bluuebunny/crossref_metadata_2025_split huggingface dataset:
Competing Metal Ion Influences on Chromium(III) Oxidation by Birnessite
Authors: Fendorf Scott E. , Zasoski Robert J. , Burau Richard G. 
Published: July 2010

AbstractThe oxidation of Cr(III) to Cr(VI) presents a significant environmental hazard due to the much greater mobility and toxicity of Cr(VI). Despite the importance of Cr(III) oxidation, many factors influencing this important chemical process in soils and waters remain unknown. In this study we investigated the effects of competing metal sorbates on Cr(III) oxidation by δ‐MnO2. Aluminum, La, Co(II), Mn(II), and Cr(VI) were reacted with δ‐MnO2 prior to the addition of Cr(III). Only Al affected the extent of Cr(III) oxidation at pH ≥ 4, and at pH 5 the presence of Al, with 2.84 µmol Cr(III) initially present, decreased oxidation from 2.80 to 0.28 µmol Cr(VI). None of the competing ions influenced the degree of oxidation at pH 3. Neither of the oxidation reaction products, Mn(II) or Cr(VI), affected the extent of oxidation. Electrokinetic investigations revealed that both Al and La induced a charge reversal on δ‐MnO2. As pH increased from 3 to 5, the electrophoretic mobility (EM) of δ‐MnO2 sharply increased at pH 4 in the presence of 2.90 × 10−4 M Al. The sorption behavior and influences on EM of Al indicate that a surface alteration occurs whereby the oxidizing ability of δ‐MnO2 (birnessite) is inhibited. High‐resolution transmission electron microscopy revealed that an Al‐hydroxide surface precipitate formed on δ‐MnO2, thus accounting for the sorption, EM trends, and Cr(III) oxidation inhibition.
Nitrate Dynamics during the Aerobic Soil Phase in Lowland Rice‐Based Cropping Systems
Authors: George T. , Ladha J. K. , Buresh R. J. , Garrity D. P. 
Published: July 2010

AbstractIn tropical rice (Oryza sativa L.) lowlands, soil NO3 is lost during the transition from the dry to the wet season. To understand how soil and crop management influences NO3 loss, we examined NO3 dynamics during a 2‐yr period in an Alfisol in the Philippines: weedy, weed‐free, and frequently tilled main plots during the February to May dry season (DS), and Sesbania rostrata (Brem. & Oberm), mungbean [Vigna radiata (L.) R. Wilczek var. radiata], weedy, and weed‐free subplots during the May to July dry‐to‐wet transition (DWT). Weed‐free plots were maintained by removing weeds as they emerged. Soil NH4 (0–60 cm), which was not affected by management, averaged only 9 kg N ha−1. While soil NO3 increased under frequent tillage and weed‐free fallowing, it decreased rapidly under weedy fallowing. On most sampling dates, NO3 was the highest in DS tilled main plots. The widest range of NO3 during the DS or DWT was 14 to 110 kg N ha−1 in the first year, and 12 to 155 kg N ha−1 in the second. During the second half of the DWT, NO3 declined in all plots, but more markedly when plants were present than when not, indicating plant N uptake. Above‐ground plant N prior to permanent flooding ranged widely from 31 kg N ha−1 in weeds to 222 kg N ha−1 in N2‐fixing S. rostrata plants in the first year, and 37 to 193 kg N ha−1 in the second. The data also indicate NO3 leaching following heavy rains. Further, the high water‐filled pore space, exceeding 0.7 L L−1 in the second half of the DWT and approaching 1 L L−1 with permanent flooding, is presumed to have favored denitrification. Regardless of DS management or DWT plant N accumulation, the soil was virtually depleted of NO3 soon after permanent flooding; NO3 rarely exceeded 10 kg N ha−1 when measured after 9 d (first year) and 11 d (second year) of permanent flooding. Our data indicate the immense capacity of this lowland soil to accumulate NO3 and the marked effect of DS and DWT management on the amount of NO3 that actually accumulates. In tropical rice lowlands, soil and crop management during the DS should be designed to limit NO3 buildup so as to reduce NO3 that is prone to loss during the DWT.
Tillage and Winter Wheat Residue Management Effects on Water Infiltration and Storage
Authors: Dao Thanh H. 
Published: July 2010

AbstractIn traditional winter wheat (Triticum aestivum L.) cropping regions of the southern Great Plains, production constraints exist because of extreme variability in precipitation during planting periods. Intensive tillage aggravates dry early fall conditions to further hamper wheat emergence and growth. From 1983 through 1991, we determined the effects of three tillage and residue management practices on soil water storage in Bethany (fine, mixed, thermic Pachic Paleustoll) and Renfrow (fine, mixed, thermic Udertic Paleustoll) silt loams on a 2% slope near El Reno, OK. We measured soil management cumulative effects on soil bulk density and water infiltration during and after the 1990–1991 growing season. Every season, no‐till soil consistently had higher volumetric water content in the 0‐ to 1.2‐m depth, except in late fall or early spring when root‐zone recharge took place for both soils. The gain was corroborated by increased water‐holding capacity and decreased bulk density of no‐till soils. Seasonal variability of field infiltration was more evident in plowed soil than in no‐till soil. Such temporal dependence would affect surface distribution and flow of precipitation to explain differences in runoff, soil erosion, and environmental impacts of tillage systems between October and June. Water infiltration into no‐till soil was significantly higher than into plowed soil at similar water contents. Under ponding, recharge occurred through macropores, directly wetting depths of 0.4 to 0.6 m of no‐till soil, in contrast to a layered pattern in plowed soil. The phenomenon has many implications on profile recharge rate and solute transport in the field. Therefore, elimination of inversion tillage enhanced precipitation storage, thereby alleviating detrimental effects of climate variability in annual winter wheat cultivation.
Environmental Tracers for Water Movement in Desert Soils of the American Southwest
Authors: Phillips Fred M. 
Published: July 2010

AbstractTritium and 36Cl from nuclear weapons testing fallout can serve as tracers for water and solute movement in desert soils on the time scale of decades. Chloride deposited from the atmosphere can provide a tracer for much longer periods. We reviewed and compared studies using these tracers at locations across the southwestern USA in order to assess the controls on water and solute movement across time scales ranging from decades to millennia. The displacements of all the tracers were quite similar despite variations in location, climate, and soil properties. The time‐averaged 36Cl fallout transport rate velocity is 23 ± 17 mm yr−1. The Cl concentration profiles indicate that, prior to about 15 000 yr ago, soil‐water fluxes were approximately 20 times the magnitude of modern fluxes, and that the soil water shifted rapidly (on a geological time scale) to the dry regime between 16 000 and 13 000 yr ago. The remarkable uniformity of the water and solute transport processes across the region may be dictated by the water extraction efficiency of the vegetation.
The Feasibility of Recharge Rate Determinations Using the Steady‐State Centrifuge Method
Authors: Nimmo John R. , Stonestrom David A. , Akstin Katherine C. 
Published: July 2010

AbstractThe establishment of steady unsaturated flow in a centrifuge permits accurate measurement of small values of hydraulic conductivity (K). This method can provide a recharge determination if it is applied to an unsaturated core sample from a depth at which gravity alone drives the flow. A K value determined at the in situ water content indicates the long‐term average recharge rate at a point. Tests of this approach have been made at two sites. Unsaturated K values were measured easily for sandy core samples from a site in the San Joaquin Valley of California. The results indicate that a better knowledge of the matric pressure profiles is required before a recharge rate can be determined. Fine‐textured cores from a site in southeastern Washington required new developments of apparatus and procedures, especially for making centrifuge measurements with minimal compaction of the samples. Measured K values led to preliminary recharge rate determinations that are reasonable considering the known hydrology and topography of the site.
Accumulation of Water in Soils under Gravel and Sand Mulches
Authors: Kemper W. D. , Nicks A. D. , Corey A. T. 
Published: July 2010

AbstractOpportunities to influence the portion of the precipitation that percolates through the soil to aquifers lie primarily in the management of vegetation to control transpiration and of the surface to control infiltration and evaporation. Rates of percolation and recharge are of major interest to those concerned with the quantity and quality of water in our aquifers. Evaporative loss, precipitation, and water accumulation were measured on 0.9‐m‐long columns containing soil topped by sand and gravel mulches in the field for 388 d. Results show evaporation reductions due to gravel and sand mulches of differing thickness, color, and particle size on soil surfaces. These data show effects of mulch thickness, particle size, and color on the steady and transient components of evaporation and provide coefficients for equations to help predict effects of such mulches on evaporation and accumulation of water in soils and aquifers. Gravel mulches 5 cm thick resulted in accumulation of 80 to 85% of the annual precipitation.
Groundwater Mounding below a Surface Line Source in a Typic Fragiudalf
Authors: Daniels M. B. , Fritton D. D. 
Published: July 2010

AbstractNearly one‐third of the soils in Pennsylvania contain fragipans. Onsite sewage disposal systems on these soils historically have been failure prone. This leads to a public health hazard due to contamination of surface and groundwaters with unrenovated effluent. In order to gain a better understanding of water flow in a soil that contains a fragipan, a field study was conducted to determine in situ, two‐dimensional, steady‐state water flow patterns from a surface line source. Tensiometers were used to determine the soil water pressure head distribution for five application rates ranging from 125 to 625 mm d−1 in 125 mm d−1 increments. Field results indicated that steady‐state groundwater mounds (mound‐shaped regions of saturation) developed for all application rates because of the reduced permeability of the fragipan and the presence of small lateral hydraulic gradients on either side of the saturated region. Field results were simulated with a finite difference solution of the steady‐state Richards' equation. Simulated results agreed well with field measurements within the region of saturation for the three highest application rates. However, the model underpredicted the height of the mounds for the two lowest application rates. The application rate both experimentally and theoretically seemed to have little influence on the hydraulic head beyond 2 m laterally in either direction from the source.
Profile Nitrous Oxide and Carbon Dioxide Concentrations in a Soil Subject to Freezing
Authors: Burton D. L. , Beauchamp E. G. 
Published: July 2010

AbstractSoil is an important source for the production of greenhouse gases such as CO2 and N2O. Significant temporal trends exist in the production and concentration of these gases in temperate climates where soils are subject to freezing. We examined the effect freeze‐thaw cycles had on soil profile CO2 and N2O concentrations. A multilevel sampling probe was designed to allow sampling the atmosphere composition of soil profiles. Changes in CO2 and N2O gas concentrations in the profile of a loamy sand were studied during two winter periods. Fluxes of N2O were strongly influenced by the formation of a frozen layer that segregated the soil profile into two distinct regions. The surface region was characterized by brief, intense events, which contribute to highly variable CO2 and N2O concentrations near the surface. The subsurface region beneath the ice layer allowed N2O accumulation. The highest concentrations of N2O were observed in the subsurface region following ice‐layer formation, indicating that N2O production is not restricted to surface horizons in this soil. Thawing of the frozen layer in the spring resulted in the release of N2O from the subsurface region. The formation of a frozen layer influenced subsurface CO2 accumulation through its influence on water percolation.
Comparison of Lysimeter Types in Collecting Microbial Constituents from Sewage Effluent
Authors: Krejsl Jana , Harrison Rob , Henry Chuck , Turner Nedda , Tone Dennis 
Published: July 2010

AbstractThere are no standard methods of determining the impact of septic systems on contamination of groundwater aquifers. Sampling of water for microbiological properties in unsaturated soil is particularly difficult. Successful water sampling devices should collect large amounts of percolating water with minimal change in chemical and biological properties of the water. This laboratory study compared the effectiveness of four types of soil water sampling devices for qualitative sampling of water, using total coliform, fecal coliform, and fecal streptococcus as the primary indicators of water quality. The devices tested were: (i) high‐flow ceramic tension lysimeter, (ii) high‐flow fritted glass tension lysimeter, (iii) sand‐filled lysimeters, and (iv) perforatedtube wells. A constant source of vacuum (0.01 MPa) was applied to all devices to collect water samples. High‐flow ceramic tension lysimeters collected adequate volumes of water (an average of 0.340 L after 6 h) but excessive filtering led to underestimation of microbial numbers (only 6% of total coliform, 2.2% of fecal coliform, and no fecal streptococcus were collected). Perforated‐tube wells did not collect any water under partially saturated soil conditions; collection occurred only below the water table. Sand‐filled lysimeters showed the best combination of volume collection (an average of 0.660 L after 6 h) with good estimation of microbial numbers (90% for total coliform, 83% for fecal coliform, and 45% for fecal streptococcus).
Map Unit Development for Sand‐ and Gravel‐Pit Soils in New Hampshire
Authors: Strain M. R. , Evans C. V. 
Published: July 2010

AbstractCurrent growth rates of human population have increased the areal extent of anthropogenic soils. One of the most important aspects of this disturbance is the creation of new soil surfaces and landscapes, most of which are not currently characterized, classified, or mapped in sufficient detail to develop adequate interpretations for subsequent uses. We characterized 20 pedons in four abandoned sand and gravel pits in order to determine which physical, chemical, and morphological properties were most useful in the development of soil map units and interpretations. Organic C and bulk density values significantly differentiated groups of pedons, and we expanded on concepts presented by others by using bulk density and organic C to define great groups and subgroups. The resulting classes reflect soil characteristics that are important for use and management of these soils, and are also more connotative of soil genesis than the names “pits”, “gravel”, or “Udorthents”, which are used in most soil survey legends.
Use of Theissen Areas in Models of Nutrient Uptake in Forested Ecosystems
Authors: Porter P. S. , Comerford N. B. , Escamilla J. A. 
Published: July 2010

AbstractNutrient uptake models have generally incorporated simplifying assumptions, one of which is that roots are regularly arrayed in space. This allowed an evaluation of an average root to be extrapolated to a whole plant by simply multiplying the single root result by the total root length. In low‐fertility soils, particularly those with very low buffer powers, this regular root assumption causes nutrient uptake to be overestimated. Nutrient uptake models would be more realistic if Theissen areas were used as the area of influence of roots. A computer program for computing Theissen maps for a hydrological application has been adapted, tested, and applied to nutrient uptake by roots in a forested ecosystem. Nutrient uptake using Theissen areas is compared with uptake based on the assumption of regularly arrayed roots and with worst‐case situations of uptake influenced by nearest‐neighbor roots. For slash pine (Pinus elliottii Engelm. var. elliottii) growing on a Spodosol of the lower Coastal Plain of the USA, root patterns of the A horizon have been found to be random, not regular. Computer simulations of nutrient uptake showed that the average root procedure was appropriate for K under the conditions investigated, but suggested that P uptake would be overestimated unless the spatial pattern of roots was included. Ratios of Theissen radii to 1/2 nearest neighbor distances show that root areas of influence tend to be noncircular or that roots are eccentrically positioned, either of which are violations of assumptions used in nutrient uptake models.
Downed Bole‐Wood Decomposition in Lodgepole Pine Forests of Central Oregon
Authors: Busse M. D. 
Published: July 2010

AbstractInput of decaying wood from natural disturbances may benefit nutrient cycling processes in lodgepole pine [Pinus contorta var. murrayana (Grev. & Balf.) Engelm.] forests of central Oregon by supplementing detrital C and nutrient pools. This study was conducted to determine the decomposition rate and nutrient retention of downed lodgepole pine boles, and to characterize their effect on soil biological and chemical properties. Three sites, in stands recently damaged by insects, had an average downed wood biomass of 38.7 Mg ha−1. Bole‐wood decay was rapid once in contact with the soil surface. The decomposition rate constant based on the single‐exponential decay model was 0.027 yr−1 and the turnover time of C was 37 yr. Nitrogen content per unit volume was 75% greater for downed boles after 38 yr of decay compared witb their initial content. A net release of Ca (38%), Mg (54%), and K (42%) was found, but P content remained constant during decomposition. With the exception of Mg, however, downed boles comprised <3% of the combined mineral soil, O horizons, and downed wood nutrient pool. In comparison, downed boles comprised 23.5% of the detrital C. Microbial biomass C (CM) and the ratio of microbial C to total organic C (CM/CT) were significantly greater in the surface 0 to 4 cm of soil beneath rapidly decaying boles than in soil without a bole‐wood component. The CM/CT ratio remained elevated throughout the advanced stages of wood decomposition, indicating a long‐term change in the efficiency of C utilization by soil microbial communities associated with decaying wood.
Effect of Tensiometer Cup Size on Field Soil Water Tension Variability
Authors: Hendrickx J. M. H. , Nieber J. L. , Siccama P. D. 
Published: July 2010

AbstractReliable estimates of soil water tension in field soils using few tensiometers are often difficult to obtain because of the large spatial variability of soil water tensions. Therefore, the objective of this study was to evaluate the effect of tensiometer cup size on soil water tension variability. We installed three sets of tensiometers with different effective outside cup surface areas (4.8, 42.3, and 88.3 cm2) in a silty clay loam that was flood‐irrigated for sorghum [Sorghum bicolor (L.) Moench] production. During a period of 10 mo, soil water tensions were measured with a tensiometer under fallow and cropped conditions on 71 nonconsecutive days. We found that an increase in tensiometer cup size reduced the variability of soil water tension measurements. This reduction in variability suggests that the medium cup size (42.3 cm2) extensively used for irrigation scheduling and environmental monitoring, is rather small and consequently causes a relatively large variability. Therefore, the medium cup should be replaced by a larger cup size. We also demonstrate that a logarithmic transformation of the water tensions is necessary to stabilize their variance and to allow pooling of the variances. The use of larger tensiometer cup sizes and the pooling of variances of log‐transformed soil water tension measurements will lead to a lower number of tensiometers per irrigated field or environmental site.
Organic Matter Comparison of Wettable and Nonwettable Soils from Bentgrass Sand Greens
Authors: Hudson R. A. , Traina S. J. , Shane W. W. 
Published: July 2010

AbstractPrevious studies have attributed hydrophobicity in sandy soils to alkaline extractable macromolecular complexes, as well as lipid fractions, but have not included wettable soils for comparison. Our study was conducted to compare the alkaline‐extractable and lipid fractions of a nonwettable soil to a wettable soil from creeping bentgrass (Agrostis stolonifera L. var. stolonifera) sand greens. Samples were collected from two sites and several extraction sequences performed on each. Humates were extracted in 1.25 mol L−1 NaOH. Alkaline‐extractable fractions were separated by precipitation with 6 mol L−1 HCl. Acid precipitated and nonprecipitated fractions were purified, lyophilized, and analyzed by Fourier transform infrared spectroscopy. In addition, the acid nonprecipitated fractions, which included fulvic acids, were analyzed by solid‐phase 13C nuclear magnetic resonance spectroscopy. Lipid fractions were extracted with a soxhlet apparatus using either hexane or methanol as solvent. Lipid fractions were analyzed by gas chromatography‐mass spectroscopy. No qualitative differences were observed with Site 1 extracts, and it appeared that hydrophobicity may have been at least partly due to physical or structural differences. Qualitative differences were observed with Site 2 extracts when initially extracted with methanol.
Stability Constants of Pseudobactin Complexes with Transition Metals
Authors: Chen Yona , Jurkevitch Edouard , Bar‐Ness Eli , Hadar Yitzhak 
Published: July 2010

AbstractThe stability constants of the fluorescent siderophore pseudobactin St3 (PSB3) produced by Pseudomonas putida strain 3 with Fe3, Cu2+, Mn2+, Zn2+, and Fe2+ were determined using fluorescence spectroscopy and potentiometric titrations. Stability constants for PSB3, with Fe3+, Fe2+, Mn2+, and Zn2+ were determined based on titration to saturation of a PSB3 ligand solution with either of the metals, then back‐titrating the solution with an EDTA solution along with simultaneous measurements of fluorescence and visible spectra. A nonlinear curve fitting between the fluorescence intensity (Y) and the concentration (C) of the metal or EDTA was used for the determination of the concentrations of the free and complexed ligands. The overall stability constant (log KML) obtained for Fe3+ by this method was the same as that obtained by visible spectrosopy. The log KML. values obtained by fluorescence spectroscopy for Mn2+ and Zn2+ (17.5 and 19.4, respectively) were in good agreement with log KML values obtained by potentiometric titration (17.3 and 19.8, respectively). It was found that two chromatography bands obtained from PSB3 solutions isolated and purified from cultures grown under different conditions chelated Fe3+ with practically the same affinity. The log KML of PSB3 with Fe3+, Zn2+, Cu2+, Mn2+, and Fe2+ were calculated using the protonation constants determined by potentiometry (pKa1 = 11.28, pKa2 = 7.74, pKa3 = 5.35) and were found to be 29.6, 19.8, 22.3, 17.3, and 8.3, respectively.