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ANNUAL REPORT OF REGIONAL RESEARCH PROJECT W-188 January 1 to December 31, 2000

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

PROCESSES IN SOILS AT DIFFERRENT SCALES 2. ACTIVE COOPERATING AGENCIES AND PRINCIPAL LEADERS: Arizona A.W. Warrick, Department of Soil, Water and Environmental Sciences, University o

Arizona, Tucson, AZ 85721

P.J. Wierenga, Department of Soil, Water and Environmental Sciences, University oArizona, Tucson, AZ 85721

W. Rasmussen, Department of Soil, Water and Environmental Sciences, Universitof Arizona, Tucson, AZ 85721

California M. Ghodrati, Dept. of Env. Sci. Pol. Mang., University of California, Berkeley, CA

94720-3110

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

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

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

B. Mohanty, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507

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

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

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

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

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

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

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

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

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, University of Delaware, Newark, DE 10717-

1303 Idaho J.B. Sisson, EG&G, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107

J. Hubbel, EG&G, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107 Illinois T.R. Ellsworth, University of Illinois, Urbana, IL 61801 Indiana J. Cushman, Mathematics Dept., Purdue University, W. Lafayette, IN 47905

P.S.C. Rao, School of Civil Engineering, Purdue University, W. Lafayette, IN 47905 Iowa R. Horton, Dept. of Agronomy, Iowa State University, Ames, IA 50011

D. Jaynes, National Soil Tilth Lab, USDA-ARS, Ames, IA 50011 Kansas G. Kluitenberg, Dept. of Agronomy, Kansas State University, Manhattan, KS 66506 Kentucky E. Perfect, Dep. of Agronomy, University of Kentucky, Lexington, KY 40546 Montana J. M. Wraith, Land Resources and Environ. Sciences, Montana State University,

Bozeman, MT 59717-3120 Nevada S.W. Tyler, Hydrologic Sciences Graduate Program, University of Nevada, Reno,

NV 89532

M. Young, Desert Research Institute, University of Nevada, Reno, NV 89512 New Mexico J.H.M. Hendrickx, New Mexico Tech, Dept. of Geoscience, Soccoro, NM 87801 North Dakota F. Casey, Dept. of Soil Science, North Dakota State University, Fargo, ND 58105-

5638

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Utah D. Or, Dept. of Plants, Soils & Biomet., Utah State University, Logan, UT 84322 Washington M. Flury, Dept. of Crop & Soil Sciences, Washington State University, Pullman, W

99164

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

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

82071 CSREES R. Knighton, USAD-CSREES, Washington, DC 20250-2200 Adm. Adv. G.A. Mitchell, Palmer Research Center, 533 E. Fireweed, Palmer, AK 99645 3. PROGRESS OF WORK AND MAIN ACCOMPLISHMENTS: OBJECTIVE 1: To study relationships between flow and transport properties or processes and the spatial and temporal scales at which these are observed Short-term consistency in solute transport processes in a field plot was studied b California-Berkeley. Although spatial variability in solute transport in field soils has been intensivelexamined, there is far less information available on temporal changes in transport processes. If there are changes in transport over time, then simply calibrating a model with a breakthrough curve for a single time period may not be adequate. W-188 project members examined the consistency in soluttransport measurements in a field soil using two in situ nondestructive techniques, fiber optic miniprobes (FOMPs) and time domain reflectrometry (TDR) probes. There was moderate consistency in transport response measured by the TDR probes. Nonetheless, the FOMP data suggested that solute transport converged into fewer flow pathways over time with repeated leaching. The 5 cm long TDR probes also provided evidence of increased lateral flow in the first 5 cm of soil with time. The temporal variability was surprisingly similar between the FOMPs and TDR probes, even though their sampling volumes differ by more than four orders of magnitude. Relationships between probe responses within the plot were examined using a Spearman’s rank test, confirming that transport response pattern may not be temporally stable.

At California-Davis, soil spatial variability of hydraulic functions was described using simultaneous scaling and a single set of scaling factors. The scaling approach has been extensivelused to characterize soil hydraulic spatial variability and to develop a standard methodology to assess the variability of soil hydraulic functions and their parameters. The procedure consists of using scaling factors to relate the hydraulic properties in a given location to the mean pr operties at an arbitrary reference point. The conventional scaling approach is based on empirical curve fitting, without paying much attention to the physical significance of the scaling factors. In this study, the

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concept of simultaneous scaling of the soil water retention and unsaturated hydraulic conductivitfunctions is applied to a physically based scaling theory. In this approach, it is assumed that soils are characterized by a lognormal pore-size distribution, which leads directly to lognormally distributed scaling factors.

Iowa investigated the influence of ionic strength and flow velocity on sorption and transport of naphthalene in soil. The potential for soil and groundwater contamination by organic chemicals such as polycyclic aromatic hydrocarbons (PAHs) is a national problem. Sorption and desorption kinetics affect the fate and transport of PAHs. Reliable estimates of the sorption and desorption kinetics are important for both risk assessment and efficient remediation of contaminated soils and aquifers. W-188 project members conducted both batch and column studies to characterize fate and transport of naphthalene in soil. In the column studies, the influence of ionic strength (0.01 to 0.5 M of Calcium Chloride) and pore water velocity (2 to100 cm h-1) on sorption-desorption kinetics of naphthalene was investigated. For the batch studies, the effect of ionic strength was examined. We compared the rates of sorption and desorption in the column studies with those determined in batch studies. The aqueous-phase ionic strength affected the sorption behavior and transport of naphthalenby influencing the degree of aggregation. Greater aggregation at higher ionic strength resulted in enhanced sorption affinity and capacity, and thus retarded the transport of naphthalene. The sorption behavior from the batch and column studies was similar, having enhanced sorption at higher ionic strength. However, a particular mechanism responsible for enhanced sorption of naphthalene at higher ionic strength is unclear. Flow velocity also influenced sorption behavior. Iowa also investigated temporal and spatial scale effects on diffusion in rock matrices. In some pore spaces such as those in fracture networks (such as aggregate interiors and cracking clasoils) and roc k matrices (such as sand grains and gravel aquifer material), diffusion can displaanomalous, non-Fickian behavior. Such pore spaces are said to be at the percolation threshold, meaning that the pores are very sparsely interconnected, and as a consequence much of the pore volume is composed of dead-end pore complexes rather than flow pathways. Project members conducted a simulation study of diffusion in both well- and sparsel -interconnected pore spaces over a wide range of both times and distances, in order to assess long-term, long-distance behavior of diffusing pollutants and to understand how macroscopic observations relate to the anomalous diffusion. In well-connected porous media, diffusivity is unaffected by sample size and the mean molecular travel time for diffusion through a sample scales with the square of the distance traveled

(e.g., the sample size, L2), but in sparsel -connected media diffusivity decreases with sample size,

and mean molecular travel time scales as approximately L3.8. In other words, applying diffusivitmeasurements from a lab sample to a large rock formation can grossly over-estimate the diffusive mass transfer. Additionally, in sparsely connected media, the effective porosity decreases with sample size, and rather than being constant over the entire sample, it is greater in the center of the sample than at the two ends. This means that, in order to see the linear concentration gradient insidthe sample, one has to adjust for the effective porosity. Simply examining solute concentrations across the sample will not account for the difference between effective (connected to both ends) and dead-end porosity. It requires more than a single measurement or a single sample to determine whether a particular rock material displa s anomalous diffusion.

Kansas studied the temporal stability of spatial yield patterns. Yield monitors have been used to obtain yield data for three fields in Kansas cropped continuously to corn (center pivot irrigation).

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Four years of data have been obtained from Fields A and C; seven years of data have been obtained from Field B. Yield data from each field was block -averaged to 55-m square cells. Frequencdistributions for all fields and years exhibited strong negative skew. Therefore, relative differences in yield for cell i in year j were computed using the expression

j

jjiji Y

YY −=δ ,

,

where Yi, j is the yield for cell i in year j and jY is the median yield for year j. Mean relative

difference for cell i was computed using

∑=

δ=δn

jjii n 1

,

1

where n is the number of years of yield data. All subsequent computations were made using mean relative difference iδ and its associated standard deviation.

Temporal stability of spatial yield patterns was assessed by using Spearman rank correlation to characterize the degree of association between yield maps from the same field. Ranges for coefficients of determination were 0.34 < r2 < 0.44 for Field A, 0 < r2 < 0.56 for Field B, and 0.06 < r2 < 0.29 for Field C. Temporal stability appears to be stronger for Field A than for the other fields. Although these results suggest much stronger correlation than that found by Jaynes and Colvin (1997, Agron. J. 89:30-37), temporal stability is still quite weak. This was confirmed by plotting

iδ as a function of rank. Only for Field A can we say with confidence that some locations have

systematically lower yield. An analysis of change in rank caused by the addition of each new year oyield data showed that mean change in rank approached an asymptotic value of approximately 7 for all fields. Furthermore, it appears that this asymptotic value is obtained after accumulating 4-5 years of data. This suggests that long -term yield monitoring (> 5 years) may not prove useful in establishing temporall -persistent spatial yield patterns.

North Dakota conducted field infiltration experiments that measured water transfer and solute transport in a structured field soil. The objective was to examine correlations between water transfer and solute transport properties of a soil that exhibits preferential flow. Time domain reflectometry probes were placed horizontally 2 cm below an infiltrometer disk and water was infiltrated until steady infiltration was reached. The water content continued to increase after the steady flow rate was achieved, suggesting that was being transferred from, rapidly filling, highlconductive pores to slowly filling, less conductive pores (i.e., immobile pores). Also, a suite of three benzoic acid tracer were sequentially applied through the tension infiltrometer using the Jaynes et al. (1995) method (W-188, Iowa). After the tracers were applied the soil was sampled to a depth of 4 cm on one half of the infiltration area. After sam pling the infiltrometer was placed back on the infiltration area and tracer application continued. Steady infiltration was achieved quickly on the unsampled area and there was little change in infiltration rate. The tracers were then sequentiallremoved from the infiltration solution after which the soil was again sampled. The sequential

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application and removal was done to observe the exchange of solute into and out of the immobile domain, respectively. California-USSL further improved the windows-based HYDRUS-1D and HYDRUS-2D software packages by incorporating pedotransfer functions that enable users to rapidly estimate the hydraulic input parameters for specific applications, and by coupling the codes with parameter estimation subroutines. A three-dimensional version of HYDRUS is currently under development. The HYDRUS codes have been applied to a large number of agricultural problems (infiltration, tile drainage design, crop production, fate and transport of agricultural chemicals in the subsurface), as well as to many problems in the general area of soil and groundwater pollution involving non -agricultural chemicals (such as radionuclides and contaminants released from industrial and municipal waste disposal sites). The coupling of the HYDRUS codes with parameter estimation subroutines enables the inverse estimation of a variety of hydraulic and solute transport parameters from laboratory and/or field experiments. The parameter estimation options provide much more effective methods for estimating the unsaturated soil hydraulic properties from relatively standard infiltration, multistep outflow, and evaporation experiments.

California-USSL also conducted a study to determine if it is possible to predict particl -size distribution (PSD) from limited soil texture data. A procedure was developed to predict PSD based on measurements of the clay, silt, and fine plus very fine sand (particle diameters between .05 and .25 mm) fractions. The procedure was shown to work well except in soils with very high silt contents (> 70 percent silt).

Research continued at the California-USSL on random resister networks. Network models of randomly sized capillary tubes are commonly used as surrogate media in theoretical investigations of the transport properties of soils and rocks. The conductivity of network models can be calculated by critical path analysis, a method based on the connectivity of highly conducting pathways and the statistics of percolation theory. USSL used percolation cluster statistics and critical path analysis to derive an analytical expression for the expected value of the hydraulic conductivity as a function of system size, and have numerically verified the theory. They also derived a relationship between the expected values of the hydraulic and electrical conductivities.

Soil moisture is an important state variable in the hydrologic cycle, and its spatio-temporal distribution depends on many geophysical processes operating at different spatial and temporal scales. To achieve a better accounting of the water and energy budgets at the land-atmosphere boundary, it is necessary to understand the spatio-temporal variability of soil moisture under different hydrologic and climatic conditions, and at a hierarchy of space and time scales. During the Southern Great Plains 1997 (SGP97) Hydrology Experiment, W188 members at California-USSL and California-Riverside measured the 0 to 6 cm soil water content on consecutive afternoons at four hundred locations in a small, gently sloping range field. The soil moisture measurements were madusing portable impedance probes. Spatio-temporal data analyses of the two sampling events showed a significant change in the field variance but a constant field mean, suggesting moisture was redistributed by (differential) base flow, evapotranspiration, and condensation. Among the different relative landscape positions (hill-top, slope, valley), the slope was the largest contributor to the temporal variability of the soil moisture content. Using a sequential aggregation scheme it was observed that the relative position influencing the field mean and variance changed between the two sampling events, indicating time -instability in the spatial soil moisture data. Furthermore, high

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resolution (impedance probe) sampling and limited (gravimetric) sampling gave different field means and variances.

Kentucky investigated statistical relations between water retention parameters and solute dispersivity for small, undisturbed soil cores. Differences in solute dispersion at any given flow ratare controlled by pore characteristics under saturated conditions. Thus, if breakthrough curves and pore characteristics are measured simultaneously, statistical relations can be developed to predict the dispersivity (α) from independent measurements of the po e space geometry. We measured both α and pore characteristics on short (6-cm long) undisturbed soil columns from six soil types, ranging in texture from loamy sand to silty clay. Pore space geometry was characterized in terms of total porosity (φ), the Campbell water retention parameters ( ψa and b), and saturated hydraulic conductivity (Ksat). Breakthrough curves were determined by monitoring changes in effluent electrical conductivity in response a step decrease in influent CaCl2 concentration under st ady state flow conditions using a computerized data acquisition system. Dispersivities were computed from the resulting breakthrough curves by the method of moments. Mean dispersivities ranged from < 0.5 cm for the loamy sand to > 20 cm for the silty cla . Stepwise multiple regression analyses indicated that α increased as both ψa and b increased. All other factors being equal, the positive relationship between α and ψa implies that fine textured soils are more dispersive than coarse textured soils. Similarly, the positive relationship between α and b means that dispersion increases as the width of the pore size distribution increases. Neither φ nor Ksat contributed to the prediction of α once ψa and b were included in the regression model. Using this statistical approach we were able to explain 47% of the observed variation in α. Additional data for sands and clays may improve the predictability of the regression model. Kentucky also studied percolation thresholds in the pore space of 2-dimensional geometric prefractals. Considerable effort has been directed towards developing fractal models of soil pore space. Less has been done on applying percolation theory to soils. We combined these two areas of research to investigate percolation behavior in prefractal porous media. Percolation thresholds in thpore space of homogeneous random 2-dimensional prefractals were estimated as a function of the scale invariance ratio (b) and iteration level (i) using the Hoshen-Kopelman algorithm and Monte-Carlo simulation. The resulting percolation thresholds increased beyond the 0.593 porosity expected in regular 2-dimensional site percolation networks. Percolation in prefractal networks occurs through large pores connected by small pores. The thresholds increased with increasing b and i values. Extrapolation to infinite iterations suggests there may be a critical fractal dimension (D) of the solid phase at which the pore space percolates. The extrapolated value of D was approximatel1.89, which is close to the well-known fractal dimension of percolation clusters in regular 2 -dimensional site percolation networks. The percolation behavior of prefractal porous media has important implications for analytical models of the soil water retention curve that are based on the assumption of a power law distribution of pore sizes. Prefractal percolation models may also be useful for simulating the transport of air, water and solutes in heterogeneous porous media. Unstable flow was the subject of experim ents conducted by California-Riverside. Two fields comprised of sandy loam and loamy sand textures were chosen to represent a range of conditions favorable to preferential flow during redistribution. The experiment consisted of the uniform addition of infiltrating water under unsaturated flow conditions to the field surface by a specialized low impact spray boom that adds the water to the surface at a spatially and temporall

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uniform flow rate. Within the infiltrating water are a pulse of potassium bromide and ammonium carbonate so that the pulse may be monitored in the soil by both analysis of soil samples and bvisible dye tracing both at the end of the infiltration phase and during four days of subsequent redistribution. A series of preliminary studies were performed on the fields over a period of 4 months at a variety of input flow rates, until we were able both to induce and prevent preferential flow in each field. Following these preliminary studies, a flow rate was chosen that maximized the appearance of preferential flow and also contrasted its characteristics on the two fields.

The progress of the infiltrating and redistributing front was monitored on the two fields usina combination of soil sampling and dye trace photography. The monitored region of the study area was a soil cube 1.2 m on each side and 1 m deep that was photographed by shaving a trench face in successive 10 cm increments to 50 cm from the end over several days following the end of infiltration, spraying the face with a special solution to stain the regions that contained ammonium, photographing the region with a precision digital camera over a prescribed grid, and then taking 120 soil samples on a 10 cm unit grid along the entire face. At the conclusion of the sampling, the remaining undisturbed 50 cm half of the soil block was intensively sampled vertically by soil coring. In all, some 3000 samples were taken and are now being analyzed for water content, nitrogen, bromide, and select hydraulic properties. Until the samples are analyzed, it will not be possible to assess fully the degree to which we were able to create preferential flow during the redistribution phase. However, from the evidence obtained from the dye trace studies, we are optimistic that we have detected preferential flow and can associate it with fluid and soil characteristics as indicated in our proposal. California-Riverside also studied atmospheric deposition and landscape controls on watershed response. Large cities with high vehicle use and some agricultural operations such as feedlots or dairy farms are areas of high emissions of ammonia or oxides of nitrogen (N). Terrestriaand aquatic ecosystems located downwind of these N source areas are being “fertilized” batmospheric N deposition. In watersheds with chronic N deposition it is common to find elevated nitrate (NO3

-) concentrations in streamwater and groundwater. Few studies have addressed the impacts of chronic N deposition on semiarid catchments. Semiarid catchments are particularlsensitive to excessive NO3

- loss because of alternating dry periods of N accumulation followed bhigh precipitation inputs. Streamwater monitoring along a deposition gradient in the San Bernardino Mountains in southern California suggest that NO 3

- export in streamwater is a function of N deposition and N processing within the coupled terrestrial and aquatic ecosystems. Large variations in NO3

- concentrations among the streams within Devil Canyon (near San Bernardino), located on the western, high -deposition end of a pollu tion gradient, provide an opportunity to evaluate the factors that control NO 3

- loss from forested and chaparral semiarid watersheds. Our research project will determine the relative influence of N deposition, nitrate production rates in soils, stream source waters, in-stream processes, and catchment properties on stream NO3

- concentrations. This project will determine the biogeochemical and hydrologic controls on stream nitrate concentration in five steps. We have begun monitoring deposition throughout the Devil Canyon watershed using throughfall collectors. We are measuring stream, soil, and ground water chemical composition and will use these measurements to determine the variable contributions of different catchment source waters to stream chemical composition and particularly the impact of changes in hydrologic flowpath on stream 3

- concentration. We will compare geographic data sets

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for these watersheds to determine if differences in land cover properties are capable of explaining thobserved variability of stream NO3

-. We also plan on conducting tracer experiments in the stream to determine effective rates of nutrient uptake and hydrologic exchange in the stream.

Utah conducted a theoretical study on using thermodielectric effects on radar backscattering towards developing correction factors for remotely sensed water content information, and for remotdelineation of differences in surface soil texture at large scales.

In several projects, Washington studied the relationship between flow and transpor t properties and their spatial and temporal scales. Experimental, theoretical and numerical analyses were carried out to examine (1) remediation of uranium contaminated mine waste, (2) virus transport and sorption/inactivation in unsaturated porous media, (3) erosion processes in agricultural field under the unique climatic conditions of the Northwest Wheat and Range Region (NWRR), and (4) characteristics of subsurface hydrological processes in forest watersheds.

Washington also used column experiments to determine reaction rate coefficients of uranium sorption/precipitation and to determine the sorption capacity of apatite suggested as leaching barrier. In column studies uranium was not detected in the column outflow during 270 days of column throughflow. EDAX analyses demonstrated that uranium migrated to a depth of about 3 to 4 cm, showing that apatite is a very effective material to remove uranium from the liquid phase.

Washington and Delaware collaborated on a study of virus transport in unsaturated porous media. Project members developed a model to describe virus movement under sorption/inactivation to solid-liquid and solid -gas interfaces. The results suggest that in the presence of reactive solid surfaces, increased reactions at the solid -water interface, rather than at the air -water interface, dominates in virus removal and transport under unsaturated conditions (Chu et al., 2001).

In Nevada, research efforts have focused on the dynamics of nitrogen transport in desert soils. Investigators drilled and analyzed deep vadose zone profiles in southern Nevada to determinthe nitrogen dynamics of these ecosystems. Soil water chemistry from the Nevada Test Site at depths up to 50 meters below land surface show that deep percolation to the water table was limited to the late Pleistocene, a period of higher precipitation in the area. High levels of soil water chloride and chloride profiles were used to age date the period of recharge. Surprisingly, elevated levels of nitrate (up to 5000 mg/L) were found in the soil waters below the zone of active rooting. The accumulation of elevated nitrate was shown to be derived from atmospheric deposition combined with a small percentage of nitrogen fixation from soil microbial crusts (Hartsough et al, submitted). Most significantly, the elevated leached nitrogen levels below the active rooting zone suggest that desert ecosystem response is not limited by nitrogen as has been previously postulated, but that nitrogen availability is closely tied to water availability which may not coincide with periods of biotic activity. The soil core data also suggest that nitrogen leaching from these desert profiles has been relativelconsistent throughout the Holocene (the last 10,000 years) in spite of significant changes in the vegetation communities.

Also at Nevada, work is also beginning in the alpine regions of Nevada and California to study the dynamics of nitrogen and phosphorous transport in watersheds during and following forest management practices. Field plots have been l aid out and sampling of soil nutrient and soil hydraulic properties has just been initiated. During the upcoming year, forest management (clearing, thinning and prescribed fire) will be initiated on these plots to develop relationships between nutrient loading to watercourses and these management practices.

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OBJECTIVE 2: To develop and evaluate instrumentation and methods of analysis for characterization of flow and transport at different scales California-Berkeley developed methods for in situ characterization of solute transport in a hillslopsoil. The natural heterogeneity in water and solute movement in hillslope soils makes it difficult to accurately characterize the transport of surface applied pollutants without first gathering spatialldistributed hydrologic data. Currently the most common technique to measure solute transport on hillslopes has been to cut trenches in the soil and monitor the effluent. As it is not possible to place such infrastructure in every watershed, portable in situ measurement devices must be developed. This year we have examined the application of time domain reflectometry (TDR) to measure solute transport in hillslopes. Three different plot designs were used to examine the transport of a conservative tracer in the sloping soil from various perspectives. The TDR system was shown to be an effective means to characterize solute travel times in hillslope soils. In addition, a consistent qualitative pattern of tracer transport was described which identifies dominant processes and soil features relevant to solute transport. The data demonstrate the preferential flow of the tracers; where in one instance rapid solute transport was estimated to occur in as little as 3% of the available pore space. Lateral subsurface flow was measured in all plots, most significantly in the two sets designed to gather information on lateral flow. Finally, it was demonstrated that the soil anisotropy, while partially responsible for causing lateral subsurface transport, may also homogenize the t ransport response across the hillslope by decreasing solute spreading.

The dependence of soil strength on water content, and its variations within the soil profile and across the field, was investigated at California-Davis. Soil mechanical impedance affects root growth and water flow, and controls nutrient and contaminant transport below the rooting zone. Among the soil parameters affecting soil strength, soil water content and bulk density are the most significant. However, field water content changes both spatially and temporally, limiting the application of cone penetrometers as an indicator of soil strength. A combined coiled penetromete -moisture probe was developed to study the influence of water content on soil strength. The coiled TDR moisture probe consists of a 2 parallel copper wires, each 0.8 mm diameter and 30 cm long, coiled around a 5 cm long PVC core with a 3 mm separation between wires. The performance of the combined probe was compared with a conventional 2 parallel TDR probe for a Columbia fine sand loam, a Yolo silt clay loam and washed sand. Calibration curves relating the soil bulk dielectric constant measured by the coiled probe with water content were obtained in the laboratory and data. In a followup study, the coiled TDR is integrated into the porous cup of a tensiometer, so that in situ soil water retention and/or simultaneous soil water content and water potential is measured within identical soil bulk volumes.

California-Davis and California-USSL jointly developed inverse modeling methods to estimate soil hydraulic properties from transient experiments, giving much more flexibility in experimental boundary conditions than required for steady state methods. As an additional advantage, inverse modeling allows the simultaneous estim tion of both the soil water retention and unsaturated hydraulic conductivity function from a single transient experiment. In other ways, inverse modeling of transient water flow is not much different than methods applied to steady flow. In either case, inversion of the governing equation is required to estimate the unsaturated hydraulic conductivity function from

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experimental data. Whereas the steady state methods invert Darcy’s equation, the governing equation for a transient flow regime is Richards’ equation. Its inversion requires repeated numerical simulation of the governing transient flow problem. Successful application of the inverse modeling techniquimproves both speed and accuracy, as there is no specific need to attain steady state flow. Various experiments were designed to estimated flow and transport parameters using the inverse modelinapproach.

In order to better understand diffusive and advective transport of volatile contaminants in soil, the density of gas-phase contaminants responsible for several important transport phenomena in natural soil systems were studied in the laboratory at California-Davis. One-dimensional laboratory experiments were conducted to explore the transport of a dense gas (Freon-113) through ai -dry sand. Gas densities and fluxes were measured during transport through a column filled with Oso-Flaco sand. Significant differences in fluxes and density profiles were observed for the three primary flow directions (horizontal, vertically upward, vertically downward) at high source densities. Pressure gradients due to the non-equimolar diffusion of freon and air were measured in the first 2.5 cm of thsoil column, but only for the horizontal and vertically downward experiments. Numerical models based on the standard Darcy-Fickian transport equation did not fit the measured fluxes. Slip flow was found to be significant relative to Darcy advective flow, but did not account for the discrepancbetween model simulations and data. Further research and theory development will be necessary in order to ascertain why the standard equations do not adequately describe the diffusive and advectivtransport processes for dense gases. Iowa studied soil thermal properties as a function of soil volume fractions. The soil thermal properties—heat capacity (C), thermal diffusivity (α), and thermal conductivity (λ)—are important in many agricultural, engineering, and meteorological applications. Soil thermal properties are largely dependent on the volume fraction of water (θ), volume fraction of solids (vs), and volume

fraction of air (na) in the soil. In many natural settings θ, vs, and na vary greatly over time and space,

but data showing the effects of these variations on thermal properties is not readily available. In the laboratory, we used a heat pulse method to measure the thermal properties of 62 packed columns of four medium textured soils covering large ranges of θ, vs, and na. The resulting data revealed that

soil thermal properties are more strongly correlated with na (r2 = 0.86, 0.71, and 0.93 for C, α, and

λ, respectively) than with θ (r2 = 0.90, 0.32, and 0.63) and that vs has the weakest correlation to soil

thermal properties (r2 = 0.23, 0.69, and 0.57). The strong correlations of thermal properties with air-filled porosity have not been previously reported, and may be useful for improved modeling of soil thermal properties. Iowa also measured soil thermal properties using the heat pulse method in the field in two separate experiments. In the first experiment, they measured thermal properties of surface soil with and without organic amendments. These measurements were made as one component in a larger study on the ecological effects of incorporating organic materials, such as compost and red clover, into the soil. In the second experiment, they measured surface thermal properties at 120 locations along two 20-m transects in a soybean field. One transect was in the row and one transect was in thtrafficked inter-row. In both field experiments, they collected soil samples from all the measurement sites and determined the water content and bulk density gravimetrically. Data processing from thes

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two experiments has not yet been completed. Iowa also developed and evaluated methods for rapid field measurement of soil hydraulic and transport properties. The procedure of Lee et al. (2000) was extended to study solute transport properties at multiple field locations over a short time period. Solute transport properties included the immobile water content ( θim), the mass transfer ra te coefficient ( α), and the dispersion

coefficient (Dm). These parameters are required in predicting solute transport using the

mobile/immobile model (MIM). The setup of Al -Jabri et al. (2001) was utilized to conduct measurements at field scale. A total of 38 field locations were rapidly evaluated for chemical transport properties. TDR probes were installed at an angle from the soil surface, and measurements were assumed to take place over the top 20 mm. Background and long step solutions were applied from point sources at each location using a dripper line. The bulk electrical conductivity of the applied solution was measured using the TDR. Automated measurements were facilitated by using the TACQ package (Evett, 1998). Breakthrough curves (BTCs) for all field sites were constructed. The solute transport parameters were estimated from on the observed (measured) BTCs using the CXTFIT package. The estimated parameters were found to be comparable with values reported bprevious studies for nearby field locations. The setup and procedure allowed rapid estimation of all transport parameters (θim, α, and Dm) with minimal time and labor requirements.

In a related study, hydraulic and solute transport parameters were measured in soils treated to different cropping, tillage, and compaction levels. Hydraulic properties included the saturated hydraulic conductivity (Ks) and the macroscopic capillary length (λ). The field experiments were

conducted on corn and soybean field locations (same soil type). The chemical transport properties are as mentioned above. The corn and soybean fields were under no -till and chisel plow management. Hydraulic and chemical transport properties were estimated in both the trafficked (compacted) and untrafficked interrows. Thus, a combination of crop, tillage, and compaction levels were evaluated for such properties. Data and chemical analyses are under way. Kansas investigated methods for measuring soil water flux. Ren et al. (2000, SSSAJ 64:552-560) proposed a new method for measuring soil water flux density in which a heat tracer was used to quantify the magnitude of convective heat transfer resulting from soil water movement. Their method utilized analytical solutions of the heat equation to describe temperature changes that occur upstream and downstream of a line heat source following the emission of a heat pulse. Unfortunately, these solutions contain integrals that must be evaluated using numerical integration techniques. Insofar as one of the integrals is improper, specialized numerical integration procedures are required. Collaborative work between Kansas and Arizona during the past year has focused on reducing the integrals in the aforementioned solutions to the integral

( )⌡⌠ β−−=β

∞−

u

zzzzuW d4exp),( 21

known in the groundwater hydrology literature as the well function for leaky aquifers. Furthermore, an efficient method for evaluating W(u,β) has been developed. The method, which involves summing the first few terms of an infinite series, also provides a simple means of determining the approximation error. Approximations can be made with

13

∑=

+

β−≈βn

mm

mm

uEum

uW0

1

2

)(4!

)1(),( [1]

which converges rapidly for u > β/2, or with

∑=

+

β−−β≈βn

mm

mm

uEu

mKuW

0

2

10 4)(

!

)1()(2),( [2]

which converges rapidly for u < β/2. The series in Eq. [1] and [2] converge at the same rate along the line u = β/2. The magnitude of the error incurred by using the truncated series in Eq. [1] and [2] is no greater than the absolute value of the first truncated term. Thus, W(u,β) can be approximated with known accuracy. We have investigated the number of terms required in Eq. [4] or [5] to approximate W(u,β) with error ≤ 10−4 in absolute value. W(u,β) can be approximated with excellent accuracy by using only 0, 1, or 2 terms throughout much of the u-β domain. More than 2 terms are required only near the line u = β/2 for large values of β.

Also at Kansas, the effect of forced convection on θ measurements was studied. The dual-probe heat-pulse (DPHP) method is useful for measuring soil volumetric water content θ). Previous work has shown that, because of their small size, DPHP sensors are useful for measuring water content near heterogeneities. One such heterogeneity is the soil surface. The performance of DPHP sensors in obtaining near -surface measurements of θ is of considerable interest and practical importance.

Heterogeneity imposed by the soil surface is only one of several issues that must be addressed in order to evaluate DPHP sensors for this application. Another issue of importance is the possibilitof heat convection due to the movement of soil water (forced convection). The usual heat transfer theory for the DPHP method assumes only conductive heat transfer and thus implicitly neglects forced convection. Inasmuch as water infiltration rates are often greatest near the soil surface, it seems desirable to determine whether forced convection due to infiltrating water will cause error in near-surface θ measurements obtained with DPHP sensors.

The effect of forced convection on θ measurement error has been estimated by developing models that explicitly account for forced convection. Three DPHP sensor configurations have been examined. Configuration I has the heater and temperature sensor probes in a plane parallel to the soil surface. Configuration II has the probes in a plane normal to the surface with the heater probe nearer the surface. Configuration III in similar to Configuration II, but has the sensor probe nearer the surface. Water (saturated or unsaturated) flows downward at a constant rate for all configurations. Water-saturated Hanlon sand (Ren et al., 2000, SSSAJ 64:552-560) with volumetric heat capacit C = 3.07 MJ m−3 K−1 and thermal diffusivit κ = 6.33 x 10−7 m2 s−1 was used for calculations. Probe spacing and heat duration were set to r = 0.006 m and t0 = 8 s.

The effect of forced convection on absolute error in water content (∆θ) is predicted to be substantially smaller for Configuration I than it is for Configuration II or III. And, for all practical all purposes, it appears that the effec t of forced convection will be insignificant for DPHP sensors

14

positioned in Configuration I (∆θ < 0.002 if J < 5.58 cm h−1). Experimental work to examine the effect of forced convection in Configuration I is underway. Montana and Utah introduced and verified the concept of using calibrated reference soils oother porous media having known and reproducible water retention characteristics as a means to estimate the unknown retention properties of soils in situ. Pockets of the reference soil/media may bburied at experimental soil locations, with embedded time domain reflectometry (TDR) probes in !"#$% #$&% #'()&#%'*+%'+,'-&*#% (&.&(&*-&%/&+0'1%2"*0#"(0*)%-$'*)&3%0*%4'#&(%-"*#&*#%567%!8%9:;%allows inference of the retention properties of surrounding soil in h draulic equilibrium via the reference media retention curve(s). The method may be used to obtain both wetting and drying relationships in contrast to many conventional techniques which generally provide only the desorption (retention) response. Use of calibrated reference soils has several important advantages over alternative approaches. Among these are in situ characterization of undisturbed intact soils, ability to measure over the entire soil wetness range, measurement economy in using only paired TDR sensors, and ability to maximize hydraulic continuity between the sensor and target soil through selection of reference media properties. Seven different soils were used in experiments conducted in a laboratory pressure plate apparatus, greenhouse, and a remote field site. Results indicate that the '!0<0#8%#"%-'=#>(&%-"*#0*>">3%='0(&+%6%"?&(%#$&%&*#0(&%4&#*&33%('*)&%5>30*)%'>#"/'#&+%383#&/37%/'8%=("?0+&%/"(&%'-->('#&%65$7%#$'*%>30*)%=(&33>(&%3#&=3%"*<8@%'3%A0*#&(?&*0*)B%0*."(/'#0"*%-"*-&(*0*)%sorption and/or desorption behavior is not lost. Potential concerns include realizing consistent bulk densities for the buried reference soil pockets, and obtaining measurements at the very wet end (near effective saturation) for field applications. Imposed irrigation n address the latter issue, but may binconvenient or impractical in some cases. Routine application of the proposed paired sensor method might be enhanced by fabrication of well -characterized, cylindrical soil or other porous media packets enclosed in wa ter-permeable liner material. This would address the related issues of reference media sensor stability and reproducibility.

Montana continues to work towards development of improved methods to intensively and nondestructively measure transport of ionic solutes in soils. The concentration Ci) of ionic solutes in 3"0<3%03%+0(&-#<8%=("="(#0"*'<%#"%3"0<%3"<>#0"*%&<&-#(0-'<%-"*+>-#0?0#8%5Cw). Time domain reflectometry 59:;7%/&'3>(&3%!"#$%3"0<%4'#&(%-"*#&*#%567%'*+%!><D%3"0<%&<&-#(0-'<%-"*+>-#0?0#8%5Ca) using the same probes. However, physical/conceptual models are required along with TDR measurements in order to use TDR for in situ estimates of Ci. We addressed a modeling approach [Mualem and Friedman, 1991] based on assumed analogy between tortuosity of electrical and hydraulic flow paths in variably saturated soils. We derived a general expression for a pore geometry factor (FG) considering flow of electrical current through randomly distributed capillary soil pores. Two FG were derived based on two conceptual considerations of tortuous capillar length. Four water retention models (WRM) were used to describe soil hydraulic properties in the FGs. When fitted to the same measured water retention data, the four WRMs provided substantially different magnitudes for FG. The model using the two new FG was then compared with field-/&'3>(&+%6%'*+%Ca. One of the new FGs produced 3/'<<&(%&3#0/'#&+%Cw than did that proposed in the original (1991) model. This is desirable based on our own and several other published comparisons that indicated the original mod l may overestimatCw in comparison with independent measurements.

Montana also assisted Department of Energy contractors in evaluating potential efficacy of a proposed unsaturated flow encapsulation system. A portion of the sandy unsaturated zone beneath

15

the Brookhaven LINAC Isotope Producer (BLIP) located at the DOE Brookhaven National Laboratory (BNL) on Long Island, New York was impacted through activation of soil immediatelaround the proton beam target assembly. The block of activated soil is about 7 m below grade and 8 m above the water table. High energy neutrons and protons created by the proton beam hitting the target are absorbed by the soil creating radioactive isotopes of natural-occurring elements in the soil. The two principle isotopes of concern are tritium and sodium 22, which are easily transported to groundwater. To minimize transport of contaminants to the aquifer, unsaturated flow through the impacted soil needs to be reduced. A viscous liquid barrier (VLB) has been proposed as the preferred method for preventing groundwater contamination. Formation of a VLB involves injectina low viscosity colloidal silica (CS) grout into the soil to fill the void space where it sets into a gel. The grout will be injected to encapsulate the activation-zone soils. This creates a monolithic region forming a barrier of reduced permeability and significantly altered soil water retention characteristics. Results of unsaturated flow simulations, using VLB hydraulic properties measured in the laboratory, demonstrated that the performance goal of the barrier constructed using CS grout, variant MSE-6, would be met.

North Dakota, in collaboration with Iowa, developed and evaluated a miscibl -displacement system with an on-line HPLC for hydrophobic volatile organic chemicals. The system is capable of measuring multiple solutes present in the column effluent and there is minimal chemical loss from volatilization and sorption because the system is completely enclosed and constructed of nonsorbinmaterials. A complete description and evaluation of this miscible -displacement system was published recently (Casey et al., 2000 Soil Sci. 165:841-847).

North Dakota and California-USSL collaborated on the development of inverse methods for the transport of chlorinated hydrocarbons subject to sequential transformation reactions. To improve the parameter estimates from the simultaneous TCE and ethylene breakthrough curves an inverse modeling method was added to HYDRUS-1D. The HYDRUS-1D was modified to include parameters from both the TCE and ethylene breakthrough curves in the objective function for the inverse model solutions. We evaluated the modified HYDRUS-1D with breakthrough curves of TCundergoing reduction through columns of zero-valent metals. The TCE and ethylene breakthrough curves were successfully fitted with an equilibrium and nonequilibrium sorption model. The simultaneous inverse model solution improved the reliability of the parameter estimates by adding constraints to the optimized parameters. Analysis with modified HYDRUS-1D model also showed that the nonequilibrium model provided better description of the fate and transport of TCE and its degradation product ethylene.

California-USSL continued research on the estimation of soil hydraulic properties. Reliablestimates of unsaturated soil hydraulic properties (water retention, hydraulic conductivity) are needed in many hydrologic, subsurface pollution and crop production studies; unfortunately, these properties are very difficult to measure rapidly and accurate ly in the field. As an alternative, they can be estimated indirectly using pedotransfer functions (PTFs) from more easily measured soil survey typdata such as soil texture and bulk density. USSL developed a hierarchical neural network-based PTF approach that is both flexibility (by providing better estimates when additional information is available) and accurate (neural networks provide the best possible models). The approach also leads to uncertainty estimates, and hence gives insight into the reliability of the predictions. This research resulted in a computer software package, called Rosetta, that may be used to estimate the unsaturated

16

soil hydraulic properties from more easily measured or more readily available soil survey type data. Users are able to download the software from the hope page (www.ussl.ars.usda.gov) of the SalinitLaboratory. The information should help users to obtain better estimates for infiltration, drainage, leaching, and surface runoff or related flow processes, for specific soil types. California-USSL and California-Riverside developed a new methodology to directlmeasure the porosity and its microscopic characteristics. The methodology is based on the analysis obinary images collected with a backscattered electron detect or from thin sections of soils. Pore surface area, perimeter, roughness, circularity, and maximum and average diameter were quantified in 36 thin sections prepared from undisturbed soils. Saturated hydraulic conductivity (Ks), particle size distribution, particle density, bulk density and chemical properties were determined on the samcores. We used the Kozen -Carman equation and a combined neural network and bootstrap analysis to predict the formation factor from microscopic, macroscopic, and chemical data. The predicted Ks was in excellent agreement with the measured value R2=0.91) when a hydraulic radius defined as rH =pore area/pore perimeter and the formation factor were included in the Kozen -Carman equation.

California-Riverside evaluated methods for measuring Oxygen Diffusion Rate (ODR). Ithis research, a 100-kPa ceramic plate was attached and sealed to the bottom of each undisturbed soil column. Two pressure-transducer equipped tensiometers and two TDR probes were used to monitor water potential and content during the experiment. The ODR was measured by platinum electrode. After the column was saturated, a vacuum pump was used to apply suction to drain water from the bottom. The experiment was conducted in the soil matric potential ranged from 0 to 40 kPa. Results showed that the threshold ODR value of 0.2 µg cm-2 min-1 occurs at 4.5 kPa for the sandy soil and at 10 kPa for the loamy soil, which indicates that at field capacity (10 or 33 kPa), none of the soil will have aeration problem. Indeed, maximum ODR values were achieved at water suctions that are lower than considered as field capacity. The threshold ODR value occurred at air-filled porosity close to 8% for the sandy loam and 17% for the loamy sand. Although the air-filled porosit at field capacity can provide a comparison among different soils in consideration, it does not provide any information on how it will affect plant growth. This research showed that different textured soils could reach to the same ODR level at different air-filled porosities, implying that comparison of ai -filled porosity among different soils has little meaning relative to root growth. The diffusion coefficients of the two soils are substantialldifferent at the same threshold ODR value o 0.2 µg cm-2 min-1. It indicates that ODR is affected bwater contents, not just by gas diffusion through the gas phase. This again implies that comparison odiffusion coefficients among soils offer little information relative to soil aeration capability and influence on root growth.

California-Riverside also investigated the effects of imposing differing water-pressure heads on infiltration into water-repellent soils. Water repellent soils exhibit a positive water entry pressure head, hp, in contrast to wettable soils that have a negative hp. A sand of particulate size between 0.05 and 2.0 mm was treated with two concentrations of octadecylamine to create a sand with hp values of 8.4 and 3.5 cm. The hydraulic conductivity (K) of the water repellent sands increased with increasing values of h0. The K of the treated sand was equal to K of untreated sand when the ratio h0/hp was approximately 3.1 for each treated sand. The infiltration rate increased with increased timfor lower h0 values, but decreased with increased time for higher h0 values. The transition from increasing to decreasing infiltration rates with time occurred when h0/hp was approximately equal to

17

2.6. A positive hydraulic head was created at the interface of an overlying wettable and underlying water which affected the infiltration rate consistent with the effects of h0 on a non-layered water repellent sand. The following mechanism is proposed to explain the increase in infiltration rate with time. In water repellent materials, positive hydraulic heads can be created within the profile during infiltration which can increase as the depth to the wetting front increases. The higher hydraulic head induces an increase in hydraulic conductivity that contributes to increased infiltration rate. Alternatively, if the depth of ponded water is sufficient to cause a hydraulic conductivity equal to that of the wettable material, the infiltration rate behavior is the same as traditionally observed for wettable soils.

Utah developed a method for predicting unsaturated hydraulic conductivity functions based on pore scale hydrodynamics of flowing films and flow in corners bounded by a liquid vapor interfaces. The pore scale results were upscaled to represent sample scale hydraulic functions using measurements of soil porosity, pore size distribution (inferred from retention curve), surface area, and possibly, the saturated hydraulic conductivity. This modeling approach could be extended to represent unsaturated properties of unsaturated fractured rock and macroporous soils.

Washington developed an experimental and theoretical methodology to determine the moisture characteristics from freezing experiments. The instrumental methodology has been improved considerably during the past year. A new TDR transmission line has been constructed and improved insulating material has been tested. Systematic instrument tests have been, and are currently being, performed to assess the effects of ionic strengths, the spatial sensitivity of measurements, and the hysteresis of the freezing phenomenon. Soils and porous media of different composition have been tested and measurement results compared with results obtained with classical methods.

Washington is also testing dyes as vadose zone tracers to visualize flow pathways in soils. Systematic laboratory tests have been conducted with Brilliant Blue FCF, a frequently used dye tracer (German-Heins and Flury, 2000). The pH and ionic strength effect on sorption of the dye to soil media has been investigated. Substantial sorption was found for the soil sample with the highest clay content and the lowest pH. Increasing ionic strength led to increased sorption of Brilliant Blue FCF. In aqueous solution, the absorption spectrum of Brilliant Blue FCF is not sensitive to pH nor ionic strength.

Arizona conducted a flow and transport experiment at the Apache Leap Research Site, near Superior, Arizona. Water was ponded on 9x9 meter area, subdivided into nine 3x3 meter square subplots. The movement of water and tracer through the initially unsaturated, fractured tuff was monitored using a neutron probe, tensiometers, and suction lysimeters. Each subplot had one neutron probe access tube ( 5m deep), 5 tensiometers, and 5 suction lysimeters. Tensiometers and suction lysimeters were installed at depths of 0.5, 1, 2, 3, and 5 meters. Ponding of water on each plot started November, 1999. After 200 days of ponding, increases in water content and decreases in tension were measured at all observation points down to 3m, but no significant changes in water content and tension were noted at the 5 meter depth. Among the nine subplots, great variations in infiltration rates were found. The infiltration rates varied from 0.036 cm/day to 0.75 cm/day. No clear evidence of fracture flow was observed from our water monitoring devices, except infiltration rates were higher for two subplots with apparent surface fractures. Plots with apparent surface fractures maintained similar infiltration rate throughout the experiment. The pressure transducer

18

equipped tensiometers successfully recorded the wetting front arrivals at different depths in various locations but no clear early wetting front arrivals, indicative of fracture flow, were observed. Bromide was added to the irrigation water and all plots on May 30, 2000. Bromi de was first observed in the subsurface at the 1.0 m depth of the north central plot and at the 0.5 m depth in the central plot, 14 days and 25 days after the first bromide application, respectively. Fort -four days after bromide was first applied it was detected at 3 and 5 meter in two of the nine plots only. At this time bromide was found in only 7 of the fort -five suction lysimeters with concentration higher than 3 ppm. The transport of bromide to some deeper depths in a relatively short time and the bypass of bromide at many shallower depths is clear evidence of fracture flow, which was not evidenced from the water content and tension data. Nevada, in collaboration with the California-USSL, investigated flow and transport processes through highly heterogeneous mining wastes commonly found in Nevada. Specifically, the project members have been studying the transport processes of arsenic though gold heap leach sites and gold waste rock dumps. Arsenic is present in many of the ores found in Nevada and its transport from these large, artificial vadose zones to the underlying ground water has significant environmental consequences. The collaborative effort involved modifying the coupled flow and reactive geochemical transport code UNSATCHEM to include th dominant transport mechanism oarsenic (pH dependant non-linear sorption, arsenic dissolution/precipitation, oxygen diffusion and pyrite dissolution). Simulation results, using laboratory data on mine rock, shows multiple reaction fronts as arsenic migrates through waste rock. Specifically, pH changes due to pyrite dissolution tend to reduce arsenic mobility, however redox shifts to anoxic conditions counterbalances this reduce mobility through transformations to more mobile As(III). Results indicate that elevated levels of arsenic in drainage water from these sites will continue for significant time (>100 years) periods. OBJECTIVE 3: To apply scale-appropriate methodologies for the management of soil and water resources In a four-year study, Iowa is using a paired watershed approach to gauge the effect of an optimum N-fertilizer program on water quality in tile drainage. The treated watershed is 1000 ac and has 16 fields managed by 8 farmers. The late spring nitrate test, LSNT, as developed for Iowa, is being used in conjunction with starter and a side -dress application of liquid N to manage N within a corn/soybean rotations. Anhydrous ammonia is not being used due the inherent variability in its application. In addition to surface water quality, yield, soil N, chlorophyll meter values, crop growth is being collected. LSNT recommended N-fertilizer rates were slightly higher in 1997 and about 50 kg/ha less in 1998, and slightly lower in 1999 than farmer program rates. Since the project was initiated in 1997, there has been a 3.5 mg/L reduction in the nitrate -N concentration leaving the LSNT watershed compared to the control watershed (Fig. 3), while corn yields have been

comparable in two out of three years. Overall, the LSNT sub-basin has shown a 41.5% (7.3 mg L-1) reduction in NO3 concentration by early fall of the fourth year (2000). This is the first study to

document the impact of an LSNT program on water quality at a spatial scale that is environmentallmeaningful.

Since 1996, NO3 loss from a subsurface drained field in central Iowa has been measured at

three N-fertilizer rates; a low (L) rate of 57 - 67 kg ha-1, a medium (M) rate of 114 - 135 kg ha-1, and

19

a high (H) rate of 172 - 202 kg ha-1. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were grown in rotation with N-fertilizer applied in the spring to corn only. For the L treatment, NO 3 concentrations in the drainage water exceeded the 10 mg-N L-1 maximum contaminant level (MCL) established by the USEPA for drinking water only during the years that corn was grown. For the M and H treatments, NO3 concentrations exceeded the MCL in all years, regardless of crop grown. Foall years, the NO 3 mass loss in tile drainage water from the H treatment (48 kg -N ha -1) was

significantly greater than the mass losses from the M (35 k -N ha-1-) and L (29 k -N ha-1) treatments, which were not significantly different.

Economic optimum N-fertilizer rates for corn grain production were between the L and M treatments (67 to 135 kg ha-1) in 1996 and between the M and H treatments (114 and 172 kg ha-1) in 1998. Soybean grain production was unaffected by N-fertilizer treatments during the corn year of throtation. To balance the inputs and outputs of N to the system for the 2-yr rotation, N-fertilizer rates needed to be at least at the H rate (202 kg -N ha-1 in 1996 and 172 kg-N ha-1 in 1998) given the current tile drainage losses experienced by this system. However, NO

3 concentrations in tile

drainage consistently exceeded the MCL for drinking water in the years corn was grown for all N-fertilizer treatments and also during the years soybean was grown on the M and H treatments. Thus, it appears that economic corn production cannot be sustained within this field under the current rotation and management scheme without producing tile drainage water that exceeds the MCL for NO3. The problem is not simply one of N-fertilizer use, but of a corn-soybean production

system created by artificial soil drainage and intensive tillage. Thus, NO3 concentrations exceedin

the MCL appears endemic to artificially drained soils cropped to corn within the Midwest. Montana designed, constructed and field-tested a heavy-duty time domain reflectometr

(TDR) probe that fits hydraulic soil sampling machines. Mapping soil water content for sit -specific management of farm fields is commonly achieved through grid soil sampling. This effort frequentlrequires intensive soil coring, which is destructive and time consuming. Precision farming and research can be facilitated if soil sampling techniques are improved and made cost effective. The new heavy-duty probe is simple enough to be adapted to the TDR equipment and hydraulic sampler that a researcher or practitioner may already possess. The probe consists of a housing and adapter that can be fabricated in a local machine shop from materials that are easily obtainable. Utility of thprobe to help in developing kriged field -scale soil water maps was demonstrated in several production agricultural fields.

Montana established two 70-acre on-farm study locations in cooperation with agricultural producers in northern Montana. Eighty neutron access tubes were installed at each study location, and soil water content was measured at two-week intervals during the growing season. Phenology and surface cover of the spring wheat crop was also monitored. An automated climate station was located at each site, to provide real-time weather information including precipitation and potential evapotranspiration. These are used in our combined compute r simulation modeling and remote sensing approach to provide continuously updated and spatiall -distributed estimates of soil water status and crop yield forecasts. Substantial progress was made in converting the computer model to MS Access/Visual Basic fo rmat to facilitate interface with GIS programs currently used bproducers. Two Landsat 7 ETM+ images were acquired for each location, though one of these images may be of limited utility due to presence of clouds. The MODIS remote sensing data for planned use in regional modeling for the project was not available this year. Preparations are

20

currently underway to evaluate potential utility of hyperspectral remote sensing to infer progression of crop water deficit.

Invasive plants such as spotted knapweed h ave been repeatedly implicated in potential degradation of soil and water resources. Altered soil conditions might result from several factors including increased erosion due to lower canopy and basal cover, reduced soil organic matter contribution from tap-roots, and modified seasonal water and nutrient cycles. Degradation of soil resources resulting in increased runoff and sedimentation might impact quality of surface waters. However, evidence for invasive plant impacts on soil and water resources is mainly anecdotal, as very little related research has been completed. Montana completed a study to evaluate impacts of spotted knapweed on selected soil physical properties, soil hydraulic properties, soil water status, and near-surface soil thermal properties. Six field study sites containing both spotted knapweed and native grass plots were used. Basic near -surface soil measurements included particle size distribution, bulk density, and total organic carbon content. Disk permeameters were used to obtain soil hydraulic properties. Steady state infiltration was measured at four supply pressures at the same location in each plot, and these were fitted to Wooding’s equation to obtain the hydraulic conductivity function. Soil water content was monitored using neutron moisture meter and TDR. Near-surface soil thermal regime was monitored using thermocouples. We found that the relationships between vegetation effects and measured soil properties were variable and inconsistent among blocks and study sites. Saturated h draulic conductivity, estimated time to ponding, and a parameter related to range in water conducting pore sizes were not significantly different between infested and noninfested areas. Thermal properties including damping depth and apparent thermal diffusivity were similarly not different between vegetative types. Infested areas had lower soil water storage than noninfested areas from 60 to 100 cm depth during early to mid-growing season, and in the upper 40 cm late in the growing season. This is likely due to differences in root architecture and phenology. The results do not support a hypothesis of altered soil physical, soil hydraulic, or soil thermal properties in response to spotted knapweed infestation. Degradation of soils by spotted knapweed therefore remains mainly anecdotal.

North Dakota studied degradation and transformation of trichloroethylene in miscible-displacement experiments through zero-valent metals. Miscible-displacement experiments were used to study the fate and transport of trichloroethylene (TCE) in the presence of zero-valent metals. Zero-valent metals (e.g., iron filings) are now being used in the development of new technology to remediate groundwater contaminated with organic pollutants such as TCE. Previous research has used batch experiments to study the degradation of TCE and design permeable reactive barriers, which are permeable subsurface walls made of zero -valent metals through which polluted groundwater passes. It is difficult to measure sorption with batch experiments while TCE degradation is also occurring; furthermore, other dynamic processes (e.g., advection) are not simulated with batch experiments. Miscible-displacement experiments were used to study the transport and transformation processes that occur when TCE passed through three columns made o1) sand, 2) iron filings, and 3) iron filings with copper coating. Results indicate that sorption is an important process to be considered when TCE is flowing through zero-valent metal systems. Both the equilibrium and non-equilibrium models did good jobs describing the breakthrough curves; however, the confidence in the estimated parameters were low due to a wide range in the confidenintervals. Nonetheless the normalized degradation rate coefficients were similar to earlier reported

21

rates, although at the lower end. This study was published recently in Environmental Science and Technology (Casey, Ong, and Horton, 2000; ES&T 34:5023-5029).

Although solutions of multidimensional transient water flow can be obtained by numerical modeling, their application may be limited in part as root water uptake is generally considered to be one-dimensional only. California-Davis developed a two-dimensional root water uptake model which was incorporated in a numerical multidimensional flow model. Root water uptake parameters were optimized, minimizing the residuals between measured and simulated water content data. To calibrate the flow and root water uptake model, a genetic algorithm was used to find the approximatglobal minimum of the optimized parameter space. The final fitting parameters were determined using the Simplex optimization algorithm. With the optimized root water uptake parameters, simulated and measured water contents values were in excellent agreement, with R2 values ranging between 0.94 and 0.99 and a root mean squared error of 0.013 m3 m-3. The developed root water uptake model is extremely flexible and allows spatial variations of water uptake as influenced bnon-uniform (drip irrigation) and uniform water application patterns.

California-Riverside initiated a project that deals with agricultural operations (including nursery operations) in the Newport/San Diego Creek, CA. The main objective is t o evaluate the effectiveness of implementing Management Measures (MMs) with the long-term goal of meeting nutrient total maximum daily load (TMDL) established by the Regional Water Quality Control Board. Two sampling stations were established with each station monitoring a separate plot. Upon completion of baseline monitoring in 20 01, the plots will be designated untreated and treated. Management Measures and Management Practices will be initiated on treated plots with surface runoff sampling continuing to determine the effectiveness of MM and MP implementation. Four othe five sites were established in agricultural fields under strawberry production for the majority of the year. The final site was established at a nursery operation. Flow is monitored continuously at all ten sampling sites with water samples taken weekly over a 24-h sampling period. In addition, storm sampling is initiated when precipitation is expected to be more than 6.35 mm (0.25”). In 2000, flofrom agricultural fields was minimal or non-existent since drip irrigation was utilized by the majoritof the operators in the watershed. Overhead irrigation events for establishing crops and protecting against frost and wind produced the most significant flow rates. In contrast, surface runoff from the nursery site occurred daily due to a combination of overhead irrigation and leaching requirements ocontainer-grown plants. A vegetative filter strip, installed in the main runoff channel, seeks to reduce the flow rate allowing settling of sediment and the uptake of nitrate by the vegetation. The vegetation filter strip provides a demonstration of a Management Practice that can be utilized to minimize off-site movement of nutrients and possibly other contaminants.

California-Riverside also developed and tested a sensitive and rapid method for determininthe concentration of PAM. Application of polyacrylamide (PAM) to reduce soil erosion in irrigated land has increased rapidly in recent years. A simple and reliable method to measure PAM in soil extracts is of great need. The new rapid method is based on a combination of determining the total amide-group concentration by the N-bromination method (NBM) and determining the dissolved organic matter (DOM) content by spectrophotometry. The total amide-group concentration of both PAM and DOM was determined by NBM at 570 nm. The DOM moiety, as proportional to DOM concentration, was determined by spectrophotometry using an UV 254-nm wavelength. The actual PAM concentration of a sample was obtained through NBM readings after subtracting the

22

interferential DOM contribution b a correction curve. The correction was based on the highly linear relationship between NBM readings and readings of DOM at 254 nm. Since the composition of the organic matter of each soil may differ, individual DOM correction curves should be used for each soil. Analysis of PAM in extracts from two soils showed that recoveries ranged from 94% to 100.3for the 2 mg/L PAM, and from 98.4% to 101.4% for the 10 mg/L PAM with various DOM concentrations. The coefficients of variation were less than 6% in all cas es. Thus the proposed method is efficacious for measuring PAM concentrations in soil extracts.

Knowing the adsorptive behavior of anionic polyacrylamide (PAM) by soils is useful in predicting appropriate dose of application, depth of effective treatment, and its mobility in soil. Adsorption isotherms of PAM by soil materials, six natural soils and their subsamples with partial organic matter (OM) removed by H2O2 oxidization under different dissolved salt concentrations were examined. The PAM adsorption isotherms fitted Langmuir equation well. Results showed that soil texture, organic matter content, and dissolved salts (a combinative contribution of soil salinity and irrigation water quality) influenced the extent of PAM adsorption. Soils with high clay or silt content and low organic matter content had a high adsorptive affinity to anionic polyacrylamide. The amount of PAM saturation adsorption increased significantly as the total dissolved salts (TDS) increased. Divalent cations such as Ca 2+ and Mg2+ were about 28 times more effective in enhancing PAM adsorption than monovalent cations like Na+ and K+, mainly due to their stronger charge screening ability. Soil samples after OM oxidization adsorbed more PAM than natural soils. The negative effect of OM on PAM adsorption was attributed to the reduction of accessible adsorption sites bcementing inorganic soil components to form aggregates and to the enhancement of electrostatic repulsion between PAM and soil surface by its negatively charged functional groups.

California-Riverside also began work on a long-term program that will test the structure oGLEAMS, RZWQM and similar models for appropriateness of model structure. The steps in this process include: conducting a sensitivity analysis on “ideal data” sets, conducting a multi-criteria calibration on “ideal sets”, utilize results to design tests of model weakness, test model with field data. Preliminary results indicate that of the hydrologic parameters in the GLEAMS model onlCONA, CN2, and porosit are important in determining model output. Field measurements should therefore focus on measurements of porosity and soil texture (used to calculate the CONA parameter), while calibration exercises should focus on CN2 since this parameter cannot be readily measured in the field. Further sensitivity analysis and calibration exercises are planned with field data from field research sites. Testing is also planned for other agronomic water quality models.

Utah continued its collaboration with California-USSL, Dr. Snyder (UPR), and Dr. Hadas (Volcani, Israel) in modeling soil pore space dynamics in aggregated soil subjected to wettin -drying cycles and rapid loading by passage of farm implements. W-188 members extended an analytical model for the rate of deformation soil aggregates as a function of capillary forces to represent the behavior of an aggregate bed. Moreover, the model was extended to calculate strains (compaction) and pore size evolution under rapid loading. We compiled a review paper on rheological properties of wet soils and their relevance to modeling structural and resultant changes in soil pore space and hydraulic properties. The aggregate deformation models were implemented in a stochastic framework for modeling post-tillage soil pore size evolution.

Washington completed its research project on using Chitosan as an antitranspirant in agricultural applications (Bittelli et al., 2001). Chitosan was applied foliarly to pepper plants and

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water use was monitored. Peppers were grown in pots in a growth-chamber and a green-house, where transpiration was measured by weighing pots. In an accompanying field study, water use was determined by soil moisture measurement with TDR and an automated irrigation system. Foliar application of chitosan reduced water u se of pepper plants by 13, 26 and 43% for green-house, growth-chamber and field conditions, respectively. Yields were only marginally affected by chitosan treatment. In an effort to evaluate the adequacy of the improved USDA WEPP (Water Erosion Prediction Project) model for better modeling hydraulic structure functions and forest road erosion, Washington (Wu et al., 2000) applied the model to a small conceptual forest watershed. A segment of an insloping forest road with an impoundment or surface cross drain structure, together with the roadside ditch channel and a waterway channel below the drainage structure, formed the main components of a watershed. Different road system configurations with respect to the density of the drainage structures along a road and downslope road gradient were examined under climate and soil conditions for a representative forest watershed in Idaho State. Soil erosion and delivery ratios resulting from the two road drainage system designs were compared. Results from this study show that WEPP is a useful tool in predicting water erosion from insloping forest roads with impoundment or cross drain structures as well as in helping establish optimum road drainage system designs.

Another effort devoted to improve the WEPP model involve s adapting the model's hydrologic subroutines for forest watershed applications. WEPP was originally developed to evaluatthe erosion effects of agricultural management practices, spatial and temporal variability in topography, soil properties, and land u se conditions within small agricultural watersheds. Forestlands, typified by steep slopes, and shallow, young, and coarse -grained soils, are highly different from common croplands. As a result, hydrologic processes in forest settings exhibit significantl different characteristics (e.g., extremely low soil evaporation and surface runoff, and predominant subsurface runoff) than in agricultural land uses. In refining the WEPP model, modifications were primarily made in the approach to, and algorithms for mod ling deep percolation of soil water and subsurface lateral flow (Wu et al., 2000). The modified model was applied to a conceptual Pacific Northwest forest watershed using local data. Results indicate that, compared to the original model, the modified model can represent the hydrologic processes in forest settings in a more realistic and adequate manner.

Water eroding cropland soil in the Northwestern Wheat and Range Region (NWRR) creates major agricultural, economic, and environmental problems. Past studies show that most water erosion in the NWRR is related to rain on high water content thawing soils. This process is often exacerbated by warm, moist Pacific air masses that bring precipitation and rapid soil surface thaw. Although water erosion is recognized as a serious problem, the effects of freezing and thawing on soil detachment and transport remains one of the least understood aspects of the physical erosion process. A comprehensive water erosion study began in the summer of 2000 with two main objectives: to elucidate the mechanisms by which soil freezing and thawing affects runoff and erosion through laboratory experimentation, and to mathematically formulate the mechanisms for potential incorporation into erosion prediction models. The research has bee n divided into three phases: experimental design and facility construction, experimentation and analysis of results, and incorporation of results into a process-based erosion model. To date, phase one is near completion (Place et al., 2000; Wu et al., 2001; Cuhaciyan et al., 2000). A full -scale tilting flume has been

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designed and its construction is soon to be finished. The model allows for the testing of different drainage designs. Laboratory tests of major soil hydraulic properties have been conducted on the Palouse silt loam soil. Results obtained are comparable to those from previous studies. Through the model tests, it was concluded that different porous materials should be used under different soil, floand tension conditions. In addition, one saturation cycle is sufficient to consolidate the soil to field conditions.

Arizona examined the effect of gravity on flow from spheroids. This work came about from collaborative research with Utah looking at relationships useful for describing subsurface, tension permeameter. Known analytical relationships include: a. Stead -state absorption for all spheroids and all hydraulic properties; b. Stead -state solution with gravity included for Gardner function (K exponential with h); and c. Time -dependent case for absorption from spheres with and without gravity but only for small times. The following illustrates relationships derived from Philip (1985 SSSAJ, p. 828 and 1986 WRR, p. 1874). In review, a prolate spheroid (sort of like a football) has a small axis (ro) in the r direction and a longer axis ω ro about which the ellipse is rotated. An oblate spheroid (sort of like a grapefruit) has a longer axis ro and the shorter axis of rotation is ω ro with ω now less than one. A sphere is simply in between with ω = 1. For all spheroids steady sorption is

Qsorp = 4π (Kwet - Kdry) τ λc r0

where τ is related to ω and λc is the capillary length. Pressure distributions were calculated and compared with results obtained with HYDRUS. Results for both the Vinton fine sand and for the Millville silt loam showed that for sperical sources (ro = 2.5 and 5.0 cm) the calculated flow rates using the van Genuchten function were within about 5% of that using the analytical Gardner function solution (the same Ks and λc are used).

Ground water recharge in arid and semi arid regions is extremely difficult to quantify at spatial scales relevant for most contaminated sites and for water resource evaluation. However, the development and subsequent closure of mining sites has offered a unique opportunity to monitor deep infiltration and recharge in disturbed land areas. Nevada has assembled data from long term drainage rates from closed or inactive heap leach mining operations across Nevada to estimate deep infiltration. These heap leach facilities are large (> 100 hectares) and are situated completely on impermeable liners. As a result, they represent enormous lysimeters capable of measuring deep infiltration at scales appropriate for model development. All deep infiltration through the tops of these mine sites travels through the vadose zone, intersects the impermeable liner and exists through a single collection pipe. Data from drainage rates from 9 mine sites have been collected to date and indicate that significant deep infil tration occurs. Recharge rates (as a function of annual precipitation) at these sites range from less than 1% to as high as 60%. Table 1 shows the distribution of annual precipitation as a function of mean annual precipitation at each site. Mine sites located in the most arid regions (<150 mm/year) show recharge rates as high as 50% or 75 mm/year. Such high recharge rates are consistent with previous work at PNNL that showed that significant deep infiltration occurs in arid regions if the soil surfaces are coarse textured and vegetation is limited. We are currently expanding this data base to several new mine sites and are assembling data from active mine sites. Data from this study will be used to assess the long-term drainage rates and potential for g round water degradation from closed mining sites and will be extended to prediction of drainage fluxes through the adjacent waste rock dumpsites, where no measurements of integrated deep infiltration can be made.

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4. IMPACT STATEMENT: Research conducted by the W-188 in 2000 made significant contributions to our current understanding of water, heat and solute transfer in soils and porous media. Major impacts of the W-188 research include: Instrument development and improvement: A variety of soil physical instruments have been developed, evaluated, and improved. Among these instruments are sensors to measure water contents, bulk densities, porosities, soil moisture retention, heat and solute fluxes, and tracer concentrations. The development of such instruments and the corresponding measurement theories is an essential prerequisite for measurement of soil physical parameters at laboratory and field scales. Soil physical parameters, such as water content or soil moisture retention, are being used by managricultural and environmental disciplines other than soil physics. New and improved instruments will therefore have a broad and important impact on any basic and applied research and extension dealing with soils and porous media in general. Model development and improvement: Mathematical models are being used more and more frequently to predict and estimate water flow and solute transport. Many models are difficult to use and therefore often susceptible to operator errors. W-188 members have put emphasis on developinuser-friendly interfaces to ease the use and application of complicated models. A variety of new models have been developed that will help to make more realistic predictions of kinetic reactions and of root water uptake and evaporation, thus ultimately leading to an improvement of environmental fate predictions and irrigation scheduling in agriculture. W -188 members have also successfullimplemented new algorithms to estimate soil hydraulic properties from readily available data, such as soil texture and bulk densities. These algorithms will help to make better use of existing soil data and improve site-specific management practices through more realistic predictions of water flow and solute transport. Many of the models developed by W-188 members are readily available on-line. Theoretical Advances of Water Flow and Solute Transport: Theoretical advances have been made in flow and transport processes. In 2000, temporal and spatial scale effects on diffusion were investigated. The effects of io nic strength, kinetic sorption, and physical nonequilibrium were studied. Various upscaling procedures were proposed and investigated. Methods for quantifying model uncertainty were developed. Pore -scale models of soil hydraulic properties have been proposed. These types of theoretical advances will serve as building blocks in future development osustainable agricultural and resource management. Spatial and Temporal Variabilit : W-188 research has improved our understanding of spatial and temporal variability of soil physical and agronomic parameters. In 2000, research demonstrated that slope is one of the most important factors in determining the spatial and temporal variability of soil moisture across a landscape. The temporal consistency in solute transport measurements was been evaluated. New physically based scaling techniques for heterogeneous soils were developed. The temporal stability of yield and soil moisture patterns were evaluated. The improved understanding and descriptions of soil variability provided by this research is crucial to the development of scale-appropriate theories, models, and management. Experimental Findings: In 2000, the W-188 group conducted or initiated a number of important experiments. W-188 members initiated the first study to document the impact of a Late

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Spring Nitrate Test program on water quality at a spatial scale that is environmentally meaningful. Data were collected on correlations between water transfer and solute transport properties of a soil that exhibits preferential flow, and on correlations between soil thermal properties and other soil physical properties. The influence of water content on soil strength was measured, as was the effect of air filled porosity on oxygen diffusion rates. Long -term inf iltration in fractured tuff was measured. New experimental techniques for characterizing unstable flow and preferential transport have been developed. These types of experiments and data are needed to validate and improve theories, models, and resource management. The W-188 group is prolific in publishing its scientific results in technical journals. The lonlist of publications shows the productivity of the group and emphasizes its impact on the scientific literature. 5. ACTIVITIES PLANNED FOR 2001: This is the second progress report for the W-188 5-year research project (1999-2004). Research in 2001 will continue on the objectives as described in Section 3. Some specific plans are:

• Kansas will conduct field experiment will be conducted in which near-surface water content variations are characterized over a range of spatial and temporal scales. This will provide a data set that can be used to evaluate upscaling techniques.

• Kansas will extend the above-described work on the temporal stability of yield patterns using spectral analysis to characterize the spatial scales at which temporal stability or instability occurs.

• Kansas will continue experimental work on the effects of forced convection on θ measurements.

• Montana and Utah will further pursue measurement of soil specific surface area using TDR, through analysis of measurement responses to thermal perturbation.

• Montana and Utah will evaluate potential importance of the Maxwell-Wagner effect for measured TDR travel times in soils and porous media.

• The data base obtained for the Maricopa field site (Arizona) will be used to test a variety of 1D, 2D and 3D models. The infiltration and redistribution data will be used in conjunction with a variety of methods to determine unsaturated hydraulic properties at this site.

• The effect of gravity on stead -state infiltration will be further pursued at Arizona. New cases to be considered include generalization of the numerical results by scaling out the saturated hydraulic conductivity and capillary length. Also, other boundary conditions will be completed using HYDRUS, including unsaturated-saturated regimes with partially filled sources.

• North Dakota will collaborate with California-USSL on inverse analyses of infiltration experiments using HYDRUS-1D.

• Collaborative work (Montana, Minnesota, South Dakota, and North Dakota) will begin on a four-year precision agriculture project. The project is funded by REEUSDA’s Initiativfor Future Agriculture & Food Sources (IFAFS).

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6. PUBLICATIONS DURING 2000:

Abbaspour, K. C., A. Kohler, J. Šimùnek, M. Fritsch, and R. Schulin, Application of a two -dimensional model to simulate flow and transport in a macroporous agricultural field with tile drains, European J. of Soil Sci. (in press).

Ahmed, S.I., D.B. Jaynes, R.S. Kanwar, and S.J. Kung. 1999. Herbicide and tracer movement to subsurface drains under simulated rainfall conditions. ASAE Paper No. 99-2200.

Ayars, J.E., R.A. Schoneman, F. Dale, B. Meso, and P.J. Shouse. 2000. Managing subsurface drip irrigation in the presence of shallow groundwater. Agric. Water Management (in press).

Bachmann, J., R. Horton, R. R. van der Ploeg, and S. Woche. 2000. Modified sessile drop method for assessing initial soil-water contact angle of sandy soil. Soil Sci. Soc. Am. J. 64:564-567.

Bakhsh, A., Colvin, T. S., Jaynes, D. B., Kanwar, R. S., and Tim, U. S. 1999. Applying GIS for interpretation of spatial variability in yield: A case study. ASAE Paper No.MC99-125.

Bakhsh, A., D.B. Jaynes, T.S. Colvin, and R.S. Kanwar. 2000. Spatio-temporal analysis of yield variability for a corn-soybean field in Iowa. Trans. ASAE. 43:31-38.

Bakhsh, A., R.S. Kanwar, D.B. Jaynes, T.S. Colvin, and L.R. Ahuja. 2000. Predicting effects of variable nitrogen application rates on corn yields and NO3-N losses with subsurface drain water. Trans. ASAE. (In press)

Bakhsh, A., R.S. Kanwar, D.B. Jaynes, T.S. Colvin, and L.R. Ahuja. 2000. Prediction of NO3-N

losses with subsurface drainage from manured and UAN -fertilized plots using GLEAMS. Trans. ASAE. 43:69-77.

Barger, B., J.B. Swan, and D.B. Jaynes. 1999. Soil water recharge under uncropped ridges and furrows. Soil Sci. Soc. Am. J. 63:1290-1299.

Bejat, L., E. Perfect, V.L. Quisenberry, M.S. Coyne, and G.R. Haszler. 2000. Solute transport as related to soil structure in unsaturated intact soil blocks. Soil Science Society of America Journal 64:818-826

Bingham, G.E., S.B. Jones, D. Or., D., I.G. Podolski, M.A. Levinskikh, V.N. Sytchov, T. Ivanova, P. Kostov, S. Sapunova, I. Dandolov, D.B. Bubenheim, G. Jahns. 2000. Microgravity effects on water supply and substrate properties in porous matrix root support systems. Acta Astronautica 47:1-10.

Bittelli, M., Flury, M., Campbell, G.S. and Nichols, E.J., 2001. Reduction of transpiration through foliar application of Chitosan. Agric. For. Meteorol., (in press).

Bristow, K. L., G. J. Kluitenberg, C. J. Goding, and T. S. Fitzgerald. 2001. A small multi-needle

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probe for measuring soil thermal properties, water content and electrical conductivity. Comput. Electron. Agric. (in press).

Brown, P.W., C.F. Mancino, M.H. Young, T.L. Thompson, P.J. Wierenga and D.M. Kopec. 2001. Penman Monteith crop coefficients for use with desert turf systems. Crop Science (accepted).

Casey, F.X.M., R.P. Ewing, and R. Horton. 2000. Automated apparatus for miscible displacement through soil of multiple volatile organic compounds. Soil Sci.165:841-847.

Casey, F.X.M., S. K. Ong, and R. Horton. 2000. Degradation and transformation of trichloroethylene in miscible-displacement experiments through zero-valent metals. Environ. Sci. Technol. 34:5023-5029.

Chu, Y., Jin, Y., Flury, M. and Yates, M.V., 2001. Mechanisms of virus removal during transport in unsaturated porous media. Water Resour. Res., (in press).

Colvin, T.S., Jaynes, D.B., Kaspar, T.C., James, D.E., and Meek, D.W. 2000. Yield certainty with plots or fields. Fifth International Conf. Precision Agriculture, July 16-19, 2000. Bloomington, MN (in press)

Cooper, C., R.J. Glass and S.W. Tyler. 2001. Assessment of mass fluxes under double diffusive convection in porous media. Water Resources Research. (In Press)

Costanza, M.S., T.D. Carlson, M.L. Brusseau and P.J. Wierenga. 2001. Trichloroethene vapor transport in an intermediate-scale vadose zone system: Retention processes and partitioning tracer based prediction. J. Cont. Hydrol. (in press).

Cuhaciyan, C.O., Wu, J.Q., Place, M.K., McCool, D.K. and Palmer, C.R., 2000. Design of a tilting flume for testing frozen soil erosion. ASAE Pap. 200009, Am. Soc. of Agric. Eng., St. Joseph, MI

Das, B. S., R. S. Govindaraju, G. J. Kluitenberg, A. J. Valocchi, and J. M. Wraith. 2001. Theorand applications of time moment analysis to study the fate of reactive solutes in soil. In R. S. Govindaraju (ed.) Stochastic methods in subsurface contaminant hydrology. American Society of Civil Engineering (in press).

Das, B.S., and J.M. Wraith. 2000. New geometry factors for hydraulic propert -based soil solution electrical conductivity models. Water Resour. Res. 36:3383-3387.

Dinnes, D. L., Jaynes, D. B., Cambardella, C. A., Colvin, T. S., Hatfield, J. L., and Karlen, D. L. Split application nitrogen fertilizer management effects on corn yield and water quality. Farm Bureau Spokesman Press (Autumn Harvest). 1999.

Dinnes, D.L., Jaynes, D.B., Meek, D.W., Cambardella, C.A., Colvin, T.S., Hatfield, J.L., and Karlen, D.L. 2000. Intensive N fertilizer management effects on water quality at the watershed scale. March 28-30, 2000. La Crosse, WI

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Ewing, R.P. and B. Berkowitz. 2001. Stochastic Pore-Scale Growth Models of DNAPL Migration in Porous Media, Adv. Water Resour. 24 (3-4) 309-323.

Feng, G.L., J. Letey and L. Wu. 2001. Water Ponding Depths Affect Temporal Infiltration Rates in a Water Repellent Sand. Soil Sci. Soc. Am. J. (Accepted).

Fennemore, G. G., Andy Davis, L. Goss and A. W. Warrick. 2000. A rapid screening-level method to optimize location of infiltration pond. Ground Water (Accepted)

Gan, J., S.R. Yates, F. F. Ernst, and W.A. Jury, 2000. Degradation and volatilization of the fumigant Chloropicrin after soil treatment. J. environ. Qual. 29: 1391-1397.

Gangloff, W. J., M. Ghodrati, J. T. Sims and B. L. Vasilas. 2000. Impact of fly ash amendment and tillage method on water status of a sandy soil. Water Air Soil Pollut. 119: 231-245.

Garrido, F. M. Ghodrati, CG Campbell, M. Chendorain. 2001. Detailed characterization of solute transport in a heterogeneous field soil. J. of Environ Qual. In Press.

Garrido. F., M. Ghodrati, CG Campbell. 2000. A method for In Situ field calibration of fiber optic miniprobes. Soil Sci. Soc. Am. J. 64(1): 836-843.

German-Heins, J. and Flury, M., 2000. Sorption of Brilliant Blue FCF in soils as affected by pH and ionic strength. Geoderma, 97:87-101.

Ghezzehei, T.A., and D. Or. 2000. Dynamics of soil aggregate coalescence governed by capillary and rheological processes. Water Resour. Res. 36:367-379.

Ghezzehei, T.A., and D. Or. 2000. Rheological properties of wet soils and clays under steady and oscillatory stresses. Soil Sci. Soc. Am. J. (in press).

Ghodrati, M. F. Garrido, CG Campbell, M. Chendorain. 2000. A multiplexed fiber optic mini-probe system for measuring convective dispersive solute transport in soil. J. of Environ Qual. 29(2): 540-550.

Green, R. L., L. Wu, and G. Klin. 2001. Summer cultivation treatment effects on field infiltration rates and soil salinity on an annual bluegrass putting green. HortScience. (Accepted, August 2000. 20 manuscript pages).

Guo, L., Jury, W., Wagenet, R.J. and Flury, M., 2000. Dependence of pesticide degradation on sorption: nonequilibrium model and application to soil reactors. J. Contam. Hydrol., 43:45-62.

Guo, L., W. Frankenberger, and W. Jury 2000 Characterizing kinetics of sequential selenium transformations in soil. J. Environ. Qual. (in press).

Guo, L., W. Frankenberger, and W. Jury 2000. Measurement of Henry's law constant of dimethyselenide as a function of temperature. J. Environ. Qual. (in press).

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Guo, Lei, W. Jury, R. Wagenet, and M. Flury 2000 Dependence of pesticide degradation on sorption: nonequilibrium model and application to batch reactors. J. contaminent Hydrol. 43:45-62.

Henry, E. J., J. E. Smith and A. W. Warrick. 2000. Surfactant effects on unsaturated flow in porous media with hysteresis: Horizontal column experiments and numerical modeling. J. Hydrol ogy (Accepted).

Holland, D. F., M. Yitayew and A. W. Warrick. 2000. Measurement of subsurface unsaturated hydraulic conductivity. J. Irrig. Dr. Engr. 126:21-27.

Hollenbeck, K. J., J. Šimùnek, and M. Th. van Genuchten. 2000. RETCML: Incorporating maximum-likelihood estimation principles in the RETC soil hydraulic parameter estimation code. Computers and Geosciences 26(3):319-327.

Hopmans, J. W. and J. Šimùnek. 2001. Review of inverse estimation of soil hydraulic properties. In: Characterization and Measurement of the Hydraulic Properties of Unsaturated Porous Media, eds. M. Th. van Genuchten, F. J. Leij and L. Wu, University of California, Riverside, CA, 643-659, 1999.

Hopmans, J. W., J. Šimùnek, N. Romano, and W. Durner, Inverse Modeling of Transient Water Flow, In: Methods of Soil Analysis, Part 1, Physical Methods, Chapter 3.6.2, Eds. J. H. Dane and G. C. Topp, Third edition, SSSA, Madison, WI (in press).

Inoue, M., J. Šimùnek, S. Shiozawa, and J. W. Hopmans, Estimation of soil hydraulic and solute transport parameters from transient infiltration experiments, Advances in Water Resources, 23, 677-688, 2000.

Kaspar, T.C., Colvin, T.S., Jaynes, D.B., Karlen, D.L., James, D.E., Meek, D.W., Pulido,D., and Butler,H.C. 2000. Estimating corn yield using tem poral yield data and terrain attributes. Fifth International Conf. Precision Agriculture. July 16-19, 2000. Bloomington, MN (in press)

Kluitenberg, G. J., and A. W. Warrick. 2001. Improved evaluation procedure for heat -pulse soil water flux density method. Soil Sci. Soc. Am. J. (in press).

Lee, J., D.B. Jaynes, and R.L. Horton. 2000. Evaluation of a simple method for estimating solute transport parameters: Laboratory studies. Soil Sci. Soc. Am. J. 64:492-498.

Lee, J.H., R. Horton, and D.B. Jaynes. 2000. A time domain reflectometry method to measure immobile water content and mass exchange coefficient. Soil Sci. Soc. Am. J. 64:1911-1917.

Leij, F. J., and J. H. Dane. 2000. Comment on "A moment method for analyzing breakthrough curves of step inputs" by C. Yu et al. Water Resour. Res. (in press).

Leij, F. J., and M. Th. van Genuchten. 2000. Analytical modeling of nonaqueous phase liquid dissolution with Green’s functions. Transport in Porous Media 38:141-166.

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Leij, F. J., and M. Th. van Genuchten. 2000. Analytical modeling of nonaqueous phase liquid dissolution with Green's functions. Transport in Porous Media 38:141-166.

Leij, F. J., E. Priesack, and M. G. Schaap. 2000. Solute transport modeled with Green's functions with application to persistent solute sources. J. Contam. Hydrol. 41:155-173.

Leij, F.J. 2000. Book review of "Analytical solutions of geohydrological problems" by G.A. Bruggeman. J. Contam. Hydrol. 43:187-189.

Leung, S., L. Wu, B. Sanden, and J. Mitchell. 2000. Effect irrigation uniformity on nitrogen use and nitrate leaching. Agri. Water Management. 1599:1-14.

Macur R.E., H.M. Gaber, J.M. Wraith, and W.P. Inskeep. 2000. Predicting solute transport using mapping-unit data: Model simulations versus observed data at four field sites. . Environ. Qual. 29:1939-1946.

Mitchell, J. B. Sanden, S. Allaire-Lueng, L. Wu. 2000. Sprinkler spacing does not affect carrot yield and quality. HortTechnology 10:370-373.

Mmolawa, K. B., and D. Or, 2000. Root zone solute dynamics under drip irrigation: A review. Plant and Soil 222:161-189.

Mmolawa, K. B., and D. Or, 2000. Water and solute dynamics under a drip irrigated crop: Experiments and analytical model. Transactions of the ASAE (in press).

Mohanty, B.P., and T.H. Skaggs, 2000. Spatio-temporal evolution and time-stable characteristics osoil moisture within remote sensing footprints with varying soil, slope, and vegetation. Adv. Water Resour. (in press).

Mohanty, B.P., J.S. Famigletti, and T.H. Skaggs, 2000. Evolution of soil moisture spatial structure in a mixed-vegetation pixel during the SGP97 hydrology experiment, Water Resour. Res., 36(12):3675--3686.

Mohanty, B.P., T.H. Skaggs, and J.S. Famigletti, 2000. Analysis and mapping of field -scale soil moisture variability using high resolution, ground-based data during the Southern Great Plains 1997 (SGP97) Hydrology Experiment, Water Resour. Res., 36(4):1023-1031.

Nassar, I. N., R. Horton, and G.N. Flerchinger. 2000. Simultaneous heat and mass transfer in soil columns exposed to freezing/thawing conditions. Soil Sci. 165-208-216.

Novák, V., and J. Šimùnek. 2000. Modeling of water infiltration into soils with cracks, Acta Hydrologica Slovaca, 1, 119-125 (in Slovak, with English summary).

Novák, V., J. Šimùnek, and M. Th. van Genuchten. 2000. Infiltration of water into soil with cracks. J. Irrig. and Drain. Engrg. 126(1):41-47.

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Or, D., 2001. Who invented the tensiometer? Soil Sci. Soc. Am. J. 65:000-000.

Or, D. and T.A. Ghezzehei. 2000. Dripping into cavities from unsaturated fractures under evaporative conditions. Water Resour. Res. 36:381-393.

Or, D., F. J. Leij, V. Snyder, and T. A. Ghezzehei. 2000. Stochastic model for posttillage soil pore size evolution. Water Resour. Res. 36(7):1641-1652.

Or, D., U. Shani, and A.W. Warrick. 2000. Subsurface tension permeametry. Water Resour. Res. 36:2043-2053.

Or, D., and J.M. Wraith. 2000. Comment on “On water vapor transport in field soils” by Anthony T. Cahill and Marc B. Parlange (Water Resour. Res. 34: 731-739, 1998). Water Resour. Res. 36:3103-3105.

Perfect, E. 2000. Estimating soil mass fractal dimensions from water retention curves. In: Pachepsky, Ya. A., J.W. Crawford, and W.J. Rawls (eds.), Fractals in Soil Science, Developments in Soil Science 27, Elsevier, Amsterdam, the Netherlands, p.131-141

Perfect, E., and M.C. Sukop. 2000. Models relating solute dispersion to pore space geometry in saturated media: A review. In: Physical and Chemical Processes of Water and Solute Transport/Retention in Soil, Soil Science Society of America Special Publi cation, Soil Science Society of America, Madison WI (in press)

Place, M.K., Wu, J.Q., Cuhaciyan, C.O. and McCool, D.K., 2000. The big freeze and thaw. Resource, 11/12, Am. Soc. of Agric. Eng., St. Joseph, MI

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Ren, T., G. J. Kluitenberg, and R. Horton. 2000. Determining soil water flux and pore water velocity by a heat pulse technique. Soil Sci. Soc. Am. J. 64:552-560.

Ressler, D. E., R. Horton, J. L. Baker, and T. C. Kaspar. 2000. Improved fertilizer applicator to reduce nitrate fertilizer leaching from crop lands. In J. M. Laflen, J. Tian, and C. H. Huang (eds.) Soil Erosion and Dryland Farming. p. 177-189. CRC Press, Boca Raton, Florida.

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7. SIGNATURES _______________________________________________ ____________ T.H. Skaggs, Chair Date Technical Committee, W-188 ________________________________________________ ___________ G.A. Mitchell Date Administrative Advisor, W-188