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Clay Content (clay + content)
Kinds of Clay Content Selected AbstractsMineral soil surface crusts and wind and water erosionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2004Michael J. Singer Abstract The ,rst few millimetres of soil largely control the soil's response to the eroding forces of wind and water. The tendency of soils to form surface seals and crusts in,uences the processes of wind and water erosion differently. For wind, dry particle size distribution and particle organization determine the shear strength and threshold wind velocity necessary to initiate particle movement. In loams and clay loams, seals and crusts decrease roughness but increase surface soil strength, generally decreasing wind erosion. Conversely, in sand and sandy loams, loose erodible sandy material may either deposit on the crust and is subject to erosion or it may disrupt the crust, accelerating the erosion process. For water erosion, particle size distribution and structure determine in,ltration rate, time to ponding, and energy required for soil particle detachment. Seals and crusts tend to decrease in,ltration rate and time to ponding thus increasing overland ,ow and soil erosion. This paper brie,y reviews how permanent and time-dependent soil properties in,uence surface seals and crusts and how these affect soil erosion by wind and water. The tendency of a soil to form a seal and crust depends to some degree on the time-dependent property of soil structural stability, which tends to increase with increasing clay content and smectitic mineralogy which are permanent properties. These permanent properties and their effect on structure are variable depending on dynamic properties of exchangeable sodium percentage and soil solution electrical conductivity. Antecedent water content prior to irrigation or rainfall, rate of wetting before an erosive event and aging, the time between wetting and an erosive event, greatly in,uence the response of soil structure to raindrop impact. The effect of these dynamic processes is further in,uenced by the static and dynamic properties of the soil. Weak structure will be less in,uenced by wetting rate than will a soil with strong structure. Process-based models of wind and water erosion need to consider the details of the interactions between soil static and dynamic properties and the dynamic processes that occur prior to erosive events. Copyright © 2004 John Wiley & Sons, Ltd. [source] Determining toxicity of lead and zinc runoff in soils: Salinity effects on metal partitioning and on phytotoxicityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2003Daryl P. Stevens Abstract When assessingcationic metal toxicity in soils, metals are often added to soil as the chloride, nitrate, or sulfate salts. In many studies, the effects of these anions are ignored or discounted; rarely are appropriate controls included. This study used five soils varying in pH, clay content, and organic matter to determine whether salinity from counter-ions contributed to or confounded metal phytotoxicity. Varying rates of Pb and Zn were applied to soils with or without a leaching treatment to remove the metal counter-ion (NO3 -). Lactuca sattva (lettuce) plants were grown in metal-treated soils, and plant dry weights were used to determine median effective concentrations where there was a 50% reduction in yield (EC50s) on the basis of total metals measured in the soil after harvest. In two of the five soils, leaching increased the EC50s significantly for Zn by 1.4- to 3.7-fold. In three of the five soils, leaching increased the EC50s significantly for Pb by 1.6- to 3.0-fold. The shift in EC50s was not a direct result of toxicity of the nitrate ion but was an indirect effect of the salinity increasing metal concentrations in soil solution and increasing its bioavailability for a given total metal concentration. In addition, calculation of potential salinity changes in toxicological studies from the addition of metals exhibiting strong sorption to soil suggested that if the anion associated with the metal is not leached from the soil, direct salinity responses could also lead to significant overestimation of the EC50 for those metals. These findings question the relevance of the application of single-metal salts to soils as a method of assessing metal phytotoxicity when, in many cases in our environment, Zn and Pb accumulate in soil over a period of time and the associated counter-ions are commonly removed from the soil during the accumulation process (e.g., roof and galvanized tower runoff). [source] Quantifying the relationship between soil organic carbon and soil physical properties using shrinkage modellingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2009P. Boivin Summary Changes in soil organic carbon (SOC) may strongly affect soil structure and soil physical properties, which in turn may have feedback effects on the soil microbial activity and SOC dynamics. Such interactions are still not quantitatively described and accounted for in SOC dynamics modelling. The objective of this study was to test the hypothesis that soil shrinkage curve (ShC) analysis allows the establishment of close relationships between soil physical properties and SOC. We sampled a rice-cropped vertisol, a cambisol under conventional tillage and no-tillage and a restored cambisol. Soil samples were analysed for clay and SOC content, bulk volume, hydro-structural stability and plasma and structural pore volumes changes on the full water content range using ShC analysis. Although the soils behaved differently according to their constituents and history, changes in SOC linearly affected most of the soil physical properties, with stronger effects than changes in clay content. The observed effects of increasing SOC, such as increasing hydro-structural stability, specific bulk volume and water retention, agreed well with previously reported results. However, using ShC measurement and modelling allowed the observation of all these different effects simultaneously for small changes in SOC, and in a single measurement. Moreover, the relation between SOC changes and physical properties could be quantified. ShC analysis may, therefore, be used to account for the effect of changes in SOC on soil physical properties. [source] Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal developmentEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2009D. N. Warrington Summary Primary particle size distribution (PSD) of eroded sediment can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 × 40 × 4 cm), that had undergone either minimal aggregate slaking (MAS) or severe aggregate slaking (SAS) prior to a 60 mm simulated rainstorm (kinetic energy, 15.9 kJ m,3; droplet diameter, 2.97 mm) and collected runoff at regular intervals. The degree of aggregate slaking was controlled by the rate at which soils were wetted to saturation. The PSDs of eroded materials and of parent soils were determined using a laser particle size analyser. For each soil, PSD frequency curves of eroded sediments and parent soils were generally of a similar shape but most eroded sediments had larger clay contents than their parent soils. In the SAS treatment, cumulative clay enrichment in the eroded materials was inversely related to the parent soil clay content, these being 28.5, 26.6 and 22.8% richer in clay than their parent soils for the loam, sandy clay and clay, respectively. Generally, total clay loss was greater from soils with SAS than from those with MAS because of erosion rates; however, clay enrichment of sediments, compared with parent soil clay contents, was mostly greater in samples with MAS. Greater clay enrichment took place during the early seal development stage in the loam, but could not readily be associated with specific stages of seal development for the clay. In the sandy clay, the relation between seal development and clay enrichment in the eroded material depended on the initial degree of aggregate slaking. The observed large preferential loss of clay by erosion in cultivated soils re-emphasizes the need to employ erosion control measures. [source] Using soil knowledge for the evaluation of mid-infrared diffuse reflectance spectroscopy for predicting soil physical and mechanical propertiesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008B. Minasny Summary Mid-infrared diffuse reflectance spectroscopy can provide rapid, cheap and relatively accurate predictions for a number of soil properties. Most studies have found that it is possible to estimate chemical properties that are related to surface and solid material composition. This paper focuses on prediction of physical and mechanical properties, with emphasis on the elucidation of possible mechanisms of prediction. Soil physical properties that are based on pore-space relationships such as bulk density, water retention and hydraulic conductivity cannot be predicted well using MIR spectroscopy. Hydraulic conductivity was measured using a tension-disc permeameter, excluding the macropore effect, but MIR spectroscopy did not give a good prediction. Properties based on the soil solid composition and surfaces such as clay content and shrink-swell potential can be predicted reasonably well. Macro-aggregate stability in water can be predicted reasonably as it has a strong correlation with carbon content in the soil. We found that most of the physical and mechanical properties can be related back to the fundamental soil properties such as clay content, carbon content, cation exchange capacity and bulk density. These connections have been explored previously in pedotransfer functions studies. The concept of a spectral soil inference system is reiterated: linking the spectra to basic soil properties and connecting basic soil properties to other functional soil properties via pedotransfer functions. [source] Soil organic carbon in density fractions of tropical soils under forest , pasture , secondary forest land use changesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2008S. Paul Summary Our knowledge of effects of land use changes and soil types on the storage and stability of different soil organic carbon (SOC) fractions in the tropics is limited. We analysed the effect of land use (natural forest, pasture, secondary forest) on SOC storage (depth 0,0.1 m) in density fractions of soils developed on marine Tertiary sediments and on volcanic ashes in the humid tropics of northwest Ecuador. The origin of organic carbon stored in free light (< 1.6 g cm,3) fractions, and in two light fractions (LF) occluded within aggregates of different stability, was determined by means of ,13C natural abundance. Light occluded organic matter was isolated in a first step after aggregate disruption by shaking aggregates with glass pearls (occluded I LF) and in a subsequent step by manual destruction of the most stable microaggregates that survived the first step (occluded II LF). SOC storage in LFs was greater in volcanic ash soils (7.6 ± 0.6 Mg C ha,1) than in sedimentary soils (4.3 ± 0.3 Mg C ha,1). The contribution of the LFs to SOC storage was greater in natural forest (19.2 ± 1.2%) and secondary forest (16.6 ± 1.0%) than in pasture soils (12.8 ± 1.0%), independent of soil parent material. The amount of SOC stored in the occluded I LF material increased with increasing silt + clay content (sedimentary soils, r = 0.73; volcanic ash soils, r = 0.58) and aggregation (sedimentary soils, r = 0.52; volcanic ash soils, r = 0.45). SOC associated with occluded I LF, had the smallest proportion of new, pasture-derived carbon, indicating the stabilizing effect of aggregation. Fast turnover of the occluded II LF material, which was separated from highly stable microaggregates, strongly suggested that this fraction is important in the initial process of aggregate formation. No pasture-derived carbon could be detected in any density fractions of volcanic ash soils under secondary forest, indicating fast turnover of these fractions in tropical volcanic ash soils. [source] Effect of earthworm activity (Aporrectodea giardi) on atrazine adsorption and biodegradationEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2006T. Alekseeva Summary We investigated the influence of earthworm (Aporrectodea giardi) activity on soil properties and on atrazine (AT) adsorption and biodegradation by comparing a coarse-textured smectite-free wetland soil (Brittany, France) with the earthworm casts derived from the top horizon of this soil. Casts are characterized by lower pH, are enriched in organic carbon (OC) and clay content, have a larger cation exchange capacity, and a greater exchangeable Ca content. The clay mineralogy of the soil studied and casts is characterized by a muscovite,kaolinite,chlorite association. In addition, the clay fraction of the soil contains lepidocrocite (,-FeOOH), which was not found in the casts. Atrazine adsorption isotherms were reasonably well described by the Freundlich equation and were all non-linear. The mean amounts of adsorbed AT for starting concentrations of 3,30 mg litre,1 ranged from 8 to 34%, being largest in earthworm casts. Soil AT adsorption capacity was well correlated with OC content. Non-decomposed organic matter present in the coarse size fractions and specific compounds present in earthworm casts (proteins, mono- and polysaccharides, polyphenols, sugars, lignin) and microbial and fungal biomass contribute to AT adsorption. Weak electrostatic (physical) sorption of AT on organic compounds and on mineral surfaces prevails. For casts, the formation of additional hydrophobic interactions between AT and SOM is proposed. We also studied AT biodegradation by the model bacterium Pseudomonas sp. strain ADP in the presence of soils or earthworm casts. An enhancement of the AT disappearance rate was observed in the presence of all the solid matrices tested compared with that obtained in an aqueous medium. The biodegradation rate was shown to be dependent not only on the OC content of the solid matrix, but mainly on its composition and structure. [source] Concentrations of Ag, In, Sn, Sb and Bi, and their chemical fractionation in typical soils in JapanEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2006H. Hou Summary We determined concentrations of Ag, In, Sn, Sb and Bi, and fractionated them by sequential extraction procedures, in five Japanese soils: Andosol-1 (grassland), Andosol-2 (forest), Cambisol (forest), Fluvisol (vegetable garden) and Regosol (forest). Average concentrations of Ag, In, Sn, Sb and Bi were 0.17 ± 0.08, 0.081 ± 0.019, 2.2 ± 0.5, 0.83 ± 0.32 and 0.32 ± 0.12 mg kg,1, respectively. Average distributions of the chemical fractions (omitting those with an abundance < 5%) were: Ag, residual (60%) > H2O2 -extractable, organically bound (H2O2 -Org) (18%) > metal,organic complex-bound (Me-Org) (10%) > amorphous metal oxide-bound (am-MeOx) (8.3%); In, residual (61%) > H2O2 -Org (12%) > Me-Org (8.7%) , crystalline Fe oxide-bound (cr-FeOx) (8.2%) > am-MeOx (7.4%); Sn, residual (40%) > Me-Org (19%) > carbonate-bound (12%) > cr-FeOx (9.0%) > H2O2 -Org (7.8%) > am-MeOx (6.9%); Sb, residual (34%) > Me-Org (18%) > am-MeOx (16%) > cr-FeOx (8.9%) , H2O2 -Org (8.7%) > easily reducible metal oxide-bound (re-MeOx) (6.8%) > carbonate-bound (6.1%); Bi, am-MeOx (26%) , H2O2 -Org (26%) > Me-Org (19%) > residual (17%) > cr-FeOx (12%). Proportions of the mobilizable (exchangeable + carbonate-bound + Me-Org + re-MeOx) metal fractions were in the order Sn , Sb > Bi > Ag ? In, and Cambisol > Andosol-2 > Regosol > Andosol-1 > Fluvisol. The proportions were predicted by multiple regression equations including pH, surface area, C contents, cation exchange capacity and clay content of the soils as independent variables (R2 > 0.96, P < 0.02). [source] Poorly crystalline mineral phases protect organic matter in acid subsoil horizonsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2005M. Kleber Summary Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite,citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites. [source] Neural network models to predict cation exchange capacity in arid regions of IranEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2005M. Amini Summary Design and analysis of land-use management scenarios requires detailed soil data. When such data are needed on a large scale, pedotransfer functions (PTFs) could be used to estimate different soil properties. Because existing regression-based PTFs for estimating cation exchange capacity (CEC) do not, in general, apply well to arid areas, this study was conducted (i) to evaluate the existing models and (ii) to develop neural network-based PTFs for predicting CEC in Aridisols of Isfahan in central Iran. As most researches have found a significant correlation between CEC and soil organic matter content (OM) and clay content, we also used these two variables for modelling of CEC. We tested several published PTFs and developed two neural network algorithms using multilayer perceptron and general regression neural networks based on a set of 170 soil samples. The data set was divided into two subsets for calibration and testing of the models. In general, the neural network-based models provided more reliable predictions than the regression-based PTFs. [source] The inherent ,safety-net' of an Acrisol: measuring and modelling retarded leaching of mineral nitrogenEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2002D. Suprayogo Summary The inherent features of Acrisols with their increasing clay content with depth are conducive to reducing nutrient losses by nutrient adsorption on the matrix soil surfaces. Ammonium (NH4+) and nitrate (NO3,) adsorption by a Plinthic Acrisol from Lampung, Indonesia was studied in column experiments. The peak of the H218O breakthrough occurred at 1 pore volume, whereas the median pore volumes for NH4+ and NO3, ranged from 6.4 to 6.9 and 1.1 to 1.6, respectively. The adsorption coefficients (Ka in cm3 g,1) measured were 1.81, 1.51, 1.64 and 1.47 for NH4+ and 0.03, 0.09, 0.10 and 0.17 for NO3,, respectively, in the 0,0.2, 0.2,0.4, 0.4,0.6 and 0.6,0.8 m soil depth layers. The NH4+ and NO3, adsorption coefficients derived from this study were put in to the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model to evaluate their effect on leaching in the context of several cropping systems in the humid tropics. The resulting simulations indicate that the inherent ,safety-net' (retardation mechanism) of a shallow (0.8,1 m) Plinthic Acrisol can reduce the leaching of mineral N by between 5 and 33% (or up to 2.1 g m,2), mainly due to the NH4+ retardation factor, and that the effectiveness in reducing N leaching increases with increasing depth. However, the inherent ,safety-net' is useful only if deep-rooted plants can recover the N subsequently. [source] Changes in variance and correlation of soil properties with scale and location: analysis using an adapted maximal overlap discrete wavelet transformEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2001R. M. Lark Summary The magnitude of variation in soil properties can change from place to place, and this lack of stationarity can preclude conventional geostatistical and spectral analysis. In contrast, wavelets and their scaling functions, which take non-zero values only over short intervals and are therefore local, enable us to handle such variation. Wavelets can be used to analyse scale-dependence and spatial changes in the correlation of two variables where the linear model of coregionalization is inadmissible. We have adapted wavelet methods to analyse soil properties with non-stationary variation and covariation in fairly small sets of data, such as we can expect in soil survey, and we have applied them to measurements of pH and the contents of clay and calcium carbonate on a 3-km transect in Central England. Places on the transect where significant changes in the variance of the soil properties occur were identified. The scale-dependence of the correlations of soil properties was investigated by calculating wavelet correlations for each spatial scale. We identified where the covariance of the properties appeared to change and then computed the wavelet correlations on each side of the change point and compared them. The correlation of topsoil and subsoil clay content was found to be uniform along the transect at one important scale, although there were significant changes in the variance. In contrast, carbonate content and pH of the topsoil were correlated only in parts of the transect. [source] Welche Bedeutung hat die sexuelle Reproduktion für den Erfolg der Art Calamagrostis epigejos (L.) Roth?FEDDES REPERTORIUM, Issue 3-4 2003A. Grüttner Dr. Als Quellen der Variabilität im Potential der sexuellen Reproduktion fanden sich Unterschiede in der Keimungsgeschwindigkeit (entspelzte Karyopsen keimten rascher und synchroner), bei den Keimraten und vor allem bei der Zahl keimfähiger Diasporen pro Rispe. Von den anderen abweichend zeigten kleine isolierte Bestände geringere Keimraten und brachten , wohl bedingt durch Selbstinkompatibilität , kaum keimfähige Diasporen hervor. Bei gezielter Suche fanden sich Keimlinge auf offenen, zumindest leicht tonhaltigen Rohböden. Das Wachstum der Keimlinge stagnierte und keiner von über 6000 überlebte bis zum nächsten Jahr. Da Bewässerung die Entwicklung auf dem selben Substrat sehr förderte, war offenbar Wassermangel für das geringe Wachstum ausschlaggebend. Die erfolgreiche generative Etablierung ist also auf den Zufall günstiger Witterungsphasen oder Standorte angewiesen. Auch im Frühjahr waren noch keimfähige Diasporen in aufrechten Rispen nachweisbar, sodass sich der Diasporenfall mehr oder weniger über das gesamte Jahr erstreckt. Im Zusammenspiel mit dem Fehlen von Dormanz ermöglicht das die Nutzung nicht vorhersagbarer günstiger Witterungsphasen. Bei einem Kulturversuch kamen einzelne Individuen auch mit schwierigen Substraten gut zurecht, auf denen die Mehrzahl kümmerte. Danach ergibt sich die standörtliche Breite der Art C.,epigejos als Summe sehr unterschiedlicher Reaktionsnormen der Individuen. Die angeführten Befunde unterstreichen insgesamt die Bedeutung der sexuellen Reproduktion und der genetischen Diversität für den Erfolg der Art. Is sexual reproduction important to the success of Calamagrostis epigejos (L.) Roth? Calamagrostis epigejos is very common in Central Europe and occupies an extraordinary wide range of habitats. As up to now nearly no reports exist on spontaneous seedling emergence, we aimed to investigate several aspects of sexual reproduction, thereby refering to contrasting habitat types. Components in the variability of the potential of sexual reproduction were differences in germination speed and rates and, above all, number of germinable seeds per panicle. Unlike the others, small isolated stands produced very low numbers of germinable seeds, probably caused by selfincompatibility. Our search for seedlings was successful at several sites , all distinguished by raw soil, a certain clay content, and little cover of vegetation and plant litter. The seedlings grew very slowly and none of more than 6000 survived the first year. Additional water enabling much better growth indicates the necessity of favorable weather or favorable habitats (with constant water supply) for successful seedling establishment. Seed dispersal nearly all around the year, combined with the lack of dormancy, allows to make use of the unpredictable opportunities of suitable weather periods. A growth experiment on different substrates demonstrated: the more extreme the conditions, the more differentiated the amount of biomass achieved by each of 20 genets. Some genets grew well even on substrates where most others stagnated. This outcome suggests the wide range of habitats covered by C. epigejos to be the result of the genetic diversity, which in turn is maintained by sexual reproduction and avoidance of inbreeding. [source] Biological control of beech and hornbeam affects species richness via changes in the organic layer, pH and soil moisture characteristicsFUNCTIONAL ECOLOGY, Issue 2 2010Anne Mieke Kooijman Summary 1. ,Litter quality is an important ecosystem factor, which may affect undergrowth species richness via decomposition and organic layers directly, but also via longer-term changes in soil pH and moisture. The impact of beech trees with low-degradable and hornbeam trees with high-degradable litter on biodiversity and soil characteristics was studied in ancient forests on decalcified marl, a parent material sensitive to changes in pH and clay content, and characteristic of large parts of western Europe. 2. ,Vegetation analysis clearly separated beech and hornbeam plots, and showed that species richness was consistently lower under beech. Low species richness under beech was associated with low pH, high mass of the organic layer and low soil moisture, which were all interrelated. 3. ,Development of the organic layer was affected by, not only litter quality, but also by pH levels and soil moisture. Under hornbeam, older organic matter increased from almost zero to 1 kg m,2 in drier and more acid soil. Under beech tree litter decay was generally slow, but slowed further in acid soils, where older organic matter amounted to 4 kg m,2. 4. ,Soil moisture and pH levels were strongly related, possibly due to long-term soil development. Under hornbeam, which is more palatable to soil organisms, moisture, bulk density, clay content and pH were high. Acidification and clay eluviation may be counteracted by earthworms, which bring base cations and clay particles back to the surface, and stimulate erosion, so that the impermeable, clay-rich subsoil remains close to the surface. Soils remain base-rich and moist, which further stimulates litter decay and species richness. 5. ,The unpalatable beech showed low pH and clay content, and high porosity, air-filled pore space and depth to the impermeable subsoil. Acidification and clay eluviation may proceed uninhibited, because earthworm activity is low, and erosion limited by protective litter covers. This may lead to drier and more acid soils, which reduce litter decay and species richness even further. 6. ,Trees with low and high litter quality may thus act as an ecosystem engineer, and not only affect ecosystem functioning via mass of the organic layer, but also via longer-term changes in soil characteristics, which in turn affect species richness of the understorey. [source] Elastic properties of dry clay mineral aggregates, suspensions and sandstonesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2003Tiziana Vanorio SUMMARY The presence of clay minerals can alter the elastic behaviour of rocks significantly. Although clay minerals are common in sedimentary formations and seismic measurements are our main tools for studying subsurface lithologies, measurements of elastic properties of clay minerals have proven difficult. Theoretical values for the bulk modulus of clay are reported between 20 and 50 GPa. The only published experimental measurement of Young's modulus in a clay mineral using atomic force acoustic microscopy (AFAM) gave a much lower value of 6.2 GPa. This study has concentrated on using independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. First, ultrasonic P - and S -wave velocities were measured as functions of hydrostatic pressure in cold-pressed clay aggregates with porosity and grain density ranging from 4 to 43 per cent and 2.13 to 2.83 g cm,3, respectively. In the second experiment, P - and S -wave velocities in clay powders were measured under uniaxial stresses compaction. In the third experiment, P -wave velocity and attenuation in a kaolinite,water suspension with clay concentrations between 0 and 60 per cent were measured at ambient conditions. Our elastic moduli measurements of kaolinite, montmorillonite and smectite are consistent for all experiments and with reported AFAM measurements on a nanometre scale. The bulk modulus values of the solid clay phase (Ks) lie between 6 and 12 GPa and shear (,s) modulus values vary between 4 and 6 GPa. A comparison is made between the accuracy of velocity prediction in shaley sandstones and clay,water and clay,sand mixtures using the values measured in this study and those from theoretical models. Using Ks= 12 GPa and ,s= 6 GPa from this study, the models give a much better prediction both of experimental velocity reduction due to increase in clay content in sandstones and velocity measurements in a kaolinite,water suspension. [source] The stress sensitivity of shaley sandstonesGEOPHYSICAL PROSPECTING, Issue 2 2007Colin MacBeth ABSTRACT The link between the stress sensitivity of shaley sandstones and their porosity and clay content is investigated. This is achieved by firstly fitting a compliance-based stress-sensitivity law to laboratory measurements of ultrasonic velocity taken from four sets of reservoir sandstones, extracted from a variety of depositional settings. Correlations are then sought between the independent parameters of this law and the porosity or clay fraction of the rocks, which are then subsequently interpreted in terms of framework or pore-space-related microstructural clay models. The general conclusion drawn from the results is that both of the parameters defining the stress-sensitivity law (the asymptotic modulus and the stress-dependent excess compliance) clearly vary with porosity. However, only the asymptotic modulus shows a convincing trend with clay and there is little observed variation of the stress-dependent compliance with clay. There is therefore a resultant variation of stress sensitivity with clay, but it is controlled only by the asymptotic modulus. The analysis also concludes that all four data sets fall into a framework-related category of clay model. [source] 3D imaging of a reservoir analogue in point bar deposits in the Ferron Sandstone, Utah, using ground-penetrating radarGEOPHYSICAL PROSPECTING, Issue 3 2004Xiaoxian Zeng ABSTRACT Most existing reservoir models are based on 2D outcrop studies; 3D aspects are inferred from correlation between wells, and so are inadequately constrained for reservoir simulations. To overcome these deficiencies, we have initiated a multidimensional characterization of reservoir analogues in the Cretaceous Ferron Sandstone in Utah. Detailed sedimentary facies maps of cliff faces define the geometry and distribution of reservoir flow units, barriers and baffles at the outcrop. High-resolution 2D and 3D ground-penetrating radar (GPR) images extend these reservoir characteristics into 3D to allow the development of realistic 3D reservoir models. Models use geometric information from mapping and the GPR data, combined with petrophysical data from surface and cliff-face outcrops, and laboratory analyses of outcrop and core samples. The site of the field work is Corbula Gulch, on the western flank of the San Rafael Swell, in east-central Utah. The outcrop consists of an 8,17 m thick sandstone body which contains various sedimentary structures, such as cross-bedding, inclined stratification and erosional surfaces, which range in scale from less than a metre to hundreds of metres. 3D depth migration of the common-offset GPR data produces data volumes within which the inclined surfaces and erosional surfaces are visible. Correlation between fluid permeability, clay content, instantaneous frequency and instantaneous amplitude of the GPR data provides estimates of the 3D distribution of fluid permeability and clay content. [source] Effects of pore aspect ratios on velocity prediction from well-log dataGEOPHYSICAL PROSPECTING, Issue 3 2002Jun Yan ABSTRACT We develop a semi-empirical model which combines the theoretical model of Xu and White and the empirical formula of Han, Nur and Morgan in sand,clay environments. This new model may be used for petrophysical interpretation of P- and S-wave velocities. In particular, we are able to obtain an independent estimation of aspect ratios based on log data and seismic velocity, and also the relationship between velocities and other reservoir parameters (e.g. porosity and clay content), thus providing a prediction of shear-wave velocity. To achieve this, we first use Kuster and Toksöz's theory to derive bulk and shear moduli in a sand,clay mixture. Secondly, Xu and White's model is combined with an artificial neural network to invert the depth-dependent variation of pore aspect ratios. Finally these aspect ratio results are linked to the empirical formula of Han, Nur and Morgan, using a multiple regression algorithm for petrophysical interpretation. Tests on field data from a North Sea reservoir show that this semi-empirical model provides simple but satisfactory results for the prediction of shear-wave velocities and the estimation of reservoir parameters. [source] Aquifer vulnerability assessment to heavy metals using ordinal logistic regressionGROUND WATER, Issue 2 2005Navin K.C. Twarakavi A methodology using ordinal logistic regression is proposed to predict the probability of occurrence of heavy metals in ground water. The predicted probabilities are defined with reference to the background concentration and the maximum contaminant level. The model is able to predict the occurrence due to different influencing variables such as the land use, soil hydrologic group (SHG), and surface elevation. The methodology was applied to the Sumas-Blaine Aquifer located in Washington State to predict the occurrence of five heavy metals. The influencing variables considered were (1) SHG; (2) land use; (3) elevation; (4) clay content; (5) hydraulic conductivity; and (6) well depth. The predicted probabilities were in agreement with the observed probabilities under existing conditions. The results showed that aquifer vulnerability to each heavy metal was related to different sets of influencing variables. However, all heavy metals had a strong influence from land use and SHG. The model results also provided good insight into the influence of various hydrogeochemical factors and land uses on the presence of each heavy metal. A simple economic analysis was proposed and demonstrated to evaluate the cost effects of changing the land use on heavy metal occurrence. [source] Polymer,Clay Nanocomposites Exhibiting Abnormal Necking Phenomena Accompanied by Extremely Large Reversible Elongations and Excellent Transparency,ADVANCED MATERIALS, Issue 17 2006K. Haraguchi Soft and transparent polymer,clay nanocomposites (see figure), consisting of hydrophobic poly(2-methoxyethylacrylate) and hydrophilic inorganic clay, with a unique clay-network morphology have been synthesized by in,situ free-radical polymerization. The nanocomposites exhibit the first observation of abnormal necking behavior accompanied by extremely large reversible elongation (1000,3000,%) and excellent optical transparency, regardless of the clay content (1,30,wt,%). [source] Stabilization of soft clay in irrigation projects,IRRIGATION AND DRAINAGE, Issue 2 2005M. M. Mubeen stabilisation de chaux; utilisation d'argile molle; déchet de pierre pulvérisée; ouvrage d'irrigation Abstract Clay,lime improvement is an effective means to improve soft clay soil. Lime stabilization especially improves the strength and the workability of the clay soil. In addition, lime improvement provides more resistance to the soil structure and to the effect of weather on the soil structure. This study has investigated lime stabilization of soft clay and the possibility of utilizing waste rock powder produced in crusher plants as a supplemental material for lime stabilization in order to increase the strength of the soil structure. The purpose of the study was to apply the results especially in irrigation projects in order to avoid the problems of soft clay on irrigation structures in Sri Lanka. However, the results and conclusions can be considered for other regions, where the same type of soft clay problems exists. The Dutch Oostvaardersplassen (OVP) soft clay, which has a high plasticity, low shear strength and high natural water content, was chosen for the investigations. The results of unconfined compressive strength for different water contents of clay and also for different lime and waste rock powder contents show an excellent increase in strength and workability. The waste rock powder proved to increase the effect of lime stabilization. The strength improvement caused by waste rock powder is more significant for those soils which have a low clay content. Since in irrigation projects a wide range of clay soils exist, this investigation may be useful to utilize waste rock powder in order to improve the quality and the durability of the foundation of irrigation structures in the long run. Therefore the application of lime and rock material improvement on soft clay in irrigation projects may be a useful approach to stabilize soft soils and improve medium-scale shallow foundation irrigation structures and road and canal embankments, including repairing canal leaks. It has also been found that by applying this method in irrigation projects in Sri Lanka, the stabilization cost for structures on soft clay can be significantly reduced compared to other methods. Copyright © 2005 John Wiley & Sons, Ltd. L'amélioration de l'argile avec de la chaux est une moyenne effective pour améliorer la terre de l'argile molle. Spécialement la stabilisation de chaux améliore la force et la maniabilité de la terre argileuse. De plus l'amélioration de chaux fournit plus de résistance à la structure de la terre avec l'effet du temps sur la structure de la terre pendant les conditions atmosphériques différentes. Dans cette étude on a examiné la stabilisation de chaux dans l'argile molle et la possibilité de utiliser des déchets de pierre pulvérisée, obtenus par pulvériser des usines, comme une matérielle supplémentaire pour la stabilisation de chaux afin que la force de la structure de la terre s'améliore. L'objective de cette étude était d'appliquer les résultats spécialement dans des projets d'irrigation pour éviter des problèmes de l'argile molle dans des structures d'irrigation en Sri Lanka. Les résultats et les conclusions peuvent être considérés pour d'autres régions, ayant le même problème de l'argile molle. Les Oostvaarderplassen (OVP) en Hollande ont de l'argile molle ayant une plasticité haute, une résistance au cisaillement basse et un haut pourcentage de l'eau naturelle. C'est pour ça les Oostvaardersplassen ont été choisis pour accomplir la recherche. Les résultats de la force de pression indéfinie pour des teneurs en eau différents dans l'argile, aussi pour les teneurs en chaux différents et des déchets de pierres pulvérisées montrent une augmentation excellente de la force et de la maniabilité. Les déchets de pierre pulvérisée se révèlent d'augmenter l'effet de la stabilisation de chaux. L'amélioration de la force, causée par les déchets de pierre pulvérisée, est plus significative pour ces terres ayant un teneur d'argile bas. Parce que les projets d'irrigation ont beaucoup de la terre d'argile cette recherche peut être utile pour user des déchets de pierre pulvérisée pour améliorer la qualité et la durabilité de la fondation des structures d'irrigation à long terme. C'est pourquoi l'application du matériel de chaux et de pierre sur de l'argile molle dans des projets d'irrigation peut être une approche utile pour stabiliser des terres molles et peut améliorer des structures de fondations d'irrigation dans des eaux pas profondes, dans des remblais de chemins et de canaux, inclus dans des réparations des fuites de canaux. Aussi on a révélé qu'en appliquant ce méthode dans des projets d'irrigation en Sri Lanka les coûts de la stabilisation des structures sur de l'argile molle peuvent être réduits d'une manière importante comparée avec d'autres méthodes. Copyright © 2005 John Wiley & Sons, Ltd. [source] Nanostructure and micromechanical properties of reversibly crosslinked isotactic polypropylene/clay compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010S. Bouhelal Abstract Recent developments concerning the methodology used to prepare composites of iPP and nanoclays are reported. Conventional (reactive melt mixing) and in situ preparations were performed, and the structural properties exhibited by the composites are discussed. Results suggest that the nanoclay could exhibit partial and, maybe, total exfoliation within the composites. Adhesion between the polymeric matrix and the nanoclay layers is similar to that obtained after grafting. The experimental procedure used and the analysis performed by means of the wide-angle X-ray scattering and differential scanning calorimetry techniques permit to describe, at nanoscale level, the contribution of the nanoclay to the polymer composite system. The microhardness values of the iPP,clay composites depend on the clay content and on the preparation method, and linearly correlate, according to the additivity law, with the degree of crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] The thermal conductivity of Nylon 6/clay nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Hu Zhou Abstract Nylon 6/clay nanocomposites (NCNs) of different clay loadings are prepared by melt compounding. The effects of clay loading and dispersion on the thermal conductivity of NCNs are investigated using XRD, TEM, DSC, and POM. The results show that the thermal conductivity of the exfoliated NCNs decreases with an increase of clay content; but the thermal conductivity of the intercalated NCNs does not decrease, indeed, it increase markedly at high clay content. Such results observed in the exfoliated NCNs are opposite to the expectation of the classic Maxwell thermal conduction model. The further investigations indicate that such decrease observed in the exfoliated NCNs is due mainly to the exfoliation of clay layers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Colorless polyimide nanocomposite films: Thermomechanical properties, morphology, and optical transparencyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Hyo-Seong Jin Abstract Polyimide (PI)/organoclay hybrid films were prepared by the solution intercalation method, using dodecyltriphenylphosphonium-mica (C12PPh-Mica) as the organoclay. The variations with organoclay content of the thermomechanical properties, morphology, and optical transparency of the hybrids were examined for concentrations from 0 to 1.0 wt %. For low clay contents (, 0.5 wt %), the clay particles are better dispersed in the matrix polymer, without the formation of large agglomerates of particles, than they are for high clay contents. However, agglomerated structures form and become denser in the PI matrix for clay contents , 0.75 wt %. This is in agreement with the observed trends in the thermomechanical properties and the optical transparency, which worsen drastically when the clay content of the C12PPh-Mica/PI hybrids reaches 0.75 wt %. However, when the amount of organoclay in the hybrid is 0.75 wt %, the initial modulus of the hybrid film is at its maximum value. The PI hybrid films were found to exhibit excellent optical transparencies and to be almost colorless. It was found, however, that the transparency decreases slightly with increases in the organoclay content because of agglomeration of the clay particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis and characterization of poly(butylene terephthalate)/mica nanocomposite fibers via in situ interlayer polymerizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007Jin-Hae Chang Abstract Intercalated nanocomposites consisting of poly(butylene terephthalate) (PBT) incorporated between mica layers were synthesized from dimethyl terephthalate (DMT) and 1,4-butanediol (BD) by in situ interlayer polymerization. PBT nanocomposites of varying organoclay content were melt-spun to produce monofilaments. The samples were characterized using wide angle X-ray diffraction, electron microscopy, thermal analysis, and tensile testing. Some of the clay particles were found to be well dispersed in the PBT matrix, but other clay particles were agglomerated at a size level greater than approximately 20 nm. The glass transition temperatures (Tg) and the thermal degradation properties (TDi) of undrawn PBT hybrid fibers were found to improve with increases in the clay content. At draw ratio (DR) = 1, the ultimate tensile strengths of the hybrid fibers increased with the addition of clay up to a critical content and then decreased. However, the initial moduli monotonically increased with increases in the amount of organoclay in the PBT matrix. The ultimate strengths were found to decrease linearly with increases in DR from 1 to 18. In contrast to the trend for the tensile strengths, the initial moduli of the hybrid fibers increased only slightly with increases in DR up to 18. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Microstructure dependent properties of polypropylene-clay nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Y. Fan Abstract The mechanical properties of melt processed polypropylene-montmorillonite nanocomposites were studied as a function of clay content. The measurement of tensile properties at room temperature and dynamic mechanical properties over a wide temperature range reveal a decrease in modulus and tensile strength of the composite with increasing clay content. The origins of this anomalous result were examined in detail using X-ray diffraction and differential scanning calorimeter, which averaged the microstructure over reasonable specimen volumes. Micromechanical models could be used to adequately describe the composite properties, provided appropriate properties for the matrix and particle were used. The matrix properties were found to affect the average properties significantly. © Wiley Periodicals, Inc. J Appl Polym Sci 103: 204,210, 2007 [source] Comparison of critical limits for crop plant growth based on different indicators for the state of soil compactionJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2010Manfred Kaufmann Abstract Soil compaction affects physical soil condition, in particular aeration, soil strength, and water availability and has adverse effects on plant growth. Bulk density is the most frequently used indicator to describe the state of compaction of a soil. However, this parameter lacks a direct functional relationship with plant growth. Various indicators have been proposed to simultaneously characterize the state of compaction of agricultural soil and its suitability for plant growth. This paper examines and compares the critical limits for crop plant growth based on three of these indicators: packing density, least limiting water range, and S parameter (the latter is the slope of the soil water-retention curve in the inflexion point). In a first step, we reviewed the literature for published optimum and limiting values of bulk density and found that these values were highly dependent on clay and silt content. Converting them into corresponding values of packing density (composite index of bulk density and clay content), a value of 1.70 was found to effectively distinguish between optimum and limiting soil conditions for plant growth. In a second step, the packing density of 59 soil horizons sampled in N Switzerland was compared with the least limiting water range and the S parameter of these soil horizons (both determined by means of pedotransfer functions taken from the literature). A linear relationship between the three parameters was found, which allowed for a comparison of the published critical limits for plant growth based on these parameters. The critical limits of the three indicators, which had been postulated independently of each other in the literature, were found to agree well with each other. This means that all of them could equally be used to describe the compaction state of a soil and its physical suitability for plant growth. However, the proposed critical limits of packing density, least limiting water range, and S parameter still need further validation by field studies relating plant growth to soil compaction. [source] Soil-aggregate formation as influenced by clay content and organic-matter amendmentJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2007Stephen Wagner Abstract Naturally occurring wetting-and-drying cycles often enhance aggregation and give rise to a stable soil structure. In comparatively dry regions, such as large areas of Australia, organic-matter (OM) contents in topsoils of arable land are usually small. Therefore, the effects of wetting and drying are almost solely reliant on the clay content. To investigate the relations between wetting-and-drying cycles, aggregation, clay content, and OM in the Australian environment, an experiment was set up to determine the relative influence of both clay content (23%, 31%, 34%, and 38%) and OM amendments of barley straw (equivalent to 3.1,t,ha,1, 6.2,t,ha,1, and 12.4,t,ha,1) on the development of water-stable aggregates in agricultural soil. The aggregate stability of each of the sixteen composite soils was determined after one, three, and six wet/dry cycles and subsequent fast and slow prewetting and was then compared to the aggregate stabilities of all other composite soils. While a single wet/dry cycle initiated soil structural evolution in all composite soils, enhancing macroaggregation, the incorporation of barley straw was most effective for the development of water-stable aggregates in those soils with 34% and 38% clay. Repeated wetting-and-drying events revealed that soil aggregation is primarily based on the clay content of the soil, but that large straw additions also tend to enhance soil aggregation. Relative to untreated soil, straw additions equivalent to 3.1,t,ha,1 and 12.4,t,ha,1 increased soil aggregation by about 100% and 250%, respectively, after three wet/dry cycles and fast prewetting, but were of less influence with subsequent wet/dry cycles. Straw additions were even more effective in aggregating soil when combined with slow prewetting; after three wet/dry cycles, the mean weight diameters of aggregates were increased by 70% and 140% with the same OM additions and by 160% and 290% after six wet/dry cycles, compared to samples without organic amendments. We suggest that in arable soils poor in OM and with a field texture grade of clay loam or finer, the addition of straw, which is often available from preceding crops, may be useful for improving aggregation. For a satisfactory degree of aggregate stability and an improved soil structural form, we found that straw additions of at least 6.2,t,ha,1 were required. However, rapid wetting of straw-amended soil will disrupt newly formed aggregates, and straw has only a limited ability to sustain structural improvement. [source] Correlation of morphology, rheology, and performance improvement in gasoline tubes based on PA-6 nanocompositesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2010Mehdi Moghri PA-6/organo-modified layered silicate nanocompounds were prepared by the melt mixing of PA-6 with different nanoclay loadings in a corotating twin-screw extruder. Gasoline tubes based on these nanocompounds were produced at different silicate loadings. Thermal, mechanical, rheological, and barrier properties of the different samples were investigated and correlated to their morphology. Transmission electron microscopy, wide angle X-ray scattering, and linear melt state viscoelastic measurements were used to characterize the different aspects of nanoclay dispersion in the nanocomposite samples. While tensile modulus, softening point, heat distortion temperature, and gasoline barrier properties of the prepared tubes were improved considerably by increasing the clay content, performance improvement with respect to clay content (after a certain value) decreased with increasing clay loading. It could be attributed to the re-agglomeration of tactoids at higher concentrations. These findings were correlated with the rheological and morphological observations. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers [source] Sediment phosphorus characteristics in the clearwater state of Lake Mogan, TurkeyLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 3 2008Serap Pulatsü Abstract This study examined the vertical distributions of total phosphorus (TP) and phosphorus fractions, and the iron and organic matter, in the littoral sediment in a macrophyte-dominated, clearwater state in Lake Mogan between September 2005 and August 2006. Benthic macroinvertebrates and total bacteria in the sediment also were determined. No clear seasonal or depth-related (0,20 cm) patterns were found in sediment concentrations for the measured parameters. The phosphorus release was quantitatively very low, and a negative phosphorus release (,0.132 µg m,2 day,1) was measured during the summer months. The TP concentrations of the sediment samples ranged between 675.00 and 1463.80 µg g,1 dry weight (DW), and the trophic level of the lake was eutrophic. On average, inorganic phosphorus fractions comprised the largest fraction (63%), while organic-bound phosphorus (Org , P) constituted 37% of the TP in Lake Mogan. The most important phosphorus-immobilizing factors are high iron content (14 200,47 750 µg g,1 DW), the sediment's clay content (47.80,51.80%), and an abundance of macrophytes at the sampling station. The low abundance of benthic macroinvertebrates (510,850 individuals m,2), which depend on sediments with high iron and low organic matter (5.42,13.30%), played a role in the sediment phosphorus retention. Although bacterial abundance in the surficial sediment appeared to be positively correlated to temperature, the overlying water did not experience anoxic conditions, supporting a state in which bacteria were able to retain phosphorus in their cell structures. Long-term changes in the sediments of Lake Mogan must be monitored lake. In order to optimize the management of the lake, and to determine the longevity of a clearwater state following management measures and continued external phosphorus loading, long-term changes in the sediments of Lake Morgan must be monitored. [source] | ||||||||||||||||||||||||||||||||||