ANNUAL REPORT OF REGIONAL RESEARCH PROJECT W-1188

CHARACTERIZING MASS AND ENERGY TRANSPORT AT DIFFERRENT SCALES

January 1 to December 31, 2007

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1. PROJECT: W-1188 CHARACTERIZING MASS AND ENERGY TRANSPORT 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

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

Marcel Schaap, Dept. of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721

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

California S. A. Bradford, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507

T. Harter, Dept. of LAWR, Hydrologic Science, University of California Davis, CA 95616

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

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

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

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

J. Šimůnek, Dept. of Environmental Sciences, University of California, Riverside, CA 92521

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, Department of Earth and Environmental Sciences, California State University, Fresno, CA 93720

L.Wu, Dept. of Environmental 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

Delaware Y. Jin, Dept. of Plant and Soil Sciences, Univ. of Delaware, Newark, DE 19716

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

Toby Ewing, Dept. of Agronomy, Iowa State University, Ames, IA 50011

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

Kentucky O. Wendroth, Dept. of Plant & Soil Sciences, University of Kentucky, Lexington, KY 40546

Minnesota J. Nieber, Dept. Biosystems and Agricultural Eng., University of Minnesota, St.

Paul, MN 55108

T. Ochsner, USDA, Agricultural Research Services, St. Paul, MN 55108-6030

Montana J. M. Wraith, and Brian L. McGlynn, Land Resources and Environ. Sciences,

Montana State University, Bozeman, MT 59717-3120

Nevada T. Caldwell, Desert Research Institute, University of Nevada, Reno, 89512

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

J. Zhu, 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

Oregon Maria Dragila, Oregon State University, Dept. of Crop and Soil Science, 3017 Agriculture and Life Aciences, Corvallis, Oregon 97331-7306

Tennessee J. Lee, Biosys Engin & Envir Sci., University 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. Schwartz, USDA-ARS-CPRL, P.O. Drawer 10, Bushland, TX 79012

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B.P. Mohanty, Texas A&M University, College Station, TX 77843-2117

Utah S. Jones, 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

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

M. Oostrom, Battelle Pacific Northwest Division, Richland, WA 99352

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 Thijs Kelleners, Dept. of Renewable Resources, University of Wyoming, Laramie, WY 82071

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

Adm. Adv. Jeff Jacobsen, Dean and Director, 202 Linfield Hall, P.O. Box 172860, College of Agriculture, Montana State University, Bozeman, MT 59717-2860

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3. ACCOMPLISHMENTS UNDER THREE SPECIFIC OBJECTIVES OBJECTIVE 1: To develop and improved understanding of the fundamental soil physical properties and processes governing mass and energy transport, and the biogeochemical interactions these mediate. Desert Research Institute, University of Nevada, Las Vegas, NV Investigators: Markus Berli (DRI, Visitor), Todd Caldwell (DRI), Karletta Chief (DRI, Visitor), Scott Tyler (UNR), Wally Miller (UNR), Michael Young (DRI), Jianting Zhu (DRI) Nevada scientists have been conducting research to understand how physical properties of unsaturated porous media mediate energy and mass balance and transport.

Interrelated, biotic (flora and fauna) and abiotic (pedogenesis and hydrology) processes were examined at four sites (30, and approximately 1000–3000, 7000–12 000, and 125 000 years before present) in the northern Mojave Desert (Shafer et al., 2007). Data collected at each included floral and faunal surveys; soil texture, structure, and morphology; and soil hydraulic properties. Separate measurements were made in shrub undercanopy and intercanopy microsites. At all sites, shrubs made up greater than 86 percent of total perennial cover, being least on the youngest site (4 percent) and most on the 7000–12 000-year-old site (31 percent). In the intercanopy, winter annual density was highest on the 1000- to 3000-year-old site (249 plants/m2) and lowest on the oldest site (4 plants/m2). Faunal activity, measured by burrow density, was highest on the 1000–3000- and 7000–12 000-year-old sites (0.21 burrows/m2) and density was twice as high in the undercanopy versus the intercanopy. Burrow density was lower at the two oldest sites, although density was not statistically greater in the undercanopy than intercanopy. At the older sites, the soil water balance was increasingly controlled by Av horizons in intercanopy soils in which Ksat decreased 95 percent from the youngest to the oldest site. No significant reduction in Ksat in undercanopy soils was observed. Decreases in the intercanopy sites correlated with decreases in annual plant density and bioturbation, suggesting these processes are interrelated with surface age.

Following the above results, Nevada looked more closely at the near-surface soil layer to determine whether increased pedogenic development of the Av (vesicular) horizon over relative time impacts the hydraulic properties of individual soil peds and the mechanism of infiltration as inferred by dye patterns (Meadows et al., 2007). Individual peds were examined from the Av horizons associated with desert pavements that mantled three different alluvial deposits with different relative surface ages (Qf5 (∼10 ka), Qf3 (∼50–100 ka), and Qf2 (∼10–50 ka)). An additional surface (Qf6 (∼4 ka)) was chosen for dye studies. They hypothesized that increases in the development of the Av over time would lead to a more structured soil surface with greater potential for flow between soil peds and lower hydraulic conductivity of the soil peds themselves. Results showed that average Ksat and Gardner’s α of the Qf5 peds were significantly greater than estimated for the Qf2 and Qf3 peds. Although Ksat was greater for the Qf5 peds, the steady-state infiltration rate was equal for the Qf3, Qf2, and Qf5 surfaces, perhaps indicating a reduction in matrix flow through soil peds and an increase in interped flow between soil peds. Studies were also conducted using dyed water and a tension disc infiltrometer set to saturation. Following the tests, the soil was excavated in 2-cm increments and photographed. The dye patterns for the Qf6 indicated that the water moved rapidly through the soil matrix into deeper

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soil, and without any preferential flow around peds. The Qf5 exhibited more dye-stained soil at depth than seen in the Qf2 and Qf3, perhaps due to higher ped conductivity. Qualitative observations on the Qf2 and Qf3 suggest that water flowed primarily along the ped faces and then toward the ped interiors. The results suggest that infiltration through Av horizons evolves from a matrix-dominated process on the younger soils to a preferential flow-dominated process on older surfaces.

One of the key properties of the soil hydraulic parameters at the Hanford Site is the existence of a layered structure. The layered structure causes anisotropy in unsaturated flow and contaminant transport. The effects of saturation degree (or tension) on hydraulic conductivity anisotropy in unsaturated soils have long been recognized, but they have not been fully described conceptually. Previous models included quantifying saturation-dependent anisotropy of soil formations that consist of many thin layers, each with its own hydraulic properties, characterized by a uniform density distribution of saturated hydraulic conductivity or soil bulk density. Some other approaches have been developed to study the soil anisotropy behavior when dealing with flow and transport problems in saturated and unsaturated soils, such as the tensorial connectivity-tortuosity concept. In this study, soil unsaturated hydraulic conductivity anisotropy was investigated (Zhu and Sun, 2007a) that mainly arises from a combination of a wide range of soil texture variations and within narrow range of texture units in conjunction with pedotransfer functions (PTFs) of soil hydraulic properties. Nevada developed a new approach to combine the neural network based PTF results with the thin layer approach to explore saturation-dependent anisotropy behavior for a wide range of texture and bulk density conditions, a new conceptualization which has not been explored to date. Anisotropy models were developed that quantify saturated and unsaturated hydraulic conductivities for soils composed of many thin layers distinguished by texture, organic carbon content and bulk density. Results indicated that the vertical variability of soil texture and bulk density was a significant factor that impacts tension-dependent hydraulic conductivity anisotropy of unsaturated soils.

Nevada scientists, in collaboration with other researchers from Florida, Arizona, and Washington State, developed a methodology to integrate data that can be easily obtained (i.e., initial moisture content, bulk density, and soil texture) with soil hydraulic property data via cokriging and artificial neural network (ANN)-based pedotransfer functions (PTFs) (Ye et al., 2007). The method was used to generate heterogeneous soil hydraulic parameters at a field injection site at the Hanford site. Cokriging was first used to generate three-dimensional heterogeneous fields of bulk density and soil texture using an extensive data set of field-measured moisture content, which carry a signature about site heterogeneity and stratigraphy. Soil texture and bulk density were subsequently input into an ANN-based site-specific PTF to generate three-dimensional heterogeneous soil hydraulic parameter fields. The stratigraphy at the site was well represented by the estimated pedotransfer variables and soil hydraulic parameters. The soil hydraulic property data included laboratory measurements of Ksat and van Genuchten moisture retention parameters obtained from 70 core samples. Another type of data used, also referred to as pedotransfer variables, included bulk density and percentages of gravel, coarse sand, fine sand, silt, and clay measured for the same 70 core samples. The data set also included 1,376 observations of initial moisture content before the injection experiment. The hydraulic parameter estimates were then used to simulate a field injection experiment site the Hanford 200E Area. A relatively good agreement was obtained between the simulated and observed moisture contents, including their spatial distribution pattern. In contrast to earlier work using an effective parameter approach, the observed moisture plume was reproduced in a coarse sand unit

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that was sandwiched between two fine-textured units. The method of combining cokriging and ANN for site characterization provided unbiased predictions of the observed moisture plume and was flexible so that additional measurements of various types can be included as they become available.

Nevada scientists and collaborators from Florida State University and Lawrence Berkeley National Laboratory have been addressing issues of uncertainty when used in predictions of water flow and tracer transport in heterogeneous fractured media (Pan et al., 2007). To quantify predictive uncertainty of fluid flow and contaminant transport at the field scale, two fundamental issues need to be addressed: how to characterize multi-scale heterogeneity of model parameters and how to evaluate propagation of parametric uncertainty through complicated field-scale models. This study develops a method of characterizing layer- and local-scale heterogeneity of hydraulic parameters (i.e., matrix permeability and porosity), and investigates effect of the heterogeneity (especially at the local scale) on uncertainty assessments of unsaturated flow and tracer transport at Yucca Mountain, NV. The layer scale refers to hydrogeologic layers with layer-wise average properties, and local scale refers to the spatial variation of hydraulic properties within a layer. A Monte Carlo method is used to estimate mean, variance, and 5th and 95th percentiles for quantities of interest (e.g., matrix saturation, percolation fluxes, and normalized cumulative mass arrival). Predictions of unsaturated flow are examined by comparing them with observations of matrix saturation and water-potential data. Mean predictions are in reasonable agreement with the trend of the observations, and the 5th and 95th percentiles (uncertainty bounds) bracket a large portion of the observations. By comparing simulations of this study with those that exclusively consider layer-scale heterogeneity, the local-scale heterogeneity are found to increase the predictive uncertainty of percolation flux and cumulative mass arrival for computational blocks below the footprint of the proposed repository of high-level radioactive waste, whereas mean predictions are hardly affected. The local-scale heterogeneity significantly affects travel times to the water table for both conservative and reactive tracers. In the early simulation period, tracer mean travel times are delayed, whereas the influence of local-scale heterogeneity diminishes during the late simulation period.

Another topic of ongoing research in Nevada is the question how matrix deformation influences fluid flow in porous media, an area of interest for many applications in hydrology, geophysics and environmental engineering at scales ranging from individual pore- to field-scale. In the study by Eggers et al. (2007), fluid permeability through a stack of deforming spherical aggregates was described using analytical and Finite Element (FE) analyses. The permeability of an entire sample cross section was constructed from analytical estimates of individual pore permeabilities, and from numerical solution to steady flow through the entire cross section of the sample. Experimental results of pore deformation within a stack of modeling clay aggregates were compared to FE calculations for two-dimensional cross sections. Results showed that pores within a cubic pack of aggregates deform isotropically even under anisotropic stress conditions. Therefore aggregate arrangement seems to be as important as stress anisotropy to predict pore shape evolution. Observations of cross sections through a porous sample under compaction showed reduction in both the mean and variance of pore permeability with increasing compaction. Despite predominantly vertical compaction, sample permeability remained nearly isotropic (with only a slight additional decrease in the vertical direction). The Aissen analytical approximation for pore permeability was very similar to numerical results for the entire range of sample deformation, thereby providing a useful tool for estimating sample permeability from images of complex pore cross-sectional areas. As an extension of Eggers et al. (2007), Berli et

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al. (2007a) proposed an analytical model for aggregate contact size evolution as a basis to quantify compaction effects on unsaturated hydraulic conductivity of aggregated soil. Relating confined one-dimensional sample strain with aggregate deformation facilitates prediction of the increase in inter-aggregate contact area and concurrent decrease in macro-pore size with degree of sample compression. The hydrologic component of the model predicts unsaturated hydraulic conductivity of a pack of idealized aggregates (spheres) based on contact size and saturation conditions under prescribed sample deformation. Calculated contact areas and hydraulic conductivity for pairs of aggregates agreed surprisingly well with measured values, determined from compaction experiments employing Neutron- and X-ray-radiography and image analysis.

Desert dust has long been recognized as an important parameter for testing military vehicles and equipment, due to the potential that dust could adversely affect performance and durability. Vehicle dust test courses were originally established in areas of coarse-textured soils underlying fine particulate layers (silt and clay) and were used for cyclic tests. These desert pavement soils are geomorphically old, developing slowly through the trapping of atmospheric dust over tens of thousands of years. They represent both a sink and source for eolian material when disturbed. This dust is a finite resource for military testing at the Yuma Proving Ground (YPG), because continuous use of YPG dust test courses over the past half century have eroded through the overlying dust-rich soil to the extent that the true natural environmental conditions are no longer adequately represented. The objectives of this study (Caldwell et al., 2007a) were to 1) characterize current dust courses at YPG to gain a better understanding of the current state of dust availability and 2) assess the overall sustainability of high dust-potential soils needed for proper military testing. Soil samples collected from both courses and adjacent undisturbed soils, as well as dust collected on tactical vehicles, were analyzed for mineralogy, geochemistry, and physical properties. Results indicate adjacent undisturbed soils exhibit a relatively higher dust potential (higher silt and clay) and elevated reactive salts and carbonates indicating a significant loss of fines from the dust test courses. Routine vehicle traffic and surface preparation have eroded and mixed the dust layer with the underlying sand and gravel-rich horizons, depleting the test courses of their dust-producing potential. Desert pavements are stable geomorphic landforms but the soils have finite dust content when disturbed and therefore are unsustainable for repeated dust testing. Disturbance of these soils may potentially affect ecologically sensitive areas. As such, more geomorphically active areas such as floodplains may provide greater sustainability for long-term testing (Caldwell et al., 2007a).

Desert pavement deterioration from military and civilian off-road vehicle operations is of increasing interest for military training purposes as well as for soil protection and remediation activities. The goal of a study by Berli et al. (2007b) was to model the deterioration of a fine-textured desert pavement with distinct secondary structure due to heavy vehicle traffic. Analytical Terzaghi- and Bekker-type models were used to predict onset and evolution of rut formation from multiple passes of an eight-wheeled “Stryker” vehicle. Rut depth and soil bulk density measurements from traffic experiments at Yuma Proving Ground (YPG) were used for model evaluation. We found that rut formation can be simulated reasonably well employing Terzaghi and Bekker-type models. Key issues are the correct soil mechanical input parameters determined for undisturbed soil for the respective models to avoid overestimation of rut formation in desert pavements. Comparison of rut depth and bulk density measurements with respective model calculations show that rut formation probably consists of two parallel processes: (1) compaction of the soil due to the first vehicle pass and (2) soil surface wear (“abrasion”) due shear stresses at the tire-soil-interface for subsequent passes. For multiple

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passes rut depth increases linearly at an average rate of 0.75 mm per wheel and 3 mm per vehicle pass, respectively. USDA-ARS, Salinity Laboratory, Riverside California Investigators: Scott Bradford, Eran Segal, Saeed Torkzaban, Martinus Th. van Genuchten, Scott Yates, Todd Skaggs, and Peter Shouse Experimental studies (measurements of surface chemistry, batch studies, and column experiments) were undertaken to quantify the retention mechanisms of various microorganisms under a wide variety of conditions. Results indicate that microorganism retention is a strongly coupled process that is dependent on the surface and aqueous chemistry, the hydrodynamics, the pore space geometry, the microorganism concentration, and the water content. We have recently found that pathogenic E. coli O157:H7 exhibited less retention at higher ionic strengths (IS) than at lower IS. This unexpected finding was attributed to changes in the conformation of their surface macromolecules.

Mathematical models are currently being refined and utilized to examine pore-scale pathogen transport and deposition processes in both saturated and unsaturated conditions. Insight on colloid deposition processes is obtained by conducting force and torque balances on colloids near solid surfaces. Chemical forces are described using conventional DLVO theory and hydrodynamic forces are determined from the solution of the Navier-Stokes equation for fluid flow. Results indicate that deposition is very sensitive to the pore-scale hydrodynamics, DLVO forces, and the geometry of the pore space. Micromodel studies are being conducted to validate our pore-scale modeling results.

We have continued working on the development of more realistic models for colloid and microorganism transport and retention in porous media. Experimental research has demonstrated that much greater retention is possible in the smallest regions of the pore space that are associated with lower flow rates. We have therefore developed models that are based upon physical and chemical nonequilibrium (PCNE), dual permeability, and stochastic stream tube formulations. The PCNE and dual permeability models also account for exchange between mobile and low velocity regions in both the liquid (advention and diffusion) and solid (rolling and sliding) phases. The various model formulations are currently being used to better describe measured deposition profiles for colloids and microorganisms. Washington State University, Pullman, WA Investigators: Markus Flury, Joan Wu Our activities focused on (1) elucidating mechanisms of colloid mobilization in unsaturated porous media, (2) quantification of interfacial forces responsible for colloid mobilization, and (3) field-scale nitrate leaching from agricultural soils.

We explored the role of transient flow in mobilizing in situ colloids from unsaturated Hanford sediments. We hypothesized that multipulse transient irrigation releases more colloids than single-pulse continuous irrigation. A series of laboratory-scale column experiments were

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conducted to characterize the effects of the irrigation pattern in relation to solution ionic strength, irrigation rate, and sediment texture (Zhuang et al., 2007). Results show that transient flow mobilized more colloids than steady-state flow. The number of short-term hydrological pulses was more important than total irrigation volume for increasing the amount of mobilized colloids. At an irrigation rate equal to 5% of the saturated hydraulic conductivity, a transient multipulse flow in 100 mM NaNO3 was equivalent to a 50-fold reduction of ionic strength (from 100 mM to 2 mM) with a single-pulse flow in terms of their positive effects on colloid mobilization. In addition to water velocity, mechanical straining of colloids was partly responsible for the smaller colloid mobilization in the fine than in the coarse sands.

In a subsequent study, we have quantified the release rate coefficient for colloids under unsaturated flow. We calculated forces exerted on colloids, and found that electrostatic and van der Waals interactions, calculated based on the DLVO theory, and hydrodynamic forces, were all less important than capillary forces in controlling colloid release. In one experiment, the ionic strength of the infiltration solution was increased, such that colloid attachment was favorable. Nonetheless, colloids were mobilized and eluted with the infiltration front, implying that non-DLVO forces, such as capillary forces, played a prominent role in colloid mobilization.

We further investigated the means by which, and the extent to which, europium may be transported in the vadose zone. Europium hydroxycarbonate was introduced to an unsaturated laboratory column packed with Hanford sediments. The column was then flushed with simulated pore water at variable flow rates. Europium was found to be eluted with the infiltrating pore water and peak europium concentrations coincided with the colloid breakthroughs, indicating europium transport was facilitated by colloids. Larger flow rates led to increased colloid mobilization and europium elution. We used MINTEQ, a geochemical equilibrium speciation model to simulate europium speciation in solution.

A field experiment was conducted to examine the relationship between N fertilization rate, soil NO3-N, and NO3-N groundwater contamination (Zhao et al., 2007). Two adjacent fields were fertilized with local farmers’ N fertilization rate (LN) and double the normal application rate (HN), respectively, and managed under otherwise identical conditions. The fields were under a summer corn/winter wheat rotation. We monitored NO3-N concentrations in both bulk soil and soil pore water in 20-40 cm increments up to 180 cm depth. We also monitored NO3-N concentrations in groundwater and the depth of the groundwater table. No significant differences in soil NO3-N were observed between the LN and HN treatment. The HN treatment resulted in significantly higher groundwater NO3-N, relative to the LN treatment, with groundwater NO3-N consistently exceeding the maximum safe level of 10 mg L-1. Concurrent increase of the groundwater table into NO3-N rich soil layers also contributed to increased NO3-N concentrations in the groundwater. Impact: From our experimental observations, we developed a conceptual model for colloid release under unsaturated flow. As the flow rate in a porous medium increases, more and more pores become filled with water and contribute to flow; a larger and larger fraction of the porous medium contributes to water flow. Under initially dry conditions, colloids are pinned to the sediment surfaces by strong attractive capillary forces. When the flow rates, and consequently the water contents, increase, water film thicknesses increase and more and more pores become water filled. Consequently, capillary forces become less dominant, until at a critical water content, the capillary forces vanish and even become repulsive, leading to colloid release. This conceptual model will form the basis to develop predictive mathematical models to describe colloid fate and transport in the vadose zone.

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University of Wyoming, Laramie, WY Investigator: Thijs Kelleners Work continued on a distributed watershed model for the calculation of the water and energy balance in mountainous areas prone to snow accumulation. The main improvement concerned the implementation of a non-iterative solution to Richards’ equation for vertical soil water flow. Advantages of the non-iterative solution are speed, and the absence of water balance errors. Also, relatively coarse grids and relatively large time steps may be used. Comparisons with Hydrus-1D will be used to assess the accuracy of the soil water content predictions with the new algorithm. The watershed model now calculates soil water flow (Richards’ equation), heat transport (conduction and convection), and soil water freezing (Clapeyron equation) for each grid cell. Results of the improved model were presented at the Soil Science Society of America Annual meeting in New Orleans, LA. North Dakota State University, Fargo,ND Investigator: Frank Casey Fate and Transport of Natural Hormones in Soil-Water Systems Outputs: Estrogenic and androgenic hormones are endocrine disruptors that can be potent at part per billion concentration levels. The persistence and fate of 17β-estradiol (E2) and testosterone (T) were investigated in natural and sterile soil under aerobic and anaerobic conditions using incubation microcosm experiments. The results indicated that 6% of E2 and 63% of T could be mineralized in native soils under aerobic conditions. In native soils under anaerobic conditions, 2% of T and no E2 was methanogenized. Essentially, no mineralization of either T or E2 to CO2 occurred in sterile soils under aerobic or anaerobic condition. The fate and transport of E2 and T was also investigated in undisturbed soil columns and a complex model was developed to discern and describe these experiments. An advanced parameter estimation technique was implemented to successfully model the hormone fate and transport in the soil column. The results from these column experiments indicated little parent hormone was distributed through depth in the soil and that much of the hormone was bound irreversibly to the soil. Minimal E2 was converted to CO2 during these column experiments; however, an appreciable amount of T (23%) was converted to CO2. The fate of E2 and T was also investigated in the field using a controlled lysimeter experiment, where the steady-state transport of a conservative non-sorbing tracer, PFBA, was compared to the transport of E2 and T. Lysimeter effluent and resident soil distributions of hormones and PFBA were measured. It was found that water content and organic matter were significant in explaining hormone distributions in the soil. Water content indicated that biological degradation was a significant factor, while organic matter indicated soil sorption as a significant factor. Effluent hormones concentrations suggested that colloidal facilitated transport and/or antecedent hormones were likely present in the lysimeter. Additionally, a reconnaissance study was done where soil cores were taken from fields before and after manure application. Little or no E2 were found; however, significant amounts of E2’s metabolite, estrone, was found.

The results from the laboratory studies were reported in the dissertation of Zhaosheng Fan (Fan, 2007) and also in two peer reviewed journals (Fan et al., 2007a; Fan et al., 2007b). The

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lysimeter (Casey et al., 2007) and reconnaissance (Schuh et al., 2007) studies was presented a the annual meetings of the Agronomy Society of America (ASA) in New Orleans. The reconnaissance study research was also conducted as part of Ms. Mary Schuh’s M.S. graduate program. Outcomes: Results from the laboratory and field experiments suggest or indicate that soil humic substances can immobilize the majority of hormones (~50% irreversibly bound to the soil), and thereby reduce their bioavailability and toxicity. Also, the biologically available hormones are readily degraded under aerobic conditions. The fate and transport model was also helpful in discerning and implementing fate and transport processes, which is useful in the prediction of hormone distribution. The information gained from these studies will be useful in developing better management methods for handling hormones in animal manures or from waste treatment facilities. University of California, Riverside, CA Investigator: Laosheng Wu Fate and Transport of Disinfection Byproducts (DBPs) and Pharmaceutical/Personal Care Products (PPCPs) in Turfgrass Irrigated with Reclaimed Wastewater The practice of irrigation with reclaimed water on landscape has been employed for many years in many areas of the world. The fate and transport of trace organic contaminants including pharmaceutical and personal care products (PPCPs, such as endocrine disruptors, and steroid hormones) and disinfection byproducts (DBPs) in the reclaimed water have not been well documented for irrigated soils. This project studied the fate and transport of these contaminants in an experimental fairway at the University of California, Riverside, by spiking irrigation water with 2 DBPs (Haloacetic acids and trihalomethanes) and 11 PPCPs. The compounds were mixed thoroughly in a 5000-gallon tank. Two irrigation rates (1.1~1.2ET0 and 1.5~1.6ET0) were applied on two types of soils (sandy loam and loamy sand). Irrigation was applied three times a week, and the leachates were collected twice a week and analyzed for the target compounds. The control treatment of four plots (two of each soil type) was established by removing the turfgrass (with bare soil surface) and irrigated in the same way as for other treatments. The DBPs and PPCPs were analyzed by GC/MSD. Irrigation for this experiment started September 15, 2007, and is ongoing. Preliminary results demonstrate that after 80-d irrigation with spiked water, no chemical was detected in the leachate samples. The experiment will continue until December 2007. After that, soil core samples will be collected and sliced into several layers. Concentrations of the chemicals in the soil profile will be measured. Laboratory work will also be carried out to characterize the adsorption and degradation of these compounds in turf soils. Non-linear diffusion in external fields and non-ideal systems Based on the macroscopic thermodynamic analysis, we have established a generalized linear theory for non-linear diffusion in external fields and non-ideal systems, which was classically described by the Fokker-Planck equation (or the Smoluchowski equation) and the non-linear Fickian equation, respectively. The new theory includes three basic equations expressed in “apparent variables” as defined in this paper: (1) a generalized linear flux equation for non-linear

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diffusion; (2) an apparent mass conservation equation; and (3) a generalized linear non-steady state equation for non-linear diffusion. Our analysis shows that (1) all of the existing linear and non-linear equations are the special cases of the new non-steady state general diffusion equation. It was also demonstrated that the general equation of the non-steady state is equivalent to the Fokker-Planck equation; (2) coupling diffusion with multiple driving forces can be unified to a single force: the apparent concentration gradient; (3) the exact relationship between the diffusion coefficient and the concentration in non-linear Fickian equation under non-ideal conditions could be established; and (4) the potential energy is conservative in a diffusion process. An application of the generalized linear equation showed that the solution is simple. For the first time, an analytic solution of the Smoluchowski equation with a time-dependent potential in algebraic form was obtained. Estimate Ion Distribution between the Exchanger and Solution Phases Currently there are two approaches to treat ion exchange equilibrium between the exchanger phase and solution phase: the chemical reaction equilibrium and the Donnan equilibrium. Nevertheless, theoretical calculation of the ion distribution between these two phases remains impossible using these two approaches because of the difficulty of obtaining the activity coefficient of an ion in the exchanger phase for a solution mixture containing two or more types of electrolytes. Our analysis of ion diffusion in an electric field showed that the exchange process of electrostatic adsorption can be treated as a diffusion process. A new equilibrium equation was obtained by treating ion exchange as a diffusion process. The new equation can be used to predict the ion distribution between the exchanger and solution phases without knowing the activity coefficients of the adsorbed ions. The new approach was tested and verified using published experimental data for a Na–Ca-illite system. The experimental data and the theoretical predictions matched very well. The new ion distribution equation can provide another way to calculate ion exchange equilibrium for a well-dispersed suspension of dilute bulk solution containing two types of electrolytes. Nitrogen Fate in California Lawns Residential lawns represent a great portion of the land use in California. Due to the demand for visually attractive lawns, relatively large amounts of nitrogen (N) from various sources are often applied. The overall objective of this research was to investigate the effect of N source and application rate on tall fescue (Festuca arundinacea Schreb.) visual quality and color, clipping yield, N uptake, and nitrate leaching under normal irrigation practice. Three rates of N (195, 293, and 390 kg ha-1 yr-1) and four N sources (ammonium nitrate, Milorganite, Nutralene, and Polyon) were applied. The 3 (N application rates) by 4 (N sources) factorial experiment was replicated 4 times and was conducted on a Hanford fine sandy loam at the University of California-Riverside’s Agricultural Operations Turfgrass Research Facility from Nov. 2002 to Oct. 2004. Visual turfgrass quality and color ratings were evaluated once every 2 weeks. Clipping yield, total clipping N concentration, and N uptake were measured or calculated in four growth periods per year (mostly 4 weeks per period). Suction lysimeters were used to collect leaching water samples to determine nitrate and ammonium concentrations once every 2 weeks. Soil nitrate and ammonium concentrations were analyzed at 0, 12, and 24 mo. after initial fertilizer treatments. Results indicated that an annual N rate of 195 kg ha-1 produced an acceptable to good quality tall fescue lawn. Higher rates were not necessary and may increase the risk of nitrate leaching. Among the different N sources, slow-release N resulted in less nitrate leaching than the fast-

13

release N source. It was further recognized that irrigation management could also significantly affect N leaching. Battelle Pacific Northwest Division, Richland, WA Investigators: Z. F. Zhang, and R. Khaleel Comparison of Models of Saturation-Dependent Anisotropy in Unsaturated Hydraulic Conductivity Natural geological formations in the Hanford Site are three-dimensionally heterogeneous and anisotropic. In the vadose zone, the anisotropy is also dependent on the soil saturation condition. These features must be taken into account for accurate modeling of water and contaminant transport in the subsurface. Researchers have developed different models to describe saturation-dependent anisotropy. In this investigation, core-scale hydraulic properties were upscaled and/or described using the tensorial connectivity-tortuosity (TCT), modified stochastic anisotropy (MSA), and pancake anisotropy (PA) models as well as the conventional isotropic (ISO) model. The models were tested by three-dimensional simulations of an injection experiment in Hanford’s Sisson and Lu Site by treating the soil as an equivalent homogeneous medium. An additional simulation was conducted using the TCT model and treating the medium as one with five layers. Spatial moment analysis was conducted for quantitative comparisons: the zeroth moment corresponds to the total mass, the first moments correspond to the center of mass, and the second moments correspond to the spreading of the plume. Average percentage errors of these components of moment for each simulation case relative to those of the observations were calculated. Overall, among the four anisotropy/isotropy models, the TCT model had the smallest average error. The MSA and PA models produced similar errors, while the MSA model predicted the plume shape better than the PA model. However, the PA model predicted the total mass of the injected water in the region of observation better than the MSA model. As expected, the ISO model predicted the plume the worst. By including the layering structure in the TCT model, the simulation results had the smallest overall error. USDA-ARS National Soil Tilth Laboratory and Iowa State University, Ames, IA Investigators: Dan Jaynes, Toby Ewing, Robert Horton Testing Coupled Soil Heat and Water Transfer Prediction under Transient Conditions (Heitman) Accomplishments: Diffusion-based coupled soil heat and water transfer theory was tested by comparing theory-based predictions with measured transient temperature and water content distributions for a series of conditions including 2 soils, 2 initial water contents, 3 mean temperatures, and 3 sequentially-imposed temperature gradients. Outcome: Results indicated that the theory can be calibrated for a single boundary condition with adjustment of soil saturated hydraulic conductivity and/or the vapor enhancement factor,

14

A. Measured

θ L (m

3 m-3

)

0.05

0.10

0.15initial24 h48 h96 h

C. Measured

Distance from cool end (cm)

0 2 4 6 8 10

T (o C

)

17.5

20.0

22.5

25.0

27.5

B. Calculated

D. Calculated

Distance from cool end (cm)

0 2 4 6 8 1

0 Fig. 1. Water content (θL) and temperature (T) distributions after reversal of the imposed temperature gradient. which respectively adjust the liquid and vapor fluxes. For a silt loam soil, calibration reduces the root mean square error (RMSE) by 67% for water content (θ) and 18 % for temperature (T) distributions. For sand, RMSE is reduced by 14% for θ and 46% for T. After calibration, calculated and measured properties agreed, with RMSE ≤ 0.03 m3 m-3 for θ and 1.28 °C for T, over subsequently imposed boundary and initial conditions. However, when the boundary temperature gradient was reversed instantaneously, noticeable differences arose between measured and calculated patterns of temperature and water content (Fig. 1). Impact: While the theory described observations well when boundary temperature conditions changed gradually, these results indicate a need for further development of coupled heat and water transfer theory combined with testing under transient conditions. Determining Soil-Water Evaporation In Situ through Heat Balance (Heitman) Accomplishments: Estimates of soil-water evaporation are commonly driven by micrometeorological models or by water balance. We have performed a series of field studies with the objective of determining in situ soil-water evaporation dynamics from heat balance. Three-needle heat-pulse probes were installed at multiple depths in the upper centimeters of bare

15

and cropped field plots. The probes provided temporal measurements of soil temperature, thermal properties, and water content, which allow calculation of the subsurface sensible heat balance. The residual to the heat balance is attributed to latent heat from water vaporization. Independent estimates of evaporation and evapotranspiration were obtained with microlysimeters and eddy covariance flux towers, respectively. Data were collected for naturally occurring wetting and drying cycles throughout the growing season. Outcome: Results reveal shifting patterns of evaporation within the soil (Fig. 2). Near-surface soil heat fluxes account for as much as 80% of net radiation as the evaporation zone proceeds below the surface. Data from the bare surface plot indicate that the heat-balance approach for estimating soil-water evaporation can provide accurate results for Stage 2 and 3 evaporation (Fig. 2). Data analysis for the cropped field experiments is currently on-going. Impact: Results from this study will provide further insight into coupled heat and water transfer in the near-surface field environment and the partitioning between transpiration and evaporation. Predicting Thermal Conductivity at Low Water Contents (Ewing) Accomplishments: We developed a method for calculating the effect on thermal conductivity of a capillary bridge connecting two touching equal-sized spheres. Outcome: The finite-element method agrees well with two complementary analytical approaches, providing some validation. The main result is that for constituent thermal conductivities λair < λwater < λsolid, conductivity of the system in the presence of capillary bridges (which, for equal-size spheres, corresponds to volume saturation in the range 0.0 < θ < 0.087) is described by λ(θ) = λ(0) + aθb, where a and b are primarily functions of θ. The exponent b < 1.0. The relationship also holds when the spheres are compressed together, if the λ(0) used is based on the compressed spheres. Impact: The work provides a quantitative explanation for the observed steep rise in λ(θ) with the addition of small amounts of water. Qualitative explanations have been given, but without any quantitative justification. The work is currently being extended to distributions of sphere sizes. We hope to have a fully numerical model of λ(θ), valid for cases where vapor transport makes a negligible contribution to total heat transfer.

Two or more days after rainfall.

Microlysimeter evap. (mm)0.4 0.8 1.2 1.

Hea

t-bal

ance

eva

p. (m

m)

0.4

0.8

1.2

1.6

1:124 h

Days after rainfall2 3 10 11

Evap

. rat

e (m

m d

-1)

-2

0

2

4

6 3-8 mm8-13 mm13-18 mm3-23 mm

6

Fig. 2. Temporal patterns in evaporation near the soil surface (left) and comparison of soil heat balance estimates of evaporation to independent estimates (right).

16

Fig. 3. Comparison of thermal conductivity values over a range of conductivity ratios, calculated using McPhedran and McKenzie (1978) (solid line), Sangani and Acrivos’ (1983) asymptotic approximation for high α, (dashed line), and three FEM approximations. University of Arizona, Tucson, AZ Investigator: Marcel Schaap Determine the fundamental relations between the soil matrix and flow and interfacial processes at the microscale In the past decade, lattice Boltzmann (LB) methods have become increasingly popular for simulating fluid dynamics in a wide variety of applications such as laminar and turbulent flow in simple and complex geometries, as well as advection and dispersion. The LB method is essentially a cellular automaton that incorporates microscopic processes that recover Navier Stokes fluid behavior at a larger scale. A clear advantage of the LB method over finite difference methods is its relative simplicity and its ability to deal with arbitrary geometries. In addition, LB methods can be coded very efficiently and run on parallel computers or computer clusters, reducing cost and computation time. Lattice Boltzmann simulations have successfully been applied to saturated porous media and there is also an increasingly large body of work on multi-phase LB simulations in porous media. However, despite recent advances comparison of multi-phase LB results with microscopic observations still remains a somewhat unexplored terrain. We have recently shown (Schaap et al., 2007a) that it is possible to attain a high degree of similarity between LBM simulated and micro-scale computed tomography (CMT) data obtained with the high-brilliance Argonne National Laboratory GEOSECARS synchrotron facility. A Shan-Chen type multi-phase lattice Boltzmann (LB) model was applied to observed computed microtomography data from water-air and water-Soltrol displacement experiments in a glass bead porous medium. (Figure 4). Analysis of the Bond, Reynolds, and Capillary numbers for these systems showed that capillary forces were dominant removing the need to model viscous

17

Fig. 4. Schematic overview of the experimental setup (left), the CMT imaged part and the representation of the experimental system in the Lattice Boltzmann simulations (right, not to scale).

Fig. 5. Tube simulations with enclosed wetting (blue) and non-wetting (red) fluids. The top row shows an increase in curvature for a non-wetting bubble in a duct with a wall to wall size of 38 pixels. Bottom row shows results for Ga=0.012 for ducts with wall to wall sizes between 6 and 38 voxels. viscous, gravitational, and density effects. A numerical parameterization of the cohesion (suface tension) parameter, Gc, and adhesion (contact angle) parameter LB model yielded lattice surface tension and contact angle (Fig. 5), and appropriate pressure boundary conditions. These analyses

18

were later refined in Huang et al. (2007) by using Young’s equation instead of numerical calibration for the contact angle. Two scaling relations provided a link between lattice pressure and physical pressure and lattice time and physical time. It turns out that for the chosen resolution (17 microns) we can simulate pressures between 0 and 1500 Pa (0 and 15 cm), which covers the experimental conditions sufficiently well. Time scaling through the viscosity of water reveals that lattice Boltzmann simulations are extremely slow. One time step is 1/20,000'th of a second. Simulations on multiple cpu systems (clusters) typically take several weeks to several months.

Results showed that there was a good match between measured and simulated pressure-satur

ig. 6. Simulated (large symbols) and measured (small symbols connected with lines) pressure-saturation characteristics for the water-air (A) and the water-Soltrol (B) systems. Data points for secondary drainage simulations were deleted from Figure B for clarity.

ation data for the water-air system (Fig 6a), but that there were large differences between the simulations and observations for the water-Soltrol system (Fig 6b). It is important to note here that both the observations and simulations were done at the same scale, using a resolution of 17 microns per voxel (a 3D pixel). No calibration, other than a-priori setting the surface tension and contact angle, were carried out. The total simulated domain contained approximately 12 million voxels. The discrepancies for the water-Soltrol system were probably due to inconsistencies between experimental conditions and simulated conditions such as non-zero contact angle in the experiments. Analysis of saturation profiles (Figure 7) indicated increasing saturation near the wetting boundary and decreasing saturations near the non-wetting boundary. We attribute these saturation transitions to pore-neck and percolation effects.The results in of this research are very exiting, indicating -for the first time- that it is possible to obtain a realistic water retention characteristic for arbitrary geometries using Lattice Boltzmann simulations. Although the study by Schaap et al. (2007a) was carried out for a glass bead system with an average bead diameter of 0.8 mm and a pressure head range between 0 and 10 cm (0 to 1000 Pa in Figure 4), it is likely that similar results with the same degree of accuracy can be obtained for other porous media and other pressure ranges. This opens a wealth of research possibilities that allow the fundamental study of pore-scale processes and their relations with larger scale soil properties and processes. Current research is trying to compare observed and simulated

F

19

Fig. 7. Simulated wetting phase saturation profiles. Figure A shows the evolution of the saturation profile for 0 to 980 Pa primary drainage step; Figure B shows a imbibition step to 0 Pa for a initially fully NW saturated medium. Dashed lines in A and B are for every 10,000 iterations until 90,000 iterations, thereafter solid lines denote every 100,000 iterations. Figure C

of Arizona), we are studying macropore flow in porous edia (Schaap et al., 2007c,d). It appears that two orders of magnitude variation in saturated

on).

and D give final saturation profiles for the drainage and imbibition steps, respectively. Dashed lines in Fig. C denote the secondary drainage steps. The area between the horizontal lines in C and D indicate the section that was used to calculate saturations. Dashed lines were used in D for 99 and 182 Pa to enhance legibility. interfacial areas with applications for soil water hysteresis and mixed wetting solid phase particles (Porter et al., 2007), which may help to understand hydrophobic media. Additionally, with Dr. Tuller (Universitymhydraulic conductivity may be obtained, depending on the segmentation algorithm used to analyse 3D computed tomography volumes (see Tullers report for further informati

20

The University of Arizona, Tucson AZ

vestigator: Markus Tuller

ch Project W-1188 in 2006 were primarily focused on bjectives 1 and 2; development and improvement of understanding of the fundamental soil

esses governing mass and energy transport, and development and valuation of instrumentation and methods of analysis for characterizing mass and energy

age segmentation is extremely important for all subsequent analy

DA EMSL Beltsville).

In Our contributions to the Multistate Researophysical properties and procetransport in soils at different scales.

We continued theoretical and experimental studies on initiation and evolution of surface crack networks in active clay soils and performed well controlled dehydration experiments in conjunction with X-Ray Computed Tomography (CT) observations. During quantitative analysis of X-Ray CT data we found that im

sis and modeling efforts, yet it seems that consequences of this important step is widely ignored. This provided the motivation to initiate a comprehensive study to evaluate and refine various binarization approaches.

Besides these major projects, we also worked on issues of liquid behavior in porous materials under reduced gravity in collaboration with Scott Jones (Utah State University) and Dani Or (EPFL), and on pathogen transport in macroporous soils in collaboration with Yakov Pachepsky and Andrey Guber (US

Initiation and Evolution of Surface Crack Networks in Active Clay Soils Observed with X Ray Computed Tomography (Markus Tuller & Thomas Gebrenegus) Development and evolution of desiccation cracks in bentonite-sand mixtures are strongly

ependent on physico-chemical boundary conditions. To investigate effects of solution chemistry

study geometrical features of

ent is strongly depen

was initiated during the first day of dehydration.

dand mixture bentonite content on cracking behavior, we conducted well-controlled dehydration experiments and applied X-ray Computed Tomography (CT) toevolving crack networks. Samples with varying bentonite content were saturated with 0.05 and 0.5 molar NaCl solutions, dehydrated under constant temperature, and scanned with X-ray CT at constant time intervals. Obtained 3-D images were analyzed to quantify crack porosity, specific surface area, and aperture distributions of crack networks. Due to challenges with image segmentation mentioned above, results at this point are of qualitative nature only.

The experiments were primarily motivated by potential applications for bentonite liner design. Our ongoing study and data reported by Revil and Cathles (1999) show the existence of a critical bentonite content, which marks the lowest medium porosity and hydraulic permeability. As shown in a recent thesis by Gebrehawariat (2005), this critical bentonite cont

dent on the chemistry of the permeant liquid as well as the effective confinement pressure. Increase in bentonite content beyond the critical value leads to a significant increase in porosity and a slight increase in saturated permeability, which is not desirable for waste containment applications. Mixing bentonite with sand- or silt-like materials furthermore increases the mechanical stability of a potential hydraulic barrier and also reduces susceptibility to formation of desiccation cracks as shown in Fig. 8.

Figure 9 depicts effects of solution concentration and bentonite contents on evolution of crack porosities with time. It is apparent that increasing bentonite content yields significantly higher porosities. The opposite is the case for solute concentration. We observed that crack formation in bentonite containing samples

21

constant temperature of 40°C.

Fig. 8. Sequences of digital images illustrating the effect of sand content on initiation and evolution of desiccation cracks (sand content decreases from top to bottom) in samples saturatedwith a monovalent solution (0.05M NaCl). In the depicted experiment, samples were exposed to a

Fig. 9. Evolution of crack porosities with time as affected by solute concentration and bentonite content.

22

While samples with low bentonite content (10-20 %) attained constant crack porosities after approximately 30 days, samples with higher bentonite content (30-50 %) reached a stable value after about 55 days.

Determined crack porosity values indicate that samples saturated with lower concentrated solutions (e.g. 0.05 M NaCl) are more susceptible to cracking. This is clearly evidenced by the evolving aperture distributions depicted in Fig. 10. The mixture containing 40 % bentonite saturated with 0.05 M NaCl solution shows the highest crack frequency. It is interesting to note that samples saturated with higher concentrated solutions develop less frequent cracks that however seem to have larger apertures.

Fig. 10. Evolution of aperture distributions with time as affected by bentonite content and lution chemistry.

For liner design it is also important to determine permeability and swelling potential for saturated conditions. While addition of silt or sand material to bentonite yields favorable mechanical properties and alleviates cracking potential under dehydrative conditions, there is a potential for increase in hydraulic permeability that could affect liner performance. To investigate effects of solution chemistry and sand content on saturated hydraulic properties we simultaneously conducted measurements with a flexible wall permeameter and volume change apparatus. Figure 11 depicts results for monovalent solutions.

Our data show that X-ray Computed Tomography is a powerful tool to visualize geometrical and topological properties of evolving desiccation crack networks. To really quantify and measure pore space attributes it is imperative to find a suitable procedure for image segmentation (binarization). The obtained parameters are crucial for performance based design

f economic and safe waste containment systems and are useful for modeling potential preferential flow and transport in cracked barriers. It is clear that more work is required to

shed experiments with different concentrated CaCl2 solutions to cover potential effects of divalent elect

so

o

optimize image analysis as well as to investigate effects of additional solutes and varying drying conditions. We fini

rolytes. In addition we are looking at different drying rates and potential amendments such as polyacrylamide (PAM) and polypropylene fibers that can be used to alleviate crack formation.

23

Fig. 11. Swelling potential (water ratios) and permeability of bentonite sand mixtures permeated with 0.5M and 0.05M NaCl solutions. References Revil, A., and Cathles, L. M. 1999. Permeability of shaly sands. Water Resources Research.

35:651-662. Gebrehawariat, K. 2005. Saturated permeability and volume change behavior of Na-bentonite -

sand mixtures, Masters Thesis, University of Idaho University of California, Davis, Hydrology (Dept. LAWR) Investigators: Jan Hopmans, Thomas Harter Microirrigation Evaluation: Microirrigation with fertigation provides an effective and cost-efficient way to supply water and nutrients to crops. However, less-than-optimum management

ing to ground water pollution if water and nitrogen pplications are excessive. The quality of soils, ground and surface waters is specifically

climatic regions where agricultural production occurs mostly by irrigation such as

princ inable agriculture are satisfied. Studies were conducted using an adapted

tools environmental effects. This software ackage can simulate the transient two-dimensional or axi-symmetrical three dimensional ovement of water and nutrients in soils. In addition, the model allows for specification of root

of water and nitrate availability etween irrigation cycles.

ne option for coping with the high soil salinity levels caused by saline, shallow ground water

of microirrigation systems may cause inefficient water and nutrient use, thereby diminishing expected yield benefits and contributavulnerable inin California. Robust guidelines for managing microirrigation systems are needed so that the

iples of sustaversion of the HYDRUS-2D computer model to develop irrigation and fertigation management

that maximize production, yet minimize adversepmwater and nitrate uptake, affecting the spatial distribution b Oconditions along the west side of the San Joaquin Valley is to convert from sprinkler or surface irrigation methods to drip irrigation. Experiments in commercial fields revealed that subsurface

24

drip irrigation of processing tomatoes is highly profitable under these conditions compared with other irrigation methods. The experiments also showed that little or no field-wide leaching occurred, based on the conventional or water balance approach to estimating leaching fraction (LF). Yet, soil salinity measurements showed considerable leaching around the drip lines. Actual leaching fractions could not be calculated because leaching fraction, soil salinity, soil water content, and root density all varied with distance and depth around the drip lines. Therefore, we conducted a numerical modeling study using the HYDRUS-2D computer simulation model to evaluate leaching with drip irrigation under saline, shallow ground water conditions for different amounts of applied water, water table depths, and irrigation water salinity. Results showed that LF values ranged from 7.7% to 30.9% as applied water amounts increased from 60% to 115% of the potential evapotranspiration (ETpot) for the ECiw = 0.3 dS m-1 irrigation water, even though the water balance method showed no leaching for applied water amounts equal to or smaller than

Tpot. The spatially-varying soil wetting patterns that occur under drip irrigation caused the Elocalized leaching, which was concentrated near the drip line. Utah State University, Logan, UT Investigator: Scott Jones The Utah State University contribution to W-1188 in 2007 addressed three research objectives listed below. These contributions included an International Space Station experiment focused on basic soil physics principles applied to long-term reduced gravity. An experimental forest site has been instrumented for improved prediction and understanding of snow melt and carbon dynamics in four common mountain vegetative species. Finally, ongoing work relating electromagnetic induction mapping to spatial soil properties is progressing with statistical methods being applied to improve the utility of this mapping approach Scientists Uncovering Challenges for Watering Plants in Space – CSA News Cover Story Our recent article in Vadose Zone Journal made the cover of CSA News (Fig. 12) with the ollowing citation, “Growing plants can be challenging under the best of circumstances, rimarily because the roots require a steady supply of water and oxygen. Too much water

ts. Potting soils have been designed to drain under Earth’s ravity, thereby avoiding aeration problems. Capillary forces act against gravity and retain water

ravitational force is reduced as is the case on the international space tation, capillary forces absorb all available water like a sponge. Maintaining plant health in the

hysics to understand the ffects of reduced gravity on water in potting soil. Results from the study are published in the

fpreduces the supply of oxygen to roogin smaller pores. When gsabsence of gravity is an important part of space research and future manned space travel to the Moon or Mars. Plants are important for psychological health, provide a fresh source of food, can recycle waste water and generate oxygen from carbon dioxide.

The study of water behavior in porous media in reduced gravity has been undertaken by researchers at Utah State University in cooperation with The University of Arizona, the Universities Space Research Association and the Ecole Polytechnique Federale de Lausanne in Switzerland. The NASA-funded research applied principles of soil peNovember issue of Vadose Zone Journal.

25

A key question asked is how water configures itself in porous media without the draining effect of gravity? Parabolic flights aboard NASA’s KC-135 and C-9 aircraft provided 20-second snapshots of reduced gravity for measuring the energy of water held in the porous media over a range of water contents. This key property is known as the soil-water retention function and provides a basis for designing irrigation or water control systems. Small experimental cells were developed to minimize the time required for establishment of equilibrium conditions because of the short duration of weightlessness.

The study demonstrated similar water retention functions and hydraulic conductivities in microgravity when compared to earth-based results, which bodes well for applying earth-based porous media hydraulic models. However, more detailed measurements revealed an unexpected distri

University in conjunction with the Space Dynamics aboratory to investigate the distribution of water in microgravity on the international space

statio

bution of water in microgravity. This discovery suggests that highly localized non-uniform water contents may arise during addition or removal of water. This may lead to potential problems with oxygen supply to plant roots within zones of higher water content. This problem is a result of hysteresis that is inherent in the soil-water retention function and further study is needed to determine the extent and longevity of this phenomena.

Research is ongoing at Utah State L

n. Scientists are currently watching the progress of an experiment on the International Space Station conducted together with Russian scientists. Their efforts will facilitate design of root modules for vigorous and reliable plant growth in space and for future manned travel to the moon and Mars.” Optimization of Root Zone Substrates ISS Experiment The Optimization of Root Zone Substrates (ORZS) experiment began in 2001 with the objective of de

e project engineer found a way to res

iffusion data were significantly different on the draining path as compared to arth-based measurements, which occurred in the finest pore-sized media. This puzzling result

failed, so we are not confident about the

veloping an automated oxygen diffusion measurement system for testing water retention and gas diffusion in 3 different particle-sized media. This would all take place in microgravity aboard a space ship or station. After years of design, construction and code development, in May 2007 the experiment launched to the International Space Station (ISS) and began testing July11, 2007. The experiment was fully automated once initiated by cosmonauts. The planned experiment went according to plan for about 3 weeks before a space shuttle docked to the ISS. At this point an unplanned shutdown of the experiment occurred, which left the system in limbo for several weeks while we worked to understand what happened. Th

tart the experiment at the point we left off, but during the down time the pressure regulator apparently ‘glued’ itself shut preventing us from proceeding with the remainder of the experiment. We obtained approximately 75 percent of the first series of desired experimental data. A replicate series was planned to follow the first. From the data obtained, we found that the water retention measurements were virtually identical to measurements made on Earth. By contrast, oxygen dEunfortunately began showing up just before the systemresults at this point. A repeat experiment is planned for the summer of 2008 where we hope to obtain definitive data regarding oxygen diffusion and confirm our findings with respect to water retention.

26

Impact: CSA News is distributed monthly to 11,000 members worldwide. The ORZS experiment provided insight into unexpected gas diffusion behavior in microgravity while confirming the validity of earth-based water retention measurements for use in microgravity. Fig. 12. Decembpplies soil physics to liquid behavior in porous media under a variable gravity environment.

regon State University, Corvallis, OR

er 2007 cover of CSA News highlighting our Vadose Zone Journal article which a O

vestigator: Maria Dragila

his project is part of a larger effort focused on elucidating the mechanisms that govern the ovement of liquid and solutes when cracks are present in a soil profile. The 5-year project is udying the mechanism of: (1) convective thermal venting of soil cracks and open fractures; and ) the effect this thermal venting has on enhanced evaporation from the vadose zone and on

recipitation of salts along the walls of soil cracks and fractures. The project is comprised of four istinct activities:

In Tmst(2pd

27

(A) Theoretical approach is used to define the bounds of the system: (1) quantify the

sulting from convective venting; and (3) quantify the rate and maximum amount of

recipitated salts expected to accumulate onto the surface of crack/fracture walls. ate four important questions: (1) What is the

xpected evaporative flux rate from a fractured matrix as a function of matrix properties and w much salt is expected to be deposited on fracture walls as a

unction of time, for different matrix properties and climatic conditions? (3) What is the impact

cell to determine whether the convective pattern is a plane-circular cell or sipho

lled nature of labor

f field and l

far greater than those

ent, and providing a concentrated saline plume that may migrate to the water table. eing able to quantify the salt redistribution will permit more accurate quantification of

minimal conditions necessary for open (air-filled) cracks to vent convectively; (2) quantify the relationship between matrix properties and the redistribution of solutes inside the matrixrep

(B) Numerical work is used to investigeclimatic conditions? (2) Hofof this salt mechanism on salt dynamics at the basin scale? And, (4) what is the potential impact on salinization of a phreatic aquifer by the presence of precipitated salt on fracture walls?

(C) Field work is used to determine if convective venting indeed exists in natural fracture systems. Field data is used to test the validity of the theoretical construct, specifically quantitatively determine the time-of-day and climatic conditions that trigger convective venting, map a convection

n-style (convective patterns control the flux venting efficiency), and determine if convection cells are temporally and spatially stable or if they fluctuate rapidly.

(D) Laboratory work is used to accurately quantify the net amount of deposited salt, the decrease in evaporation rate and salt deposition rate as the salt crust thickens, and the change in permeability of the matrix as salt is deposited. Because of the highly contro

atory work, it will be used to test the theoretical constructs and also to refine the numerical models. Project Background: Soil cracks can significantly enhance the amount of evaporation from agricultural soils and fractured-rock vadose zones. The understanding that net evaporation was greater from cracked soil than from soil without cracks evolved from an extensive series o

aboratory experiments in the 1970’s (e.g., Ritchie and Adams, 1974). However, at the time, and since then, no mechanisms were suggested for the observed enhanced evaporative flux, limiting our ability to predict flux quantities beyond the specific field conditions tested. As part of this project, we proposed a mechanism for enhanced evaporation consisting of thermally driven convective venting of the fractures occurring at night when soil at depth is warmer than near-surface soil. Convective venting leads to evaporative fluxes that can be

driven by diffusive venting. Recent work has demonstrated that this enhanced evaporative flux, caused by the presence of cracks, may be responsible for the formation of salt crusts along fracture walls in semi-arid areas (Weisbrod and Dragila, 2006). During precipitation events, these salts may dissolve and move further down the soil profile, affecting soil chemical developmBevaporative fluxes, infiltration rates, and solute transport rates important for field-scale water balance and contaminant migration calculations. Project work: During 2004, we investigated the theoretical constraints of the mechanism and tested the concept of nighttime venting. (Dragila, 2005a, 2005b; Weisbrod and Dragila, 2006).

During 2005, we began development of a numerical model to investigate the redistribution of solutes within the matrix caused by evaporation and convective venting, and the proportion of downward salt flux expected for different matrix permeabilities. (Dragila 2006a, 2006b).

28

During 2006, we instrumented a field site comprised of a natural fracture that was open to the surface. The fracture was in a chalk rock, which has the advantages of permeability similar to that of soil with high clay content but does not collapse or move with rain events. Relative humidity and thermocouples were installed to a depth of 120 cm and data collected continuously at 20-minute intervals. Convection cells were clearly seen to form within the natural fracture. Initiation (at dusk) and cessation (at dawn) of convective venting matched theoretical results. Relative humidity data showed that convective venting does dry out the fracture. Convection cell properties are described in the 2006 report, which includes the shape and wavelength of convection cells, seasonal stability of cells, relationship of convective venting to thermal profile, nd timing at which venting starts and stops each day.

Havin

pact of venti

the impact that this pore clogging has on e permeability of the matrix.

al model for salt formation is that nighttime venting drives evaporation form

ores, then we would not expect rock

bility and spatial dimension of the convection cells, the cause of the sm

a Progress in 2007

g proven the existence of convective venting in natural fractures (Ref: 2006 Project Report) leads us to the next higher level question: How important is this venting process to the function of natural soil systems? We are especially interested in quantifying the im

ng on the transport, exchange and redistribution of mass and energy. We have identified five sub-processes that we posit could be significantly affected by convective venting: (1) redistribution of salinity within the profile; (2) vapor loss from the profile; (3) heat loss from the soil profile and net heat loss from the soil surface; (4) extension of soil cracking; and (5) exchange of gasses with the atmosphere. The impact of convective venting on these processes will be investigated during the remainder of our project period.

During 2007 the team began to work on the first of the five processes listed above, that is, understand how nightly convective venting drives redistribution of salt within the profile. There are many components of this process that are not well understood. During 2007 we focused on the effect of pore clogging during salt precipitation andth

The conceptuthe fracture face, which in turn drives soil solution from the matrix towards the fracture face. As water evaporates, saline concentration increases until salts precipitate. Our laboratory experiments, and work by other groups, unmistakably show that as salt precipitates on the fracture wall the evaporation rate decreases significantly. Although the mechanism causing this decrease is not well understood, possible mechanisms are osmotic pressure, internal-pore clogging (reducing permeability) and surface clogging (reducing evaporation surface area).

This year we focused on the mechanism of internal pore clogging by the salt precipitation process. Specifically we aimed to determine if salt precipitates on the smaller pores or the larger pores. For example, if salt precipitates and clogs the smaller p

permeability to be significantly affected since permeability is dominated by the larger (connected) pore sizes. There is a second reason for investigating the role of pore clogging. Both in-the-field and in-the-laboratory experiments demonstrated that salt precipitation on the surface is patchy, both at large (decimeter) and small (millimeter) scales. While the cause of the large-scale patchiness may be the sta

all-scale patchiness is not known and we hypothesize that it is associated with pore-size heterogeneity.

To investigate the role of pore-size heterogeneity on salt deposition we initiated a series of small-scale experiments using a CT scanner. The following questions were asked: What is the spatial distribution of salt within the matrix? Is salt location correlated with pore size? Is

29

permeability affected by salt deposition? Is the spatial distribution of salt patchiness associated with pore size heterogeneity?

The first series of experiments were completed in 2007. Small (2 cm diameter x 5 cm long) cylinders of Berea sandstone were saturated with NaI and allowed to evaporate. Cores were scanned in the CT before, during and after evaporation. Cores where then vacuum dried and air permeability was tested using a Klinkenberg method.

Further experiments are planned for 2008 to investigate two (2) different salt species and two (2) rock permeabilities: chalk (1 md) and sandstone (100 md). Results The key result of this investigation is that salt is depositing in the smaller pores and that surface precipitation occurs over the area of small pores. Thus, we conclude from this first series of exper

As time progresses and air entry into the larger pores occurs, then evapo

implies that salt precipitation may significantly reduce the permeability of the small pore but leave the large pore network open to participate in air movement. Thus, while the

rocesses into numerical models that will be used for redicting the fate and transport of either vapor or gas (i.e., greenhouse and agriculturally

es) between soil systems and the atmosphere. Most predictive models do not

iments that the surface patchiness is associated with the location of smaller pores. It appears that since air-entry occurs into the larger pores first, the smaller pores serve as the connection between the supply of internal matrix pore water and the evaporation surface. During early stages, water evaporates from both large and small pores at the surface, and salt deposits everywhere along the surface.

ration and salt precipitation occurs only from the smaller pore system. The solution that is located in the larger pore network is moved to the smaller pores and from there taken to the evaporation surface. This is a very significant finding with implications not only for salt precipitation, but also for gas exchange.

Implications Itnetwork,water permeability at higher tension may be reduced by this evaporation and salt precipitation process, the air permeability may be unscathed, permitting continued gas exchange between the matrix and the atmosphere. Impact: Our 2007 research project advanced our fundamental understanding of the mechanisms that control evaporation and salt precipitation in porous media. We have found that internal matrix micro-heterogeneity (distribution of pore sizes) poses significant controls on the internal distribution of salt precipitation, the distribution of clogged pores, the distribution of patchiness on fracture surfaces, and impacts air and water permeability values.

An important implication of our 2007 work is the realization that we need to incorporate a better understanding of pore clogging ppimportant gassinclude pore clogging as part of the evaporation algorithms, nor do they include the effect of pore micro-heterogeneity on the enhancement of the evaporation process.

This project continues to quantify a mechanism that we propose is very important in calculations of land-atmosphere dynamics, water and gas cycles, ecosystem stability, and heat fluxes.

30

California State University, Fresno, CA Investigator: Zhi Wang Parameterization of a fractured hardrock aquifer in western foothills of the Sierra Nevada, California This study was carried out at the field scale to characterize groundwater flow in the fractured granite aquifers in the foothill areas of western Sierra Nevada, Madera County of California. Model selection and parameterization were conducted to obtain the “best” values of Trans

ater drawdown relations in the area. Theoretical feasibility studies of the aquifer-testing methods were first conducted, with the

onclusion that the constant-drawdown pumping method, as compared to the constant-discharge nd step-drawdown methods, was more appropriate for the fractured aquifer, which did not cause

ischarge from the local fractures. Lineaments studies ere carried out using Digital Elevation Models and Geographical Information System (GIS)

e directions and depths of the major fracture sets in the region. The ultiple-borehole tests were conducted and ran for up to 34 days, involving two test wells and

near flow patterns) were assumed and tested using the field experimental data (Fig.

misivity (T) and Storativity (S) of the specific aquifer through long term pumping tests, which can be used to predict the long-term well yield (pumping rates and volume) versus groundw

cathe wells to dry out due to limited water dwsoftware to delineate thm17 observation wells at a 540-acre study area enclosing Madera Ranch Quarry. Two hypotheses (radial or li13).

Fig. 13. Hypotheses of flow to a well in a fractured aquifer (modified from Karasaki, 1987).

The Theis solution (Theis, 1935) of the radial flow to a well was used:

W(u)T4π

Qt)s(r, =

du;u

e W(u)u−∞

∫=υ Tt4

S ru2

=

31

where, s is the drawdown, Q is the discharge, r is distance, t is time, W(u) is the well function. W(u) can be expanded to the following convergent series:

...4!4

u3!3

u2!2

u -u u ln - 0.577216- W(u)432

+⋅

−⋅

+⋅

+=

Constant Head Pumping Test: Jacob and Lohman (1952, in Lohman, 1979) derived equations for determining T and S from tests in which the drawdown is constant and the discharge varies with time,

tlog1/Q)/(s42.3T

10w ∆∆=

π

ay be determined within the data region of the straight-line plot from and S m

⎥⎦

⎤⎡=

/Q)(sS

w1-⎢⎣∆ /Q)(s

log

t/rT 2.25

w10

w

where, T is transmissivity low rate (L3T-1) as a function of time (t), rw is the radius of the well (L), S is the storage coefficient (dimensionless), and sw is the difference in head (L) between the point of discharge on the wellhead and the aquifer at the beginning of flow.

Variations in the results of d atterns adial or linear) and the model parameters (T and S) were scale-dependent, and the “scale

racterize a large area of the fractured ardrock aquifer, at least 15 days was required to get a realistic trend line of drawdown versus

time. The long term pumping-test results also indicated tha vation wells as

far as 4,000 feet radius can still be influenced by linear flow intersecting the pumping well, but

References Karasaki, K., 1987, Well test analysis in fractured media: Univ. of California, Berkeley, Ph.D.

dissertation, 239 p. ohman, S.W. 1979. Ground-water hydraulics: U.S. Geological Survey Professional Paper 708,

Theis, C. V., 1935, The relation between lowering of the piezometric surface and rate and duration of discharge of a well using groundwater storage: Transactions of the American Geophysical Union, v. 16, p. 519-524.

2

(L2T-1), Q(t) is f

ifferent pumping tests suggested that both the flow p(reffect” is related to heterogeneity within the aquifer, not to the testing methods. The long-term pumping tests at two wells on the site suggested that, to chah

t drawdowns at obser

the influence radius (with > 0.5 ft drawdown) did not exceed 5000 feet. Models that assumed uniform aquifer properties can not be applied to the site, although some generalization can be made.

L70 p.

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Montana State University, Bozeman, MT Investigators: Jon Wraith, Brian McGlynn

flow generation. These integral soil physical processes are generally treated only super

ocal-Scale Controls, and their Variability, for Soil Water and CO

Watershed-scale processes represent an aggregate of smaller-scale properties and processes. Many of these involve mass and energy interactions with, and/or in, soils. For example, soil physical properties are critical to the evolution and transport of water and greenhouse gases, including CO2. Water flow within and across soils drives catchment water storage and stream

ficially (sometimes not at all) by those working at larger scales. Our knowledge of how these translate into emergent watershed processes is limited. Measurement scales (space, time) complicate quantification of ecosystem carbon exchange and the redistribution of water. We seek to address these limitations in the following projects. L 2 Dynamics in a Forested Watershed Evaluating how, and how well, instrumented flux towers integrate spatially- and temporally-variable soil processes is important to understanding mass and energy exchange processes at

driven processes that will enhance understanding and prediction of landscape water and CO2

inforTend out 2.5 hours north of Bozeman, MT (Fig. 14).

levation ranges from 6,000 to 8,000 feet, and dominant vegetation is lodgepole pine. During ugust, 2007 we instrumented a monitoring site which we consider as representative of the ajor upland landscape and vegetation in the watershed. The site is about 75 m downslope, and

riance flux tower. We installed a 4 x 4 grid of soil its, 24 m on a side. At each node, we established a depth array of automated (datalogger) TDR

50 cm), and CO2 concentration (Vaisala GMM221 arbocap) at 5, 10, and 50 cm. Soil gas diffusivity values will be measured on intact cores, and

landscape scales. Our goal is to evaluate critical relationships, seasonal thresholds, and event-

dynamics. We hope to determine which are most critical, how they are linked, and how they can m large-scale models. We are working in the Stringer Creek sub-catchment of the USFS erfoot Creek Experimental Forest, ab

EAmupwind (prevailing) from a 40-m eddy covapprobes, thermocouples (both at 5, 10, 20,Cthus the measured concentration profile will facilitate use of the gradient method to predict CO2 efflux. We will couple belowground measurements with surface flux (portable chamber, tower) measurements. The smaller-scale/fundamental process analyzed at this location will be integrated with larger-scale studies conducted by other collaborators at MSU, Utah, Idaho, and elsewhere. Watershed carbon distribution and flux across environmental gradients The concept of biogeochemical similarity, related to hydrological similarity, has been identified as a powerful tool in understanding the spatial patterns of biogeochemical processes. Our

search will test the applicability of this concept for soil respiration and DOC export and will

-order controls on soil CO2 production and surface efflux. This field-derived

reidentify the critical set of measurements necessary to quantify the spatial and temporal variability in the firstinformation will then inform and constrain our model that simulates the variability of these parameters through space and time. These spatially distributed data are central to simulation of the production and transport of soil CO2. By combining extensive field measurements and quantification of the factors influencing soil respiration such as soil temperature, soil moisture,

33

soil fertility, and climatic variables with numerical modeling techniques, this work will provide a way forward for measuring and modeling the extensive but poorly understood exchange of water, C, and energy between soils and the atmosphere. The objectives of this research are (1) to quantify CO2 efflux and to develop and apply a model of catchment respiration, incorporating soil air pCO2, vertical soil water transport of dissolved CO2, and surface CO2 efflux, (2) to explore the extent to which topography can be used to explain the variability inherent in the factors driving respiration, and (3) to quantify the topographic controls on the distribution of soil C in the watershed and link C accumulation in the landscape, DOC transport, and stream DOC export at the watershed scale. This work will provide empirical information and the foundation for development and application of a framework for understanding the spatial and temporal variably of soil respiration and resultant soil air CO2 concentration, atmospheric exchange, and streamwater C export.

Some of the infrastructure and data resources available in the Stringer Creek watershed, Tenderfoot Creek Experimental Forest, Montana to address our objectives include: 2 full eddy covariance and energy balance flux towers from a riparian meadow and above a lodgepole pine

rest, 4 real-time data stations located in upland and riparian settings log soil CO2 d 20 cm), 75 wells and

foconcentrations, soil moisture, and soil temperature at two depths (5 anpiezometers with GW level loggers, 124 soil gas wells (5, 20, and 50 cm) to measure soil CO2 concentrations, 62 soil respiration plots to measure soil surface CO2 efflux, 16 soil water tension lysimeters (8 riparian, 8 hillslope), 2 permanent flumes to gauge streamflow, logging stream electrical conductivity and temperature probes distributed across 3 sites, Two satellite linked real-time snow survey telemetry (SNOTEL) stations (2259 m and 1996 m), 4 logging snowmelt lysimeters, IKONOS remote sensing coverage, ALSM topography and vegetation data (<1m resolution), and forest biometry measurements over time. Hydrological linkages between landscapes and streams: Transferring reach and plot scale understanding to the network and catchment scales Our objective is to combine novel landscape and topographic analysis techniques with plot and reach-scale field research to provide context for field investigations, to develop a method for scaling process understanding to the catchment scale, and ultimately to transfer this understanding to other catchments for comparison and catchment classification.

How can plot-scale measurements of the hydrologic processes that link uplands to streams be scaled up to whole catchments? How can reach-scale measurements of groundwater-surface water mixing in riparian and hyporheic zones be scaled up to entire stream networks? How can we transfer our small catchment scale understanding to larger portions of the landscape or other catchments? These questions highlight our inability to transfer our understanding of hydrological processes studied at the plot or reach scale to larger catchments. These questions beg integrated, multi-scale approaches that combine landscape level topographic analysis, process-based field investigations, and catchment-scale integration to identify the factors controlling the hydrologic connectivity between source areas generating runoff and the flow paths that link source areas to streams. In this project we seek to address these questions using a combination of 1) spatially distributed recording groundwater wells (140), 2) recording soil water content nests (six nests with 2 depths), 3) natural tracers and source water mixing models applied to high spatial and temporal resolution groundwater, soil water, and streamwater sampling across 6 watersheds, and 4) new terrain analysis algorithms and combined analyses (1-4) to scale and transfer plot and point scale observations to the watershed and landscape scales. Our methods combine landscape

34

analysis of sub-meter ALSM topography data and field scale investigative approaches. The overall approach is iterative, in that the landscape analysis both guides the selection of field sites for the experimental studies and provides the basis to scale up the results of these studies to the network/catchment scale. The central concept of this research objective is that landscape nalysis can be used to link plot and reach scale hydrological dynamics with

Experimental Forest, Little Belt Mountains,

Fig. 14. The instrumentation of the Stringer Creek sub-catchment. Impacts: We are investigating the critical drivers and relationships that govern catchment water, carbon, and gas behavior and movement; how (where, when, how much) these vary on the landscape; and how they are integrated by larger-scale measurements such as flux towers and stream gauges. Additionally, this objective will provide for a better understanding of the watershed and stream network controls on the sources generating runoff and the role of stream network in modulating the hydrologic and solute/isotopic signals measured at the watershed

atopographic/geomorphic controls. This research is conducted in 7 nested catchments ranging in size from 300 ha to 22 km2 in the Tenderfoot Creekcentral Montana (Fig. 14).

35

outlet across watersheds of variable structure and increasing size. Further, this research willaddress the landscape structure controls on riparian buffering of the quantity, quality, and timof water delivered from alpine headwater watersheds.

: Montana is conducting research that will fill critical gaps in our knowledge ing emerging issues of water availability in space and time and watershed

lling stream biogeochemistry, carbon cycling, global change ecology, and greenhouse gas issions.

ing

Outcomeconcern processes controem

36

OBJECTIVE 2: To develop and evaluate instrumentation and methods of analysis for characterizing mass and energy transport in soils at different scales Desert Research Institute, University of Nevada, Las Vegas Investigators: Markus Berli (DRI, Visitor), Todd Caldwell (DRI), Karletta Chief (DRI, Visitor), Scott Tyler (UNR), Wally Miller (UNR), Michael Young (DRI), Jianting Zhu (DRI) Nevada has been working to develop methodologies to characterize vadose zone heterogeneity and variability in soil hydraulic properties and processes through the development of portable infiltrometer arrays, fiber optic distributed temperature sensing cables, improved analysis of dual-probe heat pulse data, and development of an air permeameter for estimating hydraulic conductivity.

In the first study, gradients in soil physical and hydraulic properties were characterized from canopy to interspace in the Mojave Desert using a 1.5 m long array of mini-disk tension infiltrometers (MDTI) and typical physical characterization techniques. In this study, different averaging techniques were used to upscale the point-scale measurements to the field scale, including arithmetic, areal weighting, and inverse modeling. The effective parameters are then tested in larger-scale water balance simulations to examine water and nutrient movement and uptake, as functions of proximity to shrubs. The study, still ongoing with results expected in early 2008, was conducted under typical environmental conditions at the Mojave Global Change Facility (MGCF), located at the Nevada Test Site.

Nevada’s researchers have been examining the application of Raman Spectra Fiber Optic Distributed Temperature Sensing (DTS). Nevada currently maintains a DTS system with capacity for measuring up to 8 km of fiber optic cable temperatures with spatial resolution of ~1 m and temperature resolution of better than 0.05 °C. Nevada has installed fibers in estuaries (Moffet et al., 2007), beneath snow covered areas to monitor snow melt dynamics (Tyler et al., in review) and most recently buried beneath agricultural fields to monitor both soil temperature, and to infer soil moisture and infiltration (Suarez et al., 2007). Currently 2 km of fiber optic cable are buried 15 cm below the soil surface at two experimental plots in central Nevada to monitor seedbed temperatures and, during irrigation, infiltration variability.

In the third study listed under this objective (Young et al., 2007a), Nevada scientists in collaboration with researchers in Washington State, examined three methods of analyzing dual-probe heat-pulse (DPHP) data for estimating volumetric water content of near-surface materials where diurnal temperature variations can approach ±20°C. The three methods of analyzing thermal responses include: (i) the single-point method (SPM); (ii) a method that uses a Levenburg–Marquardt optimization of thermal conductivity, volumetric heat capacity, and drift in ambient temperature with subsequent calculation of water content (LM-Uncorrected); and (iii) an expansion of LM-Uncorrected method that incorporates temperature dependencies of soil thermal conductivity, and optimizes on volumetric water content, apparent needle spacing, and drift in ambient temperature during the measurement (LM-Corrected). Ambient temperature measurements were made with either a soil thermistor installed away from the DPHP sensor (SPM), or from the temperature response of the DPHP sensor itself (LM-Uncorrected and LM-Corrected). Methods were tested using measurements made in April and August 2006 from

37

sensors installed at ground surface in the Mojave Desert. The SPM results showed that large (summertime) diurnal temperature variations led to significant oscillations of water content, recorded as high as ±0.10 m3 m-3. The LM-Uncorrected method showed a significant reduction in water content oscillations, but variations were still large. The LM-Corrected method showed that the time series of water content was significantly smoother than uncorrected water contents (i.e., ±0.005 m3 m-3 in August). DPHP-derived water contents were shown to compare favorably to data from water content reflectometers installed nearby. The results show that soil water content estimates from the LM-Corrected method were substantially less affected by ambient temperature variations.

Finally, air permeability (ka) is a viable alternative to water- and texture-based methods to rapidly map saturated hydraulic conductivity (Ksat). Previous research established a correlation between ka and Ksat for agricultural soils based on ex situ measurements. The ability to measure this important hydraulic property without the use of more cumbersome and time-consuming direct methods may provide a practical approach to generate more complete data to describe hydrologic conditions. The Soil Corer Air Permeameter (SCAP), a field-based air permeameter suitable for use in gravelly desert soils (Chief et al., 2006) is compatible with a standard soil corer to facilitate insertion into desert soils and also employs digital components to measure flowrates under low-pressure gradients to improve accuracy, ease of use, and portability. SCAP allows for the extraction of undisturbed soil samples for laboratory analysis, providing direct comparisons of ka with other soil physical and hydraulic properties. The applicability of a regression equation to estimate Ksat from field-measured ka using SCAP was examined in unburned and burned soils. Ex situ field ka and laboratory Ksat measurements were compared and air to water permeability (ka/kw) ratios were calculated to determine structural changes due to water saturation. For soils that could be extracted with minimal structural changes, a correlation between in situ ka and Ksat was found and the correlation was in reasonable agreement with previously published results. In addition, the changes in permeability due to fire in woodland-chaparral and coniferous soils was characterized (Chief et al., 2007a). Results show ka and Ksat measurements for unburned and burned soils were within the 95% confidence intervals of a ka-Ksat regression developed for agricultural soils. However, correlations for in situ ka measurements in some burned soils showed a decrease in accuracy and may be attributed to soil anisotropy (Chief et al., 2007b). A three-dimensional steady-state finite element air flow model was developed using FEMLAB 3.0A to consider the effects of anisotropy on in situ ka measurements. Results show that anisotropic conditions can introduce an error as high as a factor of 2 especially for air permeameters with high diameter to height (D/H) ratios; however, the error is much smaller than the anisotropy ratio. If anisotropy is important to characterize, it was shown that paired measurements of in situ and ex situ ka can be used to infer the anisotropy ratio. This approach is more sensitive for larger D/H ratios, and when horizontal permeability is lower than vertical permeability. Field application of this method showed qualitative agreement but anisotropy alone was not able to fully explain the difference between in situ and ex situ permeability measurements.

The study by Zhu and Young (2007a) is an integral part of a larger effort to quantify the water budget of the alluvial and carbonate aquifers in the Great Basin area of the U.S. Here we developed an approach to quantify the sensitivity of ground-water discharge by evapotranspiration (ET) to several input variables. The objectives of this study are three-fold: 1) to investigate uncertainty associated with estimates of annual ground-water discharge from 12 valleys (30 sub-basins in total) for the study area, 2) to quantify sensitivity of ground-water

38

discharge to three relevant input categories (ET rates of all individual ET units, areas associated with the ET units, and precipitation rates), and 3) to identify the most sensitive input variables that would help facilitate future data collection efforts to further reduce uncertainty. Monte Carlo simulations were conducted with input parameters taken from randomly generated values for each sub-basin based on estimated statistics and assumed probability distributions of the input parameters. The results show that uncertainty of annual ground-water discharge is augmented in relation to the coefficients of variation (CVs) for the input parameters. The results illustrate that in general the uncertainty of ET rates is the most significant contributor to the uncertainty of ground-water discharge. The sensitivity analysis indicates that, while as many as 630 input parameters potentially contribute to the calculation of total annual ground-water discharge, a selection of seven parameters could be used to develop an accurate regression model (r > 0.98). Both regression coefficients and standardized regression coefficients are quantified and discussed in the context of estimating ground-water discharge. The standardized regression coefficients are useful in ranking the relative importance of their corresponding variables because they account for contributions in terms of both magnitude and variability of individual input parameters. Results show that the variability of ET rate for moderately dense desert shrubland contributed to over 78% of the variance in total ground-water discharge, by far the largest single source of uncertainty in this study. These results point to a need to better quantify ET rates in this ET unit to reduce overall uncertainty in estimates of ground-water discharge. Washington State University, Pullman, WA Investigators: Markus Flury, Joan Wu Fate and transport models neglecting colloid-facilitated transport often underpredict contaminant movement. Long-term predictions of contaminant fate and transport as well as risk assessment rely on an accurate representation of subsurface processes, and in the case of strongly-sorbing contaminants, need to consider mobile colloids as potential contaminant carriers. We reviewed the current knowledge and recent developments of modeling colloid-facilitated contaminant transport in the vadose zone (Flury and Qiu, 2007). Modeling of colloid-facilitated contaminant transport involves various interactions, including colloid attachment/detachment to/from the solid matrix and the air-water interface, contaminant adsorption/desorption to/from colloids and transport with mobile colloids, and contaminant adsorption/desorption to/from the solid matrix. Most of these processes in colloid-facilitated contaminant transport models have been described by first- or second-order kinetics. The unique feature of the vadose zone is the presence of an air-phase, which affects colloid and contaminant transport in several ways. Colloids can be trapped in immobile water, strained in thin water films and in the smallest regions of the pore space, or attached to the air-water interface itself. The modeling of colloid-facilitated contaminant transport in the vadose zone has mostly been theoretical, and tested only with column experiments; field applications are still lacking.

Accurate prediction of evaporative water loss from dryland agricultural soils requires knowledge of diffusive resistance. We experimentally determined the effective vapor diffusion coefficients and the diffusive resistances for water vapor through wheat residue layers. A laboratory diffusion chamber was designed to investigate the effects of wheat residue type (straw vs chaff), residue amount, and residue orientation (horizontal vs vertical straw) on vapor

39

diffusion. The diffusion chamber consisted of two well-stirred chambers, separated by a residue layer. The diffusion equation was used to obtain the effective diffusion coefficient from the measured data by inverse modeling. Results showed that for both straw and chaff residues, increasing the amount of residue did not necessarily decrease the effective diffusion coefficient, but did increase the diffusive resistance. For the same amount of residue, chaff had a lower effective diffusion coefficient than straw, but the diffusive resistances were similar. The factor affecting the diffusive resistance the most was the thickness of the residue layer: the thicker the residue layer, the larger the diffusive resistance.

A principal task of evaluating large wildfires is to assess fire’s effect on the soil in order to predict the potential watershed response. Two types of soil water repellency tests, the water drop penetration time (WDPT) test and the mini-disk infiltrometer (MDI) test, were performed after the Hayman Fire in Colorado, in the summer of 2002 to assess the infiltration potential of the soil (Lewis et al., 2007). Remotely sensed hyperspectral imagery was also collected to map post-wildfire ground cover and soil condition. Detailed ground cover measurements were collected to validate the remotely sensed imagery and to examine the relationship between ground cover and soil water repellency. Percent ash cover measured on the ground was significantly correlated to WDPT and the MDI tests. A spectral unmixing algorithm was applied to the hyperspectral imagery, which produced fractional cover maps of ash, soil, and scorched and green vegetation. The remotely sensed ash image had significant correlations to both water repellency tests. An iterative threshold analysis was also applied to the ash and water repellency data to evaluate the relationship at increasingly higher levels of ash cover. Regression analysis between the means of grouped data: MDI time vs. ash cover data and vs. Ash MTMF scores yielded significantly stronger relationships. From these results we found on-the-ground ash cover (> 49%) and remotely sensed ash cover (> 33%) to be indicative of strongly water repellent soils. Combining these results with geostatistical analyses indicated a spatial autocorrelation range of 15–40 m. Image pixels with high ash cover (>33%), including pixels within 15 m of these pixel patches, were used to create a likelihood map of soil water repellency. This map is a good indicator of areas where soil experienced severe fire effects—areas that likely have strong water repellent soil conditions and higher potential for post-fire erosion. Impact: Much progress has been made in the understanding of colloid and colloid-facilitated contaminant transport in the vadose zone in recent years, and this understanding has led to improved conceptual models to describe the various processes involved in colloid-facilitated contaminant transport. A general conceptual model for colloid-facilitated contaminant transport is complex, as it builds on models for water flow, contaminant and colloid transport, and in addition, includes colloid-contaminant interactions. Colloid transport itself in the vadose zone, particularly under conditions unfavorable for colloid attachment, is still not well understood. Moving air-water interfaces and their effect on colloid mobilization and transport are also not well understood. Consequently, a theory for colloid transport under conditions typical for the vadose zone still remains to be developed.

Residue management in the dryland farming areas, such as the Inland Pacific Northwest, is economically and environmentally relevant. Seed-zone moisture preservation in fallowed fields during the hot dry summer months is of utmost importance allowing for planting of winter wheat and timely establishment of stands. Many farmers are interested in practicing chemical summer fallow, where weeds are controlled with herbicides and no tillage is used, in lieu of tillage-based summer fallow that is prone to wind erosion. Through careful experimentation, we provide evidence of reduced vapor transport by residue covers, and we quantified the diffusive

40

resistances of different wheat residue layers. The reduced vapor transport leads to a temporary reduction of evaporation; however, whether it also leads to an overall reduction of evaporation during an extended period depends on the frequency and amount of rainfall. Numerical modeling of water and vapor flow allows addressing these questions, and the diffusion resistances presented in this paper provide an important parameter for such models.

Immediate post-fire measurements of ground cover and water repellency indicated that ash cover, both measured on the ground and remotely, was the variable most significantly correlated to strong water repellency after the Hayman Fire. Discovery of such significant correlation relationship allowed for mapping strong water repellent soil conditions. These results, combined with other information typically available in a post-fire situation, such as burn severity, soil characteristics, and slope, increase the ability to examine the potential for post-fire runoff and erosion. The study by Lewis and colleagues was among the first efforts examining the use of hyperspectral imagery as a potential tool for determining post-fire soil water repellency. University of Wyoming, Laramie, WY Investigator: Thijs Kelleners An electric circuit model was developed for the Hydra probe sensor. These sensors are attractive for soil physics research because they are able to measure real permittivity, imaginary permittivity and temperature in the same soil volume. The real permittivity can be converted into soil water content by using a soil-specific calibration. The imaginary permittivity can be converted into bulk soil electrical conductivity using:

0"εωεσ r=

where ω=2πF is the angular frequency (with F being the frequency), is the relative imaginary permittivity, and

"rε

0ε is the permittivity in vacuum (8.8542×10-12 F/m). Real permittivity

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Fig. 15. Theoretical and calculated real (left) and imaginary (right) permittivity.

The electric circuit model contains 7 physically based parameters whose values may be optimized to improve the goodness of fit between theoretical and calculated real and imaginary permittivities. The result of such an optimization for a single sensor is given in Fig. 15. The performance of the factory calibration is also shown.

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In a separate study, we are upgrading a state-wide soil moisture network for the WY state climatologists office. This sensor network consists of 18 sites fitted with Campbell Scientific CS630 water content reflectometers. We are calibrating these sensors in the laboratory for the different soil types. Simultaneous measurements with a TDR100 and a Hydra probe sensor will yield a comprehensive data set that can be used to assess the quality of the reflectometer soil water content predictions. USDA-ARS, Soil and Water Management Research Unit, St. Paul, MN Investigator: Tyson Ochsner Accomplishment: Developed new method for in situ monitoring of soil thermal properties and heat flux during freezing and thawing.

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When soil freezes or thaws, latent heat fluxes occur and conventional methods for monitoring soil heat flux are inaccurate, often wildly so. This prevents the forcing of surface energy balance closure that is used in Bowen ratio flux measurements and the assessment of closure that is used as a check on the accuracy of eddy covariance measurements. We hypothesize that heat pulse sensors can be used to obtain accurate measurements of apparent thermal conductivity (λa) and apparent volumetric heat capacity (Ca) which, together with soil temperature data, will permit accurate monitoring of soil heat flux under freezing and thawing conditions. Wintertime apparent thermal properties were monitored in situ using heat pulse sensors and independently predicted using a theoretical model. The measurements and the model both showed that for temperatures between -5 and 0°C λa and Ca were strongly temperature dependent, varying more than two orders of magnitude (Fig. 16). This temperature dependence is primarily the result of latent heat Fig. 16. February and March 2007 soil temperatures at 2.5 and 5 cm depths under soybean residue in field G19 (top panel). Measured apparent heat capacity at 2.5 cm depth and apparent thermal conductivity at 5 cm depth (bottom panel).

42

transfer processes. Good agreement existed between the measured and modeled thermal properties with mean absolute differences of 20% for Ca and 37% for λa. Measured and modeled soil heat flux during spring thaw and snowmelt were similar with cumulative totals differing by only 6% over a seven day period (Fig. 17). During that same period, we measured a latent heat flux into the soil of 7.9 MJ m-2, a sizeable heat flux completely undetectable by previous methods. The results of this study support our hypothesis and indicate that this method may be useful in wintertime surface energy balance studies.

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Fig. 17. March 2007 instantaneous (upper panel) and cumulative (lower panel) heat fluxes at the soil surface under soybean residue in field G19. Measured, modeled, and conduction-only soil heat flux estimates are shown. University of California, Riverside, CA Investigator: Laosheng Wu Unsaturated water flow induced by naturally occurring dissolved organic matter The majority of dissolved organic matter (DOM) in soils consists of complex, high molecular weight (MW) molecules, commonly classified as humic substances (HS). Evidence shows that for a given HS, the surface tension at the liquid-air interface (γL) can be significantly reduced (as low as 50 mN m-1) with increasing dissolved organic carbon (DOC) concentration. However, in most studies, the measurements of (γL) were employed for studying the chemical nature of HS per se; and/or for studying the enhanced solubility observed for some hydrophobic organic pollutants, rather than its potential role on unsaturated water flow. For a given moisture content, a γL of 50 mN m-1 may result in about 30% lower capillary pressure in soils containing DOM relative to the same soil retaining water (γL=72 mN m-1). Consequently, a pressure gradient can be induced at the interface between a soil containing DOM and a soil with lower DOM

43

concentration or that is DOM-free, that induces water movement from the high DOM soil to the lower one. In this study, we use naturally occurring DOM solutions extracted from citrus orchard topsoil and adopt the experimental design and modeling approach developed by Henry et al., (1999) and Henry et al. (2001) for surfactants, to study the DOM effect on water movement. A modified HYDRUS version 3.003 (Šimunek et al., 2007) that considers the concentration dependence of γL and contact angle dependence of capillary pressure was also developed to simulate the DOM effect on water transport. The surfactant-like behavior of DOM facilitating water movement was confirmed in this study, and therefore the occurrence of a capillary pressure gradient was proved to be the governing mechanism. It was noted, however, even though the γL of the DOM solutions employed was about 50% higher than those employed in previous studies, the changes in the moisture content were similar and at times even higher. The variations in the E2/E3 ratio implied that higher MW molecules, which are likely to be more hydrophobic, remained in the DOM-side, whereas the lower MW molecules, which are likely to be more hydrophilic, migrate to the initially DOM-free side. These observations should be further investigated to improve our understanding on the mechanism involved in the surfactant-like behavior of naturally occurring DOM solutions. Battelle Pacific Northwest Division, Richland, WA Investigators: Z. F. Zhang, and R. Khaleel Vadose Zone Monitoring Under an Interim Surface Barrier in Hanford (Z. Fred Zhang, Jason M. Keller, Christopher J. Strickland, and Curtis D. Wittreich) Many of single-shell tanks and their associated infrastructure (e.g., pipelines, diversion boxes) in Hanford have leaked. Most of the radioactive contaminants from the leaks still reside within the vadose zone. A demonstrative surface barrier is to be emplaced in the T Tank Farm to prevent meteoric water from reaching the plume and moving it further. Due to the existence of radioactive contaminants, access to the site as well as sampling and digging are strictly controlled. Further, AC power is not available within the site. We used a solar-powered and remotely-controlled (SPARC) system to continuously monitor soil water and temperature conditions and the site meteorological condition. The system contained multiple equipment nests, which are powered by a 12-volt rechargeable battery, and a receiver that connected to a computer. The batteries are charged by a solar panel. Each equipment nest is composed of a capacitance probe, multiple heat-dissipation units and a datalogger. Data from the each of the dataloggers were transmitted remotely by a spread spectrum radio to the receiving computer. Additionally, a neutron probe access tube was included in each nest and quarterly manual measurements of soil water content using a neutron probe were carried out. This SPARC system combined with the manual neutron probe measurement was used to monitor the soil water condition in the soil with and without a surface barrier in Hanford T Tank Farm. From September 2006 (the time the SPARC system started in operation) to present (August 2007), the solar system could continuously provide sufficient power to the equipment. Data collected and stored in the dataloggers could be retrieved remotely any time. To date, the SPARC system has provided continuous high-quality data without unplanned interruption.

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USDA-ARS National Soil Tilth Laboratory and Iowa State University, Ames, IA Investigators: Dan Jaynes, Toby Ewing, Robert Horton Predicting Pollutant Release from Intra-Granular Pores (Ewing) Accomplishments: We examined the effect of low connectivity of intra-granular pores on diffusion and retardation of an inert conservative tracer. We have completed most of our study of systems starting from equilibrium, and have started some follow-up studies on dynamic systems. Outcomes: At high pore connectivity, tracer uptake and release is precisely in accordance with Crank’s analytical solution. But as intra-granular pore connectivity approaches the percolation threshold – as is expected for intra-granular pores – Crank under-predicts early release and over-predicts late release. Unfortunately our method is quite time-consuming, and we are working on a semi-analytical approach to speed it up. Impacts: Our model system applies to the common scenario of a granular aquifer polluted with an organic compound. It has long been observed that sorption and desorption rates of organics in granular media are time- and history-dependent, but no comprehensive explanations have been offered. Predictions of (say) 99.9% release of a pollutant, based on Crank’s analytical solution and our model may differ by an order of magnitude or more. Because many organic pollutants are toxic at low concentrations, and remediation is diffusion-limited, accurate prediction of the mass remaining at long times is important.

University of California, Davis, Hydrology (Dept. LAWR) Investigators: Jan Hopmans, Thomas Harter The overall motivation for the development of these multi-functional techniques is to achieve an improved characterization of flow and transport processes. Several benefits are achieved by combining measurements. First, by measuring several parameters at the same time and place, the coupling of related transport properties are determined in concert, thereby allowing examination of the nature of their interdependency, such as for the coupled transport of water and solute, and water and heat. Second, by using the same instrument for various measurements within approximately the same measurement volume at about the same time, the need to interpolate different measurement types in space and time is largely eliminated. Thirdly, simultaneous analysis of flow and transport using combined soil measurements of water content, temperature, and solute concentration, decreases parameter uncertainty. Thus, using multi-functional measurement techniques allows determination of inter-dependent soil properties and processes, providing an improved understanding of coupled flow and transport. MFHPP Simultaneous measurement of coupled water, heat, and solute transport in unsaturated porous media is made possible with the multi-functional heat pulse probe (MFHPP). The probe combines a heat pulse technique for estimating soil heat properties, water flux, and water content, and uses a Wenner array to measure bulk soil electrical conductivity. The heat pulse probe (HPP) has received more attention as it allows in-situ, simultaneous, and automated

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measurements of soil hydraulic and thermal properties, as well as soil water fluxes. Although the currently-used design allows many applications, changes in HPP design and analyses are needed to increase the sensitivity to smaller water fluxes. In this study, numerical simulations were used to evaluate the effects of 1) sensor locations and thermal properties of the HPP sensor body material, 2) the heater diameter and heat pulse intensity, and 3) vapor flow on HPP performance. A numerical study was carried out using the HYDRUS code for the HPP consisting of three parallel needles, spaced 6-mm apart. A heater of varying diameter in the center is surrounded by a pair of thermistor needles. Our results show that significantly different temperature responses will be obtained depending on the axial location of thermistors, and that only temperature measurements near the middle of the 33-mm long heater fulfill the assumption of an infinite line heat source. It is shown that larger heater needle diameters allow larger heat pulses, leading to larger temperature differences between upstream and downstream thermistor needles and a higher sensitivity to water flux measurements. For example, for a standard 1-mm diameter heater needle, ten times greater heat pulse input results in ten times greater sensitivity, but with the maximum temperature at the heater exceeding 100 °C. This maximum temperature can be reduced to 80 °C by increasing the heater diameter to 4-mm, while maintaining equal sensitivity. Consideration of vapor transport significantly reduced temperature increases near the heater, caused by latent heat of vaporization. Larger heat pulses are beneficial for estimation of liquid water fluxes in the 1 cm d-1 range, provided vapor transport is considered. Neutron computed tomography Neutron radiography is a non-invasive imaging technique that measures the attenuation of thermal neutrons, as is done with x-ray and γ-ray radiography, to characterize the internal composition of materials. Neutron and x-ray imaging are complementary techniques, with neutron imaging especially well-suited for materials containing hydrogen atoms and other low atomic weight attenuating materials. Although neutron computed tomography (NCT) techniques are routinely used in engineering, relatively little is known about their application to soils. We present results from newly developed techniques that use thermal neutron attenuation to measure spatial and temporal distribution of water in soils and near roots at near 0.5 millimeter spatial resolution or higher. The neutron source is a Mark II Triga Reactor at McClellan Nuclear Radiation Center (MNRC) in Sacramento, CA (Fig. 18). After calibration using both deuterated and regular water, the effects of beam hardening and neutron scattering could be corrected for, provided that the total path length for a soil-water mixture does not exceed 1.0 cm, limiting soil sample thickness to about 2.5 cm. Using regular water, for a wide range of soil water content values, experiments demonstrated that the NCT is sensitive to small changes in soil volumetric water content, allowing estimation of the spatial distribution of soil water, roots and root water uptake (Fig. 19). Though the spatial resolution of the applied NCT system was 80 µm, an error analysis showed that the averaging measurement volume should be not less than about 0.5 mm, for the uncertainty in volumetric water content to be minimized to near 0.01 cm3 cm-3. A single root water uptake experiment with a corn seedling demonstrated the successful application of NCT, with images showing spatially-variable soil water content gradients in the rhizosphere and bulk soil.

46

Fig. 18. Three dimensional and plan view, A and B, respectively, of the tomography system in Bay 3 at MNRC (not to scale). D is aperture width and L is distance between aperture and screen. Fig. 19. (a) Two vertical slices of root experiment (A and B) at different positions through the 3D data, showing the location of each transect taken across each image.

47

The University of Arizona, Tucson AZ Investigator: Markus Tuller Binarization of X-Ray Computed Tomography Images: A Crucial Step for Quantitative Analysis of Phase Distributions and Flow Processes in Porous Media (Markus Tuller, Thomas Gebrenegus, Pavel Iassonov, and Marcel Schaap) Nondestructive imaging methods such as X-Ray Computed Tomography (CT) yield high-resolution 3-D representations of pore space and fluid distribution. Steadily increasing computational capabilities and improved access to X-Ray CT facilities have contributed to a recent surge in microporous media research with objectives ranging from theoretical aspects of fluid and interfacial dynamics at the pore-scale to practical applications such as enhanced oil recovery and (D)NAPL transport and dissolution. In recent years, significant efforts and resources have been devoted to improve CT technology, micro-scale analysis, and fluid dynamics simulations. However, the development of adequate image binarization methods for conversion of fuzzy grayscale CT volumes into a discrete form that permits quantitative characterization of pore space features and subsequent modeling of liquid distribution and flow processes seems to lack far behind.

We conducted a preliminary study on binarization and analysis techniques suitable for CT data and found about 60 different methods for determining the separating grayscale threshold documented in literature, each of them yielding different results. Many of these methods that were originally developed for pattern recognition purposes were not previously applied, or are not thoroughly tested for application to X-Ray CT images of porous materials. Image binarization (thresholding) is probably the most critical step prior to quantitative image analysis. It involves dividing the image into two regions to distinguish objects of interest (e.g. solid particles and voids). The binarization process is also crucial for analysis of three-phase systems, where the same sample is scanned at different saturation stages (i.e. dry and liquid saturated) or at different energy levels. Subsequent alignment of binarized images from individual scans and application of “subtraction analysis” allows separation of fluid phases and geometrical analysis and visualization of phase distributions within the porous structure.

Image binarization methods can be divided into six major categories that analyze the histogram shape (HS-Methods), the statistical distribution of back- and foreground pixel clusters (CL-Methods), the correlation between back- and foreground pixel entropies (EN-Methods), the similarity of attributes between the grayscale and binarized image (AT Methods), higher-order probability distributions and spatial correlations between image pixels (SP-Methods), or adapt the threshold value based on local image characteristics (LA-Methods).

Many studies that rely on X-Ray CT images for quantitative pore space analysis and fluid dynamics modeling apply global thresholding techniques (HS-, CL-, and EN-Methods) or even manually adjust the threshold value based on matching calculated and measured medium porosities. Manual selection of a global threshold is operator-biased and often impractical due to the large number of images that need to be processed for a single sample. Based on our experience, manual and global thresholding methods produce satisfactory results only for highly contrasting images with a clear bimodal grayscale histogram such as depicted in Fig. 20a. In many instances however, porous materials exhibit a highly heterogeneous composition that leads to ill-defined and noisy histograms with irregular and often multiple peaks and valleys. Many times, we also experience transitions from unimodal to bimodal to multimodal histograms within

48

the same sample (Fig. 20b). Under such circumstances it is advisable to consider local image characteristics and correlations to neighboring pixels, or the similarity between the grayscale and binarized image for selection of the grayscale threshold (AT-, SP, and LA-Methods).

Fig. 20. (a) Sketch that illustrates image binarization for a fractured bentonite-sand specimen. (b) Sequence of grayscale histograms showing a transition from bimodal to multimodal to unimodal shapes for the same sample.

To illustrate the vast contrast between binarization approaches, we applied HS-Methods proposed by Zack et al. (1977) (HS-Zack) and a simple derivative method (HS-Derivative), CL-Methods proposed by Otsu (1979) (CL-Otsu) and by Kittler and Illingworth (1986) (CL-Kittler), EN-Methods developed by Kapur et al. (1985) (EN-Kapur) and Yen et al. (1995) (EN-Yen), and a LA-Method developed by Oh and Lindquist (1999) (LA-Oh) to stacks of 500 images obtained for samples comprised of uniform 1.0, 3.5, and 6.5-mm glass beads and compared the porosities obtained from binarized images (voxel counting) with measured values. Results listed in Table 1 show significant deviations among binarization methods and between derived and measured values. None of the methods was able to identify small pores in the 1.0 mm glass bead sample. This is mainly due to the poor spatial and contrast resolutions of the X-Ray CT images that exhibit a very narrow, spike-shaped, unimodal grayscale histogram. Binarization of the 3.5 and 6.5-mm samples produced better results because the grayscale histograms had a bimodal shape we clearly distinguishable peaks. Nevertheless, there are big deviations among various methods, some of them underestimating and some of them overestimating measured porosities. It is interesting to note that the indicator kriging method (LA-Oh) only slightly deviates from EN-Kapur, which was used for prescreening and initial allocation of image pixels. The deviations are also visualized for a representative cross-section of the 3.5-mm sample in Fig. 21. Similar large deviations where observed for fractured bentonite-sand mixtures and macroporous soils.

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Table 1.Comparison between derived and measured porosities of glass bead samples, and porosity values obtained for fractured bentonite-sand and macroporous soil samples.

Porosity

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1.0 mm Glass B. 0.024 0.024 0.006 0.002 0.010 0.012 0.012 0.375 3.5 mm Glass B. 0.418 0.549 0.339 0.171 0.338 0.271 0.268 0.370 6.5 mm Glass B. 0.280 0.288 0.432 0.269 0.339 0.324 0.328 0.372 B-S Mixtures 0.390 0.422 0.374 0.313 0.402 0.343 0.350 ---- Macroporous Soil 0.041 0.040 0.024 0.013 0.034 0.038 0.038 ----

Fig. 21. Visualization of deviations between applied binarization methods for a representative cross-section of a 3.5-mm glass bead sample.

To further illustrate effects of image binarization on hydrodynamic fluid behavior in reconstructed, discrete, three-dimensional pore structures we applied a single component lattice-Boltzmann (LB) model to predict saturated hydraulic conductivity of a macroporous silt loam soil and compared predicted and measured Ksat values. It can be assumed that the choice of binarization method is even more significant when considering flow processes where pore connectivity and tortuosity are important factors.

From results presented in Table 2 it is apparent that there are significant deviations among binarization procedures. The CL-Methods by Otsu (1979) and Kittler and Illingworth (1985) came closest to the measured value. As mentioned above, the kriging method proposed by Oh and Lindquist (1999) yielded identical results as the Kapur et al. (1985) method, which was used to determine the two group threshold values prior to kriging.

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Table 2. Simulated and Measured Saturated Hydraulic Conductivities. Binarization Method Property Kittler Kapur Yen Derivative Za

3 -3ck Oh Otsu

acroporosity (m m ) 0.024 0.038 0.03 0.038 0.013 M 4 0.040 0.041 LB Simulation Ksat (m day-1) 8.2 20.2 16.6 23.3

4 22.5 20.2 0.2

Measured Ksat (m day-1) 5. To f effect of image binarization, we oduced renderings of the 3-D

acropore structures (Fig. 22) for the two extreme cases (CL-Otsu and HS-Derivative). While

he units of the graph axis are pixels).

apur, J.N., P.K. Sahoo, and A.K.C. Wong. 1985. A new method for gray-level picture ding using the entropy of the histogram. Graphical Models Image Process. 29:273-

KittleMan Cybern., SMC-15:652–655.

ce. 21:590-602.

Processing. 4:370-378.

urther illustrate the prmthe rendering based on Otsu’s method only shows 2 or 3 connected macropores, it seems that a large portion of pores is connected in the rendering based on the HS-Derivative method. These highly contrasting preliminary results provide further evidence for the importance of image binarization for pore space characterization and fluid dynamics modeling. It is clear, that if the binarization step produces an unrealistic representation of the medium pore space, all subsequent characterization and modeling efforts lead to orders of magnitude deviations from real medium properties, thereby rendering the application of advanced simulation methods to mere mathematical exercises. We are currently looking for funding to improve image binarization and to make robust binarization codes available to the scientific community.

Fig. 22. Rendered macropore structures based on Otsu’s and the Derivative binarization methods (t References: K

threshol285. r, J., and J. Illingworth. 1985. On threshold selection using clustering criteria. IEEE Trans. Syst.

Oh, W., and B. Lindquist. 1999. Image thresholding by indicator kriging. IEEE Transactions on Pattern Analysis and Machine Intelligen

Otsu, N. 1979. A threshold selection method from gray-level histograms. IEEE Transactions on Systems, Man, and Cybernetics, 9:62-66.

Yen, J.C., F.J. Chang, and S. Chang. 1995. A new criterion for automatic multilevel thresholding. IEEC Transactions on Image

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Zack, G.W., W.E. Rogers, and S.A. Latt. 1977. Automatic measurement of sister chromatid exchange frequency. J. Histochemistry and Cytochemistry, 25(7):741-753.

tah State University, Logan, UT

U

Probe (PHPP) development

Investigator: Scott Jones Penta-needle Heat Pulse

Penta-needle Heat Pulse Probe (PHPP) was developed for estimation of snowmelt water realm, heat-pulse based sensors typically

Ainfiltration in a forest ecosystem. Within the researchhave one heater probe and one pair of upstream and downstream temperature sensing needles for flux determination. However, such heat pulse sensors may not be suitable for inferring hillslope percolation rates due to the likelihood of multidimensional water flux. Advanced heat-pulse based sensors with one heater probe and two pairs of orthogonally arranged temperature sensors have been proposed to measure horizontal and vertical fluxes simultaneously. In order to evaluate the PPH method in estimating 2-D water fluxes, a set of synthetic numerical simulations were carried out using a CORE2D V4 numerical model. Then a laboratory experiment was performed to test a PPHP sensor which was located at the center of a cylindrical flow cell (Fig. 23). The flow cell comprised of an outer lexan wall and inner porous stainless steel wall was divided into four sections (i.e., two inlets and two outlets) leaving the center of the cylinder packed with porous media (glass beads). By adjusting pressure head at each inlet and outlet, a 2-D flow field was formed. 2-D flux estimated from the PPHP method was compared to the results of a flow model. Water velocities derived from numerical simulations and temperature responses show good agreements and therefore the PPHP method can provide good estimation of 2-D soil water fluxes.

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Fig. 23. Design of a 2-dimensional water flux cell for evaluation of the PHPP. Each inlet is maintained as a fixed head that can be varied to adjust the direction of flow. The cell is comprised of an outer lexan cylinder with a porous stainless steel inner wall. Four separate water compartments are created using o-ring seals between the two cylinders.

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UMS TS1 Tensiometer Evaluation In 2005 we received a batch of 24 self filling tensiometers (UMS model TS-1, Germany) for

onitoring soil matric potential in a forest ecosystem. The specifications of the tensiometers en -85 and +100 kPa ((+/- 0.5 kPa) over a temperature range

imilar to the soil moisture sensor (not

mwere pressure measurements betweof -30 to +70 oC. In addition to pressure, the sensors output temperature and cup bubble volume, which was automatically maintained at less than 1 % of the 100 ml volume. Pressure measurement errors increase when the bubble volume becomes too large. Initial testing of the tensiometers uncovered a number of problems that UMS worked on over the ensuing two years. A number of firmware updates were developed and uploaded to the sensors as well as some hardware repairs that were required due to ill fitting tubing within the housing. We attempted to evaluate the temperature-dependent performance of 3 of the sensors in a sand-filled column immersed in a water bath. We mixed Kidman Sand to a uniform water content below field capacity and sealed the sensors inside to prevent evaporation. A water content sensor was installed in the middle of the tensiometers to track volumetric water content. Temperature steps beginning at 30 °C were maintained for about 12 hours reducing the temperature of the bath by 5 °C at each step. The tensiometers have a default temperature setting of 2 °C at which point they should automatically purge water from the ceramic cup prior to freezing to avoid breaking. When the temperature rises above 2 °C and water content is sufficiently high, the sensor is designed to re-fill the cup from the surrounding soil water by imposing a negative potential within the cup by means of a miniature peristaltic pump. The temperature response from all three tensiometers followed the expected route illustrated in Fig. 24 down to 2 °C at which point 2 or 3 sensors failed to continue following the expected response while the 3rd sensor tracked the temperature sshown). Figure 24 also shows the bubble size in each cup, which should remain less than 1 ml under normal operation and increases drastically when cups are purged of their water prior to freezing. In test none of the cups were purged of water at the specified temperature. Freezing of

Fig. 24. Tensiometer pressure response and porous cup bubble size. All three tensiometer temperature sensors are consistent as temperature steps down to the purge set point temperature of 2 oC. At this point 2 of the 3 sensors fail to correctly report the soil temperature. The bubble size, which should increase, is unchanged as the temperatures each reach the threshold temperature.

Purge setpointPurge setpoint

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the soil began about 9 hours after the threshold temperature was reached. The water content sensor based on soil dielectric demonstrated the gradual freezing which occurred over about 9 hours (data not shown here). The result was that 1 of the cups broke off and in a prior test, all 3 cups were found broken after testing. Our conclusions from this and prior testing is that this batch of sensors produced in 2005 are not suitable for our forest soil application where freeze/thaw conditions are prevalent during spring and fall. We are working with the manufacturer to determine if they have resolved these problems in newer model sensors and if so we will repeat this test with a new batch of sensors. Portable TDR Circuit Development A portable TDR circuit with push button activation and LCD readout was developed. The circuit

terfaced with a CR1000 datalogger coupled with a TDR100 time domain reflectometer ry. A handheld GPS provided spatial locations for each

ig. 25.oints. Water contents ranged from 5 up to 70 percent.

y or had any knowledge of the sensor erformance. The portable TDR circuit facilitated rapid mapping of water content in rugged

inpowered by a small 12 volt battemeasurement point. Components were all contained in a backpack with the pushbutton circuit attached to a pogo-stick handle that extended to a housing for a TDR probe (Fig. 25). The system provided water content measurements within 2 seconds of activation and added EC with an additional 10 second wait time. The Reynolds Mountain East watershed was probed for water content within the Reynolds Creek Experimental Watershed south of Boise, ID. Three hundred plus measurements were made in 6 hours across rugged terrain covered with a variety of vegetation. F Portable TDR probe used to map the Reynolds Mountain East Watershed with over 300 p Impact: Results of the UMS-TS1 sensor evaluation were presented to the W-1188 workgroup meeting where none had used the sensors previouslpterrain and has potential benefit for field use for anyone with TDR100 and datalogging instrumentation.

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California State University, Fresno, CA Investigator: Zhi Wang

table isotopic analysis of the regional hydrology of the upper San Joaquin River, Fresno, SCalifornia Samples of rain, surface, and groundwater were collected along the San Joaquin River, during

large, dammed river flowing through an arid region. Rain samples, collected at 3

the 2005-2007 season for stable isotope analysis. The purpose was to understand the hydrologic nature of a locations, showed large variations in isotope depletions (D) between -61.6 ‰ and -28.6 ‰. The river was sampled on 3 occasions and showed little variations in D between -103.7 ‰ and -98.4 ‰. Groundwater was collected during the rainy season and after a significant increase in river discharge. Groundwater collected near continually flowing portions of the river was composed of rain and river water. However, surprisingly the proportions were observed to fluctuate by almost 10 %. Groundwater collected near the river where it is most commonly dry is on average 4 ‰ more depleted than samples from the San Joaquin River, and thus has no obvious origin. This groundwater may have been recharged during a pre-dam period.

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Fig. 26. Isotope diagram representing the four main types of waters investigated in the watershed.

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Montana State University, Bozeman, MT Investigators: Jon Wraith, Brian McGlynn

onvTDR: a GUI Software for Numerical Convolution of Time Domain Signals C

urements is critical to characterization of flow and ansport processes. We are continuing our work to advance measurement techniques and

t to time domain reflectometry (TDR). In time domain reflectometry the measured waveform (WF) results from the convolution of

setup. Detailed

p on TDR signa

ects for different textured

oduce synthetic waveforms free of measurement artifact/error to test

Ability to obtain accurate and detailed meastrassociated capabilities, particularly with respec

the incident voltage with a response function characterizing sample and TDRmodeling of the transfer function, along with an effective algorithm for the numerical convolution, allows us to produce very accurate synthetic waveforms. Using synthetic waveforms it is possible, for example, to investigate the effects of the hardware setu

ls with no need to perform laborious experiments. Moreover, the impact that the different characteristics of the sample material have on TDR measurement (travel time analysis), can be studied and predicted. We found that the commonly used Nicolson ramp method performed poorly for convolution processes. Errors resulting from the product of the transfer and input functions in the frequency domain, a phenomenon known as circular convolution, were virtually eliminated by the zero-padding technique. Moreover, sophisticated modeling of the feeding line and probe which takes into account frequency dependent losses such as those resulting from the skin effect ensures very accurate reproduction of the waveforms. The software features a graphical user interface. Users can select cable length and cable type (from among the most commonly used), as well as the probe geometry. The sample material can be chosen from a library including many common solvents. Alternatively, a number of mixing models (such as the 2- and the 3-phase Hanai models) are available. A newly developed mixing models (Hanai-Castiglione) was also implemented, which takes into account the temperature dependent permittivity of both bound and free water. The agreement between observed and synthetic results for this study was encouraging, and reinforced our confidence in the conceptual schematization provided by the Hanai-Castiglione mixing model. We are currently testing and improving an algorithm recently developed for obtaining the sample permittivity spectrum from the analysis of waveforms, which performs very accurately in all but saline samples. Impact: One fundamental application of our software is to predict the outcome of the travel time analysis for a generic dispersive medium. In particular, we can determine the effective frequency range in TDR measurement for different scenarios. This is a fundamental and not yet resolved issue for comparing moisture measurements obtained with different electromagnetic techniques. Moreover, using ConTDR we were able to predict temperature effsoils. A further important application is to provide synthetic waveform data for studying deconvolution models. Outcome: Montana developed a user-friendly software application to generate synthetic Time Domain Reflectometry (TDR) waveforms, based on numerical convolution of discrete signals. The program may be used to: 1) design/evaluate probes for specific conditions (e.g., high salinity, long cables, sensitivity to changes); 2) predict/improve travel time analysis outcomes for dispersive media; 3) prdeconvolution algorithms for spectroscopy models; and 4) as a tool to instruct TDR methodology and basic signal processing concepts (e.g., Nyquist frequency, circular convolution, etc.).

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Development of Digital Elevation Model Analysis Algorithms and methodologies We are applying and further developing topographic and topologic analysis methods to define, map, and quantify connections between dominant landscape elements, such as uplands and riparian zones, and to scale-up process hydrological understanding to the stream network and atchment scales. We are further working to link topography, geomorphic form, and landscape

off and land

explicit associations between topographic/topological controls and hydro

generation (hydrologic response), streamwater residence

cstructure to hydrological and biogeochemical signatures in watershed runatmosphere exchange.

Currently, no framework exists for integrating landscape analysis with field measurements and process understanding. We will demonstrate one way forward by generating maps and statistical distributions of computed indices to provide insight into catchment structure and the potential landscape level controls on hydrologic and biogeochemical variability observed in the field. We will make

logical and biogeochemical processes. This approach provides context for field scale observations and can provide a means to scale-up process level understanding. Landscape analysis techniques and information are increasingly needed for geomorphologic and hydrological analyses, especially as the importance of stream network organization and stream-catchment connections are recognized. Impact: The results of integrating field studies and landscape analysis will be valuable for the refinement of hydrological and water quality models on the catchment scale by providing insight into key catchment topography, topology, and landscape organization controls on runoff measured at the catchment outlet. Outcome: Montana is evaluating floodtimes (water age), the sources and pathways of runoff, riparian buffering of hillslope runoff, water quality dynamics (biogeochemical response), and the heterogeneity of CO2 generation and flux across watersheds. Kansas State University, Manhattan, KS Investigator: Kluitenberg Characterization of Effective Measurement Scales for Thermal Sensors

CSIRO Land & Water), has continued to investigate atial weighting functions for a broad class of methods that involve heat-pulse sensors. During

ed our investigation of the weighting functions for volumetric heat apacity, thermal conductivity, and thermal diffusivity as measured with the dual-probe heat-

thermal properties are

Kansas, in collaboration with John Knight (spthe past year we continucpulse (DPHP) method of Bristow et al. (1994). In this method, theestimated from the maximum temperature rise observed at the temperature probe after a pulse of heat is released from the heater probe. Our ultimate goal is to obtain a complete volumetric characterization of the spatial sensitivity of the DPHP method, but our work to date has focused on characterizing the spatial sensitivity of the DPHP method in a plane normal to the line heat source that passes through the location at which temperature is measured with the DPHP method (Fig. 27). Spatial integration of the weighting functions within this plane has allowed us to calculate contours of equal fractional spatial sensitivity that characterize the size and shape of the sampled region for each of the three thermal properties estimated with the DPHP method.

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Fig. 27. obe and temperature probe. The plane passing

rough the heater and temperature probes defines the area in which the spatial sensitivity of the PHP method is characterized.

During the past year we have also extended this work to characterize the sampling volume

inear least-squares regression theory with the spatial sensitivity eory developed in our previous work.

Sketch of a DPHP sensor with heater prthD

of a DPHP sensor for the case where thermal properties are estimated from the complete temperature response signal (temperature vs. time curve). To accomplish this, a novel approach was developed to combine nonlth

Evaluation of PTF Approach for Estimation of Saturated Hydraulic Conductivity Current methods for measuring saturated hydraulic conductivity (Ks) are costly, time-consuming, require specialized equipment, and are subject to numerous sources of uncertainty. An alternative approach is to use pedotransfer functions (PTFs) to estimate Ks from surrogate data that are more easily measured, or are already available. The primary purpose of this work is to

date, field data

s and bulk density. Rosetta Ks es

collect data that will permit evaluation of PTF approaches for estimating Ks. To have been collected at 16 field sites in collaboration with a team of NRCS soil scientist. A pit was excavated at each site to describe soil horizons. Samples from each horizon were sent to the NRCS National Soil Survey Laboratory for detailed physical and chemical property determination. Field measurements of Ks were obtained for the major soil horizons (five replicates per horizon) at each site using the constant-head borehole permeameter method. The field campaign has resulted in a data set consisting of 53 samples. Of these samples, 14 are from A horizons, 29 are from B horizons, and 10 are form 10 C horizons.

The data set has been used to evaluate a number of existing PTFs for Ks estimation. Here we present results obtained by using Rosetta (Schaap et al., 2001) to estimate Ks. Analysis of the results revealed only modest correlation between predicted and measured Ks (Table 3, Fig. 28). The use of water content at matric potentials of –33 kPa and –1.5 MPa did not enhance the predictive ability achieved using only sand, silt, and clay percentage

timates were biased towards overestimation for low Ks and underestimation at high Ks. The bias and modest correlation of the Rosetta Ks predictions were most likely the result of limitations of the calibration data used in the development of Rosetta. This finding underscores the need for high-quality data sets that can be used for the evaluation and calibration of pedotransfer functions.

Spatial Variation in Water-Table Fluctuations in Vegetated Riparian Zones

Diurnal water-table fluctuations observed in shallow wells in vegetated riparian zones are a diagnostic indicator of groundwater consumption by evapotranspiration (ETG). In order to better

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understand how these fluctuations vary across a riparian zone, analytical solutions for strip-sinks with periodic forcing functions were developed. The periodic forcing functions, which represent the evapotranspirative consumption of groundwater, are finite within the strips and zero outside.

tions in ETG due to variaLinearity allows superposition of the strip solutions to simulate spatial varia

tions in vegetation density within the riparian zone. The solution has been applied to data from a field site in a riparian zone along the Arkansas River in west-central Kansas where groundwater levels in shallow wells have been monitored at 15-minute intervals for up to five years. A series of strips were used to represent the largely dry unvegetated river channel, two zones within the vegetated riparian zone, and adjacent pastures and cultivated fields. The spatial variations in the phase and amplitude of the simulated fluctuations were consistent with general patterns observed in the field data during both wet and dry years. Several empirical methods have been developed for estimating ETG using characteristics of the diurnal water-table fluctuations. This solution reveals where best to place wells for use with those methods. Table 3. Summary statistics for evaluation of Rosetta Ks predictions. Agreement between predicted and measured values was assessed using Coefficient of Determination (R2), Root Mean Square Error (RMSE), and Mean Error (ME).

Hierarchical input level R2 RMSE ME Textural class 0.30 0.777 0.131 Sand, silt, and clay percentages (SSC) 0.32 0.756 0.068

ter content at –

SSC and bulk density 0.57 0.651 0.093 SSC, bulk density, and water content at –33 kPa 0.35 0.769 −0.191

SSC, bulk density, and wa1.5 MPa 0.32 0.773 0.149

Fig. 28. Comparisons of predicted and measured saturated hydraulic conductivity (Ks). Results in Panel A were obtained using Rosetta with inputs of sand, silt, and clay percentages and bulk density. Results in panel B were obtained using Rosetta with inputs of sand, silt, and clay percentages; bulk density; water content at –33 kPa; and water content at –1.5 MPa.

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REFERENCES Bristow, K. L., G. J. Kluitenberg, and R. Horton. 1994. Measurement of soil thermal properties

with a dual-probe heat-pulse technique. Soil Sci. Soc. Am 58:1288-1294. Schaap, M.G., F.J. Leij, M.Th. van Genuchten. 2001. ROSETTA: a computer program for

estimating soil hydraulic parameters with hierarchical Pedotransfer functions. J. Hydrology. 251:163-176.

. J.

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OBJECTIVE 3: To develop and evaluate scale-appropriate methodologies for the management of soil and water resources

Desert Research Institute, University of Nevada, Las Vegas, NV Investigators: Markus Berli (DRI, Visitor), Todd Caldwell (DRI), Karletta Chief (DRI, Visitor), Scott Tyler (UNR), Wally Miller (UNR), Michael Young (DRI), Jianting Zhu (DRI) Nevada’s researchers focused on several scale-related issues pertinent to management of land and water resources. Their work spanned several technical areas in which soil physics and soil hydrology were applied to other technical areas, including surface runoff prediction, land restoration, and hydraulic conductivity manipulation to improve water resource availability.

One of the greatest challenges to the U.S. Department of Defense, the largest landholder in the Mojave Desert, is maintaining the sustainability of military lands while maximizing their use for training activities. Restoration of disturbed lands in the Mojave Desert has proven to be a challenge; particularly revegetation of military lands from the more economical practice of seed application. This study by Caldwell et al. (2007b) complements the revegetation component of a larger study, presenting near-surface soil moisture dynamics from three active restoration sites in coarse-textured soils at the National Training Center, Ft. Irwin, CA. The soil microclimate (soil temperature, matric potential, and soil-water balance) were monitored beneath various surface treatments during active restoration practices to better assess their effects on the seed germination and establishment. Results show that under the typically hot and dry climatic conditions that prevail, the near-surface soil microclimate is a hostile environment. Irrigation had the most significant positive effect on the seedbed microclimate. With the exception of plastic which increased soil temperatures and available soil moisture, other surface treatments (gravel, straw, and bark) had limited effects. Seedlings initially germinated at all three sites, but survival after three months was negligible. The stochastic nature of Mojave Desert precipitation, coupled with the high ET requirements, make seedling establishment from seed on disturbed soils a difficult task. Improved knowledge of the germination requirements for Mojave seeds, applied numerical modeling to more strategically irrigate, and soil-moisture forecasting could aid in meeting the goals required for successful seedbed microclimate management (Caldwell et al., 2007b).

It is well known that, for saturated flow, the equivalent macroscopic scale hydraulic conductivity is equal to a simple arithmetic average of all individual saturated hydraulic conductivities for horizontally heterogeneous (parallel column) media and the harmonic average of all individual saturated hydraulic conductivity for vertically heterogeneous (layered) media. The same average schemes were often assumed and extended to the more complex unsaturated flows in many studies. Due to the strongly non-linear relationship between the unsaturated hydraulic conductivity and saturation, the validity of using the same average schemes for unsaturated flow conditions needs to be examined. In this study (Zhu, 2007), Nevada scientists investigated the appropriateness of using the arithmetic and harmonic averages of hydraulic conductivity for unsaturated flows horizontal and perpendicular to the heterogeneous soil profiles or layers under steady-state flow conditions. The macroscopic hydraulic conductivity in this study is the derived equivalent macroscopic hydraulic conductivity from either horizontally or vertically heterogeneous soil profile or layers distinguishable by variations of hydraulic parameters. Specifically, for horizontally heterogeneous soils, the macroscopic hydraulic

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conductivity function should be able to predict the actual average flux of the parallel column soil system and for vertically heterogeneous soils, it should simulate the actual moisture flux of the layered soil formations. The relative error of calculated flux against the actual average flux of the heterogeneous soils, using various averaged hydraulic conductivity functions was also assessed. In general, the results illustrated that while the arithmetic mean of the hydraulic conductivity function performed reasonably well when simulating the actual average flux for the horizontally heterogeneous columns, the harmonic mean of hydraulic conductivity function introduced quite large error into the predictions of actual flux for the vertically heterogeneous soil layers, especially for highly heterogeneous soils. Some of the other main conclusions from this study were: (1) the optimal macroscopic hydraulic conductivities for both horizontally and vertically heterogeneous soils also depended on the pressure head conditions at the land surface, and it was more a challenge when the pressure head at the land surface was higher (i.e., dry surface conditions); (2) the arithmetic mean for horizontally heterogeneous soil columns and the harmonic mean for vertically heterogeneous soil layers, extended from saturated flow situations would introduce larger errors when simulating the actual flux for coarser-textured soils and for more heterogeneous soils with large hydraulic parameter variances; and (3) the parametric correlations among the hydraulic parameters were also important when determining the appropriate macroscopic hydraulic conductivity for the heterogeneous soils.

Nevada researchers in collaboration with University of Houston (Zhu and Sun, 2007b) investigate soil effective hydraulic properties (expressed in terms of hydraulic parameters) that are applicable for large-scale transient infiltration in heterogeneous soils. The effective hydraulic parameters are examined in relation to uncertainties of the hydraulic parameters based on field-measured and synthetically re-generated hydraulic parameter data sets. The main objectives are to investigate: 1) which effective hydraulic parameters schemes are suitable of representing ensemble behavior and can be used in practical applications of large-scale infiltration processes, 2) how the effective hydraulic parameter schemes are sensitive to the time frame of hydrologic processes, and 3) how the hydraulic parameter correlation and variability impact effective hydraulic parameter schemes. An inverse procedure used with the HYDRUS-1D code is used to find the optimal effective hydraulic parameters for infiltration processes, which minimizes the difference between the ensemble cumulative infiltration and the cumulative infiltration calculated using a single set of effective parameters. Three scenarios were designed that optimize either multiple hydraulic parameters simultaneously, or only one hydraulic parameter but using the arithmetic mean for the other parameter. Results illustrate that while the resulting effective hydraulic parameters can be used to simulate ensemble infiltration of a heterogeneous medium more effectively, if multiple hydraulic parameters are optimized simultaneously, the effective parameter values need to be adjusted as time evolves. On the other hand, a simpler effective parameter scheme of optimizing only one hydraulic parameter while keeping the simple arithmetic mean for the other hydraulic parameter results in more uniform effective hydraulic parameters, but they are not as good in representing the ensemble infiltration behavior of a heterogeneous medium. The impact on the effective hydraulic parameters of other factors, such as surface ponding depth, groundwater table depth, the correlation between hydraulic parameters are also investigated and discussed.

Upscaled soil hydraulic properties are needed for many large-scale hydrologic applications such as regional and global climate studies and investigations of land–atmosphere interactions. Many larger scale subsurface flow and contaminant transport studies also require upscaled hydraulic property estimates. The objectives of the study by Zhu et al. (2007) were to develop a

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methodology for upscaling hydraulic property functions using a p-norm approach, to examine how p-norm values differ for two commonly used soil hydraulic property models (the Gardner and van Genuchten functions), and to investigate the relative sensitivities of p-norms and the effective hydraulic parameters to the degree of soil heterogeneity (expressed in terms of variances and auto-correlation lengths of the hydraulic parameters) and other environmental conditions. The p-norm approach expresses upscaling schemes such that it reduces their sensitivity to uncertainties (heterogeneities) in site conditions. The upscaling schemes are obtained as the result of two new criteria proposed to upscale soil hydraulic properties in this study—one preserving the ensemble vertical moisture flux across the land–atmosphere boundary, and a second preserving the ensemble soil surface moisture content. The effective soil hydraulic parameters of a heterogeneous soil formation are then derived by conceptualizing the formation as an equivalent homogeneous medium that satisfies the upscaling criteria. Upscaling relationships between the Gardner and van Genuchten models can then also be established for steady-state vertical flow using the statistical structures of the hydraulic parameters of these two models as estimated from field measurements. The upscaling scheme is demonstrated using hydraulic property data collected at 84 locations across a site in the Mojave Desert. Results show that the p-norms generally vary less in magnitude than the effective parameters when the variances of the hydraulic parameters increase. Results also show that, in general, p-norm values are better defined for the van Genuchten model than the Gardner model. Hydraulic parameter auto correlations, as defined by correlation lengths, were found to have little impact in relating the upscaling schemes (p-norm values) for the two hydraulic property models, but correlation between the hydraulic parameters within the hydraulic property models can significantly affect p-norm relationships.

In the study by Mohanty and Zhu (2007), effective soil hydraulic parameter averaging schemes are investigated for steady-state flow in heterogeneous shallow subsurface useful to land-atmosphere interaction modeling. “Effective” soil hydraulic parameters of the heterogeneous shallow subsurface are obtained by conceptualizing the soil as an equivalent homogeneous medium. The approach requires that the “effective” homogeneous soil discharges the same mean surface moisture flux (evaporation or infiltration) as the heterogeneous media. Using the simple Gardner’s (1958) unsaturated hydraulic conductivity function, the effective value for the saturated hydraulic conductivity Ks or the shape factor α under various hydrologic scenarios and input hydraulic parameter statistics were derived. Assuming one-dimensional vertical moisture movement in shallow unsaturated soils, both scenarios of horizontal (across the surface landscape) and vertical (across the soil profile) heterogeneities are investigated. The effects of hydraulic parameter statistics, surface boundary conditions, domain scales and fractal dimensions in cases of nested soil hydraulic property structures are addressed. Results show that the effective parameters are dictated more by the α-heterogeneity for the evaporation scenario and mainly by Ks- variability for the infiltration scenario. Also, heterogeneity orientation (horizontal or vertical) of soil hydraulic parameters impacts the effective parameters. In general, an increase in both the fractal dimension and the domain scale enhances the heterogeneous effects of the parameter fields on the effective parameters. The impact of the domain scale on the effective hydraulic parameters is more significant as the fractal dimension increases.

Nevada researchers have focused considerable effort in the last several years on the use of linear, anionic polyacrylamide (PAM) as a technology to reduce seepage in unlined water delivery (i.e., irrigation) canals. By some estimates, as much as 50% of water being transferred in these canals could be lost from seepage. PAM, which has been extensively tested in irrigation

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furrows, was shown to effectively flocculate suspended sediment in the canal water, and (anecdotally) to reduce seepage as the flocculates settle to the canal bottom. Laboratory, field and modeling studies were undertaken to quantify the benefits and the risks of using PAM in these canals. In the laboratory study by Young et al. (2007b), the specific goals were to quantify the optimum PAM and suspended sediment concentrations (SSC) that most efficiently reduce saturated hydraulic conductivity (Ksat) of soils, and to better understand the mechanisms contributing to reduction in Ksat. Testing was conducted using a constant head method in soil columns (15-cm length, 6.35-cm diameter). An unbalanced multi-factorial design was used with experimental variables including soil type (#70 mesh sand, C33 sand, loam soil), PAM treatment level (0, 5.6, 11.2, 22.4, 44.8 kg ha-1), and SSC (0, 150, 300 mg L-1). Results show that PAM treatment reduced Ksat 40% to 98% in the sandy soils but reductions were much less in loam (from 0 to 56%). Adding suspended sediment to the test solution reduced Ksat of the entire soil column from 8 to 11 times more than adding PAM without suspended sediment. Mechanisms that reduced Ksat included higher viscosity from dissolved PAM, creation of a separate and distinct PAM layer, and the plugging of larger soil pores near the soil surface. Significance of these mechanisms was found to be a function of experimental conditions. The results were weighed against the potential human health and environmental risks associated with the use of PAM and the release of residual acrylamide (AMD) that is found within the PAM molecule. The results of the risk characterization showed that AMD release posed a manageable risk to human health when used according to application guidelines (Young et al., 2007c)

In a companion study (Zhu and Young, 2007b), Nevada investigated the mechanism of reducing water seepage loss by using a two-layer one-dimensional steady-state conceptual model. The objectives of this study are two-fold: (1) to examine the effectiveness of PAM-treated layer formed at the bottom of the water delivery canal in reducing water seepage loss, and (2) to investigate the sensitivity of seepage reduction to the hydraulic parameters of both the untreated and PAM-treated thin soil layer formed on the canal bottom. Laboratory-measured saturated soil hydraulic conductivity results were incorporated into the model to examine the seepage ratio of PAM-treated versus untreated soils and the uncertainty of seepage ratio. Results indicate that, in cases when PAM applications and SSC treatment are effective, the impact of soil hydraulic parameter (i.e., pore-size distribution parameter) α ratio of the PAM-treated soil layer over the original soil on the uncertainty of the seepage ratio is significant. For cases when seepage ratio is insensitive to PAM and SSC, the α ratio of the treated soil layer over the original soil layer is not significant. For a canal bottom with coarse-textured sand, uncertainty in the α ratio is propagated to the uncertainty of seepage ratio and augmented more significantly, while for relatively fine-textured sand (reflected in the small α values used in this study) the uncertainty propagation and augmentation are relatively gradual. For coarse-textured sand, small uncertainty in the α ratio can lead to large uncertainty in the prediction of seepage ratio.

Nevada researchers have been collaborating with colleagues in China to examine data and methods of characterizing the changes in soil hydraulic properties associated with land and soil stabilization (Wang et al., 2007). Improving structure of soils found at 0–5 cm depth, and increasing the thickness of biological soil crusts are both associated with sand dune revegetation-stabilization in arid northwestern China. Since 1956, research on sand dune stabilization has included the use of straw chequer-boards to facilitate development of soil structure. One method to gauge the degree of stabilization is to compare undisturbed soil hydraulic properties, including water retention [h(θ)] and hydraulic conductivity [K(h)] functions, with properties from stabilized sites of different ages. This study examined properties at five experimental sites of

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different ages since revegetation (51, 42, 34, 20 and 0 years). Soil Ksat was determined in-situ from all five sites, and the h(θ) curve was determined from samples collected from three sites. A significant negative correlation existed between Ksat and the clay, silt and organic matter contents. Differences in most van Genuchten parameters for h(θ) were observed between the revegetated plots and the migrating sand dune area. Results of this long-term study show that changes in soil hydraulic properties and improvement in soil structure were associated with migrating dune stabilization. This study was published as part of a special issue of Geophysical Research Letters that sought to better link together the efforts of researchers involved with ecohydrology and hydropedology (Young et al., 2007d).

Small-scale variations of hydrologic processes both in space and time have a significant impact on the simulation of hydrologic processes at different scales in the watershed. Nevada researcher in collaboration with University of Waterloo, Canada investigate: 1) how the spatial and temporal grid scales affect the results of hydrologic processes, and 2) how the variability of input driving parameters (e.g., elevation and precipitation intensity) at different grid scales is related to the simulated discharge response (Yu et al., 2007). A hydrologic model system (HMS) was used to simulate hydrologic processes at different spatial and temporal grid scales in a small watershed (7.29 km2) within the Susquehanna River Basin (SRB) in Pennsylvania, USA. The spatial distributions of various hydrologic properties, such as soil and land use/land cover data, were included in the simulations along with digital elevation model (DEM) and precipitation data. Five-minute precipitation records collected from four gauge stations within the watershed were used to drive fifty model runs, which were designed to examine the effects of grid size change and different parameterization schemes on hydrologic responses. Simulation results showed that small-scale variations in elevation and precipitation both in space and time have significant impacts on the streamflow hydrograph and the discharge volume. Results illustrated that the grid scale effect on the hydrologic response is highly correlated to the variability of elevation and precipitation at the corresponding scales, and therefore the variance variations in elevation and precipitation are strong indication of the hydrologic response in the watershed.

USDA-ARS, Salinity Laboratory, Riverside California Investigators: Scott Bradford, Eran Segal, Saeed Torkzaban, Martinus Th. van Genuchten, Scott Yates, Todd Skaggs, and Peter Shouse We have implemented a nutrient management plan (NMP) using cyclic and blending irrigation strategies for dairy lagoon water application at a heavily instrumented field site (interagency project with EPA). We have monitored the transport and fate of nutrients and indicator microorganisms at this site over the course of winter (barley) and summer (sorghum) growing seasons. We have examined contaminant concentrations (salts, heavy metals, nutrients, hormones, and antibiotics) in various lagoon water samples (swine, beef, dairy, and poultry) and estimated contaminant loading rates under various NMP conditions. In addition, we have instrumented and initiated the characterization of a 70 acre field-site for studies examining the transport and fate of pathogens and nutrients under NMP conditions (project with SJRCD).

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Washington State University, Pullman, WA Investigators: Markus Flury, Joan Wu Digital elevation models (DEMs) vary in resolution and accuracy by the production method. DEMs with different resolutions and accuracies can generate varied topographic and hydrologic features, which can in turn affect predictions by soil erosion models, such as the WEPP (Water Erosion Prediction Project) model. In a study investigating the effects of DEMs on deriving topographic and hydrologic attributes, and on predicting watershed erosion using WEPP, we assessed six DEMs at three resolutions from three sources for two small forested watersheds in northern Idaho, USA (Zhang et al., 2007). These DEMs were used to calculate topographic and hydrologic parameters that served as inputs to WEPP. The model results of sediment yields and runoffs were compared with field observations. For both watersheds, DEMs with different resolutions and sources generated varied watershed shapes and structures, which in turn led to different extracted hillslope and channel lengths and gradients, and produced substantially different erosion predictions by WEPP.

Impact: Soil erosion is a serious and continuous environmental problem nation- and worldwide. DEM is a key input to watershed hydrology and erosion models, including the widely used Water Erosion Prediction Project (WEPP) model. Results and findings from this study should be useful to researchers in selecting appropriate DEMs with proper accuracy and resolution for hydrologic and environmental modeling. University of Wyoming, Laramie, WY Investigator: Thijs Kelleners A new study was initiated on the leaching potential of trace elements like Arsenic and Selenium from Coalbed Methane water disposal ponds. Coalbed Methane extraction involves pumping from coal seams to reduce the water pressure and release the gas. The produced water that may be of marginal quality is generally released into streams and surface ponds. This work includes laboratory measurements of the hydraulic properties and the adsorption characteristics of the pond soils. A multi-phase numerical model will be used to quantify the downward water flow and solute transport from the ponds. This study is conducted in collaboration with the University of Wyoming mathematics department who will provide the numerical model. North Dakota State University, Fargo, ND Investigator: Frank Casey Evaluation and Effectiveness of Nutrient Management Zone Determination Methods in the Northern Plains Outputs: Three different methods for delineation of management zones and nitrogen application based on (i) bare soil color, (ii) clustering of soil test nitrate, deep apparent electrical conductivity (ECa), and yield, and (iii) summation of standardized deep ECa, elevation, and five

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years of ranked yield, were compared to each other and to a uniform N application treatment as related to corn grain yield over four years. Variable rate N application was based on a constant yield goal and zone averaged soil test N for the zones delineated based on soil color. Nitrogen was variable rate applied to the cluster and summation zones based on zone averaged soil test N and variable yield goals. The zone delineation methods resulted in similar zones, with some differences in the patterns and order of the zone rank. Yield results were inconsistent from year to year, the higher N rates applied to the zones with higher yield goals did not necessarily result in higher yields, and the uniform N application treatment resulted in yields that were not statistically different from most of the other treatments. Even though this field site had significant variation in soil ECa, topography, and soil color, zone management seemed to result in uniformity of yield across the site.

The results from this study were summarized in a manuscript and published in a peer reviewed journal (Derby et al., 2007). Also, the zone delineation method that was developed was taught in a precision agriculture course. Furthermore, an algorithm was created for Matlab to simplify this zone delineation method in hopes to further disseminate this method. Outcomes: Yield results from the zone management methods were inconsistent from year to year, indicating no clear benefit to one zone delineation method over another. The higher N rates applied to the zones with higher yield goals did not necessarily result in higher yields, indicating that additional N for variable yield goals wasn’t justified in at least two years of the study. However, crop damage from wind in one year and insufficient heat units the other year may have affected yield response to N. Yield monitoring across the entire field did suggest that the zone management methods were effective in creating a uniform yield through space, which indicates nutrient conservation was achieved, i.e. conserving it in low yielding locations and optimizing it in high yielding locations. University of California, Riverside, CA Investigator: Laosheng Wu Metal Uptake of Corn Grown on Size-fractionized Biosolids Treated Media Corn (Zea mays L.) was grown on biosolids-treated sand culturing media to study effects of particle size distribution on the uptake of Cr, Cd, Cu, Ni, Pb, and Zn. Two distinctive biosolids were utilized in the study. The Nu-Earth biosolids exhibited porous and spongy structure and had considerably greater specific surface area than that of the Los Angeles biosolids which was granular and blocky. The specific surface area of Los Angeles biosolids was inversely proportional to its particle size, while that of Nu-Earth biosolids did not change significantly with particle size. Analysis results showed that the metal contents were not affected by the particle size distribution. As the biosolid particle size decreased, the biomass yields grown on the treated media increased, indicating that the adsorption of nutrients from biosolids was dependent on the root- biosolids interface interactions. The effect of particle size distribution on the bioavailability was metal-specific. The uptake of Cd and Zn were closely correlated to particle morphology. Smaller particles with higher surface area provided greater root-biosolids contact and resulted in enhanced Cd and Zn uptake. The effect of particle-size distribution on uptake of Cu and Ni was less pronounced than that on Cd and Zn, while the uptake of Cr and Pb were dominated by their chemical speciation of the biosolids.

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Battelle Pacific Northwest Division, Richland, WA Investigators: Z. F. Zhang, and R. Khaleel The Concept of Tensorial Connectivity-Tortuosity for Multiple Fluids (TCT-MF) to Describe Saturation-Dependent Anisotropy in Hydraulic Conductivity (Z. F. Zhang, M. Oostrom, and A.L. Ward) Natural geological formations are heterogeneous and often anisotropic. Numerous researches have found that the anisotropy in hydraulic conductivity is dependent on fluid saturation. The tensorial connectivity-tortuosity (TCT) concept has been used to describe the hydraulic conductivity tensor of unsaturated soils with saturation-dependent anisotropy. In this investigation, this concept is extended as the concept of tensorial connectivity-tortuosity for multiple fluids (TCT-MF) in unsaturated porous media. The hydraulic conductivity of each fluid in an anisotropic porous medium under unsaturated conditions is described in the form of a symmetric second-order tensor. The TCT-MF theory applies to the generalized hydraulic conductivity model and compatible types of saturation-pressure formulations. The model shows that the anisotropic coefficient of any one of the fluids is dependent only on the saturation of the fluid being considered but independent of the saturation of other fluids. The TCT-MF concept was tested using numerical experiments of infiltration in synthetic Miller-similar soils with four levels of heterogeneity and four levels of anisotropy. The synthetic soils were generated to be anisotropic by allowing the saturated hydraulic conductivity to have different correlation ranges for different directions of flow. The numerical experiments of infiltration of two liquid phases, i.e., water and the nonaqueous phase liquid (NAPL) carbon tetrachloride, were conducted. The results show that, similar to water in a two-fluid (air-water) system, NAPL retention curves in a three-fluid (air-NAPL-water) system were independent of flow direction but dependent on soil heterogeneity; the connectivity-tortuosity coefficients were functions of both soil heterogeneity and anisotropy. The TCT-MF model accurately described the unsaturated hydraulic function of each fluid of the anisotropic soils and can be combined into commonly used relative permeability functions for use in multifluid flow-and-transport numerical simulations. USDA-ARS National Soil Tilth Laboratory and Iowa State University, Ames, IA Investigators: Dan Jaynes, Toby Ewing, Robert Horton The Extent of Farm Drainage in the United States (Jaynes) Accomplishments: Artificial drainage, whether surface or subsurface, profoundly affects the productivity of soils and the hydrology of watersheds. Modern production agriculture would not be possible without the extensive drainage network that has been built up starting in about the 1850’s. While an unqualified success for increasing agricultural production, research over the past quarter century has illustrated the important role drainage plays in determining the quality of surface water where drainage is used. Because of its distributed nature, extended installation history, the invisibility of subsurface drains, and the lack of a systematic survey in recent years, the extent of drainage in the US is poorly known. In this study, we used the information contained in the NRCS STATSGO soils database in conjunction with the National Land Cover Dataset for 1992 compiled by the USGS to estimate the distribution and extent of drainage

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across the U.S. Various soil characteristics within the database such as drainage class, hydrologic class, and land capability class are compared to existing surveys and NRI data for determining the distribution of drainage. Outcome: None of the STATSGO/NLCD estimates agree well with either the 1978 Census or NRI estimates for every state. While there is no absolute criteria for comparison because of the different definitions used for drained agricultural land in the historic surveys, it appears that the water, “w”, limitation for land capability classes II, III, and IV combined with the NLCD row crop and small grain land cover classification give a reasonable estimate of the extent of drained lands used for annual-crop production (Fig. 29). Impact. The approach used here could be refined by using the more recent 2001 NLCD database or substituting SSURGO data for STATSGO data. In addition, higher resolution spatial maps can be easily produced even from the STATSGO data by estimating drained area per map unit rather than aggregating up to county or state levels. Accurate estimates of the extent and location of drained land are important for determining the effect of agricultural practices on water quality at local, regional, and national scales. Fig. 29: Drained land estimate from STATSGO land capability class IIw, IIIw, and IVw combined with NLCD row crop and small grain land cover classification. Simulating Long-term Effects of Nitrogen Fertilizer Application Rates on Corn Yield and Nitrogen Dynamics (Jaynes): Accomplishments: Thoroughly tested agricultural systems models can be used to quantify the long-term effects of crop management practices under conditions where measurements are lacking. In a field near Story City, Iowa, USA, ten years (1996-2005) of measured data were collected from plots receiving low, medium, and high (57-67, 114-135, and 172-202 kg N ha-1) nitrogen (N) fertilizer application rates during corn (Zea mays L.) years. Using this data, the Root Zone Water Quality Model linked with the CERES and CROPGRO plant growth models (RZWQM-DSSAT) was evaluated for simulating the various N application rates to corn. The evaluated model was then

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used with a sequence of historical weather data (1961-2005) to quantify the long-term effects of different N rates on corn yield and nitrogen dynamics for this agricultural system. Outcome: Simulated and measured dry-weight corn yields, averaged over plots and years, were 7452 and 7343 kg ha-1 for the low N rate, 8982 and 9224 kg ha-1 for the medium N rate, and 9143 and 9484 kg ha-1 for the high N rate, respectively. Simulated and measured flow-weighted average nitrate concentrations (FWANC) in drainage water were 10.6 and 10.3 mg L-1 for the low N rate, 13.4 and 13.2 mg L-1 for the medium N rate, and 18.0 and 19.1 mg L-1 for the high N rate, respectively. The simulated N rate for optimum corn yield over the long-term was between 100 and 150 kg N ha-1. Currently, the owner-operator of the farm applies 180 kg N ha-1 to corn in nearby production fields. Reducing long-term N rates from 180 to 130 kg N ha-1 corresponded to an 18% simulated long-term reduction in N mass lost to water resources. Median annual FWANC in subsurface drainage water was decreased from 19.5 to 16.4 mg N L-1 with this change in management. Current goals for diminishing the hypoxic zone in the Gulf of Mexico call for N loss reductions of 30% and greater. Thus, long-term simulations suggest that at least half of this N loss reduction goal could be met by reducing N application rates to the production optimum. However, additional changes in management will be necessary to completely satisfy N loss reduction goals while maintaining acceptable crop production for the soil and meteorological conditions of this study. Impact: The results suggest that after calibration and thorough testing, RZWQM-DSSAT can be used to quantify the long-term effects of different N application rates on corn production and subsurface drainage FWANC in Iowa. Simulating the Long-term Performance of Drainage Water Management Across the Midwestern United States (Jaynes): Accomplishment: Drainage water management (DWM) has been proposed as a solution to reduce losses of nitrate-nitrogen (NO3-N) from subsurface drainage systems in the midwestern United States; however, measurements of DWM performance have only been collected over short-term periods of time and at a limited number of sites across the region. To fill this gap, the RZWQM-DSSAT hybrid model, previously evaluated for a subsurface-drained agricultural system in Iowa, was used to simulate both conventional drainage (CVD) and DWM over 25 years of historical weather data at 48 locations across the midwestern United States. Model simulations were used to demonstrate how variability in both climate and management practices across the region affects the ability of DWM to reduce losses of NO3-N in subsurface drainage. Outcome: Across the 48 locations, the simulated annual average reduction in subsurface drain flow ranged from 22 to 364 mm yr-1 when using DWM instead of CVD (Fig. 30); percent reductions in total subsurface drain flow over the long term ranged from 35% to 68%. Similarly for nitrogen (N), the simulated average annual reduction in NO3-N losses through subsurface drains ranged from 8 to 46 kg N ha-1 yr-1 when using DWM instead of CVD, and the percent reduction of NO3-N losses through subsurface drains over the long term ranged from 33% to 56% across the region. To counter the 151 mm yr-1 regional average annual decrease in subsurface drainage in response to DWM, the model simulated increases of 85 and 51 mm yr-1 for surface runoff and evapotranspiration, respectively. For the N cycle, the regional average annual decrease in NO3-N losses to subsurface drains in response to DWM was 19.4 kg N ha-1 yr-1, which was countered by 8.5, 5.9, 3.2, and 2.9 kg N ha-1 yr-1 increases in soil N storage, plant N uptake, N losses in seepage, and denitrification, respectively. When considering the pathways of subsurface drainage, surface runoff, and deep seepage collectively, DWM still reduced

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Fig. 30. (a) Average annual reduction in NO3-N losses through subsurface drains and (b) long-term percent reduction of NO3-N losses through subsurface drains when using drainage watermanagement instead of conventional drainage across the midwestern United States. undesirable waterborne NO3-N losses by 27% regionally. Spatial regression analysis demonstrated that precipitation amount and planting date were the most important model inputs affecting simulated reductions in subsurface drain flow across the region, and daily minimum temperature, precipitation amount, and the number of days between planting and harvest were the most important variables affecting simulated reductions in NO3-N loss through subsurface drains. Impact: The simulation results suggest that if DWM can be practically implemented on a large scale, particularly in the southern states of the region, significant reductions in the amount of NO3-N entering surface waters from agricultural systems can be expected. Modeling BiogeochemicalIimpacts of Alternative Management Practices for a Row-crop Field in Iowa (Jaynes): Accomplishments: The management of contemporary agriculture is rapidly shifting from single-goal to multi-goal strategies. The bottleneck of implementing the strategies is the capacity of predicting the simultaneous impacts of change in management practices on agricultural production, soil and water resources and environmental safety. Process-based models provide an opportunity to quantify the impacts of farm management options on various pools and fluxes of carbon (C) and nitrogen (N) in agroecosystems. The denitrification–decomposition or DNDC

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model was recently modified for simulating N cycling for the U.S. Midwestern agricultural systems. This paper reports a continuous effort on applying the model for estimating the impacts of alternative management practices (e.g., no-till, cover crop, change in fertilizer rate or timing) on agroecosystems in the Midwestern U.S. A typical row-crop field in Iowa was selected for the sensitivity tests. The modeled results were assessed with a focus on four major indicators of agro-ecosystems, namely crop yield, soil organic carbon (SOC) sequestration, nitrate–N leaching loss and nitrous oxide (N2O) emissions. Outcome: The results indicated that no-till practice significantly increased SOC storage and reduced nitrate–N leaching rate, but slightly decreased crop yield and increased N2O emissions. By modifying the methods of fertilizer application in conjunction with the no-till practice, the disadvantages of no-till could be overcome. For example, increasing the fertilizing depth and using a nitrification inhibitor could substantially reduce N2O emissions and increase crop yield under the no-till conditions. Impact: This study revealed the complexity of impacts of the alternative farming management practices across different climate conditions, soil properties and management regimes. Process-based models can play an important role in quantifying the comprehensive effects of management alternatives on agricultural production and the environment. University of Arizona, Tucson, AZ Investigator: Marcel Schaap Simulation of a contaminant plume in Hanford, WA (Ye et al, WRR, 2007) using artificial neural networks, geostatistics and vadose zone modelling Simulations of moisture flow in heterogeneous soils are often hampered by lack of measurements of soil hydraulic parameters, making it necessary to rely on other sources of information. In this paper, we develop a methodology to integrate data that can be easily obtained (e.g., initial moisture content, θi, bulk density, and soil texture) with data on soil hydraulic properties via cokriging and Artificial Neural Network (ANN) based pedotransfer functions. The method is applied to generate heterogeneous soil hydraulic parameters at a field injection site in southeastern Washington State. Stratigraphy at the site consists of imperfectly stratified layers with irregular layer boundaries. Cokriging is first used to generate three-dimensional (3-D) heterogeneous fields of bulk density and soil texture using an extensive dataset of field-measured θi, which carry signature about site heterogeneity and stratigraphy. Soil texture and bulk density are subsequently input into an ANN-based site-specific pedotransfer function to generate 3-D heterogeneous soil hydraulic parameter fields. The stratigraphy at the site is well represented by the estimated pedotransfer variables and soil hydraulic parameters. The parameter estimates are then used to simulate a field injection experiment at the site. A relatively good agreement is obtained between the simulated and observed moisture contents. The spatial distribution pattern of observed moisture content (Fig. 31) as well as the southeastward moisture movement is captured well in the simulations. In contrast to earlier work using an effective parameter approach, we are able to reproduce the observed splitting of the moisture plume in a coarse sand unit that is sandwiched between two fine-textured units. The simple method of combining cokriging and ANN for site

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characterization provides unbiased prediction of the observed moisture plume and is flexible so that additional measurements of various types can be included as they become available.

We think that the published work is a major advancement as it allows to predict where water and contaminants migrate in heterogeneous materials. We note that in this work no inverse simulation was carried out, only one forward simulation was needed. One assumption, however, was that the layering of the sediments necessitated an anisotropic hydraulic conductivity (vertical hydraulic conductivity was 10% of the horizontal conductivity). Other members of W-1188 (n.b. Fred Zhang) are currently developing anisotropic conductivity tensors that maybe helpful to further elucidate the effects of anisotropic sediments on water and solute transport.

Current activities involve a further assessment of uncertainty in modelled transport at the Hanford site. Essentially the generated medium was only one possible realization, with two major sources of uncertainty: uncertainty in the ANN estimates for hydraulic properties and kriging/co-kriging uncertainty that is used to generate the structured random fields of hydraulic parameters. It currently appears that the kriging/co-kriging uncertainty is the largest contributor to uncertainty in transport (Deng et al., 2007).

Fig. 31. (a-1 and b-1) Three-dimensional fields of observed (a-1) and simulated (b-1) water content on June 2, 2000; (a-2 and b-2) three-dimensional fields of observed (a-2) and simulated (b-2) water content on July 31, 2000. University of California, Davis, Hydrology (Dept. LAWR)

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Investigators: Jan Hopmans, Thomas Harter Soil moisture is a key variable controlling hydrological and energy fluxes in soils. Due to the heterogeneity of soils, atmospheric forcing, vegetation, and topography, soil moisture is spatially variable. Understanding and characterizing this spatial variability is one of the major challenges within hydrological sciences.

Understanding soil moisture variability and its relationship with water content at various scales is a key issue in hydrological research. In this paper we predict this relationship by stochastic analysis of the unsaturated Brooks-Corey flow in heterogeneous soils. Using sensitivity analysis, we show that parameters of the moisture retention characteristic and their spatial variability determine to a large extent the shape of the soil moisture variance-mean water content function. Our results show that the relationship between soil moisture variability and mean moisture content is controlled by soil hydraulic properties, their statistical moments and their spatial correlation. We demonstrate that soil hydraulic properties and their variability can be inversely estimated from spatially distributed measurements of soil moisture content. Predicting this relationship for eleven textural classes we found that the standard deviation of soil moisture peaked between 0.17 and 0.23 for most textural classes. It was found that the β parameter, which describes the pore-size distribution of soils, controls the maximum value of the soil moisture standard deviation. Collaborative arrangements Collaboration within the Regional Project has occurred with the US Salinity Laboratory (Simunek, van Genuchten) and with KSU (Kluitenberg), continuing the development of alternative laboratory and field methods for the estimation of soil physical properties using inverse modeling and parameter optimization across spatial scales. In addition, recent BARD funding made possible the collaboration between USDA Salinity Laboratory (Simunek) and UCD (Hopmans) on development of innovative approaches to model the compensated and active uptake of water and nutrients by plant roots. USDA NRI funding provided the support for collaborations with Northwestern University (Packman) on measuring and modeling Cryptosporidium parvum transport in the stream-streambed continuum. Impact: Both measurement and modeling methodologies were developed that allow for hydrological characterization of the vadose zone across spatial scales, using inverse modeling and scaling techniques. Utah State University, Logan, UT Investigator: Scott Jones Field-scale mapping of soil properties (David Robinson, Hiruy Abdu and Scott Jones) We continue to develop watershed-scale soil property mapping capabilities using electromagnetic induction. This past year the Reynolds Mountain East Watershed was mapped again with water content measurements made on the same day as the EMI map. A methodology paper is being developed to describe the process of obtaining statistically significant soil properties from the EMI maps of electrical conductivity. David Robinson is pursuing the

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additional idea of correlating vegetation maps with the EMI map to link hydrological properties with vegetation community structure. Impact: Two invited talks were given this year addressing the concept of linking ecological community structure with soil properties using electromagnetic induction mapping, one at AGU Joint Assembly and another at the Ecological Society of America meeting. Keywords: Electromagnetic induction, soil moisture, microgravity, water retention, soil mapping. Collaborative Arrangements: Collaboration is ongoing with the Dani Or (EPFL, Lausanne, Switzerland), Markus Tuller (U of Arizona), Gail Bingham and Bruce Bugbee (Utah State Univ.). I submitted proposals with David Robinson (Stanford University) and Fred Ogden at (Univ. of Wyoming). University of California, Riverside, CA Investigators: Jirka Šimůnek, Twarakawi, Sakai We have continued working in similar research areas as before, except that our research focus has shifted from issues associated with water quantity towards water quality. We have been active in the following research areas: (i) development and application of geochemical transport models, including HYDRUS, CW2D, and HP1, (ii) development and application of models capable to simulate colloid and colloid-facilitated solute transport, (iii) development and application of models capable to consider preferential/nonequilibrium flow and transport, (iv) application of numerical models to evaluate various micro-irrigation and fertigation schemes, (v) transport of various contaminants, (vi) developing and applying models for coupled transport of water, vapor and energy, (vii) development of HYDRUS (2D/3D), and (viii) miscellaneous work. i) Geochemical Modeling In the past three numerical models that have capabilities to consider simultaneously both physical (flow and transport) and biogeochemical (reactions) processes have been developed in our group. During the last year we applied these models to various scenarios (both real and hypothetical) and thus verified and validated the underlying assumptions and numerical implementation. a) The HP1 model resulted from coupling of the flow and transport code HYDRUS with a

geochemical model PHREEQC developed by USGS. The program can simulate a broad range of low-temperature biogeochemical reactions in water, soil and ground water systems including interactions with minerals, gases, exchangers, and sorption surfaces, based on thermodynamic equilibrium, kinetics, or mixed equilibrium-kinetic reactions. After releasing this program to the public in 2005 we have worked mostly on applications and are preparing a new release for 2008. We have been able to simulate transient flow simulations involving heavy metals and/or radionuclides involved in cation exchange, surface complexation, and aqueous complexation. We have compared Uranium fluxes under transient and steady-state flow conditions, and demonstrated that U migrated considerably faster under transient flow conditions, mainly due to changing geochemical conditions in the soil profile.

b) A new module CW2D (part of HYDRUS-2D) that models the biochemical transformation and degradation processes in subsurface flow constructed wetlands have been released to the public. The components defined in CW2D include: dissolved oxygen, organic matter

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(3 fractions of chemical oxygen demand: readily- and slowly-biodegradable, and inert), 4 nitrogen compounds (NH4

+, NO2-, NO3

-, and N2O), inorganic P, and heterotrophic and autotrophic microorganisms.

ii) Colloid, Virus, and Bacteria Transport Models and Colloid-Facilitated Solute Transport Models Models simulating the transport of colloids were further expanded by considering new processes, such as attachment to the air water interface and different blocking mechanisms and applied them to new data sets involving the transport of both colloids and bacteria. A model that can consider transport of solutes facilitated by the presence of colloids has also been developed. This model was applied to experimental data involving saturated column experiments, conducted to investigate the transport of cadmium (Cd) in the presence of Bacillus subtilis spores in alluvial gravel aquifer media. iii) Preferential/Nonequilibrium Flow and Transport Previously developed models capable of simulating preferential flow and transport using various dual-porosity and dual-permeability models were applied at both laboratory and field scales. A lot of new information is being obtained from these various applications at different spatial and temporal scales. iv) Applying Numerical Models to Evaluate Various Micro-Irrigation and Fertigation Schemes We have been working on applications of numerical models to analyze various micro-irrigation schemes involving fertigation. We managed to simulate the distribution of soil nitrogen, phosphorus, potassium, and nitrate for the subsurface drip irrigation system after applying a urea-ammonium-nitrate-phosphorus-potassium (NPK) fertilizer, commonly used for fertigation under drip irrigation. v) Transport of Various Contaminants Subsurface transport of various contaminants (not reported in other sections above) has been studied using my numerical models. For example, the HYDRUS-1D model was applied to simulate the transport of copper, TNT, RDX, and Composition B, pesticide isoproturon and antibiotics sulfadiazine. The HYDRUS-2D model was used to simulate the transport of nitrogen and herbicide bentazone. vi) Models for Coupled Transport of Water, Vapor and Energy. We have recently developed and applied to field data models that can consider simultaneous movement and transport of water, vapor, and energy, including the mass and energy balance at the soil surface. The model was also used to study theoretically function of heat pulse probe. vii) HYDRUS (2D/3D) We have released a major upgrade and extension of the popularly used HYDRUS-2D/MESHGEN-2D software package called HYDRUS (2D/3D). The new version has a completely new graphical environment for both two- and three-dimensional applications, and as such should provide users with much more flexibility and ease of use than the original HYDRUS-2D. The software also includes many new features in the computational modules. This new program is documented in two research reports.

Various applications of these programs can be found in many references given in the Publications section.

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California State University, Fresno, CA Investigator: Zhi Wang Spatial analysis of snowpack water resources in Sierra Nevada at the watershed scale The goal of this project was to quantify the amount of snowfalls and snowmelt in the Upper San Joaquin River Watershed. The snow pack data were collected from NOAA’s Hydrologic Remote Sensing Center for the Upper San Joaquin River watershed above Friant Dam. Little data were available before the year of 2003. Therefore, this project covers the more recent period from November 2003 to September 2006. The data sets included the observed snow depth in centimeters, the modeled snow depth (where and when measurements were not possible) and the modeled snow water depth in centimeters. A Digital Elevation Model (DEM) and a GRID file for the Upper San Joaquin River Watershed were created in ArcGIS software, and the GRID map was cut into the shape of the watershed for spatial analysis. Using the available data from 31 stations, contour maps of monthly and annual snow depth and snowmelts were created using the Kriging interpolation method and the volumes of water were calculated using 3-D Analysis (Fig. 32). These maps enabled visualization of the temporal and spatial changes of the snow packs and the snow melts. Our calculation showed that the cumulative snowfall started to increase in November, maximize in March and diminish in June. The volume of snowmelt started to increase in November, maximize in April and diminish in later September.

Fig. 32. Kriged maps of cumulative snowfall for the 2003-2004 and the 2004 to 2005 season.

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Montana State University, Bozeman, MT Investigators: Jon Wraith, Brian McGlynn Performance of Ash Disposal Pond Vegetated Cap System Coal-fired power plants generate large amounts of fly ash, often containing undesirable components (heavy metals, salts). The ash is transported (piped) to disposal ponds via water slurry (air pressure may be used, but is more expensive). Engineered vegetative caps are established on some ash disposal ponds with intent to prevent leaching of water through the ash, and into underlying groundwater. Most newer ponds are lined, but older ponds are generally not. We were asked to evaluate the performance of a vegetated cap on an ash disposal pond in Montana. The cap had previously been monitored using neutron moisture meter. More recently, automated TDR and climatic sensors were installed in selected locations of the cap. Most precipitation occurs at this location during late Spring, and sometimes during Fall. Based on two years of automated hourly monitoring, we found that the cap soil water storage reflects seasonal climate-vegetation-soil dynamics, as expected. Direct measurements confirmed our water balance calculations, and showed that meteoric water clearly reached the underlying ash layer during both years of observation. Thus occurred during late spring and early summer months, as the water holding capacity of the cap was exceeded. This phenomenon was not previously ‘visible’ through intermittent neutron meter measurements. Future work will include improved climatic measurements for ETp estimates (Penman-Monteith), and computer simulation (Hydrus-1D) to better evaluate options for improved management. Outcomes: Montana found that a vegetated cap system designed to prevent leaching of meteoric water into the underlying fly ash material failed to function as desired during both years of available data. Impacts: Work by W-1188 members will lead to improved function of disposal pond caps, representing critical inputs to environmental aspects of energy production. The study combines knowledge and tools developed/advanced by W-1188 scientists (e.g., soil physical processes, automated TDR, Hydrus computer simulation model) leading to improved soil/water resource management and protection. Effects of mountain resort development on water quality: Coupling upland flowpaths, N loading, and instream processing This research is being conducted in the 212 km2 West Fork of the Gallatin River watershed which drains the rapidly expanding resort community of Big Sky, Montana. Our first objective is to: 1) Identify geographic distribution of land use/land cover (LULC), and watershed characteristics and the spatial and seasonal variability of nitrogen (N) export. Our approach is to:

• Determine present LULC and watershed characteristics in the West Fork watershed using a combination of high-resolution remote-sensing imagery data (QuickBird) and airborne laser mapping (ALSM) topography data (both recently acquired).

• Perform synoptic sampling (spatially distributed “snapshot-in-time”) for water quality (major ions, N species, 15N and 18O of NO3

-) in the West Fork and selected tributaries (50+ locations) quarterly for two years, to capture major hydrologic conditions (onset of peak flow, peak flow, recession, and baseflow).

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• Perform weekly streamwater sampling in seven subwatersheds with varying levels of development (and distribution of LULC), to assess differences in the seasonal variability of N export in developed versus undeveloped watersheds.

• Apply novel isotopic techniques to streamwater to track N sources and calibrate N Export Model.

2) Our second objective is to quantify N uptake and address how present LULC and watershed characteristics translate to changes in N cycling in streams using NO3

- enrichment techniques. Our approach is to:

• Perform N releases in nine streams to quantify stream NO3- uptake. Focused effort in

four characteristic reaches during winter (low discharge, low biological activity, high NO3

-) and summer (low Q, high biological activity, low NO3-). Quantify the efficiency

and absolute rates of N uptake by streams and generate uptake coefficients for use in the N export model.

• Use NO3- enrichment releases to establish broadly applicable approaches to assessing N

uptake without the practical and financial limitations associated with heavy isotopic releases.

• Address how stream NO3- uptake differs with scale, landuse, and background N by conducting a synoptic study of N uptake (enrichment approach) within the West Fork watershed. Tie stream N uptake to LULC and watershed characteristics to link channel processes to spatially explicit distribution of LULC.

3) Our third objective is to develop and validate a spatially and topographically-based N export model to ascertain and model first-order controls of streamwater NO3

- concentration and provide a spatial mapping tool for land managers to determine vulnerability of N export in mountainous watersheds. Our approach is to:

• Develop a N export model incorporating results (above). • Construct a time series of LULC from the1940’s to present using aerial photos and

satellite imagery. Use the N export model to estimate historical NO3- concentrations and

assess occurrence of N saturation. • Determine the relationships among LULC, watershed characteristics and stages of N

saturation using the results above. • Develop a methodology (and mapping technique) for land managers to assess the impact

of various development scenarios on NO3-export.

Outcomes: This research develops an innovative method to examine the impact of geographic location and spatial distribution of land use/land cover change on the spatial, seasonal, and temporal patterns of streamwater nitrogen (N) by combining topographic and topologic analyses with distributed streamwater sampling, isotopic techniques, in-stream processing assessment, and a new N export coefficient model. This objective will help establish a benchmark research site to examine the impact of mountain resort development on stream function and water quality. Impacts: Montana is developing a simplified methodology, incorporating land use/land cover and topography data, to provide critical insight for land managers, planners and consulting agencies to examine the potential impacts of development scenarios on stream water quality. The results will give insight into the impact of human alteration of natural landscapes.

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University of Kentucky, Lexington, KY Investigator: Ole Wendroth How close to each other do soil samples need to be taken to monitor the spatial process of solute concentration and transport? Under certain conditions, surface-applied agrochemicals, i.e., fertilizers and pesticides can move rapidly downward through the unsaturated zone and cause negative effects on groundwater quality. Little is known on the impact and the coincidence of soil structural conditions, initial soil moisture, and upper boundary conditions subsequent to chemical application, especially amount and intensity of rainfall (Warnemuende et al., 2007) on leaching depth of surface-applied chemicals. Plot experiments will be performed with continuously changing surface boundary conditions to study the impact of different rainfall scenarios on leaching depth and vertical solute distribution. An important question is: How many soil samples are necessary and how big should a sample be to obtain the local solute concentration?

Bronswijk et al. (1995) determined solute depth profiles from 1-m-soil cores, and derived field-average solute transport behavior. Wendroth et al. (1998) observed field-average bromide transport using the same method but observations of solute concentration were spatially not structured. Spatial representativity of solute concentrations can generally not easily be determined due to pronounced heterogeneity (Tseng and Jury, 1994). However, in the experiment outlined above, local transport behavior and a spatial correlation of solute concentration needs to be obtained in order to derive site-specifically representative results on solute concentration and leaching depth.

The objective of this study was to apply an anionic tracer (KBr) to a field with changing initial soil moisture conditions and to measure solute concentration at a high spatial resolution of 0.25 m sampling distances using two augers of different size spatially alternatingly. Spatial analysis should show whether solute concentration was spatially distributed randomly or with structure, and whether solute concentrations at different depths were crosscorrelated with each other.

The soil is a well-drained Maury silt loam under pasture land, located at the Experimental Farm Spindletop of the Agricultural Experiment Station, University of Kentucky, Lexington, Kentucky. An area of 13 by 4 m was prewetted. Adjacent to this prewetted area, an area of 6.5 by 4 m was located which was initially dry (Fig. 33). A KBr tracer was applied with 40 g m-2 with 5.8 mm or irrigation water at a rate of 22 mm hr-1. The surface was covered with a plastic sheet after tracer application. A second irrigation of 40 mm was applied at the same intensity four days after tracer application. Soil samples were taken at 64 locations with depth increments of 10 cm down to 1 m at a spatial sampling distance of 0.25 m. A total of 640 samples was obtained. Two different types of augers were used, i.e., an Edelman auger with a diameter of 5 cm, and a jack-hammer driven Puerckhauer rill auger with a rill diameter of 2 cm. The sampling volumes obtained were 200 cm3 and 30 cm3, respectively. Use of the two auger types should clarify whether there was an effect of sample volume on the resulting soil water content and solute concentration.

Soil water content measurements after the tracer application and the subsequent irrigation of 40 mm are shown in Fig. 33 as well as the initial soil water storage in the 1 m profile. Results show the different initial moisture conditions distinctively. In the 0-10 cm sampling depth, water

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0 4 8 12 16DISTANCE, m

0.0

0.2

0.4

0.6SO

IL W

ATER

CO

NTE

NT,

m3 m

-3

20

25

30

35

40

INIT

IAL

WAT

ER S

TOR

AGE,

cm

INITIAL WATER STORAGE

0 - 10 cm

20 - 30 cm10 - 20 cm

Fig. 33. Initial soil water storage in the 1-m-profile and soil water content in the upper three sampled depths after tracer application. The zone from 0 to 11 m was prewetted, the zoen from 11 to 16 m was initially dry.

contents fluctuate regularly from 6 to 11 m. These alternatingly higher and lower values do not appear in any other zone, nor at any other depth.

Spatial distributions of anion concentration at the upper three and the subsequent three sampling depths are shown in Fig. 34 and 35, respectively.

0 4 8 12 16DISTANCE, m

0

20

40

60

80

ANIO

N C

ON

CEN

TRAT

ION

, ppm

20

25

30

35

40IN

ITIA

L W

ATER

STO

RAG

E, c

m

INITIAL WATER STORAGE0 - 10 cm

20 - 30 cm

10 - 20 cm

Fig. 34. Anion concentration for the upper three sampling depths along the transect. The zone from 0 to 11 m was prewetted, the zone from 11 to 16 m was initially dry.

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0 4 8 12 16DISTANCE, m

0

10

20

30

40

50

ANIO

N C

ON

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TRAT

ION

, ppm

20

25

30

35

40

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IAL

WAT

ER S

TOR

AGE,

cm

INITIAL WATER STORAGE

30 - 40 cm

50 - 60 cm40 - 50 cm

Fig. 35. Anion concentration for the three three sampling depths between 30 and 60 cm along the transect. The zone from 0 to 11 m was prewetted, the zone from 11 to 16 m was initially dry.

Anion concentration data in the 0 – 10 cm depth show no distinctive pattern and exhibit a large variance. The variance does not exhibit any spatial structure as obvious from the autocorrelation function. On the other hand, anion concentration values observed at depths between 10 and 40 cm show a distinct pattern (Figs. 34 and 35) and exhibit spatial structure (Fig. 36). Concentration measurements are spatially related (95 %) over a distance of four lags, corresponding to 1 m.

0 5 10 15 20LAG h, 0.25 m

-1.0

-0.5

0.0

0.5

1.0

AUTO

CO

RR

ELAT

ION

r(h) ANIONS, 10 - 20 cm DEPTH

Fig. 36. Spatial autocorrelation function of anion concentration at 10 -20 cm depth.

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Below 50 cm depth, the concentration values become relatively small, and do not exhibit a distinct spatial pattern, nor spatial autocorrelation structure. Probably, this result manifests that the applied tracer did not reach soil depths below 50 cm.

Observations in each of the subsequent depths between 10 and 40 cm depth are significantly spatially crosscorrelated over distances of up to 1 m.

Ellsworth and Boast (1996) derived shorter ranges of spatial dependence than in this study but in general, their findings of solute concentration being spatially correlated at distances below 1 m corresponds to our findings. References Bronswijk, J.J.B., W. Hamminga, and K. Oostindie. 1995. Field-scale solute transport in a heavy

clay soil. Water Resour. Res. 31:517-526. Ellsworth, T.R., and C.W. Boast. 1996. Spatial structure of solute transport variability in an

unsaturated field soil. Soil Sci. Soc. Am. J. 60:1355-1367. Tseng, P.H. and W.A. Jury. 1994. Comparison of transfer function and deterministic modeling of

area-averaged solute transport in a heterogeneous field. Water Resour. Res. 30:2051-2063. Warnemuende, E.A., J.P. Patterson, D.R. Smith, and C. Huang. 2007. effects of tilling no-till soil

on losses of atrazine and glyphosate to runoff water under variable intensity simulated rainfall. Soil Till Res. 95:19-26.

Wendroth, O., W. Pohl, S. Koszinski, and D.R. Nielsen. 1998. Field-scale soil water and solute transport in sandy and clayey soils. Proc. 16th Conf. ISSS. Montpellier, France.

Texas A&M University, College Station, TX Investigator: Binayak Mohanty Soil hydraulic properties (hydraulic conductivity, water retention) are by far the most important land surface parameters to govern the partitioning of soil moisture between infiltration and evaporation fluxes at a range of spatial scales. However, an obstacle to their practical application in the field, catchment, watershed, or regional scale is the difficulty of quantifying the “effective” soil hydraulic functions θ(h) and K(h), where theta is the soil water content, h is the pressure head and K is unsaturated hydraulic conductivity. Proper evaluation of the water balance near the land-atmosphere boundary depends strongly on appropriate characterization of soil hydraulic parameters under field conditions and at the appropriate process scale. In recent years we have adopted a multi-facet approach to this problem including: (1) a bottom-up approach, where larger-scale effective parameters are calculated by aggregating point-scale insitu hydraulic property measurements, (2) a top-down approach, where effective soil hydraulic parameters are estimated by inverse modeling using remotely sensed soil moisture measurements, and (3) an artificial neural network approach, where effective soil hydraulic parameters were estimated by exploiting the correlations with soil texture, topographic attributes, and vegetation characteristics at multiple spatial resolutions. Numerical and experimental results using these various effective soil hydraulic parameter estimation approaches including some comparisons between the approaches are presented in various publications for the SGP and SMEX remote sensing experimental regions well as for the Rio Grande river basin. Results show great promise for the use of remote sensing platforms for better understanding and characterization of the scale relationships in soil moisture and vadose zone hydraulic properties.

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University of California, Davis, Hydrology (Dept LAWR) Investigators: Thomas Harter, Farag Botros, Anthony O’Geen, and Peter Hernes Nonpoint Source Pollutant Transfer across Deep Vadose Zones – A Multiscale Investigation to Inform Regulatory Monitoring, Assessment, and Decision Making Project Objectives and Previous Work The overall objective of this project is to provide a rigorously upscaled modeling tool for basin-scale assessment of nonpoint source (NPS) pollutant transport in the heterogeneous, alluvial, and often deep vadose zones of California agricultural landscapes. Our principal research hypothesis is that flow and transport in these unsaturated sediment systems is subject to highly non-uniform, localized preferential flow and transport patterns that lead to accelerated solute transfer across the vadose zone with potentially limited attenuation not captured by current deterministic or stochastic vadose zone models. To test our hypothesis, we link core scale vadose zone information from two extensive deep vadose zone drilling projects (one completed, one ongoing) to the effective vadose zone transport of NPS pollutants at the field scale (orchard, field, corral, land application unit) and at the farm scale (farm, dairy) by using geostatistical analysis and by applying a high resolution vadose zone flow and a transport model.

An extensive characterization and geostatistical analysis of the geology, hydraulic properties, and nitrogen distribution in a 16 m deep vadose zone across a nectarine orchard in Fresno County has been the starting point for this project. Significant variability of hydraulic properties was found between and within the different lithofacies that make up the vadose zone. Most importantly, we found that the total amount of nitrogen mass contained within the deep vadose zone was significantly (4x) smaller than would be expected based on a nitrogen mass balance analysis (NMBA). Based on isotopic field evidence and a survey of literature data, large-scale denitrification and volatilization could not account for this discrepancy. Preferential flow was hypothesized to be the main reason for the lack of nitrogen stored in the vadose zone. Onsoy (2005) completed modeling of heterogeneous, transient flow and transport model of the entire 16 m deep vadose zone. In that work, heterogeneity of the flow parameters was implemented using a scaling factor approach (SFA) where a single parameter describes the heterogeneity of the unsaturated flow parameters. However, Oliveira et al. (2006) demonstrated in principle that the SFA may lead to significant underestimation of unsaturated flow and transport variability. Current Work: The previous modeling efforts were reviewed. Minor errors in the geostatistical analysis and in the flow and transport model implementation were fixed. To overcome the potential shortcomings of the SFA, we developed a fully non-linear, multi-parameter heterogeneity representation (MPHR). Unsaturated flow and transport simulations for both types of heterogeneity representations of the vadose zone were implemented with HYDRUS (Simunek et al., 2006). The flow velocity distribution in the MPHR-based simulations is indeed significantly more variable than in the SFA-based simulations (Fig. 37a, b). Yet, after seven years of nitrogen management, which is simulated using the actual, transient weather, irrigation, and fertilization history of this site during 1990 – 1996, the concentration distribution for both simulation types did not show a significant difference (Fig. 37c, d). Neither approach explained the low N storage in the deep vadose zone observed in the field.

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A) B)

C) D)

Fig. 37. Simulation results after 4 years for velocity in cm/day using A) scaling factors, B) full heterogeneity and log10 concentrations in mg/l for C) scaling factors, and D) full heterogeneity.

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A) B)

C) D)

Fig. 38. Number of particles after 7 years of continuous fertilizer application using A), scaling factors, B) full heterogeneous case. Mass flux using C), scaling factors, D) full heterogeneous case.

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We then hypothesized that we overestimated dispersion, which would counterbalance the strong heterogeneity in the advective transport of nitrate, effectively preventing preferential transport to be simulated accurately. We tested this hypothesis by implementing a transport model with negligible dispersion. HYDRUS does not offer such a transport code, hence a particle tracking technique was developed that we could couple with HYDRUS. To simplify the coupling, a steady-state (constant) infiltration flux of 0.2 cm/day (the average flux during 7-year record) was assumed and the corresponding steady-state flow field was computed with HYDRUS prior to the transport simulation. Transient, advection-only transport was simulated for 7 years during which 40,000 particles were applied to the top of the domain each day. Figure 38 shows that many of the particles cluster along narrow strips of the domain which supports our preferential flow hypothesis. Moreover, these narrow strips are associated with the highest water flux, hence most of the mass moves along relatively narrow pathways. Mass flux along preferential flow paths exceeds that in the remainder of the domain typically by a factor 2 – 5. Advection-only based results showed a notable decrease in the amount of nitrogen stored in the vadose zone but still show far higher vadose zone storage than was observed in our field measurements. Discussion We are finding that significant preferential flow occurs in the unsaturated zone due to its heterogeneous lithofacies composition. Yet, our initial hypothesis that a full accounting of heterogeneity in the simulation of flow based on Richards equation would explain the low nitrogen mass stored in the vadose zone, has been disproven. This is consistent with De Rooij (2000), Simunek et al. (2003), and Gardenas et al. (2006) who showed that Richards equation may be an inadequate model as it generally lead to relatively uniform flow and transport. Other expressions or assumptions such as dual porosity or mobile-immobile domains need to be included in the model to yield results that account for strong non-equilibrium preferential flow and transport. There was initially not enough evidence in our field measurements that supports using these type of models, but we are reconsidering such a conceptual approach. Other conceptual elements to test include denitrification that impacts more stagnant zones of water flow, but not as much denitrification in preferential flow paths, nitrogen losses due to volatilization at the land surface, and a re-examination of the orchard nitrogen budget, particularly the N cycling through the leaf mass. References Gardenas, A. I., J. Simunek, N. Jarvis, M. Th. Van Genuchten. 2006. Two-dimensional modeling

of preferential water flow and pesticide transport from a tile-drain field. J. Hydrol. 329: 647-660.

Oliveira L. I., A. H. Demond, L. M. Abriola, P. Goovaerts. 2006. Simulation of solute transport in a heterogeneous vadose zone describing the hydraulic properties using a multistep stochastic approach. Water Resour. Res. 42(5): W05420, doi:10.1029/2005WR004580.

Onsoy, Y. S., 2005. Modeling Nitrate Transport in Deep Unsaturated Alluvial Sediments and Assessing Impact of Agricultural Management Practices on Groundwater Quality. Ph.D. Dissertation, University of California, Davis.

de Rooij, G. H. 2000. Modeling fingered flow of water in soils owing to wetting front instability: a review. J. Hydrol. 231-232: 277-294.

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Simunek, J., N. J. Jarvis, M. Th. Van Genuchten, A. Gardenas. 2003. Review and comparison of models for describing non-equilibrium and preferential flow and transport in the vadose zone. J. Hydrol. 272: 14-35.

Simunek, J., M. Th. van Genuchten, M. Sejna. 2006. The HYDRUS Software Package for Simulating the Two- and Three-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated Media, PC Progress, Prague, Czech Republic.

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Publications – W1188 – January 1 – December 31, 2007 Abdu, H., D.A. Robinson and S. B. Jones. 2007. Comparing bulk soil electrical conductivity

determination using the DUALEM 1-S and EM-38DD EMI instruments. Soil Sci. Soc. Am. J. 71:189-196.

Baker, J.M., T.E. Ochsner, R.T. Venterea, and T.J. Griffis. 2007. Tillage and carbon sequestration--What do we really know? Agr. Ecosyst. Environ. 118:1-5.

Berli, M., A. Carminati, T.A. Ghezzehei, and D. Or. 2007a. Unsaturated hydraulic conductivity of aggregated soils under compression. Water Resour. Res. (Special Issue). In revision.

Berli, M., T. Caldwell, E.V. McDonald, and D.A. Gilewitch. 2007b. Modeling desert pavement deterioration due to heavy vehicle traffic. J. Terramechanics. In review.

Børgesen, C.D., B.V. Iversen, O.H. Jacobsen, M.G. Schaap. 2007. Pedotransfer functions estimating soil hydraulic properties using different soil parameters. Hydrol. Proc. In press.

Bradford, S. A., and N. Toride. 2007. A stochastic model for colloid transport and deposition. J. Environ. Qual. 36: 1346-1356.

Bradford, S. A., and S. Torkzaban. 2008. Colloid transport and retention in unsaturated porous media: A review of interface, collector, and pore scale processes and models. Vadose Zone J. In press.

Bradford, S. A., E. Segal, W. Zheng, Q. Wang, and S. R. Hutchins. 2008. Reuse of CAFO waterwater on agricultural lands: Potential environmental contaminants, transport pathways, and treatments. J. Environ. Qual. In press.

Bradford, S. A., S. Torkzaban, and S. L. Walker. 2007. Coupling of physical and chemical mechanisms of colloid straining in saturated porous media. Water Res. 41: 3012-3024.

Butler, J. J., Jr., G. J. Kluitenberg, D. O. Whittemore, S. P. Loheide, II, W. Jin, M. A. Billinger, and X. Zhan. 2007. A field investigation of phreatophyte-induced fluctuations in the water table. Water Resour. Res. 43:W02404 doi:10.1029/2005WR004627.

Caldwell, T.G., E.V. McDonald, and M.H. Young. 2007b. The seedbed microclimate and active revegetation of disturbed lands in the Mojave Desert. J. Arid Environ. In revision

Caldwell, T.G., E.V. McDonald, S.N. Bacon, and G. Stullenbarger. 2007a. The performance and sustainability of vehicle dust courses for military testing. J. Terramechanics. In press.

Casey, F.X.M., P. Odour, H. Hakk, and G.L. Larsen. 2007. Transport of 17ß-Estradiol and Testosterone in a field lysimeter. In Annual Meetings Abstracts [CD-ROM]. ASA, CSSA, and SSSA, Madison, WI.

Chen, W., A.C. Chang, and L. Wu. 2007. Assessing long-term environmental risks of trace elements in Phosphate fertilizers. Ecotoxicol. Environ. Safety 67:48-58.

Chen, W., A.C. Chang, L. Wu, L. Li, S.-I. Kwon, and A.L. Page. 2007. Probability distribution of Cd partitioning coefficients of cropland soils. Soil Sci. 172:132-140.

Chen, W., L. Li, A.C. Chang, L. Wu, S.-I. Kwon, and R. Bottoms. 2007. Modeling the uptake kinetics of cadmium by field-grown lettuce. Environ. Pollut. doi:10.1016/j.envpol.2007.05.004.

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Chief, K., T.P.A. Ferré, and A. C. Hinnell. 2007b. The effects of anisotropy on in situ air permeability measurements. Vadose Zone J. Accepted.

Chief, K., T.P.A. Ferré, and B. Nijssen. 2006. Field testing of a soil corer air permeameter (SCAP) in desert soils. Vadose Zone J. 5:1257-1263.

Chief, K., T.P.A. Ferré, and B. Nijssen. 2007a. Predicting saturated hydraulic conductivity from air permeability in unburned and burned soils. Soil Sci. Soc. Am. J. Accepted.

Conrad, M. E., D. J. DePaolo, K. Maher, G. W. Gee, and A. L. Ward. 2007. Field evidence for strong chemical separation of contaminants in the Hanford vadose zone. Vadose Zone J. 6:1031-1041.

Corwin, D. L., J. D. Rhoades, and J. Šimůnek. 2007. Leaching requirement for soil salinity control: Steady-state vs. transient-state models. Agric. Water Manage. 90:165-180.

Covino, T.P., and B.L. McGlynn. 2007. Stream gains and losses across a mountain-to-valley transition: Impacts on watershed hydrology and stream water chemistry. Water Resour. Res. 43, W10431, doi:10.1029/2006WR005544.

Das, N.N., and B.P. Mohanty. 2007. Dynamics of PSR-based soil moisture in a large agricultural landscape during SMEX02: A wavelet approach wavelet analyses. Rem. Sens. Environ.

Das, N.N., B.P. Mohanty, M.H. Cosh, and T.J. Jackson. 2007. Modeling and assimilation of root zone soil moisture using remote sensing observations in Walnut Gulch watershed during SMEX04. Rem. Sens. Environ.

Derby, N.E., F.X.M. Casey, and D.W. Franzen. 2007. Comparison of Nitrogen management zone delineation methods for Corn grain yield. Agron J. 10.2134/agronj2006.0027 99:405-414.

Devitt, D.A., M.H. Young, M. Baghzouz, and B.M. Bird. 2007. Surface temperature, heat loading, and spectral reflectance of artificial turfgrass. J. Turfgrass Res. In press.

Dousset, S., M. Thevenot, V. Pot, J. Šimunek, and F. Andreux. 2007. Evaluating equilibrium and non-equilibrium transport of bromide and isoproturon in disturbed and undisturbed soil columns. J. Contam. Hydrol. 94, 261-276.

Doyle, T.E., D.A. Robinson, S.B. Jones, K.H. Warnick and B.L. Carruth. 2007. Modeling the permittivity of two-phase media containing monodisperse spheres: Effects of microstructure and multiple scattering. Physical Review B 76 (5), 054203.

Dragila, M. I. 2007. Improved characterization and quantification of flow and transport processes in soils. W-1188 Regional Project Annual Report for 2007

Eggers C.G., M. Berli, M.L. Accorsi, D. Or. 2007. Permeability of deformable soft aggregated earth materials: From single pore to sample cross section. Water Resour. Res. 43. Art. No. W08424.

Ewing, R. P., and R. Horton. 2007. Thermal conductivity of a cubic lattice of spheres with capillary bridges. J. Phys. D Appl. Phys. 40: 4959-4965.

Fan, Z. 2007. Measuring and modeling fate and transport of natural hormones in soil-water systems. Research Dissertation, North Dakota State University, Fargo.

Fan, Z.S., F.X.M. Casey, H. Hakk, and G.L. Larsen. 2007a. Persistence and fate of 17β-estradiol and testosterone in agricultural soils. Chemosphere 67:886-895.

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Fan, Z.S., F.X.M. Casey, H. Hakk, and G.L. Larsen. 2007b. Discerning and modeling the fate and transport of testosterone in undisturbed soil. J. Environ. Qual. 36:864-873.

Farahbakhshazad, N., D.L. Dinnes, C. Li, D.B. Jaynes, and W. Salas. 2008. Modeling biogeochemical impacts of alternative management practices for a row-crop field in Iowa. Agricult. Ecosys. Environ. 123:30–48.

Flury, M. and J. Mon. 2007. Dyes as hydrological tracers. In: The Encyclopedia of Water, edited by J. H. Lehr, J. Keeley, and J. Lehr, John Wiley, New York. In press.

Flury, M., and H. Qiu. 2007. Modeling colloid-facilitated contaminant transport in the vadose zone. Vadose Zone J. In press.

Flynn, E.S., C.T. Dougherty, and O. Wendroth. 2007. Assessment of Grassland Condition with the Normalized Difference Vegetation Index. Agron. J. (accepted, in press).

Gargiulo, G., S. A. Bradford, J. Simunek, P. Ustohal, H. Vereecken, and E. Klumpp. 2007. Bacteria transport and deposition under unsaturated conditions: the role of the matrix grain size and the bacteria surface protein. J. Contam. Hydrol. 92: 255-273.

Gargiulo, G., S. A. Bradford, J. Šimůnek, P. Ustohal, H. Vereecken, and E. Klumpp. 2007. Transport and deposition of metabolically active and stationary phase Deinococcus Radiodurans in unsaturated porous media. Environ. Sci. Technol. 41:1265-1271.

Gaur, A., D. B. Jaynes, R. Horton, and T. E. Ochsner. 2007. Surface and subsurface solute transport properties at row and inter-row positions. Soil Sci. 172:419-431.

Gee, G. W., M. Oostrom, M. D. Freshley, M. L. Rockhold, and J. M. Zachara. 2007. Hanford site vadose zone studies: An overview. Vadose Zone J. 6:899-905.

Hanson, B. R., J. Šimůnek, and J. W. Hopmans. 2008. Leaching with subsurface drip irrigation under saline, shallow ground water conditions. Vadose Zone J. In press.

Hanson, B.R., J.W. Hopmans, and J. Simunek. 2007. Leaching with subsurface drip irrigation under saline, shallow groundwater conditions. Vadose Zone J. In press.

Haruta, S., W. Chen, J. Gan, J. Simunek, A. Chang, and L. Wu. 2007. Leaching risk of N-nitrosodimethylamine (NDMA) in soil receiving reclaimed wastewater.

Heinse, R., S.B. Jones, S. Steinberg, M. Tuller, and D. Or. 2007. Effects of variable gravity on liquid behavior in particulate porous media: Measurements and modeling. Vadose Zone J. In press.

Heinse, R., S.B. Jones, S. Steinberg, M. Tuller, and D. Or. 2007. Uncovering the challenges of watering plants in space. Crops, Soils, Agronomy (CSA) News. 52(12):1-4.

Heinse, R., S.B. Jones, S.L. Steinberg, M. Tuller, and D. Or, 2007. Measurements and modeling of variable gravity effects on water distribution and flow in unsaturated porous media. Vadose Zone J. 6:713-724, doi:10.2136/vzj2006.0105.

Heitman, J.L., A. Gaur, R. Horton, D.B. Jaynes, and T.C. Kaspar. 2007. Field measurement of soil surface chemical transport properties for comparison of management zones. Soil Sci. Soc. Am. J. 71:529-536.

Heitman, J.L., R. Horton, T. Ren, and T.E. Ochsner. 2007. An improved approach for measurement of coupled heat and water transfer in soil cells. Soil Sci. Soc. Am. J. 71:872-880. 10.2136/sssaj2006.0327.

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Heitman, J.L., R. Horton, T.J. Sauer, and T.M. DeSutter. 2008. Sensible heat observations reveal soil-water evaporation dynamics. J. Hydromet. In press.

Hopmans, J.W. 2006. Plant water and nutrient uptake in soil-root systems. 5.1. Rhizosphere Models. In Handbook of Methods used in rhizosphere research. COST. Swiss Federal Research Institute WSL, Birmensdorf, pg. 495-96.

Hopmans, J.W. 2007. A plea to reform soil science education. Commentary. Soil Sci. Soc. Am. J. 71:639-640.

Huang, H., D.T. Thorne, M.G. Schaap, and M.C. Sukop. 2007. A priori determination of contact angles in Shan-and- Chen-type multi-component multiphase lattice Boltzmann models. Phys Rev E., 76, 066701

Hyatt, J., O. Wendroth, D.B. Egli, and D.M. TeKrony. 2007. Soil Compaction and Soybean Seedling Emergence. Crop Sci. 47:2495–2503.

Istok, J.D., M.M. Park, A.D. Peacock, M. Oostrom, and T.W. Wietsma. 2007. An experimental investigation of nitrogen gas produced during denitrification. Ground Water 45:461-467.

Jacques, D., J. Šimůnek, D. Mallants, and M. Th. van Genuchten. 2008. Modeling coupled hydrological and chemical processes in the vadose zone: a case study on long term uranium migration following mineral P-fertilization. Vadose Zone J. Special Issue “Vadose Zone Modeling”. In press.

Jana, R., B.P. Mohanty, and E.P. Springer. 2007. Multi-scale pedo-transfer functions for soil water retention. Vadose Zone J. 6:868-878.

Jaynes, D.B., D.C. Olk, T.S. Colvin, T.C. Kaspar, and D.L. Karlen. 2007. Response to “Comments on ‘Need for a soil-based approach in managing nitrogen fertilizers for profitable Corn production’ and ‘soil organic nitrogen enrichment following Soybean in an Iowa Corn-Soybean rotation’”. Soil Sci. Soc. Am. J. 71:255.

Jones, S.B., and K. Shenai. 2007. Subsurface measurement needs for ecological, hydrological and agricultural applications. Proc. 50th IEEE Int. Midwest Symp. on Circuits and Systems (MWSCAS). August 5-7, Montreal, CA, Invited.

Kaspar, T.C., D.B. Jaynes, T.B. Parkin, and T.B. Moorman. 2007. Rye cover crop and gamagrass strip effects on NO3 concentration and load in tile drainage. J. Environ. Qual. 36:1503–1511.

Khaleel, R., M. D. White, M. Oostrom, M. I. Wood, F. M. Mann, and J. G. Kristofzski. 2007. Impact assessment of existing vadose zone contamination at the Hanford Site SX tank farm. Vadose Zone J. 6:935-945.

Kim, S.B., H.S. On, D.J. Kim, W. A. Jury, and Z. Wang. 2007. Determination of bromacil transport as a function of water and carbon content in soils. J. Environ. Sci. Health Part B 42:529–537.

Kluitenberg, G.J., T.E. Ochsner, and R. Horton. 2007. Improved analysis of heat pulse signals for soil water flux determination. Soil Sci. Soc. Am. J. 71:53-55. 10.2136/sssaj2006.0073N.

Knight, J.H., W. Jin, and G. J. Kluitenberg. 2007. Sensitivity of the dual-probe heat-pulse method to spatial variations in heat capacity and water content. Vadose Zone J. 6:746-758.

Kodešová, R., M. Kočárek, V. Kodeš, J. Šimůnek, and J. Kozák. 2008. Impact of soil micromorphological features on water flow and herbicide transport in soils. Vadose Zone

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J. Special Issue “Vadose Zone Modeling”. In press. Last, G. V., C. J. Murray, D. A. Bush, E. C. Sullivan, M. L. Rockhold, R. D. Mackley, and B. N.

Bjornstad. 2007. Standardization of borehole data to support vadose zone flow and transport modeling. Vadose Zone J. 6:906-912.

Lazarovitch, N., A. Ben-Gal, J. Šimůnek, and U. Shani. 2007. Uniqueness of soil hydraulic parameters determined by a combined Wooding inverse approach. Soil Sci. Soc. Am. J. 71, doi:10.2136/sssaj2005.0420, 860-865.

Lazarovitch, N., A. W. Warrick, A. Furman, and J. Šimůnek. 2007. Subsurface water distribution from drip irrigation described by moment analyses, Vadose Zone J. 6:116-123.

Lebron, I., M.D. Madsen, D.G. Chandler, D.A. Robinson, O. Wendroth, and J. Belnap. 2007. Ecohydrological controls on soil moisture and hydraulic conductivity within Pinyon-Juniper Woodland. Water Resour. Res. 43, W08422, doi:10.1029/2006WR005398.

Lee, K. H., N. Zhang, and G. Kluitenberg. 2007. A frequency-response permittivity sensor for simultaneous measurement of multiple soil properties: Part I. The frequency-response method. Trans. ASABE 50:2315-2326.

Lewis, S.A., P.R. Robichaud, B.E. Frazier, J.Q. Wu. and D.W. Laes. 2007. Using hyperspectral imagery to predict post-wildfire soil water repellency. Geomorphol. In press.

Li, H., and L. Wu. 2007. A generalized linear equation for non-linear diffusion in external fields and non-ideal systems. New J. Physics 9:357.

Li, H., and L. Wu. 2007. A new approach to estimate ion distribution between the exchanger phase and solution phase. Soil Sci. Soc. Am. J. 71:1694-1698.

Li, H., H. Li, W.-J. Shi, and Z. Wang. 2007. Research of finger flow in porous media - Summary and perspective. Soils.

Liu, G., B. Li, T. Ren, and R. Horton. 2007. Analytical solution of heat pulse method in a parallelepiped sample space. Soil Sci. Soc. Am. J. 71: 1607-1619.

Loescher, H.W., J. Jacobs, O. Wendroth, D.A. Robinson, G.S. Poulos, K. McGuire, P. Reed, B.P. Mohanty, J.B. Shanley, W. Krajewski. 2007. Enhancing water cycle measurements for future hydrologic research. Bulletin of American Meteorological Society (BAMS) 88:669-676. DOI:10.1175/BAMS-88-5-669.

Lu, S., T. Ren, Y. Gong, and R. Horton. 2007. An improved model for predicting room temperature soil thermal conductivity versus water content. Soil Sci. Soc. Am. J. 71:8-14.

Ma, L., R.W. Malone, P. Heilman, D.B. Jaynes, L.R. Ahuja, S.A. Saseendran, R.S. Kanwar, and J.C. Ascough II. 2007. RZWQM simulated effects of crop rotation, tillage, and controlled drainage on crop yield and nitrate-N loss in drain flow. Geoderma 140:260–271.

Meadows, D.G., M.H. Young, E.V. McDonald. 2007. Influence of surface age on infiltration mechanisms of desert pavements, Mojave Desert. Catena 72:169-178.

Moffett, K., S. Tyler, T. Torgersen, M. Menon, J. Selker and S. Gorelick. 2007. Distributed temperature sensing of thermal trends and anomalies in the bed of an intertidal salt marsh and channel: The tidal thermal blanket effect. Environ. Science Tech. In press.

Mohanty, B. P., and J. Zhu. 2007. Effective hydraulic parameters in horizontally and vertically heterogeneous soils for steady-state land–atmosphere interaction. J. Hydrometeorol. 8: 715-729.

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Murray, C. J., A. L. Ward, and J. L. Wilson. 2007. Influence of clastic dikes on vertical migration of contaminants at the Hanford Site. Vadose Zone J. 6:959-970.

Nachshon, U., N. Weisbrod, M.I. Dragila. 2007. Quantifying air convection through surface-exposed fractures. Vadose Zone J. Submitted.

Ochsner, T.E., T.J. Sauer, and R. Horton. 2007. Soil heat storage measurements in energy balance studies. Agron. J. 99:311-319. 10.2134/agronj2005.0103S.

Oostrom, M., J.H. Dane, and T.W. Wietsma. 2007. A review of multidimensional, multifluid intermediate-scale experiments: Flow behavior, saturation imaging, and tracer detection and quantification . Vadose Zone J. 6:610-637. doi:10.2136/vzj2006.0178

Oostrom, M., M. L. Rockhold, P. D. Thorne, M. J. Truex, G. V. Last, and V. J. Rohay. 2007. Carbon Tetrachloride flow and transport in the subsurface of the 216-Z-9 trench at the Hanford Site. Vadose Zone J. 6:971-984.

Oostrom, M., M.J. Truex, P.D. Thorne, and T.W. Wietsma. 2007. Three-dimensional multifluid flow and transport at the Brooklawn site near Baton Rouge, LA: A Case Study. Soil Sediment Contamin. 16:109-141.

Oostrom, M., T.W. Wietsma, M.A. Covert, and V.R. Vermeul. 2007. Zero-valent iron emplacement in permeable porous media using polymer additions. Ground Water Monit. Remed. 27:122-130.

Or, D., B.F. Smets, J.M. Wraith, A. Duchesne, and S.P. Friedman. 2007. Physical constraints affecting bacterial habitats and activity in unsaturated porous media - a review. Adv. Water Resour. Special Issue: Biological processes in porous media: from the pore scale to the field. 30:1505-1527.

Pan, F., M. Ye, Y.-S. Wu, B.X. Hu, J. Zhu, and Z. Yu. 2007. Uncertainty assessment of unsaturated flow and tracer transport in heterogeneous fractured media. J. Contam. Hydrol. In revision.

Pang, L., M. McLeod, J. Aislabie, J. Šimůnek, M. Close, and R. Hector. 2008. Modeling transport of fecal coliforms and Salmonella bacteriophage in ten undisturbed New Zealand soils under dairy shed effluent irrigation. Vadose Zone J. In press.

Riveros-Iregui, D.A., R.E. Emanuel, D.J. Muth, B.L. McGlynn, H.E. Epstein, D.L. Welsch, V.J. Pacific, and J.M. Wraith. 2007. Diurnal hysteresis between soil CO2 and soil temperature is controlled by soil water content. Geophys. Res. Lett. 34. L17404. doi:10.1029/2007GL030938.

Robinson, D.A., S.B. Jones, T. Doyle, J.M. Blonquist, H. Abdu, V. Urdanoz, R. Aragues. 2007. Hydrological processes and properties of soil using electromagnetic measurement. Proc. Int. Conf. Microwaves Optoelectronics 2007 (ICMO), December 17-20, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, India.

Saito, H., J. Šimůnek, J. W. Hopmans, and A. Tuli. 2007. Numerical evaluation of the heat pulse probe for simultaneous estimation of water fluxes and soil hydraulic and thermal properties. Water Resour. Res. 43: W07408, doi:10.1029/2006WR005320.

Saleh, A., E. Osei, D.B. Jaynes, B. Du, and J.G Arnold. 2007. Economic and environmental impacts of LSNT and cover crops for nitrate-nitrogen reduction in Walnut Creek watershed, Iowa, using FEM and enhanced SWAT models. Trans. ASABE 50: 1251-1259.

Sansoulet, J., Y.-M. Cabidoche, P. Cattan, S. Ruy, and J. Šimůnek. 2008. Spatially distributed

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water fluxes in an Andisol under banana plants: experiments and 3D modelling. Vadose Zone J. Special issue “Vadose Zone Modeling”. In press.

Sauer, T.J., T.E. Ochsner, and R. Horton. 2007. Soil heat flux plates: Heat flow distortion and thermal contact resistance. Agron. J. 99:304-310. 10.2134/agronj2005.0038s.

Schaap, M.G, M.L. Porter, B.S.B. Christensen, and D. Wildenschild, 2007a. Comparison of pressure-saturation characteristics derived from computed tomography and lattice Boltzmann simulations. Water Resour. Res. 43, W12S06, doi:10.1029/2006WR005730

Segal., E., S. A. Bradford, P. Shouse, N. Lazarovitch, and D. Corwin. 2008. Integration of hard and soft data to characterize field-scale hydraulic properties for flow and transport studies. Vadose Zone J. In press.

Seibert J., and B.L. McGlynn. 2007. A new triangular multiple flow-direction algorithm for computing upslope areas from gridded digital elevation models. Water Resour. Res. 43, W04501, doi:10.1029/2006WR005128.

Shafer, D.S., M.H. Young, S.F. Zitzer, T.G. Caldwell, E.V. McDonald. 2007. Impacts of interrelated biotic and abiotic processes during the past 125,000 years of landscape evolution in the northern Mojave Desert, Nevada, U.S.A. J. Arid Environ. 69:633-657.

Šimůnek, J. 2007. Models for soil pollution risk assessment, Proc. of NATO Advanced Research Workshop “Air, Water and Soil Quality Modelling for Risk and Impact Assessment”, Eds. A. Ebel and T. Davitashvili, NATO Security through Science Series – C: Environmental Security, Springer, ISBN-10 1-4020-5876-4 (PB), 221-233.

Šimůnek, J., and M. Th. van Genuchten. 2008. Modeling nonequilibrium flow and transport with HYDRUS. Vadose Zone J. Special Issue “Vadose Zone Modeling”. In press.

Šimůnek, J., M. Th. van Genuchten, and M. Šejna. 2007. Modeling subsurface water flow and solute transport with HYDRUS and related numerical software packages, In: Garcia-Navarro & Playán (eds.), Numerical Modelling of Hydrodynamics for Water Resources, An International Workshop, Centro Politecnico Superior, University of Zaragoza Spain, June 18-21 2007. Taylor & Francis Group, London, ISBN 978-0-415-44056-1, 95-114.

Šimůnek, J., M. Th. van Genuchten, and M. Šejna. 2008. Development and applications of the HYDRUS and STANMOD software packages, and related codes. Vadose Zone J. Special Issue “Vadose Zone Modeling”. In press.

Smucker, A., and J.W. Hopmans. 2007. Soil biophysics. doi:10.2136/vzj2007.0057. Vadose Zone J. 6:267-268.

Srivastava, P., K. W. Migliaccio, and J. Šimunek. 2007. Centennial manuscript: Terrestrial models for simulating water quality at point, field, and watershed scales, Trans. ASAE 50:1683-1693.

Suarez, F., J. Bachmann, J.F. Munoz, C. Ortiz, S. Tyler, C. Alister and M. Kogan. 2007. Transport of Simazine in unsaturated sandy soils and prediction of leaching under field conditions. J. Contam. Hydrol. 94(3/4):166-177.

Thornton, E. C., L. Zhong, M. Oostrom, and B. Deng. 2007. Experimental and theoretical assessment of the lifetime of a gaseous-reduced vadose zone permeable reactive barrier. Vadose Zone J. 6:1050-1056.

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Thorp, K.R., R.W. Malone, and D.B. Jaynes. 2007. Simulating long-term effects of nitrogen fertilizer application rates on corn yield and nitrogen dynamics. Trans. ASABE 50:1287-1303.

Torkzaban, S., S. A. Bradford, and S. L. Walker. 2007. Resolving the coupled effects of hydrodynamics and DLVO forces on colloid attachment to porous media. Langmuir 23: 9652-9660.

Torkzaban, S., S. A. Bradford, M. Th. van Genuchten, and S. L. Walker. 2007. Colloid transport in unsaturated porous media: The role of water content and ionic strength on particle straining. J. Contam. Hydrol. In press.

Torkzaban, S., S. S. Tazehkand, S. L. Walker, and S. A. Bradford. 2008. Transport and fate of bacteria in porous media: Coupled effects of chemical conditions and pore space geometry. Water Resour. Res. In press.

Tumlinson, L.G., J.W. Hopmans, Liu, and W.K. Silk. 2008. Thermal neutron computed tomography of soil water and plant roots. Soil Sci. Soc. Am. J. In press.

Twarakavi, N. K. C., H. Saito, and J. Šimůnek. 2008. A new approach to estimate soil hydraulic parameters using only soil water retention data. Soil Sci. Soc. Am. J. In press.

Twarakavi, N. K. C., J. Šimůnek, and H. S. Seo. 2008. Evaluating interactions between groundwater and vadose zone using HYDRUS-based flow package for MODFLOW. Vadose Zone J. Special Issue “Vadose Zone Modeling”. In press.

Tyler, S.W., S. Burak, J. McNamara, A. Lamontagne, J. Selker and J. Dozier. 2007. Fiber optic measurement of distributed base temperatures of two snowpacks. Journal of Glaciology. Submitted

Vereecken, H., T. Kamai, T. Harter, R. Kasteel, J. Hopmans, and J. Vanderborght (2007), Explaining soil moisture variability as a function of mean soil moisture: A stochastic unsaturated flow perspective. Geophys. Res. Lett. 34, L22402, doi:10.1029/2007GL031813.

Wang, Q., and R. Horton. 2007. Boundary layer theory description of solute transport in soil. Soil Sci. 172:835–841.

Wang, X.-P., M.H. Young, Z. Yu, and Z.-S. Zhang. 2007 Long-term effects of restoration on soil hydraulic properties in revegetation-stabilized desert ecosystems. Geophys. Res. Lett. doi:10.1029/2007GL031725.

Ward, A. L., and Z. F. Zhang. 2007. Effective hydraulic properties determined from transient unsaturated flow in anisotropic soils. Vadose Zone J. 6:913-924.

Watanabe, K., N. Toride, M. Sakai, and J. Šimůnek. 2007. Numerical modeling of water, heat, and solute transport during soil freezing. J. Jpn. Soc. Soil Physics, 106, 21-32.

Wehrhan, A., R. Kasteel, J. Šimůnek, J. Groeneweg, and H. Vereecken. 2007. Transport of sulfadiazine in soil columns – experiments and modeling approaches, J. Contam. Hydrology, 89(1-2), 107-135.

Wendroth, O. and D.A. Robinson. 2007. Scaling processes in watersheds. Encyclopedia of Water Science 2. Taylor and Francis. In press.

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Wendroth, O., and N. Wypler. 2007. Unsaturated hydraulic properties: Laboratory evaporation. In: M.R. Carter and E.G. Gregorich (Eds.) Soil sampling and methods of analysis. Canadian Society of Soil Science, 2nd ed., CRC Press, Boca Raton, FL, pp. 1089-1106.

Winowiecki, L., E. Somarriba, P. McDaniel, M. Tuller, J. Jonson-Maynard, and A. Falen, 2007. Biogeochemical cycling of base cations in a cacao agroforestry system in the Cabecar Indigenous Territory, Talamanca, Costa Rica. Proc. 15th Int. Cocoa Res. Conf. VOL I, pp. 423-429.

Wondzell, S.M., M. Gooseff, and B.L. McGlynn. 2007. Flow Velocity and the hydrologic behavior of streams during baseflow. Geophys. Res. Lett. 34, L24404, doi:10.1029/2007GL031256.

Wood, Y.A., M. Fenn, T. Meixner, P. J. Shouse, J. Breiner, E. Allen, and Laosheng. Wu. 2007. Smog nitrogen and the rapid acidification of forest soil, San Bernardino Mountains, southern California. The Scientific World J. 7: 175-180.

Wu, L., R. Green, M. Yates, P. Pacheco, and G. Klein. 2007. Nitrate leaching in overseeded Bermudagrass fairways in two Southern California irrigated soils. Crop Sci. 47:2521-2528.

Ye, M., M.G. Schaap, R. Khaleel, and J. Zhu. 2007. Simulation of field injection experiments in heterogeneous unsaturated media using cokriging and artificial neural network. Water Resour. Res. 43, W07413, doi:10.1029/2006WR005030.

Ye, M., R. Khaleel, M.G. Schaap, and J. Zhu, 2007. Simulation of field injection experiments in a layered formation using geostatistical methods and artificial neural network. Water Resour. Res. 43, W07413, doi:10.1029/2006WR005030).

Yin, J., M.H. Young, Z. Yu. 2007. Effects of Paleoclimate and time-varying canopy structures on Paleo-water fluxes. J. Geophysical Res. – Atmospheres. In press.

Young, C., W. Wallender, G. Schoups, G. Fogg, B. Hanson, T. Harter, J. Hopmans, R. Howitt, T. Hsiao, S. Panday, K. Tanji, S. Ustin, and K. Ward. 2007. Modeling shallow water table evaporation in irrigated regions. Irrig. Drain. Syst. 21:119-132. DOI.1007/s10795-007-9024-4.

Young, M. H., H. Lin, and B. P. Wilcox. 2007d. Introduction to special section on Bridging Hydrology, Soil Science, and Ecology: Hydropedology and Ecohydrology. Geophys. Res. Lett., 34, L24S20, doi:10.1029/2007GL031998.

Young, M.H., E.A. Moran, Z. Yu, J. Zhu, D.M. Smith. 2007b. Reducing saturated hydraulic conductivity of soil with polyacrylamide. Soil Sci. Soc. Am. J. Submitted.

Young, M.H., G.S. Campbell, J. Yin. 2007a. Correcting dual-probe heat-pulse readings for ambient temperature fluctuations. Vadose Zone J. In press.

Young, M.H., J.J. Tappen, R.B. Susfalk, G.C. Miller. 2007c. Characterizing the risk of using linear anionic polyacrylamide (LA-PAM) to reduce seepage from unlined water delivery canals. J. Soc. Risk Assess. In revision.

Yu, Z., Q. Lu, J. Zhu, and E. A. Sudicky, 2007. Spatial and temporal scale effect in simulating hydrologic processes in a watershed. Water Resour. Res. Submitted.

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Zachara, J M., J. Serne, M. D. Freshley, F. M. Mann, F. Anderson, M. I. Wood, T. Jones, and D. Myers. 2007. Geochemical processes controlling migration of tank wastes in Hanford's vadose zone. Vadose Zone J. 6:985-1003.

Zhang Z. F., M. Oostrom, and A.L. Ward. 2007. Saturation-dependent hydraulic conductivity anisotropy for multifluid systems in porous media. Vadose Zone J. 6:925-934.

Zhang, J.X., K.-T. Chang, and J.Q. Wu. 2007. Effects of DEM resolution and source on soil erosion modelling: a case study using the WEPP model. Int. J. Geogr. Info. Syst. In press.

Zhang, Y., J. Lu, L. Wu, A. Chang, and W.T. Frankenberger Jr. 2007. Simultaneous removal of Chlorothalonil and nitrate by bacillus cereus Strain NS1. Sci. Total Environ. 383: 383-387.

Zhao, B., J. Zhang, M. Flury, A. Zhu, Q. Jiang, and J. Bi. 2007. Groundwater contamination with NO3-N from an intensive agriculture system in the North China Plain. Pedosphere. In press.

Zheng, W., S. R. Yates, and S. A. Bradford. 2007. Analysis of steroid hormones in dairy manure and wastewaters. Environ Sci. Technol. In press.

Zhu, J. 2007. Equivalent parallel and perpendicular unsaturated hydraulic conductivities: arithmetic mean or harmonic mean? Soil Sci. Soc. Am. J. In revision.

Zhu, J., and D. Sun. 2007a. Tension-dependent hydraulic conductivity anisotropy of unsaturated soils. Geophysical Res. Lett. Submitted.

Zhu, J., and D. Sun. 2007b. Effective soil hydraulic parameters for transient flows in heterogeneous soils. Vadose Zone J. Submitted.

Zhu, J., and M.H. Young. 2007a. Uncertainty and sensitivity of evapotranspiration estimates for semi-arid shrublands. J. Am. Water Resour. Assoc. Submitted.

Zhu, J., and M.H. Young. 2007b. Sensitivity of unlined canal seepage to hydraulic properties of Polyacrylamide (PAM) treated soil. Soil Sci. Soc. Am. J. Submitted.

Zhu, J., M.H. Young, and M.Th. van Genuchten. 2007. Upscaling schemes and relationships for Gardner and van Genuchten hydraulic functions for heterogeneous soils. Vadose Zone J. 6:186-195.

Zhuang, J., J.F. McCarthy, J.S. Tyner, E. Perfect, and M. Flury. 2007. In-situ colloid mobilization in Hanford sediments under unsaturated transient flow conditions: Effect of irrigation pattern. Environ. Sci. Technol., 41: 3199-3204.

Zlotnik, V. A., T. Wang, J. Nieber, and J. Šimůnek. 2007. Verification of numerical solutions of the Richards equation using a traveling wave solution. Adv. Water Resour. 30:1973-1980.

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Abstracts Arora, Bhavna, Binayak Mohanty, Jennifer T. McGuire, J. M. Köhne, and Paolo Castiglione.

2007. Comparison of two-domain models for simulating bromide transport in three different column setups. ASA abstracts, ASA, Madison, WI.

Bradford, S. A., S. Torkzaban, F. J. Leij, N. Toride, and J. Simunek, Modeling the coupled effects of pore space geometry and velocity on colloid and nanoparticle transport and retention, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract H54C-04, 2007.

Bradford, S. A., S. Torkzaban, S. L. Walker, and J. Simunek, Colloid retention in porous media at different scales: Processes and models, American Chemical Society, 81st ACS Colloid and Surface Science Symposium, University of Delaware, Newark, Delaware, June 24-27, 2007.

Buchner, J., J. Šimůnek, J. H. Dane, A. King, J. Lee, D. Rolston, and J. W. Hopmans, Using a process-based numerical model and simple empirical relationships to evaluate CO2 fluxes from agricultural soils, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract H13F-1654 INVITED, 2007.

Castiglione, P., and J.M. Wraith. 2007. ConvTDR: Software for numerical convolution of time domain signals. ASA abstracts, ASA, Madison, WI.

Castiglione, Paolo, Yongping Chen, Jon M. Wraith and Dani Or. 2007. Temperature effects on soil dielectric permittivity. ASA abstracts, ASA, Madison, WI.

Conde, K, V. Pacific, B.L. McGlynn, and D. Welsch. 2007. Relationship between soil CO2 concentrations and soil water alkalinity. Posters on the Hill, Counsel for Undergraduate Research and the American Chemical Society. Conference on Capitol Hill, Washington DC.

Conde, K., V. Pacific, D. Riveros, B.L. McGlynn, and D. Welsch. 2007. Relationship between soil CO2 concentrations and soil water alkalinity. Undergraduate Scholars Research Conference, Montana State University, Bozeman, Montana.

Deng, H, Ye, M, Schaap, M.G., and R. Khaleel, 2007. Uncertainty Assessment of Soil Hydraulic Parameter Estimated From Cokriging and Artificial Neural Network, AGU Fall meeting San Francisco, H23B-1316.

Dinwiddie, C., D. Or, S. Stothoff, R. Fedors, J. Pohle, and M. Tuller, 2007. Sensors and Monitoring Techniques for the Deep Unsaturated Zone: Reducing Uncertainty Related to Seepage and Transport in Fractured Rock. Unsaturated Zone Interest Group (UZIG) Meeting, Los Alamos, New Mexico, August 27-30, 2007.

Dinwiddie, C.L., D. Or, S.A. Stothoff, R.W. Fedors, J.A. Pohle, and M. Tuller, 2007. Sensors and Monitoring Techniques for the Deep Unsaturated Zone: Reducing Uncertainty Related to Seepage and Transport in Fractured Rock. AGU Fall Meeting, San Francisco, CA, December 10-14, 2007.

Dontsova, K., J. Šimůnek, J. Pennington, and C. Price, Facilitated transport of high explosives in mineral soils, Soil Science Society America annual meeting, Agronomy Abstracts, published on a CD-ROM as abstract 283-9, ASA, Madison, 2007.

Fayer MJ, and JM Keller. 2007. Recharge Data Package for Hanford Single-Shell Tank Waste Management Areas. PNNL-16688, Pacific Northwest National Laboratory, Richland, WA

99

Forkutsa, I., M. Gribb, J Šimůnek, J. McNamara, and D. Chandler, Effect of different soil hydraulic properties estimates on soil water content predictions, Dry Creek Experimental Watershed, Idaho, Soil Science Society America annual meeting, Agronomy Abstracts, published on a CD-ROM as abstract 183-8, ASA, Madison, 2007.

Forkutsa, I., M. Gribb, J. Šimůnek, J. McNamara, D. Chandler, Estimation of effective soil hydraulic properties at Treeline site, Dry Creek experimental watershed, Idaho, Environmental Sensing Symposium, October 25-26, 2007, Boise State University, Boise, Idaho, 52, 2007.

Freedman VL, ZF Zhang, JM Keller, and Y Chen. 2007. Development of Waste Acceptance Criteria at 221-U Building: Initial Flow and Transport Scoping Calculations . PNNL-16585, Pacific Northwest National Laboratory, Richland, WA.

Fuentes, R., J. Šimůnek, L. Cáceres, Mauricio Escudey, Simulacion y modelacion matematica del perfil de temperatura de suelos derivados de materiales volcanicos afectados por un impacto termivo mediante la aplicacion del software HYDRUS -1D, XVII Congreso Latinoamericano de la Ciencia del Suelo, Leon Guanajuato, Mexico, Septiembre 17 al 21, 2007.

Gardner, K. and B.L. McGlynn. 2007. Spatio-Temporal Controls of Stream Water Nitrogen Export in a Rapidly Developing Watershed in the Northern Rockies. American Geophysical Union Fall Meeting, 2007.

Gebrenegus, Th., B.E. Lassiter, N. Araki, and M. Tuller, 2007. Evaluation of Global and Local Image Binarization Techniques for Quantitative Analysis of X-Ray CT Images of Geological Materials. SSSA International Annual Meeting, New Orleans, LA, November 4-8, 2007.

Guber, A. K., Ya. A. Pachepsky, D. Jacques, M. Th. van Genuchten, J. Šimůnek, T. J. Nicholson, and R. E. Cady, Multimodel prediction of water flow in field soil using pedotransfer functions, AGU Spring meeting, Acapulco, Mexico, 2007.

Hanson, B. R., D. M. May, J. Hopmans, and J. Simunek, Drip Irrigation As A Sustainable Practice Under Saline Shallow Ground Water Conditions, USCID Fourth International Conference, Sacramento, CA, 715-725, September 30- October 6, 2007.

Hardelauf, H., M. Javaux, M. Herbst, S. Gottschalk, R. Kasteel, J. Vanderborght, H. Vereecken, and J. Šimůnek, PARSWMS: a parallelized model for simulating 3-D water flow and solute transport in soils, EGU Annual meeting, April, 2007.

Jencso, K, B.L. McGlynn, M.N. Gooseff, S.M. Wondzell, K.E. Bencala, and R.A. Payn. 2007. Topographic controls on hillslope–riparian water table continuity in a set of nested catchments, Northern Rocky Mountains, Montana. American Geophysical Union Fall Meeting. Fall, 2007.

Jones, S. B., R. Heinse, J. Šimůnek, M. Tuller and D. Or, Numerical modeling of porous-media hydrodynamics in variable-gravity during parabolic flight, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract H53E-1471, 2007.

Jones, S.B., R. Heinse, J. Simunek, M. Tuller, and D. Or, 2007. Numerical Modeling of Unsaturated Flows in Variable Gravity During Parabolic Flight. AGU Fall Meeting, San Francisco, CA, December 10-14, 2007.

Kleissl, J., J. M. H. Hendrickx, and J. Šimůnek, HYDRUS Simulations of Surface Temperatures,

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SPIE, 2007. Kleissl, J., J. M. H. Hendrickx, H. Moreno, and J. Šimůnek, HYDRUS Simulations of Soil

Surface Temperatures, SPIE, 2007. Knight RJ, JD Irving, P Tercier, EJ Freeman, CJ Murray, and ML Rockhold. 2007. "A

Comparison of the Use of Radar Images and Neutron Probe Data to Determine the Horizontal Correlation Length of Water Content ." In Subsurface Hydrology: Data Integration for Properties and Processes: Geophysical Monograph Series, vol. 171, ed. David W. Hyndman, Frederick D. Day-Lewis, Kamini Singha, pp. 31-44. American Geophysical Union, Washington, DC.

Köhne, J. M. and J. Šimůnek, Modeling surface runoff and infiltration in soil with mobile and immobile water regions, EGU Annual meeting, April, 2007.

Kuroda, S., H. Saito, T. Okuyama, M. Takeuchi, J Šimůnek, and M. Th. van Genuchten, Quasi 3D model construction of artificial recharge through the vadose zone using time-lapse zero-offset profiling of cross borehole radar, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract H41H-06, 2007.

M.G. Schaap, M. Porter, and D. Wildenschild, 2007b. Simulating Water Retention Characteristics with Lattice Boltzmann Methods. ASA-CSSA-SSSA meetings in New Orleans, November 4-8, 2007. Poster 183-4, Tuesday November 6, 2007

M.G. Schaap, M. Tuller, A. Guber, and Y. Pachepsky, 2007c. Observing and Simulating Macropore Flow with Computed Tomography and Lattice Boltzmann Methods. ASA-CSSA-SSSA meetings in New Orleans, November 4-8, 2007. Poster 184-7, Tuesday November 6, 2007.

Martín, M.A., M. Tuller, A. Guber, C. García-Gutiérrez, F. San José, Y. Pachepsky, and J. Caniego, 2007. CT Data and Analysis for Large Soil Columns. International Meeting on X-ray Computed Tomography of Soil, University of Guelph, Guelph, Canada August 19-22, 2007.

Martin, M.A., M. Tuller, A.K. Guber, C. García-Gutiérrez, F. San Jose Martinez, Y.A. Pachepsky, and J.F. Caniego, 2007. Pore Space Statistics From the X-ray CT of Large Undisturbed Soil Columns. AGU Fall Meeting, San Francisco, CA, December 10-14, 2007.

McGlynn, B.L., K. Jencso, R. Payn, M. Gooseff, T. Covino, and J. Seibert. 2007. Conceptualizing, testing, and transferring watershed characteristic-runoff generation relationships. Fall AGU [Invited].

McGlynn, B.L., Riveros-Iregui, D.A., Emanuel, R.E., Muth, D.J., Epstein, H.E., Welsch, D.L., Pacific, V.J., and Wraith, J.M., Diurnal Hysteresis between Soil CO2 and Soil Temperature is controlled by Soil Water Content. American Geophysical Union Fall Meeting, 2007.

McNamara, R., B.L. McGlynn, K. Gardner, and P. Jenkins. 2007. In-Stream Nitrate Immobilization Across Development Gradients and Stream Network Position in a Rapidly Developing Mountain Watershed, West Fork of the Gallatin River, Big Sky, Montana. American Geophysical Union Fall Meeting, 2007.

Muth, D.J., H. Epstein, R. Emanuel, B.L. McGlynn, D. Welsch. 2007. Net Ecosystem Exchange in a Forested Montane Watershed: Trends and Trials in Complex Terrain. Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract B21D-06.

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Oostrom M, PD Thorne, GV Last, and MJ Truex. 2007. Modeling of Carbon Tetrachloride Flow and Transport in the Subsurface of the 200 West Disposal Sites: Large-Scale Model Configuration and Predicted Future Carbon Tetrachloride Distribution beneath the 216-Z-9 Disposal Site. PNNL-17181, Pacific Northwest National Laboratory, Richland, WA.

Pacific, V.J., D.A. Riveros-Iregui, B.L. McGlynn, D.L. Welsch, and H.E. Epstein. 2007. Comparison of soil CO2 concentrations and surface CO2 efflux across riparian-hillslope transitions: wet versus dry growing seasons. American Geophysical Union Fall Meeting. Fall, 2007.

Pang, L., M. McLeod, J. Aislabie, J. Šimůnek, M. Close, and R. Hector, Removal rates of faecal bacteria and phage viruses in 10 NZ soils under dairy-shed effluent irrigation, Proc. of New Zealand Hydrological Society Conference, Rotorua, New Zealand, 20-23 November 2007.

Payn, R., M. Gooseff, B.L. McGlynn, K.E. Bencala, and S.M. Wondzell. 2007. Multiple spatial scales of surface water - groundwater exchange in a headwater stream in Montana, USA. 2007 Geological Society of America Annual Meeting, Denver.

Payn, R., M. Gooseff, B.L. McGlynn, S. Thomas. 2007. Sensitivity of whole-stream metabolism estimates to fully characterized stream-groundwater exchange. North American Benthological Society Annual Meeting. #497.

Payn, R.A., M.N. Gooseff, B.L. McGlynn, K.E. Bencala, S.M. Wondzell, K. Jencso. 2007. Relationships between stream – ground water exchange and topography of the channel, valley, and watershed. American Geophysical Union Fall Meeting. Fall, 2007.

Peterson RE, RJ Serne, PD Thorne, MD Williams, and ML Rockhold. 2007. Uranium Contamination in the Subsurface Beneath the 300 Area, Hanford Site, Washington . PNNL-17034, Pacific Northwest National Laboratory, Richland, WA.

Pontedeiro, E. M., J. Šimůnek, M. van Genuchten, and R. Cotta, Performance assessment modeling of a radioactive mining waste disposal site, Soil Science Society America annual meeting, Agronomy Abstracts, published on a CD-ROM as abstract 184-5, ASA, Madison, 2007.

Pontedeiro, E., M. Cipriani, M. Th. van Genuchten, and J. Šimůnek, Evaluation of the transport of natural radioactive materials in large lysimeters using Hydrus-1D, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract H53F-1496, 2007.

Porter, M.L, D. Wildenschild, and M.G. Schaap, 2007. Investigating Interfacial Area in a Multiphase Porous System Using Computed Microtomography and Lattice-Boltzmann Simulations, AGU Fall meeting San Francisco, H43J-04.

Riveros-Iregui, D.A., McGlynn, B.L., Epstein, H.E., Welsch, D.L., Pacific, V.J., Muth, D.J., Emanuel, R.E., Jencso, K.G., Wraith, J.M., 2007. Tenderfoot Creek Experimental Forest, Montana: Measuring and modeling carbon and water fluxes from point to watershed scales (Part I). AmeriFlux Annual Meeting, October 17-19, Boulder, CO.

Riveros-Iregui, D.A., McGlynn, B.L., Pacific, V.J., Epstein, H.E., and Welsch, D.L, Soil CO2 Efflux Variability in Complex Terrain: Towards Estimation of Watershed-Level Rates. American Geophysical Union Fall Meeting, 2007.

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Riveros-Iregui, D.A., McGlynn, B.L., Pacific, V.J., Epstein, H.E., Welsch, D.L. and Jencso, K.G. Soil CO2 Efflux from a Subalpine Catchment. National Center for Atmospheric Research "Regional Biogeochemistry: Needs and Methodologies." June 2007, Boulder, CO.

Saito, H., J Šimůnek, A. Tuli, and J. W. Hopmans, Improving heat pulse probe sensitivity without changing its geometry, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract H53F-1477, 2007.

Saito, H., J. Šimůnek, J. W. Hopmans, and A. Tuli, Numerical evaluation of alternative heat pulse probe designs and analyses, 2007 Environmental Sensing Symposium, October 25-26, 2007, Boise State University, Boise, Idaho, 119-123, 2007.

Saito, H., K. Seki, and J. Šimůnek. Variably-saturated water flow in kriged hydrological parameter fields, Soil Science Society America annual meeting, Agronomy Abstracts, published on a CD-ROM as abstract 282-5, ASA, Madison, 2007.

Schaap, M., M. Tuller, A. Guber, and Y. Pachepsky, 2007. Observing and Simulating Macropore Flow with Computed Tomography and Lattice Boltzmann Methods. SSSA International Annual Meeting, New Orleans, LA, November 4-8, 2007.

Schaap, M.G, M. Tuller, A. Guber, M.A. Martin, F.S. Martinez, and Y. Pachepsky, 2007. Macropore Flow in Soil Columns: Investigations with Computer Tomography and Lattice Boltzmann Simulations. AGU Fall Meeting, San Francisco, CA, December 10-14, 2007.

Schaap, M.G. 2007. Hydraulic Functions, Lecture in “Vadose Zone Modeling Course” (Lead J.W. Hopmans), University of California, Davis. April 26, 2007.

Schaap, M.G. 2007. Lattice Boltzmann Methods for Interfacial Processes in Porous Media. Invited presentation. Workshop on Modelling, Analysis, and Simulation of Multiscale Nonlinear Systems, Oregon State University, Corvallis, June 25-29, 2007.

Schaap, M.G. 2007. Soil Physics and Micro-Meteorology at the Soil-Atmosphere Interface. Invited lecture for the Atmospheric Sciences Department, University of Arizona. October 18, 2007.

Schaap, M.G., M. Tuller, A. Guber, M.A. Martin, F.S. Martinez, and Y. Pachepsky, 2007d. Macropore Flow in Soil Columns: Investigations with Computer Tomography and Lattice Boltzmann Simulations. AGU Fall meeting San Francisco, H53E-1457. Šimůnek, J., K. Dontsova, J. Pennington, and H. Saito, Implementation of new physical and chemical nonequilibrium models into the HYDRUS-1D software package and their application to column experiments with explosives under saturated and unsaturated conditions, Army Research Office Meeting, Springfield, Virginia, January 31-February 1, 2007.

Schuh, M. F.X.M. Casey, and H. Hakk. 2007. Farm-scale reconnaissance of Estrogens in subsurface waters. In Annual Meetings Abstracts [CD-ROM]. ASA, CSSA, and SSSA, Madison, WI.

Seo, H. S., J. Šimůnek, and E. P. Poeter, Documentation of the HYDRUS Package for MODFLOW-2000, the U.S. Geological Survey Modular Ground-Water Model, GWMI 2007-01, International Ground Water Modeling Center, Colorado School of Mines, Golden, Colorado, 96 pp., 2007.

Šimůnek, J., H. Saito, J. W. Hopmans, and A. Tuli, Numerical evaluation of alternative heat pulse probe designs and analyses, Environmental Sensing Symposium, October 25-26,

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2007, Boise State University, Boise, Idaho, 35, 2007. Šimůnek, J., K. Dontsova, and J. Pennington, Implementation of colloid and colloid-facilitated

solute transport module into the HYDRUS-1D software package: numerical verification and applications, ARO meetings, September 23-24, 2007, Vicksburg, MS, 2007.

Tartakovsky AM, AL Ward, and P Meakin. 2007. Pore-scale Simulations of Drainage of Heterogeneous and Anisotropic Porous Media. PHYSICS OF FLUIDS, vol. 19 (10), pp. NIL 240-NIL 247.

Truex MJ, VR Vermeul, PE Long, FJ Brockman, M Oostrom, S Hubbard, RC Borden, and JS Fruchter. 2007. Treatability Test Plan for an In Situ Biostimulation Reducing Barrier . PNNL-16424 Rev. 1, Pacific Northwest National Laboratory, Richland, WA.

Tuli, A., T. Kamai, H. Saito, J. Hopmans, and J. Šimůnek, Experimental and numerical sensitivity analyses of heat pulse probe designs, Soil Science Society America annual meeting, Agronomy Abstracts, published on a CD-ROM as abstract 88-8, ASA, Madison, 2007.

Tuller, M., and Th. Gebrenegus, 2007. Assessment of the Impact of Physico-Chemical Factors on Initiation and Evolution of Dessication Cracks in Bentonite-Sand Mixtures with X-Ray Computed Tomography. SSSA International Annual Meeting, New Orleans, LA, November 4-8, 2007.

Tuller, M., and Th. Gebrenegus, 2007. Evaluation of Local and Global Segmentation Techniques for Quantitative Analysis of X-Ray CT Images of Geological Materials. AGU Fall Meeting, San Francisco, CA, December 10-14, 2007.

Twarakavi, N. K. C., J. Šimůnek, and M. Schaap, New pedotransfer functions for estimating soil hydraulic parameters using the Support Vector Machines method, Soil Science Society America annual meeting, Agronomy Abstracts, published on a CD-ROM as abstract 180-9, ASA, Madison, 2007.

van Genuchten, M., Th., F. J. Leij, N. Toride, and J. Šimůnek, Analytical solute transport modeling using the STANMOD computer software package, Soil Science Society America annual meeting, Agronomy Abstracts, published on a CD-ROM as abstract 284-2, ASA, Madison, 2007.

Vermeul VR, MD Williams, BG Fritz, RD Mackley, DP Mendoza, DR Newcomer, ML Rockhold, BA Williams, and DM Wellman. 2007. Treatability Test Plan for 300 Area Uranium Stabilization through Polyphosphate Injection. PNNL-16571, Pacific Northwest National Laboratory, Richland, WA.

Wang, T., V. A. Zlotnik, J. Šimůnek, and D. Wedin, Using process-based models and pedotransfer functions for soil hydraulic characteristics to estimate groundwater recharge in semi-arid regions: Is this a right approach? Paper #128602, GSA Denver Annual Meeting, 28–31 October, 2007.

Ward AL, SO Link, CE Strickland, K Draper, and RE Clayton. 2007. 200-BP-1 Prototype Hanford Barrier Annual Monitoring Report for Fiscal Years 2005 Through 2007 . PNNL-17176, Pacific Northwest National Laboratory, Richland, WA.

Ward AL. 2007. Geotechnical, Hydrogeologic and Vegetation Data Package for 200-UW-1 Waste Site Engineered Surface Barrier Design . PNNL-17134, Pacific Northwest National Laboratory, Richland, WA.

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Wellman DM, EM Pierce, M Oostrom, and JS Fruchter. 2007. Experimental Plan: 300 Area Treatability Test: In Situ Treatment of the Vadose Zone and Smear Zone Uranium Contamination by Polyphosphate Infiltration . PNNL-16823, Pacific Northwest National Laboratory, Richland, WA.

Winowiecki, L., E. Somarriba, P. McDaniel, J. Johnson-Maynard, M. Tuller, and A. Falen, 2007. Biogeochemical Cycling of Base Cations in a Diverse Cacao Agroforestry System, Cabécar Indigenous Territories, Talamanca, Costa Rica. 2nd International Symposium on Multi-Strata Agroforestry Systems with Perennial Crops: Making Ecosystem Services Count for Farmers, Consumers and the Environment, CATIE, Turrialba, Costa Rica, 17-21 September 2007.

Zhang ZF, JM Keller, and CE Strickland. 2007. T Tank Farm Interim Surface Barrier Demonstration--Vadose Zone Monitoring Plan . PNNL-16538, Pacific Northwest National Laboratory, Richland, WA.

Zhang, Z.F., and R. Khaleel. 2007. Comparison of models of saturation-dependent anisotropy in unsaturated hydraulic conductivity. PNNL-16886, Pacific Northwest National Laboratory, Richland, Washington.

Respectfully submitted,

Ole Wendroth (Secretary W-1188) Feb. 28, 2008

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