摘要:

Estimating unsaturated hydraulic conductivity often relies on using water retention characteristics. Because the water retention curves do not provide information about the pore connectivity, an empirical correction is used in capillary bundle models that are fitted to unsaturated hydraulic conductivity data. The majority of authors have applied the macroscopic correction expressed as a function of water content. A microscopic correction term expressed as a power function of a pore radius was proposed in the literature but was not tested with a large representative soil data set. The purpose of this work was to apply the "hydraulic conductivity-water retention" model with the microscopic connectivity correction to a large data set to see what accuracy can be achieved and whether it is possible to relate the connectivity parameters to some readily available soil properties. Data for 147 soil horizons were extracted from the unsaturated soil hydraulic database UNSODA. Water retention and hydraulic conductivity data were in the range of capillary pressures >5 kPa and from 5 to 200 kPa, respectively. The model provided an accurate approximation, and root mean square error (RMSE) in estimated log10kwas 0.21. Two parameters of the model appeared to be correlated closely so that using only one connectivity parameter was sufficient. Reducing the number of parameters from two to one and refitting the one-parametric model to data decreased the accuracy of the estimates. The RMSE increased from 0.21 to 0.31. That only one empirical parameter was needed to describe the unsaturated hydraulic conductivity helps to reduce the number of measurements of this hydraulic property because a single parameter can be estimated from a limited number of observations.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Apatite has been used to remediate Pb contamination; apatite dissolution releases phosphate, which combines with Pb to form highly insoluble Pb-phosphate minerals. This research focused on the effects of aqueous Pb (initial [Pbaq] = 0.185 mM) on the kinetics of apatite dissolution. Synthetic microcrystalline hydroxylapatite (HAP) and natural chlorapatite (CAP) and fluorapatite (FAP) were used in batch experiments at 22°C, with pH within the range of 4.2-7.0, and in the presence of aqueous Cl. In these batch experiments, apatites followed linear (zeroth-order) dissolution kinetics. Dissolution experiments were performed using 1 g apatite/L for all three apatites. When dissolution rate constants (kAP) are adjusted for particle specific surface area (As), kCAP> kFAP> kHAP.In the presence of Pbaqand Cl, all three apatites reacted to form pyromorphite (PY; Pb10(PO4)6Cl2). Rates of Pbaquptake by the apatites decreased in the same order as the apparent (not normalized for As) dissolution rate constants of apatite (kAp°): HAP > CAP > FAP, suggesting that Pbaquptake is controlled by the total amount of dissolved phosphate in the system. While HAP and CAP removed more than 98% of Pbaqduring 2 weeks of the experiment, FAP decreased the initial [Pbaq] by ∼30%. Pb uptake rates calculated on a molar basis correlated with Ca release rates. Concentration of dissolved phosphate during the reaction with Pbaqwas below the detection limit of 10−7mol/L. Phosphate concentration was probably controlled by solute equilibrium with precipitating PY, which has very low solubility (log Ksp= −167). This indicates that the rate-controlling step was apatite dissolution.The presence of Pbaqincreased apatite batch dissolution rates, most probably because formation of PY acted as a sink for dissolved phosphate, hence increasing the thermodynamic drive for dissolution. Although PY formed heterogeneously on the surfaces of apatite particles, the PY did not prevent continued apatite dissolution.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

The nature of oxide in soil and associated environments in influencing the abiotic transformations of polyphenols still remains to be established. The objective of this study was to investigate the catalytic power of Mn(IV), Fe(III), Al, and Si oxides in the abiotic ring cleavage of pyrogallol and the polycondensation of the resulting fragments in air and N2atmosphere. The catalytic power varied greatly with the nature of the oxides. The synergistic effects of oxygen molecules and oxides also played an important role in affecting the transformations of pyrogallol. The results indicate that the release of CO2as a result of ring cleavage of pyrogallol enhanced the development of carboxylic group contents of humic polymers formed in the reaction systems. The abiotic ring cleavage of polyphenols catalyzed by soil inorganic components such as short-range ordered oxides of Al and especially Fe and Mn may account, in part, for the carboxylic group contents and the origin of the aliphaticity of humic substances in soils.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Concern over the transport of phosphorus from agricultural soils to surface waters has focused attention on the role of soil phosphorus in environmental risk assessment. This study explores the existence of natural soil phosphorus thresholds as expressed by Quantity/Intensity relationships. Fifty-nine samples, collected from agricultural soils in New York's Delaware River Watershed, were analyzed for Morgan, Mehlich III, and 0.01MCaCl2extractable P. Soil P sorption saturation was calculated as a function of oxalate extractable P, Fe, and Al. In addition, P sorption isotherms were determined for all soils. Thresholds in the relationships between CaCl2P and Morgan P, Mehlich III P, and P sorption saturation were identified by segmented linear regression (change point analysis). Thresholds in the relationship between CaCl2P and Morgan P, Mehlich III P, and P sorption saturation occurred at CaCl2P concentrations of 0.9 mg kg−1, suggesting a threshold for soil P that may have use in environmental risk assessment. A P sorption threshold was also identified by segmented, quadratic-linear regression of the sorption isotherms. Results described a fundamental property of soils: a nonlinear sorption of P in soils that exhibits a threshold, above which the potential for P release from soil to water increases. This threshold describes a critical point in the release of P and, therefore, may be of environmental importance in estimating the potential for soluble P loss from soil by runoff and leaching.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

A study was made of the adsorption and mobility of the fungicide penconazole (1-[2-(2,4-dichlorophenyl)pentyl]-1H-1,2,4-triazole) in 19 vineyard soils with low organic matter contents (0.31-1.98%) and in seven uncropped soils from oak and beech forests or grasslands with higher organic matter contents (3.30-8.24%). Adsorption isotherms were obtained using the batch equilibrium technique, and mobility was studied using soil thin layer chromatography. The aim of this study was to evaluate the adsorption and mobility behavior of this relatively new fungicide in vineyard soils. The adsorption isotherms fit the Freundlich adsorption equation, the Kf values ranged between 10.3 and 151, and the nf values were always lower than unity. The Kf constants were correlated positively with the soil organic matter content. According to ther2determination coefficients, the organic matter content accounted for 85% of the variance in adsorption when all soils were considered together and for 76% and 36%, respectively, when considering the natural and vineyard soils. In no case was any influence of clay or silt contents on adsorption observed. According to the Rf values obtained, penconazole is immobile in 8% of soils and slightly mobile in 92% of soils. Adsorption of the fungicide by individual soil components, clay minerals and humic acid, confirms the importance of the organic matter fraction as the only soil parameter that affects adsorption. The results obtained indicate that vertical leaching of penconazole is low. The fungicide may, however, cause surface pollution of the soil because of its accumulation. If its degradation rate is low, this accumulation may lead to the pollution of surface water through runoff of the sorbed pesticide.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Soil-landscape models have prediction errors that can be reduced by using auxiliary soil data. However, standard soil surveys using auger hole and laboratory analysis encounter both methodological and economical constraints because of, for example, the short-range variability of soils and the expensive field work. In the present study, the objective was to test the use of auxiliary geophysical data to improve a soil-landscape model for two Digital Elevation Model (DEM) resolutions (10 and 50 m). The study site was an agricultural parcel comprising an entire hillslope of a small (0.6 km2) catchment in Normandy, France. Prediction models based on multiple regression and co-kriging techniques were established using topographic, soil and geophysical data. For high DEM resolution (10 m), soil-landscape models based only on surface features seemed to be efficient. The use of additional geophysical or soil data improved the prediction quality slightly. For coarser DEM (50-m resolution), the prediction quality of models established using only terrain attributes was faulty. The soil hydromorphic prediction could be improved greatly by the use of auxiliary geophysical data. In this case, the improved accuracy was similar to that obtained by high soil density data (50 observations/ha). Finally, we discuss the use of both geophysical and topographical data in order to describe better the spatial distribution of soils.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

An important issue in the making of soil surveys is quantifying the value of the information generated and contained in the soil survey. This study uses decision trees, Bayes' Theorem, and map quality evaluation procedures to assess the economic value and economic efficiency of soil surveys. To develop this methodology, a case study is used that considers three different scenarios in which the level of information regarding soil changes. The three scenarios are: (i) site-specific soil information is unavailable, (ii) perfect site-specific soil information is available (not realistic), and (iii) imperfect site-specific soil information is available. The calculated economic value of this hypothetical soil survey was US$ 17.14 ha−1year−1, which is higher than the estimated soil survey cost of US$ 2.09 ha−1. This simple comparison indicates that the soil survey is cost effective and that its costs would be paid off with the gain from the first year of its application. The combination of the calculated economic efficiency (55%) with the physical quality of the map (total percent correct in the map was 80%) allowed a better understanding of the actual value of the soil survey. The use of this method provided a means of calculating analytically a more complex and realistic value of soil surveys.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID