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ANNUAL REPORT OF REGIONAL RESEARCH PROJECT W-188

January 1 to December 31, 2002

1. PROJECT: W-188 CHARACTERIZATION OF FLOW AND TRANSPORT

PROCESSES IN SOILS AT DIFFERRENT SCALES

2. ACTIVE COOPERATING AGENCIES AND PRINCIPAL LEADERS:

Arizona A.W. Warrick, Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721

P.J. Wierenga, Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721

W. Rasmussen, Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721

P. Ferre, Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721

California M. Ghodrati, Dept. of Env. Sci. Pol. Mgmt., University of California, Berkeley, CA 94720-3110

J.W. Hopmans, Dept. of LAWR, Hydrologic Science, University of California Davis, CA 95616

W.A. Jury, Dept. of Envir. Sciences, University of California, Riverside, CA 92521

F. Leij, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507

D.R. Nielsen, Dept. of LAWR, Hydrologic Science, University of California Davis, CA 95616

D.E. Rolston, Dept. of LAWR, Soil and BioGeochemistry, University of California Davis, CA 95616

P.J. Shouse, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507-

J. Šimůnek, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507-

T. Skaggs, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507-

M.Th. van Genuchten, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507

Z. Wang California State University, Fresno, CA

L.Wu, Dept. of Envir. Sciences, University of California, Riverside, CA 92521

Colorado L.R. Ahuja, USDA-ARS, Great Plains System Research Unit Fort Collins, CO 80522

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T. Green, USDA-ARS, Great Plains System Research Unit Fort Collins, CO 80522

G. Butters, Dept. of Agronomy, Colorado State University, Ft Collins, CO 80523

Connecticut D. Or, Civil & Environmental Engineering, University of Connecticut, Storrs, CT 06269-2037

Delaware Y. Jin, Dept. of Plant and Soil Sciences, Univ. of Delaware, Newark, DE 10717-1303

Idaho J.B. Sisson, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107

J. Hubbel, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107

Markus Tuller, Dept. of Plant, Soils & Ent. Sci. Univ. of Idaho, Moscow, ID 83844

Illinois T.R. Ellsworth, University of Illinois, Urbana, IL 61801

Indiana J. Cushman, Mathematics Dept., Purdue University, W. Lafayette, IN 47905

P.S.C. Rao, School of Civil Engineering, Purdue University, W. Lafayette, IN 47905

Iowa R. Horton, Dept. of Agronomy, Iowa State University, Ames, IA 50011

D. Jaynes, National Soil Tilth Lab, USDA-ARS, Ames, IA 50011

Kansas G. Kluitenberg, Dept. of Agronomy, Kansas State University, Manhattan, KS 66506

Montana J. M. Wraith, Land Resources and Environ. Sciences, Montana State University, Bozeman, MT 59717-3120

Nevada S.W. Tyler, Hydrologic Sciences Graduate Program, University of Nevada, Reno, NV 89532

M.H. Young, Desert Research Institute, University of Nevada, Las Vegas, NV 89119

New Mexico J.H.M. Hendrickx, New Mexico Tech, Dept. of Geoscience, Socorro, NM 87801

North Dakota F. Casey, Dept. of Soil Science, North Dakota State University, Fargo, ND 58105-5638

Tennessee J. Lee, Biosys Engin & Envir SciUniversity of Tennessee, Knoxville, TN 37996

E. Perfect, Dept. of Geo. Sciences, Univ. Tennessee Knoxville, TN 37996-1410

Texas S.R. Evett, USDA-ARS-CPRL, P.O. Drawer 10, Bushland, TX 79012

R.C. Scwartz, USDA-ARS-CPRL, P.O. Drawer 10, Bushland, TX 79012

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Utah S. Jones (and D. Or now in Connecticut), Dept. of Plants, Soils & Biomet., Utah State University, Logan, UT 84322

Washington M. Flury, Dept. of Crop & Soil Sciences, Washington State University, Pullman, WA 99164

J. Wu, Dept. of Biological System Engineering, Washington State University, Pullman, WA 99164

G. W. Gee, Battelle Pacific Northwest Division, Richland, WA 99352

P. D. Meyer, Battelle Pacific Northwest Division, Portland, OR 97204

M. L. Rockhold Battelle Pacific Northwest Division Richland, WA 99352

A. L Ward, Battelle Pacific Northwest Division, Richland, WA 99352

Z. F. Zhang Battelle Pacific Northwest Division, Richland WA 99352

Wyoming R. Zhang, Dept. of Renewable Resources, University of Wyoming, Laramie, WY 82071

CSREES R. Knighton, USDA-CSREES, Washington, DC 20250-2200

Adm. Adv. G.A. Mitchell, Palmer Research Center, 533 E. Fireweed, Palmer, AK 99645

3. PROGRESS OF WORK AND MAIN ACCOMPLISHMENTS:

OBJECTIVE 1: To study relationships between flow and transport properties or

processes and the spatial and temporal scales at which these are observed

The issue of downscaling (disaggregation) and upscaling (aggregation) of flow or

transport processes and their measurement across a range of spatial or temporal scales were investigated at the University of California – Davis. Various numerical studies were done to demonstrate that scaling theory and inverse modeling can be applied in concert, whereby scale-appropriate and effective soil hydraulic functions were optimized. Also at UC – Davis, physically based methods that improve the understanding of the control of tortuosity and pore continuity on transport (as a function of fluid saturation) were investigated to improve the predictive capability of transport models. Since all soil transport processes occur in the same soil pore space, one may intuitively expect a possible link between the different transport coefficients and key soil pore geometry characteristics such as pore

Figure 1. Combination of all four relative transport coefficients as

a function of fluid saturation (Tuli and Hopmans, 2002).

0.0 0.2 0.4 0.6 0.8 1.0

Sew , Sea

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1.0

Krw

,

Kra

,

Drg

,

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ra

Krw

Kra

Drg

ECra

Oso Flaco fine sand

0.0 0.2 0.4 0.6 0.8 1.0

Sew , Sea

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Columbia sandy loam

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tortuosity and connectivity. A relation was developed between the fluid content and four analyzed transport coefficients, normalized to their maximum measured values for Oso Flaco sand (Figure 1). Although this relation was well described in the Oso Flaco sand, the presence of a universal relationship between fluid saturation and transport is doubtful. At the University of California – Riverside nitrogen best management practices (BMPs) for fertilizing lawns were investigated. The objectives of this project were to develop BMPs for fertilizing lawns, a major urban source of NO3

B contamination of groundwater. This was accomplished by optimizing plant performance and N uptake while reducing the potential for NO3

B leaching. A random complete block (RCB) design of N treatments on plots was used to study N uptake and leaching under irrigation. The effectiveness of the treatments was determined using measurements that include visual turfgrass quality and color ratings, clipping yield, tissue N concentration, N uptake and NO3–N concentration of soil water below the root zone. Additionally, the cause of unstable flow in field soils was investigated at UC –

Riverside. Reversal of the matric potential gradient during redistribution of soil water following infiltration has been hypothesized as a cause of preferential flow by inducing a fluid instability at the leading edge of the wetting front. Over the past two years, seventeen field experiments were carried out to quantify the effects of redistribution on preferential flow in non-structured soils in three field soils (Superstition sand, Delhi sand and Hanford sandy loam) under saturating and non-saturating water application rates. Water flow patterns during redistribution were monitored using anionic dyes and intensive core sampling. The observed two- and three-dimensional distribution of the water-tracers clearly indicated the development of unstable flow during redistribution in two of the three soil types studied, but not in the coarsest-textured Superstition sand. The measured tortuosity of the wetting front was near 1.0 at the end of infiltration, indicating a stable front, but increased significantly during redistribution until finally declining due to the effects of capillary diffusion. Mean finger thicknesses were comparable (about 13 cm) in the two soils where instabilities were observed, and were found to be consistent with predictions using an equation developed from stability theory. In addition to field studies, the UC – Riverside used two-dimensional slabs uniformly packed with coarse sand to study unstable flow in the laboratory during redistribution. The results demonstrated that fingers form and propagated rapidly as soon as infiltration stopped when the soil was initially dry, but formed more slowly and were larger when the soil was wet. Finger diameters ranged from about 4.5 cm when the soil was dry to 17 cm when the soil was very wet, and the fraction of the cross sectional area occupied by fingers also increased (from 36% to 66%). Finger velocities declined with time in all studies, with averages that ranged from 3.6 to 9.6 cm/min. Also, it was found that ponded infiltration was stable and uniform, so it was concluded that fingering was not due to soil heterogeneity. The porous medium retained a memory of the fingers formed in the first experiment, so that fingers formed in subsequent redistribution cycles followed the old finger paths, even after 28 days had elapsed. Fingers provided channels for rapid drainage of previously infiltrated water, especially when the soil ahead of the front was dry. These findings clearly contradicted predictions made by Richard's equation, which calculates stable flow during redistribution in homogeneous soil. A conceptual model was developed that represents unstable flow in uniform soils during redistribution. The model used soil retention and hydraulic functions, plus relationships

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describing finger size and spatial frequency. The model assumed that all soils were unstable during redistribution, but showed that only coarse-textured soils formed fingers capable of moving appreciable distances.

Several researchers at the USDA-Salinity Lab (USDA – USSL, Riverside, CA) have done studies to address Objective 1. The first project was initiated by concerns for public health and environmental contamination and involved improving the understanding of the processes and mechanisms that affect pesticide emissions from fields. A field study was designed to study the coupling of atmospheric processes to the rate of volatilization of methyl bromide as a function of time. A one-dimensional numerical model was developed to simulate simultaneously water, heat, and solute transport, which also included chemical transport in the vapor phase. Other research at the USDA-USSL has shown that combinations of plastic vapor barriers and soil amendments can be effective in reducing pesticide vapor emissions.

USDA-USSL scientists also investigated the packing homogeneity of soils using two-dimensional rectangular slabs of soils. These studies found that during repacking soil materials may appear to have similar bulk properties such as bulk density and porosity, but the micro-scale structural properties were found to be a function of the packing method. Using traditional packing methods, it was unlikely that uniform distribution at the micro-scale would be achieved. The rate at which a material was poured determined the uniformity of the grain size distribution.

Knowledge of the release behavior of pathogens from animal waste is needed to determine cumulative loading of pathogens to surface and groundwater. Researchers at USDA-USSL developed, calibrated, and applied a conceptual model to describe and predict manure and protozoan parasite (oo)cyst (Giardia cysts and Cryptosporidium oocysts) release rates and cumulative loading (i.e., manure release into water was characterized as a diffusion controlled processes). Additionally, pathogen concentration was predicted from the dissolved manure concentration, the initial pathogen concentration in the manure, and the release efficiency of the pathogens (relative to that of manure). Furthermore, a conceptual model was developed, calibrated and applied that accounts for attachment and detachment of pathogens using a conventional first-order rate expressions. This model described straining using a depth-dependent first-order rate expression, and modeled exclusions by employing the pathogen accessible pore space in transport parameters. In addition to these experiments and modeling efforts, a series of soil column experiments were done to explore the influence of colloid input concentration on the transport and fate of several colloid sizes in three soils. Results suggested that theory and models for colloid transport need to be improved to account for the observed concentration dependent transport behavior, and that pathogen transport may be enhanced in porous media at higher colloid concentrations typical of manure release. Other studies at USDA – USSL related to pathogens included the modeling of bacteriophage removal in soils.

USDA – USSL scientist also performed laboratory experiments involving both homogeneous and heterogeneous porous media to demonstrate that fluid flow and chemical transport occurred regularly in the capillary fringe (CF), which included both vertical (upwards as well as downwards) and horizontal flow velocities. Results from this study suggested that the CF might affect, more significantly than assumed, the natural

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geochemical and microbial conditions present in the region of transition from unsaturated to saturated groundwater flow.

Lastly, scientist at the USDA – USSL developed and evaluated several numerical models that investigated the following: 1) how errors in estimation of hourly values of solar radiation and air temperature affect errors in simulation of soil temperature; 2) the nitrogen budget of a forest ecosystem and identification of storage and release of nitrogen from a site; and 3) the use of Monte Carlo simulation to identify the critical path calculation of the conductivity of a random resistor network that has a logarithmically broad distribution of bond conductances.

At USDA – ARS (Fort Collins, CO), spatial soil water and crop data from a cooperative farm near Sterling, Colorado have been analyzed for within-field variability and spatial patterns related to landscape attributes. Geostatistical analyses showed that both crop yield and soil moisture displayed spatial structure that could be represented with non-stationary variograms and fractal geometry, indicative of nested scales of variability. Directional dependence (i.e., anisotropy) in these spatial relationships was also quantified using a new measure of fractal anisotropy. Results indicated that the predictions of spatial patterns of crop yield in semi-arid regions from topographic information are a prerequisite for ongoing research to aid site-specific land management decisions. Additionally, to further this work, new on-farm spatial measurements have been initiated on a farm near Ault, Colorado (~20 miles east of Fort Collins). These efforts will also make it possible to test more mechanistic models of water and chemical movement between topographically defined land areas. At the University of Delaware virus retention and transport through Al-oxide coated sand columns, the effects of organic matter (OM) on the virus transport, and the removal of viruses by layered double hydroxides (LDHs) were all investigated. To accomplish these objectives, the bacteriophages, MS2 and φX174, were used as model viruses in a series of batch sorption and column experiments. Results from the Al-oxide experiments indicated that 1) metal oxide, which commonly exists in natural soils and aquifer formations, increased the removal and hence decreased the transport of both MS-2 and φX174; and 2) transport of MS-2 and φX174 through Al-oxide coated sand was increased by increasing ionic strength but did not impact the mass recovery of the two viruses. The results from the studies of OM effects on MS-2 and φX174 sorption and transport indicated that the OM effects on virus retention were very complex, and dependent on both the nature of the OM and the type of viruses involved. The collective results seem to suggest that if the dominant mechanisms controlling OM-virus interaction were electrostatic, then virus transport would be promoted. Likewise, if the dominant OM-virus interactions were hydrophobic, then virus transport would be retarded. The results from the studies on the removal of viruses by LDHs indicated that LDHs wer effective sorbents under most environmental pH conditions. Column experiment results indicated that there was no MS-2 breakthrough from columns packed with Mg-Al LDH 2-coated sand, which suggested a complete MS-2 retention. Results of this research were important to the potential utilization of LDHs as filtration/sorption materials in point-of-use water treatment device or for microbial contaminant remediation practices. Significant efforts have been devoted to the remediation of radionuclide contamination originating from underground waste tanks at the Hanford Site in eastern Washington, USA. The University of Delaware, in a collaborative project with

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Washington State University and Battle PNNL, conducted a series of batch sorption and saturated column experiments to investigate the effects of colloids on Cs transport in two types of porous media (Hanford sediment characteristic of 2:1 clay minerals and silica Ottawa sand). The results from these studies indicated that the efficiency of colloid-facilitated Cs transport was controlled by the non-linear nature of Cs sorption by both solid surfaces and colloids, and that colloid-associated Cs could be partially stripped off from colloids during the transport. Experimental results indicated that under otherwise identical conditions, the efficiency of colloid-facilitated Cs transport was greater in contaminated than in uncontaminated transport medium. At Iowa State University, the relation between solute transport at the soil surface with subsurface tile drainage was investigated. Forty-five time domain (TDR) probes were installed in a field soil to determine the near-surface chemical transport properties by measuring the bulk electrical conductivity in the top 2 cm of soil. Additionally electrical conductivity of the subsurface drainage tile flow was continuously monitored with an EC probe and datalogger. The breakthrough curves measured by the TDR probes were used to estimate the near-surface solute transport properties that would subsequently be applied to predict the tile flow EC. Evaluation of the soil solute transport properties is ongoing. Other solute transport research at Iowa State University was investigated. Researchers used percolation theory to study temporal and spatial scale effects on aqueous diffusion in rock matrices. Simulation results suggested a way to estimate tortuosity, and thereby effective diffusion, based upon the proximity to the percolation threshold. By using this new approach, predicted and simulated effective diffusion compared well, as indicated in Figure 2. Values of tortuosity (τ) were τ < 10 until the medium reached connectivity values at which there were few redundant pathways. At University of Minnesota stability analysis of the Richards equation (RE) and alternative mass balance equations was done. The Richards equation was found to be unconditionally stable. Linear stability analysis was done to find what forms of the equation were conditionally stable. Two other mass balance equation were used, the Sharp Front Richards Equation (SFRE) and a Relaxation Richards Equation (RRE). The results of the linear stability analysis showed that the RE is unconditionally stable, the SFRE is unconditionally unstable, and the RRE is conditionally stable. With these results we found that the dynamic capillary pressure-saturation (CPS) is necessary to produce instabilities in the flow, and that hysteresis in the equilibrium CPS is necessary for the persistence of fingers that form from the instability. A numerical solution to the RRE

Figure 2. Simulated (circles) versus calculated (triangles)

diffusivity.

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equation for two-dimensional flow was developed and applied to investigate the effect of boundary conditions on the formation of fingers in unstable flows. This solution accounts for hysteresis in the equilibrium CPS. A limitation of the current model is that it cannot efficiently treat sharp wetting fronts. Additionally at the University of Minnesota unstable flow in water repellent soils was investigated. A numerical solution of the Relaxation Richards equation was applied to the simulation of flow instability for water repellent soils. The specific moisture capacity of an unsaturated porous medium is very sensitive to the degree of water repellency. The results from the numerical studies showed that for a water wettable porous medium, the flow was stable, while for increasing levels of water repellency the flow became increasingly unstable. The effect of infiltration rate (wetting rate) on flow stability was also investigated. Two-dimensional simulation indicated that as the rate of wetting approach zero, the flow became increasingly more stable.

Research under Objective 1 at Desert Research Institute (DRI) focused on the development of a field experimental site to characterize unsaturated flow and transport in highly heterogeneous media; specifically mining waste and gold ores. A large gold heap leach facility was instrumented with 29 large or small gravity-pan lysimeters to determine spatial variability of infiltration and geochemical heterogeneity during gold ore heap leaching, drain-down and rinsing. Large gold ore heap leach facilities are widely used across Nevada and can potentially be a source of long-term groundwater contamination. So far, results indicated no significant trend in infiltration collection efficiency between the small and large lysimeters; a surprising result given the evidence of large fractions of macropore flow that have occurred. In addition, most lysimeters show infiltration rates approximately 50% below the surface application rate, suggesting that significant portions of infiltration have bypassed all of the lysimeters. This further implies that leaching efficiency for gold production was significantly below that desired.

Figure 3. Time series nitrate concentrations in a lysimeter, tile drainage, and

shallow and deep wells. There is a rise in nitrate concentrations just after

dryland agriculture is converted to irrigation.

At North Dakota State University, the initiation of irrigation effects on temporal nitrate nitrogen (NO3–N) leaching was investigated in collaboration with the USDA-

CSREES (Ray Knighton). An 11-yr study was started in 1989 near Oakes, ND that

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continuously monitored NO3–N concentrations in subsurface water of a field that was converted from dryland to center-pivot irrigation in 1989. The water quality in vadose zone and surficial aquifer was extensively monitored with lysimeters and wells at various depths. The time series NO3–N concentration data (Figure 3) from each of the monitoring locations exhibited the similar three-phase trend where 1) NO3–N concentrations increased, 2) then decreased, and 3) then reached a steady-state level that was maintained. The first and second phases of this trend were shorter (approx. 3 yrs total) for the lysimeters and increased as the depth of observation increased. Also, the peak NO3–N concentration decreased as the observation went deeper into the profile. The increase in NO3–N concentrations in subsurface waters could be partially explained by the residual N in the soil from dryland agriculture. As soil moisture increased the availability and mobility of N increased, which attributed to the flush of NO3–N through the soil profile.

Additionally at North Dakota

State University, the fate and transport of bioactive chemicals in agricultural soils was investigated. A series of kinetic and equilibrium batch sorption and miscible-displacement experiments have been done using agriculturally significant soil, which ranged in particle size distribution and organic matter contents. These experiments were done to identify the fate and transport of 14C radiolabeled hormones (i.e., 17β-estradiol, estrone, and testosterone) and sulfa-based antibiotics. The hormone, 17β-estradiol (Figure 4), rapidly underwent transformations in the soil and produced metabolites of different polarities. The metabolites with the higher polarities appeared to be more mobile in the soil, while the metabolites with lower polarities were strongly sorbed to the soil. Miscible-displacement experiments of the 17β-estradiol showed that no parent (i.e., 17β-estradiol) compound was present in the effluent, but rather a highly polar compound, which was not identified but speculated to be a quinone or seminquinone. Breakthrough curves were inversely modeled, albeit with non-unique solutions, and indicate that transformations occurred mainly on the sorbed phase and that the sorption was primarily kinetic. The fate and transport experiments of testosterone indicated that testosterone was more mobile in the soil

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Gardena - Clay Loam

LaDelle - Silt Loam

Sioux - Loam

Measure Concentration

First Model Fit

Second Model Fit

Figure 4. The 17β-estradiol miscible-displacement

experiments and corresponding model fits for each

soil. 17b-estradiol was not present in the effluent

only a highly polar metabolite. The models that

were used were two-site sorption models where the

first model had transformations, and the second

model did not include transformations.

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Figure 5. Effluent breakthrough curves from the

testosterone column experiments. The model that

was used to describe the data was a fully kinetic

model with degradation.

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than 17β-estradiol. Testosterone was present in the effluent of the breakthrough curves (Figure 5) and was modeled using a fully kinetic model with degradation and no transformations. The results from these experiments indicated that hormones or their metabolites (at concentrations found in manures) have the potential to be transported through the organic-rich portion of the soil.

A series of more detail experiments have been completed that used longer application times of the hormonal compounds, and soils with a larger range of organic matter content. These experiments will help identify exact fate and transport processes of these compounds, and identify specific soil components that influence these processes. Additionally, radiolabel metabolites of 17β-estradiol were obtained and fate and transport experiments were done using these compounds.

Utah State University investigated grain moisture determination with TDR and acoustic distance sensors for bulk volume tracking in ear corn drying bins. Modeled results yielded predictions of ear and bulk densities and drying rate as a function of moisture content. Measurements of the individual ear density and ear dielectric were compared with measurements in the bulk sample based on geometrical scaling considerations. The combination of acoustic and dielectric methods in the bulk measurements provided much greater correlation to actual drying rates than either of these methods alone (Figure 6). Water content was related to dielectric measurements using dielectric mixing theory. The overall objective of these activities was to improve monitoring capabilities in ear corn drying operations using real-time measurements of dielectric, acoustic and other monitoring methods. Results from last year’s work, have been used to implement novel methods for estimating critical parameters for permittivity modeling, such as packing density and porosity, water binding surface area, and water phase permittivity.

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Figure 6. Drying rates obtained from averaging the acoustic (Volume) and dielectric measurements

in A) the 2001 measurements and B) the 2002) experiment.

Researchers at Pacific Northwest National Laboratory (PNNL) have developed several new approaches to quantify spatial and temporal heterogeneities affecting water and solute transport in field soils. Ongoing large-scale field studies at the Hanford Site near Richland, Washington have included measurements of simulated tank leaks, which included multiple injections from 1) a point source (5m-deep buried pipe) and 2) a surface line-source (over a 60 m transect). These studies provided data sets that new theories and models of vadose zone transport could be tested. Observations from the point-source studies have led to the development of two distinct approaches for improved vadose zone transport analyses. The combination parameter-scaling and inverse methods

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were developed and related hydraulic-parameter values measured at different spatial scales for different soil textures. Parameter scaling factors relevant to a reference texture were determined using local-scale parameter values, e.g., those measured in the lab using small soil cores. After parameter scaling was applied, the total number of unknown variables in hydraulic parameters was reduced by a factor equal to the number of soil textures. The field-scale values of the unknown variables could be estimated using inverse techniques and a well-designed field experiment. Finally, parameters for individual textures were obtained through inverse scaling of the reference values using an a priori relationship between reference parameter values and the specific values for each texture. This approach has been applied successfully to a variety of infiltration experiments. In this approach, the whole parameter estimation process was performed using a combination of two computer models, one for forward flow modeling and the other for nonlinear regression. The forward model used to simulate water flow was the Subsurface Transport Over Multiple Phases (STOMP) numerical simulator. The Universal CODE (UCODE) model was used to perform inverse modeling posed as a parameter-estimation problem using nonlinear regression. The advantage of this method was that it does not require the constitutional materials to be similar and the number of unknown parameters were reduced such that multiple realizations of the flow or transport problem can be efficiently computed. The PNNL was also involved in developing vadose zone parameterization (VZP) tools, a library of Fortran subroutines and pre-processor utilities for the STOMP code, that implement a systematic approach (methodology) for vadose zone parameterization in field-scale model applications. VZP Tools were an extension of the parameterization approaches applied to the Las Cruces (New Mexico) trench experiments and to an injection test (tank leak problems) at the Hanford Site. A third development by PNNL was the Tensorial Connectivity Tortuosity (TCT) concept for describing anisotropy of the unsaturated hydraulic conductivity. The idea was that soil pore connectivity and/or tortuosity were anisotropic and could be described using a tensor. The anisotropic hydraulic properties could then be described by extending the existing hydraulic conductivity models so that the connectivity-tortuosity coefficient (l) was a tensor. Test of the concept using synthetic Miller-similar soils with four levels of heterogeneity and four levels of anisotropy indicated that the model could accurately describe the unsaturated hydraulic function of anisotropic soils. The values of l were found to be a function of both soil heterogeneity and anisotropy. The values of l were found to decrease linearly as the ratio of vertical to horizontal conductivity increased. Larger values of l indicated less connected pores and/or more tortuous flow paths. Numerical experiments using a simulated coarse-textured (sandy) soil demonstrated that soil-water retention curves of anisotropic soils were independent of the observation direction but dependent on soil heterogeneity. The unsaturated conductivity of the anisotropic soils tested in the initial application of the new theory (concept) differed by several orders of magnitude depending on the orientation direction. Soil anisotropy in hydraulic conductivity increased as the soil dried but did so in a much more realistic fashion than other models of anisotropy based on stochastic theory. The TCT concept has already been implemented in VZP Tools. (see above) and should be readily implemented into existing vadose zone flow and transport models.

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OBJECTIVE 2: To develop and evaluate instrumentation and methods of analysis for

characterization of flow and transport at different scales

At the University of Arizona, a controlled field study was continued at the

Maricopa Agricultural Center (MAC) near Phoenix, Arizona, which used a conservative bromide transport experiment. Water transfer and solute transport were modeled numerically in addition to the transport measurements. The average R value was 0.63 with a range of 0.45 to 1.02 at 3 m (CV = 28 percent). The low R value was indicative of anion exclusion, immobile water, or some other phenomenon difficult to identify from field data. These field data indicate that if a transport model with a bulk retardation factor is used for predicting bromide transport through unsaturated soil a range of retardation values may need to be used. For our soil the highest R value needed to be at least twice its lowest value. In a different analysis, various methods were used to postulate, compare and rank alternative conceptual-mathematical models of unsaturated flow and transport during infiltration and redistribution at the Maricopa site. The models include one- and two-dimensional flow and transport in a uniform soil, a soil that consisted of uniform layers, and in a stratified soil that had laterally varying properties. Characterization of the soil as a uniform medium with a relatively deep regional water table was based on information obtained from public sources. Characterization of the soil as a layered medium with a relatively shallow water table was based on site data. Only a handful of soil hydraulic property measurements were available for the site. Soil hydraulic properties were therefore estimated from pedologic data. Uniform soil hydraulic properties were ascribed to each layer on the basis of soil type using mean values of three generic databases. Variable soil hydraulic properties were ascribed to individual soil samples with regression and neural network pedotransfer models based on soil type and bulk density. These variable hydraulic property estimates were treated as measurements, and then they were incorporated into the original databases to obtain Bayesian updates of their mean values (together with the variance of each such estimate). Geostatistical analysis of soil pedologic and hydraulic properties provided support for a layered conceptual model with relatively large-scale lateral variability in each layer. The above conceptual-mathematical models and hydraulic parameter estimates were used to compare simulated and observed water contents during one of the infiltration experiments at the MAC. It was shown that in order to reproduce observed behavior, it was necessary to further modify the hydraulic parameter estimates through inverse modeling. The various conceptual-mathematical models and parameter estimates were compared and ranked by likelihood-based model discrimination criteria, which confirmed the choice of best model by successfully simulating flow during an earlier infiltration experiment. Finally, one-dimensional inverse estimates of soil hydraulic parameters were adopted based on one infiltration experiment for one-dimensional solute transport modeling of bromide tracer data.

At UC – Davis a combined TDR-tensiometer probe was developed that could be used to determine soil water retention curves in both laboratory and field conditions, by including a coiled TDR probe around the porous cup of a standard tensiometer. The main advantage of the combined probe design was the simultaneous measurement of soil water content and soil water matric potential at the same spatial location within approximately

13

the same bulk soil volume around the porous cup. This new TDR development provided in situ soil water retention data from simultaneous soil water matric potential and water content measurements within approximately the same small soil volume. However, this system required soil specific calibration because of slight desaturation of the porous cup of the tensiometer. In a separate study at UC – Davis, a small multi-functional sensor consisting of a heater needle with four additional thermistors, and electrodes needle was developed to measure soil water, soil thermal properties, water flow velocity, and soil solution concentration. Volumetric heat capacity and diffusivity were obtained by applying heat pulse and measuring temperature responses at 6-mm away from the heater. This study concluded that parameter optimization including soil water, solute, and heat transport properties gives more accurate results than when obtained from single property measurements.

A new method to quantify substrate-borne Polyacrylamide (PAM) was developed by UC – Riverside, which was based on a modified method of N-bromination of amide groups and spectrophotometric determination of the formed starch-triiodide complex (a method that was originally developed for determining PAM in aqueous solutions). This technique could serve as an effective tool in improving PAM application to soil and facilitating PAM-related research. Additionally, PAM distributions in soil columns were used to investigate the transport of PAM in soils. At the USDA – USSL, chemical movement and distribution in the soil profile was simultaneously monitored with chemical volatilization in a two-dimensional rectangular soil column. In another study, the temperature response of soil electrical conductivity measured by the Geonics EM-38 was investigated. Results indicated measurement error with temperature fluctuations and a simple and practical solution to this problem was to shade the instrument, which would reduce the instrument panel temperature by as much as 200C when left out in the sun. Field results suggested that it was best to maintain the instrument temperature below 350C to ensure that the instrument temperature compensation was fully working and that the measurement response was due solely to ground conductivity as required. In another study at USDA – USSL, an electric circuit model was developed that related the capacitance probe sensor frequency to the permittivity of a medium and was able to correct for small values of ionic conductivity, which typically confounds capacitance measurements in saline soils. At Colorado State University, work continued on testing and applying a continuous flow method for rapid and accurate measurement of soil hydraulic conductivity K(h) and moisture retention θ(h) functions including hysteresis. With the aid of simple direct measurements and Darcian analysis to condition parameter estimates, the numerical inversion of Richards’ Equation for was found to yield physically relevant parameter estimates of the conductivity and retention functions. A key advantage of this experimental approach was identification of the air-entry pressure, which allowed for unambiguous treatment of outflow data near saturation. The continuous flow method was ideally suited for evaluating fundamental problems in soil water flow such as temporal variation and spatial scaling/averaging of soil hydraulic properties. For example, in an on-going study, this method was used to evaluate the impact of microbial growth on soil hydraulic properties by comparing water flow in soils treated with a microbial inhibitor to treatment with glucose. This information could be used in management models where temporal effects in hydraulic properties are included.

14

At the University of Idaho in collaboration with the University of

Connecticut, work has been done to develop a new pore-scale framework for predicting hydraulic properties of structurally active clay soils. To do this a comprehensive geometrical picture was built that included the arrangement and evolution of clay fabric mixed with other textural constituents, which was linked to a physico-chemical model. Clay fabric was considered as an assembly of colloidal-size stacks of lamellae whose spatial organization and the spacing between individual clay sheets was a function of clay hydration state. Silt and sand textural constituents were represented as rigid spheres interspaced by clay fabric in two basic configurations of "expansive" and "reductive" unit cells. Bulk media properties such as porosity and surface area provided constraints for the idealized geometry. Preliminary qualitative model evaluation demonstrated great potential of the proposed framework as depicted in Figure 7, where model predictions for permeability of clay sand mixtures were compared with measured data. Also at the Idaho State University, research was started to evaluate the effects of clay type, clay content, electrolyte type, and electrolyte concentration on pore space evolution. Experiments for this research used a fully automated flexible wall permeameter (Figure 8). This research has accomplished the optimization of mixing and saturation procedures suitable for series measurements.

Figure 8. (a) Flexible wall permeameter setup (GEOCOMP), and (b) volume

change apparatus (Wykeham Farrance) to measure shrink-swell behavior and

water ratio. At Iowa State University, heat pulse sensor theory was extended to measure

subsurface water fluxes. Past results have shown that a simple theoretical relationship exists between water flux and the natural log of the ratio of the temperature increase downstream from a line heat source to the temperature increase upstream from a line heat source. To test this simple relationship, experiments were performed that use heat pulse measurements in packed columns of sand, sandy loam, and silt loam subjected to a wide range of water flow rates. In initial tests the heat pulse method provided accurate measurements of water fluxes from 0.5 to 25 cm hr-1 in sand. For this same range of

Figure 7. Permeability calculations for different clay

contents (square symbols) versus measurements

reported by Revil and Cathles (1999).

15

fluxes, the heat pulse method tended to underestimate the water flux in the sandy loam and silt loam, particularly at the higher flow rates. At Kansas State University, research was done to characterize the effective measurement scales for thermal sensors. In collaboration with John Knight (CSRIO

Land & Water), a theoretical framework has been developed that allows spatial weighting functions to be obtained for a broad class of methods used to quantify thermal properties, which include weighting functions for volumetric heat capacity as measured by the dual-probe heat-pulse (DPHP) method, and for thermal conductivity as measured with a line-source thermal conductivity probe. Also at Kansas State University a simplified computational approach was developed for the DPHP. Kansas State University also was involved in a study to investigate the NO3–N leaching losses under irrigated corn. A field experiment was conducted in 2002 in north central Kansas to quantify nitrate mass flux from the root zone under irrigated corn production and evaluate split application of nitrogen fertilizer as a management practice for reducing leaching losses. Plots were instrumented with and with ceramic-cup solution samplers to measure nitrate concentrations in the soil solution. A neutron probe was used to measure water content at regular depth intervals on a weekly basis. Soil samples were collected from the plots before planting and after harvest to quantity profile NO3–N and NH4-N. Plant samples were collected to quantify N removed by the crop. The neutron probe was calibrated in an area adjacent to field plots in conjunction with a measurement of K(h) via the instantaneous profile method. Nitrate concentrations in the soil solution ranged from 10 to nearly 100 mg L-1 and remained relatively constant throughout the growing season. Nitrogen fertilizer treatments of 0, 112/112 (pre-season/side-dress), and 224 (pre-season) kg N ha-1 resulted in no significant differences in corn yield. Nitrate mass flux will be computed after spatially-distributed measurements of K(h) are obtained during the summer of 2003. Several different methods for measuring K(h) will be used and the methods will be compared by taking measurements in the area used for the instantaneous profile method. A new shaft-mounted TDR probe was designed and evaluated, in a collaborative project between Montana State University and Sweden. In contrast to previous shaft-mounted TDR probes (SMPs), the new design may be used to measure both dielectric constant (Ka) and bulk electrical conductivity (ECa) of soils. This provided greater flexibility in monitoring fertilizer status, solute distribution or transport, and other processes of interest in agricultural soils. Two SMP prototypes, 0.03 and 0.04 m long, and having diameters of 0.006 m, were evaluated. The probes were calibrated in several fluids having different Ka and ECa. We demonstrated that the minimal physical probe length of the SMP was achieved without sacrificing accuracy of Ka readings. Accuracy of Ka measurements for the new probes was similar to that of standard 0.20-m length three-rod probes.

Montana State University, in collaboration with the University of Connecticut, conducted an ongoing study that evaluates variation in soil water characteristic measurements of uniform, homogenized soil samples within and among commercial and research laboratories. Many of the research laboratories used are those of W-188 committee members. Preliminary results from the commercial laboratories showed that measurements close to saturation exhibited largest variation. In contrast, variation among research laboratories was similar across the 0.01 to 1.5 MPa pressure range, and may be a

16

result of greater variation in specific procedures employed. Repeated measurements of the same soils by a given commercial laboratory exhibited variability similar to that among the different laboratories, which suggested that the sources of variation were not methodological. The results highlight the inherent uncertainty in such measurements (and related parameters) that cannot be attributed to spatial variability or measurement errors only. Rather, some irreproducibility arose from the physical processes underlying these measurements and from confounding effects of non-equilibrium. This collaborative, cross-Committee study will help us to identify some of the inherent limitations and to establish realistic measurement goals based on these, to consider potential tradeoffs between accuracy and intended use, may provide additional impetus to emphasize in situ measurements for field-relevant properties (e.g., wet end for θ(h)), and for standardization of critical measurement components such as soil packing, equilibration time, measurement range overlap, et cetera.

At DRI in Nevada Objective 2 research has focused on a number of different approaches to analyze site conditions and characterize hydraulic properties, in both unsaturated and saturated media. Work in Nevada has long focused on development of natural soil water tracers to predict groundwater recharge in arid regions. Recent collaborative work with New Mexico have shown that both vegetation and vapor transport in deep vadose zones commonly found in the arid west plays important roles in the development of tracer profiles. Upward flow to the root zone was shown to be necessary to include in numerical simulations of soil water transport over millennial timescales to best match observed profiles. In addition, the commonly observed unit gradients in the deepest parts of the vadose zone was shown to be primarily the result of countercurrent water vapor transport, as opposed to the previously developed concepts of gravity drainage in the absence of non-isothermal vapor transport. The chloride mass balance method used to calculate recharge in non-equilibrium deep vadose zones was shown to produce some errors in precise estimation of recharge reconstructions; however, the overall balance of chloride (or nitrate) present in deep vadose profiles continued to be valuable to estimate times of last major recharge events.

With respect to measuring hydraulic properties of unsaturated material, researchers at DRI described a modified upward infiltration method, which combines laboratory experiments and inverse parameter estimation for determining soil hydraulic properties in the wetting direction. The laboratory method used a Mariotte system to impose a constant head boundary condition on the bottom of a soil column, allowing water to be taken up by the soil material under negative pressure head. Tensiometers installed along the column measured the change in soil pressure head before and after wetting front arrival. The HYDRUS-1D code was used to obtain an optimal set of van Genuchten parameters, using pressure head and cumulative flux data as auxiliary variables in the objective function. Two soil types (a fine sand and a sandy loam) were tested in triplicate in uniformly-packed soil columns. The results of the uniform column experiments were repeatable, and showed excellent fits between observed and predicted data. The relative simplicity of the experimental procedure and the availability of appropriate numerical models render the modified upward infiltration method an alternative for determining wetting hydraulic properties of soils.

Other researchers at DRI studied the impact of surfactants on unsaturated hydraulic properties. Due to their amphiphilic nature, surfactants – often used as

17

adjuvants in agricultural situations – tend to accumulate at gas-liquid and solid-liquid interfaces, and thus, have the potential to influence water flow and retention in unsaturated soils. The objective of this study was to investigate the effects of a nonionic surfactant, Triton X-100, on the interfacial properties and capillary pressure-water content relationships of F-70 Ottawa sand and Appling soil. The experimental results were used to develop and evaluate alternative scaling approaches to describe concentration dependent changes in soil water characteristics based on the van Genuchten model. Although further validation of the simplified scaling factor will be required, this approach offers an efficient means to describe the effects of concentration dependent changes in interfacial properties on soil water characteristics.

In the field, DRI worked on two projects. The first projected focused on an improved methodology of conducting aquifer tests, which used off-the-shelf components in an innovative way. This work was done because substantial uncertainties in the flow rate across the borehole-formation interface can be induced by dynamic head losses, caused by rapid changes in borehole water levels early in an aquifer test, which can greatly affect the calculations of hydraulic properties. The system substantially reduces these sources of uncertainty by explicitly accounting for dynamic head losses. It employs commonly available components (including a datalogger, pressure transducers, a variable-speed pump motor, a flow controller, and flow meters), and is inexpensive, highly mobile, and easily set up. The system optimizes the flow rate at the borehole-formation interface, lending it suitable for any type of aquifer test, including constant, step, or ramped withdrawal and injection, as well as sinusoidal. The second field project involved the development if a new type of TDR system that can be deployed into deep boreholes, even with irregularly shaped borehole walls.

To improve estimates of field hydraulic parameters, infiltration from a tension disc infiltrometer was used conjointly with measurements of soil water content using TDR by researchers at the USDA Conservation and

Production Research Laboratory (USDA–

CPRL, Bushland, TX). Because TDR probes may be partially within the wetted zone, this can complicate interpretations of measured water contents for use in inverse optimizations. The USDA – CPRL researchers compared water contents measured by diagonally placed probes with predicted water contents obtained from inverse optimization of hydraulic parameters. Infiltration experiments with a disc infiltrometer were completed for a 0.58-m diameter cylinder re-packed with a sandy soil. Three TDR probes were inserted diagonally (Figure 9) into the soil to measure transient water contents during infiltration. Inverse optimization of hydraulic parameters was completed using measured cumulative infiltration, water contents from diagonally placed TDR probes, and a wetting branch of the soil water characteristic curve. Inverse optimizations using cumulative infiltration and diagonal TDR water content data also required several points

Figure 9. Detail of horizontal TDR probe

placement at 50, 100, 150, and 200 mm

depth.

18

of the water characteristic curve to satisfactorily describe soil hydraulic properties. Spatially averaged soil water contents modeled using optimized parameters compared closely with water contents measured by TDR. The diagonal placement of TDR probes at 30° from the horizontal minimized errors associated with assuming a uniform weighting of water content within the sampling volume (Figure 10).

To improve the accuracy of shallow soil moisture neutron probe (SMNP) measurements, and to improve operator safety, the researchers at USDA – CPRL added a stand to the design of the SMNP (Figure 11). This new design improved the calibration and accuracy of the shallow water content readings. Additionally at the USDA – CPRL, researchers compared the Sentek EnviroSCAN and Diviner 2000 capacitance devices, the Delta-T PR1/6 Profiler capacitance probe, the Trime T3 tube-probe (all called electrical devices) with the SMNP and TDR. All but conventional TDR can be used in access tubes. Measurements were made before, during and after wetting to saturation in triplicate re-packed columns of three soils: 1) a silty clay loam, 2) a clay, and 3) a calcic clay loam containing 50% CaCO3. The weighed of each column was continuously monitored. Additionally, thermocouple measurements of temperature were made at various depths in each column, through time. Comparisons of soil water content reported by the devices vs. soil temperature showed that all of the devices were sensitive to temperature except for TDR and the SMNP. The Trime T3 and Delta-T PR1/6 devices were so sensitive to temperature (0.020 and 0.025 m3 m-3 °C-1, respectively, at the wet end) as to be inappropriate for routine field measurements of soil water content. All devices exhibited measurement precision better than 0.01 m3 m-3 as evidenced by repeated measures through time under isothermal conditions. Accuracy of the devices was judged by the root mean squared difference (RMSD) between column mean water contents determined by mass

Figure 10. Two-dimensional progression of wetting front

(optimization 2) and corresponding TDR waveforms for a diagonally

(30°) placed probe. The diagonal line represents the center rod of a

trifilar probe.

Figure 11. Schematic of the depth

control stand.

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19

balance and those determined by the devices using factory calibrations. Smaller values of the RMSD metric indicated more accurate factory calibration. The Delta-T system was most inaccurate, with an RMSD of 1.299 m3 m-3 on the wet end. At the saturated end, the Diviner, EnviroSCAN and Trime devices all exhibited RMSD values >0.05 m3 m-3, while the neutron probe and TDR exhibited RMSD <0.03 m3 m-3. All of the devices would require separate calibrations for soil horizons with widely different properties. Of the electrical devices, only the Delta-T PR1/6 exhibited axial sensitivity larger than the axial height of the sensor, indicating small measurement volumes generally, and suggesting that these systems may be susceptible to soil disturbance close to the access tube during installation. The PR1/6 was too sensitive to temperature and too inaccurate to be considered appropriate for routine use.

Utah State University, USDA – USSL and the University of Connecticut collaborated to improve water content determination in saline and clayey soils using TDR. Accomplishments in the early stages of this work were the development of analysis software for processing TDR waveforms and transforming these to the frequency domain for water content determination in porous media. Additionally, dielectric measurements were made in saline soils using a range of ‘short’ TDR probes demonstrating the capability to extend the range of water content. Extensive work was carried out using probes coated with a number of different materials in saline solutions. Model development has begun to characterize the effect of coating on the dielectric measurement. Work was published about the use of dielectric mixture models for interpretation of the dielectric measurement, specifically in quantifying and characterizing effects from surface area, particle shape and other factors of interest

Utah State University in conjunction with Space Dynamics Laboratory, and University of Connecticut have worked on the development of a gas diffusion characterization measurement system for the International Space Station. The motivation for this study stems from NASA’s interest in long terms space travel where plants play an integral role as a bioregenerative life support system. The objective of this collaborative project was to characterizing the particulate porous media forming the plant-rooting environment, whose hydraulic properties are influenced by reduced gravitational force. Hydrostatically distributed water within coarse-textured and structured (aggregated) porous media, create non-uniformities in air-filled porosity, precluded the use of conventional gas diffusion measurement approaches. An automated diffusion measurement system for minimizing hydrostatic effects on earth in coarse media has been developed and evaluated.

Air-filled Porosity

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Oxygen

Diffu

sio

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oe

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ient (c

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10

Rectangular Cell (1 - 2 mm)

Rectangular Cell (0.25 - 1 mm)

Cylindrical Cell (1 - 2 mm)

Cylindrical Cell (0.25 - 1 mm)

Millington and Shearer (1971)

Moldrup et al. (2000) WLR

Figure 12. Oxygen diffusion measurements as a function of air-

filled porosity in Turface and Profile using two different

diffusion chamber designs. Modeled results are from

Millington and Shearer (1971) for aggregated media and from

Moldrup et al. (2000) for non-aggregated media.

20

Furthermore, diffusion models for describing the gas diffusion character of dual-porosity (aggregated) media and found the model of Millington and Shearer (1971) described well the measured results shown in Figure 12. Air-filled porosity dependent gas diffusion was modeled in mm-sized aggregated porous media, where internal aggregate porosity has only a minor contribution to the diffusion of gas compared to the external aggregate pore space. This measurement approach was amenable to measurements in other porous media such as potting soils, coarse-sands, and aggregated soils.

Utah State University in conjunction with University of Connecticut and University of Idaho developed a test module to observe liquid configurations as related to matric potential in micromodels during KC-135 flight experiments that are scheduled for February and August 2003. The objective of the planned experiments was the development of relationships between fluid configuration (patterns) and matric potential within different pore geometries and substrates in micro-gravity. Both, a video microscope and video camera will be used to observe particle separation and rearrangement, and the evolution of liquid patterns during wetting and drying of different material and pore structures, such as glass beads, TURFACE®, PROFILE®, or angular quartz micromodels. A set of tensiometers with small exchange volumes and high porous membrane conductivity will be inserted into the substrate for matric potential measurements. A preliminary tensiometer design was tested during a KC-135 flight in fall of 2002 by investigators from Kennedy Space Center (Levine and Norikane). Evaluation of the tensiometer data suggested the need for accurate monitoring of cabin air pressure changes, which vary with altitude.

Washington State University (WSU) has continued work to develop a freezing technique that will be able to determine soil moisture characteristic in porous media. The prototype instrument has been completed and is used for further testing the freezing characteristic of different soils. Effort has been made to determine volumetric liquid water and ice fractions in frozen porous media. The frequency-dependent dielectric properties of different porous media were determined with the aim to find suitable frequencies for a quantitative determination of ice contents. A dielectric-mixing model was developed and tested with experimental data.

Another ongoing research activity at WSU was the testing of dyes as vadose zone tracers, in order to visualize flow pathways in soils. Systematic laboratory tests have been conducted with different dyes. Sorption and transport experiments were carried out and structure-activity relationships were employed to find relations between molecular structures and sorption behavior in soils.

Also at WSU water flow and soil erosion processes were studied under cyclic freezing and thawing conditions. A tilting flume was constructed in 2001 and was tested for further improvement and final instrumentation for soil moisture and temperature monitoring. Laboratory column tests were conducted to identify optimum soil packing configuration and procedures. Through the flume experiments, soon to be started, it is anticipate to establish a quantitative relationships between soil strength variables (critical shear stress and erodibility) and soil water status (soil water content and matric potential) for the tested soils, and to incorporate these relationships into the USDA's WEPP model. At PNNL a vadose zone water flux meter has been developed and tested. The unit was essentially a buried wick-lysimeter that passively controls the tension at the base of the lysimeter. Extension of the upper part of the lysimeter controls diversion of flow. A

21

tipping spoon, monitors drainage and provides cumulative flux measurements. A small reservoir at the base of the unit provides means to monitor solution chemistry either manually or with inline sensors. The resolution of the fluxmeter is about 0.1 mm of water. Units are being tested at a variety of locations throughout the world. Water fluxmeters will be available commercially from several sources in FY 2003. Additionally, at PNNL it has been determined that analysis of outflow from pressure plates, used to obtain soil-water retention data, suggests that coarse soils seldom come into equilibrium with applied pressures. This results in overestimates of equilibrium water contents and underestimates of matric suction values. Pressure plates with low conductance can also limit flow and cause non-equilibrium errors in water content and matric suction values. In the absence of detailed hydraulic properties, when particle-size data are available, water retention can be estimated using continuum percolation theory. This can be accomplished using the known particle-size distribution and an assumed proportionality between pore radii and particle radii. Deviations between predicted and observed water retention at low water contents may in part be due to measurement error as described above.

OBJECTIVE 3: To apply scale-appropriate methodologies for the management of soil

and water resources

Investigators at the University of Arizona have been analyzing flow through heterogeneous soil profiles using the analytical element and other closely related techniques. For unsaturated flow and a Gardner soil, the steady-state Richards’ equation reduces to the Helmholtz equation as previously used by Philip and colleagues for flow around cavities. The solutions are simpler for saturated flow, for unsaturated flow without gravity, and for electrical resistance. A numerical modeling study was conducted at University of California – Davis

to inversely apply models to obtain effective soil hydraulic properties at various spatial scales, which ranged from the size of a soil core to the size of a water district. For example, inverse modeling was successful in determining effective root zone hydraulic parameters for a 2-m by 3-m field plot, by minimizing the residuals between measured and simulated water content data. At the water district scale with a total size of 10 by 8 miles, its effective hydraulic properties were estimated using scaling factors and measured weekly values of spatial-averaged district drainage rates and groundwater tables. At the University of California – Riverside, Surface runoff from a nursery was treated with a series of mitigation practices in an effort to improve its quality prior to leaving the site. A vegetative filter in a concrete-lined channel was installed to act both as a biological active filtration system as well as a source for the production of plant material. The vegetative filter consisted of baskets of Canna lilies sunk directly into the channel. The channel was divided into smaller basins allowing for the harvesting of one basin every eight weeks with the goal of maintaining the vegetative filter with a significant portion of mature plants at all times. During both the summer season and the winter season, the vegetative filter strip was effective in reducing certain amount of N leaving the nursery.

22

At the USDA-ARS Colorado, an Object Modeling System (OMS) is being developed in collaboration with the USGS and NRCS. The beta version of the framework was completed in 2002, and the Root Zone Water Quality Model has been modularized to “Level 1” under OMS for demonstration purposes and future utility. These new model development efforts can be much more efficient in building models from a library of existing modules.

At USDA-ARS Nation Soil Tilth Laboratory (USDA – NSTL, Ames, IA), three methods for determining corn (Zea mays L.) yield potential zones based on 6-yr of yield information were investigated. The methods included cluster analysis of multiple year yield data, cluster analysis of easily-measured field attributes believed to be important in determining corn yield, and multiple regression of these field attributes on corn yield. All methods were applied to corn yield data collected from 224 plots arranged along eight transects spanning a 16-ha field. Each method divided the 6 yr of yield data into years having wetter than average and drier than average growing season precipitation (Figure 13). This reflects the importance of water availability in determining corn yield in this rain fed field. All three methods illustrated the importance of landscape position on corn yield, with yield generally decreasing from foot-slope to summit positions in dry years. All three methods illustrated that excess precipitation caused increased yield variability especially in lower landscape positions. Clustering was particularly effective

in separating a pothole area from the remainder of the field. Multiple regression and yield clustering were superior in reducing the residual yield variance. Overall, each method was effective in delineating areas of similar yield potential within the field. If response curves for inputs such as nitrogen prove to be unique for the different yield clusters, then clustering of multiple year yield data may prove an effective method for determining management zones within fields. We are currently developing corn yield response curves to N fertilizer application for each cluster. If the response curves prove to

Figure 13. Transect yield plots colored by cluster group found from

terrain and yield clustering superimposed on regression results with a)

terrain clusters and regression for wet years, b) terrain clusters and

regression for dry years, c) yield clusters and regression for wet years,

and d)

23

be unique, we will have an effect method for varying N inputs across fields sharing this physiography. At Montana State University, four 25- to 60-ha farm fields were used to evaluate relationships between topography and soil water content. Soil water contents were monitored using neutron moisture meter, and digital elevation models were applied to portray terrain. Relationships using multiple soil depths were examined for the beginning and end of the growing season through two methods. Topographic region partitioning divided the fields into areas of presumed similar soil water status, and differences between regions were tested using ANOVA. The compound topographic index (CTI) was correlated with soil water content in a regression model, with study sites and topographic regions as covariates. Differences in soil water content between regions were commonly identified, but no consistent patterns were found for the regions across sites at a given soil depth. Reduction in across-field variance in soil water status prediction was relatively low (≤21%), with the strongest correlation between the CTI and soil water content found at the end of the growing season for 20 cm depth. The relationships between the CTI and soil wetness varied from field to field, and between methods used to delineate the topographic regions within fields. Inconsistency in model performance across the four study sites suggests that the underlying relationships may vary with different soils and terrain. Greater location-specific soils, climate, and terrain information may be required to reliably predict spatial attributes of soil water status within farmer fields such that this information may be gainfully used.

At North Dakota State University, the second year of a four-year collaborative project was completed, which investigated the evaluation and effectiveness of nutrient management zone determination methods in the Northern Plains. Collaboration involved researchers from Montana, Minnesota, South Dakota, and North Dakota. North Dakota

State University was primarily involved in the following three major objectives: 1) development of methods to automate zone boundary delineation through the development of a computer driven algorithms; 2) evaluation of the water quality impacts from precision agriculture practices; 3) evaluation of the effectiveness of the different nutrient management schemes. The primary field site for this research in ND was the Best Management Practices (BMP) research field near Oakes, ND, where a randomized complete block design (Figure

Figure 14. The randomized complete block design of the four-

year nutrient management zone field study located near Oakes,

ND under a quarter section pivot irrigation field.

Figure 15. Frequency analysis for six years of yields prior to

precision agriculture. The rank indicates the relative departure

from the mean yield of the entire field, where a low number is

below the average yield and a high number is above.

Figure 16. The spatial patterns that emerged from the clustered

data using yield, soil N, and EC measurements. Nutrient

management zones were developed from these clusters.

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14) was established to compare various nutrient management methods and monitor water quality. Three different methods (U, V1, and V2) of nutrient management were used, which included uniform application (U), variable rate nutrient application based on bare soil imaging (V1), and variable rate nutrient application based on cluster analysis (V2). Yields in this field varied from year to year, which was indicated by the frequency analysis done using yield monitoring data over a six-year period (Figure 15). Various layers of spatial information (Nitrogen, Phosphorous, elevation, aerial images, EC) could not describe the variations in yield using 1:1 cross-correlation tests. A new zone delineation method, cluster analysis, was applied to the field data to develop nutrient management zones. Cluster analysis separated data into “families” or clusters and used multiple data layers (shallow N, EC and Yield data layers). The clusters clearly showed spatial patterns (Figure 16) that were then used to develop nutrient management zones. Nutrient application amounts were based upon yield potentials developed from the frequency analysis. This method provided a simple means to develop nutrient management zones that used readily obtained data. Furthermore, this method was completely dependent on quantified measurements to develop the nutrient zones and nutrient application amounts, while other methods rely on qualitative information (e.g., farmer’s knowledge of yield potentials) to develop nutrient application amounts. Development was started of an automated algorithm based on the cluster analysis and frequency analysis, which defines nutrient management zones and provides nutrient application recommendations.

Washington State University was involved in the development of a comprehensive methodology that integrated erosion models, GIS techniques, and a sediment delivery concept for estimating water erosion and sediment delivery at the watershed scale. The Revised Universal Soil Loss Equation (RUSLE) was used to assess mean annual water erosion. The Sediment Delivery Distributed (SEDD) model was adapted to determine sediment transport to perennial streams. The spatial pattern of annual soil erosion and sediment yield was obtained by integrating RUSLE, SEDD, and a raster GIS. The integrated approach allows for relatively easy, fast, and cost-effective estimation of spatially distributed soil erosion and sediment delivery. A comprehensive evaluation of this integrated method and model uncertainty analysis are currently being performed.

PNNL has been involved in studies to develop novel methods for nondestructive observation and modeling of interactions between microbial dynamics and transport processes in soils. These interactions are important in a variety of applied problems such and water and wastewater treatment, bioremediation, and oil-field recovery operations. These processes and interactions also have great ecological significance, with global-scale implications for carbon cycling in the environment and the related issue of climate change. Ongoing work was focused on evaluating the role of surface thermodynamic properties (Gibbs free energies of surface interaction) and interfacial areas on bacterial transport in variably saturated porous media. The efficacy of gas-phase nutrient injection as a means to stimulate biodegradation of contaminants in the vadose zone was investigated. In a collaborative study between PNNL and INEEL, a hysteretic constitutive model describing relations among fluid relative permeabilities, saturations, and pressures of air-NAPL-water fluid systems was developed to account for residual NAPL in the

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vadose zone. Two intermediate-scale flow cell experiments have been conducted to produce data sets to test the new theory. NAPL that was not trapped by water was divided into mobile (free) and immobile (residual) components. Relations between fluid saturations and pressures were modified to predict that part of the NAPL saturation in the vadose zone that becomes immobile (residual) after it fills small pore spaces and forms thin films or lenses on water and solid surfaces. Using the modified model, water and NAPL (free, trapped by water, and residual) saturations can be predicted from the capillary pressures and the water and total-liquid saturation-path histories. Relations between relative permeabilities and saturations were modified to account for the residual NAPL by adjusting the limits of integration in the integral expression used for predicting the NAPL relative permeability. When all of the NAPL was residual NAPL, then the NAPL relative permeability was zero. Residual NAPL was modeled using concepts similar to those used to model residual water. The definition of residual NAPL that was used was different from what was commonly used (i.e., NAPL that does not drain from the vadose zone), because all immobile non-trapped NAPL was considered to be residual NAPL, regardless of whether the free NAPL was draining from or imbibed into pore spaces. In addition, residual NAPL was conceptualized to be either continuous and/or discontinuous in the pore spaces. Trapped NAPL differed from residual NAPL because it was always discontinuous and occluded by water. The mechanisms for the formation of residual and trapped NAPL were also different. Modeling residual NAPL in the vadose zone was important because it was a long-term source for groundwater contamination. At the University of Wyoming, stochastic analysis was carried out to assess the effect of soil spatial variability and heterogeneity on the recovery of denser-than-water nonaqueous phase liquids (DNAPL) during the process of surfactant enhanced remediation. UTCHEM, a three-dimensional, multi-component, multiphase, compositional model, was utilized to simulate water flow and chemical transport processes in heterogeneous soils. Soil spatial variability and heterogeneity were accounted for by considering the soil permeability as a spatial random variable and a geostatistical method was used to generate random distributions of the permeability. The randomly generated permeability fields were incorporated into UTCHEM to simulate DNAPL transport in heterogeneous media and stochastic analysis was conducted based on the simulated results. From the analysis, an exponential relationship between average DNAPL recovery and soil heterogeneity (defined as the standard deviation of log of permeability) was established with a coefficient of determination (r2) of 0.991, which indicated that DNAPL recovery decreased exponentially with increasing soil heterogeneity. Temporal and spatial distributions of relative saturations in the water phase, DNAPL, and microemulsion in heterogeneous soils were compared with those in homogeneous soils and related to soil heterogeneity. Cleanup time and uncertainty to determine DNAPL distributions in heterogeneous soils were also quantified. The study would provide useful information to design strategies for the characterization and remediation of nonaqueous phase liquid contaminated soils with spatial variability and heterogeneity.

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4. IMPACT STATEMENT:

To be completed by Allen Mitchell

5. ACTIVITIES PLANNED FOR 2002:

This is the third progress report for the W-188 5-year research project (1999-2004). Research in 2002 will continue on the objectives as described in Section 3. Some specific plans are:

• Arizona - Several more inclusion problems will be solved using the analytic element method and for stratified soils. These will used to investigate problems of TDR and ERT related to sensitivity of results to heterogeneities.

• USDA – USSL - Fate and transport experiments of pathogenic microorganisms in weighing lysimeters will be done. The completed lysimeters will provide a powerful tool for examining pathogen transport potential in the Chino Basin and for investigating the upscaling of column derived transport parameters to larger scales.

• USDA – USSL - This year researchers will release a new fully three-dimensional version of the HYDRUS model, including a Windows-based GUI.

• Colorado - Development efforts will continue on a spatially distributed agricultural model implemented under ArcGIS. The first version will include cascading runoff and re-infiltration from one land unit to another, thus allowing for hydrologic and chemical interactions between land areas with either uniform or differential (precision) management. This distributed model will serve as a prototype for a major project that will include routing of both overland and subsurface lateral water flow and chemical transport between land units, where the model parameters will be scale-appropriate for each land unit.

• Colorado - Spatial data collection will continue using the recently installed instruments in Colorado. Further collaboration with the ARS National Soil Tilth Lab in Iowa is planned to compare and contrast space-time behaviors related to topography under more humid conditions.

• Colorado - At CSU, research will continue using the continuous flow method in clarifying basic and applied problems in soil water flow. Experiments are planned to evaluate changes in unsaturated hydraulic properties with changes in the SAR and EC of the soil water. On-going experiments investigating microbial impacts, the averaging of hydraulic properties in layered soils, and the scaling of hydraulic properties with lateral heterogeneity will continue.

• Idaho - Ongoing and future work includes development of a statistical upscaling scheme based on sand and silt particle size distributions and constrained by clay content, total porosity, and mass-volume “universal” relationships to derive sample- and profile-scale liquid retention and hydraulic conductivity functions. At the profile-scale we will consider effects of overburden on depth-dependent shrink-swell behavior, and formation of near-surface crack networks and their

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impact on surface intake properties. Direct computed tomography observations of the spatial distribution of clay domains among sand and silt fractions (for different clay contents and ambient conditions) will be used to test and refine key modeling assumptions and to introduce anisotropy considerations. To receive feedback for profile-scale modeling we will utilize a geotechnical centrifuge suitable for larger samples.

• Iowa - Relationship between Solute Transport at the soil Surface and to Tile Drains. The breakthrough curves measured by the TDR probes will be used to estimate the near-surface solute transport properties that would subsequently be applied to predict the tile flow EC. Evaluation of the soil solute transport properties is ongoing.

• Iowa - Investigation of temporal and spatial scale effects on diffusion in rock matrices. The present work strictly applies only to random media, that is, media in which there is no spatial correlation between pore sizes and/or pore connectivity. However, investigators have recently shown that such structure is present even in “unstructured” sandstones. Future work will evaluate the influence of this kind of structure, hoping to gain new insights into soil structure in general.

• Iowa - Measuring Subsurface Water Fluxes Using a Heat Pulse Sensor. Laboratory experiments and data analysis are ongoing.

• Iowa - Comparison of Techniques For Defining Yield Potential Zones in an Iowa Field. If response curves for inputs such as nitrogen prove to be unique for the different yield clusters, then clustering of multiple year yield data may prove an effective method for determining management zones within fields. We are currently developing corn yield response curves to N fertilizer application for each cluster. If the response curves prove to be unique, we will have an effect method for varying N inputs across fields sharing this physiography.

• Kansas - Characterization of Effective Measurement Scales for Thermal Sensors: Work will continue on characterizing the effective measurement scale of DPHP sensors, the line-source thermal conductivity probe, and other methods for measuring thermal properties.

• Kansas - Quantification of Nitrate Leaching Losses Under Irrigated Corn: The field experiment described above will repeated in 2003. Emphasis will be placed on obtaining spatially-distributed measurements of K(h) by various methods.

• Kansas - Field Assessment of Method for Estimating Groundwater Consumption by Phreatophytes: Low streamflows are an increasing problem in Kansas and other areas of the U.S. Groundwater consumption by phreatophytes is thought to be an important component of the hydrologic cycle in riparian corridors in central and western Kansas and could be a significant contributor to low streamflows. However, reliable estimates of groundwater consumption by phreatophytes and its impact on stream-aquifer systems have yet to be obtained. The Kansas Geological Survey and Kansas State University will initiate a project in 2003 to address groundwater consumption by phreatophytes. The objectives of this project are to 1) develop a new method for quantifying the consumption of ground water by phreatophytes in hydrologic conditions common to central and western Kansas, 2) evaluate this method at a well-controlled field site, and 3) quantify ground-water

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consumption by phreatophytes along a portion of the middle reach of the Arkansas River in Kansas.

• Minnesota - Investigate fully the characteristic of the relaxation coefficient in the first-order relaxation law;

• Minnesota - Develop a numerical solution more capable of handling extremely sharp wetting fronts;

• Minnesota - Investigate more fully the process of wetting from air-dry conditions, and the effect of the initial water content on flow stability;

• Minnesota - Investigate the effect of the degree of water repellency on finger width and velocity.

• Montana - Montana will continue to evaluate repeatability of soil water retention measurements, in collaboration with several western regional and W-188 cooperating scientists.

• Montana - Collaborating with Connecticut/Utah will continue to pursue development of a new measurement technique for soil specific surface area using TDR, through analysis of measurement responses to thermal perturbation.

• Montana – Collaborating with Connecticut/Utah will continue to evaluate potential importance of the Maxwell-Wagner effect for measured TDR travel times in soils and porous media.

• North Dakota - Investigating relationships of mid-season evapotranspiration (ET) and growing-degree days (GDD), soil N, and fertilizer N to corn grain yield. A relationship between cumulative ET and/or GDD at July 10 and final corn grain yield was determined. When using split fertilizer applications, this relationship is included in a simple regression model, which also includes fertilizer and soil N to adjust the yield goal and to alter the fertilizer recommendation if the growing conditions are not favorable to achieve maximum yield.

• Nevada - Draindown and cyanide rinsing experiments are planned for 2003, with further experiments in developing infiltration covers for the facilities planned in the out years.

• North Dakota - A series of more detail experiments are underway using longer application times of the hormonal compounds, and using soils with a larger range of organic matter content. These experiments will help identify exact fate and transport processes of these compounds, and identify specific soil components that influence these processes. Additionally, radiolabel metabolites of 17β-estradiol were obtained and fate and transport experiments have been done using these compounds. Future fate and transport experiments will include the influence of soil structure and the influence of mixtures of hormones and pharmaceuticals.

• North Dakota - To develop an algorithm based on the cluster analysis and frequency analysis in order to automatically define nutrient management zones and provide nutrient application recommendations. To compare various nutrient management zones and uniform nutrient management application methods using data comparison methods that remove spatial variability (e.g., Papadakis analysis). Compare water quality between farmer-managed field and between the various nutrient management methods.

• Texas - Completion of field comparisons of neutron thermalization, capacitance, and time domain reflectometry methods of soil water measurement, and writing of

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a book from the combined research results of the international project on soil moisture sensor comparison funded by the International Atomic Energy Agency. Continuation of conjunctive use of TDR and tension infiltrometry in inverse analysis of field soil hydraulic characteristics applied to conventional tillage, limited tillage, no-tillage, and grassed fields in the Southern High Plains.

• Washington (PNNL). Work will continue in testing methods to address spatial variability and anisotropy. Flow cells will be tested for anisotropic ratios using Hanford sediments that have distinct bedding planes and expected large anisotropic ratios. Field studies, with specially designed infiltrometers placed on trench faces, will measure anisotropy under field conditions. A field experiment will be conducted using reactive tracers to document transport parameters under conditions similar to that observed in deep Hanford sediments where significant lateral flow has been observed. Analysis of past experiments with combined parameter scaling and inverse techniques will continue as will application of the VZP (vadose zone parameterization tools) software for analyzing deep migration of contaminants at Hanford and elsewhere. An international program to measure water and solute fluxes in the vadose zone will be initiated. This three year program will be continued through FY 2006 and will be reported at the WCSS (World Congress of Soil Science in 2006 in Philadelphia). Work in innovative methods to describe DNAPL (e.g., CCl4) transport will continue and intermediate scale flow models will be tested.

6. PUBLICATIONS DURING 2002:

Abbasi, F., J. Šimůnek, M. Th. van Genuchten, J. Feyen, F. J. Adamsen, D. Hunsaker, T. S. Strelkoff and P. Shouse, 2002. Overland water flow and solute transport: Model development and field data analysis. J. Irrig. Drain. Eng., ASCE, (In press).

Abriola, L. M., D. M. O’Carroll, S. A. Bradford, and T. J. Phelan. 2002. Compositional effects on interfacial properties in contaminated systems: Implications for organic liquid migration and recovery. XIV International Conference on Computational Methods in Water Resources, Delft, The Netherlands.

Ahuja, L.R., and Ma, L. 2002. Parameterization of agricultural system models: Current issues and techniques. In: Ahuja, L.R., Ma, L. and Howell, T.A. (eds.) Agricultural System Models in Field Research and Technology Transfer. CRC Publishers, Boca Raton, FL. p. 273-316.

Ahuja, L.R., Ma, L. and Howell, T.A. 2002. Whole system integration and modeling: Essential to agricultural science and technology in the 21st century. In: Ahuja, L.R., Ma, L. and Howell, T.A. (eds.) Agricultural System Models in Field Research and Technology Transfer. CRC Publishers, Boca Raton, FL. p. 1-8.

Ahuja, L.R., T.R. Green, R.H. Erskine1, L. Ma, J.C. Ascough II, G.H. Dunn, M.J. Shaffer, and A. Martinez. 2002. Topographic analysis, scaling and models to evaluate

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spatial/temporal variability of landscape processes and management. In: Ahuja, L.R., Ma, L., and Howell, T.A. (Eds), Agricultural System Models in Field Research and Technology Transfer. CRC Publishers, Boca Raton, FL. p. 265-272.

Al-Jabri, S. A., R. Horton, D. B. Jaynes, and A. Gaur. 2002. Field determination of soil hydraulic and chemical transport properties. Soil Sci. 167:353-368.

Al-Jabri, S.A., R. Horton, and D.B. Jaynes. 2002. A point source method for rapid estimation of soil hydraulic and chemical transport properties. Soil Sci. Soc. Am. J. 66:12-18.

Allaire, S.E., Yates, S.R., Ernst, F.F. and Gan, J. 2002. Dynamic 2-D system for measuring VOC volatilization and movement in soils. J. Environ. Qual., 31:1079-1087.

Bachmann, J., R. Horton, S.A. Grant, and R.R. van der Ploeg. 2002. Temperature dependence of water retention curves for wettable and water repellent soils. Soil Sci. Soc. Am. J. 66:44-52.

Bittelli, M., Flury, M. and Campbell, G. S., 2003. A thermo-dielectric analyzer to measure the freezing and moisture characteristic of porous media. Water Resour. Res. (In press).

Blicker, P.B., B.E. Olson, and J.M. Wraith. 2003. Water use and water use efficiency of the invasive Centaurea maculosa and three native grasses. Plant Soil (In press)

Bradford, S. A., and J. Schijven. 2002. Release of Cryptosporidium and Giardia from dairy calf manure: Impact of solution salinity. Environ. Sci. & Technol. 36:3916-3923.

Bradford, S. A., M. Bettahar, J. Šimůnek, and M. Th. van Genuchten. 2002a. Transport and fate of colloids in physically heterogeneous porous media. International Workshop on "Colloids and colloid-facilitated transport of contaminants in soils and sediments" Tjele, Denmark.

Bradford, S. A., J. Šimůnek, M. Bettahar, M. Th. van Genuchten, and S. R. Yates. 2002b. Experimental and modeling studies of colloid attachment, straining, and exclusion in saturated porous media. International Workshop on "Colloids and colloid-facilitated transport of contaminants in soils and sediments", Tjele, Denmark.

Bradford, S. A., S. R. Yates, M. Bettahar, and J. Šimůnek. 2002c. Physical factors affecting the transport and fate of colloids in saturated porous media. Water Resour. Res. (In press).

Butters, G.L., and DuChateau, P., 2002. Continuous flow method for rapid measurement of soil hydraulic properties. I. Experimental considerations. Vadose Zone J. 1:239-251.

Casey, F.X.M., G. L. Larsen, H. Hakk, and J Šimůnek. 2002. Fate and transport of 17β-Estradiol in soil-water systems, Environ. Sci. & Technol. (Accepted).

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Casey, F.X.M., and N.E. Derby. 2002. Improved design for automated tension infiltrometer. Soil Sci. Soc. Am. J. 66: 64-67.

Casey, F.X.M., N.E. Derby, R.E. Knighton, D.D. Steele, and E.C. Stegman. 2002. Initiation of irrigation effects on temporal nitrate leaching. Vadose Zone J. 1:300-309.

Cassel Sharmasarkar, F., S. Sharmasarkar, L.J. Held, S.D. Miller, G.F. Vance, and R. Zhang. 2001. Agroeconomic analysis of drip irrigation for sugarbeet production. Agronomy J. 93:517-523.

Cassel Sharmasarkar, F., S. Sharmasarkar, S.D. Miller, G.F. Vance, and R. Zhang. 2001. Assessment of drip and flood irrigation on water and fertilizer use efficiencies for sugarbeets. Agricultural Water Management 46:241-251.

Cassel, D.K., O. Wendroth and D.R. Nielsen. 2000. Assessing spatial variability in an agricultural experiment station field: Opportunities arising from spatial dependence. Agron. J. 92:706-714.

Castiglione, P., and P.J. Shouse. 2003. The effect of the ohmic losses on TDR measurements of electrical conductivity. Soil Sci. Soc. Am. J.(In press).

Corwin D.L., S. R. Kaffka, J. D. Oster, J.W. Hopmans, Y. Mori, J. W. van Groenigen, C. van Kessel, and S. M. Lesch. 2003.Assessment and Field-scale Mapping of Soil Quality Properties of a Saline-sodic Soils. Geoderma. (In press).

Corwin, D.L., S.M. Lesch, P.J. Shouse, R. Soppe, and J.E. Ayars. 2002. Identifying soil properties that influence cotton yield using ECa-directed soil sampling. Agron. J. (In press).

Dane, J.H., and J.W. Hopmans. 2002. Chapter 2.9.4.2. Saturation-capillary pressure relationships. Encyclopedia of Life Support Systems (EOLSS). (In press).

Dane, J.H., and J.W. Hopmans. 2002. Soil Water Retention and Storage - Introduction. IN: Methods of Soil Analysis. Part 4. Physical Methods. (J.H. Dane and G.C. Topp, Eds.). Soil Science Society of America Book Series No. 5. Pages 671-674.

Dane, J.H., J.W. Hopmans, and M. Jalbert. 2002. Hydraulic conductivity. Encyclopedia of Soils. Rattan Lal (Ed.). Pg. 667-670..Marcel Dekker Inc.

Dane, J.H., J.W. Hopmans, N. Romano, J. Nimmo and K.A. Winfield. 2002. Soil Water Retention and Storage - Laboratory Methods. IN: Methods of Soil Analysis. Part 4. Physical Methods. (J.H. Dane and G.C. Topp, Eds.). Soil Science Society of America Book Series No. 5. Pages 675-720.

Dautov, R., Egorov, A., J.L. Nieber, and A. Sheshukov, 2002. Simulation of Two-Dimensional Gravity-Driven Unstable Flow, Proceedings of the XIV International Conference on Computational Methods in Water Resources, June 23-28, 2002, Delft, The Netherlands, pp 9-16.

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Das, B. S., R. S. Govindaraju, G. J. Kluitenberg, A. J. Valocchi, and J. M. Wraith. 2002. Theory and applications of time moment analysis to study the fate of reactive solutes in soil. p. 239-279. In R. S. Govindaraju (ed.) Stochastic methods in subsurface contaminant hydrology. ASCE Press. American Society of Civil Engineers, Reston, VA.

David, O., Markstrom, S.L., Rojas, K.W., Ahuja, L.R., and Schneider, I.W. 2002. The object modeling system. In: Ahuja, L.R., Ma, L., and Howell, T.A. (eds.) Agricultural System Models in Field Research and Technology Transfer. CRC Press. Boca Raton, FL. p. 317-330.

Dinnes, D.L., D.L. Karlen, D.B. Jaynes, T.C. Kaspar, J.L. Hatfield, T.S. Colvin, and C.A. Cambardella. 2002. Nitrogen management strategies to reduce nitrate leaching in tile-drained Midwestern soils. Agron. J. 94:153-171.

Dinnes, D.L., Jaynes, D.B., Hatfield, J.L., Burkart, M.R., Parkin, T.B., Cambardella, C.A., Karlen, D.L., Colvin, T.S., Kaspar, T.C., and James, D.E. 2001. N management and hypoxia: A research focus of the USDA-ARS National Soil Tilth Laboratory. Farm Bureau Members National Convention. p. 6-6.

Dinnes, D.L., Jaynes, D.B., Karlen, D.L., Meek, D.W., Cambardella, C.A., Colvin, T.S., and Hatfield, J.L. 2002. Surface water quality response to a nitrogen fertilizer BMP at the watershed scale. Soil and Water Conservation Society 2002 Conf. Indianapolis, IN July 13-17.

Dinnes, D.L., Jaynes, D.B., Kaspar, T.C., Colvin, T.S., Cambardella, C.A., and Karlen, D.L. 2001. Plant-soil-microbe N relationships in high residue management systems. p. 44-49. South Dakota No-Till Association Annual Conference, Aberdeen, SD, January 24-25.

Dungan, R., Gan, J. and Yates, S.R. 2002. Accelerated degradation of methyl isothiocyanate in soil. Water Air Soil Poll. (Accepted)

Dungan, R.S., Ibekwe, A.K. and Yates, S.R. Effect of propargyl bromide and 1,3-dichloropropene on microbial communities in an organically amended soil. FEMS Microb. Ecol. (Accepted)

Dungan, R.S., Yates, S.R. and Frankenberger, W.T. Volatilization and degradation of soil-applied dimethylselenide. J. Environ. Qual. (Accepted)

Edmunds, W.M. and S.W.Tyler. 2002. Unsaturated zones as archives of paleoclimate: Towards a new proxy for continental regions. Hydrogeology J. 10: 216-228.

Egorov, A., R. Dautov, J.L. Nieber, and A. Sheshukov, 2002. Stability Analysis of Traveling Wave Solution for Gravity-Driven Flow, Proceedings of the XIV International Conference on Computational Methods in Water Resources, June 23-28, 2002, Delft, The Netherlands, pp 120-127.

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Ella, V. B., S. W. Melvin, R. S. Kanwar, L. C. Jones, R. Horton. 2002. Inverse three-dimensional groundwater modeling using the finite-difference method for recharge estimation in a glacial till aquitard. Trans. ASAE. Vol. 45:703–715.

Evett, S.R., N. Ibragimov, B. Kamilov, Y. Esanbekov, M. Sarimsakov, J. Shadmanov, R. Mirhashimov, R. Musaev, T. Radjabov, and B. Muhammadiev. 2002. Soil moisture neutron probe calibration and use in five soils of Uzbekistan. 17th World Congress of Soil Science, August 14-21, Bangkok, Thailand, Transactions, pp. 839-1 - 839-10. (CD-ROM)

Evett, S.R., B.B. Ruthardt, S.T. Kottkamp, T.A. Howell, A.D. Schneider, and J.A. Tolk. 2002. Accuracy and Precision of Soil Water Measurements by Neutron, Capacitance, and TDR Methods. 17th World Congress of Soil Science, August 14-21, Bangkok, Thailand, Transactions, pp. 318-1 - 318-8. (CD-ROM)

Evett, Steven, Jean-Paul Laurent, Peter Cepuder, and Clifford Hignett. 2002. Neutron Scattering, Capacitance, and TDR Soil Water Content Measurements Compared on Four Continents. 17th World Congress of Soil Science, August 14-21, Bangkok, Thailand, Transactions, pp. 1021-1 - 1021-10. (CD-ROM)

Ewing, R. P. and R. Horton. 2002. Diffusion in sparsely connected pore spaces: Temporal and spatial scaling. Water Resour. Res. 38:10.1029/2002WR001412.

Ewing, R. P. and R. Horton. 2003. Diffusion scaling in low connectivity porous media, CRC monograph Bridging Scales in Soil Physics (Ya. Pachepsky, ed.), pp 49-60.

Farahbakhshazad, N., Mclaughlin, D., Dinnes, D.L., Jaynes, D.B., and Li, C. 2002. A site-specific evaluation of a crop-denitrification/decomposition model based upon a US Midwestern row-crop field. 6th Int. Conf. on Precision Agriculture. Minneapolis, MN July 14-17.

Fares, A., L. R. Parsons, J. Šimůnek, and M. Th. van Genuchten. 2001. Effects of emitter distribution patterns and soil type on water and solute distribution, Proceedings of the Florida Soil and Crop Sci. Soc.

Fares, A., L. R. Parsons, J. Šimůnek, T. A. Wheaton, and K. T. Morgan. 2001 Simulated drip irrigation with different soil types, Proc. Fla. State Hort. Soc.

Feng, G.L., J. Letey, L. Wu. 2002. The influence of two surfactants on infiltration into a water-repellent soil. Soil Sci. Soc. Am. J. 66:361-367.

Feng, G.L., L. Wu, and J. Letey. 2002. Evaluating aeration criteria by simultaneous measurement of oxygen diffusion rate and soil-water regime. Soil Sci. 167:495-503.

Fernandez, C., Wu, J. Q., McCool, D. K. and Stockle, C. O., 2003b. Estimating water erosion and sediment yield with GIS, RUSLE, and SEDD. J. Soil Water Conserv., p. (In press).

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Ferré, T. P.A., Nissen, H. H., and J. Šimůnek. 2002. The effect of the spatial sensitivity of TDR on inferring soil hydraulic properties from water content measurements made during the advance of a wetting front, Vadoze Zone J. 1:281-288.

Flury, M. and Gimmi, T. 2002. Solute diffusion. In: J. H. Dane and G. C. Topp (Editors), Methods of Soil Analysis, Part 4, Physical Methods. Soil Science Society of America, Madison, WI, pp. 1323-1351.

Flury, M., Mathison, J. B. and Harsh, J. B., 2002. In situ mobilization of colloids and transport of cesium in Hanford sediments. Environ. Sci. Technol. 36: 5335-5341.

Frazier, C.S., R.C. Graham, P.J. Shouse, M.V. Yates, and M.A. Anderson. 2002. A field study of water flow and virus transport in weathered granitic bedrock. Vadose Zone J.1:113-124.

Freedman, V. L., K. P. Saripalli, and P. D. Meyer. 2002. Comparative assessment of mineral precipitation and dissolution potential and its influence on hydrologic properties in static and dynamic flow systems, Applied Geochemistry (In press).

Friedman S.P. and D.A. Robinson. 2002. Particle shape characterization using angle of repose measurements for predicting the effective permittivity and electrical conductivity of saturated granular media. Water Resour. Res. (In press)

Fuentes, J.P., Flury, M., Huggins, D. R. and Bezdicek, D. F., 2003. Soil water and nitrogen dynamics in dryland cropping systems of Washington state. Soil Till. Res. (In press).

Furman, A., A.W. Warrick, and T.P.A. Ferré. 2002. Electrical potential distributions in a heterogeneous subsurface in response to applied current: Solution for circular inclusions. Vadose Zone J. 1:273-280.

Gan, J., Wang, Q., Yates, S.R., Koskinen, W.C. and Jury, W.A. Dehalogenation of Chloroacetanilide Herbicides by Thiosulfate Salts. Proceedings of National Academy of Sciences of The United States of America. 99:5189 -5194. 2002.

Gee, G. W., and A. L. Ward. 2002. Predicting deep drainage using soil hydraulic properties and soil texture data. 9pp. In Transaction of the 17th World Congress of Soil Science. Bangkok, Thailand, August 2002 (Electronic).

Gee, G. W. and D. Or. 2002. Particle-size analysis . In Ch 2. Methods of Soil Analysis, Part 1. J. Dane and C. Topp (eds.). Soil Sci. Soc. Am., Madison, Wisconsin

Gee, G. W., A. L. Ward, T. G. Caldwell, and J. C. Ritter. 2002a. A vadose-zone water fluxmeter with divergence control. Water Resour. Res. 38; 10.1029/2001WR00816

Gee, G. W., A. L. Ward, Z. F. Zhang, G. S. Campbell, and J. Mathison. 2002b. The influence of hydraulic non-equilibrium on pressure plate data. Vadose Zone J. 1:172-178

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Gee, G. W., J. S. Carr, J. O. Goreham, and C. E. Strickland. 2002c. Water Monitoring report for the 200 W Area Tree Shelter Belt, Hanford Site, Richland, Washington. PNNL-14074. Pacific Northwest National Laboratory, Richland, Washington.

Germino, M.J., and J.M. Wraith. 2003. Water relations influence carbon gain in a grass occurring along sharp gradients of soil-temperature. New Phytol. (In press)

Goldberg, S., P.J. Shouse, S.M. Lesch, C.M. Grieve, J.A. Poss, H.S. Forster, and D.L. Suarez. 2002. Soil boron extractions as indicators of boron content of field -grown crops. Soil Sci. (Accepted).

Gowda, P.H., D.J. Mulla, and D.B. Jaynes. 2002. Modeling long-term nitrogen losses in Walnut Creek watershed, IA. ASAE-CICR World Congress Chicago, IL July 28-31. No.02-2134.

Green, T.R. and J. van Schilfgaarde. 2002. Watershed Approach: Context, Strategy and Practice, In: Encylc. Soil Sci., R. Lal (ed.), Marcel Dekker. www.dekker.com

Green, T.R. and R.H. Erskine. 2002 Measurement, scaling, and topographic analyses of spatial crop yield and soil water content, Hydrological Processes (Accepted).

Green, T.R., Salas, J.D., and Ruan, H. 2002. Space-time measurement of soil water and simulation of coupled overland/subsurface flow in undulating terrain, Proc. AGU Hydrology Days, http://hydrologydays.colostate.edu/Abstracts_02/Green.pdf, Fort Collins, CO, April 1-4, 2002. (Invited)

Gustafson, D.I., C. Gustin, and T.R. Green. 2002. Fractal-Based, Scale-Dependent Models for Characterizing Peak Concentrations of Crop Protection Chemicals in Surface Waters, SETAC, Salt Lake City, Utah, November 16-20, 2002 (Invited).

Gustafson, D.I., K.H. Carr, C. Gustin, T.R. Green, R.L. Jones and R.P. Richards. 2002. Fractal-Based, Scale-Dependent Models for Characterizing Peak Concentrations of Crop Protection Chemicals in Surface Waters, 10th IUPAC International Congress on the Chemistry of Crop Protection, Basel, Switzerland, August 4-9.

Hakk, H., F.X.M. Casey and G. Larsen. 2002. Sorption, mobility and fate of 1,3,7,8-tetrachloro-dibenzo-p-dioxin in soils and sand, In review to Organohalogen Compounds and to be presented at the Dioxin 2002 International Meeting, August 11-16, Barcelona, Spain.

Hendrickx, J.M.H, J.M. Wraith, D.L. Corwin, and R.G. Kachanoski. 2002. Solute content and concentration. p. 1253-1322. In J.H. Dane and G.C. Topp (ed.). Methods of Soil Analysis. Part 4. Physical Methods. ASA, Madison, WI.

Henry, E.J., J.E. Smith and A.W. Warrick. 2002. Two-dimensional modeling of flow and transport in the vadose zone with surfactant induced-flow. Water Resour. Res. 10.1029/2001WR000674.

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Hermsmeyer, D., J. Ilsemann, J. Bachmann, R.R. van der Ploeg, and R. Horton. 2002. Model calculations of water dynamics in lysimeters filled with granular wastes. J. Plant Nutr. Soil Sci. 165:339-346.

Hermsmeyer, D., R. Diekmann, R. R. van der Ploeg, and R. Horton. 2002. Physical properties of a soil substitute derived from an aluminum recycling by-product. J. Hazard. Mater. 95:107-124.

Hermsmeyer, R.R. van der Ploeg, R. Horton, and J. Bachmann. 2002. Lysimeter study of water and salt dynamics in a saline metallurgical waste. J. Plant Nutr. Soil Sci. 165:211-219.

Hignett, C., and S.R. Evett. 2002. Neutron Thermalization. Section 3.1.3.10 In Jacob H. Dane and G. Clarke Topp (eds.) Methods of Soil Analysis. Part 4 – Physical Methods. pp. 501-521.

Hopmans, J.W. 2003. Soil Hydrological properties and processes and their variability in space and time. Preface Special Issue J. Hydrol.

Hopmans, J.W., and K.L. Bristow. 2002. Current capabilities and future needs of root water and nutrient uptake modeling. Advances in Agronomy. Volume 77: 104-175.

Hopmans, Jan W., K.L. Bristow, and J. Šimůnek. 2001. Indirect estimation of soil thermal properties and water flux from heat pulse measurements: Geometry and dispersion effects. Water Resources Research 38(1):7-1 to 7-14.

Hopmans, J.W., and J.H. Dane. 2002. Chapter 2.9.4.1. Physical properties of solid and fluid matrices. Encyclopedia of Life Support Systems (EOLSS).(In press).

Hopmans, J.W., D.R. Nielsen and K.L. Bristow. 2002. How useful are small-scale soil hydraulic property measurements for large-scale vadose zone modeling? In: Environmental Mechanics:Water, Mass and Energy Transfer in the Biosphere. Geophysical Monograph 129. American Geophysical Union. pp. 247-258.

Hopmans, J.W., D.R. Nielsen, and K.L. Bristow. 2002a. How Useful are Small-scale Soil Hydraulic Property Measurements for Large-scale Vadose Zone Modeling. IN, Heat and Mass Transfer in the Natural Environment, The Philip Volume. Editors: D.Smiles, P.A.C. Raats, and A. Warrick. AGU, Geophysical Monograph Series No 129. Pages 247-258.

Hopmans, J. W., J. Šimůnek, and K. L. Bristow. 2002. Indirect estimation of soil thermal properties and water flux from heat pulse measurements: Geometry and Dispersion effects, Water Resour. Res., 38(1), 10.1029/2000WR000071, 7.1-7.14.

Hopmans, J. W., J. Šimůnek, N. Romano, and W. Durner. 2002 Inverse Modeling of Transient Water Flow, In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 3.6.2, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI, 963-1008.

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Hopmans, J.W., J. Šimůnek, N. Romano, and W. Durner. 2002. Simultaneous determination of water transmission and retention properties. Inverse Methods. IN: Methods of Soil Analysis. Part 4. Physical Methods. (J.H. Dane and G.C. Topp, Eds.). Soil Science Society of America Book Series No. 5. Pages 963-1008.

Hu, Q. and R. P. Ewing. 2002. Pore connectivity effects on solute transport in rocks, Proc. IAHR International Symposium on Groundwater Bridging the gap between measurement and modeling in heterogeneous media, CD-ROM, Berkeley, CA, March.

Huang, G. and R. Zhang. 2002. Stochastic analysis of unsaturated flow with the normal distribution of soil hydraulic conductivity. J. Hydrodynamics (In press).

Hunt, A. G., and G. W. Gee. 2002a. Application of critical path analysis to fractal porous media: Comparison with examples from the Hanford Site. Adv. Water Resour. 25:129-146

Hunt, A. G., and G. W. Gee. 2002b. Water-retention estimates using continuum percolation theory: Test of Hanford Site soils. Vadose Zone J. 1: 252-260.

Ilsemann, J., R. R. van der Ploeg, R. Horton, and J. Bachmann. 2002. Laboratory method for determining immobile water content and mass exchange coefficient. J. Plant Nutr. Soil Sci. 165:332-338.

Ishizaki, T., T. Nishiura, J. Šimůnek, and M. Th. van Genuchten. 2002. Numerical analysis of the water regime of Budha monuments in Skhothai, Thailand, Science for Conservation, 39:43-50 (In Japanese with English summary).

Jacques, D., J. Šimůnek, A. Timmerman, and J. Feyen. 2002. Calibration of Richards' and convection-dispersion equations to field-scale water flow and solute transport under rainfall conditions, J. Hydrol. 259:15-31.

Jandl, R., H. Spögler, J. Šimůnek, and L. K. Heng. 2002. Simulation of soil hydrology and establishment of a nitrogen budget of a mountain forest, Environ. Sci. & Poll. Res. 9 (Special Issue 2), 42-45.

Jaynes, D.B. 2002. Soil water hysteresis. Encyclopedia of Water Science.

Jaynes, D.B., Kaspar, T.C., and Colvin, T.S. 2002. Comparison of techniques for defining yield potential zones in an Iowa field. Proc. 6th Intl. Conf. on Precision Agric. Minneapolis, MN July 14-17, 2002.

Jaynes, D.B., Kaspar, T.C., Moorman, T.B., and Parkin, T.B. 2002. Subsurface drainage modifications to reduce nitrate losses in drainage. ASAE-CICR World Congress Chicago, IL July 28-31.

Jaynes, D.B., S.I. Ahmed, R.S. Kanwar, and K.J. Kung. 2001. Temporal dynamics of preferential flow to a subsurface drain. J. Environ. Qual. 65:1368-1376.

38

Jin Y. and M. Flury. Fate and transport of viruses in porous media. 2002. Advances in Agronomy. Vol 77: 39-102.

Jin, Y. and Flury, M., 2002. Fate and transport of viruses in porous media. Adv. Agron., 77: 39-102.

Jin, Y., Yates, M.V. and Yates, S.R. 2002. Microbial transport. In J.H. Dane and G.C. Topp (eds.), Methods of Soil Analysis, Part 4, Physical Methods. Soil Science Society of America, Madison, WI. pp. 1481-1505.

Johnson-Maynard, J.L., R.C. Graham, L. Wu, and P.J. Shouse. 2002. Modification of soil structural and hydraulic properties after 50 years of imposed chaparral and pine vegetation. Geoderma. 110: 227-240.

Johnson-Maynard, J.L., R.C. Graham, L. Wu, and P.J. Shouse. 2002.Modification of soil structural and hydraulic properties after 50 years of imposed chaparral and pine vegetation. Geoderma 110:3-4 pp. 227-240.

Jones, S., Bingham, G.E., D. Or and R.C. Morrow. ORZS: Optimization of Root Zone Substrates for Microgravity. The 32nd International Conference on Environmental Systems (ICES), SAE Technical Paper # 2002-01-2380, San Antonio, Texas, USA, July 15-18, 2002.

S. Steinberg, N. Daidzek, S. Jones, G. Kluitenberg, D. Or, L. Reddi, , I. Alexander and M. Tuller. 2002. Flow and distribution of fluid phases through porous plant growth media in microgravity. The 32nd International Conference on Environmental Systems (ICES), SAE Technical Paper # 2002-01-2386, San Antonio, Texas, USA, July 15-18.

Jones, S.B. and D. Or. 2002. Surface area, geometrical and configurational effects on permittivity of porous media. J. Non-Crystalline Solids, 305:247-254.

Jones, S.B., J.M. Wraith and D. Or. 2002. Time Domain Reflectometry (TDR) Measurement Principles and Applications. Hydrol. Process. 16:141-153, DOI: 10.1002/hyp.513.

Jury, W. A., Atac Tuli, and John Letey. 2003. The effect of travel time on management of a sequential reuse drainage operation. Soil Sci. Soc. Am. J. (In press).

Kamilov, Bakhtiyor; Ibragimov, Nazirbay; Esanbekov, Yusupbek; Evett, Steven; and Heng, Lee. 2002. Irrigation Scheduling Study of Drip Irrigated Cotton by use of Soil Moisture Neutron Probe. Accepted for publication In Proceedings of the UNCGRI/IAEA National Workshop "Optimization of water and fertilizer use for major crops of cotton rotation", December 24 and 25, Tashkent, Uzbekistan.

Kamilov, B., N. Ibragimov, Y. Esanbekov, S. Evett, and L. Heng. 2002. Use of neutron probe for investigations of winter wheat irrigation scheduling in automorphic and semi-hydromorphic soils of Uzbekistan. In Proc. International Workshop on Conservation

39

Agriculture for Sustainable Wheat Production in Rotation with Cotton in Limited Water Resource Areas, October 13-18, Tashkent, Uzbekistan.

Kampf, S., M. Salazar and S. Tyler. 2002. Preliminary Investigation of Effluent Drainage from Mine Heap Leach Facilities. Vadose Zone Journal 1: 186-196.

Kelleners, T.J., R.W.O Soppe, D.A. Robinson, J.E. Ayars, T.H. Skaggs, 2003. Use of Electric Circuit Theory to Calibrate Capacitance Probe Sensors for Permittivity Measurements in Non-Conductive and Conductive Media, Soil Sci. Soc. Am. J. (In Review).

Kim, D., I. Hwang, S. Kim, and W. Jury. 2001. Quantification of irreversible sorption coefficients of Benzene in sandy aquifer materials. Geoderma.

Kim, J., Farmer, W., Gan, J., Yates, S.R, Papiernik, S.K. and Dungan, R.S. 2003.Organic matter effects on phase partition of 1,3-dichloropropene in soil, J. Agricultural and Food Chemistry. (Accepted)

Kim, S., C. Park, D. Kim, and W. Jury. 2003. Kinetics of Benzene Biodegradation by Pseudomonas aeruginosa: Parameter estimation, Environ. Tox. and Chem.

Kluitenberg, G. J. 2002. Heat capacity and specific heat. p. 1201-1208. In J. H. Dane and G. C. Topp (ed.) Methods of soil analysis. Part 4. SSSA Book Ser. 5. SSSA and ASA, Madison, WI.

Kluitenberg, G. J., and J. L. Heitman. 2002. Effect of forced convection on soil water content measurement with the dual-probe heat-pulse method. p. 275-283. In P. A. C. Raats et al. (ed.) Environmental mechanics: Water, mass and energy transfer in the biosphere. Geophysical Monograph Series, Vol. 129, American Geophysical Union, Washington, DC.

Kosugi, K., J.W. Hopmans and J.H. Dane. 2002. Water Retention and Storage - Parametric Models. IN: Methods of Soil Analysis. Part 4. Physical Methods. (J.H. Dane and G.C. Topp, Eds.). Soil Science Society of America Book Series No. 5. Pages 739-758.

Larsen, G., F.X.M. Casey, B. Magelky, C. Pfaff, H. Hakk and D. Smith. 2002. Sorption, mobility and fate of sulfadimethoxine, sulfamethazine, and sulfaquinoxaline in various soil types, SETAC International Meeting, May 10-18, Vienna, Austria.

Lee, J., L. S. Hundal, R. Horton, and M. L. Thompson. 2002. Sorption and transport behavior of Naphthalene in an aggregated soil. J. Environ. Qual. 31:1716-1721.

Lee, J., R. Horton, and D. B. Jaynes. 2002. The feasibility of shallow time domain reflectometry probes to describe solute transport through undisturbed soil cores. Soil Sci. Soc. Am. J. 66:53-57.

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Lenhard, R.J., M. Oostrom, and J.H. Dane. 2003. A constitutive model for air-NAPL-water flow in the vadose zone accounting for residual NAPL in strongly water-wet porous media. J. of Contaminant Hydrology. (In press)

Letey, J., D. Birkle, W. Jury, and I. Kan. 2003. Long-term consequences of reusing agricultural drainage water. Calif. Agriculture. (In press)

Liu, W.P., Gan, J.Y. and Yates, S. R. 2002. Influence of herbicide structure, clay acidity, and humic acid coating on acetanilide herbicide adsorption on homoionic clays. J. Agricultural and Food Chemistry 50:4003-4008.

Long, Dan S., Jon M. Wraith, and Greg Kegel. 2002. A heavy-duty TDR soil moisture probe for use in intensive field sampling. Soil Sci. Soc. Am. J. 66:396-401.

Lu, J. and L. Wu. 2002. Spectrophotometric determination of substrate-borne polyacrylamide. J. Food & Agri. Chem. 50:5038-5041.

Lu, J. and L. Wu. 2003. Visualizing Br- tracer in preferential flow study. J Environ. Qual. (In press)

Lu, J., L. Wu, John Letey, and Walter J. Farmer. 2002. Picloram and Napropamide Sorption as Affected by Polymer Addition and Salt Concentration. J Environ. Qual. 31: 1234-1239.

Ma, L., Nielsen, D.C., Ahuja, L.R., Kiniry, J.R., Hanson, J.D., and Hoogenboom, G. 2002. An evaluation of RZWQM, CROPGRO, and CERES-maize for responses to water stress in the Central Great Plains of the U.S. In: Ahuja, L.R., Ma, L. and Howell, T.A. (eds.) Agricultural System Models in Field Research and Technology Transfer. CRC Press. Boca Raton, FL. p. 119-148.

Mansell, R. S., Ma, L., Ahuja, L. R., and Bloom, S., A. 2002. Adaptive grid refinement in numerical models for water flow and chemical transport in soil: A review. Vadose Zone J. 1: 222-238.

Meyer, P. D. and S. Orr. 2002. Evaluation of Hydrologic Uncertainty Assessments for Decommissioning Sites Using Complex and Simplified Models, NUREG/CR-6767, U.S. Nuclear Regulatory Commission, Washington, DC.

Nachabe, M.H., Ahuja, L.R., and Rokicki, R. 2002. Full capacity of water in soils, concepts, measurement and approximations: Encyclopedia Water Science, Stewart, B.A. and Howell, T.A. (eds.) Marcel-Dekker.

Neuman, S. P. and P.J. Wierenga. 2002. A comprehensive strategy of hydrogeologic modeling and uncertainty analysis for nuclear facilities and sites. NUREG report.

Nieber, J.L., A. Sheshukov, A. Egorov, R. Dautov. 2003. “Non-equilibrium Model for Gravity-Driven Fingering in Water Repellent Soils: Formulationand 2-D Simulations”, Special Publication on Soil Water Repellency, Elsevier, Chapter 25. (Accepted).

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Nielsen, D.C., Ma, L., Ahuja, L.R., and Hoogenboom, G. 2002. Simulating soybean water stress effects with RZWQM and CROPGRO models. Agron. J. 94: 1234-1243.

Nielsen, D.R., and O. Wendroth. 2003. Spatial and Temporal Statistics -Sampling Field Soils and Their Vegetation. Catena Verlag, Cremlingen-Destedt. (In press).

Niemet, M. R., M. L. Rockhold, N. Weisbrod, and J. S. Selker. 2002. Relationships between gas-liquid interfacial surface area, liquid saturation, and light transmission in variably saturated porous media. Water Resour. Res. 38:10.1029.

Norris, T.B., J.M. Wraith, R.W. Castenholz, and T.R. McDermott. 2002. Soil microbial community structure across a thermal gradient following a geothermal heating event. Appl. Environ. Microbiol. 68:6300-6309.

Novák, V., J. Šimůnek, and M. Th. van Genuchten. 2002. Infiltration into soil with cracks changing their dimensions during the process, J. Hydrol. Hydromech., 50:3-19.

Oostrom, M. and R.J. Lenhard. 2003. Carbon tetrachloride flow behavior in unsaturated Hanford caliche material: An investigation of residual NAPL. Vadose Zone J. (In press).

Oostrom, M., C. Hofstee, R.J. Lenhard, and M. Oostrom. 2003. Flow behavior and residual saturation formation of injected carbon tetrachloride in unsaturated heterogeneous porous media. J. of Contaminant Hydrology. (In press).

Or, D., and M. Tuller, 2002. Cavitation during desaturation of porous media under tension. Water Resour. Res., vol.38, no.5, 19.

Papiernik, S.K. and Yates, S.R. 2002. Effect of environmental conditions on the permeability of high density polyethylene film to fumigant vapors. Environ. Sci. & Technol. 36:1833 -1838.

Papiernik, S.K., Ernst, F.F. and Yates, S.R. An apparatus for measuring the gas permeability of films. J. Environ. Qual. 31:358 -361. 2002.

Papiernik, S.K., Gan, J. and Yates, S.R. 2002. Organic Transport. In J.H. Dane and G.C. Topp (eds.), Methods of Soil Analysis, Part 4, Physical Methods. Soil Science Society of America, Madison, WI. pp. 1451-1476.

Papiernik, S.K., Gan, J. and Yates, S.R. 2002. Characterization of propargyl bromide transformation in soil. Pest Manag. Sci. 58:1055 -1062.

Persson, Magnus, and Jon M. Wraith. 2002. Shaft-mounted time domain reflectometry probe for water content and electrical conductivity measurements. Vadose Zone J. 1:316-319.

Prunty, L. and F.X.M Casey. 2002. Soil water retention curve description using a flexible smooth function. Vadose Zone J. 1:179-185.

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Qualls, R. G., B.L. Haines, W.T. Swank and S. W. Tyler. 2002. Retention of soluble organic nutrients by a forested ecosystem. Biogeochemistry 61:135-171.

Ralston, D.P.V., N.E. Derby, and F.X.M. Casey. 2002. Developing Nutrient Management Zones and Monitoring their Effect on Water Quality. 6th International Conference on Precision Agriculture and Other Precision Resources Management. July – Minneapolis, MN.

Ren, L., M. Mao, and R. Zhang. 2002. Estimating nitrate leaching with a transfer function model incorporating net-mineralization and uptake of nitrogen. J. Env. Qual. (In press).

Ren, L., M. Mao, and R. Zhang. 2002. Predictions of adsorbed agro-chemical transport in saturated soils. J. Environ. (in Chinese) (In press).

Robinson, D.A. and Friedman, S.P. 2002. A method for measuring the solid particle permittivity of rocks, sediments and granular materials. J. Geophys. Res. B. (In press)

Robinson, D.A. and Friedman, S.P. 2002. Observations of the effects of particle shape and particle size distribution on avalanching of granular media. Physica A. 311:97-110.

Robinson, D.A. and Friedman, S.P. 2002. The effective permittivity of dense packings of glass beads, quartz sand and their mixtures immersed in different dielectric backgrounds. J. Non-crystalline Solids. 305:261-267.

Robinson, D.A., J.D. Cooper and C.M.K. Gardner. 2002. Modeling the relative permittivity of soils using hygroscopic water content. J. Hydrol. 255:39-49.

Robinson, D.A., M. Schaap, S.B. Jones, S.P. Friedman, and C.M.K. Gardner. 2002. Considerations for improving the accuracy of permittivity measurement using TDR: Air/water calibration, effects of cable length. Soil Sci. Soc. Am. J. 67:62-70.

Rockhold, M. L., R. R. Yarwood, M. R. Niemet, P. J. Bottomley, and J. S. Selker. 2002. Considerations for modeling bacterial-induced changes in hydraulic properties of variably saturated porous media. Adv. Water Resour. 25: 477-495.

Russell, A.E., Cambardella, C.A., Laird, D.A., Jaynes, D.B., Colvin, T.S., and Meek, D.W. 2002. Nitrogen fertilizer effects on soil organic carbon dynamics in corn-soybean agroecosystems. Ecological Society of America 86th Annual Meeting. August 4-9.

Saripalli, K. P., R. J. Serne, P. D. Meyer and B. P. McGrail. 2002. Prediction of Diffusion Coefficients in Porous Media using Tortuosity Factors based on Interfacial Areas, Ground Water, 40:346-352.

Scanlon, B. R., M., Christman, R. Reedy, I. Porro, J. Šimůnek, and G. Flerchinger, Intercode comparisons for simulating water balance of surficial sediments in semiarid regions, Water Resour. Res. (In press).

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Schwartz, R.C. 2002. The IDSfit Code for Inverse Estimation of Field Hydraulic Properties Using a Disc Infiltrometer. Conservation and Production Research Laboratory, Agricultural Research Service, USDA, Bushland, TX, 31 pp.

Schwartz, R.C., and S.R. Evett. 2002. Estimating hydraulic properties of a fine-textured soil using a disc infiltrometer. Soil Sci. Soc. Amer. J. 66:1409-1423.

Schwartz, R.C., S.R. Evett, and P.W. Unger. 2002. Soil hydraulic properties of cropland compared with reestablished and native grassland. Geoderma (In Press).

Schijven, J., and J. Šimůnek. 2002 Kinetic modeling of virus transport at field scale, J. of Contam. Hydrology, 55(1 -2), 113 -135.

Schoups, G. and J.W. Hopmans. 2002. Analytical solution of vadose zone convective solute transport with root water and nutrient uptake. Vadose Zone J. 1:158-171.

Seuntjens, P., D. Mallants, J. Šimůnek, J. Patyn, and D. Jacques. 2002. Sensitivity analysis of physical and chemical properties affecting field-scale cadmium transport in a heterogeneous soil profile, J. of Hydrology, 264, 185-200.

Shangguan, Z., M. Shao, R. Horton, T. Lei, L. Qin, and J. Ma. 2002. A model for regional optimal allocation of irrigation water resources under deficit irrigation and its applications. Agric. Water Manage. 52:139-154.

Shukla, M.K., F.J. Kastanek and D.R. Nielsen. 2000. Transport of chloride through water-saturated soil columns. Die Bodenkultur, Austrian J. Agric. Res. 51: 235-246.

Shukla, M.K., F.J. Kastanek and D.R. Nielsen. 2002. Inspectional analysis of convective-dispersion equation and application on measured breakthrough curves. Soil Sci. Soc. Am. J. 66: 1087-1094.

Shukla, M.K., T.R. Ellsworth, R.J. Hudson and D.R. Nielsen. 2002. Effect of Water Flux on Solute Velocity and Dispersion. Soil Sci. Soc. Am. J. 66:(In press).

Silliman, S., B. Berkowitz, J. Šimůnek, and M. Th. van Genuchten, Fluid flow and chemical migration within the capillary fringe, Ground Water, 40(1), 76-84, 2002.

Šimůnek, J., and J. W. Hopmans, Parameter Optimization and Nonlinear Fitting, In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 1.7, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI, 139-157, 2002.

Šimůnek, J., J W. Hopmans, D.R. Nielsen and M.Th. van Genuchten. 2000. Horizontal infiltration revisited using parameter estimation. Soil Sci. 165: 708-717.

Šimůnek, J., D. Jacques, J. W. Hopmans, M. Inoue, M. Flury, and M. Th. van Genuchten, Solute Transport During Variably-Saturated Flow - Inverse Methods, In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 6.6, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI, 1435-1449, 2002.

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Šimůnek, J., N. J. Jarvis, M. Th. van Genuchten, and A. Gärdenäs, Nonequilibrium and preferential flow and transport in the vadose zone: review and case study, J. Hydrol. (In press).

Šimůnek, J., van Genuchten, M. T., Jacques, D., Hopmans, J. W., Inoue, M. and Flury, M., 2002. Solute transport during variably saturated flow-inverse methods. In: J. H. Dane and G. C. Topp (Editors), Methods of Soil Analysis, Part 4, Physical Methods. Soil Science Society of America, Madison, WI, pp. 1435--1449.

Šimůnek, J. and A. J. Valocchi, Geochemical Transport, In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 6.9, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI, 1511-1536, 2002.

Sisson, J. B., G. W. Gee, J. M. Hubbell, W. L. Bratton, J. C. Ritter, A. L. Ward, and T. G. Caldwell. 2002. Advances in tensiometry for long-term monitoring of soil water pressures. Vadose Zone J. 1: 310-315.

Skaggs, T.H., and F.J. Leij, 2002. Solute Transport: Theoretical Background. p. 1353-1380. In J. Dane and C. Topp (eds.) In Methods of Soil Analysis. Part 4. ASA and SSSA, Madison, WI.

Skaggs, T.H., D.B. Jaynes, R.G. Kachanoski, P.J. Shouse, and A.L. Ward, 2002. Solute Transport: Data Analysis and Parameter Estimation. p. 1403-1434. In J. Dane and C. Topp (eds.) Methods of Soil Analysis. Part 4. ASA and SSSA, Madison, WI.

Skaggs, T.H., G.V. Wilson, P.J. Shouse, and F.J. Leij, 2002. Solute Transport: Experimental Methods. p. 1381-1402. In J. Dane and C. Topp (eds.) Methods of Soil Analysis. Part 4. ASA and SSSA, Madison, WI.

Sperber, T.D., J.M. Wraith, and B.E. Olson. 2003. Soil physical properties associated with spotted knapweed and native grasses are similar. Plant Soil (In press)

Steinberg, S., I. Alexander, N. Daidzic, S. Jones, G. Kluitenberg, D. Or, L. Reddi, and M. Tuller, 2002. Flow and distribution of fluid phases through porous plant growth media in microgravity: progress to date. Proceedings of the 32nd international conference on environmental systems (ices), July 15-18, 2002, San Antonio, Texas, USA.

Thomasson, M.L. and P.J. Wierenga. 2002.Spatial variability of the effective retardation factor in an unsaturated field soil. J. Hydrology (In press).

Timlin, D. J., Y. Pachepsky, B. A. Acock, J. Šimůnek, G. Flerchinger, and F. Whisler. 2002. Error analysis of soil temperature simulations using measured and estimated hourly weather data with 2DSOIL, Agricultural Systems, 72:215-239.

Tomer, M.D., Jaynes, D.B., Hatfield, J.L., Cole, K.J., Dinnes, D.L., and Jaquis, R.J. 2002. Characterization of water and nitrate fluxes from a tile-drained watershed. Soil and Water Conservation Society 2002 Conf. Indianapolis, IN July 13-17.

45

Tomer, M.D., Meek, D.W., Jaynes, D.B., and Hatfield, J.L. 2002. Evaluation of nitrate-N fluxes from a tile-drained watershed. Proc. National TMDL Science and Policy Conf. Phoenix, AZ Nov. 13-16, 2002

Tomer, M. D., Meek, D. W., Jaynes, D. B., and Hatfield, J. L. Evaluation of Nitrate-N fluxes from a tile-drained watershed. Agriculture and the Environment Ames, IA March 4-6, 2002.

Tuli, A., and J.W. Hopmans. Fluid saturation dependency of transport for disturbed soils. European J. Soil Sci.. 2003.(In press).

Tuller, M., and D. Or, 2002. Hydraulic functions for swelling soils: pore scale considerations. J. Hydrol. (In press).

Tuller, M., and D. Or, 2002. Hydraulic properties of partially saturated fractured porous media, proceedings of the international groundwater symposium, lbnl, Berkeley, California, March 25-28, pp.416-420, isbn 90-805649-4-x.

Tuller, M., and D. Or, 2002. Preferential flow in structured soils - hydraulic functions derived from pore-scale processes. Proceedings of the 17th world congress of soil science, August 14-21, Bangkok, Thailand.

Tuller, M., and D. Or, 2002. Unsaturated hydraulic conductivity of structured porous media: a review of liquid configuration-based models. Vadose Zone J. 1:14-37.

Vargas-Guzman, J.A., A.W. Warrick and D.E. Myers. 2002.Coregionalization by linear combination of nonorthogonal components. Math. Geology 34:401-415.

Vaz, C.M. P., A. Macedo, L.H. Bassoi, D. Wildenschild and Jan. W. Hopmans. 2002. Retention curves obtained by a combined tensiometer-coiled TDR probe. Soil Sci. Soc. Am. J. 66:1752-1759.

Walvoord, M.A., F.M. Phillips, S.W. Tyler and P.C. Hartsough. 2002. Deep arid system hydrodynamics Part 2: Application to paleohydrologic reconstruction using vadose zone profiles from the Northern Mojave Desert. Water Resources Research. 38(12).

Wang, D., M.C. Shannon, C.M. Grieve, P.J. Shouse, and D.L. Suarez. 2002. Ion partitioning among soil and plant components under drip, furrow, and sprinkler irrigation regimes: Field and modeling assessment. J. Environ. Qual. (Accepted).

Wang, Q., R. Horton, and M. Shao. 2002. Effective raindrop kinetic energy influence on soil potassium transport into runoff. Soil Sci. 167:369-376.

Wang, Q., R. Horton, and M. Shao. 2002. Horizontal infiltration method for determining Brooks-Corey model parameters. Soil Sci. Soc. Am. J. 66:1733-1740.

Wang, Q., T.E. Ochsner, and R. Horton. 2002. Mathematical analysis of heat pulse signals for soil water flux determination. Water Resour. Res. 38:10.1029/2001WR1089.

46

Wang, Z., Harter, T., Wu, L., and Jury, W., 2003. A field study of preferential flow during soil water redistribution. Water Resour. Res. (In press)

Wang, Z., Lu, W., Wu, L., Harter, T., and Jury, W. 2002. Visualizing preferential flow paths using a pH-indicator. Soil Sci. Soc. Am. J. 66:347-351.

Ward, A. L., G. W. Gee, Z. F. Zhang and J.M. Keller. 2002. Vadose Zone Transport Field Study: FY 2002 Status Report. PNNL 14150 Pacific Northwest National Laboratory, Richland, Washington.

Warrick, A.W. and D. Or. 2002.Effect of gravity and model characteristics on steady infiltration from spheroids. In: Smiles, D.E., P. A.C. Raats and A.W. Warrick (Ed.), Environmental mechanics: Heat and mass transfer in the biosphere. The Philip volume. American Geophysical Union, Washington, D.C. pp. 65-70.

Warrick, A.W. and J.H. Knight. 2002.Two-dimensional unsaturated flow through a circular inclusion. Water Resources Res. 38, 10.1029/2001WR001041.

Wendroth, O., P. Jürschik, K.C. Kersebaum, H. Reuter, C. Van Kessel, and D.R. Nielsen. 2001. Identifying, understanding, and describing spatial processes in agricultural landscapes - four case studies. In: Van Kessel, C. and O. Wendroth (Eds.) Special issue: Landscape Research - Exploring Ecosystem Processes and their Relations at different Scales in Space and Time. Soil Till. Res. 58:113-128.

Wendroth, O., and D.R. Nielsen. 2002 Time and Space Series p. 119-137. In: J.H. Dane and G.C. Topp (eds.), Methods of Soil Analysis, Part 4, Physical Methods. SSSA Book Series No.5, Soil Sci. Soc. Am. Madison, WI.

Wildenschild, D., J.W. Hopmans, C.M.P. Vaz, and M.L. Rivers. 2001. Using x-ray beams to study flow processes in underground porous media. Advan. Photon Source Res. 4:48-50.

Wildenschild, D., J.W. Hopmans, C.M.P. Vaz, M.L. Rivers, D. Rikard, and B.S.B. Christensen. 2002. Using X-ray computed tomography in hydrology: systems, resolutions, and limitations. J. Hydrology 267:285-297.

Williams, R.D., and Ahuja, L.R. 2002. Scaling of soil hydraulic properties across soil types using a one-parameter model. Elsevier, book chapter. (Accepted)

Wu, J., M. D. Ransom, M. D. Nellis, G. J. Kluitenberg, H. L. Seyler, and B. C. Rundquist. 2002. Using GIS to assess and manage the conservation reserve program in Finney County, Kansas. Photogrammetric Engin. & Remote Sensing 68:735-744.

Wu, L., G.L. Feng, J. Letey, L. Ferguson, J. Mitchell, B. M. Sanden, G. Markegard. 2003. Soil Management Effects on the Nonlimiting Water Range (NLWR). Geoderma. (Accepted)

47

Xue, X., and R. Zhang, 2001. Calculation of soil hydraulic properties using the data measured from disk infiltrometers. J. Hydraul. Engin. 10:12-19 (In Chinese).

Xue, X., R. Zhang, and S. Gui, 2001. The effect of measurement scales on soil hydraulic properties and their spatial variability. Bulletin Soil Water Conserv. 21:47-51 (In Chinese).

Xue, X., R. Zhang, and S. Gui, 2002. Estimating wilting point and the retention function at high suctions using evaporation process from a thin soil sample. J. Soil Sci. (In Chinese) (In press).

Yao, T., C.J. Mai, P. J. Wierenga, S.P. Neuman, and A.R. Graham. 2002. Results of ponding infiltration and tracer experiments at the Apache Leap research site, Arizona. NUREG report

Yarwood, R. R., M. L. Rockhold, M. R. Niemet, J. S. Selker, and P. J. Bottomley. 2002. Noninvasive quantitative measurement of bacterial growth in porous media under unsaturated flow conditions. App. Environ. Microbiol. 68:3597-3605.

Yates, S.R, Gan, J. and Papiernik, S.K. 2003a. Environmental fate of methyl bromide as a soil fumigant. Reviews of Environ. Contam. Toxicol. 177:45-122.

Yates, S.R., Gan, J., Papiernik, S.K., Dungan, R. and Wang, D. 2003b. Reducing fumigant emissions after soil application, J. Phytopathology (Accepted)

Yates, S.R. and Warrick, A.W. Chapter 1.5 Geostatistics. In J.H. Dane and G.C. Topp (eds.), Methods of Soil Analysis, Part 4, Physical Methods. Soil Science Society of America, Madison, WI. pp. 81-118. 2002.

Yates, S.R., Wang, D., Papiernik, S.K. and Gan, J. 2002. Predicting pesticide volatilization from soils, Environmentrics 13:569-578.

Yeh, T.C.J., J. Šimůnek, and M. Th. Van Genuchten. 2002. Stochastic fusion of information for characterizing and monitoring the vadose zone, Vadoze Zone J. 1:207-221.

Young, M., Karagunduz, A., J. Šimůnek, and K. D. Pennell. 2002. Modified upward infiltration method for characterizing soil hydraulic properties, Soil Sci. Soc. Am. J., 66, 57-64.

Young, M.H., T.C. Rasmussen, F.C. Lyons, K.D. Pennell. 2002. Optimized system to improve pumping rate stability during aquifer tests. Ground Water. 40:629-637.

Zhang, F., R. Zhang, and S. Kang. 2002. Estimating Temperature Effects on Water Flow in Variably Saturated Soils Using Activation Energy. Soil Sci. Soc. Am. J. (In press).

Zhang, R., A. L Wood, C G. Enfield. 2002. Stochastical analysis of surfactant enhanced remediation of DNAPL contaminated soils. J. Environ. Qual. (In press).

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Zhang, Z. F., A. L. Ward and G. W. Gee. 2002. A Parameter Scaling Concept for Estimating Field-Scale Hydraulic Functions of Layered Soils. p. 103-107. In A. N Findkakis (ed.) Proceedings of the 2002 International Groundwater Symposium, Lawrence Berkeley National Laboratory, Berkeley, California, March.

Zhang, Z. F., A. L. Ward, and G. W. Gee. 2003. Estimating soil hydraulic parameters of a field drainage experiment using inverse techniques. Vadose Zone J. (In press)

Zhang, Z. F., A. L. Ward, G. W. Gee. 2002. Estimating Field-Scale Hydraulic Parameters Using a Combination of Parameter Scaling and Inverse Methods. PNNL-14109. Pacific Northwest National Laboratory, Richland, Washington.

Zhang, Z. F., G. W. Parkin, R. G. Kachanoski, and J. E. Smith. 2002. Effects of soil heterogeneity on steady state soil water pressure head under a surface line source.Water Resour. Res. 38 (7) 10,1029/2000WR000019.

Zheng, W., Papiernik, S.K., Guo, M. and Yates, S.R. 2002. Accelerated Degradation of Methyl Iodide by Agrochemicals. J. Agricult. Food Chem. (Accepted)

Zhuang J. and Y. Jin. Virus retention and transport as influenced by different forms of organic matter. J. Environ. Qual. (In press).

Zhuang J. and Y. Jin. Virus retention and transport through Al-oxide coated sand columns: effects of ionic strength and composition. J. Contamin. Hydrol. (In press).

Zuo, Q. and R. Zhang. 2002. Estimating root-water-uptake using an inverse method. Soil Sci. 167:561-571.

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7. SIGNATURES

F.X.M. Casey, Chair Technical Committee, W-188

Date

G.A. Mitchell Administrative Advisor, W-188

Date