Water-saturated Soil Research Articles

Investigating the controls on greenhouse gas emission in the riparian zone of a small headwater catchment using an automated monitoring system

AbstractRiparian zones as the transition zone between terrestrial and aquatic ecosystems play an important role in C and N cycling and greenhouse gas (GHG) emissions. As such, they may help to mitigate climate change but could also accelerate it, depending on the particular processes affected by changes in the hydrologic regime. Hydrological observations indicated frequent shallow groundwater in the riparian zone, especially near the stream and during the wet winter and spring seasons with consequently frequent occurrence of soil water saturation. The redox potential was mainly governed by the soil water regime: under water saturation conditions, the redox potential of the soil decreased and returned to the oxic state after soil drainage. We found that soil temperature and soil water content were the main drivers of the variations in CO2 fluxes, with highest CO2 emission during summer and the lowest emissions in the winter period (162.2–5.4 mg CO2–C m−2 h−1). The annual average daily N2O emission rate was low (2.3 μg N2O‐N m−2 h−1), with the highest average daily N2O emission in March as a result of low temperature and partial soil saturation after heavy precipitation events (37.5 μg N2O‐N m−2 h−1). Our study showed that continuous measurement of redox potential, soil temperature, and soil water content can improve the understanding of GHG emissions in riparian zones.

Changing controls of soil water retention in an alpine catchment: Integrating sedimentological and pedological processes

Soil’s hydrological and ecological functions depend largely on soil water retention, which is affected by both structural and compositional soil properties. Studies have shown that alpine soils derived from sediments with different origins in the northeast Qinghai-Tibetan Plateau differ significantly in terms of particle size distribution, bulk density and soil organic carbon content. However, the variation pattern and its drivers of soil water retention in this region remain unclear. In this study, soil water retention characteristics (saturated soil water capacity, field capacity, wilting point and plant available water capacity) from different geomorphic settings (i.e., hillslopes, alluvial fans and floodplains) of an alpine catchment in the western part of the Qilian Mountains were analyzed in relation to sediment types and soil properties. Results show that soil water retention varies significantly with sediment types. Soils with an aeolian origin have a higher capacity to retain water compared with soils developed on fluvial sediments. Variations in soil water retention are mainly controlled by particle size distribution for fluvial sediments and by soil organic carbon content for aeolian sediments. The accumulation of soil organic carbon enhances plant available water capacity for sandy fluvial sediments but not for silty fluvial and aeolian sediments. The critical eco-hydrological functions of the mattic surface soil horizon in relation to water retention, runoff regulation and erosion control were highlighted for the alpine ecosystems. By deciphering sedimentological and pedological controls of soil water retention, this study improves the understanding of the evolution and functioning of alpine soils, which has further implications for other sedimentary ecosystems.

A new quasi-3-D model with a dual iterative coupling scheme for simulating unsaturated-saturated water flow and solute transport at a regional scale

Soil water in an unsaturated zone is the major source of groundwater recharge, and likewise soil contaminants are the major source of groundwater contamination. It is thus essential to jointly consider soil water movement and solute transport together with groundwater movement and solute transport, which is particularly important when addressing regional-scale problems. This study developed a new quasi-3-D model for simulating regional-scale saturated–unsaturated water movement and solute transport in arid and semi-arid agricultural areas. The unsaturated soil water movement and solute transport processes are simulated by a 1-D soil water and solute transport model referred to as UBMOD, and the saturated groundwater movement and solute transport are simulated by MODFLOW and MT3DMS. In the quasi-3-D model, the soil water movement and groundwater movement modules are iteratively coupled and the soil solute transport and groundwater solute transport modules are iteratively couple. This is referred to as a dual iterative coupling scheme. Strength and weakness of the quasi-3-D model and the coupling scheme were evaluated with two synthetic cases and a real-world application. Results indicate satisfactory performance of the model, which demonstrates the reliability of the dual iterative coupling scheme. Besides, the impacts of spatial and temporal discretization and stress period on model stability and accuracy has been evaluated. And the model is more computationally efficient than the fully numerical methods based on Richards’ equation when the problem is a 2D/3D problem with a scale larger than 10 m. Moreover, the application to the Hetao Irrigation District indicates that the developed model is effective and efficient for the real-world regional-scale agricultural problems. Above all, it is concluded that the new model is more suitable than existing models for simulating regional-scale unsaturated–saturated soil water movement and solute transport in arid and semi-arid agricultural areas.

Carbon supply–consumption balance in plant roots: effects of carbon use efficiency and root anatomical plasticity

The growth and maintenance of the plant root system may consume more than 50% of all photosynthates, making the root system a major carbon sink (Lambers et al., 2002). Carbon is supplied to roots via sieve tubes that are located in the phloem of the root stele, and is consumed for anabolic and catabolic processes. In a recent paper, Kong et al., (2021) proposed a framework to assess the carbon supply-consumption balance in plant roots that bridges root anatomical structures and root functioning using 'structural allometric relationships'. Their framework highlights the pivotal role of root radius and associated anatomical properties such as sieve tube radius and the size and number of root cells for the carbon supply-consumption balance.

The role of biochar particle size and application rate in promoting the hydraulic and physical properties of sandy desert soil

Enhancing the resistance of sandy desert soil to drought and wind erosion is key to controlling aeolian desertification. Using biochar as an amendment can improve soil quality. This study aimed to determine the impacts of biochar particle size and application rate on the hydraulic and physical properties of sandy desert soil. Biochars were produced by pyrolyzing corn straw at 500 °C with limited oxygen. Samples of sandy desert soil were collected from the Tengger Desert in Northwestern China. Tests were designed with three biochar particle sizes (0–0.25, 0.25–1, and 1–2 mm) and five biochar application rates (wt%: 0, 0.5%, 1%, 2%, and 4%). Soil hydraulic and physical properties were characterized by the soil–water characteristic curve, soil porosity, soil specific surface area (SSA), and soil structural index (SI). The results showed that biochar significantly increased the soil porosity and the number of extreme micropores, micropores, and small pores. As a consequence, the saturated soil water content (θs), permanent wilting point (PWP), field capacity (FC), and available water content (AWC) were significantly enhanced. The significant improvement in SI demonstrated that biochar enhanced the soil aggregate stability, therefore, the resistance of sandy desert soil to wind erosion is enhanced. Biochar dosage was a more important factor that influenced the FC, AWC, PWP, SI, and SSA of the soil more than biochar particle size. The properties of θs, PWP, FC, AWC, and SI were all closely related to SSA, indicating that SSA played a key role in the mechanism affecting the response of the soil to biochar application. The significant increase in water retention and aggregate stability of sandy desert soil with added biochar suggests a novel strategy to control aeolian desertification by amending the soil.

Concomitant tracking of NH3, N2O and soil mineral-N using steady-state incubation cells to enhance sustainability of urea fertilization approaches

Enhancing nitrogen use efficiency to assure sustainable intensification of crop production, while minimizing N-environmental threats, is a major challenge. These drive important developments of N-fertilization approaches and enhanced efficiency N-fertilizers (EENFs). The complexity of N-dynamics under different soils, environmental conditions, and application modes requires improvement of decision-making tools. Meta-analyses demonstrate the contribution of EENFs to sustainable intensification. Yet, improvements based on local field specific information, and particularly with new N-fertilization approaches, are needed. This project focuses on an upgraded laboratory designed steady state incubation system connected to a Long-Path gas cell mounted on an FTIR spectrometer, allowing fast determination of NH3 and N2O emissions concomitant with mineral N-dynamics in soils under different N-fertilization approaches. The system was tested with four representative soils, fertilized with surface applied urea or urea amended with urease inhibitors (UI). Different soil water saturation (WS) levels and urea application rates were tested over 14 days of incubation·NH3 losses (%N-applied) in the steady state system were 2 to 7 times higher than in the previously designed non-steady state system. Highest losses were observed when urea was applied to lighter soils with pH above 7.5 (~13% to 46%), especially under low (30%) water saturation (WS). Substituting to UI reduced the accumulated NH3 losses (14 days) by 55 to 92%. Highest N2O losses were obtained with the lighter soils (1.2% to 1.7%) at 50% WS and lowest urea application rate. UI assisted in reducing N2O losses in some of the tested soils, showing different dependencies on WS and urea concentration. This variety demonstrates the complexity of the N-processes involved under different soils and conditions, and was also expressed in the mineral-N concentrations. This simple experimental design has the potential to improve our insights and help evaluate EENFs sustainability.

ERECTION OF FOUNDATION-BASEMENT PART OF UNDERGROUND STRUCTURES IN WATER-SATURATED SOILS OF ODESSA REGION

According to the General Plan of the city's perspective development, it is planned to develop the territories of the irrigation fields and the adjoining dam. The article details the engineering tasks of erecting the foundation-basement construction of underground structures considering the geological and hydrogeological conditions of the low-lying area of the Odessa region. Features of occurrence and genesis of low-lying part sites have been elaborated. The paper also elucidates the methods of orientation employed and water lowering during the erection of underground structures. Technological order of work execution for reliable and effective structural scheme of underground structures in water-saturated soils is proposed. A device for vertical waterproofing of external walls and horizontal waterproofing of the floor of an underground structure has been developed.

The influence of time on the bearing capacity of piles in water-saturated clay soils

The change in the bearing capacity of piles over time is an established fact that is carefully studied by many researchers. Depending on the type of soils and their condition, there is both a decrease (in sandy) and an increase (in clay) in the bearing capacity of piles over time. The most effective increase in bearing capacity occurs in water-saturated, clayey soils with the property of thixotropy. The results of experimental studies of soils with piles in natural conditions, carried out with different periods of their rest, are of considerable value in the study of this phenomenon. During the construction of a multi-storey residential complex in Odessa, which began in 2019, it became necessary to increase the load on the pile foundation made of prismatic piles with a length of 16 m and a cross-section of 350×350 mm. According to research in 2019, the bearing capacity of the piles was 1500 kN. In February 2021, static soil tests were carried out with the existing piles from under the grillage of the building, which was installed by 90%, while the bearing capacity of the piles was 1800 kN. Thus, for the period from July 2019 to February 2021, the bearing capacity of C160.35-11 piles at the construction site in water-saturated soils in Odessa increased from 1500 kN to 1800 kN, which is 20%.

Heat transfer by seepage in sand: Influence of saturated hydraulic conductivity and porosity

Heat transfer within the soil is a complex process in the presence of seepage flow. In such conditions, the soil’s thermal behavior is influenced by the thermal and hydraulic properties of the medium as well as the initial conditions and boundary conditions to which the medium is subjected. This paper presents the experimental and numerical studies of heat transfer within the sand subjected to the seepage flow. It focuses on the influence of saturated hydraulic conductivity and the porosity of medium on the heat transfer process. The temperature distribution within the sand was monitored by the optical fiber Distributed Temperature Sensor (DTS). The experiment was performed on three types of silica-dominated sands with different saturated hydraulic conductivities and different Soil Water Characteristic Curve (SWCC). In addition to the experimental study, a coupled hydrothermal numerical model was designed in FEFLOW software and validated by comparing its results with the experimental measurements. To determine the influence of porosity and saturated hydraulic conductivity on heat transfer, we analyzed the numerical models for different values of porosity and saturated hydraulic conductivity. The numerical and experimental studies showed that the thermal velocity is higher in sand with higher saturated hydraulic conductivity and temperature declination occurs more quickly due to the heat convection process. Saturated sand with larger porosity has an overall higher heat capacity, wherefore the temperature declination started later in the measuring points but dropped down lower close to the temperature of the upstream water.

RETRACTED: Biochar and compost amendment impacts on soil water and pore size distribution of a loamy sand soil

AbstractSoil structure, which refers to aggregates and pore characteristics, reflects the spatial arrangement of soil particles and is a key component for crop yield and soil health. Well‐formed soil structure has favorable pore size distribution, which supports soil water flow and retention and healthy plant growth. Compost and biochar, important organic amendments, have a potential to influence soil structure, but their effects on specific soil types and soil properties have not been fully investigated. The main objective of this study was to investigate the impact of the additions of compost and/or date palm biochar on selected soil water indicators and pore size distribution of a loamy sand soil using disturbed soil samples. Statistical parameters of pore size distribution properties such as SD, kurtosis, skewness, modal diameter (dmode), median diameter (dmedian), and mean diameter (dmean) as well as plant available water capacity (PAWC), available soil water capacity (ASWC), saturated soil water content, and measured saturated hydraulic conductivity (Ksat) were measured and evaluated. The results showed that the dmode, dmedian, dmean, SD, skewness, and kurtosis values for untreated soil (control) were 31.6 μm, 25.8 μm, 23.5 μm, 3.3, −0.16, and 1.14, respectively. Biochar, compost, and a mixture of biochar–compost additions to a loamy sand soil significantly reduced dmode, dmedian, and dmean values in comparison with nonamended soil. Application of these amendments increased PAWC and ASWC and reduced Ksat of the loamy sand soil, significantly. Biochar–compost mixture has the most significant effect on improving soil water retention and PAWC.

Analysis of surface runoff water and sediment generations using a short-term water budget in the steeply sloping agricultural land of northern Laos

ABSTRACT A field experiment was conducted during the rainy season of 2014, in the steeply sloping agricultural land of northern Laos to determine the factors that cause the generation of surface runoff water and sediment (i.e., soil erosion). Four treatments (upland rice cropping, maize cropping, maize cropping with mulch treatment, and bare land) were installed on a 2 square meters plot sloping 25°, or 45%. The surface runoff water was measured at 10 min intervals, and the total eroded water and sediment were collected after each rainfall event. The total rainfall during the experiment was 1,480 mm, equivalent to more than 80% of the annual rainfall, with the largest rainfall of 413 mm occurring in July. Strong rainfall, exceeding 10 mm in 10 min, occurred frequently (26 times). More than 50% of the surface runoff water and sediment were generated during the mid-rainy season. Short-term water budget analysis revealed that the amount of the surface runoff water and sediment depended on the soil surface conditions and the initial volumetric water content of the soil. Specifically, 1) rapid water infiltration and percolation suppress the surface runoff water and sediment during the early rainy season, 2) water saturation in the surface soil, clogging of soil pores, and sealing induce soil loss during the mid-rainy season, and 3) crust formation and/or clogging of soil pores induces surface runoff during the late rainy season. Mulching suppressed surface runoff generation by facilitating water infiltration into the soil and mitigating the disturbance of the soil surface by raindrops.

Centrifuge Model Tests of the Effect of the Ground Motion Coherence Function on the Amplification of a Saturated Soil–Water Site

Two sets of dynamic centrifugal model tests were designed and implemented in this study: the overlying waterless surface and the water-covered surface. Based on the use of the El Centro waves with different intensities as the base input, the seismic time history at the surface of two sets of free site models was obtained. According to the results of the site response at two sets of the free site surface obtained with a traditional spectral ratio, the coherence functions at the surface and the base were used to modify the traditional spectral ratio for analysis and to evaluate the effect of the ground motion coherence function for site amplification. The modal characteristics and the amplification effect of a typical saturated soil water free site were summarized at the same time. The results showed that the ground response results of the two groups of typical free site centrifugal models were greatly influenced by the coherence function. In the low frequency phase, the coherence function of the amplification spectrum of the site response decreased significantly, while in the high frequency phase, the decrease trend decreased. The coherence function had a significant effect on the first-order mode of the free site. The first-order mode frequency and the amplification factor of a typical free site could be identified effectively. Compared with the saturated land free site model, the saturated soil water free site model had higher-order modes due to the overlying water. It was shown that the overlying water, as part of a complex medium system, could be ignored in the site response and basic cycle estimation.

Thermal conductivity of undisturbed soil – Measurements and predictions

Soil thermal conductivity, λ, is decisive for a range of soil ecosystem services related to soil temperature. Soil functions affected by temperature comprise microbial as well as abiotic processes of importance to crop growth, leaching of nutrients, carbon sequestration, and emission of greenhouse gases. Models for crop production and climate change include λ for simulation of heat transfer in the natural environment. Nevertheless, most prediction equations for λ are based on measurements deriving from physically disturbed soil. We identified nine Danish soils with a gradient in clay from ~ 0.03 to 0.35 kg kg−1 and measured λ in situ at six soil depths from 5 to 85 cm with the heat pulse method. Soil cores were collected and used for measurements of λ at a range of moisture conditions in the laboratory. The degree of soil water saturation, S, ranged from 0.01 to 0.98, and measured λ was in the range 0.18–2.98 W m−1 K−1. A model for λ identified by multiple regression across all laboratory measurements explained 87% of the variation in data and pointed out a convex polynomial relation between S and λ. It included significant positive effects of bulk density (BD) and soil organic matter (SOM), while λ decreased with soil clay content for a given S. The stochastic model predicted λ for three independent data sets from the literature with little bias and root mean square errors in the range 0.15–0.23 W m−1 K−1. A polynomial regression of λ versus S was performed for combinations of site and soil depth. By this λ was estimated at completely dry conditions, λdry, and at the fully saturated state, λsat. The estimates of λdry as well as λsat had a wider range than reported in the literature. This study calls for re-evaluation of existing pedotransfer functions for λdry. Measurements of λ in soil of undisturbed structural conditions are encouraged.

Diffusion of perfluoroalkyl acids through clay-rich soil

Diffusion through a water saturated silty clay soil column was measured for six perfluoroalkyl acids (PFAAs), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). An aqueous pore diffusion model, which incorporated linear adsorption parameters measured independently in batch tests and a tortuosity factor determined independently using a bromide tracer test, was used to describe the experimental diffusion data. The diffusion model substantially underpredicted PFAA diffusion through the soil column for the more strongly sorbing PFAAs (most notably PFOS). Instead, application of a diffusion model that included a surface diffusion-like process provided substantially improved prediction of PFAA diffusion through the soil. The ratio of the observed pore diffusion coefficient to the observed surface diffusion coefficient ranged from 13 (for perfluorohexane sulfonate) to 0.88 for PFOS. These results suggest that surface diffusion serves a potentially important role for strongly sorbing PFAAs in clay-rich soils, and highlights the need for additional studies into the coupled adsorption and diffusion of PFAAs in low permeability media.

Towards moss biocrust effects on surface soil water holding capacity: Soil water retention curve analysis and modeling

As ecosystem engineers in drylands, biocrusts possibly generate great influences on surface soil water holding capacity and availability, but these effects have not yet been sufficiently investigated, especially through analyzing and modeling their soil water retention curve (SWRC). On the Loess Plateau of China, the naturally developed moss biocrusts and surface bare soil were sampled in five replicates on loess soil and aeolian sand respectively, and their SWRCs from saturation (soil water potential = 0 hPa) to dry (soil water potential = −15,000 hPa) were measured with a sandbox (low water potential range) in combination with a pressure plate (high water potential range). The measured SWRCs were compared to the van Genuchten (VG), Brooks and Corey (BC), and Log-Normal Distribution (LND) models, and the model with best performance was adopted to further determine the effects of biocrusts on surface soil water holding capacity and water availability through comparing the differences in soil water content (θ) at specific water potentials between the biocrusts and uncrusted soil. Our results showed that (i) the biocrusts always had higher θ as compared with the bare soil across the whole water potential range, and the increasing effects of the biocrusts was much stronger on aeolian sand (165%) in comparison to that on loess soil (15%). (ii) As compared with the bare soil, the saturated water content, field capacity, wilting point, and available water content of the aeolian sand increased by 52%, 256% (0.192 vs. 0.054 cm3 cm−3), 65%, and 1000% by the biocrusts, respectively; while that of the loess soil increased by 28%, 9% (0.240 vs.0.220 cm3 cm−3), 27%, and 8% by the biocrusts, respectively. (iii) The increased water holding capacity of the biocrusts was possibly attributed to their higher percentage (18% vs. 16%) of microscopic pores (0.3–5 μm) on the loess soil and their increasing (16% vs. 1%) microscopic pores and decreasing (18% vs. 50%) medium pores (30–75 μm) on the aeolian sand. (iv) The VG and LND models performed better (R2 > 0.98, RMSE ≤ 0.019 cm3 cm−3, RE ≤ 7.4%) than the BC model in simulating the SWRCs of the biocrusts and bare soil, and their fitting errors were mostly distributed in the high (−500 to −1000 hPa) and low (<−5000 hPa) water potential ranges. As indicated by SWRCs, we conclude that biocrusts greatly increase surface soil water holding capacity and water availability, leading in turn to a positive feedback mechanism of the biocrusted layer, which may affect surface hydropedological process (e.g., infiltration and evaporation) in drylands.

Process-Based Modeling of the High Flow of a Semi-Mountain River under Current and Future Climatic Conditions: A Case Study of the Iya River (Eastern Siberia)

The purpose of the study was to analyze the formation conditions of catastrophic floods in the Iya River basin over the observation period, as well as a long-term forecast of the impacts of future climate change on the characteristics of the high flow in the 21st century. The semi-distributed process-based Ecological Model for Applied Geophysics (ECOMAG) was applied to the Iya River basin. Successful model testing results were obtained for daily discharge, annual peak discharge, and discharges exceeding the critical water level threshold over the multiyear period of 1970–2019. Modeling of the high flow of the Iya River was carried out according to a Kling–Gupta efficiency (KGE) of 0.91, a percent bias (PBIAS) of −1%, and a ratio of the root mean square error to the standard deviation of measured data (RSR) of 0.41. The preflood coefficient of water-saturated soil and the runoff coefficient of flood-forming precipitation in the Iya River basin were calculated in 1980, 1984, 2006, and 2019. Possible changes in the characteristics of high flow over summers in the 21st century were calculated using the atmosphere–ocean general circulation model (AOGCM) and the Hadley Centre Global Environment Model version 2-Earth System (HadGEM2-ES) as the boundary conditions in the runoff generation model. Anomalies in values were estimated for the middle and end of the current century relative to the observed runoff over the period 1990–2019. According to various Representative Concentration Pathways (RCP-scenarios) of the future climate in the Iya River basin, there will be less change in the annual peak discharge or precipitation and more change in the hazardous flow and its duration, exceeding the critical water level threshold, at which residential buildings are flooded.

Unsaturated flow effects on solute transport in porous media

A major contaminant transport process in soils is hydrodynamic dispersion by affecting the spreading and arrival of surface-applied pollutants at underlying groundwater reservoirs. When a soil is unsaturated, hydrodynamic dispersion is very much affected by soil water saturation. Centimeter- and decimeter-scale column experiments were carried out to explore the effects of fluid saturation and particle size on the unsaturated solute dispersivity. Measured in-situ breakthrough curves were analyzed in terms of both classical advection–dispersion and dual-porosity (mobile-immobile) type transport equations. A clear non-monotonic relationship was found between the dispersivity and soil water saturation. The extent of non-monotonicity was more pronounced for a relatively coarse-textured sand compared to a finer sand. This finding has been reported rarely before; it explains some of the inconsistencies of saturation-dispersivity relationships in the literature.

Low mobility of CuO and TiO2 nanoparticles in agricultural soils of contrasting texture and organic matter content

The fate of nanoparticles (NPs) in soil under relevant environmental conditions is still poorly understood. In this study, the mobility of two metal-oxide nanoparticles (CuO and TiO2) in contrasting agricultural soils was investigated in water-saturated soil columns. The transport of TiO2 and CuO-NPs were assessed in six soils with three different textures (from sand to clay) and two contrasted organic matter (OM) contents for each texture. TiO2 mobility was very low in all soils, regardless of texture and OM content. Mass recoveries were always less than 5%, probably in relation with the strong homo-aggregation of TiO2-NPs observed in all soil solutions, with apparent sizes 3–6 times larger than their nominal size. This low mobility suggests that TiO2-NPs present a low risk of direct groundwater contamination in contrasted surface soils. Although their retention was also generally high (more than 86%), CuO nanoparticles were found to be mobile in all soils. This is probably related to their smaller apparent size and low capacity of homo-aggregation of CuO-NPs in all soil solutions. No clear influence of neither soil texture or soil total organic matter content could be observed on CuO transport. However, this study shows that in contrasted agricultural soils, CuO-NPs transport is mainly controlled by the solutes dissolved in soil solution (DOC and PO4 species), rather than by the properties of the soil solid phase.

Watershed spatial heterogeneity of soil saturated hydraulic conductivity as affected by landscape unit in the critical zone

The spatial heterogeneity and related driving factors of the saturated hydraulic conductivity (Ks) in the Earth’s critical zones (CZs) have been documented widely in the literature. However, information regarding the effect of distinct landscape units (i.e., Slope-land, Gully-land, and Tableland) on such heterogeneity at the watershed scale in CZs characterized by complex topographic conditions remains scant. In the current study, we collected undisturbed and disturbed soil samples from the surface soil layer (0–5 cm) at 1195 sampling sites across the ShuangChaGou watershed (0.22 km2) in the Chinese Loess Plateau (CLP). According to classical and geostatistical analyses combined with the structural equation model (SEM), the mean Ks followed the sequence Slope-land (0.25 cm·min−1) > Gully-land (0.187 cm·min−1) > All samples (0.186 cm·min−1) > Tableland (0.14 cm·min−1) (p < 0.05), with the Ks values exhibiting moderate variations except for the Gully-land (strong variation). The LogKs spatial variation characteristics (i.e., the anisotropy ratio, effective range, and C/(C0 + C)) considering the influence of topography varied among the landscape units and the entire watershed. The SEM identified that soil bulk density, saturated soil water content, silt content, plan curvature, NDVI, and slope gradient were the controlling factors in sequence affecting the Ks variation for All samples (AS). In contrast, factors controlling Ks variations were different under the Tableland, Gully-land, Slope-land, and AS. The magnitudes, spatial variations and controlling factors of the surface Ks were greatly affected by the landscape units. Our study provided a robust assessment of the spatial variation of Ks in CZs involving complicated topographic features, highlighting the utility of dividing distinct landscape units when evaluating the Ks variation. A good understanding of this information is helpful for developing distributed hydrological models and for evaluating water and solute transportation in CZs of the CLP and similar regions around the world.

Settlement and bearing capacity of water-saturated soils of foundations of finite width under static impact

Introduction. In case of brief exposure to static loads or dynamic loads, in conditions of absence of drainage, distribution of total stresses between the skeleton of soil and pore gas-containing water should be taken in account. The situation of the stress-strain state of the base is further complicated when we consider the degree of water-saturation of soil of the foundation (0.8 &lt; Sr ≤ 1). The aim of the study is to pose and solve problem of the stress-strain state of a water-saturated soil massif, Including settlement and bearing capacity of a water-saturated base of a foundation of finite width, depending on the degree of water saturation of soils, taking into account the linear and nonlinear properties of the skeleton of soil and the compressibility of pore gas-containing water.&#x0D; Materials and methods. Henckyʼs system of physical equations are used as a calculation model to describe the relationship between deformation and stresses of soil, which takes into account the influence of the average stress on the deformation and strength properties of the soil. This system allows us to represent the linear deformation of the soil as the sum of the volumetric and shear components of the soil of this deformation. In addition allows us too to determine the deformation of the layer of soil, as part of the compressible thickness of the base of foundation with finite width under conditions of free deformations.&#x0D; Results. Depending on the linear and nonlinear deformation parameters, the settlement can be developed with a damped curve (S – p) and stabilize, and can be developed with a non-damped curve (S – p) and moved to the stage of progressive settlement.&#x0D; Conclusions. Solutions have been made for cases when the water-saturation of the base soils changes in the range of 0.8 to 1.0. It is shown that the settlement and bearing capacity of a water-saturated base significantly depends on the degree of water saturation of soils.