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Analyses of metabolite secretions by field-grown plants remain scarce. We analyzed daidzein secretion by field-grown soybean. Daidzein secretion was higher during early vegetative stages than reproductive stages, a trend that was also seen for hydroponically grown soybean. Daidzein secretion was up to 10 000-fold higher under field conditions than hydroponic conditions, leading to a more accurate simulation of rhizosphere daidzein content.

Microbial community structure reflects the surrounding natural environment and changes to that environment. Although the subsurface at 5–100 m depth is important for human activities and there are ...

An understanding of nanobubble (NB) migration in porous media is needed for potential environmental applications. The solution chemistry is well known to be a critical factor in determining interactions of other colloids and nanoparticles with surfaces. However, little quantitative research has examined the influence of solution chemistry on NB transport. One-dimensional column experiments were therefore conducted to investigate the transport, retention, and release of NBs in glass beads under different solution chemistry conditions. NB concentrations in the effluent were reduced with an increase in ionic strength (IS) or a decrease in pH due to a reduction in the repulsive force between the glass surface and NBs, especially when the solution contained Ca2+ as compared to Na+ and for larger NBs. This result was somewhat surprising because electrostatic and van der Waals interactions for NBs were both repulsive on a homogeneous glass bead surface. NB retention on the surface was explained by ubiquitous nan...

Nanobubbles have recently attracted much interest for their practical use and potential applications in environmental issues. The pre-existence of deposited colloidal particles in porous media commonly occurs when nanobubbles applied to porous media interact with deposited colloidal particles. However, the current understanding of the effect of the interactions with pre-deposited colloidal particles on nanobubble transport in saturated porous media remains incomplete, and the effects are often overlooked. Therefore, we performed 1D column experiments with sequential injections of colloidal and nanobubble suspensions to study the effect of pre-deposited materials on the retention and release of colloids and nanobubbles in packed glass beads. In this study, we used resonant mass measurements to measure the number concentrations of colloids and nanobubbles during transport experiments for the first time to distinguish between coexisting solid colloidal particles and nanobubbles with different buoyancies in mixed effluent during transport. The nanobubble retention increased because of the pre-existence of deposited colloidal particles, indicating that the deposited colloidal particles act as additional deposition sites and physical obstacles for nanobubbles through physicochemical (including hydrophobic) interactions. This study also provides a future reference for the applicability of resonant mass measurement to cotransport experiments of different buoyant particles, including colloids, nanobubbles, and oil droplets.

After the accident at the Fukushima Daiichi nuclear power plant in Japan, the migration of radioactive cesium (Cs) in soils has become a crucial issue since this can negatively affect human health and the surrounding environment. Dissolved organic matter (DOM) may have different influences on Cs migration in soils depending on Cs adsorption sites with different selectivity. It is unclear how DOM affects the rapid migration of Cs in soils under flowing water conditions during rainfall events. This study evaluated the effects of DOM on Cs migration in weathered granite soil depending on Cs adsorption sites by conducting laboratory experiments under different DOM conditions and Cs concentrations in the liquid phase. Cs concentration can affect the fraction of Cs adsorbed onto differently selective sites, and DOM can have different influences on Cs migration in the soil accordingly. Under condition of high-Cs concentration, the DOM adsorbed on the soil reduced Cs migration due to increasing Cs electrostatic adsorption to less selective sites in the soil. Meanwhile, under low-Cs concentration, the DOM adsorbed on the soil enhanced Cs migration because the DOM on the soil decreased the Cs adsorption to highly selective sites. Furthermore, DOM in the liquid phase detached the Cs adsorbed on the less selective sites and enhanced Cs migration in the soil, regardless of the Cs concentration.

International audience; Groundwater is essential for the Earth biosphere but is often contaminated by harmful chemical compounds due to both anthropogenic and natural causes. A key factor controlling the fate of harmful chemicals in groundwater is the reduction/oxidation (redox) conditions. The formation factors for the groundwater redox conditions are insufficiently understood. In this study, long-term groundwater quality beneath one of the world megacities was monitored and evaluated. We measured and compared hydrogeochemical conditions including groundwater quality (35 chemical parameters) and redox conditions of five aquifers in the Arakawa Lowland and Musashino Upland, southern Kanto Plain of the Tokyo Metropolitan area, Japan. Monitoring results suggested the following: The main origin of groundwater is precipitation in both the Lowland and Upland areas. The three aquifers in the Arakawa Lowland are likely fully separated, with one unconfined and two confined aquifers under iron reducing and methanogenic conditions, respectively. Oppositely, in the Musashino Upland, the water masses in the two aquifers are likely partly connected, under aerobic conditions, and undergoing the same groundwater recharge and flow processes under similar hydrogeological conditions. The different groundwater redox conditions observed are likely caused by the very different groundwater residence times for the Arakawa Lowland and Musashino Upland.

Along with the increase of autoclaved aerated concrete (AAC) production, the amount of scrap waste (industrial by-products) is increasing. AAC waste, however, is not yet being fully reused ...

An understanding of nano-scale bubble (NB) transport in porous media is important for potential application of NBs in soil/groundwater remediation. It is expected that the solution chemistry of NB water highly influences the surface characteristics of NBs and porous media and the interaction between them, thus affecting the stability and transport characteristics of NB. In this study, in addition to stability experiments, one-dimensional column transport experiments using glass beads were conducted to investigate the effects of pH on the NB transport behavior. The results showed that the NBs were more stable under higher pH. Column transport experiments revealed that entrapment of NBs, especially larger ones, was enhanced in lower-pH water, likely suggesting pH-dependent NB attachment and physical straining, both of which are also probably influenced by bubble size. Although relatively smaller NBs were released after switching the eluting fluid to one with lower ionic strength, most of the NBs in lower-pH water were still retained in the porous media even altering the chemical condition.

Thermal dispersion, caused by fluid velocity and temperature fluctuations in the pore space and the effects of hydrodynamic mixing on the temperature field, controls convective heat transport in saturated porous media. While the thermal dispersion coefficient, a governing parameter in the thermal equilibrium model (TEM), has been investigated for natural systems, the dependence of the thermal dispersion coefficient on particle size remains undetermined. Previous research found that the relationship between the thermal dispersion coefficient and flow velocity follows a power law and that there may be a temperature difference between the solid and fluid phase (thermal non-equilibrium). However, experiments are limited to discrete particle sizes and comparison of the dispersion-velocity relationship is impeded by different experimental approaches. We conducted a series of separate heat and solute transport experiments in a column filled with uniform porous media consisting of different sized glass spheres for a range of flow velocities. The thermal and solute dispersion coefficients obtained from experimental measurements were correlated with flow velocities through the thermal or solute Peclet number. Our results demonstrate that, while solute dispersion is independent of particle size, the dependence of the TEM based thermal dispersion coefficient on flow rates is influenced by the particle size. This is caused by the fact that, unlike solute transport, heat exchanges between fluid and particles and that this induces thermal non-equilibrium between both phases. The results have significant implications for quantifying forced convective heat transport in natural porous media because thermal non-equilibrium between the phases is not considered. The porous media particle size must be considered when selecting appropriate values for the thermal dispersion coefficient.

It is important to understand the migration of Cesium (Cs) in soils, particularly after the nuclear power plant accident at Fukushima Dai-ichi, Japan. Dissolved organic matter (DOM) is one of factors affecting the migration of Cs in soils under flowing water conditions. We investigated the effect of DOM on the migration of Cs adsorbed to the clay planar site via laboratory column experiments. The sequence of DOM application had a significant influence on Cs transport in the soil. When DOM was applied concurrently with or prior to Cs application, the DOM adsorbed on to the clay planar site adsorbed onto the soil solid surface and enhanced Cs adsorption; consequently, it slowed Cs migration in the soil. In particular, in the case of DOM loaded prior to the application of Cs solution, a noticeable delay in Cs migration was observed. On the other hand, when DOM was applied to the soil where the Cs solution had been previously applied, the DOM desorbed Cs from the soil. DOM in liquid phase enhanced the migration of Cs through the formation of binding to organic matter. Majority of Cs affected by DOM was the exchangeable fraction that adsorbed to the clay planar site. In other words, DOM attached to the soil would adsorb Cs as a easily exchangeable form and depress migration of Cs. On the other hand, DOM in the soil solution may up take adsorbed Cs from the soil and enhanced the transport in the form of Cs bound to DOM.

Radioactive materials, primarily radiocesium (134Cs + 137Cs), were released into the environment by the Fukushima Daiichi Nuclear Power Plant accident in March 2011. The percentage of soybean plants that had a concentration of radiocesium over 100 Bq/kg was higher than that of other crops. To examine the reason why the concentration of radiocesium in soybeans was high, its concentration and distribution in seeds were analyzed and compared to rice.

Summary Gas and water transport in peat soil are of increasing interest because of their potentially large environmental and climatic effects under different types of land use. In this research, the water retention curve (WRC), gas diffusion coefficient (Dg) and air and water permeabilities (ka and kw) of layers in peat soil from two profiles were measured under different moisture conditions. A two-region Archie's Law (2RAL)-type model was applied successfully to the four properties; the reference point was taken at −9.8 kPa of soil-water matric potential where volume shrinkage typically started to occur. For WRC in the very decomposed peat soil, the 2RAL saturation exponents (n) obtained for both the wetter (nw) and drier regions (nd) were smaller than those for the less decomposed peat. For Dg, the saturation exponent in the wetter region was larger than that in the drier one for all layers, which indicated enhanced blocking effects of water on gas diffusion in the wetter region. For the peat layers within each soil, there was a linear relation between saturation exponents in the drier region for ka and Dg. The larger saturation exponent of the wetter region for kw in peat than in sand suggests a need for specific hydraulic functions for peat soil. The 2RAL model for Dg agreed well with measured data, and performed better than existing unimodal models. To facilitate use of the 2RAL for Dg, we developed a simple predictive expression for Dg at the reference point. The pore-network tortuosity factor and equivalent pore diameter for gas transport confirmed very different pore structure and mass transport behaviour for peat soil and uniform sand.

Landfill sites are significant sources of methane gas globally. Understanding the temporal variabilities of methane emissions from landfill sites is necessary for estimating such emissions. In this study, an automated monitoring system was used to monitor methane emission flux and concentration on daily and hourly time scales at a landfill site. Measured methane emission fluxes were almost negligible in the studied area. However, methane concentration at landfill surface at nighttime was significantly higher than those in the daytime, which demonstrates the importance of investigating methane emissions at an hourly time scale, including during nighttime. The daily and hourly variations in methane concentration were well correlated with either soil temperature or volumetric water content near the surface. The obtained relations indicate that the automated monitoring system measurements can facilitate a more comprehensive understanding of the methane emission mechanisms at different time scales.

Underground developments such as subways and shopping facilities have been increasing in number and magnitude in the relatively shallow subsurface of many urban areas where the earth materials commonly are composed of marine sediments. Marine sediments can contain significant amounts of toxic trace elements such as arsenic, boron, and lead. Changes in the subsurface environment caused by excavation and construction in underground developments could potentially cause these toxic elements to be dissolved into pore water of the sediments, which might lead to groundwater pollution. The purpose of this study is to investigate correlations among chemical properties of marine sediments, such as pH and electrical conductivity (EC), concentrations of toxic trace elements, and stratigraphic characteristics of the sediments. We selected three sites with different stratigraphic settings in the southern Kanto Plain around the Tokyo Metropolis. We collected core samples from shallow strata at a site in the Arakawa Lowland, southern Saitama, and at two sites in the Musashino Upland, Middle Tokyo. All sites have both marine and non-marine sediments up to 50–60 m in thickness. We determined trace element concentrations in the pore water, pH, EC, and loss on ignition. The results show that (1) the marine sediments tend to have low pH, high EC, and high sulfur concentration compared to the non-marine sediments (2) the concentration of most of the soluble heavy metals vary depending on the concentration of sulfate, the pH, and the formation processes of the strata, (3) the arsenic concentration is not related to sulfur concentration but apparently to Fe and Al concentrations, (4) the boron concentration is not related to any other properties implying that the boron level is independent of and cannot be predicted by common chemical properties, and (5) for all three sites, concentrations of most of the trace elements, EC, pH, and sulfate concentration were correlated with each other. This study shows that the concentration and potential mobilization of many toxic trace elements in marine sediments could be predicted by easily measurable pore water chemical properties such as pH and EC. This could be useful for predicting and avoiding the risk of groundwater pollution during underground development projects.

Isoflavones play important roles in rhizosphere plant-microbe interactions. Daidzein and genistein secreted by soybean roots induce the symbiotic interaction with rhizobia and may modulate rhizosphere interactions with microbes. Yet despite their important roles, little is known about the biosynthesis, secretion and fate of isoflavones in field-grown soybeans. Here, we analyzed isoflavone contents and the expression of isoflavone biosynthesis genes in field-grown soybeans. In roots, isoflavone contents and composition did not change with crop growth, but the expression of UGT4, an isoflavone-specific 7-O-glucosyltransferase, and of ICHG (isoflavone conjugates hydrolyzing beta-glucosidase) was decreased during the reproductive stages. Isoflavone contents were higher in rhizosphere soil than in bulk soil during both vegetative and reproductive stages, and were comparable in the rhizosphere soil between these two stages. We analyzed the degradation dynamics of daidzein and its glucosides to develop a model for predicting rhizosphere isoflavone contents from the amount of isoflavones secreted in hydroponic culture. Conjugates of daidzein were degraded much faster than daidzein, with degradation rate constants of 8.51 d-1 for malonyldaidzin and 11.6 d-1 for daidzin, vs. 9.15 × 10-2 d-1 for daidzein. The model suggested that secretion of isoflavones into the rhizosphere is higher during vegetative stages than during reproductive stages in field-grown soybean.

The impact of biodiversity loss on soil functions is well established via laboratory experiments that generally consider soil biota groups in isolation from each other, a condition rarely present in field soils. As a result, our knowledge about anthropogenic-induced changes in biodiversity and associated soil functions is limited. We quantified an array of soil biological constituents (plants, earthworms, nematodes, bacteria, and fungi) to explore their interactions and to characterize their influence on various soil functions (habitat for soil organisms, air and water regulation, and recycling of nutrients and organic waste) along a legacy Cu pollution gradient. Increasing Cu concentrations had a detrimental impact on both plant growth and species richness. Belowground soil biota showed similar responses, with their sensitivity to elevated Cu concentrations decreasing in the order: earthworms > bacteria > nematodes > fungi. The observed loss of soil biota adversely affected natural soil bioturbation, aggregate formation and stabilization, and decomposition and mineralization processes and therefore resulted in compacted soil with narrow pore size distributions and overall smaller pores, restricted air and water storage and flow, and impeded C, N, and P cycling. The simultaneous evolution of soil biodiversity and functions along the Cu gradient emphasized the key role of soil life in controlling ecosystem services. Furthermore, results indicated that different soil biodiversity and functional indicators started to decline (10% loss) within a Cu concentration range of 110 to 800 mg total Cu kg-1. © Soil Science Society of America, 5585 Guilford Rd.

The subsurface of the Earth is facing evermore thermal impact due to global warming, urban heat islands, and the widespread use of ground source heat pump (GSHP) systems. This potentially causes changes in its physical, mechanical, microbiological, and chemical properties, and in the subsurface water quality. To predict and evaluate this thermal impact (or thermal pollution), a better understanding and improved models for the thermal properties governing heat transport in subsurface sediments are needed. Also, data acquisition in high spatial resolution for the thermal properties and basic physical properties of the subsurface sediments are essential. In this study, the main thermal properties (the thermal conductivity, heat capacity, and thermal diffusivity) together with the basic physical properties (the soil texture, water content, and dry bulk density) were measured on boring core samples representing depths from 0 to 50 or 80 m, at three study sites in the Kanto area of Japan. Based on the measured data, models for thermal conductivity as functions of gravimetric water content, dry bulk density, and volumetric sand content were developed. The new models performed markedly better than presently available models from the literature and, in combination with a modified de Vries type model for heat capacity, the resulting model for thermal diffusivity was capable of describing the measured data well. The usefulness of the newly developed models were validated and illustrated by using data from a two-day thermal response test (TRT) performed at one of the three study sites. The new predictive models for the thermal properties used in a numerical heat transport simulation accurately predicted subsurface (5–50 m) temperature changes during the TRT.

Plant cell wall polysaccharides undergo a slower degradation process in deep subsoil layers than in topsoil. Through the identification of organic compounds in subsoil, we may gain an understanding of this degradation process. In the present study, we extracted alkali-soluble polysaccharides from subsoil bore samples at depths of 5, 18, 29, 35 and 40–43 m, and performed sugar composition and sugar linkage analyses. Based on the results, we suggest that cellulose, arabinoxylan, mannan and pectic polysaccharides derived from plant cell walls and β-1,3-glucan and/or β-1,3:1,6-glucan from fungal cell walls exist in deep subsoil layers.

The soil-gas diffusion is a primary driver of transport, reactions, emissions, and uptake of vadose zone gases, including oxygen, greenhouse gases, fumigants, and spilled volatile organics. The soil-gas diffusion coefficient, D p , depends not only on soil moisture content, texture, and compaction but also on the local-scale variability of these. Different predictive models have been developed to estimate D p in intact and repacked soil, but clear guidelines for model choice at a given soil state are lacking. In this study, the water-induced linear reduction (WLR) model for repacked soil is made adaptive for different soil structure conditions (repacked, intact) by introducing a media complexity factor ( C m ) in the dry media term of the model. With C m = 1, the new structure-dependent WLR (SWLR) model accurately predicted soil-gas diffusivity ( D p / D o , where D o is the gas diffusion coefficient in free air) in repacked soils containing between 0 and 54% clay. With C m = 2.1, the SWLR model on average gave excellent predictions for 290 intact soils, performing well across soil depths, textures, and compactions (dry bulk densities). The SWLR model generally outperformed similar, simple D p / D o models also depending solely on total and air-filled porosity. With C m = 3, the SWLR performed well as a lower-limit D p / D o model, which is useful in terms of predicting critical air-filled porosity for adequate soil aeration. Because the SWLR model distinguishes between and well represents both repacked and intact soil conditions, this model is recommended for use in simulations of gas diffusion and fate in the soil vadose zone, for example, as a key element in developing more accurate climate change models.

Gas transport parameters and X-ray computed tomography (CT) measurements in porous medium under controlled and identical conditions provide a useful methodology for studying the relationships among them, ultimately leading to a better understanding of subsurface gaseous transport and other soil physical processes. The objective of this study was to characterize the relationships between gas transport parameters and soil-pore geometry revealed by X-ray CT. Sands of different shapes with a mean particle diameter (d50) ranging from 0.19 to 1.51 mm were used as porous media under both air-dried and partially saturated conditions. Gas transport parameters including gas dispersivity (α), diffusivity (DP/D0), and permeability (ka) were measured using a unified measurement system (UMS). The 3DMA-Rock computational package was used for analysis of three-dimensional CT data. A strong linear relationship was found between α and tortuosity calculated from gas transport parameters (Equation (Uncited) Image Tools), indicating that gas dispersivity has a linear and inverse relationship with gas diffusivity. A linear relationship was also found between ka and d50/TUMS2, indicating a strong dependency of ka on mean particle size and direct correlation with gas diffusivity. Tortuosity (TMFX) and equivalent pore diameter (deq.MFX) analyzed from microfocus X-ray CT increased linearly with increasing d50 for both Granusil and Accusand and further showing no effect of particle shape. The TUMS values showed reasonably good agreement with TMFX values. The ka showed a strong relationship when plotted against deq.MFX/TMFX2, indicating its strong dependency on pore size distribution and tortuosity of pore space.

The gas diffusion coefficient (D-s,D-g) and solute diffusion coefficient (D-s,D-l) and their dependencies on fluid content (kappa) (equal to soil-air content theta for D-s,D-g and soil-water content epsilon for D-s,D-l) are controlling factors for gas and solute transport in variably saturated soils. In this study, we propose unified, predictive models for D-s,D-g(epsilon) and D-s,D-l(theta) based on modifying and extending the classical Maxwell model at fluid saturation with a fluid-induced reduction term including a percolation threshold (epsilon(th) for D-s,D-g and theta(th) for D-s,D-l). Different percolation threshold terms adopted from recent studies for gas (D-s,D-g) and solute (D-s,D-l) diffusion were applied. For gas diffusion, epsilon(th) was a function of bulk density (total porosity), while for solute diffusion theta(th) was best described by volumetric content of finer soil particles (clay and organic matter), FINESvol. The resulting LIquid and GAs diffusivity and tortuosity (LIGA) models were tested against D-s,D-g and D-s,D-l data for differently-textured soils and performed well against the measured data across soil types. A sensitivity analysis using the new Maxwell's Law based LIGA models implied that the liquid phase but not the gaseous-phase tortuosity was controlled by soil type. The analyses also suggested very different pathways and fluid-phase connectivity for gas and solute diffusion in unsaturated soil

Subsurface gaseous-phase transport is governed by three gas transportparameters: the air permeability coefficient (ka), gas diffusion coefficient(DP), and gas dispersion coefficient (DH). Among these, DH is the leastunderstood due to hitherto limited research into the relationship betweengas dispersion and soil physical characteristics. In this study, a series ofadvection–dispersion experiments was performed on granular porous mediato identify the effects of soil column dimensions (length and diameter),particle size and shape, dry bulk density, and moisture content on themagnitude of gas dispersion. Glass beads and various sands of differentshapes (angular and rounded) with mean particle diameters (d50) rangingfrom 0.19 to 1.51 mm at both air-dry and variable moisture contentswere used as granular porous media. Gas dispersion coefficients and gasdispersivities (a = DH/v, where v is the pore-gas velocity) were determinedby fitting the advection–dispersion equation to the measured breakthroughcurves. For all test conditions, DH increased linearly with v. The test resultsshowed that neither soil column length nor diameter had significant effecton gas dispersivity. Under air-dry conditions, higher gas dispersivities wereobserved for media with wider particle size distribution and higher dry bulkdensity. The minor effect of particle shape on gas dispersivity was foundunder both air-dry and wet conditions. Under wet conditions, the variationsin gas dispersivity were mainly controlled by the air-filled porosity. Anempirical model was also proposed for the prediction of gas dispersivity ingranular, unsaturated porous media.

Gas exchange through the compacted final cover soil at landfill sites plays a vital role for emission, fate, and transport of toxic landfill gases. This study involved measuring the soil-gas diffusivity (D /D , the ratio of gas diffusion coefficients in soil and free air) and air permeability (k ) for differently compacted soil samples (reddish-brown soil) from the final cover at the Maharagama landfill in Sri Lanka. The samples were prepared by either standard Proctor compaction or hand compaction to dry bulk densities of 1.60-1.94 g cm . Existing and modified models for predicting D /D and k were tested against the measured data. The simple, single-parameter Buckingham model predicted measured D /D values across compaction levels equally well or better than a dry bulk density (DBD) dependent model and a soil-water retention (SWR) dependent model. The measured k values for differently compacted samples were highly affected by the compaction level and the sample moisture preparation method. Also, for air permeability, a single-parameter Buckingham-type k model was most accurate in predicting k in the differently compacted soil samples. Equivalent air-filled pore diameters (the effective diameter of the drained pores active in leading air through the sample) for gas flow, d , were calculated from the measured D /D and k values. The d increased with compaction level, suggesting that a very high compaction level creates well-connected macropores in the reduced total pore space of the cover soil. This is an important consideration when designing cover soils for optimally low water and high oxygen exchange while minimizing climate and toxic gas emissions from the waste layer to the atmosphere.

The soil gas diffusion coefficient (D p ) and its dependency on soil air content, e, and tortuosity-connectivity of the air-filled pore networks control the transport and fate of gaseous-phase contaminants in variably saturated soil. The bimodality in pore size distribution of structured soil often yields a variation ofD with e in the intraaggregate pore region that is distinctly different from that in the interaggregate region. Data imply a highly nonlinear behavior of soil gas diffusivity, D p (e)/D o (where D o is the gas diffusion coefficient in free air), in the interaggregate region of aggregated soils similar to that of structureless soils with a unimodal pore size distribution, probably due to diffusion-limiting effects by connected water films at low e. In contrast, for the intraaggregate region, we show that the impedance factor F* (=D p /eD o ) and tortuosity factor T [= (1/F*) 1/2 ] are approximately constant for most soil media. We suggest a typically well-defined separation between the two pore regions at the minimum for the pore connectivity factor X* [= log(D p /D o )/log(e)], at which point the interaggregate pores are devoid of water while the intraaggregate pore region is water saturated. Based on this, a hierarchical two independent region (TIR) D p /D o model was developed by applying a cumulative series of Buckingham-Currie power-law functions, Fe X . A nonlinear, water-content-dependent expression for F best described the measured D p /D o in the interaggregate region, while constant F (around 0.5) and X (around 1) generally sufficed for the intraaggregate region. The TIR model better predicted gas diffusivities for both aggregate fractions and highly structured soils across the entire range of moisture conditions with RMSE reduced by two to five times compared with traditional predictive D p (e)/D o models.

The solute diffusion coefficient in soil (D ) and its dependency on the soil water content (θ), soil type, and compaction govern the transport and fate of dissolved chemicals in the soil vadose zone. Only a few studies have quantified solute diffusivity (D /D , where D and D are the solute diffusion coefficients in soil and pure water, respectively) for variably compacted soils with different textures. We measured the D for KCl on five different soils from Japan: two volcanic ash soils (Andisols) at different bulk densities, two sandy soils, and a loamy soil. The D was measured across a wide range of θ using the half-cell method. The D /D values for Andisols with bimodal pore size distribution were comparatively lower than for the other soils. Opposite to the behavior for sandy soils, the D /D for Andisols at a given θ decreased markedly with increasing bulk density under wet conditions but increased with increasing bulk density under dry conditions. Data for all soil types including sandy soils with unimodal pore size distribution implied a two-region behavior when plotted as log(D /D ) vs. θ. We suggest that the similar behavior across soil types can be explained by regions of low and high water phase connectivity for relatively structureless soils and by high intraaggregate and low interaggregate water phase tortuosity for aggregated soils. Among a number of tested predictive models for D /D , the Penman-Millington-Quirk model, which requires knowledge of only θ and total porosity, performed best across soil types. © Soil Science Society of America. s s 0 s 0 s s s 0 s 0 s 0 s 0

原位置通気係数（Ka, insitu）は，比較的低コストかつ迅速測定が可能であり，地盤内でのガスや水の移動特性を把握する上で非常に有効な物質移動パラメータである．一般に，Ka, insituの計算には，地盤内の三次元空気流れを考慮するための形状係数が組み込まれる．本研究では，有限要素法による数値解析により地盤内空気流れをシミュレーションし，得られた形状係数やKa, insituを既往の研究結果と比較するとともに，形状係数に横境界や下端境界条件の変化が及ぼす影響を数値解析および模型実験により検証した．その結果，Ka, insitu測定時の下端境界条件が形状係数やKa, insituに大きな影響を与えることが明らかにされた．特に，地盤表層付近に不透気層が存在する場合は，調査地点での境界条件を考慮した形状係数を求め，Ka, insitu を適切に算出することが必要である．

Unique physical properties of volcanic ash soils characterize the soil gas transport parameters of gas diffusivity and air permeability. Air permeability controls the density-driven flow that has been recognized as one of the important phenomena for subsurface dense gas. In this study, one-dimensional column experiments were conducted to investigate the effects of the pore structure of a volcanic ash soil on the density-driven flow of a dense gas (isohexane). The results showed that the overall horizontal gas movement in Tachikawa loam (volcanic ash soil) and Toyoura sand (sand) used as reference materials was expressed by Fick's diffusion law. On the other hand, the vertical downward gas movements in Tachikawa loam were considerably enhanced by the occurrence of density-driven flow, especially at high air contents (30-40%). Pore size distribution and pore structure analysis based on the tube model suggest that a greater volume of large pores (>0.01 cm) and a more continuous pore network led to the greater density-driven flow in Tachikawa loam than in Toyoura sand.

Soil and underground water pollution by waste heat in urban area is linked to the development of underground commercial facilities and subways and to the installation of ground source heat pump (GSHP) systems. In this study, we carried out laboratory tests of the dependence of dissolution elements on temperature, using boring core samples taken from the central Tokyo area in order to reduce the risks to underground water pollution by installed GSHP system. Our results demonstrate that we have to be careful not to risk contaminating shallow groundwater with hazardous elements, including marine and/or volcanic sediments, and by oxidizing the environment.

This study was conducted to characterize the adsorption of Cd2+ and Pb2+ by raw coconut husk (RCH) and humic acid–treated coconut husk (HACH). Grounded and sieved coconut husk (CH) from Sri Lanka was treated with humic acid to use as the adsorbent in laboratory experiments. Capacities of HACH and RCH for adsorption of Cd2+ and Pb2+ at different pH, ionic strengths, initial metal concentrations, and contact times between adsorbent and adsorbate were measured. The effects of binary metal solution, anions, and cations on adsorptions of Cd2+ and Pb2+ by treated and nontreated CH in batch experiments were also examined. The surface characteristics of HACH and RCH were investigated by scanning electron micrography (SEM), X-ray energy dispersion analysis (EDAX), methylene blue (MB), and the Brunauer, Emmett, and Teller (BET) methods to explain the results. Results showed that adsorption of Cd2+ and Pb2+ ions by HACH was independent of pH and ionic strength. The maximum adsorption capacities of Cd2+ and P...

The increased worldwide use of shallow geothermal energy systems including ground source heat pumps (GSHPs) have given concerns of possible temperature effects on soil geotechnical properties. In this study, the effects of temperature on mechanical characteristics such as consolidation settlement, shear stiffness, and permeability of kaolin clay were investigated. A modified oedometer apparatus which allows the simultaneous measurements of consolidation settlement, shear wave velocity, and hydraulic conductivity was developed and used. Consolidation tests on preconsolidated kaolin samples (two sample sizes: ϕ 6 cm x H 10 cm and ϕ 6 cm x H 2 cm) were performed under sequentially increasing consolidation pressures at three different temperatures (5 °C, 15 °C, and 40 °C). Larger apparent preconsolidation pressure, Pac, was seen at higher temperature (40 °C) for both sample sizes, but only for samples having relatively high initial void ratios between 1.53 and 1.62. Relatively higher shear modulus as a function of void ratio was observed for samples at higher temperature, suggesting that changes in fabric structure (likely caused by enhanced inter-particle forces between clay particles at higher temperature) resulted in the increased shear stiffness and, thus, higher Pac at 40 °C. Oppositely, temperature effects on the Manuscript received February 5, 2013. This work was partly funded by a grant from the Research Management Bureau, Saitama University, the grant-in-Aid for Scientific Research of Japan Society for the Promotion of Science (JSPS) (No.22860012), and a JSPS bilateral research project. This work was also partially supported by a CREST project, a research grant from the Japan Science and Technology Agency (JST). E. E. Mon is with Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (phone/fax: (+81) 48-858-3116; e-mail: nyima.eimon@gmail.com). S. Hamamoto, is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: hamasyo@mail.saitama-u.ac.jp) K. Kawamoto is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: kawamoto@mail.saitama-u.ac.jp). T. Komatsu is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: komatsu@mail.saitama-u.ac.jp). P. Modrup is with Department of Biotechnology, Chemistry, and Environmental Engineering, Aalborg University, 9000 Aalborg, Denmark. (e-mail: pm@bio.aau.dk). permeability of kaolin clay were not significant within the studied temperature range between 5 °C and 40 °C.

Gas diffusion is a dominant transport mechanism for climate and regulated gases in the vadose zone. Soil-gas diffusion is governed by the gas diffusion coefficient ( D p , m 2 s −1 ) which is highly dependent on soil texture, such as sand, silt, clay, and organic matter contents, as well as soil physical properties such as soil-air content (e, m 3 m −3 ) or total porosity (Φ, m 3 m −3 ). Soil organic matter is a key contributor to the formation of the soil pore structure (i.e., total porosity and air-filled pore tortuosity), and it highly affects D p behavior under variably saturated conditions. In this study, based on numerous D p data sets across soil types including sands, loamy clay soils, volcanic ash soils, and organic soils, predictive D p models incorporating a percolation threshold (e th , m 3 m −3 ) and pore tortuosity factor ( X ′) are proposed. The observed relations between either e th or X ′ and either Φ or volumetric organic matter fraction (OMF, m 3 m −3 ) were embedded in the proposed D p model. The proposed D p models, coupled with predictive e th and OMF models, performed well against the measured D p data across soil types. Finally, a sensitivity analysis of the OMF in relation to the D p and pore-network tortuosity ( T ) showed a reduction in D p and increase in T with increasing OMF under the same e conditions.

[1] A unified measurement system with suction control (UMS_SC) was developed for measuring soil water characteristics curves (SWCC) and gas transport parameters under alternating drying and wetting cycles. The new system consists of a diffusion chamber, sample ring, porous plate, tensiometer, moisture sensor, oxygen electrodes, and air pressure gauges. The SWCC and gas transport parameters [gas diffusion coefficient (Dp) and air permeability (ka)] for two different porous materials, Toyoura sand and granulated slag, were simultaneously measured under drying and wetting cycles. The SWCC and gas transport parameters measured by UMS_SC were consistent with recent models and independently measured data on exactly the same materials using standard experimental setups from literature. For an applied water suction head of less than 50 cm and corresponding water saturation of around 0.3–0.5, the UMS_SC data documented hysteretic (nonsingular) behavior in both measured Dp and ka under repeated drying and wetting cycles. The hysteretic behavior was insignificant for water and air contents but large for both gas transport parameters when applying suction, and hysteretic effects were larger for air permeability than for gas diffusivity. Additionally, hysteresis in the percolation threshold (soil-air content where gas transport ceases due to interconnected water-filled pores) for both gas diffusion and air permeability was insignificant for both materials. These findings should be taken into account when developing models for diffusive and convective gas transport and their parameters in variably saturated porous media.

[1] Diffusivity was measured for 12 rock and construction material samples using a diffusion chamber method with oxygen as the tracer gas. Several steps were implemented to minimize leakage between the sample and the core holder, and rigorous tests were performed to evaluate and correct the overall leakage of the diffusion apparatus. This method was proven capable of rapidly measuring the diffusion coefficient for consolidated samples having dimensionless diffusivity values greater than 4.7 × 10−4 in a relative short duration (hours to 1 day). Gas diffusion measurements were also conducted for 11 repacked sediments and sands. Our results are consistent with literature data from liquid tracer through-diffusion methods; the diffusivity versus porosity relationship for our data can be described by Archie's law. The m value in Archie's law was found to be correlated to pore size: the finer the pore size is, the larger the m value is. A linear regression equation can describe the change of m with ln d50 (the volumetric mean pore diameter) for most rocks with d50 < 1.3 μm, while the outliers can be correlated to narrower pore size distribution.

[1] Describing and predicting gas and solute diffusivities and electrical and thermal conductivities under variably saturated fluid conditions are necessary for simulating gas, solute, and heat transport in soils. On the basis of comprehensive data for gas (Dp) and solute (Ds) diffusivities and electrical (EC) and thermal (TC) conductivities for differently textured and variably saturated soils, we investigated analogies and differences between the four parameters. At fluid (water or air) saturation, relative parameter values for Dp, Ds, and EC were all well described by an excluded-volume expansion of Archie's first law. The cementation exponent in Archie's first law was close to 1.5 for all parameters. At fluid-unsaturated conditions, relative values of Dp, Ds, and EC (normalized at fluid saturation) were well described by an excluded-volume expansion of Archie's second law. In the case of relative TC, the saturation exponent in Archie's second law was substituted by the inverse of it for the three other parameters since water bridge effects dramatically enhance the TC with increasing moisture contents in relatively dry porous media. If appropriate but different expressions for a percolation threshold in Archie's second law were applied for the four parameters, a saturation exponent value of around 2.0 generally gave accurate predictions of all four parameters for differently textured soils. Finally, the excluded-volume expansion of Archie's second law was modified to also represent porous media with bimodal pore size distribution and well-described data for Dp and Ds in aggregated soil.