About the Journal

Vadose Zone Journal is an international, gold open access journal that serves as an outlet for interdisciplinary research and assessment of the vadose zone, the portion of the critical zone that comprises the earth's critical living surface down to groundwater.

Featured Article

VZJ Cover, Vol 18 Issue 1
2021 VZJ Outstanding Paper: Nutrient Leaching in Soil Affected by Fertilizer Application and Frozen Ground

Agricultural runoff containing phosphorus and nitrogen from drainage tiles contributes to nutrient loading in waterways, leading to downstream eutrophication. In this study, Grant et al. explored interactions between nutrient supply and infiltrating water during a simulated nongrowing season using a laboratory experiment to understand how water and nutrients move through partially frozen and unfrozen soil, and if fertilizer placement influences nitrate and dissolved reactive phosphorus leaching. Read more

Browse Articles

Open access

A combined flow cell–respiration box to quantify carbon transformation processes in undisturbed soil

  •  9 November 2021

Core Ideas

  • We introduce improved column breakthrough experiments with the advantage of visual monitoring processes.
  • The stated device combines laboratory precision and controllability with field conditions such as temperature regime.
  • Due to its design, it is possible to combine soil horizons, which allows us to simulate soil profiles.
  • In combination with labeled C, small-scale mass balancing of the C cycle is possible.
  • The controllability allows flow in unsaturated conditions with control over water content and flow velocity column breakthrough experiments with the advantage of visual monitoring processes.

Open access

Applicability of soil moisture sensors for monitoring water dynamics in rock: A field test in weathered limestone

  •  3 November 2021

Core Ideas

  •  EC-5 sensors proved to be successful for monitoring the water content of weathered limestone.
  •  Installation-induced errors can be avoided by following strict installation protocols.
  •  The amount of water infiltrating the weathered rock after large storms can be substantial.
  •  Rock moisture increases rapidly after storms as a result of preferential flow through fractures.
  •  Rock moisture was more depleted during the summer than during the fall dry season.

Open access

Effect of water distribution patterns on the activation energy of unsaturated soils during phase transformation

  •  2 November 2021

Core Ideas

  • Water distribution is critical to estimate the activation energy during phase transformation.
  • Specimens with higher water saturation require a higher activation energy for the freezing process.
  • More homogeneous water-distributed specimens have a greater activation energy.

Open access

Gas diffusivity‐based characterization of aggregated soils linking to methane migration in shallow subsurface

  •  13 October 2021

Core Ideas

  • Aggregated soils have bimodal properties that affect methane migration in soil.
  • Gas diffusivity, water characteristic, and thermal conductivity are bimodal fingerprints.
  • Diffusive CH4 migration is largely controlled by soil moisture than leakage rate.

Open access

Compensatory hydraulic uptake of water by tomato due to variable root‐zone salinity

  •  6 October 2021

Core Ideas

  • Instantaneous compensated water uptake was studied in split-rooted tomato lysimeters.
  • Short-term (hours) exposure to varied-strength salinity was applied in one or both compartments.
  • Uptake decreased in soil from area under stress and increased from area without.
  • Immediate compensation, no plant-scale effect and up to 85% uptake from non-stressed compartment were measured.
  • Compensation was not absolute; being an apparent function of salinity, atmospheric demand, and stress duration.

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Open access

A low‐cost environmental chamber to simulate warm climatic conditions

Core Ideas

  • We develop a low-cost environmental chamber to simulate warm climatic conditions.
  • It allows the regulation of temperature (15–50 °C) and relative humidity (10–95%).
  • All parts are available off the shelf.
  • It is affordable (<€900) and easy to replicate.

Open access

Recent Developments and Applications of the HYDRUS Computer Software Packages

Abstract

Core Ideas

  • Review of selected capabilities of HYDRUS implemented since 2008
  • New standard and nonstandard specialized add-on modules significantly expanded capabilities of the software
  • Review of selected applications of the HYDRUS models published in VZJ and elsewhere in recent years

The HYDRUS-1D and HYDRUS (2D/3D) computer software packages are widely used finite-element models for simulating the one- and two- or three-dimensional movement of water, heat, and multiple solutes in variably saturated media, respectively. In 2008, Šimůnek et al. (2008b) described the entire history of the development of the various HYDRUS programs and related models and tools such as STANMOD, RETC, ROSETTA, UNSODA, UNSATCHEM, HP1, and others. The objective of this manuscript is to review selected capabilities of HYDRUS that have been implemented since 2008. Our review is not limited to listing additional processes that were implemented in the standard computational modules, but also describes many new standard and nonstandard specialized add-on modules that significantly expanded the capabilities of the two software packages. We also review additional capabilities that have been incorporated into the graphical user interface (GUI) that supports the use of HYDRUS (2D/3D). Another objective of this manuscript is to review selected applications of the HYDRUS models such as evaluation of various irrigation schemes, evaluation of the effects of plant water uptake on groundwater recharge, assessing the transport of particle-like substances in the subsurface, and using the models in conjunction with various geophysical methods.

Estimating Uncertain Flow and Transport Parameters Using a Sequential Uncertainty Fitting Procedure

Abstract

Inversely obtained hydrologic parameters are always uncertain (nonunique) because of errors associated with the measurements and the invoked conceptual model, among other factors. Quantification of this uncertainty in multidimensional parameter space is often difficult because of complexities in the structure of the objective function. In this study we describe parameter uncertainties using uniform distributions and fit these distributions iteratively within larger absolute intervals such that two criteria are met: (i) bracketing most of the measured data (>90%) within the 95% prediction uncertainty (95PPU) and (ii) obtaining a small ratio (<1) of the average difference between the upper and lower 95PPU and the standard deviation of the measured data. We define a model as calibrated if, upon reaching these two criteria, a significant R2 exists between the observed and simulated results. A program, SUFI-2, was developed and tested for the calibration of two bottom ash landfills. SUFI-2 performs a combined optimization and uncertainty analysis using a global search procedure and can deal with a large number of parameters through Latin hypercube sampling. We explain the above concepts using an example in which two municipal solid waste incinerator bottom ash monofills were successfully calibrated and tested for flow, and one monofill also for transport. Because of high levels of heavy metals in the leachate, monitoring and modeling of such landfills is critical from environmental points of view.

Open access

Hydrologic Impacts of Thawing Permafrost—A Review

Abstract

Core Ideas

  • This review synthesizes the state of the science in permafrost hydrology.
  • Observed and projected hydrologic impacts of permafrost thaw are discussed.
  • Characterization, modeling, and knowledge gaps of permafrost systems are identified.
  • Translating results between multiple scales in cold regions presents a challenge.
  • Opportunities for advancement in the field of permafrost hydrology are described.

Where present, permafrost exerts a primary control on water fluxes, flowpaths, and distribution. Climate warming and related drivers of soil thermal change are expected to modify the distribution of permafrost, leading to changing hydrologic conditions, including alterations in soil moisture, connectivity of inland waters, streamflow seasonality, and the partitioning of water stored above and below ground. The field of permafrost hydrology is undergoing rapid advancement with respect to multiscale observations, subsurface characterization, modeling, and integration with other disciplines. However, gaining predictive capability of the many interrelated consequences of climate change is a persistent challenge due to several factors. Observations of hydrologic change have been causally linked to permafrost thaw, but applications of process-based models needed to support and enhance the transferability of empirical linkages have often been restricted to generalized representations. Limitations stem from inadequate baseline permafrost and unfrozen hydrogeologic characterization, lack of historical data, and simplifications in structure and process representation needed to counter the high computational demands of cryohydrogeologic simulations. Further, due in part to the large degree of subsurface heterogeneity of permafrost landscapes and the nonuniformity in thaw patterns and rates, associations between various modes of permafrost thaw and hydrologic change are not readily scalable; even trajectories of change can differ. This review highlights promising advances in characterization and modeling of permafrost regions and presents ongoing research challenges toward projecting hydrologic and ecologic consequences of permafrost thaw at time and spatial scales that are useful to managers and researchers.

Soil Moisture Measurement for Ecological and Hydrological Watershed‐Scale Observatories: A Review

Abstract

At the watershed scale, soil moisture is the major control for rainfall–runoff response, especially where saturation excess runoff processes dominate. From the ecological point of view, the pools of soil moisture are fundamental ecosystem resources providing the transpirable water for plants. In drylands particularly, soil moisture is one of the major controls on the structure, function, and diversity in ecosystems. In terms of the global hydrological cycle, the overall quantity of soil moisture is small, ∼0.05%; however, its importance to the global energy balance and the distribution of precipitation far outweighs its physical amount. In soils it governs microbial activity that affects important biogeochemical processes such as nitrification and CO2 production via respiration. During the past 20 years, technology has advanced considerably, with the development of different electrical sensors for determining soil moisture at a point. However, modeling of watersheds requires areal averages. As a result, point measurements and modeling grid cell data requirements are generally incommensurate. We review advances in sensor technology, particularly emerging geophysical methods and distributed sensors, aimed at bridging this gap. We consider some of the data analysis methods for upscaling from a point to give an areal average. Finally, we conclude by offering a vision for future research, listing many of the current scientific and technical challenges.

Open access

Development and Applications of the HYDRUS and STANMOD Software Packages and Related Codes

Abstract

Mathematical models have become indispensable tools for studying vadose zone flow and transport processes. We reviewed the history of development, the main processes involved, and selected applications of HYDRUS and related models and software packages developed collaboratively by several groups in the United States, the Czech Republic, Israel, Belgium, and the Netherlands. Our main focus was on modeling tools developed jointly by the U.S. Salinity Laboratory of the USDA, Agricultural Research Service, and the University of California, Riverside. This collaboration during the past three decades has resulted in the development of a large number of numerical [e.g., SWMS_2D, HYDRUS-1D, HYDRUS-2D, HYDRUS (2D/3D), and HP1] as well as analytical (e.g., CXTFIT and STANMOD) computer tools for analyzing water flow and solute transport processes in soils and groundwater. The research also produced additional programs and databases (e.g., RETC, Rosetta, and UNSODA) for quantifying unsaturated soil hydraulic properties. All of the modeling tools, with the exception of HYDRUS-2D and HYDRUS (2D/3D), are in the public domain and can be downloaded freely from several websites.

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