for estimating soil hydraulic curves are mostly developed to predict parameters of the Mualem-van Genuchten hydraulic functions. The Mualem-van Genuchten functions are recognised to be inadequate in representing soil water retention hydraulic conductivity curves at low pressure head ranges. This study presents neuroFX, a suite of PTFs, for estimating soil water retention and unsaturated hydraulic conductivity curves from saturation to complete dryness based on the Fredlund-Xing-Wang (FXW) model. The PTFs were calibrated using the neuro-m neural networks approach with three different sets of inputs: (1) SSCBD uses the sand, silt, and clay fractions, and bulk density; (2) SSC uses the sand, silt and clay fractions, and (3) soil textural class input. NeuroFX PTFs were trained using fitted parameters of the FXW model from selected data in the UNSODA database and validated using 5-fold cross-validation that was repeated 10 times. NeuroFX provides an uncertainty estimate of hydraulic parameters. The prediction quality of neuroFX was compared with two existing PTFs: ROSETTA and Brunswick-Weber (BW) PTFs. Based on multiple criteria, we found that neuroFX performed better than ROSETTA and BW PTFs in the same test sample. NeuroFX PTF with the SSCBD input yielded the best prediction of soil water retention and unsaturated hydraulic conductivity curves with RMSE in water content of 0.052 cm3 cm−3 and RMSE in log 10 (K) = 0.732 (in the magnitude of cm day−1), indicating the importance of including bulk density in the input of PTFs. NeuroFX was then used to map parameters of the FXW model for the whole of the continental USA over 6 depth intervals. The code of neuroFX in R software is available in Supplementary Material 1. [ABSTRACT FROM AUTHOR]