Taku Nishimura

The Effect of Entrapped Air on the Quasi-Saturated Soil Hydraulic Conductivity and Comparison with the Unsaturated Hydraulic Conductivity

Entrapped air can greatly affect the hydraulic conductivity at or near saturation. In this study, we measured the hydraulic conductivity and volume of entrapped air in a quasi-saturated soil. Two soils, a Masa sandy loam soil from weathered granite rock and a TUAT light clay andisol from volcanic ash, were used. The soils, with three different dry bulk densities, were packed into a steel cylinder. To attain complete saturation, the packed soil samples were immersed in a 0.02 mol L −1 gypsum solution under vacuum conditions. The soil samples were then left on a sintered porous plate with suction of −17.0 kPa for different periods of time to allow drainage and air intrusion. After this drainage process, the samples were again immersed in water to permit air entrapment. The hydraulic conductivity was measured using the falling head method, and the amount of entrapped air was determined gravimetrically. The quasi-saturated hydraulic conductivity was found to decrease with increasing entrapped air content until the soil had the maximum fraction of entrapped air, approximately 10% of the bulk soil volume. A comparison of the quasi-saturated and unsaturated hydraulic conductivities of the soil samples at or near saturation, when the suction of soil water was greater than the air-entry value, showed that the quasi-saturated hydraulic conductivity was smaller than the unsaturated hydraulic conductivity.

Contribution of shallow groundwater rapid fluctuation to soil salinization under arid and semiarid climate

Rising saline shallow groundwater and associated soil salinization problems are widespread especially in arid and semiarid areas. There have been numerous studies on groundwater-associated salinity, but more information is required on the effects of groundwater frequent and high fluctuations on soil salinization. In the present study, laboratory experiments and numerical simulations using HYDRUS-1D model were carried out for this purpose. The experimental and modeling results showed that groundwater fluctuation caused not only the accumulation of more salt in the soil profile compared to stable groundwater, but also an enhancement of the mechanism. Water table fluctuation induced a much greater spreading of the bromide (Br) tracer within the column than the constant water table. The Br content was on average five orders of magnitude greater under a fluctuating water table than under a constant one. Further, the numerical simulations showed that an increase in the groundwater fluctuation frequency brought about an increase in soil surface salinization under the same evaporation boundary conditions. Additional simulations with HYDRUS-1D were used to study the effects of various management strategies on soil salinization induced by shallow groundwater. Hence, by reducing the evaporation rate through the application of surface mulching, a significant reduction of salt concentration at the soil surface was observed. Moreover, frequent irrigations with small quantities were effective to reduce soil surface salt accumulation induced by saline shallow groundwater.

Accumulation and mobility of zinc in soil amended with different levels of pig-manure compost

Applying manure compost not only results in zinc accumulation in the soil but also causes an increase in zinc mobility and enhances zinc leaching. In this study, the physical and chemical characteristics of zinc, zinc profiles, and zinc balance were investigated to characterise the fate of zinc in fields where the quality and amount of pig manure compost applied have been known for 13 years. Moreover, we determined zinc fractionation in both 0.1 mol L−1HCl-soluble (mobile) and -insoluble (immobile) fractions. Adsorption of zinc in the soil was enhanced with increasing total carbon content following the application of pig manure compost. The 159.6 mg ha−1 year−1manure applied plot (triplicate) exceeded the Japanese regulatory level after only 6 years of applying pig manure compost, whereas the 53.2 mg ha−1 year−1 manure applied plot (standard) reached the regulatory level after 13 years. The zinc loads in the plots were 17.0 and 5.6 kg ha−1 year−1, respectively. However, 5.9 % and 17.2 % of the zinc loaded in the standard and the triplicate pig manure compost applied plots, respectively, were estimated to be lost from the plough layer. Based on the vertical distribution of mobile and immobile zinc content, a higher rate of applied manure compost caused an increase in the mobile zinc fraction to a depth of 40 cm. Although the adsorption capacity of zinc was enhanced following the application of pig manure compost, a greater amount of mobile zinc could move downward through the manure amended soil than through non manure-amended soil.

Adsorption of linear alkylbenzene sulfonates on carboxyl modified multi-walled carbon nanotubes

Understanding of the adsorption behavior of organic pollutants on carbon nanotubes (CNTs) and its governing factors are crucial for the assessment of transport and fate of organic pollutants. This study explored adsorption characteristics of linear alkylbenzene sulfonates (LAS) on carboxyl modified multi-walled carbon nanotubes (CMMWCNTs) and the effect of solution chemistry and temperature on LAS sorption. Results indicted LAS adsorption isotherms to display five distinct regions of sorption at 25°C and 60°C. Regardless of temperature, the adsorption isotherm of LAS on the CMMWCNTs was well described using the Freundlich equation. This result indicated heterogeneous distribution of adsorption sites on the CMMWCNT surface. At low initial LAS concentrations, below the critical micelle concentration, (2, 10 and 50mgL-1) LAS adsorption on the CMMWCNTs followed pseudo second-order kinetics. The highest LAS adsorption was observed at ionic strengths of 1.0molL-1 for NaCl; and 0.2molL-1 for both CaCl2 and MgCl2. However, LAS sorption was greatest in the presence of sodium-divalent anion salts and at higher temperatures. These findings are of relevance to the fate and environmental risk of LAS in the presence of CMMWCNTs in high salinity wastewaters or effluents and brackish receiving surface water bodies (e.g., at estuaries).

Effect of Gypsum and Polyacrylamide Application on Erodibility of an Acid Kunigami Mahji Soil

Calcium carbonates and gypsum are often used to improve the chemical status of acid soils. This study discusses the effects of gypsum and polyacrylamide (PAM) application on infiltration and erodibility of a Japanese acid soil. Acid Kunigami mahji soil (sedimentary rock derived, Typic Hapludult) from Okinawa was packed into an acrylic plastic box, and simulated rainfall of 40 mm h−1 was applied. Prior to the rainfall, 2.5 t ha−1 of gypsum and/or 15 kg ha−1 of non-ionic or anionic PAM were applied onto soil surface. During a rainfall, surface runoff was collected periodically, and sediment concentration, pH, and electric conductivity of the runoff were measured. Gypsum application enhanced surface runoff. During the rainfall, EC of the runoff was greater than the critical coagulation concentration of the clays of the mahji soil, however the soil became dispersive with gypsum application. PAM application could improve infiltration of gypsum amended mahji soil and reduce sediment loss.

Monitoring of Soil Surface under Wind and Water Erosion by Photogrammetry

Soil degradation resulting from accelerated water and wind-induced erosion is a serious problem in drylands, and will remain so throughout this century. The detachment and transport of soil particles degrade the fertility of agricultural land and consequently reduce its productivity (Lyles and Tartako 1986 ).Many of the particles involved in soil erosion processes, such as raindrops, wind velocity, soil aggregates, sediment, and siltation have characteristic dimensions on the millimeter scale (Huang 1998). The addition of organic matter increases the connection between aggregate by physical and chemical bounding. The strongly bonding aggregation induces the increase of soil porosity and permeability, which result the decrease of water erosion. The bigger aggregate also decrease the wind erosion due to their heaviness. The modeling and quantification of such processes require detailed measurements of the physical, chemical, and biological properties of soils (Soil Conservation Service 1976). However, these measurements are too slow, tedious, and expensive for routine or regular monitoring. Several researchers have already used aerial photography to assess soil erosion. A precise form of this photography, photogrammetry, has the advantage of very efficiently and cost effectively providing detailed information about a large area. Together with aerial photography, the use of remotely sensed data forms the basis for land use mapping and change detection (Pellikka et al. 2004). In particular, for inaccessible areas, photogrammetry is far superior to traditional ground surveys. The subsequent convergence in recent years of photogrammetry and digital imaging technology has led to an increase in the use of digital elevation models (DEMs) in modern studies involving the monitoring of landscape changes (Prosser and Aberneathy 1996; DeRose et al. 1998). The areas measured experimentally in microtopographical studies of soil erosion range from 1 to approximately 20 m2. In general, the DEMs used for analysis have grid resolutions of 1 to 15 mm (Elliot et al. 1997; Darboux and Huang 2003). A variety of instruments and methods are used by soil scientists to acquire measurement coordinates, including mechanical point gauges (Elliot et al. 1997) that make contact with the soil surface,

Effects of Flow Rate and Gas Species on Microbubble and Nanobubble Transport in Porous Media

AbstractTransport of microbubbles and nanobubbles (MNBs) in porous media has drawn increasing attention as a promising technology for soil and groundwater remediation. Understanding the transport m...

A review of source tracking techniques for fine sediment within a catchment

Excessive transport of fine sediment, and its associated pollutants, can cause detrimental impacts in aquatic environments. It is therefore important to perform accurate sediment source apportionment to identify hot spots of soil erosion. Various tracers have been adopted, often in combination, to identify sediment source type and its spatial origin; these include fallout radionuclides, geochemical tracers, mineral magnetic properties and bulk and compound-specific stable isotopes. In this review, the applicability of these techniques to particular settings and their advantages and limitations are reviewed. By synthesizing existing approaches, that make use of multiple tracers in combination with measured changes of channel geomorphological attributes, an integrated analysis of tracer profiles in deposited sediments in lakes and reservoirs can be made. Through a multi-scale approach for fine sediment tracking, temporal changes in soil erosion and sediment load can be reconstructed and the consequences of changing catchment practices evaluated. We recommend that long-term, as well as short-term, monitoring of riverine fine sediment and corresponding surface and subsurface sources at nested sites within a catchment are essential. Such monitoring will inform the development and validation of models for predicting dynamics of fine sediment transport as a function of hydro-climatic and geomorphological controls. We highlight that the need for monitoring is particularly important for hilly catchments with complex and changing land use. We recommend that research should be prioritized for sloping farmland-dominated catchments.

Applicability of soil column incubation experiments to measure CO2 efflux

Abstract Accurate measurements of CO2 efflux from soils are essential to understand dynamic changes in soil carbon storage. Column incubation experiments are commonly used to study soil water and solute transport; however, the use of column incubation experiments to study soil CO2 efflux has seldom been reported. In this study, a 150-day greenhouse experiment with two treatments (no-tillage and tillage soils) was conducted to evaluate the applicability of soil column incubation experiments to study CO2 efflux. Both the chamber measurement and the gradient method were used, and results from the two methods were consistent: tillage increased soil cumulative CO2 efflux during the incubation period. Compared with fieldwork, incubation experiments can create or precisely control experimental conditions and thus have advantages for investigating the influence of climate factors or human activities on CO2 efflux. They are superior to bottle incubation because soil column experiments maintain a soil structure that is almost the same as that in the field, and thus can facilitate analyses on CO2 behaviour in the soil profile and more accurate evaluations of CO2 efflux. Although some improvements are still required for column incubation experiments, wider application of this method to study soil CO2 behaviour is expected.

Controlling Sodic Soil Erosion by Electrolytes and Polyacrylamide Application

The anionic polyacrylamide (PAM) is recently used to rehabilitate saline and sodic soils and control soil erosion. The research on the effectiveness of anionic PAM along with gypsum or lime application on soil erosion is rare and poorly documented. Therefore, an experiment was conducted to study the effects of anionic PAM with or without gypsum on the erosion of soils under saline/sodic conditions. For this purpose, a clay loam soil was prepared to achieve three levels of exchangeable sodium percentage (ESP) 0.5, 9.9, and 25.5 with an appropriate solution of salts. Soil samples were air-dried and packed in the trays. Powdered PAM, gypsum, or a mixture of both was applied to the salt-treated soils. Thereafter, the soils were subjected to simulated rainstorm of 40 mm h−1 by a fixed rainfall simulator. Saline waters with different levels of electrical conductivity (ECw): 0.1, 2, 5, and 8 dS m−1 were used for simulated rains during the study. PAM amendment substantially controlled the erosion of the soils. The ESP was directly associated with the soil erosion and runoff. Among the treatments, the resistance to soil erosion was developed in the order of PAM > gypsum ≈ saline water > PAM mixed with gypsum ≈ PAM mixed with saline water. The magnitude of runoff water was reduced both by gypsum and saline water, whereas it was enhanced by PAM application. The mixed addition of PAM with gypsum or salts exacerbated water erosion of soils.