Spatial Variations Of Water Content Research Articles

Investigation of water transport around the root for a plant using X-ray imaging technique

Water transport in the root and soil interface has been investigated to reveal water uptake phenomena through roots. However, the mucilage-filled pore space used for water uptake has not yet been fully understood because it is difficult to analyze the multi-phase flow in an opaque porous media. In this study, the variations of water content (WC) in the region near the root of a Spathiphyllum wallisii were systematically investigated using an X-ray imaging system. Based on the spatial variations of WC around the root, the water transport phenomena in the mucilage-filled pore space were observed. To explain the water transport phenomena through the porous media around the root, the spatial variations of WC along the vertical direction were also analyzed. The present X-ray imaging technique would be helpful to understand water transport near roots of a plant.

Electrical resistance method for assessing spatial variation of water content in geosynthetics clay liners at laboratory scale

Non-uniform moisture distribution throughout pre-hydrated geosynthetics clay liner (GCL) laboratory testing specimens could significantly affect their liquid/gas permeability test results. For a reliable comparison between different pre-hydrated GCL specimens, uniform moisture distribution condition should be ensured before testing their permeabilities. This study presents a simple non-destructive electrical probing approach to assess the moisture homogeneity of GCL specimens before their use in laboratory tests. An experimental program was conducted to check the feasibility and the validity of the proposed method on GCLs hydrated at different moisture contents. The outcomes of the experimental program prove the adequacy of the proposed method.

Spatial variation of soil water content in topsoil and subsoil of a Typic Ustifluvent

Water content is a fundamental property affecting plant growth, transport and transformation of soil nutrients, and water and energy budgets in the soil–plant system. Its spatial variation has important implications for all these processes. In this study, spatial variation in soil water contents was evaluated at pressures of −0.033 ( θ −0.033 MPa ), −0.10 ( θ −0.10 MPa ), and −1.50 MPa ( θ −1.50 MPa ) at the soil depth from surface to the lower and of a plow layer in a Typic Ustifluvent in an 8.5 ha level area (1–2% slope). Topsoil (0.0–0.30 m) and subsoil (0.31–0.60 m) were sampled based on a regular grid spacing of 25 m-by-25 m. Variables θ −0.033 MPa , θ −0.10 MPa , and θ −1.50 MPa were measured with a pressure plate apparatus. Results were evaluated and compared with conventional statistics and geostatistics. Coefficient of variation (CV) for soil water content increased as soil water pressure decreased in both topsoil and subsoil. Semivariance analysis and ordinary block kriging-produced surface maps for θ −0.033 MPa , θ −0.10 MPa , and θ −1.50 MPa showed that topsoil and subsoil were similar in spatial variation of water content at all three corresponding soil water pressures. The geostatistical range values were between 298 m ( θ −0.10 MPa in topsoil) and 486 m ( θ −0.10 MPa in subsoil), both indicating a strong spatial dependence of soil water content. The semivariograms for θ −0.033 MPa , θ −0.10 MPa , and θ −1.50 MPa were similar in shape in both topsoil and subsoil. Cross-dependence between sand content and soil water contents showed that soil texture controlled the spatial variation of water contents at the site, at all depths and pressures evaluated.

Spatial variability in water content at the cold‐temperate transition surface of the polythermal Storglaciären, Sweden

The volume fraction of liquid water in temperate glacier ice is important not only for the flow of glaciers and the analysis and processing of ground penetrating radar data from glaciers but also for the stability of the thermal layering in polythermal glaciers. However, little is known about the spatial variations of water content in glaciers. We use relative backscatter strength of ground‐penetrating radar signals to estimate the spatial distribution of water content close to the cold‐temperate transition on Storglaciären, northern Sweden, in an area close to the equilibrium line. The values of relative backscatter strength are calibrated using determinations of absolute water content from temperature measurements across the cold‐temperate transition and the thermodynamic boundary condition at the freezing front. The results show a water content of 0.80%, 0.75%, and 0.58% at three calibration points and a mean water content of 0.8% with a standard deviation of ±0.26% for the extrapolated water content. The extrapolated water content shows a distinct pattern, with lower water content on one side of the glacier center line and higher water content on the other side, with higher water content on the northern side. We hypothesize that the different water contents result from the fact that the ice on either side of the center line originates from different cirques, thus implying spatial variations in the entrapment of water in the firn‐ice transition process in the different cirques.

Determining the soil hydraulic conductivity by means of a field scale internal drainage

Spatial variations of water content in large extents soils (vadose zone) are highly affected by the natural heterogeneity of the porous medium. This implies that the magnitude of the hydraulic properties, especially the conductivity, varies in an irregular manner with scale. Determining mean values of hydraulic properties will not suffice to accurately quantify water flow in the vadose zone. At field scale proper field measurements have to be carried out, similar to standard laboratory methods that also characterize the spatial variability of the hydraulic properties. Toward this aim an internal drainage test has been conducted at Ponticelli site near Naples (Italy) where water content and pressure head were monitored at 50 locations of a 2×50 m 2 plot. The present paper illustrates a method to quantify the mean value and the spatial variability of the hydraulic parameters needed to calibrate the soil conductivity curve at field scale (hereafter defined as field scale hydraulic conductivity). A stochastic model that regards the hydraulic parameters as random space functions (RSFs) is derived by adopting the stream tube approach of Dagan and Bresler (1979). Owing to the randomness of the hydraulic parameters, even the water content θ will be a RSF whose mean value (hereafter termed field scale water content) is obtained as an ensemble average over all the realizations of a local analytical solution of Richards' equation. It is shown that the most frequent data collection should be carried out in the initial stage of the internal drainage experiment, when the most significant changes in water content occur. The model parameters are obtained by a standard least square optimization procedure using water content data at a certain depth (z=30 cm) for several times ( t=5, 24, 48, 96, 144, 216, 312, 408, 576, 744, 912 h). The reliability of the proposed method is then evaluated by comparing the predicted water content with observations at different depths ( z=45, 60, 75, and 90 cm). The calibration procedure is further verified by comparing the cumulative distribution of measured water content at different times with corresponding distribution obtained from the calibrated model.

CHANGES IN CRACKING, WATER CONTENT, AND BULK DENSITY OF SALINIZED SWELLING CLAY FIELD SOILS

Shrinkage and cracking characteristics of swelling clays at two sites under border strip irrigation were examined. At one site, irrigation water salinity was varied. Image analysis of soil surface photographs was used to quantify surface ped geometry. Volumetric surface soil samples were used to find temporal and spatial variation of water content and bulk density both on the surface and with depth. Qualitative observations of cracking behavior were made in the field. There was no spatial dependence for water content and bulk density at the scale of several centimeters or between peds. Larger, more polygonal peds were observed in higher salinity treatments, wheel traffic rows, and after repeated irrigations. Surface shrinkage increased with salinity. Dry bulk density was higher on the high salinity treatment both on the surface and with depth. Despite larger area, perimeters of the 9000 ppm treatment peds were less than perimeters for other treatments. Surface percent crack area followed percent change in bulk density.