Water-saturated Soil Research Articles

ECOPHYSIOLOGY OF THE TREE SPECIES Cedrela fissilis Vell. (Meliaceae) SUBMITTED TO FLOODING

ABSTRACT Soil water saturation requires different adaptative strategies by tree species that live under such conditions. We aimed to study the responses that ensure flooding tolerance by tree species and so provide support for recovery projects with degraded areas subject to flooding. We evaluated the ecophysiology of Cedrela fissilis under different water saturations, including anatomical traits, gas exchange parameters, antioxidant system analysis and growth. We subjected 100 day-old plants to three treatments: Control (FC) where the substrate was kept at field capacity; Flooded Roots (FR), where the substrate remained submerged but with no surface layer of water, and Flooded Stem (FS), with a water layer accumulation of around 3.0 cm over the substrate, flooding part of the stems. The plants were kept under such conditions for 90 days. Plants survived in all treatments due to a marked development of cortical intercellular spaces in flooded plants. However, photosynthesis and other gaseous exchange were limited under FR and FS treatments. In addition, the periderm thickness was reduce by flooding and there was an accumulation of starch grains in the parenchyma cells of the xylem, cortex and pith of the stem. There was also a significant lipid peroxidation on the leaves under FR and FS treatments. The superoxide dismutase activity was decreased, but the activities of the ascorbate perioxidases and catalase in the leaves were increased. We concluded that young Cedrela fissilis plants partially tolerate flooding since they developed ecophysiological changes in order to survive in this condition. Consequently, this species is a good candidate for the reforestation projects in environments where intermittent flooding occurs, such as riverside and riparian forests.

Effects of decay level of fallen trees and their formed microsite types on soil physicochemical properties in a spruce-fir forest.

To reveal the effects of decay level of fallen trees and their formed microsite types on soil physicochemical properties, the differences in soil physicochemical properties (bulk density, capillary porosity, total porosity, capillary water holding capacity, saturated moisture capacity, soil organic carbon, total nitrogen, total phosphorous, available phosphorous, available potassium, and pH) and stoichiometry (C/N, N/P, and C/P) among different decay levels of treefalls and between different microsite types in the formed gaps by fallen trees were analyzed in a spruce-fir fore-st in a valley of Liangshui National Nature Reserve in Xiaoxing' an Mountains. The results showed that the effects of the decay levels of fallen trees on soil physical properties was not significant. In contrast, we found significant effects of the formed microsite types in soil physical properties. Except for saturated soil water holding capacity, the other soil physical properties were the best under the fallen trees and the worst in the pit bottom. Except of available phosphorus, the contents of the other soil nutrients exhibited a significant increase trend with the increasing decay levels of fallen trees. Among three microsites, the contents of soil nutrients were the lowest and pH were highest in the pit. As for the shallow soil layer, C/N, N/P and C/P of three microsites decreased with the increasing decay levels of fallen trees, while C/N in mound top and in pit bottom increased, N/P and C/P decreased, and the variation of C/P was consistent with that of available phosphorus. In conclusion, with the increasing decay levels of fallen trees, the contents of soil nutrients were signifi-cantly increased. There are significant differences of soil nutrients among different microsites, with the lowest values in the pit.

Year-round cooling and thermal stabilization of water-saturated soils under engineering structures

Year-round cooling and thermal stabilization of water-saturated soils under engineering structures

Study of the Processes of Consolidation of a Thick Mass of Water-Saturated Clay Soils when Erecting Unique Structures

The paper provides the results of natural studies of consolidation of weak water-saturated clay soils of large thickness performed at the experimental sites located within the Imereti lowland (Olympic objects, Media center, city of Sochi) and a stadium in the city of Kaliningrad (Oktyabrskii island). A development of deformations, stress conditions and variation of pore pressure within the bulk of the weak water-saturated soils were studies, and the calculation results were compared to the actual deformation data.

Mathematical modelling of soil massifs strained-deformed state under soil water level decreasing

The analytical solutions for the determination of vertical displacements at any point of single-layer and multilayer soil compositions under filtration water flow influence, saline solutions presence and filtration considering soil changing filtration and deformation characteristics have been obtained. The mathematical models of soil filtration and the stress-deformed state from water-saturated ground massifs and bases deformations forecast under internal volumetric forces influence (hydrodynamic forces of the filtration flow, changes in the soils own weight) have been developed and substantiated. Numerical solutions of the corresponding boundary filtration problems and SDS of soil in regions with time-varying curvilinear boundary have been obtained for these mathematical models. They have enabled to perform water-saturated soils and bases deformations forecast under the change of hydrogeological conditions and man-made factors effect.

Effects of machinery trafficking in an agricultural soil assessed by Electrical Resistivity Tomography (ERT)

Abstract Soil compaction is a serious problem, which is aggravated due to its difficulty to locate and reverse. Electrical resistivity tomography (ERT) is a non-invasive geophysical method that can be used to identify compacted areas, soil horizon thickness and assess soil physical properties. This study assesses the relationship between ERT and soil compaction. Data were collected on a 4-m transect in a fallow plot located at Braganca (Portugal). Measurements were performed before and after tillage and tractor passage. Soil samples at different depths (0-0.05, 0.05-0.1 and 0.1-0.2 m depth) were taken to determine: soil bulk density, porosity, saturated hydraulic conductivity and soil water content. The effect of tillage and tractor passage was more significant on the first 0.05 m depth. In the wheel track areas, ERT suffered a reduction of about 40%, saturated hydraulic conductivity decreased by 70% and bulk density increased by 24%. These results proved that ERT can be a useful tool for assessing soil compaction.

Permafrost Soil Moisture Monitoring Using Multi-Temporal TerraSAR-X Data in Beiluhe of Northern Tibet, China

Global change has significant impact on permafrost region in the Tibet Plateau. Soil moisture (SM) of permafrost is one of the most important factors influencing the energy flux, ecosystem, and hydrologic process. The objectives of this paper are to retrieve the permafrost SM using time-series SAR images, without the need of auxiliary survey data, and reveal its variation patterns. After analyzing the characteristics of time-series radar backscattering coefficients of different landcover types, a two-component SM retrieval model is proposed. For the alpine meadow area, a linear retrieving model is proposed using the TerraSAR-X time-series images based on the assumption that the lowest backscattering coefficient is measured when the soil moisture is at its wilting point and the highest backscattering coefficient represents the water-saturated soil state. For the alpine desert area, the surface roughness contribution is eliminated using the dual SAR images acquired in the winter season with different incidence angles when retrieving soil moisture from the radar signal. Before the model implementation, landcover types are classified based on their backscattering features. 22 TerraSAR-X images are used to derive the soil moisture in Beiluhe, Northern Tibet with different incidence angles. The results obtained from the proposed method have been validated using in-situ soil moisture measurements, thus obtaining RMSE and Bias of 0.062 cm3/cm3 and 4.7%, respectively. The retrieved time-series SM maps of the study area point out the spatial and temporal SM variation patterns of various landcover types.

Fungus-growing termite foraging activity increases water infiltration but only slightly and temporally impacts soil physical properties in southern Indian woodlands

In the tropics, termites are known to be key litter decomposers and soil bioturbators. Their foraging activity in the soil leads to the production of galleries with specific soil physical, chemical and biological properties. This study investigates the influence of these foraging galleries on water infiltration and soil properties in south-Indian woodlands. A significant increase in water infiltration (× 3 that of control plots) was measured in soil as a result of Odontotermes spp. activities, likely because of the production of galleries in the first cm of the soil. Termite foraging activity was also associated with a significantly greater amount of clay in soil, probably because termites cover the wall of their galleries with fine-size particles, resulting in an increased saturated soil water content. Conversely, no differences in C content, CO2 emission and soil bulk density were measured in comparison with the surrounding soil. Consequently, this study confirms the beneficial impact of termites on water infiltration in soil but suggests a rather low local impact on soil chemical and biological functioning.

Development of pedotransfer functions for soil hydraulic properties in the critical zone on the Loess Plateau, China

AbstractSoil hydraulic properties (SHPs) including the soil water retention curve and saturated soil hydraulic conductivity (Ks) are crucial input data for simulations of soil water and solute transport in the Earth's critical zone. However, obtaining direct measurements of SHPs at a wide range of scales is time consuming and expensive. Pedotransfer functions (PTFs) are employed as an alternative method for indirectly estimating these parameters based on readily measured soil properties. However, PTFs for SHPs for the deep soil layer in the Earth's critical zone are lacking. In this study, we developed new PTFs in the deep soil profile for Ks and soil water retention curve on the Loess Plateau, China, which were fitted with the van Genuchten equation. In total, 206 data sets comprising the hydraulic and basic soil properties were obtained from three typical sites. Samples were collected from the top of the soil profile to the bedrock by soil core drilling. PTFs were developed between the SHPs and basic soil properties using stepwise multiple linear regression. The PTFs obtained the best predictions for Ks (Radj2 = 0.561) and the worst for van Genuchten α (Radj2 = 0.474). The bulk density and sand content were important input variables for predicting Ks, α, and θs, and bulk density, clay content, and soil organic carbon were important for n. The PTFs developed in this study performed better than existing PTFs. This study contains the first set of PTFs of SHPs to be developed for the deep profile on the Loess Plateau, and they may be applicable to other regions.

Determination of Physical and Mechanical Characteristics of Macro Sample of Water Saturated Peat

The article reports results of laboratory tests of weak water-saturated soils (remoted from day surface) in stress-strain state under influence of compression with double-sided filtration of pore’s water. The authors suggested the upgraded assembly scheme of the soil pressure sensors (load cells). The laboratory research of the water-saturated macro peat sample was made in compression conditions with “ground lock” and modeling of the experiment with Plaxis 2D software system. The unit deformation-pressure graph and excessive pore pressure against time in different steps of load graph were built and based on this findings. Authors made the new experimental device for research of the water saturated peat mechanics properties with excessive pore pressure

Comparison of visible and multi-satellite global inundation datasets at high-spatial resolution

Several new satellite-derived and long-term surface water datasets at high-spatial resolution have recently become available at the global scale, showing different characteristics and abilities. They are either based on visible imagery from Landsat – the Global 3-second Water Body Map (G3WBM) and the Global Surface Water Explorer (GSWE) – or on the merging of passive/active microwave and visible observations – Global Inundation Extent from Multi-Satellite (GIEMS-D3) – that has been downscaled from a native resolution of 25 km × 25 km to the 90 m × 90 m resolution. The objective of this paper is to perform a thorough comparison of the different water surface estimates in order to identify the advantages and disadvantages of the two approaches and propose a strategy for future developments of high-resolution surface water databases. Results show that due to their very high spatial resolution (30 m) the Landsat-based datasets are well suited to retrieve open water surfaces, even at very small size. GIEMS-D3 has a better ability to detect water under vegetation and during the cloudy season, and it shows larger seasonal dynamics. However, its current version overestimates surface water extent on water-saturated soils, and due to its low original (i.e. before downscaling) spatial resolution, it is under-performing at detecting small water bodies. The permanent waters for G3WBM, GSWE, GIEMS-D3 and GLWD represent respectively: 2.76, 2.05, 3.28, and 3.04 million km2. The transitory waters shows larger discrepancies: 0.48, 3.72, 10.39 and 8.81 million km2.Synthetic Aperture Radar (SAR) data (from ENVIronment SATellite (ENVISAT), Sentinel and soon the Surface Water Ocean Topography (SWOT)) would be a good complementary information because they have a high nominal spatial resolution and are less sensitive to clouds than visible measurements. However, global SAR datasets are still not available due to difficulties in developing a retrieval scheme adequate at the global scale. In order to improve our estimates of global wetland extents at high resolution and over long-term records, three interim lines of action are proposed: (1) extend the temporal record of GIEMS-D3 to exploit the full time series of microwave observations (from 1978 to present), (2) develop an approach to fuse the GSWE and GIEMS-D3 datasets leveraging the strengths of both, and (3) prepare for the release of SAR global datasets.

ONE-DIMENSIONAL QUASI-STATIC CONSOLIDATION MODEL CONSIDERING INERTIA OF FLUID PHASE

Terzaghi’s one-dimensional classic consolidation theory ignores inertia of pore water in saturated soils, and has outstanding differences in its derivation and formulation during various publication periods. This leads to a strange phenomenon that considerable misunderstandings and confusion of it still prevail in the current literature. Within the previous framework of large strain dynamic consolidation theory, a one-dimensional infinitesimal strain consolidation wave model is obtained to consider the effect of inertia of pore water with necessary simplification and hypotheses. The present consolidation wave model is characterized by velocity dispersion and dissipative attenuation. The method of separation of variables is used to obtain an analytical solution for a consolidation wave model under the condition of one-way drainage and instantaneous loading. A numerical case study shows that behaviors of consolidation wave are actually controlled by the value of a dimensionless number D c . For cases of higher values of D c , jump and fluctuation of dimensionless excess pore water pressure between positive and negative values are prone to occur, in contrast with the cases of lower values of D c that result into special phenomena including the Mandel-Cryer effect observed in laboratory tests. The inherent ambiguities about Terzaghi’s classic theory models proposed in the early stage and the later stage respectively are investigated to draw a conclusion that the early Terzaghi’s (1923,1925) consolidation model can be interpreted as a large strain model with respect to the general soil coordinates contrasted with an infinitesimal strain model with respect to the solid-phase volume coordinates. Accordingly, the present consolidation wave model can be extended to various formulations based on the corresponding coordinate properties. Consolidation wave theory is of significance to probe into an innovative uncertainty principle which shows that for scale model testing, the observed consolidation wave response of undisturbed soil samples cannot equal the response of the same soil in practical conditions. Therefore, it is advisable to pay attention to the size effect of soil samples in consolidation study from the perspective of microscopic soil mechanics. The theoretical precision of evaluated excess pore water pressure by classic Terzaghi’s consolidation model varies with the value of dimensionless quantity D c , which is a vital parameter in the proposed consolidation wave theory.

Effect of Pyrite Oxidation in Soils on Corrosion Behavior of Steel

The oxidation of pyrite in soils causes their acidification under aerated conditions, which may promote the corrosion of buried steel structures. Hence, the purpose of this study was to elucidate the effect produced by the presence of pyrite minerals in soils on the corrosion behavior of steel. In order to assess the fundamental corrosiveness of pyrite toward steel, the chemical properties of its aqueous solution were investigated by conducting short-term laboratory tests. In addition, electrochemical measurements were performed to evaluate the effect produced by the soil particles on the diffusion rates of oxygen and hydrogen ions in the soil medium. The obtained results revealed that the corrosion rate of steel in the pyrite-containing solution was accelerated due to the continuous production of hydrogen ions during the pyrite oxidation under the aerated conditions. However, its magnitude in a water-saturated soil system was not influenced by the oxidation of pyrite, owing to the relatively low diffusion rates of dissolved oxygen and hydrogen ions.

Effect of Soft Rock Amendment on Soil Hydraulic Parameters in Mu Us Sandy Land

Effect of soft rock as soil amendment on soil saturated hydraulic conductivity and water holding capacity was investigated in a field experiment in a sandy soil in Mu Us Sandy Land of China in 2012-2014. Treatments includes four rates of soft rock to sandy soil in volume (0:1, 1:1, 1:2 and 1:5) were applied only in the first year. Adding soft rock amendments increased water hold water holding capacity; decreased soil saturated hydraulic conductivity. The treatment with rate of 1:1 (soft rock to sandy soil in volume) had the greatest effect on soil saturated hydraulic conductivity and water holding capacity averaged over the three years. Soft rock amendments showed promise for improving soil hydraulic parameters in Mu Us Sandy Land

Iron Oxides Minimize Arsenic Mobility in Soil Material Saturated with Saline Wastewater.

The soil material in constructed wetlands is effective in retaining Se from flue-gas desulfurization (FGD) wastewater (WW), but reducing conditions can enhance native-soil As mobility. A laboratory-based soil column experiment was performed to assess the effectiveness of ferrihydrite (Fh) in minimizing the mobility of native-soil As in water-saturated soil material. A saline FGD WW mixture (i.e., influent) was delivered to columns of untreated and Fh-treated soil for 60 d. One untreated column and one Fh-treated column were then subjected to drying, followed by an additional 30 d of influent delivery. Although the influent was low in As (∼1 μg L) and the soil As level was normal, the total dissolved As concentration of effluent from the untreated columns increased with time, from ∼1 μg L to a maximum of ∼27 μg L. In contrast, effluent from the Fh-treated columns remained low in As (i.e., <5 μg L). The strong correlation between total dissolved Fe and As in the effluent suggested that reductive dissolution of native-soil Fe minerals was responsible for releasing As into solution. Results from X-ray absorption spectroscopy showed newly precipitated Fe minerals in the Fh-treated soil, and the remaining As was mainly As(V) species in both the untreated and Fh-treated soils. Thus, native-soil As mobilized under saturated conditions can be sequestered by adding poorly crystalline Fe oxides to soil prior to saturation. Furthermore, results obtained by drying and rewetting the columns showed that saturated conditions must be maintained to minimize the remobilization of sequestered As and retained Se.

Switching the Richards’ equation for modeling soil water movement under unfavorable conditions

Simulation of variably saturated soil water flow requires the use of pressure head, or soil moisture, or a switching between the two, as the primary variable for solving Richards’ equation. Under unfavorable conditions, such as heterogeneity, rapidly changing atmospheric boundary, or sudden infiltration into dry soils, the traditional non-switching method suffers from numerical difficulties. Solving this problem with a primary variable switching method is less preferred due to the mathematical complexity. While the Picard method is more popular for solving the non-switching models due to its simplicity and stability, two different forms of Richards’ equation are combined into one numerical scheme for switching under specific hydraulic conditions. The method is successfully implemented in a one-dimensional model solved by a Picard iteration scheme. A threshold saturation based on the soil moisture retention relation is used for switching between either form of the Richards’ equation. The method developed here is applicable for simulating variably saturated subsurface flow in heterogeneous soils. Compared with traditional methods, the proposed model conserves mass well and is numerically more stable and efficient.

Investigation of physical and mechanical properties of peat

The article describes results of laboratory tests of weak water-saturated soils (remote from day surface) in stress-strain state under influence of compression with double-sided filtration of pore’s water. The experimental device with console-lever system of load transfer and potential of double-sided filtration was made for current research. The compression specification was controlled with the strain gauge sensor element of general pressure (i.e. the load cell).The deformation in sample were measured with the motion detecting transducer that based on indicating gage. The excessive pore pressure was measured with strain gauge sensor elements and digital manometer. Also the plots of compression deformation against pressure and changes of excessive pore pressure during the time on different load degrees were drawn. Although, authors made the new experimental device for research of the water saturated peat mechanics properties with excessive pore pressure.

Iron reductive dissolution in vadose zone soils: Implication for groundwater pollution in landfill impacted sites

Iron (Fe) contamination of groundwater has become a problem of concern at a number of landfill impacted locations, and long-term monitoring studies suggest that the reductive dissolution of iron (hydr)oxide minerals present in soils and aquifer sediments could be one the sources of dissolved Fe measured in impacted aquifers. In this study, vadose zone soil samples were collected along a gradient emphasizing differences in both soil water saturation levels and degrees of crystallization of Fe-minerals. Collected soil samples were analyzed for pH, organic matter content, particle size distribution, and Fe speciation into amorphous and crystalline fractions. Batch experiments were conducted under anaerobic conditions using soil slurries with (treatments) or without (controls) landfill leachate addition to the liquid phase. Under the experimental conditions used in this study, tested soils released Fe primarily via reductive dissolution pathways, with rates ranging from ∼0.3 to 12 mg Fe/kg.day. However, no clear trend was evident between the amount of Fe released and the crystallinity degrees of the iron minerals present in the tested soils. The addition of organic carbon sources to prepared vadose soils slurries fueled the microbial driven Fe-reductive dissolution, suggesting that organic-rich landfill leachate would play a significant role in the dissolution of iron (hydr)oxide minerals, and potentially in the mobilization of toxic metals co-precipitated with or adsorbed onto iron (hydr)oxide minerals.

Soil physicochemical properties and vegetation structure along an elevation gradient and implications for the response of alpine plant development to climate change on the northern slopes of the Qilian Mountains

Elevation is one of key factors to affect changes in the environment, particularly changes in conditions of light, water and heat. Studying the soil physicochemical properties and vegetation structure along an elevation gradient is important for understanding the responses of alpine plants and their growing environment to climate change. In this study, we studied plant coverage, plant height, species richness, soil water-holding capacity, soil organic carbon (SOC) and total nitrogen (N) on the northern slopes of the Qilian Mountains at elevations from 2124 to 3665 m. The following conclusions were drawn: (1) With the increase of elevation, plant coverage and species richness first increased and then decreased, with the maximum values being at 3177 m. Plant height was significantly and negatively correlated with elevation (r=–0.97, P<0.01), and the ratio of decrease with elevation was 0.82 cm·100 m-1. (2) Both soil water-holding capacity and soil porosity increased on the northern slopes of the Qilian Mountains with the increase of elevation. The soil saturated water content at the 0-40 cm depth first increased and then stabilized with a further increase of elevation, and the average ratio of increase was 2.44 mm·100 m-1. With the increase of elevation, the average bulk density at the 0-40 cm depth first decreased and then stabilized at 0.89 g/cm3. (3) With the increase of elevation, the average SOC content at the 0-40 cm depths first increased and then decreased, and the average total N content at the 0-40 cm depth first increased and then stabilized. The correlation between average SOC content and average total N content reached significant level. According to the results of this study, the distribution of plants showed a mono-peak curve with increasing elevation on the northern slopes of the Qilian Mountains. The limiting factor for plant growth at the high elevation areas was not soil physicochemical properties, and therefore, global warming will likely facilitate the development of plant at high elevation areas in the Qilian Mountains.

The Stress-Strain State of a Finite Rectangular Domain Under a Uniformly Distributed Strip Load

This paper presents a Ribera-Filon method-based analytical solution to the plane problem of the theory of elasticity on the stress-strain state (SSS) of a base of finite thickness and width under a uniformly distributed load acting on part of the base. A nonstabilized SSS is also considered for the water-saturated soil base (S r > 0.85), i.e., with regard to consolidation and creep processes, including secondary consolidation and anisotropic filtering