Soil-water distribution, measurement

These data were measured at or extrapolated to ambient temperature and pH values. The data are discussed in the text. NA = not available. b/ Kq = soil water distribution coefficient (K ) divided by the organic carbon content of the soil, cj Whenever possible, half-life for soil dissipation is derived from the field data half-lives described in the text rather than lab data. As such, it may not represent a true first-order process. Value has been estimated from the equation in ref. 20. e/ Hydrolysis of total residues (aldicarb + sulfoxide + sulfone). pK for p -phthalic acid is 3.5. The chlorine atoms of DCPA should lower the pK to about 2. Conditions optimized for soil metabolism. 

Various coefficients are helpful in measuring the potential of a chemical to partition between the aqueous and solid phases. These parameters are valuable in predicting the potential of a chemical to adsorb to the solid phase. The soil-water distribution ratio, Kd,... 

Price, A. G. (1984). Measurement and variability of physical properties and soil water distribution in a forest podzol. J. Hydrol. 161, 347-364. 

A comparison of measured and predicted values of the HCB soil-water distribution coefficient, AT, for the Tween 80 and Appling soil system is presented in Figure 8. The measured values of (data points) were obtained from the HCB... 

Figure 9.7 Observed increase in solid-water distribution ratios for the apolar compounds, tetrachlo-romethane (0) and 1,2-dichIoro-benzene (A) with increasing organic matter content of the solids (measured as organic carbon, /oc, see Eq. 9-21) for 32 soils and 36 sediments. Data from Kile et al. (1995).

Soil pH measurement is usually affected by a number of factors viz. salt concentration, soil-water ratios, suspension effect etc. The use of O.Ol(M) CaClg solution yields stable readings in pH-measurements. The hydrogen ions in the soil system are distributed between solid and liquid phases as follows. The dynamic equilibrium may be represented as follows. 

Size can refer to volume, area, or length, and therefore pore-size distribution may be defined in terms of any one of these properties. In practice, the definition of size adopted is highly dependent upon the method of measurement. For example, the area size distribution of pores is often measured by image analysis of soil thin sections, while water retention data are usually interpreted in terms of the distribution of pore diameters (Bullock Thomasson, 1979). For consistency with the definition of the Peclet number, we have chosen to define size in terms of length, L. Dullien (1991) has proposed the following interrelationships between the different definitions of size L = VIS in three-dimensions or L=AJP in two-dimensions, where V is volume, S is surface area, A is cross-sectional area and P is perimeter. These relations can be used to compare pore-size distributions measured using different methods. 

ABSTRACT Soil hydraulic properties parameters are the crucial input parameters in water and solute transport modeling in the vadose zone. Pedotransfer functions are an alternative to direct measurement for obtaining soil hydraulic properties. In this study, Pedotransfer functions were established from particle-size distribution, bulk density, and organic matter using linear regression method with bootstrap analysis, then its prediction performance were further compared to artificial neural network and Vereecken with the Mean Error (ME) and the Mean Absolute Errors (MAE). The developed models were ranked the best models for estimation of hydraulic parameters with ME and MAE were less than O.lOcm /cm whereas Vereecken performed the worse results for hydraulic parameters, especially ME and MAE for parameters of a reached 0.74 1/cm and 0.63 1/cm, respectively. Function uncertainty evaluation was performed in Hydrus-ID model to simulate soil water, the developed pedotransfer functions and artificial neural network provide similar higher level of accuracy and precision with ME. 

Electrical conductivity (or its mathematical inverse, resistivity) of a soil solution is strongly correlated with total salt content. Therefore, laboratory methods involving solution or saturated paste conductivity are often used to assess soil salinity. Electrical conductivity measurements of bulk soil (designated as ECa for apparent electrical conductivity) were also first used to assess salinity. Resistivity and conductivity measurements are also useful for estimating other soil properties, as reviewed by and. Factors that influence ECa include soil salinity, clay content and cation exchange capacity (CEC), clay mineralogy, soil pore size and distribution, soil moisture content, and temperature. ° For saline soils, most of the variation in ECa can be related to salt concentration. In non-saline soils, conductivity variations are primarily a function of soil texture, moisture content, bulk density, and CEC. The theoretical basis for the relationship between ECa and soil physical properties has been described by a model where ECa was a function of soil water content (both the mobile and immobile fractions), the electrical conductivity of the soil water, soil bulk density, and the electrical conductivity of the soil solid phase.Later, this model was used to predict the expected correlation structure between ECa data and multiple soil properties. ... 

Hydraulic conductivity, which is one of the important soil parameters for seepage analysis, is estimated from the pore-size distributions measured by a mercury intrusion porosimeter. Two different relations are indispensable for analysis of partial saturation soil because hydraulic conductivity depends on the capillary potential, which is usually characterized by soil-water retention. 

The toxic chemical(s) of concern must be Identified and their physical and chemical characteristics evaluated The concentrations of each of the chemicals must be measured, ideally in both the environment and In the tissues of exposed humans Depending on the nature and distribution of toxic material, environmental measurements may be required In air, water, soil, or food, or In combinations of these media The critical limiting factor at this stage of assessment relates to the degree to which particular chemicals can be identified... 

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