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Block copolymer self-assembly is a powerful tool for two-dimensional nanofabrication; however, the extension of this self-assembly concept to complex three-dimensional network structures is limited. Here we report a simple method to experimentally generate three-dimensional layered mesh morphologies through intrinsic molecular confinement self-assembly. We designed triblock bottlebrush polymers with two Janus domains: one perpendicular and one parallel to the polymer backbone. The former enforces a lamellar superstructure that intrinsically confines the intralayer self-assembly of the latter, giving rise to a mesh-like monoclinic (54°) M15network substructure with excellent long-range order, as well as a tetragonal (90°) T131mesh. Numerical simulations show that the spatial constraints exerted on the polymer backbone drive the assembly of M15and yield T131in the strong segregation regime. This work demonstrates that intrinsic molecular confinement is a viable path to bottom-up assembly of new geometrical phases of soft matter, extending the capabilities of block copolymer nanofabrication.

Landfill sites are significant sources of greenhouse gases, particularly methane. It is believed that methane gas eruptions occur under a surface ponding condition during rainfall events. In this study, based on laboratory column experiments in which mixed gas was applied to variably compacted soil columns (10 cm in diameter and 30.5 cm in height) under different rainfall intensities, the effects of the bulk density of the landfill cover soil, the gas injection rates, and the rainfall intensities on the gas eruption phenomenon were investigated. The gas pressure and the water content were monitored during rainfall events. The main results were that (1) an episodic gas compression and eruption cycle was observed under a surface ponding condition, (2) gas eruptions occurred at a higher gas pressure in the soil with a higher dry bulk density, and (3) a higher gas injection rate resulted in continuous gas eruptions. The monitoring of the gas eruption flux and gas concentration in the soil columns, using oxygen-mixed gas as an injected gas, showed that longer gas compression led to higher gas fluxes during the gas eruptions. The concentration of gas in the soil increased over time because of the upward gas flow in accordance with the eruptions. The calculation of the oxygen mass balance indicated that the eruptions had slightly promoted the emission of gas from that which had been stored in the soil prior to the rainfall events.

Mass transport in soil occurs through the soil pore network, which is highly influenced by pore structural parameters such as pore-size distribution, porosity, pore tortuosity, and coordination number. In this study, we visualised the networks of meso- and macro-pores (typical pore radius r ≥ 10 μm) using microfocus X-ray computed tomography (MFXCT) and evaluated pore structural parameters of two loamy soils from Japan and New Zealand packed at different degrees of compaction. The effect of compaction on pore structural parameters and relationships between pore structural parameters and measured mass transport parameters were examined. Results showed a clear influence of compaction on pore structural parameters, with the MFXCT-derived mean pore radii and pore tortuosities decreasing and the mean pore coordination number increasing with increasing dry bulk density. Especially, pores with r > 80 µm became finer or were not well formed due to compaction. The MFXCT-derived pore structural parameters were not well correlated with the equivalent pore radii from measured water retention curves. However, volumetric surface areas and pore-network connectivity-tortuosity factors derived from MFXCT allowed a fair prediction of several important mass transport parameters such as saturated hydraulic conductivities, soil-gas diffusion coefficients, and soil-air permeabilities. Further studies are needed to link micro-pores with radii smaller than the X-ray CT resolution to meso- and macro-pores visualised by X-ray CT to improve the prediction of mass transport parameters in soil.

Roadbed materials of base and subbase layers are frequently unsaturated caused by rainfall, drainage, and evaporation. However, the movement of water in these layers is still poorly understood because of lacking data on unsaturated properties such as the water retention curve (WRC) and unsaturated hydraulic conductivity (K). This study, therefore, recycled concrete aggregates (RCA) blended with autoclaved aerated concrete (AAC) grains (% of substitution on the mass basis from 0 to 50%) were used to examine the WRC and Kfor unbound roadbed materials in Vietnam using the evaporation method. Natural aggregates (NA) and Toyoura sand were used as control and reference material. Results showed that compared to NA100% and RCA100%, the water capacity of RCA mixed samples was much improved by blending AAC grains. Toyoura sand showed higher water capacity at saturation compared to RCA100% and NA100%, but quickly became lowest when matric potential exceeds 10 kPa. Toyoura sand showed the highest saturated hydraulic conductivity, but decreased dramatically around 10 kPa, while other tested samples remained higher K. The original van Genuchten – Mualem model was well fitted for Toyoura sand and underestimated for other tested samples, but showed an agreement with estimated conductivity parameter ranging from – 3.0 to -4.4.

The self-assembly of block copolymers (BCPs) with novel architectures offers tremendous opportunities in nanoscale patterning and fabrication. Here, the thin film morphology, annealing kinetics, and topographical templating of an unconventional Janus-type “PS-branch-PDMS” bottlebrush copolymer (BBCP) are described. In the Janus-type BBCP, each segment of the bottlebrush backbone connects two immiscible side chain blocks. Thin films of a Janus-type BBCP with Mn= 609 kg/mol exhibited 22 nm period cylindrical microdomains with long-range order under solvent vapor annealing, and the effects of as-cast film thickness, solvent vapor pressure, and composition of the binary mixture of solvent vapors are described. The dynamic self-assembly process was characterized using in situ grazing-incidence X-ray scattering. Templated self-assembly of the BBCP within lithographically patterned substrates was demonstrated, showing distinct pattern orientation and dimensions that differ from conventional BCPs. Self-consistent field theory is used to elucidate details of the templated self-assembly behavior within confinement.

ABSTRACTA long-term monitoring of composition of landfill gases in the region with high rainfall was conducted using an argon assay in order to discuss air intrusion into the dump site. Gas samples were taken from vertical gas monitoring pipes installed along transects at two sections (called new and old) of an abandoned waste dump site in Sri Lanka. N2O concentrations varied especially widely, by more than three orders of magnitude (0.046–140 ppmv). The nitrogen/argon ratio of landfill gas was normally higher than that of fresh air, implying that denitrification occurred in the dump site. Argon assays indicate that both N2and N2O production occurred inside waste and more significantly in the old section. The Ar assay would help for evaluations of N2O emission in developing countries.Implications: A long-term monitoring of composition of landfill gases in the region with high rainfall was conducted using an argon assay in order to discuss air intrusion into the dump site. Argon assays indicate that both N2and N2O production occurred inside waste and more significantly in the old section.

Granulated bentonite mixtures (GBMs) have been regarded as effective buffer materials in the deep geological disposal of radioactive waste due to their operational advantages, such as ease of transportation and in-situ placement/backfilling. Many studies have been done to characterize the hydraulic and thermal properties of GBMs as well as their swelling properties. Only limited studies, however, have investigated their gas transport properties, even though these properties affect their compactness during in-situ placement/backfilling and subsequent gas diffusion and advection in the buffer zone. The aim of this study is to understand the gas transport parameters, i.e., air permeability (ka) and gas diffusivity (Dp/Do), of tested samples compacted at different dry densities (DDs) under air-dried conditions, linking them with the measured density distribution characteristics determined by microfocus X-ray computed tomography (MFXCT) analysis. Two types of GBMs were used in this study: 1) FE-GBM (prepared from National Standard® bentonite, Wyoming, USA): this material was used in the Full-scale Emplacement (FE) experiment at the Mont Terri rock laboratory, Switzerland) and 2) OK-GBM (prepared from a bentonite, originating from Japan, with the trade name of OK bentonite, Kunimine Industries). The tested samples were firstly packed in a 100-cm3acrylic core with different DDs, ranging from loose to dense (1.09 to 1.75 g/cm3), and scanned by MFXCT. The weighting factors, wf(fine fraction; lower density) and wc(coarse fraction; higher density) (wf + wc = 1), were determined after the peak separation of the measured CT brightness histograms from the reconstructed three-dimensional multiplanar reconstruction (MPR) images of the MFXCT analysis. The measured kaand Dp/Dowere highly dependent on the DDs, the ka(ɛ) values fitted well with a power law model, and the Dp/Do(ɛ) was predicted accurately by several previously proposed models. For both FE-GBM and OK-GBM, there were good linear relationships between the gas transport parameters and wc × DD, implying that the weight of the coarse fraction controlled kaand Dp/Do. Moreover, the Kozeny-Carman model, incorporating the measured volumetric surfaces from the MFXCT analysis, was able to predict the kavalues well.

Mass transport in soils occurs through pore networks that are highly affected by basic physical properties such as the degree of compaction, and particle size and shape. In this study, micro-focus X-ray computed tomography (CT) was used to obtain information on the pore network structure at different compaction levels for repacked columns of sands and glass beads representing different size fractions and particle shapes. Mass transport parameters, including gas diffusion coefficient (Dp) and air permeability (ka) at variably saturated conditions, were measured on the same columns using standard methods, and literature data on saturated hydraulic conductivity (Ksat) for the same materials were analyzed. A comparison of X-ray CT derived pore network structure and physical parameters showed that the round sands and glass beads exhibited larger pores, a higher pore coordination number, and a lower volumetric surface area than that of angular sands at the same particle size, resulting in higher Ksatas well as higher Dpand kaunder relatively dry conditions. The X-ray CT derived the mean pore diameter (d), and the pore coordination number (Cn) for each material correlated well with key gas transport properties such as percolation thresholds and pore network connectivity. A predictive Dpmodel from wet to dry conditions based fully on X-ray CT derived parameters (dand Cn) was developed and showed good agreement with measured Dpfor both round and angular sands.

We explored the color constancy mechanisms of color-deficient observers under red, green, blue, and yellow illuminations. The red and green illuminations were defined individually by the longer axis of the color discrimination ellipsoid measured by the Cambridge Colour Test. Four dichromats (3 protanopes and 1 deuteranope), two anomalous trichromats (2 deuteranomalous observers), and five color-normal observers were asked to complete the color constancy task by making a simultaneous paper match under asymmetrical illuminations in haploscopic view on a monitor. The von Kries adaptation model was applied to estimate the cone responses. The model fits showed that for all color-deficient observers under all illuminations, the adjustment of the S-cone response or blue-yellow chromatically opponent responses modeled with the simple assumption of cone deletion in a certain type (S-M, S-L or S-(L+M)) was consistent with the principle of the von Kries model. The degree of adaptation was similar to that of color-normal observers. The results indicate that the color constancy of color-deficient observers is mediated by the simplified blue-yellow color system with a von Kries-type adaptation effect, even in the case of brightness match, as well as by a possible cone-level adaptation to the S-cone when the illumination produces a strong S-cone stimulation, such as blue illumination.

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.

The time dependency of water repellency (WR) in hydrophobic porous media plays a crucial role for water infiltration processes after rainfall and for the long‐term performance of capillary barrier systems. The contact angle (CA) of hydrophobic media normally decreases with continuous contact with water, eventually allowing water imbibition. However, the effect of the reduction in CA with soil‐water contact time on the water retention function of hydrophobic media is not yet fully understood. In this study, water retention characteristics were measured using a hanging water column apparatus equipped with a mini‐time domain reflectometry (TDR) coil probe under controlled wetting and drying in a water‐repellent volcanic ash soil (VAS) and in sands coated with different hydrophobic agents. The contact angle (CA–SWRC) under imbibition was evaluated based on the inflection points on the water retention curves. For both water‐repellent VAS and hydrophobized sand samples, the calculated CA–SWRCincreased with increasing WR. This was determined from both the water drop penetration time and the initial contact angle (CAi) by the sessile drop method. Calculated CA–SWRCvalues ranged from 20° to 48° for the water‐repellent VAS and from 40° to 63° for the hydrophobized sand. The CA reduction with contact time was quantified by relating CA–SWRCand CAi. This gave a significant linear relationship for the hydrophobized sand [CA–SWRC= 0.40CAi+11.3 (30° < CAi< 120°), R2= 0.66]. A large difference in water‐filled pore distributions under controlled wetting and drying cycles was found on calculating the soil water capacity and pore size density as a function of water potential.

Time domain reflectometry (TDR) is used widely for measuring soil‐water content. New TDR coil probe technology facilitates the development of small, nondestructive probes for simultaneous measurement of soil‐water content (θ) and soil‐water potential (ψ). In this study we developed mini tensiometer‐time domain reflectometry (T‐TDR) coil probes, 6‐mm wide and 32‐mm long. The coil probes were calibrated against a conventional three‐rod probe and were used for measuring θ for a aggregated volcanic ash soil (VAS) and a uniform sand. A commonly‐used dielectric mixing model did not accurately describe the measured relation between the dielectric constant of the T‐TDR coil probe (εcoil) and θ, and a new calibration model for εcoil(θ) was proposed instead. The new model assumes single‐region behavior for sand and two‐region behavior for aggregated VAS, when plotting the normalized dielectric constant of the coil probe (εcoil–ε dry; where εdryis the dielectric constant of the T‐TDR coil probe for air‐dried material) as a function of θ. The new calibration model accurately described the (εcoil–ε dry)‐θ relations measured by 7 T‐TDR coil probes on both sand and VAS. Additionally, there was a good agreement between measured soil‐water retention curves (ψ >–100 cm H2O) by the new T‐TDR coil probes and independent measurements by the hanging water column method.

Understanding soil–gas phase properties and processes is important for finding solutions to critical environmental problems such as greenhouse gas emissions and transport of gaseous‐phase contaminants in soils. Soil–air permeability, ka(μm2), is the key parameter governing advective gas movement in soil and is controlled by soil physical characteristics representing soil texture and structure. Models predicting kaas a function of air‐filled porosity (ɛ) often use a reference‐point measurement, for example, ka,1000at ɛ1000(where the measurement is done at a suction of –1000 cm H2O). Using kameasurements from two Danish arable fields, each located on natural clay gradients, this study presents a pore tortuosity–disconnectivity analysis to characterize the soil–gas phase. The main objective of this study is to investigate the effect of soil–moisture condition, clay content, and other potential drivers of soil texture and structure on soil‐gas phase characteristics based on a ka–based pore tortuosity parameter, Xa[= log(ka/ka,1000)/log(ɛ/ɛ,1000)]. Results showed that Xadid not vary significantly with soil matric potential (in the range of –10 to –1000 cm H2O), but the average Xaacross moisture conditions showed a strong linear relation (R2= 0.74) to clay content. The Xa,further showed promising relations to specific surface area, Rosin–Rammler particle size distribution indices, α and β (representing characteristic particle size and degree of sorting, respectively), and the Campbell water retention parameter, b. Considering clay as a main driver of soil–gas phase characteristics, we developed expressions linking clay content and ka,1000at ɛ1000and discussed the effect of clay content on general ka–ɛ behavior.

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 (), diffusivity (DPD0), 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 and tortuosity calculated from gas transport parameters (

The article presents a study which aims to characterize the relationships between soil-pore geometry and gas transport parameters reveals by X-ray computed tomography (CT). The study used unified measurement system (UMS) to measure gas transport parameters, such as gas dispersivity, diffusivity, and permeability. Study reveals the strong relationship of permeability when plotted against the equivalent pore diameter.

The dry end of the soil water characteristic (SWC) is important for modeling vapor flow dynamics and predicting soil properties such as specific surface area (SSA) and clay content (CL). Verification of new instrumentation for rapid measurement of the dry end of the SWC is relevant to avoid long equilibration times and potential for hydraulic decoupling. The objectives of this study were to measure both adsorption and desorption branches of the dry end of the SWC for 21 variably‐textured Arizona soils using new, fully automated instrumentation (AquaSorp); apply the data to parameterize the Tuller and Or (TO) and new single‐parameter non‐singularity (SPN) models; and evaluate estimates of SSA from water sorption, ethylene glycol monoethyl ether (EGME), and N2–BET methods. The AquaSorp successfully measured water sorption isotherms (∼140 data points) within a reasonably short time (1–3 d). The SPN model well described the distinct non‐singularity between the adsorption and desorption branches, while the TO model captured the adsorption data reasonably well (<5% deviation from measurements), except for matric potentials below –200 MPa. The SSA derived from water sorption and the TO model were comparable to SSAEGMEfor all soils. The matric potential at “zero” water content was confirmed as the widely accepted value of around –800 MPa. A non‐singularity coefficient based on water adsorption at monolayer coverage was positively correlated with CL. Obtained results show the potential of the AquaSorp to accurately measure the dry region of the SWC, providing a rapid determination of SSA.

Modeling water distribution and flow in partially saturated soils requires knowledge of the soil water characteristic (SWC). However, measurement of the SWC is challenging and time‐consuming and, in some cases, not feasible. This study introduces two predictive models (FW–model and AW–model) for the SWC, derived from readily available soil properties such as texture and bulk density. A total of 46 undisturbed soils from different horizons at 15 locations across Denmark were used for model evaluation. The FW–model predicts the volumetric water content as a function of volumetric fines content (organic matter and clay). It performed reasonably well for the dry‐end of SWC (above a pFvalue of 2.0; pF= log(|ψ|), where ψ is the matric potential in cm), but did not do as well closer to saturated conditions. The AW–model predicts the volumetric water content as a function of volumetric content of different particle size fractions (organic matter, clay, silt, and fine and coarse sands). The volumetric content of a particular soil particle size fraction was considered if it contributed to the pore size fraction still occupied with water at the given pFvalue. Hereby, the AW–model implicitly assumes that a given particle size fraction creates an analogue pore size fraction and further this pore size fraction filled with water is corresponding to a certain pFvalue according to the well‐known capillary rise equation. The AW–model was found to be quite robust, and it performed exceptionally well for pFvalues ranging from 0.4 to 4.2 for different soil types. For prediction of the continuous SWC, it is recommended to parameterize the van Genuchten model based on the SWC data points predicted by the AW–model.

Growing plants in extraterrestrial environments, for example on a space station or in a future lunar or Martian outpost, is a challenge that has attracted increasing interest over the last few decades. Most of the essential plant needs for optimal growth (air, water, and nutrient supply, and mechanical support) are closely linked with the basic physical properties of the growth media. Diffusion is the main process whereby oxygen and nutrients are supplied to plant roots, and gas and solute diffusivity are the key parameters controlling the diffusive movement of oxygen and nutrients in the root zone. As one among several essential aspects of optimal porous media design for plant growth, this study presents a diffusion‐based characterization of four commercial, aggregated growth media. To account for the observed large percolation threshold for gas diffusivity in the selected media, an inactive pore and density corrected (IPDC) model was developed and excellently described measured gas diffusivity in both inter‐ and intraaggregate pore regions. A strong relation (r2= 0.98) between percolation threshold for gas diffusivity and mean particle (aggregate) diameter was found and suggested to be used in future design models. Also, critical windows of diffusivity (CWD) was defined identifying the air content range where gas diffusivity (hence, oxygen supply) and solute diffusivity or the analogous electrical conductivity (hence, nutrient supply) are above pre‐defined, critical minimum values. Assuming different critical values for gas diffusivity under terrestrial and Martian conditions, the four growth media were compared and it was found that one medium did not fulfill the pre‐set criteria. Overall, the analyses suggested that particle (aggregate) sizes below 0.25 and above 5 mm should likely be avoided when designing safe plant growth media for space. The CWD concept was also applied to a natural volcanic ash soil (Nishi‐Tokyo, Japan), and the natural soil was found competitive or better than the tested commercial growth media. This could bear large perspectives for Martian outpost missions, since NASA has found that Martian dust/soil mostly resembles volcanic ash soil among terrestrial materials.

The gas diffusion coefficient (Ds,g) and solute diffusion coefficient (Ds,l) and their dependencies on fluid content (κ) (equal to soil–air content θ for Ds,gand soil–water content ɛ for Ds,l) are controlling factors for gas and solute transport in variably saturated soils. In this study, we propose unified, predictive models for Ds,g(ɛ) and Ds,l(θ) based on modifying and extending the classical Maxwell model at fluid saturation with a fluid‐induced reduction term including a percolation threshold (ɛthfor Ds,gand θthfor Ds,l). Different percolation threshold terms adopted from recent studies for gas (Ds,g) and solute (Ds,l) diffusion were applied. For gas diffusion, ɛthwas a function of bulk density (total porosity), while for solute diffusion θthwas 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 Ds,gand Ds,ldata 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. In conclusion, the commonly applied strategy of using the same, soil‐type‐independent model for gas and solute diffusivity in analytical and numerical models for chemical transport and fate in variably‐saturated soils appears invalid, except for highly sandy soils. The unified LIGA model with differing percolation thresholds for diffusion in the liquid and gaseous phases solves this problem.

Subsurface gaseous‐phase transport is governed by three gas transport parameters: the air permeability coefficient (ka), gas diffusion coefficient (DP), and gas dispersion coefficient (DH). Among these, DHis the least understood due to hitherto limited research into the relationship between gas dispersion and soil physical characteristics. In this study, a series of advection–dispersion experiments was performed on granular porous media to identify the effects of soil column dimensions (length and diameter), particle size and shape, dry bulk density, and moisture content on the magnitude of gas dispersion. Glass beads and various sands of different shapes (angular and rounded) with mean particle diameters (d50) ranging from 0.19 to 1.51 mm at both air‐dry and variable moisture contents were used as granular porous media. Gas dispersion coefficients and gas dispersivities (α = DH/v, where vis the pore‐gas velocity) were determined by fitting the advection–dispersion equation to the measured breakthrough curves. For all test conditions, DHincreased linearly with v. The test results showed that neither soil column length nor diameter had significant effect on gas dispersivity. Under air‐dry conditions, higher gas dispersivities were observed for media with wider particle size distribution and higher dry bulk density. The minor effect of particle shape on gas dispersivity was found under both air‐dry and wet conditions. Under wet conditions, the variations in gas dispersivity were mainly controlled by the air‐filled porosity. An empirical model was also proposed for the prediction of gas dispersivity in granular, unsaturated porous media.

Batch adsorption and consecutive desorption experiments were performed under different pH conditions to assess the pH dependency of 2,4-dichlorophenoxyacetic acid (2,4-D) adsorption and desorption in Andosol (having pH-dependent surface charge characteristics) and kaolinite. The adsorption-desorption isotherms for both Andosol and kaolinite were well fitted by the Freundlich isotherm model. Adsorption of 2,4-D onto Andosol increased markedly with decreasing pH and was higher than for kaolinite under the same pH condition. Hysteresis, expressing the nonsingularity of the desorption compared with the adsorption isotherm, was found at all concentrations and each pH for both Andosol and kaolinite. For Andosol, the fitted Freundlich parameters for desorption, Kf,dand nd, showed a negative, linear and a positive, exponential relationship, respectively, with pH. Higher hysteresis index (), expressing the degree of partial irreversibility of 2,4-D adsorption, was obtained under lower pH, indicating that less adsorbed 2,4-D was released back from the Andosol under acidic condition. The effect of pH on 2,4-D desorption from kaolinite was less pronounced as compared with Andosol. Combining the measured data in this study with previously reported data on 2,4-D adsorption-desorption in several types of soil including Andosols, the possible mobility of adsorbed 2,4-D in soil was evaluated. Results show that adsorbed 2,4-D in soils exhibiting a total adsorption percentage of less than 55 of the applied pesticide typically exhibited a greater potential to be mobile in the soil-water system. Opposite, a total adsorption percentage greater than 55 implied higher residual adsorption and a prolonged existence of adsorbed 2,4-D in the soils.

The article discusses a study on the hydrogen-ion concentration (pH) dependency of 2,4-dichlorophenoxyacetic acid (2,4-D) desorption and adsorption in kaolinite and andosol. It mentions that possible mobility of adsorbed 2,4-D in soil was assessed. It shows that adsorption of 2,4-D onto andosol was higher than for kaolinite under the same pH condition and that hysteresis was found at all concentrations and each pH for kaolinite and andosol.

Accurate predictions of the soil‐gas diffusivity (Dp/Do,where Dpis the soil‐gas diffusion coefficient and Dois the diffusion coefficient in free air) from easily measureable parameters like air‐filled porosity (ε) and soil total porosity (ϕ) are valuable when predicting soil aeration and the emission of greenhouse gases and gaseous‐phase contaminants from soils. Soil type (texture) and soil density (compaction) are two key factors controlling gas diffusivity in soils. We extended a recently presented density‐corrected Dp(ε)/Domodel by letting both model parameters (α and β) be interdependent and also functions of ϕ. The extension was based on literature measurements on Dutch and Danish soils ranging from sand to peat. The parameter α showed a promising linear relation to total porosity, while β also varied with α following a weak linear relation. The thus generalized density‐corrected (GDC) model gave improved predictions of diffusivity across a wide range of soil types and density levels when tested against two independent data sets (total of 280 undisturbed soils or soil layers) representing Danish soil profile data (0–8 m below the ground surface) and performed better than existing models. The GDC model was further extended to describe two‐region (bimodal) soils and could describe and predict Dp/Dowell for both different soil aggregate size fractions and variably compacted volcanic ash soils. A possible use of the new GDC model is engineering applications such as the design of highly compacted landfill site caps.

The air permeability (ka) and soil gas diffusion coefficients (Dp) are controlling factors for gas transport and fate in variably saturated soils. We developed a unified model for kaand Dpbased on the classical Archie's law, extended by: (i) allowing for two‐region gas transport behavior for structured soils, with the natural field moisture condition (set at −100 cm H2O matric potential [pF 2]) as the reference (spliced) point between the large‐pore (drained pore diameter ≥30 μm at pF ≤ 2) and the small‐pore (subsequently drained pores <30 μm at pF > 2) regions, and (ii) including a percolation threshold, set as 10% of the total porosity for structureless porous media or 10% of the porosity in the large‐pore region for structured soils. The resulting extended Archie's law with reference point (EXAR) models for kaand Dpwere fitted to the measured data. For both structureless and structured porous media, Archie's saturation exponent (n) was higher for Dpthan for ka, indicating higher water blockage effects on gas diffusion. For structured soils, the saturation exponent for the large‐pore region (n1) was lower than for the small‐pore region (n2). Generally, n1values of∼1 for kaand 2 for Dpand n2values of 4/3 for kaand 7/3 for Dpdescribed the data well. Two reference‐point expressions for kaat pF 2 were also developed and tested together with existing models for Dpat pF 2 against independent data across soil types. The best‐performing reference‐point models were a kamodel based on the classical Kozeny equation and the Moldrup Dpmodel.

Colloid-facilitated transport enhances migration of strongly sorbing compounds (e.g., radionuclides, phosphorus, heavy metals) in soil and groundwater. Mobilization, transport and deposition of soil colloids are the underlying processes governing colloid-facilitated contaminant transport. Although significant progress has been made in simulating mobilization and transport/deposition of model colloids in different collector systems, it may be inadequate for the prediction of natural colloidal behavior in the subsurface. This study quantifies the leaching of natural volcanic ash soil colloids (NC) as well as the simultaneous transport of applied water dispersible soil colloids (WDC) in aggregated volcanic ash soil columns. Two water-saturated soil columns were irrigated with artificial irrigation water (AIW) at an intensity of 80 mm/hr for 60 hours. Two additional columns were irrigated at the same intensity, but a colloidal suspension of 5 mg/L was applied after 20 hours for a period of 20 hours. Effluent colloid concentrations were measured in each experiment. HYDRUS-1D was used for the simulation and estimation of colloid transport parameters. The results clearly showed different kinetics for applied colloid transport and natural colloid leaching. Transport of applied WDC followed first-order attachment kinetics, while the two-site equilibrium/kinetic model with equal fractions of equilibrium and kinetic sites best described the leaching of NC. Coupling these best model approaches well predicted the simultaneous leaching of natural and applied colloids, hereby providing a useful tool for the design of colloid-based in-situ soil remediation systems.

Soil-water content () and soil organic carbon (SOC) are key factors controlling the occurrence and magnitude of soil-water repellency (WR). Although expressions have recently been proposed to describe the nonlinear variation of WR with , the inclusion of easily measurable parameters in predictive WR() models is still lacking. In this study, a simple empirical beta function was suggested to describe the effect of changing soil-water content on the change of WR given as apparent contact angle () measured by the molarity of ethanol droplet (MED) method. The beta function for predicting () is based on measurement of WR on air-dry soil and three additional model parameters the water contents at which the maximum WR (highest ) occurs and where WR ceases (= 90 degrees), and the maximum value. The MED data for three data sets from literature comprising WR measurements across moisture conditions for 19 soils were used to test the model. The beta function successfully reproduced all the measured soil-water repellency characteristic, (), curves. Significant correlations were found between model parameters and SOC content (1%-14%). The model was independently tested against data for further three soils and performed accurately for all three. Consequently, we suggest that the () model represents a useful strategy to predict the entire soil-water repellency characteristic curve, and thus potential risks for enhanced runoff and preferential (fingered) soil-water flow at given initial soil-water contents, from measurements of only air-dry soil-water repellency and SOC content.

The soil gas diffusion coefficient (Dp) and its dependency on soil air content, ε, 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 of Dpwith ε 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, Dp(ε)/Do(where Dois 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 ε. In contrast, for the intraaggregate region, we show that the impedance factor F* (= Dp/εDo) 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(Dp/Do)/log(ε)], 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) Dp/Domodel was developed by applying a cumulative series of Buckingham–Currie power‐law functions, FεXA nonlinear, water‐content‐dependent expression for Fbest described the measured Dp/Doin 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 Dp(ε)/Domodels.

The transport of gaseous compounds in soil takes place by gas diffusion, advection, and dispersion. Gas transport processes are influenced by the soil‐gas diffusion coefficient (Dp), air permeability (ka) and soil‐gas dispersion coefficient (DH), respectively. Of three gas transport parameters, DHis the least understood, especially how it is correlated to soil type, moisture conditions, and other transport parameters (i.e., Dpand ka). In this study, a unified measurement system (UMS) that enables sequential measurement of Dp, ka, and DHon the same soil core was developed. The experimental sequence is based on a two‐chamber measurement of DHand ka, followed by a one‐chamber measurement of DpGaseous oxygen concentration and air pressure sensors are located in inlet and outlet chambers as well as at multiple points along the soil column. Using different particle‐size fractions of non‐aggregated (Toyoura sand) and aggregated (Nishi‐Tokyo loam) soils, the effects of soil structure, particle (aggregate) size, and column scale (5‐cm i.d. and 30‐cm or 60‐cm length) on the three gas transport parameters were investigated. For both soils, DHlinearly increased with increasing pore‐air velocity. For Toyoura sand, gas dispersivity (λ = DH/u0) decreased with increasing soil‐air content, while for Nishi‐Tokyo loam, gas dispersivity decreased with increasing soil‐air content to a minimum value when inter‐aggregate pores were drained and increased again when the pores inside the soil aggregates started to act as tortuous air‐filled pathways. In the arterial pore region (corresponding to the total pore volume for Narita sand and the inter‐aggregate pore volume for Nishi‐Tokyo loam), a linear relation between tortuosity of the air‐filled pore network (T, calculated from Dp) and the gas dispersivity (λ) was observed.

Water repellency (WR) has been classically characterized at fixed (usually oven-dry) soil water content (g) in terms of the soil water contact angle (CA), . However, has been previously reported to depend upon gin a nonlinear fashion, such that WR increases from a wettable state close to saturation (g-min) up to a maximum, max, decreasing afterward either monotonically or rising again to a second local or absolute maximum nearby the dried soil state. Hence, a CA versus water content (-g) curve may be described in terms of different WR parameters, such as g-min, g-max, max, or the integrated area below the -gcurve, S. Based on previous -gmeasurements carried out with the molarity of an ethanol droplet (MED) test, both in mineral and volcanic soils from different world regions, including cultivated and natural forest soils, and textures ranging from clay-loam to sandy, we confirm here the usefulness of the integrated area below the -gcurve (S) as a WR describing index for a large variety of -gcurve shapes. We found a simple relationship between Sand the soil water content at which WR is triggered, g-min, such that S= 16.903 g-min(R2= 0.946), which provides an easy method for the rapid characterization of the overall WR degree of soils. Swas also linearly correlated with the soil organic matter (SOM) content (R2= 0.817) for 1 g (100 g)−1< SOM < 88 g (100 g)−1, such that the best estimate of Swas that obtained by combining linearly both g-minand the SOM content (R2= 0.990). Linear correlations were also found between g-max, that is, the soil water content at which is maximum, and S(R2= 0.834) or the SOM content (R2= 0.705), and consequently between g-maxand g-min(R2= 0.830). In addition, both g-minand g-maxwere found to depend linearly upon the soil water content at −33 kPa and −1500 kPa, respectively. Finally, a mean soil WR may be defined as the ratio S/g-min. We found that the maximum CA, max, and the mean soil WR S/g-minwere positively correlated (R2= 0.780), such that a particular soil with high (low) values of maximum CA is expected to exhibit a high (low) WR degree on average across the whole water regimen from −33 kPa down to oven-dry moisture. Such an estimate of the mean WR index S/g-minwas further improved if both maxand the SOM content were available (R2= 0.825).

Risk assessment and design of remediation methods at soil sites polluted with gaseous phase contaminant require an accurate description of soil-gas diffusion coefficient (Dp) which is typically governed by the variations in soil air-filled porosity (va). For undisturbed volcanic ash soils, recent studies have shown that a linear Dp(va) model, taking into account inactive air-filled pore space (threshold soil-air content, va, th), captured the Dpdata across the total soil moisture range from wet to completely dry conditions. In this study, we developed a simple, easy to apply, and still accurate linear Dp(va) model for undisturbed volcanic ash soils. The model slope Cand intercept (interpreted as va, th) were derived using the classical Buckingham (1904) Dp(va) power-law model, vaX, at two soil-water matric potentials of pF 2 (near field capacity condition) and pF 4.1 (near wilting point condition), and assuming the same value for the Buckingham exponent (X=2.3) in agreement with measured data. This linear Dp(va) prediction model performed better than the traditionally-used non-linear Dp(va) models, especially at dry soil conditions, when tested against several independent data sets from literature. Model parameter sensitivity analysis on soil compaction effects showed that a decrease in slope Cand va, thdue to uniaxial reduction of air-filled pore space in between aggregates markedly affects the magnitude of soil-gas diffusivity. We recommend the new Dp(va) model using only the soil-air contents at two soil-water matric potential conditions (field capacity and wilting point) for a rapid assessment of the entire Dp-vafunction.

Water repellency (WR) of soils can induce hydrological problems such as reduced water infiltration, enhanced surface runoff and erosion, and the forming of preferential flow patterns in soil. Although soil organic matter (SOM) may cause both soil aggregation and a hydrophobic‐material‐coating of aggregates, little is known about WR in aggregated soils. We investigated the degree of WR as functions of volumetric water content (θ) and pF [= log (‐ψ; soil‐water potential)] for sieved fractions of a volcanic ash soil samples from different depths with varying soil organic carbon (SOC) contents of between 1.1 and 12.3%. Water repellency was determined by the molarity of ethanol droplet (MED) test. Water repellency was observed in the samples with SOC ≥ 4.6%, and the effects of sample pretreatments (pressure chamber desorption, air‐drying at 20°C, and oven‐drying at 60°C) on the degree of WR were small. The degree of WR varied greatly with both SOC content, θ, and pF. Peaks of WR were observed when the water retained in intra‐aggregate pores was drained to a moderate extent with the corresponding pF values located in a relatively narrow range from 3.2 to 3.6. This indicates that the hydrophobicity of high‐SOC aggregate surfaces might be enhanced the most at a specific soil‐water potential. Examining relations between water repellency parameters, the integrated areas below the WR‐θ and WR‐pF curves were useful indexes for characterizing WR, and linear relationships between the integrated areas and both SOC and water contents at maximum repellency were found.

The soil-gas diffusion coefficient (Dp) and air permeability (ka) govern the transport and emission of greenhouse gases and volatile organic chemicals in the unsaturated zone. The effects of soil organic matter and water retention on the two gas transport parameters are not well known. In this study, we measured Dpand kain three depths of a volcanic ash soil (Andisol) profile, with organic matter contents of 17% (0-5 cm depth), 4.7% (15-20 cm), and 0.2% (55-60 cm), respectively. Measurements were made on undisturbed samples at soil-water matric potentials from = −10 cm H2O (pF 1) to −12,600 cm H2O (pF 4.1) and, for Dp, also on air- and oven-dried samples. Soil-water retention was larger in the low-organic layer (55-60 cm) and similar for the other 2 organic layers. Soil-gas diffusivity varied the most in the high-organic top layer (0-5 cm) and was lower for samples with total porosity exceeding 0.8 m3m−3likely because of additional inactive air-filled pore space created by interconnected water films. The threshold air-filled porosity (th) where Dpapproached zero was on the average 0.05 m3m−3higher in the high-organic top layer (tharound 0.2 m3m−3) compared with the lower layers. For air permeability, the low-organic layer (55-60 cm) behaved differently because of a different soil structure. A recent power law ka() model compared well with data between pF 1 and pF 3 but typically underestimated kaat pF 4.1 because of a sudden increase in pore connectivity. A recent linear Dp() model for Andisols is further developed, with thand model slope Cpredicted from soil total porosity and volumetric content of intra-aggregate pores (soil-water content at pF 3). The linear model performed better than frequently used nonlinear Dp() models, especially at low soil-water contents.

Variations in gas transport parameters at the field scale govern the transport, fate, and emission of greenhouse gases and volatile organic chemicals in soil. In this study, we evaluated predictive models for soil-gas diffusivity (Dp/Do) and air permeability (ka) based on measurements along a 117-m transect and a parallel 33-m transect of a humic volcanic ash soil (Andisol) in Nishi-Tokyo, Japan. Measurements were done on 100-cm3undisturbed soil samples, with 3-m spacing between sampling points, and included water retention, soil-gas diffusion coefficient (Dp), kaat different soil-water matric potentials, and saturated hydraulic conductivity. Traditionally used predictive gas diffusivity models underestimated Dp/Doin wet soil and largely overestimated Dp/Dounder dry conditions because of soil aggregation effects. A linear model for Dp/Doas a function of air-filled porosity (), taking into account inactive/remote air-filled pore space, accurately described Dp()/Dofrom wet to oven-dry conditions and well captured the spatial variations in Dp/Doalong the transects. The kaexhibited a nonlinear relation with , and ka() was best predicted from a recently presented power-law model, with measured kaat −100 cm H2O of soil-water matric potential (ka,100) as a reference point. Trends of decreasing soil-water retention and increasing along transects were observed. Similar trends in kaand saturated hydraulic conductivity were not observed because the convective fluid transport parameters were mainly governed by soil structure and not by fluid phase contents. Autocorrelograms suggested a spatial correlation range of 10 to 20 m for gas transport parameters (Dp/Doand ka). Measurements of and kaat conditions close to −100 cm H2O of soil-water matric potential are suggested for rapid assessment of the magnitude and spatial variations in gas transport properties at the field scale.

Linking the classical Gardner and Campbell models for soil hydraulic properties yields a combined Gardner-Campbell (GC) relationship for predicting unsaturated hydraulic conductivity (K) from soil-water retention. The new GC water retention and hydraulic conductivity relationships are described by simple linearized expressions based on Campbell-b-scaled values of volumetric soil-water content (). The GC hydraulic properties models include four parameters, the pore connectivity parameter x (typically between 1 and 2), the Campbell pore size distribution parameter b, the Gardner macroscopic capillary length , and the air-entry soil-water matric potential ()e. In the GC model for K(), these parameters are merged into a single dimensionless parameter, A. The GC models are applied to seven different undisturbed soils within a soil-water matric potential with a range of 0 to −60 cm H2O. Results show that the simple GC () model adequately describes water retention data close to saturation, and that the GC K() model performs well for predicting near-saturated hydraulic conductivity. The GC water retention and hydraulic conductivity parameters were incorporated into Wooding's equation for steady-state infiltration rate to examine the effects of variability in physical characteristics on infiltration. The steady-state infiltration rate was less sensitive to the GC water retention and hydraulic conductivity parameters than the saturated hydraulic conductivity. The GC models, which combine advantages of the Gardner model for linearization of the Richards' equation and the simple Campbell model for soil-water retention, seem useful for describing or predicting near-saturated soil hydraulic properties and for stochastic simulations of field-scale water infiltration.

In order to establish a physical model leading to stable (uniform) and unstable (non-uniform fingering) flows in unsaturated soils, two-dimensional tests on continuous rainfall infiltration were carried out by changing not only the initial water content (air dry, 0.5%, 1.0%) but also the rainfall intensity (15, 30, 180 mm/h). The physical mechanism of fingering flow was discussed on the basis of precise suction measurements inside and outside the fingers.