Issues

Two comprehensive integrated models are compared to reveal the hydrologic dynamics in shallow water table settings, based on generalized likelihood uncertainty method and Sobol’s method.

The flow rate of water into a macropore determines the effect and extent of macropore–matrix interchange. In a macro-scale experiment it was shown that macropore flow can be fully or partially “absorbed” by the surrounding matrix to an extent that no relevant vertical propagation of the water in the macropore can be observed.

A field evaluation of soil water evaporation in four soil textural classes using lysimetry to measure evaporation and infrared thermometers to measure temperature showed that (i) changes in the soil temperature and air temperature ratio could be an important tool for identifying the stages of soil water evaporation and (ii) evaporation losses can compromise early season irrigation effectiveness.

Our study suggests soils likely to exhibit reduced wettability will be drier and wetter than an equivalent wettable soil. Slope processes linked to very dry soils or water clogged soils, such us surface runoff or shallow landslides, are likely to be enhanced in these soils.

The movement of a saline tracer added to the soil surface was monitored in the unsaturated zone using cross-borehole electrical resistivity tomography (ERT) and subjected to natural rainfall conditions. The ERT data were inverted and corrected for subsurface temperature changes, and spatial moment analysis was used to calculate the tracer mass, position of the center of mass, and thereby the downwardly recharging flux.

Surfaces of soil particles are rough rather than smooth, and surface roughness can enhance water retention and conductance of flow in the form of water films. We modeled water storage and movement in soils under variable water saturation conditions, considering surface roughness effects. Our model significantly improves the predictive capability compared with the van Genuchten–Mualem model.

A percolation theoretical treatment of advective solute transport is applied to predict the thickness of weathering rinds as a function of time, assuming that their development is transport limited. Theory predicts that the thickness is a power of the time between 0.5 and 1, in correspondence with experimental results. Analysis indicates that most rinds form under unsaturated conditions, as expected.

New models that account for percolation thresholds for gas transport and diminishing water blockage effects below field capacity and directly consider compaction effects and macroporosity were developed to describe the variation of soil gas diffusivity and air permeability at variably saturated conditions across a coarse sandy field.

We evaluated using combined NH₃ and H₂S gases to reduce radionuclide ⁹⁹Tc mobility from subsurface soils to groundwater. Individual gases were ineffective, but combined gases worked well across a range of conditions.

Within-year changes in parameters of the single-porosity van Genuchten model and the dual-porosity bi-exponential model for water retention characteristics were determined for a shallow Entisol in farmland and forestland. Tension infiltration data showed that soil macropores were the main contributing pores to fast drainage under both land uses in the rainy summer.

Subsurface water retention membranes, when optimally shaped and placed, can control irrigation water losses. We demonstrate how modeling can optimize membrane design and placement in soils of four texture classes.

While spatiotemporal characteristics of soil moisture content have been frequently studied, that of soil matric potential remains sparse. This study fills in several knowledge gaps regarding the characteristics and controls of spatial variability and temporal stability of soil matric potential as a function of soil type, topography, and season across a 7.9-ha forested catchment using a 5.5-yr database.

A new upscaling method for various flow scenarios under different boundary conditions, including ponded infiltration, drainage, evaporation and mixed boundaries, uses a pre-calculation procedure to calculate the upscaled effective hydraulic functions, which remarkably reduces the computational cost without compromising accuracy.

A new parameter for representing the matrix bulk density, computed tomography (CT) number derived matrix density, was used in studying preferential flow and transport in an agricultural soil. Results illustrate that CT number derived matrix density provides useful information regarding the initiation of macropore flow and the magnitude of preferential flow.

The mobility of polyvinylpyrrolidone-coated Ag nanoparticles in soils was positively correlated with pH, cation exchange capacity, and organic matter content and was negatively correlated with Fe oxide content and specific surface area, which highlights the importance of investigating soil physicochemical properties to better understand the fate of engineered nanoparticles in natural environments at the point of disposal and protect groundwater resources.