T Ellsworth | West Hills College (original) (raw)

Papers by T Ellsworth

Journal of Environmental Quality, 2007

Scaling Methods in Soil Physics, 2003

Soil Science Society of America Journal, 1992

The majority of procedures for in situ measurement of the unsaturated hydraulic conductivity are ... more The majority of procedures for in situ measurement of the unsaturated hydraulic conductivity are variations of the instantaneous profile method. A vertically nonuniform soil requires the unsaturated hydraulic functions to be estimated at each horizon. Scaling systems have evolved in an attempt to reduce the number of hydraulic functions needed to characterize water flow through heterogeneous soils. In this study, we extended the concept of water content (O) scaling to nonuniform soil profiles, tested the effectiveness of 0 scaling for reducing apparent spatial variability, and estimated the unsaturated hydraulic functions for a naturally occurring loamy sand field site. Two instantaneous profile experiments conducted at Etiwanda, CA, provided soil water content and pressure head (h) data vs. depth (z) and time (t). Water retention, 0(h), and hydraulic conductivity, K(0), functions fitted to data from the 15-cm depth at Plot 1 were arbitrarily chosen as the reference hydraulic properties to which the other depths and plots were scaled. Based on a unit-gradient analysis of the drainage data, the slope of the hydraulic conductivity function, AK/dO, was estimated as zlt. Scaling other depths and plots to the reference location was done using an iterative procedure that provided least-squares estimates of the two O scaling parameters (S and /t) and a corresponding transformed depth variable (z*). Scaled water content, 0*, plotted vs. z*//, using data from all depths and plots, coalesced to a single curve. Scaling O successfully coalesced heterogeneous soil hydraulic properties into unique functions for both 0(h) and K(ff).

Eos, Transactions American Geophysical Union, 1998

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SSSA Special Publication, 2015

Geophysical Monograph Series, 1999

There are increasingly important challenges associated with assessing the potential non-point sou... more There are increasingly important challenges associated with assessing the potential non-point source (NPS) pollution hazards which result from regionalscale agricultural activities. The increasing availability of geographic information system (GIS) technology to those involved in assisting with land-use decisions has resulted in the proliferation of multicolored maps for many environmentally sensitive issues. How useful are these maps to those in the decision-management arena? The focus of this chapter, relative to assessing NPS pollution in a GIS framework, is what the status and shortfalls of regional-scale NPS vulnerability assessments are and what still needs to be done to make them more useful in the decision-management arena.

Water Resources Research, 1993

Analytical solutions for the advection-dispersion equation (ADE) usually assume that boundary and... more Analytical solutions for the advection-dispersion equation (ADE) usually assume that boundary and initial conditions are orthogonal to the principal axes of the dispersion tensor. However, this is not always the case in field studies or modeling scenarios. Using the method of Green's functions, a generalized analytical solution of the three-dimensional ADE set in an arbitrary Cartesian coordinate system (i.e., not orthogonal to the principal flow direction) is given for the solute resident concentration in a semi-infinite porous medium with an arbitrary initial condition, surface boundary condition, and sink/source terms. Two particular solutions for a rectangular surface flux boundary condition and a buried parallelopiped, respectively, are derived from the general solution. The corresponding frequency domain solutions are also given which provide a more efficient method of computation for generating two-and three-dimensional grids via use of a two-dimensional fast Fourier transform algorithm (as an alternative to the two-dimensional numerical integration required to calculate the concentration using the real space solution). When the arbitrary coordinate system is orthogonal to the principal axes, it is shown that these particular solutions are the same as previously published results.

Soil Science Society of America Journal, 2003

whole range of solute concentrations and water velocities can be used. In the CDE model, solute s... more whole range of solute concentrations and water velocities can be used. In the CDE model, solute spreading A systematic analysis of the effect of displacement length, soil about the mean solute velocity is represented using a texture, and steady state water flux (q) on solute transport was perlumped effective diffusion coefficient (D eff). Conceptuformed on saturated repacked loam and sandy loam soil columns to identify the simplest possible description that was consistent with the ally, D eff is assumed to reflect both the phenomenon of observations across all of the breakthrough curves (BTCs) for each ionic or molecular diffusion and mechanical dispersion, data set. All 39 BTCs obtained from loam and 21 from sandy loam although these effects may not be additive (Nielsen et soils, with column lengths of 10, 20, and 30 cm, and a two-order al., 1986). The parameter D eff has frequently been remagnitude variation in measured pore water velocity (v m), were fitted ported to be proportional to measured pore water velocsimultaneously and global estimates of parameters [dispersivity () ity (v m) provided longitudinal diffusion has negligible and molecular diffusion coefficient (D 0)] were obtained. We showed influence on the dispersion coefficient and water conthat a two-parameter global dispersion relationship (D ϭ v m ϩ D 0 , tent does not vary appreciably among different experiwhere D is the apparent diffusion coefficient) accurately represents ments (van Genuchten and Wierenga, 1977; Nkedithe spreading process for all 39 loam soil BTCs (r 2 Ͼ 0.99), whereas Kizza et al., 1984; Shukla and Kammerer, 1998). The a single global parameter (D ϭ v m) was all that was required for the sandy soil (r 2 Ͼ 0.98). The globally fitted was independent of proportionality constant between dispersion and water displacement length and v m. D remained independent of v m in the velocity is generally referred to as the dispersivity (, lower velocity ranges; however, a linear relationship between v m and Jury et al., 1991). For transient flow, it has been shown fitted D was obtained for v m Ͼ 0.1 cm h Ϫ1. The results of this study that the temporal average v m can be used instead of illustrated the importance of molecular diffusion. In addition, we a more complicated transient description (Wierenga, identified a nonlinear relationship between v m and average solute 1977). However, for spatial scales within which provelocity (v s), which suggested that the anion exclusion volume denounced local variations in v m exist, the CDE may not creased with increasing v m .

Soil Science Society of America Journal, 1996

The objectives of this study were to: (i) examine the efficacy of two sampling techniques for cha... more The objectives of this study were to: (i) examine the efficacy of two sampling techniques for characterizing solute transport under steady-state water flow, (ii) study the variation in transport model parameters with increasing depth of solute leaching, and (iii) perform model discrimination to examine the transport process operative within a field plot. Bromide, NO?, and Cl-were applied sequentially to a plot instrumented with two sets of 12 solution samplers located at depths of 0.25 and 0.65 m. At the conclusion of the experiment we destructively sampled the entire 2.0 by 2.0 m plot to a depth of 2.0 m. Mass recovery by the solution samplers ranged from 63 to 83% for the three tracers, and recovery by soil excavation ranged from 96 to 105%. The mean solute velocity estimated with the solution sampler data was significantly less than that determined by soil excavation. Mean solute velocity determined from soil excavation implied an effective transport volume equal to 0.828, (where 8, is volumetric water content) for the three tracers. Solution samplers and soil excavation provided similar measures of vertical dispersion. Both sampling methods revealed a scale-dependent dispersion process in which the dispersivity increased linearly with mean residence time. The depth profiles for all three solutes were accurately described with a stochastic convective lognormal transfer function model (CLT) using the applied mass and two constant parameters (estimated from simultaneous fitting to the depth profiles).

Microbiological Research, 1999

Effects of bioavai1ability on degradation of 14C-p-hydroxybenzoate were examined using sterile so... more Effects of bioavai1ability on degradation of 14C-p-hydroxybenzoate were examined using sterile soil inoculated with Arthrobacter sp. Physical accessibility of p-hydroxybenzoate was controlled by varying pore continuity with a range of moisture regimes (-33 to-420 kPa), whereas sorption was controlled via addition of an exchange resin. Arthrobacter sp. accessed 94% of p-hydroxybenzoate in soil at-33 kPa, owing to continuity of soil pores and sufficientcells to exploit available space.A deviationin degradationkinetics at-420 kPa soil was attributed to inaccessible p-hydroxybenzoate in solution. Addition of resin decreased extent of degradation, though the effect diminished as pore continuity decreased. Subtle differences in effects of these processeson degradation kineticsmay facilitate their separate treatment in environmental fate models.

Journal of Environmental Quality, 2001

Meirvenne et al., 1996). Logarithmic transformation is used for the data following a lognormal di... more Meirvenne et al., 1996). Logarithmic transformation is used for the data following a lognormal distribution and The spatial distribution of a pollutant in contaminated soils is then the lognormal kriging estimator can be used for usually highly skewed. As a result, the sample variogram often differs considerably from its regional counterpart and the geostatistical inter-spatial interpolation (Journel, 1980). The lognormal polation is hindered. In this study, rank-order geostatistics with stan-kriging estimator provides an approximately unbiased dardized rank transformation was used for the spatial interpolation estimate, although error estimations are often exaggerof pollutants with a highly skewed distribution in contaminated soils ated. The lognormal kriging estimator only works well when commonly used nonlinear methods, such as logarithmic and when the transformed data are a Gaussian random funcnormal-scored transformations, are not suitable. A real data set of tion. For highly skewed data, it is necessary to check soil Cd concentrations with great variation and high skewness in a whether the univariate distribution of data is lognormal contaminated site of Taiwan was used for illustration. The spatial or not before using lognormal kriging. dependence of ranks transformed from Cd concentrations was identi-On the other hand, the normal-scored transformation fied and kriging estimation was readily performed in the standardizedis an alternative for dealing with the data, which have rank space. The estimated standardized rank was back-transformed into the concentration space using the middle point model within a a positively skewed distribution with a few extreme valstandardized-rank interval of the empirical distribution function ues. This method can transform any data set having an (EDF). The spatial distribution of Cd concentrations was then obasymmetric distribution into the normal scores, which tained. The probability of Cd concentration being higher than a given have a standard normal distribution. Then, the kriging cutoff value also can be estimated by using the estimated distribution estimation can be performed in the normal-scored of standardized ranks. The contour maps of Cd concentrations and space. This approach is based on a multi-Gaussian the probabilities of Cd concentrations being higher than the cutoff model. Only when normal-scored data strictly follow the value can be simultaneously used for delineation of hazardous areas multi-Gaussian distribution (also called multi-normal of contaminated soils. distribution), the kriging estimation in the normalscored space is valid. In practice, it is difficult to ensure that normal-scored data are multi-Gaussian. Goovaerts Kai-Wei Juang and Dar-Yuan Lee, Graduate Institute of Agricultural attributes of interest being higher than a given cutoff

Journal of Environmental Quality, 2009

Journal of Environmental Quality, 1999

The information age has ushered in an awareness of and concern for global environmental problems ... more The information age has ushered in an awareness of and concern for global environmental problems such as climatic change, ozone depletion, deforestation, desertification, and nonpoint source (NPS) pollution. Nonpoint source pollution is the single greatest threat to surface and subsurface drinking water resources. Nonpoint source pollutants also pose a threat to sustainable agriculture, which is viewed as the most viable means of meeting the food demands of a world population that is expected to reach 9.4 billion by the middle of the next century. The ability to accurately assess present and future NPS pollution impacts on ecosystems ranging from local to global scales would provide a powerful tool for environmental stewardship and guiding future human activities. Assessing NPS pollutant is a multidisciplinary problem. To address the problem, advanced information technologies and methodologies are needed that draw from all areas of science and are applied in a spatial context. It was from this setting that the 1997 Joint AGU Chapman/SSSA Outreach Conference Application of GIS, Remote Sensing, Geostatistics, and Solute Transport Modeling for Assessing Nonpoint Source Pollutants in the Vadose Zone (19-24 Oct. 1997, Riverside, CA) materialized. The objective of the conference was to examine current muitidisciplinary technologies and methodologies for assessing NPS pollutants in the vadose zone, and to explore new conceptual approaches. It was the conference's goal to provide a forum to stimulate multidisciplinary interaction to enhance the development of techniques for the realtime measurement and modeling of NPS pollution in the vadose zone and subsurface waters. Tt HE INFORMATION-TECHNOLOGY AGE of the 1990s is a ime of global environmental consciousness where the ramifications of environmental stewardship stretch even into political arenas. Historically, science and technology have taken a back seat to political concerns in the decision-making process. Science and technology are no longer merely tools of national development, but rather they are becoming integral parts of the international political landscape as evidenced by the 1992 Earth Summit Conference in Rio de Janeiro and the 1997 Kyoto Climate Summit. A knowledge and understanding of how resource utilization in individual countries impacts the global environment and associated political

Journal of Environmental Quality, 2010

Communications in Soil Science and Plant Analysis, 1995

Rapid, sensitive analysis of NH4 NO3 , and NO2 in 1–150 μL of soil extract or water was achieved ... more Rapid, sensitive analysis of NH4 NO3 , and NO2 in 1–150 μL of soil extract or water was achieved using a modified indophenol blue technique adapted to microtiter plate format. The microplate technique was similar to conventional steam distillation in accuracy and precision. By varying aliquot volume, a wide linear dynamic range (0.05 to 1000 mg of NH4 ‐ or

… of soil and water Conservation, 1998

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1991

A field experiment is reported which monitored the three-dimensional movement of cubic solute plu... more A field experiment is reported which monitored the three-dimensional movement of cubic solute plumes through an unsaturated, loamy sand soil. The plumes were created with one of two methods, a two-dimensional flux application and an initial resident distribution. Soil coring was used to sample resident concentrations for the three solutes studied. The data were analyzed using the method of moments. In addition to the solute transport experiments, a detailed set of physical properties of the field was obtained by excavating three pits to a depth of 5.0 m and also by taking soil cores throughout the study area. This paper explains the experimental methodology, summarizes the relevant site characteristics, and describes the observed transport based on the zeroth and first order spatial moments. Mass balance varied between 78 and 138%. The field-averaged gravimetric water content and dry bulk density were used to accurately predict the mean vertical plume displacements. The plumes spread relatively little in the horizontal direction. INTRODUCTION Many chemicals enter and move through unsaturated soil as part of a compact plume. A solute plume may originate at the soil surface as a consequence of a spill or a leaking surface tank. It may also emanate from within the vadose zone by leaking through the bottom of a disposal pond or subsurface storage tank. The dissolution of solids, such as the leachate underneath a fly ash pit, may also create a chemical plume. In all of these scenarios, a contaminant plume is created which will likely migrate downward (depending on the soil moisture regime) toward an underlying water resource. There are numerous reasons for wanting to improve the understanding of how a chemical moves through unsaturated soil. First, in many contamination episodes such as waste spills, the only information available is the volume of fluid that enters the soil and the area over which it infiltrated. Without an understanding of the degree of lateral dispersion of the plume, it is not possible to estimate even roughly the downward penetration of the spill. In the absence of a preliminary means for making this assessment, expensive and time-consuming soil concentration measurements must be made over a dense grid in the soil to characterize the plume geometry. Furthermore, even when the initial volume