Issues

We developed a new approach for constructing reproducible, “geologically realistic” heterogeneity for near-two-dimensional transmitted-light experiments. A computer-controlled arm deposited mixtures of sand in an experimental chamber through a tube. Mechanical segregation processes within the tube and the chamber led to geologically realistic stratification.

Contamination of vadose-zone systems by chlorinated solvents is widespread and poses significant potential risk to human health through impacts on groundwater quality and vapor intrusion. We summarize recent advances in our understanding of the transport, characterization, and remediation of chlorinated solvents in the vadose zone.

Pedometricians apply mathematical and statistical methods in the study of the distribution and genesis of soil. Vadose zone scientists investigate the spatial and temporal dynamics of soil and water properties beyond the rootzone. This review highlights common research areas and suggests where potential collaborative research for pedometricians and vadose zone researchers exists.

This research demonstrates the ability to transfer a relatively small set of equilibrium sorption reactions and constants from batch to hydrodynamic column experiments under a limited set of flow conditions without arbitrary parameter fitting by using soil properties and mineralogy as constraints in model formulation.

A novel approach has been developed to estimate the subsurface electrical conductivity distribution from electromagnetic induction data and evaluate influence of prior constraints, data information content, and solution non-uniqueness. Its application to an Arctic ecosystem enabled imaging of the variability of active layer and permafrost properties.

A numerical model for coupled water flow and heat transport in seasonally frozen soils with snow is presented. The model was successfully applied to a laboratory soil column freezing experiment and to a rangeland soil field experiment.

Soil capillary and wettability properties affect evaporation dynamics and give rise to a characteristic length marking the end of Stage I and provides estimates of evaporative losses from soil data. Nonlinearities between surface water content and evaporative flux were quantified considering diffusion from discrete pores across air boundary layer.

We hypothesized that the HYDRUS-1D model could be used to predict dynamic changes in plant salinity tolerance for a greenhouse vegetable crop over a full season and to determine best management practices regarding blending of saline with desalinated water for optimization of yields and water use efficiency.

A lattice Boltzmann method–based advection dispersion–equation solver was verified against analytical solutions for two types of inlet boundary conditions in finite and semi-infinite domains. The model was able to simulate zero diffusion as well as the hydrodynamic dispersion coefficient. The model was first order accurate, and numerical diffusion was inversely proportional to the grid resolution.

The impacts of land use, irrigation, and pedological characteristics on bromide leaching were analyzed. Autoregressive state-space models incorporating the land use system, irrigation amount, changes in soil matric potential, and physical soil properties (bulk density and clay content) could describe the spatial process of bromide leaching.

This study employs a novel approach to the estimation of the economic value of digital soil maps, generated by a host of new proximal geophysical processes and technologies. Using a Choice Experiment, the study demonstrates that there is significant willingness-to-pay for the soil maps and their features.

This study explores the intensive mapping of soil reflectance using a mobile near-infrared reflectance spectrophotometer under field conditions in an organic farm. The stable soil reflectance patterns of the fields were related to specific soil fertility parameters, but correlation was location dependent and thus cross-field calibration models were difficult to obtain.

We investigated the use of pseudo-three-dimensional electrical resistivity tomography (ERT) as a field method for characterizing soil–pipe spatial distribution and connectivity on a forested hillslope, with an interest in detecting the formation of soil pipes from tree decay and root combustion. We conclude that it is not practical to rely on homogeneity assumptions commonly used to detect anomalies characterized by higher resistivities compared to the surrounding soil. The use of ERT surveys to detect large macropores may be more suitable to areas of soil where the pathways are not occurring very near and within portions of a restrictive layer.

Proximal and remote soil sensing are particularly valuable for precision agriculture application, and there is great scope for their synergic use. Different hybrid methods were compared, allowing the joint exploitation of hyperspectral satellite data and geophysical data for estimating soil properties at the field scale. Clay, sand, and available water content were estimated with a sufficient degree of accuracy, especially when using the regression-kriging technique.

The aim of this hydrogeophysical study is to assess the sensitivity of the early-time amplitude technique of the GPR signal to subsurface water content variations over the annual cycle of soil water content conditions using that extensive set of reflection profiling data acquired at three sites with different soil textures.

Using 72 undisturbedsamples, we investigated the possible use of new, easily measured soil properties like the plastic limit and specific surface area as predictors of soil hydraulic properties. Principal component analysis was used to examine multivariate relationships between soil water contents and other physical and chemical properties.

Spatial vegetation patterns can be used as a proxies of the underlying soil and soil water conditions. The study examines the use of hyperspectral remote sensing techniques for quantifying geophysical parameters from the hyperspectral reflectance of the vegetation canopy. The best prediction of EMI and gamma-ray measurements was found by a combination of elevation and hyperspectral remote sensing information.

Multiple linear regressions between gamma spectrometric data and regolith parameters allowed modeling of about 50% of the parameters modeled (chemical, textural, and mineralogical) with an acceptable error. Two main textural and mineral assemblages corresponding to weathering products and leached detrital materials were found to be the main gamma emitters.

This study focused on spatial and temporal variability of carbon dioxide fluxes from soil in two land-use systems. Longer spatial and temporal correlation lengths were found in the grass system. Spatial patterns of soil respiration were temporally stable and variation of soil respiration was more pronounced in time than in space during the study period.

Rainfall partition by Caragana microphylla L. shrub and spatial soil water content pattern were analyzed to relate soil hydraulic conductivity and macroporosity using CT, revealing shrub hydropedology of preferential water flow to deep soil layer.

The interactive relationship between soil and water (hydropedology) was exploited to determine the hydrological behavior of 52 hillslopes in South Africa. These hillslopes were qualitatively grouped into six hillslope classes based on their dominant hydrological response derived from interpretations of their hydropedology. Applications of the classification system are presented.

We strive to assess soil moisture of an alpine hillslope using time lapse electromagnetic mapping, soil sample analysis and vegetation mapping. Presence of significant soil heterogeneity in combination with required processing of the time lapse data pose a challenge to the extraction of soil moisture information from the geophysical data.

A laboratory rainfall simulation showed that Ultisols are prone to crusting and rainfall kinetic energy is a major driver of crust formation. This crusting reduced infiltration significantly and so promoted water and particle runoff. Mulching could be an effective way to alleviate crusting, to conserve more water, and to reduce erosion.

Soil-probe contact resistance and finite radius and heat capacity of the probe cause errors in thermal property estimates from the heat pulse method. This study demonstrates that the errors are reduced significantly when late-time data of the temperature change-by-time curve are used for calculations with the pulsed infinite line source theory.

Differences in intra-aggregate pore characteristics induced by long-term differences in land use and management influenced distribution of Escherichia coli. Pore characteristics that affected E. coli distribution and retention within the aggregates were porosity, presence of large and medium pores, pore tortuosity, and maximum flow rate.

We present results from the analysis of three-dimensional X-ray computed tomography images of undisturbed soil samples in grassland sites. A strong positive correlation between root parameters and the solid surface/solid volume ratio was found. Preliminary analyses suggest that the relationship between soil structure and root patterns is related to the intensity of land management at the grassland sites, with reduced root volumes at sites with increased land use intensity.

We used ground penetrating radar (GPR) and electromagnetic induction (EMI) to map small-scale soil heterogeneity on field scale. The resulting geophysical adapted soil map and the coarse scale “standard” soil map served as soil input for CANDY PLUS to model plant biomass production. The geophysical adapted soil map greatly improves model results.

The relationships between permittivity and electrical resistivity versus water content and temperature determined from geophysical laboratory measurements are investigated using known and newly developed geophysical pedo-transfer functions. A new embedding scheme for effective media models proved to yield the best results regarding the relationships to water content. The temperature effect on electrical resistivity can be reliably corrected using existing empirical relationships.

A novel sensor, based on electrical impedance spectrometry, for water content measurement in rocks was investigated. Calcarenite, a sedimentary porous rock, was used to determine the calibration functions by evaluating the effects of frequency and salinity of the saturation solution. The functions obtained have a power-law dependence with a good degree of correlation.

We describe recent advances in ecosystem services concepts for soils and the vadose zone. We developed the stock-flow and fund-service approach for the earth system and present some recent applications of this framework.

Spatiotemporal investigation of high-resolution δO and δD sampling at Susquehanna-Shale Hills Critical Zone Observatory (SSHCZO) revealed patterns of subsurface hydrology. Heavy damping of seasonal amplitude was found to occur with depth indicating the importance of hydrodynamic mixing. Variations in seasonal soil isotope profiles suggest prevalence and mechanisms of preferential flow.

A three-dimensional structure and process model was developed for balancing and visualization of hydro-geo-pedologic catchment structures. Surface topography based on digital elevation models, hydraulic pedotransfer functions, and complex spatial differentiation described initial development of the constructed “Chicken Creek” catchment.

To ensure global food security, crop production must outpace human population growth significantly during the next 40 yr. This review makes the case that this challenge can largely be met by optimizing the management of “green water” (soil water directly available to plant roots), an often overlooked resource whose annual global flow in fact matches that of all the rivers in the world flowing to the sea.

A critical review of implicit assumptions behind typical one-dimensional root water uptake and stress models is performed. Plant-scale mathematical expressions for stress and uptake functions obeying Darcy flow equations in three-dimensional systems are proposed.

The spatial heterogeneity of subsurface structures of a kettle hole catchment was modeled using two geophysical methods and field observations for better understanding of hydrological processes.

The internal heterogeneity of a real constructed catchment was modeled by simulating the specific construction processes and the conditions at the excavation site. Simulated three-dimensional distributions of sediments can be adjusted to match patterns observed in reality. The resulting spatial distribution models are useful for ecohydrological process modeling in post-mining landscapes.

Infiltration into the texture-contrast soils was largely governed by the effects of antecedent soil moisture content on water repellence, silica bridging, and clay shrinkage. Differences in soil morphology had a relatively minor influence on infiltration. The contrasting horizon textures were thought to have developed prior to and independently of the observed preferential flows.

This critical review examines the fundamental hydropedological and ecohydrological relationships that define the function of endemic Brigalow ecosystems. We use an integrated conceptual modeling framework (also known as gray box) to outline the significance of these relationships for planning and execution of rehabilitation activities on substantially disturbed postmining landscapes within the bioregion and similar water-limited ecosystems around the world.

Small-scale soil heterogeneity has a minor impact on the annual water balance as compared to ET partitioning and root water uptake with compensation. In flat terrain, one-dimensional effective models reproduce soil water budgets well, provided that the vertical series of textures in the root zones are represented well.

In our two-domain model, a source-responsive domain represents preferential flow. Applied with new elaboration of the nature of preferential-domain water and domain-transfer, the model sometimes shows good quantitative agreement and, in all cases, captures the nonsequential character of irregular wetting patterns.

Unsaturated properties of an agricultural soil were investigated simultaneously with induced polarization characteristics. Water saturation variations of field soils might be more robustly estimated by imaginary conductivity than by real conductivity because of the complicating pore fluid conductivity dependence of real conductivity

Despite the complexity of soils, topography, and land use of eight vegetated watersheds throughout the world, the runoff behavior after the threshold rainfall is exceeded is surprisingly simple and consists of a linear relationship between total rainfall and total direct runoff for each storm.

With recent climate warming and changes in the extent and depth of frozen soil and permafrost, it is important to understand frozen-soil processes and their interaction with the environment. The objective of this review is to highlight important aspects of soil freeze–thaw and related processes and to point out research challenges and opportunities in the cold vadose zone.

Existing methods of estimating spatially varying soil thermal conductivity and diffusivity using harmonic analysis of soil temperatures are applicable only at periodic steady-state, although unsteady conditions often occur in practice. Two new methods for such conditions were derived and studied using synthetic data with added noise. It was found that diffusivity and, to a lesser extent, relative conductivity could be accurately estimated.

The analytical solutions to two-dimensional coupled infiltration in an unsaturated porous medium are obtained by using the Fourier integral technique. This solution can analyze two-dimensional infiltration and evaporation in the transversely anisotropic unsaturated medium. The pressure head changes most rapidly when the unsaturated medium is hydraulically isotropic.

We assessed the impact of different types of backfill that can be used to provide hydraulic continuity between sensors and the “measured” environment. We found that any type of backfill used for monitoring fractured rock hydrology results in distorted measurements. Our analysis suggests that it is possible to quantify moisture content in rock from calibrations between native rock and backfill measurements.

Vapor flow through soils affects the flux from a new irrigation system that has the potential to improve the sustainability of irrigating with saline water. In this research, a new model is developed to simulate flux from the irrigation system by considering water vapor transport through dry soil. Simulated results are compared with experimental data.

The spatiotemporal variability of a tritium plume in the shallow unsaturated zone and the mechanisms controlling its transport were evaluated during a 10-yr study. Plume movement was minimal and its mass declined by 68%. Upward-directed diffusive-vapor tritium fluxes and radioactive decay accounted for most of the observed plume-mass declines.

Soil moisture prediction is an important application of environmental modeling. Here we compare two models that we used for soil moisture prediction: a soft-computing SVM model and a physical one based on Richards equation. Our results show that both of these models can successfully serve as soil moisture temporal estimation within the soil profile.

New techniques and technologies are unraveling processes that underpin biological and physical interactions in soils. From a review of recent literature, we argue for concurrent studies of model and natural soil systems, and show the benefits of taking approaches from other disciplines.

A review of recent developments related to soil hydraulic property estimation using remote sensing is presented.

The water retention curve (WRC) and the hydraulic conductivity function (HCF) are key ingredients in most analytical and numerical models for flow and transport in unsaturated porous media. We review some of the primary models and highlight their physical basis, assumptions, advantages and limitations.

Soil information, particularly water storage capacity, is of utmost importance for assessing and managing land resources for sustainable land management. We investigated using digital soil mapping (DSM) and digital soil functional mapping (DSFM) procedures to predict available water capacity (AWC) of soils in Nigeria using three published Pedotransfer functions (PTFs).

The first two editors of Vadose Zone Journal reflect about the professed need 10 years ago for a dedicated outlet focusing on vadose zone research, the creation of the journal in 2002 by the Soil Science Society of America in collaboration with the Geological Society of America, the rapid rise of the journal, and a thanks to all those who worked hard to made the journal so successful in a short period of time.

Celebrating ten years of publication, the authors introduce a special section commemorating the anniversary of Vadose Zone Journal and reviewing the journal’s role in an evolving understanding of vadose zone science.

The guest editors provide an introduction for the Special Section: Frontiers of Hydropedology in Vadose Zone Research, introduce the 17 contributions, and discuss the role of hydropedology in today’s vadose zone research.

The guest editors summarize the special section, Digital Soil Mapping, beginning with a look at the challenges that are pushing advances in soil mapping, and then introducing the contributors’ efforts at improving current approaches.