Duration: 10/01/2009 to 09/30/2014

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Knowledge about physical transformations occurring in the vadose zone is crucial for understanding, predicting and managing biotic and abiotic processes occurring in Earths terrestrial critical zones. Because they form an interface with the atmosphere, near-surface soils within the vadose zone are particularly important for controlling mass fluxes and transforming energy, nutrients, and organic materials. The near-surface environment of the vadose zone also sustains plants with water and essential microbiological communities. Although public awareness of the role of soils - and by extension the vadose zone - is meager, good stewardship of vadose zone functions should be among the highest priorities of our society. Meanwhile, changing societal food and energy demands, land use and climatic conditions, and introduction of man-made substances are imposing ever greater stresses on the vadose zone. The protection and sustainability of this crucial resource can only be assured through a better understanding of vadose zone processes at different spatio-temporal scales. Soil and vadose zone physics plays a critical role in managing soil resources, and outstanding progress in understanding this role has been made in recent years, though only at limited spatio-temporal scales. Indeed, storage, redistribution, transport and transformation processes of water, heat and chemicals are understood for relatively small-scale systems, and an overriding challenge for the scientific (soil physics) community has been to apply our understanding across scales. In 1997, Nielsen stated with respect to the vadose zone, it is there but nobody cares. Much has been learned and documented since then in the Vadose Zone Journal and other esteemed outlets, though knowledge gaps still remain in measurement and modeling, transfer across spatio-temporal scales, and multidisciplinary integration of results. Non-destructive imaging for understanding sub-visible scale processes--Non-destructive imaging methods such as X-Ray Computed Tomography (CT) yield high-resolution (2 microns), 3-D representations of soil pore space that can be used in conjunction with advanced simulation techniques such as smoothed particle hydrodynamics (SPH) or the lattice Boltzmann (LB) model to significantly advance our knowledge about fluid distribution, interfacial phenomena, and flow and transport processes in agricultural soils. Ongoing and future research areas include improving scanning procedures and developing image segmentation and pore-space analysis tools for quantitatively characterizing soil pore space. A number of CT systems are used today by multi-state researchers, ranging from benchtop scanners to synchrotron microtomographs. They primarily differ in x-ray source and energy, detector geometry, and sample manipulation capabilities. Comprehensive reviews about fundamentals of computed tomography are provided in Stock (1999), Ketcham and Carlson (2001), and Wildenschild et al. (2002). Some applications of CT in porous media research include pore space characterization with respect to variables such as bulk density (Rogasik et al., 1999), volumetric water content (Hopmans et al., 1992; Rogasik et al., 1999), phase distributions (Wildenschild et al., 2002), breakthrough of solutes in porous media (Clausnitzer and Hopmans, 2000; Perret et al., 2000), and pore-scale configuration of immiscible organic fluids in multiphase systems (Schnaar and Brusseau, 2005, 2006a, b). Transport and Transformations of Colloids and Compounds--Emerging contaminants, such as hormones and pharmaceuticals, are widespread in the environment (Kolpin et al., 2002). Pathogens, which include viruses, bacteria or other microorganisms, are also creating major challenges as water resources dwindle and wastewater is reused. These emerging contaminants, pathogens and metabolites present unique challenges in understanding their fate and transport in the soil-water environment. Many emerging contaminants are potent at very low concentrations and labile, associating strongly with soil solids and undergoing rapid and complex transformations. Specialized laboratory experiments together with modeling and field observations are required to fully understand their fate and transport in the vadose zone (Fan et al., 2007a, b). Often these compounds (pesticides, radionuclides, and metals) can strongly associate with soil colloid particles (10mm in size), which can significantly enhance immobility and persistence (McGechan and Lewis, 2002; Bradford et al., 2003; Bradford and Torkzaban, 2008). Colloids can be mineral particles, organic entities, or small living organisms, like bacteria or viruses, and engineered nanoparticles. They are ubiquitous in soils, and play an important role in soil formation and contaminant fate and transport. Understanding colloidal processes in soils and sediments is important for environmental quality and human health. We need to understand the mechanisms of colloid retention at different interfaces to make accurate predictions of colloid transport and to design effective management and remediation practices to prevent soil and water contamination. Vadose Zone Role in Quantifying Basin-scale Responses--A traditional soil physicists approach for explaining environmental processes is to examine small scale (~1 m3 or smaller) behaviors and then apply those results to larger, basin-scales using statistical upscaling techniques. This approach has provided significant mechanistic understanding of mass and energy balances, but it has limitations when using the results to explain basin-scale processes (surface runoff, soil moisture estimates for regional scale atmospheric models, large-scale water budgets). A review of the current status and research opportunities (Harter and Hopmans, 2004) in this area implied a need to better link small-scale physics with larger-scale hydrology through upscaling and downscaling approaches, so that soil property variability and dominant factors influencing water exchange can be placed into the appropriate context. For example, Seyfried and Wilcox (1994) identified deterministic length scales that could be applied to scale-dependent influences on hydrologic processes and models. They showed that shrub effects were limited to about 10 m and soil depth became important at length scales from 10 m to 10,000 m (for elevations below 1300 m). This has implications for hydrological response units that are used in large-scale rainfall-runoff and other models. This research program provides an excellent venue for soil physicists to participate in upscaling research, which would provide opportunities to collaborate with climate modelers and hydrologists. Soil Hydraulic and Thermal Properties--Soil hydraulic properties are key to quantitatively describing soil water flow and chemical transport. Hydraulic properties of natural soils are scale dependent, time dependent, and spatially variable. In agricultural soils, temporal changes in soil hydraulic properties are primarily caused by tillage (Or et al., 2000), clay content and clay mineralogy, and water and soil quality. Changes in soil volume and pore space induced by clay swell-shrink processes present a challenge to developing predictive models for flow and transport, in particular to develop constitutive hydraulic functions. Such functions are important not only for design of man-made hydraulic barriers such as clay liners constructed for waste isolation, but also for fluid flow predictions in porous media (Mitchell, 1993; Benson et al., 1994). Recent advances in pore scale modeling of fluid flow and liquid distribution in rigid angular pores have been developed through our collaborations. These consider both capillarity and adsorption (Tuller et al., 1999; Or and Tuller, 1999; Masad et al., 2000; Tuller and Or, 2001; Tashman et al., 2003) and provide the basis for a proposed multiscale-modeling framework in soils. Other methods for deriving hydraulic properties include pore-scale network models (Vogel, 2000; Vogel et al., 2005; Li et al., 2005) and lattice-Boltzmann methods (Vogel et al., 2005; Zhang et al., 2005; Schaap et al., 2007). The process of mass diffusion in porous media is important for understanding migration of volatile gas from contaminated sites, transport of gases through the root zone of vegetated soils, and the interaction of aqueous and gaseous chemical constituents with the solid soil matrix. Many methods have been developed for relating the mass diffusion coefficient to phase fractions (solid, liquid, gas) of porous media, most of which have been empirical in form. In recent years and especially in the last decade, the mass diffusion coefficient was related to porous media properties such as the water retention curve (Moldrup et al., 2000; Moldrup et al., 2005; Resurreccion et al., 2008). The dependence of mass diffusion on phase distribution at the pore scale has been examined with pore scale models (Steele and Nieber, 1994a, b) and lattice-Bolzmann models (Chau et al., 2005). Thermal properties of porous media are important in many environmental and industrial applications. For instance, the thermal conductivity and heat capacity of soils greatly affect the partitioning of solar radiation into components of soil heating, the transfer of long-wave radiation, and sensible and latent heat transfer. The method of DeVries (1963) is commonly used for predicting the thermal properties from texture and phase content of porous media. More recent methods have used pore-scale modeling methods to relate the core-scale thermal conductivity to phase distributions (Hu et al., 2001; Ewing and Horton, 2007). Multi-scale Flow and Transport Including Impacts from Climate Change--The design of spatial and temporal sampling schemes is based on several questions. How do we sense variation of a soil physical and related state variable or property? How do we separate measurement noise from signal? What are ways of transferring scale-specific soil physical information to different domains while maintaining important variance characteristics? Do the spatial or temporal covariance behavior manifest that our measurement design was adequate to solve the problem? Typically, measurements taken at the instrument scale are used for spatial or temporal processes at some larger domain (Ellsworth and Boast, 1996). For this purpose, a good average of the derived property is often applied with a local-scale model to make a large-scale prediction (Cahill et al., 1999). Averages can be misleading (Stockton and Warrick, 1971). For example, when averages fail to represent the horizontal variability structure (Nielsen et al., 1973), predictions over time may be fallacious when the local status deviates from the mean. Nielsen (1987) questioned, How can we integrate information from the measurement scale to our goal scales? Investigations of the spatial and temporal variability structure of relevant soil physical state variables (soil water content) and related soil hydraulic functional properties (Western et al., 2004; Comegna and Vitale, 1993; Ünlü et al., 1989; 1990; Shouse et al., 1995) reveal substantial changes of spatial correlation lengths of soil-water-related state variables with time and the magnitude of soil-water content (Roth, 1995; Wendroth et al., 1999; Vereecken et al., 2007; Green et al., 2007; 2009). Accordingly, the cross-correlation structure between soil water and related variables depends on the magnitude of soil water status (Nielsen et al., 1973; Greminger et al., 1985). Moreover, seasonal evolution of soil moisture variance and correlation length reoccurs during times of reoccurring water status (Western et al., 2004). Soil Physics and Ecological Interactions--Although soil physics and biophysics have addressed soil-plant-climate continuum issues for many decades (Russell, 1960; Campbell, 1977; Wraith and Baker, 1991; Campbell and Norman, 1998; Kirkham, 2005), the mechanistic understanding of plant root response to changing soil environmental variables such as temperature, water/salinity and nutrient concentration is still limited. Whereas a conceptual modeling framework of root response was recently developed (Simunek and Hopmans, 2009), experimental studies need to be conducted to confirm the hypothesized root responses to water, temperature and nutrient stresses, especially to compensation and nutrient uptake mechanisms. Interdisciplinary research has created a growing need and desire within this multistate project to pursue greater collaboration with ecologists and plant scientists. A decade ago, the term ecohydrology was coined and predictions of major breakthroughs and intensive activity in understanding spatio-temporal soil-plant-climate interactions were made (Zalewski et al., 1997; Baird and Wilby, 1999; Rodriguez-Iturbe, 2000). Today ecohydrology is a thriving discipline with soil physics as a major constituent informing research across scales from soil-nutrient-root interactions to desertification (Wardle et al., 2004; Hopmans, 2006; Reynolds et al., 2007). Recent inroads have been made applying principles of soil physics to vegetation and soil patterns (Robinson et al., 2008b), desert ecosystems (Shafer et al., 2007; Wang et al., 2007), Pinion-Juniper woodlands (Lebron et al., 2007), soil microbial habitat (Or et al., 2007), soil biophysics (Smucker and Hopmans, 2007) and other topics. Improved Multifunction Measurement Devices--Throughout large segments of the terrestrial sciences, including agriculture, ecology, and hydrology, there is a pressing need to improve instruments to better interrogate subsurface environments, especially those capable of providing data for multiple state variables, which affect water movement, nutrient dynamics, plant root behavior, and temperature profiles. Improvements have been highlighted (Mori et al., 2003; Ren et al., 2003), and the broader importance of the technologies toward answering multi-disciplinary questions (Ferré and Kluitenburg, 2003; Jones and Shenai, 2007). These new multi-function probes will be field and laboratory tested. Nonetheless, many of these approaches are still under development and will be improved upon. Quantifying Near-surface Processes with Instruments and Analyses--Net ecosystem production and net ecosystem exchange are closely tied to soil properties. Researchers have a significant opportunity to assist the agricultural and ecological communities by addressing the importance of soil properties and processes. Heitman et al. (2008) showed an approach that uses heat pulse probes as a means to estimate latent heat flux, a critical component of the energy budget. Upscaling these point-scale values to basin-scale (Zhu et al., 2006) would allow better assessments of regional-scale water status, yet advancement of instrumentation and analyses has lagged the potential societal applications. In particular, remote sensing tools are becoming more sophisticated, but ground truthing is needed. Computer capabilities have evolved to a point where multi-dimensional, physically-based hydrologic models can be used to study spatio-temporal patterns of mass and energy flow in the vadose zone. However, these models have so far received limited attention because of their computational, distributed input and flux parameter requirements. Global optimization algorithms may help to explore various mechanistic models with differing complexities to analyze the salt and nutrient transport in irrigated areas, at different spatial scales. For example, zone soil sampling may make precision farming practical in the Northern Great Plains, but defining zones is currently subjective. Zone determination could be automated using different scale-appropriate methods, like combining information from different sampling methods, automating nutrient zone boundary determination, and evaluating water quality impacts from precision farming. Field-scale water content, landscape topography, landform, and soil property mapping approaches could link in-field measurements and remotely sensed data to improve resource management. Future opportunities will require us to reach across disciplines and establish working relationships, proposals and integrated research with ecosystem and environmental scientists. We will continue developing interdisciplinary meetings (joint session at the Ecological Society of America meeting, August 2008) and special publications (Young et al., 2007). Experimental methodologies and instruments (large-scale soil property determination) and sampling designs targeted at geostatistics (Isaaks and Srivastava, 1989) and applied statistical time series analyses (Shumway and Stoffer, 2000) will be adapted and developed for agricultural and ecological applications (Nielsen and Wendroth, 2003). This project seeks to fill these gaps by developing new technologies for measuring transport, transfer, rate and state variables using comprehensive experimental designs that will yield appropriate scaling approaches. We will develop new measurement tools and process statistical structures for both measurements and processes essential for investigating soil ecosystem processes. We will improve conceptual and numerical modeling approaches that couple interdependent processes and improve our ability to transfer measurement and model information between scales. We will use our skills as soil and environmental physicists to advise and participate in national and international multidisciplinary projects to impart the importance of soil resources and the knowledge we have gained through decades of studying this critical zone. And, we will achieve this by participating in activities, like establishing national research site observatories and measuring the spatial distribution of soil moisture across our Nation. The collaborations created and fostered through the multistate research program have spanned generations of soil physicists and hydrologists, and it is the collective opinion of the participants that multi-institutional and multi-PI collaborations have been significantly enhanced because of the multistate program. Indeed maintaining the focus of such a large group would not be possible without this multistate program. Using these collaborations, significant benefits have been realized through understanding soil physics principles and applying them to environmental sustainability of soil resources, protecting ground and surface waters, improving agricultural production, only to name a few areas. This group has maintained a flexible organization of researchers and field sites, rather than on focused, yet restrictive, approaches like common field sites or identical experimental approaches at different locations. Members tend to form and re-form around new multi-investigator programs, while addressing critical questions. This flexible and synergistic approach has been extremely productive and it encourages a rich pollination of ideas and solutions to complex problems. The multistate committee structure is a convenient and efficient platform for establishing national research collaborations, validating approaches and techniques, pooling data, creating rigorous peer reviews, accessing unique equipment and developing the next generation of highly-educated soil scientists, environmentalists, and engineers. This proposal seeks to maintain the ties between this extremely productive and creative group that without the W1188 committee and its long line of predecessors would not be as focused on national needs research. The proposal also highlights our efforts to improve environmental monitoring, implement basic soil physics research, reach out to a broader scientific community, and educate and communicate to stakeholders and colleagues within and outside our traditional discipline.

Related, Current and Previous Work

Although other active multistate research projects examine related soil and water quality issues, none focus on the interactions and feedbacks between soil hydraulic properties, energy and mass balances, environmental impacts, and scaling issues. These projects include: " W1007: Benchmark Soilscapes to Predict Effects of Climatic change in the Western USA, " W1045: Agrochemical Impacts on Human and Environmental Health: Mechanisms and Mitigation, " W1170: Chemistry, Bioavailability, and Toxicity of Constituents in Residuals and Residual-Treated Soils, " W1190: Interfacing Technological, Economic, and Institutional Principles for Managing Inter-sector Mobilization of Water, and " W2147: Managing Plant Microbe Interactions in Soil to Promote Sustainable Agriculture. Projects outside the western region, including NC1017, NC1018, NE1021, S1028, SERA006, and WERA102 evaluate soil management, and soil and water quality. Some consider the impacts of climate change (NC1018, WERA102) and C sequestration (NC1017). Although some projects share subject matter, there is little or no duplication with past W1188 or proposed core activities. While W1007 shares some research areas, especially on the role of soil development on ecosystem functioning and energy balance, W1007 focuses more on pedologic development from a biogeosciences perspective, which is not the past or future focus of W1188. Many of the participants of W1007 are fellow colleagues and collaborators; thus direct overlap between groups is already self-regulated (Appendix E reviews). The same can be said for NE1021, with their focus on the genesis and distribution of hydromorphic soils. The results of the previous W1188 multistate project are extensive, timely and applicable to numerous agricultural and environmental issues. With the national dialog further expanding to include impacts of climate change, links between population growth in the western US and land use change, and the importance of soil to moderate and control the water budget and important ecological systems, the general themes of W1188 are even more critical. There is consensus that the soil physics community can and should be open to collaborative efforts, so that our historical knowledge and skills can also be applied to sustainable agricultural and environmental practices, natural resource stewardship and the mitigation of global climate change.

Objectives

1. To improve our fundamental understanding of vadose zone physical properties and processes, and how they interact with other environmental and biogeochemical processes across various spatial and temporal scales.
   
2. To develop and evaluate new instruments and analytical methods to connect our understanding of mass and energy transport in the vadose zone at different scales and environmental transformations.
   
3. To apply our knowledge of scale-appropriate methodologies to enhance the management of vadose zone resources that benefit agricultural systems, natural resources and environmental sustainability.
   

Methods

Objective 1--To improve our fundamental understanding of vadose zone physical properties and processes, and how they interact with other environmental and biogeochemical processes across various spatial and temporal scales. Despite our best efforts, some physical properties and processes have eluded our understanding, especially across scales. For example, at the lab or column scale, the dynamics of water and solute transport are well understood, but we are unable to fully up-scale these processes to the field scale. Many current scaling approaches are limited because of the enormous amount of data required to characterize flow of mass and energy at scales larger than a few square centimeters or meters. We will increase our ability to quantify water, gas and temperature fluxes in near surface soils. These include, but are not limited to, non-destructive imaging for understanding flow processes, transport and transformations of colloids and compounds, role of the vadose zone in quantifying basin-scale responses, measurement of soil properties, and up- and down-scaling algorithms and environmental processes. CA will design a two-dimensional split-root study, allowing for partial soil root zone water, nitrate, and temperature stresses, while measuring plant activity through total water use (ET). Innovative techniques to measure soil water and nutrient status will be ERT (electrical resistance tomography) and application of the BHPP (button heat pulse probe) developed under Objective 2. AZ, NV, and CA will continue ongoing collaborations on use of x-ray CT and neutron tomography. Our focus is on solving questions related to the basic understanding of how the soil fabric affects water flow and contaminant transport in subsurface environments. Multistate researchers will acquire and reconstruct x-ray CT image for spatial analysis. A regional consortium of instrumentation and intellectual resources will be formed for use by students, post-docs and others interested in micro-scale processes (root/soil interactions, water movement for testing lattice Boltzmann techniques, particle transport). WY, CO, ID and AZ will evaluate different electromagnetic techniques to measure soil variables such as water content, water potential, and bulk electrical conductivity in larger basins and watersheds. More efficient methods of characterizing complex landscapes, to more accurately assess the relationships between climate, soil and landscape position will result. Transport and Transformations of Colloids and Compounds--WA, CA, DE, AZ and ND will investigate interactions of colloids with interfaces, and fate and transport of potential agricultural and emerging contaminants by conducting a combination of laboratory column experiments, numerical modeling, greenhouse studies, and field scale research. Colloids in porous media interact with the solid-liquid and liquid-gas interfaces. This group will use microscopic (electron and confocal microscopy, tensiometry) and macroscopic (goniometry, light scattering, column experiments) to investigate and quantify the interactive processes. Identifying and quantifying the mechanisms controlling colloid fate and transport in the vadose zone will be incorporated into mathematical models (HYDRUS). ND, IA and CA will also use laboratory methods, primarily column breakthrough curves, batch sorption experiments, soil microcosm batch studies to examine the processes which control bioactive chemical fate and transport. Controlled experiments and observations from the field using soil extracts, lysimetry, and wells will be used to identify field fate and transport mechanisms. CA, ND, DE and NV will focus on characterizing the fate and transport of trace organic compounds (endocrine disrupting compounds) originating from reclaimed wastewaters in soil and water through field, laboratory, and numerical experiments (column scale to field scale). AK with USDA-ARS will conduct experiments on the attenuation of herbicides (2,4-D, triclopyr, and glyphosate) in sub-arctic soils incorporating lysimeters to distinguish between different attenuation modes. CO will develop a simulation model for methane fate and transport in soil. A critical task of this work will be characterizing the soil biology of methane producers and consumers, particularly in response to changing soil water content and temperature. This will be accomplished through laboratory batch methods and field flux chambers. Vadose Rone Role in Quantifying Basin-scale Responses--CA will conduct studies to examine the effects of vegetation, bulk density and particle size distribution on soil erodibility, sediment mobility and settlement process in rivers and lakes in the Fresno River watershed. This study will be conducted along with biologists and ecologists at CalSU to look at related biological and ecological impacts of erosion within the watershed. NV will conduct experiments in alluvial fan environments to develop site-specific pedo-transfer functions (PTFs) for predicting surface runoff and water balance. The goal is to extrapolate the basin-scale results to regional scales PTFs for use by NRCS and local flood control agencies. Soil Hydraulic and Thermal Properties--UT and AZ will study relationships between soil properties and greenhouse gas emissions. New inverse estimation schemes with uncertainty will be developed in collaboration with TX, CA and AZ. These researchers will estimate effective soil hydraulic and thermal properties across the USA at different resolutions by assimilating soil moisture from ground, air, and space-borne sensors. With greater access to remote sensing data in the past decade, and the application of new robust inverse techniques, effective soil physical properties data sets will provide a common resource for many Earth science applications in the 21st century. IA, OK, NV and KS will analyze shallow soil temperature gradients and thermal properties in order to estimate soil water evaporation across scales as a function of depth and time. Multi-scale Flow and Transport Including Impacts from Climate Change--These more recent investigations cause us to revisit the original question posed by Nielsen (1987): Why is understanding spatio-temporal variability of soil moisture and related transport and transformation coefficients so important? This question can be applied to many scale-dependent processes, including estimating soil water processes in space and time, classifying functional and eco-physical soil and landscapes, establishing scale hierarchy of soil physical properties and regionalization, and scale transferring soil water processes. Nielsens question and these applications highlight the need to estimate regional distributions of soil water status and related transport coefficients, fluxes, and transformation coefficients at different size domains with sufficiently fine resolution to capture management and soil impact on variable magnitude (Robinson et al., 2008a). CA will collaborate with local investigators, measuring core-scale soil hydraulic properties, and apply scaling techniques to the hillslope scale. Measurements of soil water tension and soil moisture, in concert with piezometer data will be coupled with HYDRUS to simulate hillslope-scale soil hydrology. CA will study unstable (finger) flow to quantify how soil texture promotes channeling of water and solutes to groundwater during and after rainfall or irrigation. Mechanisms of unstable flow, and implementation of new unstable flow models into the existing models for water flow and solute transport in the vadose zone will be considered. TX will evaluate two deficit irrigation strategies and a dryland treatment under two pre-irrigation levels. This will elucidate the influence of the frequency of imposed soil water deficits on root elongation and proliferation and how this affects overall water use efficiency. Soil moisture and associated biogeochemical fluxes under various hydro-climatic scenarios using ground, air, and space-borne sensors will be measured. Feedback mechanisms will also be measured (soil C storage and atmospheric release) with climate change scenarios. AZ will investigate fundamental pore-scale flow and transport phenomena by means of x-ray CT and fluid dynamics modeling. In collaboration with NV, the focus will be on a study water use and redistribution by native desert plant communities by means of weighing lysimetry, followed by expanding results to the basin-scale (ecosystem) scale. MN will use methods (Reggiani and Schellekens, 2003) for representing the hydrologic balance of a selected landscape at different scales. The method uses the so-called Representative Elementary Watersheds (REW), and integrates microscale equations (Richards equation) over the selected flow domain. The overall goal is to quantify boundary fluxes of a hydrologic system, in particular infiltration, seepage, and evapotranspiration fluxes. KY will monitor water content, soil temperature, C and nitrous gas emissions in two different land use systems (agricultural crop, pasture). The spatial sampling design is nested with 1 and 5 m spatial distances along transects. The representativity of gas flux measurements will be derived to better understand over what spatial distances soil water status and gas flux dynamics are correlated, essential information for scale transfer. Soil Physics and Ecological Interactions--UT and ID will design and model plant growth systems for reduced gravity conditions based on porous medium physical properties and plant physiological characteristics. WY will quantify water flow and heat transport in agricultural and natural ecosystem soils using automated sensors and computer simulation models. The goal is to establish a link between seasonal soil moisture, temperature dynamics and soil microbial activity and community structure. NV will examine the impacts of root water uptake and root growth on local soil properties immediately adjacent to roots. Root water uptake models and high resolution CT scan analysis will be used to test and improve models of soil/root feedback on water uptake and soil hydraulic properties within the rhizosphere. Objective 2--To develop and evaluate new instruments and analytical methods to connect our understanding of mass and energy transport in the vadose zone at different scales and environmental transformations. The multistate researchers have maintained a strong tradition of developing new instruments and techniques to collect and analyze data. As in previous years, several key areas of instrumentation and analysis will be pursued to provide sufficient accuracy in our predictions of mass and energy transport over different scales. CA will continue developing and evaluating instruments to measure soil water content, soil solution salinity and nitrate, and unsaturated soil water fluxes. This work is related to the BHPP (button heat pulse probe) (Kamai et al., 2008) and the fiber-optics soil solution analyzer by Tuli et al. (2009). The current BHPP will be adapted to include two electrodes, so that soil solution concentration can be measured in concert with soil moisture (in collaboration with KS). The in-situ soil solution sampler with fiber-optics technology will be adapted to measure soil solution organics, such as BTEXs and gasoline-derivatives to assist in bioremediation of contaminant plumes in ground water and vadose zone. IA, OK, NV and KS will develop a heat pulse sensor to determine shallow soil profile temperature, thermal properties and sensible and latent soil heat fluxes. TX and CO will collaborate on a new down-hole soil water sensor to address the problems of inaccuracy and spatial variability seen with current capacitance sensors (Baumhardt et al., 2000; Kelleners et al., 2004ab, 2005; Evett et al., 2006; Mazahrih et al., 2008). Electromagnetic (Schwank et al., 2006; Schwank and Green, 2007) and soil water dielectric (Wraith and Or, 1999; Schwartz et al., 2009ab) theory will be used to design sensors that act as waveguides rather than antennas that are relatively insensitive to interferences from bound water and bulk electrical conductivity, corrected for these interferences. CA will conduct studies to improve the detection of clay content in soils using laser diffraction with a new lens attached to a LISST-Portable (Sequoia Scientific Inc.), the only portable particle size analyzers available. The new lens will widen the usefulness of this device for rapid soil analyses. Quantifying Near-surface Processes with Instruments and Analyses--Net ecosystem production and net ecosystem exchange are closely tied to soil properties. Researchers have a significant opportunity to assist the agricultural and ecological communities by addressing the importance of soil properties and processes. Heitman et al. (2008) showed an approach that uses heat pulse probes as a means to estimate latent heat flux, a critical component of the energy budget. Upscaling these point-scale values to basin-scale (Zhu et al., 2006) would allow better assessments of regional-scale water status, yet advancement of instrumentation and analyses has lagged the potential societal applications. In particular, remote sensing tools are becoming more sophisticated, but ground truthing is needed. TX and KS will collaborate to characterize the influence of tillage on preplant water content, evaporation and redistribution of precipitation near the soil surface in two soils under a wheat-sorghum-fallow dryland rotation. This research will help delineate short-term influences of tillage on water storage and sorghum yield and help develop new soil management strategies to improve precipitation and irrigation use of soil water on fine-textured soils, where benefits of no-till may not be fully realized. This information will be used for outreach to modify tillage practices of operators, reduce regional water demand from the Ogallala Aquifer, and to ease the transition to and improving the profitability of dryland cropping. AZ, UT, and ID will develop new techniques for physical and chemical characterization of mine tailings. UT and AZ will develop frequency-dependent measurements for soil property determination, dielectric sensor characterization and evaluation techniques. They will work to develop a novel, physically-based approach for predicting evaporation rates from thermal surface signatures. These rates will be tested (with NV) using thermal surface signatures and weighing lysimeters recently installed in NV and operated by DRI. AZ will collaborate with NV to improve tools for segmentation and analysis of x-ray CT data. NV will develop the use of fiber optic temperature sensing to develop spatially distributed near surface soil moisture (Tyler et al., 2008, Moffett et al., 2008). Using fiber optic sensing, tens of thousands of continuous in time and space measurements of soil temperature and soil moisture can be made. NV and CA will expand its analysis of fiber optic temperature sensing to estimate daily water content changes in the upper 15-20 cm of soil profiles. KY will examine the representativity of several different sensors with the goal of improving the soil gas flux measurements in relation to soil water status. The measurements include water content using Sentek capacitance probes, and gas flux measurements with a photoacoustic analyzer. KY will also evaluate three spectrometers with respect to their ability to derive crop N status and predict final crop yield. CA, AZ, and MT will develop new measurement protocols, techniques, and instruments to measure soil water content under varying environmental conditions and atmospheric emissions of soil fumigants. CA and many of the other participants in this multistate program (ARS, CA, WSA, DE, ND and DRI) will continue developing numerical tools to study and evaluate environmental processes and biogeochemical reactions across scales. This research will use HYDRUS to describe processes at multiple scales, including colloid and colloid-facilitated transport; preferential flow and transport of various chemicals (viruses, colloids, and bacteria); coupled biogeochemical reactions; coupled movement of water, vapor and energy; and micro-irrigation management practices on soil leaching. Quantifying Soil Structure--Pedo-transfer functions (PTF) were developed to estimate difficult-to-collect data (soil hydraulic property functions, hydraulic conductivity) when only easy-to-collect data (soil texture, bulk density) are available. This approach uses databases of soil properties and multiple linear regression or neural network techniques (Schaap et al., 1998; 2001). One deficiency, however, is that quantifiable measures of soil structure are typically not included in the regression; indeed, there is a general lack of quantification of soil structure throughout the soil physics community. Visualization tools (x-ray and neutron tomography) and applications are now more available. These non-invasive techniques will be applied to environmental problem solving, especially those that address basic questions of water flow, soil erosion, and landscape-scale processes. Another deficiency is the lack of incorporating spatial covariance (Wendroth et al., 2006) although one of the main goals of PTFs is regionalization of soil hydraulic properties. NV, AZ and KY will examine soils of different texture with respect to soil structural indices to improve the indirect estimation of soil functional properties (hydraulic conductivity function). This task is relevant for improving PTFs. Here, auxiliary variables in combination with PTFs and their spatial covariance structure will be investigated with respect to their support of capturing field scale spatial variability of soil hydraulic properties. Objective 3--To apply our knowledge of scale-appropriate methodologies to enhance the management of vadose zone resources that benefit agricultural systems, natural resources and environmental sustainability. The scale-appropriateness of a methodology is based on the instruments ability to provide measurements (soil water content) that capture the continuity of a process in the spatial or temporal domain, or both. The continuity of a spatio-temporal process needs to be derived, not only for assuring spatial representativity of observations, but also to transfer the process of one or several variables across scales. Both, representativity of observations and continuity of a process can be quantified with the autocovariance function. Appropriate methodology is, however, not limited to a single variable, but needs to be verified for different variables through their spatial or temporal crosscovariance. The relationship between a pair or set of variables may differ depending on the spatial or temporal scale considered. Therefore, across different space-time scale combinations, scale transfer of one variable may require the consideration of different co-variates. For the CA CZO site, deployment and monitoring of approximately 150 soil moisture sensors installed around a white fir will continue. The experiment is done in parallel with eco-physiological measurements to investigate how soil environmental stresses (water, temperature, nutrients) impact forest systems and to apply the results across the rainfall-to-snow-dominated transition zone. CA will continue examining the effects of global climate change on water resources availability in the Sierra Nevadas. A representative headwater basin near the headwaters of the San Joaquin River, with natural flow in the upper watershed, was selected for hydrologic simulations using the HSPF model and climate change scenarios. Field trials will also determine BMPs for irrigating with degraded waters and applying pesticides. CO will evaluate drip irrigation in salt affected soils, including drip irrigated corn, onions, and melons, and model simulations. ND, IA and MN will study the vadose saturated zone continuum to develop nutrient management methods that reduce loading to and degradation of ground water and subsurface tile drainage, while maintaining optimal economic benefits. Field observations will primarily originate from lysimeters, soil and plant samples, nutrient input records, and tile drainage measurements of water quantity and quality. MN and, potentially CA, will develop the ability to quantify the water fluxes across the surfaces of land masses of arbitrary size, providing the basis for developing new brands of hydrologic and transport models that can incorporate flux calculating procedures into SWAT or similar models. UT and ID will apply geophysical measurements for enhancing forest ecological studies. AZ, UT, and ID will apply knowledge gained under Objective 2 to provide economic design criteria for vegetative covers of tailings impoundments and landfills in semi-arid and arid environments. WY will quantify the effect of surface disposal of coalbed methane product water on soil physical and chemical properties in Wyomings Powder River Basin, and assess the leaching potential of trace elements from surface ponds to shallow ground water. OK will combine direct measurements and PTF modeling to determine the soil water retention characteristics as a function of depth at 116 automated weather station sites comprising the OK Mesonet. The water retention curves will be used, together with existing Mesonet sensors and spatial scaling theory, to generate real-time maps of soil profile water storage and plant available water for the state of Oklahoma. NV will study native revegetation to examine how to reduce water demand for agricultural lands taken out of production in arid and semi-arid regions.

Measurement of Progress and Results

Outputs

• Generation of new information on mass and energy transport processes in soils at spatial and temporal scales appropriate for effective resource management.
• Improved understanding of the role of scale in basin-scale processes, including evapotranspiration, water balance and ecological functions and services.
• Generation of new knowledge addressing the environmental impacts on soil and water resources from agricultural practices and broader land uses.
• New instruments and analytical techniques for directly measuring water, chemical, and energy fluxes. New methodologies (computer and analytical models) that integrate knowledge of mass and energy transport, improving resource management.
• New collaborations with ecologists, hydrologists, pedologists, and engineers who are predicting landscape responses from land use/land cover changes and climate variability. Continued involvement of young faculty, post-docs and students, who are dedicated to studying the role of soil physics in environmental processes.
• Output 6 (General narrative) Information on the scientific advancements, research findings, and inter-institutional collaborations throughout the world will continue to be provided through the committee web site maintained at NDSU. This project will engage scientists and provide answers on short-term problems affecting U.S. agriculture and environmental protection in the areas of salinity, water quality, solute transport, evapotranspiration, soil water and chemical transport properties and other areas, especially ecological processes. Our research will focus on long-term problems, such as identifying and characterizing the dominant processes affecting the transport of mass and energy through soils and other porous media at various management scales. This project is unique among multistate committee efforts because, rather than collaboration on a single focused objective, many collaborative projects are conducted simultaneously by organized groups of participating members and others. These extensive collaborations are established and maintained through our organizational structure. This strategy is inevitable given the diversity of problems addressed, but is also highly desirable, as information gained from the specific collaborations are shared with global science communities.

Outcomes or Projected Impacts

• New tools, devices, analytical methods and capabilities to quantify and monitor movement of agricultural contaminants and other materials from the vadose zone to ground water and to the atmosphere.
• Develop new scientific knowledge and information about fundamental physical, chemical and biological processes affecting the transformation, mitigation and transport of pesticides, pathogens, colloids, nutrients, salts, and trace elements.
• Improve measurement techniques to better characterize the relationships between soil, climate, hydrologic processes and geomorphic position at the landscape scale.
• Develop stronger connections between atmospheric measurements and soil physical and hydraulic properties, especially under climate and land use change scenarios.
• Improve protection of soil and water resources and sustainability in use associated with energy production, water/irrigation management and mineral extraction activities.

Milestones

(2010): Model testing of methane fate and transport in grassland soil. Complete drip-irrigation experiments in salt-affected soil. Characterize different electromagnetic sensors as to their dielectric measurement capability and measurement frequency in soils and other reference media. Conduct novel evaporation experiments using an environmentally-controlled laboratory lysimeter and large weighing lysimeters.

(2011): Model testing of methane fate and transport in forest ecosystems. Conduct lysimeter studies to investigate water use and redistribution of plant communities in the desert. Improve segmentation and quantitative analysis methods for X-Ray CT images. Study greenhouse gas emissions from agricultural areas and management systems. Complete studies on the potential for water flow and contaminant transport from energy (coal) production. Apply representative elementary watershed concepts to close water budget components at the basin scale and soil and water gas fluxes as a function of land use.

(2012): Complete research on delineating short-term influence of tillage on water storage and crop yield. Model testing of methane fate and transport in desert ecosystems. Derive a physically-based model that relates soil properties, topology, and atmospheric conditions to soil evaporation rates. Design soil surface preparation strategies for agricultural and environmental management, to reduce evaporation rates. Combine measurements of water content, water potential, and soil bulk electrical conductivity at the landscape scale. Partition herbicides that leach to ground water versus metabolism in soil and plants.

(2013): Complete lysimeter measurements and analyses of nutrient movement toward ground water. Provide design criteria for vegetative covers of tailings impoundments and landfills in semiarid and arid environments. Code and distribute software package for segmenting and analyzing x-ray CT images. Complete experiments to examine temporal and spatial distribution of soil C and N dynamics and greenhouse gas emissions. Complete analyses of hydromechanical and hydraulic property impacts from expanding root structure in soils.

(2014): Review soil water sensing systems for water balance determinations. Review and ensure effectiveness of commercialization efforts. Complete experiments to examine the impact of imposed soil water deficits on root elongation. Incorporate colloidal processes into workable numerical approaches. Quantify fate and transport of bioactive compounds from manure operators. Develop strategies to reduce greenhouse gas emissions from ag soils. Link atmospheric measurements and PTF-derived soil hydraulic properties to predict the impacts on soil and water resources. Incorporate new physically-based modeling methods for simulating watershed-scale processes. Develop a physically-based conceptual model of feedback mechanisms that affect C storage and release. Describe dynamic behavior of water and soil gas emission fluxes during and after land use transition. Complete BMPs for irrigating with degraded water to reduce air contamination from pesticides. Prepare proposal for 5-year project renewal.

Projected Participation

View Appendix E: Participation

Outreach Plan

The project members comprise a group of dedicated soil, water and environmental scientists and engineers who excel in the communication of their research through different communications platforms, and who are active participants in soil and environmental research at universities and federal facilities throughout the country. They also lead in undergraduate and graduate instruction and mentoring, and by supervising post graduate, graduate and undergraduate research. Many of our members conduct workshops and classes to train other scientists and the public, contribute to state, regional and federal agencies and publish their findings in top-tier, peer-reviewed journals, targeting both science and engineering communities. W1188 members are active participants and presenters at many professional society international/ national/regional meetings (SSSA, AGU, ESA, ASCE), and major workshops and symposia sponsored by these societies. Our members are frequent initiators of major workshops and symposia. They serve on journal editorial boards and as ad hoc manuscript reviewers, and therefore, enhance the overall quality of published research. Members not only conduct research, but they serve the scientific community by their engagement in competitive grant review panels of federal and regional entities, and as peer reviewers for domestic and international grant proposals. Through entrepreneurship, committee members have developed commercially available instruments, analytical tools, and textbooks. We fully expect this type of outreach to continue and thrive. Results of our work will be available through the annual project report, the project website (http://nimss.umd.edu/homepages/home.cfm?trackID=6016), periodic joint meetings with related multistate research and/or coordinating groups, and through the international reputations and professional visibility of participants. The members will also work with consulting firms, companies and farmers to adopt measurement and management technologies.

Organization/Governance

The current W1188 multistate committee consists of members representing SAESs, other Universities, the USDA-ARS, National Laboratories, and other research units. In addition, visiting scientists (U.S. and global) participate along with member hosts. Officers of W1188 will be the Chair and Secretary. As done for some time, the Secretary is elected each year at the annual meeting and advances to Chairperson the following year. The chairperson may appoint members to serve on subcommittees as needed. Meetings will be approved by the AA. The current Secretary will be responsible for making local arrangements. Committee meetings typically have been held in Las Vegas, NV during early January, but this will evolve by choosing new locations at different host institutions (the 2009 meeting was held in Tucson, AZ). At each meeting, research accomplishments are reviewed and evaluated, new opportunities and recommendations for multistate coordination/collaboration are discussed, and strategies for maximizing the impact of committee productivity are reviewed. In addition, we are now inviting scientists from different disciplines (geomorphology, land use planning, ecology), so that invitees can discuss new cutting-edge research directions that would engage areas of our expertise. In this way, fresh perspectives are injected into the committee, encouraging outward-looking and multi-disciplinary approaches toward pressing agricultural and environmental problems. The project committee and its precursors have had strong historical participation at the annual meetings (35-40 attendees), with new members inducted each year to ensure longevity and infusion of fresh perspectives. Existing W1188 members have indicated a strong desire to continue participation.

Literature Cited

Baird, A.J., and R.L. Wilby. 1999. Eco-hydrology: Plants and Water in Terrestrial and Aquatic Environments Routledge, London. Baumhardt, R.L., R.J. Lascano, and S.R. Evett. 2000. Soil material, temperature, and salinity effects on calibration of multisensor capacitance probes. Soil Sci. Soc. Am. J. 64(6)1940-1946. Bradford, S.A., and S. Torkzaban. 2008. Colloid transport and retention in unsaturated porous media: a review of interface-, collector-, and pore-scale processes and models. Vadose Zone J. 2008 7:667-681. Bradford, S.A., `imonek, J., Bettahar, M., van Genuchten, M.T., S.R., Yates. 2003. Modeling colloid attachment, straining, and exclusion in saturated porous media. Environ. Sci. Technol. 37:2242-2250. Benson, C.H., H.M. Zhai, X.D. Wang. 1994. Estimating Hydraulic Conductivity of Compacted Clay Liners. J. Geotech. Eng. ASCE. 120:366-387. Cahill, A.T., F. Ungaro, M.B. Parlange, M. Mata, and D.R. Nielsen. 1999. Combined spatial and Kalman filter estimation of optimal soil hydraulic properties. Water Resour. Res. 35:1079-1088. Campbell, G.S. 1977. An Introduction to Environmental Biophysics. 1st ed. Springer-Verlag, New York. Campbell, G.S., and J.M. Norman. 1998. An Introduction to Environmental Biophysics. 2nd ed. Springer-Verlag, New York. Chau, J. F., D. Or, and M. C. Sukop. 2005. Simulation of gaseous diffusion in partially saturated porous media under variable gravity with lattice Boltzmann methods. Water Resour. Res., 41, W08410, doi:10.1029/2004WR003821. Clausnitzer, V., and J.W. Hopmans. 2000. Pore-scale measurements of solute breakthrough using microfocus X-ray computed tomography. Water Resour. Res., 36:2067-2079. Comegna, V., and C. Vitale. 1993. Space-time analysis of water status in a volcanic Vesuvian soil. Geoderma 60:135-158. DeVries D.A. 1963. Thermal properties of soils. In Physics of Plant Environment, van Wijk W.R., (ed.), Wiley: New York, 210-235. Ellsworth, T.R., and C.W. Boast. 1996. Spatial structure of solute transport variability in an unsaturated field soil. Soil Sci. Soc. Am. J. 60:1355-1367. Evett, S.R., J.A. Tolk, and T.A. Howell, 2006. Soil profile water content determination: Sensor accuracy, axial response, calibration, temperature dependence and precision. Vadose Zone J. 5:894-907. Ewing, R.P., and R. Horton. 2007. Thermal conductivity of a cubic lattice of spheres with capillary bridges, J. Phys. D: Appl. Phys. 40:4959-4965. Fan, Z., F.X.M. Casey, G.L. Larsen, and H. Hakk. 2007a. Persistence and fate of 17²-estradiol and testosterone in agricultural soils. Chemosphere 67:886-895. Fan, Z., Casey, F.X.M., H. Hakk, and G.L. Larsen. 2007b. Discerning and modeling the fate and transport of testosterone in undisturbed soil. J. Environ. Qual. 36:864-873. Ferré, T.P.A., and Gerard J. Kluitenberg. 2003. Preface from the Guest Editors, Advances in Measurement and Monitoring Methods. Special Section - Advances in Measurement and Monitoring Methods. Vadose Zone J. 2:443. Green, T.R., G.H. Dunn, R.H. Erskine, J.D. Salas, and L.R. Ahuja. 2009. Fractal analysis of steady infiltration and terrain on an undulating agricultural field. Vadose Zone J. (in press). Green, T., B.C. Bates, S.P. Charles, and P.M. Fleming. 2007. Physically-based simulation of potential effects of carbon dioxide-altered climates on groundwater recharge. Vadose Zone J. 6:597-609. Greminger, P.J., K. Sud, and D.R. Nielsen. 1985. Spatial variability of field-measured soil-water characteristics. Soil Sci. Soc. Am. J. 49:1075-1082. Harter, T., and J. W. Hopmans. 2004. Role of Vadose Zone Flow Processes in Regional Scale Hydrology: Review, Opportunities and Challenges. In: Feddes, R.A., G.H. de Rooij and J.C. van Dam, Unsaturated Zone Modeling: Progress, Applications, and Challenges, (Kluwer, 2004), p. 179-208. Heitman, J.L., R. Horton, T. J. Sauer, and T. M. Desutter. 2008. Sensible heat observations reveal soil-water evaporation dynamics. J. Hydrometeorology, DOI: 10.1175/2007JHM963.1 Hopmans, J.W. 2006. Plant water and nutrient uptake in soil-root systems. 5.1. Rhizosphere Models, p. 495-496 Handbook of Methods used in Rhizosphere Research. Swiss Federal Research Institute WSL, Birmensdorf. Hopmans, J.W., T. Vogel, and P.D. Koblik. 1992. X-ray tomography of soil water distribution in one-step outflow experiments. Soil Sci. Soc. Am. J., 56(2):355362. Hu, X-J, J-H Du, S-Y Lei and B-X Wang. 2001. A model for the thermal conductivity of unconsolidated porous media based on capillary pressuresaturation relation. Int. J. Heat Mass Transfer. 44:247-251. Isaaks, E.H. and R.M. Srivastava. 1989. Applied Geostatistics. Oxford University Press, New York. Jones, S.B. and K. Shenai. 2007. Subsurface measurement needs for ecological, hydrological and agricultural applications, Circuits and Systems. MWSCAS. 50th Midwest Symposium. 5-8 Aug. 2007. pp. 754-757. Kamai, T., A. Tuli, G. J. Kluitenberg, and J. W. Hopmans. 2008. Soil water flux density measurements near 1 cm d1 using an improved heat pulse probe design. Water Resour. Res., 44, W00D14, doi:10.1029/2008WR006956. Kelleners, T.J., R.W.G. Soppe, J.E. Ayars, and T.H. Skaggs. 2004a. Calibration of capacitance probe sensors in a saline silty clay soil. Soil Sci. Soc. Am. J. 68:770-778. Kelleners, T.J., R.W.G. Soppe, D.A. Robinson, M.G. Schaap, J.E. Ayars, and T.H. Skaggs. 2004b. Calibration of capacitance probe sensors using electric circuit theory. Soil Sci. Soc. Am. J. 68:430-439. Kelleners, T.J., D.A. Robinson, P.J. Shouse, J.E. Ayars, and T.H. Skaggs. 2005. Frequency dependence of the complex permittivity and its impact on dielectric sensor calibration in soils. Soil Sci. Soc. Am. J. 69:67-76. Ketcham, R.A., and W.D Carlson. 2001. Acquisition, optimization, and interpretation of X-ray computed tomographic imagery: Applications to the geosciences. Computers Geosciences. 27:381-400. Kirkham, M.B. 2005. Principles of Soil and Plant Water Relations Elsevier, Burlington, MA. Kolpin, D.W., E.T. Furlong, M.T. Meyer, E.M. Thurman, S.D. Zaugg, L.B. Barber, and H.T. Buxton. 2002. Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999-2000: A national reconnaissance. Environ. Sci. Technol. 36, 1202 -1211. Lebron, I., M.D. Madsen, D.G. Chandler, D.A. Robinson, O. Wendroth, and J. Belnap. 2007. Ecohydrological controls on soil moisture and hydraulic conductivity within a pinyon-juniper woodland. Water Resour. Res. 43. Li, H., C. Pan, and C. T. Miller. 2005. Pore-scale investigation of viscous coupling effects for two-phase flow in porous media. Phys. Rev. E., 72, 026705. Masad, E. B. Muhunthan, N. Martys. 2000. Simulation of fluid flow and permeability in cohesionless soils. Water Resour. Res. 36:851-864. Mazahrih, N.Th., N. Katbeh-Bader, S.R. Evett, J.E. Ayars and T.J. Trout. 2008. Field calibration accuracy and utility of four down-hole water content sensors. Vadose Zone J. 7: 992-1000. McGechan, M.B., and D.R. Lewis. 2002. Transport of particulate and colloid-sorbed contaminants through soil. Part 1: General principles. Biosyst. Engineer. 83, 255-273. Moffett, K., S. Tyler, T. Torgersen, M. Menon, J. Selker, and S. Gorelick. 2008. Distributed temperature sensing of thermal trends and anomalies in the bed of an intertidal salt marsh and channel: The tidal thermal blanket effect. Environ. Sci. Tech. 42(3): 671-676. DOI: 10.1021/es071309m. Mori, J., J.W. Hopmans, A.P. Mortensen and G. J. Kluitenberg. 2003. Multi-functional heat pulse probe for the simultaneous measurement of soil water content, solute concentration, and heat transport parameters. Vadose Zone J. 2:561-571. Moldrup, P., T. Olesen, P. Schjønning, T. Yamaguchi, and D.E. Rolston. 2000. Predicting the gas diffusion coefficient in undisturbed soil from soil water characteristics. Soil Sci. Soc. Am. J. 64:94100. Moldrup, P., T. Olesen, S. Yoshikawa, T. Komatsu, and D.E. Rolston. 2005. Predictive-descriptive models for gas and solute diffusion coefficients in variably saturated porous media coupled to pore-size distribution: II. Gas diffusivity in undisturbed soil. Soil Sci. 170:854866. Nielsen, D.R. 1987. Emerging frontiers in soil science. Geoderma 40:267-273. Nielsen, D.R. 1997. A challenging frontier in hydrology - The vadose zone. In: N. Buras (ed.) Reflections on hydrology: Science and practice. AGU, pp. 205-226. Nielsen, D.R., J.W. Biggar, and K.T. Erh. 1973. Spatial variability of field-measured soil water properties. Hilgardia 42:215-259. Nielsen, D.R., and O. Wendroth. 2003. Spatial and temporal statistics - sampling field soils and their vegetation. Catena, Reiskirchen, Germany. 416 p. Or, D., B.F. Smets, J.M. Wraith, A. Duchesne, and S.P. Friedman. 2007. Physical constraints affecting bacterial habitats and activity in unsaturated porous media - A review. Adv. Water Resour. 30:1505-1527. Or, D., F.J. Leij, V. Snyder, and T.A. Ghezzehei. 2000. Stochastic model for post-tillage soil pore space evolution. Water Resour. Res. 36:16411652. Or, D., and M. Tuller, 1999. Liquid retention and interfacial area in variably saturated porous media: upscaling from single pore to sample scale model. Water Resour. Res., 35:3591-3606. Perret, J., S.O. Prasher, A. Kantzas, K. Hamilton, and C. Langford. 2000. Preferential solute flow in intact soil columns measured by SPECT scanning. Soil Sci. Soc. Am. J. 64:469-477. Reggiani, P. and J. Schellekens. 2003. Modelling of hydrological responses: The representative elementary watershed approach as an alternative blueprint for watershed modeling. Hydrol Proc. 17: 3785-3789. Ren, T., T.E. Ochsner, R. Horton. 2003. Development of thermo-time domain reflectometry for vadose zone measurements. Vadose Zone J. 2:544-551. Resurreccion, A.C., P. Moldrup, K. Kawamoto, S. Yoshikawa, D.E. Rolston, and T. Komatsu, 2008. Variable pore connectivity factor model for gas diffusivity in unsaturated, aggregated soil. Vadoze Zone J. 7: 397-405 Reynolds, J.F., D.M.S. Smith, E.F. Lambin, B.L. Turner, II, M. Mortimore, S.P.J. Batterbury, T.E. Downing, H. Dowlatabadi, R.J. Fernandez, J.E. Herrick, E. Huber-Sannwald, H. Jiang, R. Leemans, T. Lynam, F.T. Maestre, M. Ayarza, and B. Walker. 2007. Global desertification: Building a science for dryland development. Science 316:847-851. Robinson D.A., C.S. Campbell, J.W. Hopmans, B.K. Hornbuckle, S.B. Jones, R. Knight, F. Ogden, J. Selker, and O. Wendroth. 2008a. Soil moisture measurement for ecological and hydrological watershed-scale observatories: A review. Vadose Zone J. 7:358-389 (doi:10.2136/vzj2007.0143). Robinson, D.A., H. Abdu, S.B. Jones, M. Seyfried, I. Lebron, and R. Knight. 2008b. Eco-geophysical imaging of watershed-scale soil patterns links with plant community spatial patterns. Vadose Zone J. 7:1132-1138. Rodriguez-Iturbe, I. 2000. Ecohydrology: A Hydrologic Perspective of Climate-Soil-Vegetation Dynamics. Water Resour. Res. 36. Rogasik, H., J.W. Crawford, O. Wendroth, I.M. Young, M. Joschko, and K. Ritz. 1999. Discrimination of soil phase by dual energy X-ray tomography. Soil Sci. Soc. Am. J. 63:741-751. Roth, K. 1995. Steady state flow in an unsaturated, two-dimensional, macroscopically homogeneous, Miller-similar medium. Water Resour. Res. 31:2127-2140. Russell, M.B. 1960. Some physical aspects of plant growth. Soil Sci. Soc. Am. J. 24:439-440. Schaap, M.G., F.J. Leij, and M. Th. Van Genuchten. 1998. Neural network analysis for hierarchical prediction of soil hydraulic properties. Soil Sci. Soc. Am. J. 62:847-855. Schaap, M.G., F.J. Leij, and M.Th. van Genuchten. 2001. ROSETTA: A computer program for estimating soil hydraulic parameters with hierarchical pedotransfer functions. J. Hydrol. 251:163-176. Schaap, M.G., M.L. Porter, B.S.B. Christensen, and D. Widenschild, 2007. Comparison of pressure-saturation characteristics derived from computed tomography and lattice Boltzmann simulations. Water Resour. Res., 43, W12S06, doi:10.1029/2006WR005730. Schnaar, G., and M.L. Brusseau. 2005. Pore-scale characterization of organic immiscible-liquid morphology in natural porous media using synchrotron X-ray microtomography. Environ. Sci. Tech. 39:8403-8410. Schnaar, G., and M.L. Brusseau. 2006a. Characterizing pore-scale configuration of organic immiscible liquid in multiphase systems with synchrotron X-ray microtomography. Vadose Zone J. 5:641-648. Schnaar, G., and M.L. Brusseau. 2006b. Characterizing pore-scale dissolution of organic immiscible liquid in natural porous media using synchrotron X-ray microtomography. Environ. Sci. Techn. 40:6622-6629. Schwank, M., and T.R. Green. 2007. Simulated effects of soil temperature and salinity on capacitance sensor measurements. Sensors. 7:548-577. Schwank, M., T.R. Green, C. Mätzler, H. Benedickter, and H. Flühler. 2006. Laboratory characterization of a commercial capacitance sensor for estimating permittivity and inferring soil water content. Vadose Zone J. 5:1048-1064. Schwartz, R.C., S.R. Evett, M.G. Pelletier, and J.M. Bell. 2009a. Complex permittivity model for time domain reflectometry soil water content sensing. I. Theory. Soil Sci. Soc. Am. J. (in press). Schwartz, R.C., S.R. Evett, M.G. Pelletier, and J.M. Bell. 2009b. Complex permittivity model for time domain reflectometry soil water content sensing. II. Calibration. Soil Sci. Soc. Am. J. (in press). Seyfried, M.S. and B.P. Wilcox. 1994. Scale and the nature of spatial variability: Field examples having implications for hydrologic modeling. Water Resour. Res. 31(1): 173-184. Shafer, D.S., M.H. Young, S.F. Zitzer, T.G. Caldwell, and E.V. McDonald. 2007. Impacts of interrelated biotic and abiotic processes during the past 125,000 years of landscape evolution in the Northern Mojave Desert, Nevada, USA. J. Arid Environ. 69:633-657. Shouse, P.J., W.B. Russel, D.S. Burden, H.M. Selim, J.B. Sisson, and M.Th. van Genuchten. 1995. Spatial variability of soil water retention functions in a silt loam soil. Soil Sci. 159:1-12. Shumway, R.H., and D. Stoffer. 2000. Time series analysis and its applications. Springer, New York, 549pp. Simunek, J., and J.W. Hopmans. 2008. Modeling compensated root water and nutrient uptake. Ecol. Modeling. doi:10.1016/j.ecolmodel.2008.11.004 . Smucker, A.J.M., and J.W. Hopmans. 2007. Soil biophysical contributions to hydrological processes in the vadose zone. Vadose Zone J. 6:267-268. Steele, D.D. and J.L. Nieber, 1994a. Network modeling of diffusion coefficients for porous media, I. Theory and model development, Soil Sci. Soc. Am. J. 58:1337-1345. Steele, D.D. and J.L. Nieber, 1994b. Network modeling of diffusion coefficients for porous media, II. Simulations, Soil Sci. Soc. Am. J. 58:1346-1354. Stock, S.R. 1999. X-ray microtomography of materials. International Materials Reviews, 44(4):141-163. Stockton, J.G., and A.W. Warrick. 1971. Spatial variability of unsaturated hydraulic conductivity. Soil Sci. Soc. Am. Proc. 35:847-848. Tashman, L. E. Masad, C. Crowe 2003 Simulation of fluid flow in granular microstructure using a non-staggered grid scheme. Computers & Fluids. 32:1299-1323. Tuli, A., J.B. Wei, B. D. Shaw, and J.W. Hopmans. 2009. In situ monitoring of soil solution nitrate. Soil Sci. Soc. Am. J. (in press). Tuller, M., and D. Or, 2001. Hydraulic conductivity of variably saturated porous media: Film and corner flow in angular pore space. Water Resour. Res. 37:1257-1276. Tuller, M., D. Or, and L.M. Dudley, 1999. Adsorption and capillary condensation in porous media -liquid retention and interfacial configurations in angular pores. Water Resour. Res. 35:1949-1964. Tyler, S.W., J.S. Selker, M.B. Hausner, C.E. Hatch, T. Torgersen and S. Schladow. 2008. Environmental temperature sensing using Raman spectra DTS fiber optic methods. Water Resour. Res. doi: 10.1029/2008WR007052. Ünlü, K., D.R. Nielsen, J.W. Biggar, and F. Morkoc. 1990. Statistical parameters characterizing the spatial variability of selected soil hydraulic properties. Soil Sci. Soc. Am. J. 54:1537-1547. Ünlü, K., M.L. Kavvas, and D.R. Nielsen. 1989. Stochastic analyses of field measured unsaturated hydraulic conductivity. Water Resour. Res. 25:2511-2519. Vereecken, H., T. Kamai, T. Harter, R. Kasteel, J. Hopmans, and J. Vanderborght. 2007. Explaining soil moisture variability as a function of mean soil moisture: A stochastic unsaturated flow perspective. Geophys. Res. Lett. 30:L22402, doi:10.1029/2007GL031813. Vogel, H.J. 2000. A numerical experiment on pore size, pore connectivity, water retention, permeability, and solute transport using network models. Eur. J. Soil. Sci. 51:99-105. Vogel, H.J., J. Tolke, V. P. Schultz, M. Krafczyk, and K. Roth, 2005. Comparison of a lattice-Boltzmann model, full morphology model, and a pore network model for determining capillary pressure-saturation relationships. Vadose Zone J. 4, 380-388. Wang, X.P., M.H. Young, Z. Yu, X.R. Li, and Z.S. Zhang. 2007. Long-term effects of restoration on soil hydraulic properties in revegetation-stabilized desert ecosystems. Geophys. Res. Lett. 34. Wardle, D.A., L.R. Walker, and R.D. Bardgett. 2004. Ecosystem properties and forest decline in contrasting long-term chronosequences. Science. 305:509-513. Wendroth, O., W. Pohl, S. Koszinski, H. Rogasik, C.J. Ritsema, and D.R. Nielsen. 1999. Spatio-temporal patterns and covariance structures of soil water status in two Northeast-German field sites. J. Hydrol. 215:38-58. Wendroth, O., S. Koszinski, and E. Pena-Yewtukhiv. 2006. Spatial association between soil hydraulic properties, soil texture and geoelectrical resistivity. Vadose Zone J. 5:341-355. Western, A.W., S.L. Zhou, R.B. Grayson, T.A. McMahon, G. Blöschl, and D.J. Wilson. 2004. Spatial correlation of soil moisture in small catchments and its relationship to dominant spatial hydrological processes. J. Hydrol. 286:113-134. Wildenschild, D., J.W. Hopmans, C.M.P Vaz, M.L. Rivers, D. Rikard, and B.S.B. Christensen. 2002. Using X-ray computed tomography in hydrology: Systems, resolutions, and limitations. J. Hydrol. 267:285-297. Wraith, J.M., and D. Or. 1999. Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry: Experimental evidence and hypothesis development. Water Resour. Res. Vol. 35. No. 2, pp. 361-369. Wraith, J.M., and J.M. Baker. 1991. High-resolution measurement of root water uptake using automated time-domain reflectometry. Soil Sci. Soc. Am. J. 55:928-932. Young, M.H., H. Lin, and B.P. Wilcox. 2007. Introduction to special section on bridging Hydrology, Soil Science, and Ecology: Hydropedology and Ecohydrology. Geophys. Res. Lett. 34. Zalewski, M., G.A. Janauer, and G. Jolankai. 1997. Ecohydrology: A New Paradigm for the Sustainable Use of Aquatic Resources. International Hydrological Programme, Paris. Zhang, X., L. K. Deeks, A. G. Bengough, J. W. Crawford, and I. M. Young. 2005. Determination of the soil hydraulic conductivity with the lattice Boltzmann method and soil thin-section technique. J. Hydrol. 306, 5970. Zhu, J., B.P. Mohanty, and N.N. 2006. On the effective averaging schemes of hydraulic properties at the landscape scale. Vadose Zone J. v.5. pp.308-316.

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