bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytical Solution of Solute Diffusion and Biodegradation in Spherical Aggregates
Authors: Priesack E. 
Published: July 2010

AbstractMicrobial degradation and transformation of substances in soils plays a crucial role in the nutrient turnover of ecosystems. To quantify these processes, a mathematical description is needed. For this purpose, an analytical solution to a model of solute diffusion and biodegradation in soil aggregates was developed. The model is a first approach toward understanding the influence of geometric arrangement of microorganisms and substrates in structured soils. These soils are considered to consist of uniformly sized and shaped aggregates surrounded by surface films of the soil solution. The model simulates transient diffusion of finite substrate amounts from the surface films into spherical aggregates. Biodegradation is considered for the special case of unlimited microbial growth, and adsorption is assumed to follow a linear Freundlich isotherm. The system is represented by a composite sphere, the outer sphere being the solution film and the inner sphere representing the soil aggregate. The diffusion equations are solved by Laplace transformation. The model solution gives a direct relationship between the initial substrate and biomass concentrations, the diffusion coefficient, the specific growth rate, and the adsorption coefficient. Good agreement between this closed form solution and numerical solutions is obtained for diffusion with and without biodegradation. Since the substrate is exhausted by organisms close to the surface, the centers of large aggregates are not reached by the diffusing substrate. These unaffected centers become larger as the growth rate is higher, the diffusion constant is lower, and adsorption of the substrate is stronger.
Fractal Fragmentation, Soil Porosity, and Soil Water Properties: I. Theory
Authors: Rieu Michel , Sposito Garrison 
Published: July 2010

AbstractRecent efforts to characterize soil water properties in terms of porosity and particle‐size distribution have turned to the possibility that a fractal representation of soil structure may be especially apt. In this paper, we develop a fully self‐consistent fractal model of aggregate and pore‐space properties for structured soils. The concept underlying the model is the representation of a soil as a fragmented fractal porous medium. This concept involves four essential components: the mathematical partitioning of a bulk soil volume into self‐similar pore‐ and aggregate‐size classes, each of which is identified with a successive fragmentation step; the definition of a uniform probability for incomplete fragmentation in each size class; the definition of fractal dimensions for both completely and incompletely fragmented porous media; and the definition of a domain of length scales across which fractal behavior occurs. Model results include a number of equations that can be tested experimentally: (i) a fractal dimension ≤3; (ii) a decrease in aggregate bulk density (or an increase in porosity) with increasing aggregate size; (iii) a power‐law aggregate‐size‐distribution function; (iv) a water potential that scales as an integer power of a similarity ratio; (v) a power‐law expression for the water‐retention curve; and (vi) an expression for hydraulic conductivity in terms of the conductivities of single‐size arrangements of fractures embedded in a regular fractal network. Future research should provide experimental data with which to evaluate these predictions in detail.
Fractal Fragmentation, Soil Porosity, and Soil Water Properties: II. Applications
Authors: Rieu Michel , Sposito Garrison 
Published: July 2010

AbstractThe fractal model of Rieu and Sposito contains seven predictive equations that can be tested experimentally with data on aggregate characteristics and soil water properties for structured soils. However, data with which to test the model are extremely limited at present because of the need to have precise, concurrent measurements of aggregate physical properties (bulk density and size distribution) along with soil water properties for an undisturbed soil. For the five sets of suitable physical soil aggregate data currently available, good agreement was found with the fractal model bulk density‐aggregate size and size‐distribution relationships. For the single set of aggregate/soil water properties data available, good agreement also was found with the fractal model water‐potential scaling relationship, moisture characteristic, and hydraulic conductivity‐water content relationship. Model simulations of the last two soil water relationships for hypothetical sandy and clayey soils also were qualitatively accurate and showed the sensitivity of the model to the value of the fractal dimension. These encouraging results suggest that the model should have success in further experimental tests with natural soils.
Diffusion of Technetium in Dense Bentonite under Oxidizing and Reducing Conditions
Authors: Sawatsky N. G. , Oscarson D. W. 
Published: July 2010

AbstractDiffusion is the principal mechanism by which most contaminants migrate through dense bentonite‐based barrier materials used in many waste‐containment strategies. Diffusion coefficients are, therefore, critical parameters for predicting migration rates of contaminants through these materials. Diffusion coefficients, D, were determined for Tc (99Tc is a relatively long‐lived radionuclide present in high‐level nuclear fuel waste) in compacted, nearly saturated bentonite under both oxidizing and reducing conditions. The D values were measured under oxidizing conditions at 25 or 80 °C in bentonite compacted to dry bulk densities, ρb, ranging from about 0.9 to 1.35 Mg/m3. In a reducing environment, D values were determined at 25 °C and ρb ≃ 1.3 Mg/m3; reducing conditions were established by mixing 1% (w/w) Fe(II)‐silicate with the bentonite and by conducting the experiment under a N2 atmosphere. Under oxidizing conditions at 25 °C, D ranged from 2.3 × 10−10 m2/s at ρb ≃ 0.9 Mg/m3 to 0.73 × 10−10 m2/s at 1.35 Mg/m3. The decrease in D with increasing density is largely attributed to an increase in the tortuosity of the diffusion path as the density increased. At 80 °C, D values were two to three times greater than those obtained at 25 °C at all densities; this is primarily due to a decrease in the viscosity of the saturating solution with increasing temperature. In a reducing environment, D was 6 ± 3 × 10−12 m2/s. The lower D values under reducing conditions are attributed to the reduction of TcO−4[Tc(VII)] to a less mobile Tc(IV) species. The results indicate that the migration of Tc through a bentonite‐based barrier material will be relatively slow in a reducing environment, such as that expected in a nuclear fuel waste disposal vault located deep in plutonic rock; this will mitigate the potential hazard associated with 99Tc in the long‐term disposal of nuclear fuel waste.
Phosphate Transport in Calcium‐Saturated Systems: II. Experimental Results in a Model System
Authors: Akinremi O. O. , Cho C. M. 
Published: July 2010

AbstractThis study investigated the diffusive transport of phosphate in a cation‐exchange‐resin model system. The objective was to demonstrate the effect of cation‐exchange reactions on the movement of the phosphate ion. To a cylindrical wax column of Ca‐saturated resin, 0.2 g of KH2PO4 was surface applied to simulate one‐dimensional diffusive transport. Other ions of interest were Ca2+, K+, and H+. Extraction and analysis of 2‐mm increments of the column after the desired incubation period (3, 7, and 14 d) revealed the following results. The pH of the system became low as a result of the interaction between added phosphate and Ca2+ from the exchange resin. The higher the cation‐exchange capacity (CEC), the lower the pH became. Calcium ions, present on the exchange sites, were displaced into solution by cation exchange with K+. The higher the CEC of the column, the higher was the amount of Ca2+ displaced into soil solution. The movement of K+ and phosphate ions was retarded in the system, and the degree of retardation increased with increasing CEC of the soil column. The retardation of K+ movement was due to ion‐exchange interaction with exchangeable Ca2+, while P movement was retarded as a result of chemical interaction with the displaced Ca2+. The experimental results showed the effect that the K‐Ca exchange reaction has on the diffusive movement of P. There is a need to take this into consideration in any model simulating P transport in the soil.
Zinc Sorption by Iron‐Oxide‐Coated Sand as a Function of pH
Authors: Stahl Randal S. , James Bruce R. 
Published: July 2010

AbstractMineralogy of Fe‐oxide coatings in soils may influence pH‐dependent sorption of heavy metals, but exchangeability of retained metals needs to be better understood to improve predictions of bioavailability. A laboratory study tested the effect of pH on the amount and form of Zn retained in exchangeable (extractable with 1 M KNO3) or nonexchangeable forms on goethite‐ and hematite‐coated sand. Batch equilibrations with 250 and 2500 µmol Zn(NO3)2/kg coated or uncoated sand were used to determine concentration effects on the form of Zn retained. Cation‐exchange capacity (CEC) of the goethite‐ or hematite‐coated sand increased with pH (4–7.6), but surface charge was a poor indicator of the amount and form of Zn retained. The goethite‐coated sand retained the Zn principally in a nonexchangeable form, while the hematite‐coated sand retained the Zn in both exchangeable and nonexchangeable forms. The distribution between the exchangeable and nonexchangeable Zn fractions changed from predominantly exchangeable to predominantly nonexchangeable Zn retention as pH increased in both oxide systems. The dominance of nonexchangeable‐Zn sorption by goethite was attributed to surface‐induced hydrolysis by OH groups, while O atoms of hydrated hematite and uncoated sand surfaces were hypothesized to be sorbing Zn in exchangeable forms.
Fecal Coliforms in Soil Detected by Polymerase Chain Reaction and DNA‐DNA Hybridizations
Authors: Josephson K. L. , Pillai S. D. , Way J. , Gerba C. P. , Pepper I. L. 
Published: July 2010

AbstractThe application of sewage sludge on agricultural lands is a common practice in the USA. The survival of pathogens and indicator organisms added to soil via sludge needs to be determined. A rapid method utilizing polymerase chain reaction (PCR) and a gene‐specific probe was used to detect low numbers of fecal coliforms in soil. Two 23‐base primers were designed from a region of the lamB gene that codes for an outer‐membrane protein present specifically in fecal coliforms. Use of these primers for PCR amplification of a 179‐bp fragment of lamB allowed specific detection of fecal‐coliform indicator organisms. Sensitivity of amplification from whole‐cell lysates of pure cultures of Escherichia coli using detection via ethidium bromide was 104 colony‐forming units (CFUs). When detection of these cell lysates was via a lamB gene‐specific probe, a total of 4 × 102 CFUs could be detected from these pure cultures. When genomic deoxyribonucleic acid (DNA) preparations were made from these pure cultures, 100 ag (10−18) of DNA was detectable. Following the inoculation of E. coli into soil, cells were extracted with CaCl2, and concentrated and purified by sucrose density centrifugation. The DNA obtained by lysing the cells was amplified using a new “double PCR” 50‐cycle protocol. Escherichia coli were detected in Brazito sandy loam (mixed, thermic Typic Torripsamment) and Pima silty clay loam (fine‐silty, mixed (calcareous), thermic Typic Torrifluvent). Using a 5′ end‐labeled lamB‐specific probe to detect PCR products, one CFU of E. coli was detectable in 1 g of soil. One PCR‐amplificable CFU g−1 would be equivalent to many copies of amplificable target DNA, due to the presence of dead and lysed cells along with cells containing more than one copy of the genome. Sample processing and PCR amplification can be completed within 7 to 8 h. Thus, the use of PCR for sensitive detection of introduced bacteria in environmental soil samples is possible.
The Growth of White Lupine on a Calciaquoll
Authors: Moraghan J. T. 
Published: July 2010

AbstractWhite lupine (Lupinus albus L.), an annual legume used for grain production in temperate climates, forms proteoid root (clusters of determinate rootlets on sections of lateral roots), accumulates Mn, and grows poorly on calcareous soils. This study was conducted to determine, under greenhouse conditions, the influence of P (0 vs. 120 mg NaH2PO4‐P kg−1), Fe (0 vs. 2 mg FeEDDHA‐Fe kg−1), and N source (inoculation with Bradyrhizobium lupini vs. 80 mg NH4NO3‐N kg−1) on growth of ‘Kiev’ white lupine on a Wheatville loam (coarse‐silty over clayey, frigid, Aeric Calciaquoll) low in available P, Fe, and N. Yield of white lupine shoots was increased by Fe and P fertilizers but was unaffected by N source. Wheat (Triticum aestivum L.) gave a three‐fold increase to N fertilizer under similar conditions. Inoculated white lupine plants were nodulated but uninoculated ones were not. Number and weight of nodules were stimulated more than twofold by application of Fe and P fertilizers. Plants without added Fe displayed leaf chlorosis that was increased by P and N fertilizers and decreased by added Fe and advancing plant age. The incidence of proteoid roots encased in hard‐to‐remove soil was depressed more than two‐thirds by P fertilizer, but was stimulated by inoculation. Concentration of Mn in white lupine shoots was depressed by P fertilizer, stimulated by inoculation, and little affected by added Fe. Iron deficiency detrimentally affected the growth of white lupine on the Wheatville soil, and its severity was intensified by N and P fertilization.
Chemistry of Smectitic and Illitic Phases in Interstratified Soil Smectite
Authors: Laird D. A. , Barak P. , Nater E. A. , Dowdy R. H. 
Published: July 2010

AbstractThe objective of this investigation was to determine the elemental composition and mineralogy of the smectitic and illitic phases in interstratified smectite‐illite from a typical upper Midwestern agricultural soil. A sample of soil clay (<2‐µm fraction) from the Ap horizon of a Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) pedon was fractionated by centrifugation to prepare various fine‐clay (<0.020‐, <0.026‐, <0.036‐, <0.045‐, <0.060‐, and <0.090‐µm size fractions) samples. X‐ray diffraction analyses indicated that interstratified smectite‐illite was the only mineral present in significant quantities in the fine‐clay samples. Elemental analyses of the fine‐clay samples were performed by inductively coupled plasma‐atomic emission spectroscopy using suspension nebulization. The elemental analyses revealed significant linear correlations for the K vs. other element relationships (P < 0.001 for K vs. Si, Al, Fe, Ca, Ti, Mn, and Zn, and P < 0.01 for K vs. Mg). A nonlinear parameter optimization technique, based on elemental mass balance, was used to estimate the elemental compositions and proportions of the smectitic (K‐free) and illitic (K‐bearing) phases in the fine‐clay samples. The results for the elemental mass balance optimization were independently verified by water mass balance. The smectitic phase was a high‐charge (0.482 per formula unit), Fe‐rich montmorillonite (46.6% tetrahedral charge). The illitic phase consisted of dioctahedral, tetrahedrally charged (86.9% tetrahedral charge) elementary illite particles. Layer charge for the illitic phase was 0.473 per formula unit, which is substantially below the lower limit for classification of illite. The interstratified smectite‐illite comprised at least 60% of the whole (<2‐µm fraction) soil clay and the illitic phase comprised at least 36% of the interstratified smectite‐illite.
Solute Transport in a Two‐Layer Medium Investigated with Time Moments
Authors: Leij Feike J. , Dane J. H. 
Published: July 2010

AbstractThe study of solute transport in porous media requires knowledge of the transport parameters. These transport parameters can be determined from data collected during displacement experiments using a number of mathematical procedures, among them the moment method. An advantage of this method is that it can also be used to theoretically analyze, and therefore enhance our understanding of, transport problems. We present theoretical time moments as derived from analytical solutions of the advection‐dispersion equation in the Laplace domain for a step‐ and pulse‐type solute input applied to a two‐layer soil with steady flow transverse to layering. These moments were used for investigating the mean breakthrough time, µ1, and variance, µ2. It was shown that, theoretically, more retardation and spreading occurs for a third‐ than for a first‐type boundary condition, but that the presence of the interface, as such, does not affect spreading for either boundary condition.
Tensile Strength of Thirty‐Three Saturated Repacked Soils
Authors: Nearing M. A. , Parker S. C. , Bradford J. M. , Elliot W. J. 
Published: July 2010

AbstractInteraggregate strength in saturated soils is important in terms of erosion processes and surface sealing during rainstorms. The objective of this study was to ascertain the soil properties that influence interparticle binding of unconsolidated, saturated soil as measured by tensile failure of disturbed samples. Tensile strength of 33 soils was measured in the laboratory. The measurements were performed on 0‐ to 1‐mm, 2‐ to 4‐mm, and mixed aggregate size class materials. Factor analysis was used to understand the patterns of relationships and correlations among all the variates, and then to select appropriate variables (from among 39 measured soil properties) for use in regression relationships for tensile strength. Clay amount and surface properties were dominant in terms of explaining the variance of tensile strength. Other important factors included variables related to soil dispersion (Na and Na‐adsorption ratio), silt, coarse sand, aggregation, and electrical conductivity. This study presents the use of a laboratory tensile test for loose, saturated soil as applied to a wide variety of soil types from across the USA.
Cesium‐Adsorption Method for Measuring Accessible Structural Surface Charge
Authors: Anderson Sharon J. , Sposito Garrison 
Published: July 2010

AbstractMeasurements of the separate contributions of structural and pH‐dependent charge are essential to understanding and predicting surface‐chemical reactions in soils and other heterogeneous adsorbents that contain a mixture of surface functional groups. An ion‐adsorption method was developed to measure the accessible structural charge density (σ0) in adsorbents that comprise both structural‐charge and variable‐charge surface functional groups. The method is based on the preference of siloxane surface sites for Cs+ over Li+ and on the much lower selectivity of ionizable surface groups for Cs+. To estimate σ0, CsCl‐saturated adsorbents were reacted with 0.05 mol CsCl kg−1 at pH 7, washed with ethanol to reduce the entrained CsCl concentration, dried at 65 °C to promote the formation of inner‐sphere surface complexes between Cs+ and permanent‐charge sites, and then extracted with 0.01 mol LiCl kg−1 to displace Cs+ from variable‐charge adsorption sites, which exhibit little or no preference for Cs+ over Li+. Finally, Cs+ was displaced from permanent‐charge sites by repeated NH4OAc extraction until no Cs was present in the equilibrium supernatant solution. According to this method, σ0 represented about 85 and 70% of the accessible cation‐adsorption sites at pH 7 on <2‐µm Wyoming montmorillonite and <106‐µm Silver Hill illite, respectively; 15% and 30%, respectively, were variable‐charge sites. These results were consistent with published reports of the amount of pH‐dependent cation adsorption on montmorillonite and with model calculations of the relative contributions of edge and structural charge in montmorillonite and illite. When the method was used to measure Cs‐accessible σ0 in four soils, the percentage of structural charge ranged from 1% in an Oxisol to 65% in an Alfisol. The method is appropriate for adsorbents that contain montmorillonite, illite, and repotassified (nonexpandable) vermiculite. It may be suitable for adsorbents that contain clay‐sized, but probably not coarse‐grained, expandable vermiculite.
Electrolyte Concentration and Composition Effects on Sulfate Sorption by Two Spodosols
Authors: Courchesne François 
Published: July 2010

AbstractFew reports exist on the influence of electrolyte concentration and composition on SO4 retention, although sorption experiments have been conducted with a variety of supporting electrolytes. Sulfate sorption by the B horizon of two forest Spodosols from Quebec was measured as a function of supporting electrolyte concentration and cationic composition, solution pH, and reaction time. The solutions had an ionic strength (I) of ≈0 (deionized H2O), 0.001, 0.01, 0.1, and 1.0 M NaCl, 0.01 M KCl, and 0.01 M CaCl2. Increasing the ionic strength of the electrolyte (NaCl) always decreased SO4 sorption at pH 4.25. It was proposed that increased Cl‐ ion competition for sorption sites and the formation of NaSO‐4 aqueous complexes (2.8, 14, and 55% of total SO4 at 0.01, 0.1, and 1.0 M NaCl) contributed to the observed trend. Increasing electrolyte concentration also lowered SO4 sorption by both horizons in the range of pH 3.0 to 5.2. Moreover, the influence of pH on sorption was more pronounced at low electrolyte concentration. At a constant I value, the cationic composition of the electrolyte also had an impact on SO4 sorption. The presence of Ca2+ and K+ favored sorption, compared with Na+. A mechanism involving the formation of a surface complex between Ca2+ or K+ and SO2‐4 is proposed to explain the experimental data. The results of this study support the hypothesis that the composition and concentration of the electrolyte influence SO4 sorption by Spodosols and that both should be considered when comparing the SO4‐sorption capacity of soil materials from distinct experiments or when projecting laboratory results to field conditions.
Zinc Sorption by B Horizon Soils as a Function of pH
Authors: Stahl Randal S. , James Bruce R. 
Published: July 2010

AbstractBetter information is needed to predict how soil acidity affects exchangeability of heavy metals in soils dominated by Fe and Mn oxides with pH‐dependent charge. Our laboratory study sought to separate exchangeable and nonexchangeable Zn sorbed by four B horizon soil materials with varied mineralogy and sesquioxide contents. A Myersville silt loam (fine‐loamy, mixed, mesic Ultic Hapludalf), a Jackland sandy loam (fine, mixed, mesic Aquic Hapludalf), a Christiana sandy loam (clayey, kaolinitic, mesic Typic Paleudult), and an Evesboro loamy sand (mesic, coated Typic Quartzipsamment) were compared for the exchangeability of Zn as a function of pH. Surface charge was measured across the pH range of 3.5 to 7.6, a 175 µmol ZnCl2/kg soil treatment was applied, and sorbed Zn was exchanged with K. Cation‐exchange capacity (CEC) was positively correlated with nonexchangeable but not with exchangeable Zn forms. All four soils retained nearly the same amount of Zn, even though CEC ranged from <10 to >80 mmolc/kg. An abrupt transition from exchangeable to nonexchangeable Zn occurred in the pH range 5.6 to 5.9 of the Myersville, Evesboro, and Christiana soils. Differences in oxide mineralogy and proton buffering intensity appeared more important than CEC as controls on the exchangeability of Zn in these soils. This result is germane to predicting retention of heavy metals in sewage‐sludge‐amended agricultural soils.