Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

Recent developments in the direct-current geoelectrical imaging method

Aquatic chemistry—An introduction emphasizing chemical equilibria in natural waters: By Werner Stumm and James J. Morgan. Second Edition, John Wiley and Sons, 1981, 780 pp. $45.00 (cloth), $27.50 (paper)

Geophysics provides a multidimensional suite of investigative methods that are transforming our ability to see into the very fabric of the subsurface environment, and monitor the dynamics of its fluids and the biogeochemical reactions that occur within it. Here we document how geophysical methods have emerged as valuable tools for investigating shallow subsurface processes over the past two decades and offer a vision for future developments relevant to hydrology and also ecosystem science. The field of “hydrogeophysics” arose in the late 1990s, prompted, in part, by the wealth of studies on stochastic subsurface hydrology that argued for better field-based investigative techniques. These new hydrogeophysical approaches benefited from the emergence of practical and robust data inversion techniques, in many cases with a view to quantify shallow subsurface heterogeneity and the associated dynamics of subsurface fluids. Furthermore, the need for quantitative characterization stimulated a wealth of new investigations into petrophysical relationships that link hydrologically relevant properties to measurable geophysical parameters. Development of time-lapse approaches provided a new suite of tools for hydrological investigation, enhanced further with the realization that some geophysical properties may be sensitive to biogeochemical transformations in the subsurface environment, thus opening up the new field of “biogeophysics.” Early hydrogeophysical studies often concentrated on relatively small “plot-scale” experiments. More recently, however, the translation to larger-scale characterization has been the focus of a number of studies. Geophysical technologies continue to develop, driven, in part, by the increasing need to understand and quantify key processes controlling sustainable water resources and ecosystem services.

/pdf/the-emergence-of-hydrogeophysics-for-improved-understanding-1kxmx4m0xa.pdf

The emergence of hydrogeophysics for improved understanding of subsurface processes over multiple scales.

Water purification for human use, ecosystem management, agriculture, and industry is emerging as a leading global priority. Access to sufficient clean water ultimately requires improvements over the current state of water filtration technology. Membrane technologies for water purification have been actively pursued for decades, but with recent innovation of both analytical and fabrication tools, more advanced membrane technologies are surfacing. Here, we review the design, development, and application of new membrane materials, fabrication methods for controlling the filtration size regime, analytical tools for performance testing, and molecular modeling for transport and separation. Membrane chemical stability, fouling, and environmental impact as open questions are also presented.

Membrane materials for water purification: design, development, and application

Agricultural Geophysics Overview General Considerations for Geophysical Methods Applied to Agriculture, Allred et al. Past, Present, and Future Trends of Soil Electrical Conductivity Measurement Using Geophysical Methods, Corwin History of Ground-Penetrating Radar Applications in Agriculture, Collins Agricultural Geophysics Measurements and Methods Theoretical Insight on the Measurement of Soil Electrical Conductivity, Corwin et al. Resistivity Methods, Allred et al. Electromagnetic Induction Methods, Daniels et al. Ground Penetrating Radar Methods, Daniels et al. Magnetometry, Self-Potential, and Seismic: Additional Geophysical Methods Having Potentially Significant Future Use in Agriculture, Allred et al. The Global Positioning System and Geographic Information Systems Integration of the Global Positioning System (GPS) to Agricultural Geophysics, Grejner-Brzezinska Integration of Geographic Information Systems (GIS) to Agricultural Geophysics, Merry Agricultural Geophysics Application Examples Resistivity and Electromagnetic Induction Case Histories Introduction to Resistivity and Electromagnetic Case Histories, Allred and Ehsani. Apparent Electrical Conductivity for Delineating Spatial Variability in Soil Properties, Wienhold and Doran Dependence of Soil Apparent Electrical Conductivity (ECa) Upon Soil Texture and Ignition Loss at Various Depths in Two Morainic Loam Soils in SE Norway, Korsaeth Relations Between a Commercial Soil Survey Map Based on Soil Apparent Electrical Conductivity (ECa) and Measured Soil Properties on a Morainic Soil in SE Norway, Korsaeth et al. Mapping Pesticide Partition Coefficients by Electromagnetic Induction, Jaynes Can Apparent Soil Electrical Conductivity Be Used to Map Soil-Herbicide Partition Coefficients? A Case Study in Three Colorado Fields, Shaner et al. Delineating Site-Specific Management Units Using Geospatial Apparent Soil Electrical Conductivity (ECa) Measurements, Corwin et al. Mapping of Soil Drainage Classes Using Topographical Data and Soil Electrical Conductivity, Kravchenko Productivity Zones Based on Bulk Soil Electrical Conductivity: Applications for Dryland Agriculture and Research, Johnson et al. A Four Year Summary of the Use of Soil Conductivity as a Measure of Soil and Crop Status, Eigenberg Mapping of Apparent Soil Electrical Conductivity (ECa) Helps Establish Research Plots at a New Research and Extension Center, Farahani et al. Mapping Golf-Course Features with Electromagnetic Induction, with Examples from Dublin, Ohio, Taylor Comparison of Geoelectrical Instruments in Different Soilscapes, Gebbers and Luck Ground Penetrating Radar Case Histories Introduction to Ground Penetrating Radar Case Histories, Allred. Ground Penetrating Radar Surveys Across a Prototype Surface Barrier to Determine Temporal and Spatial Variations in Soil Moisture, Clement and Ward Soil Water Content Measurement Using the Ground- Penetrating Radar Surface Reflectivity Method, Redman Assessing Spatial and Temporal Soil Water Content Variations with Ground Penetrating Radar, Lennartz et al. Ground Penetrating Radar Mapping of Near-Surface Preferential Flow, Freeland An Application of Ground Penetrating Radar in Golf Course Management, Boniak et al. Ground Penetrating Radar Investigation of a Golf Course Green: Computer Processing and Field Survey Set-Up Considerations, Allred et al. Agricultural Drainage Pipe Detection Using Ground Penetrating Radar, Allred and Daniels Using Ground Penetrating Radar to Estimate Tree Root Mass: Comparing Results from Two Florida Surveys, Butnor at al. Glossary Index

Handbook of Agricultural Geophysics

One of the more frustrating problems confronting farmers and land improvement contractors in the Midwest United States involves locating buried agricultural drainage pipes. Enhancing the efficiency of soil water removal on land already containing a subsurface drainage system typically involves installing new drain lines between the old ones. However, before this approach can be attempted, the older drain lines need to be located. Conventional geophysical methods have the potential to provide a solution to this problem. Therefore, in order to determine a better way to detect buried drainage pipe, the abilities of four near-surface geophysical methods were investigated, including geomagnetic surveying, electromagnetic induction, resistivity, and ground penetrating radar (GPR). Of these four, only GPR proved capable of finding agricultural drainage pipe. Furthermore, GPR grid surveys were conducted in southwest, central, and northwest Ohio at 11 test plots containing subsurface drainage systems, and in regard to locating the total amount of pipe present at each site, this technology was shown to have an average effectiveness of 81% (100% of the pipe was found at six sites, 90% at one site, 75% at two sites, 50% at one site, and 0% at one site.) GPR proved, on the whole, to be successful in finding clay tile and corrugated
plastic tubing drainage pipe down to depths of approximately 1 m (3 ft) within a variety of different soil materials. Consequently, although more research is certainly warranted, ground penetrating radar methods appear to have excellent potential with respect to agricultural drainage pipe detection.

/pdf/detection-of-buried-agricultural-drainage-pipe-with-5g04cei0oz.pdf

Detection of buried agricultural drainage pipe with geophysical methods

A Wetland Reservoir Subirrigation System (WRSIS) allows for capture, treatment, storage, and reuse of runoff and
subsurface drainage waters from cropland, in turn providing both environmental and agricultural production benefits. The
three WRSIS sites presently in operation are all located within the northwest Ohio portion of the Maumee River Basin and
have been in use for five to six complete growing seasons. WRSIS components include an underground drainage pipe network
tied to both a constructed wetland and a water storage reservoir. With this type of system, the drain pipes can be used at
different times to either add water (subirrigation) or remove water (subsurface drainage) from the root zone, thereby
enhancing crop yields, especially in dry years. Obtaining these crop yield benefits requires a proper water table management
approach that includes practicing suggested operational guidelines and initiating as needed system modification
improvements. By incorporating a proper water table management approach, and in comparison to control plots, WRSIS
subirrigated field crop yield increases for corn and soybeans, respectively, were 34.5 and 38.1% during drier growing seasons,
14.4 and 9.7% during near average to wetter growing seasons, and 19.6 and 17.4% overall.

Water table management to enhance crop yields in a wetland reservoir subirrigation system

Enhancing the efficiency of soil water removal on land already containing a subsurface drainage system typically
involves installing new drain lines between the old ones. However, the older drainage pipes need to be located before this
approach can be attempted. In ongoing research, a near-surface geophysical method, ground penetrating radar (GPR), has
been successful in locating on average 72% of the total amount of drainage pipe present at 13 test plots in southwest, central,
and northwest Ohio. The effective use of GPR for drainage pipe detection requires careful consideration of computer
processing procedures, equipment parameters, site conditions, and field operations, all of which were thoroughly investigated
in this study. 
Application of a signal saturation correction filter along with a spreading and exponential compensation gain function
were the computer processing steps most helpful for enhancing the drainage pipe response exhibited within GPR images of
the soil profile. GPR amplitude maps that show the overall subsurface drainage pipe system required additional computer
processing, which included 2-D migration, signal trace enveloping, and in some cases, a high frequency noise filter and a
spatial background subtraction filter. Equipment parameter test results indicate that a 250-MHz antenna frequency worked
best, and that data quality is good over a range of spatial sampling intervals and signal trace stacking. In regard to the site
conditions present, shallow hydrology, soil texture, and drainage pipe orientation all substantially influence the GPR
response. Additionally, drainage pipe that are as small as 5 cm (2 in.) in diameter can be detected. However, the fired clay
or plastic material of which the drainage pipe is comprised does not appear to have much of an impact. Finally, with respect
to GPR field operations, bidirectional surveys offer the best chance for finding all the buried drainage pipe possible, and for
displaying a subsurface drainage system on an amplitude map, the narrower the spacing between GPR measurement lines,
the better the result. Although it is important to note that the amplitude maps generated with a wider spacing between GPR
measurement lines, still provided plenty of useful data on drainage pipe location. The information supplied by this study can
be employed to formulate guidelines that will enhance the potential of success for using ground penetrating radar in locating
buried agricultural drainage pipe.

Important considerations for locating buried agricultural drainage pipe using ground penetrating radar

The focus of this chapter is the characterization of the vadose zone, or the unsaturated section of the subsurface, using hydrogeophysical techniques. The regions of water saturation as they relate to the physical properties are shown for reference in Figure 14.1. Characterization below the water table (in the saturated section) is described in Chapter 13 of this volume and will not be discussed in detail here. From a physical properties perspective, the zones of variable saturation above the water table are transitional, and depend upon the soil or rock type and the lateral heterogeneity of the materials. In the vertical direction, the boundaries between all of these zones are dependent upon the types of soil, regolith, or rock that are present; the current and historical climatic conditions; and the regional and local geomorphology of the site. These same factors affect the heterogeneity of the vadose zone in the horizontal (lateral) direction and generally compound the problems of defining the different regions of moisture in the vadose zone.

Hydrogeophysical Case Studies in the Vadose Zone

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