摘要:

The main objectives of the present work were to evaluate the compositional and functional differences between a sewage sludge humic acid (HA) and nonamended soil HA and to determine the effects of various sewage sludge amendments on the composition, structure, and chemical properties of HAs from uncultivated and cultivated soils. For this purpose, the HA fraction was isolated by conventional methods from a sewage sludge used as soil amendment, the nonamended soil, and soils amended with two rates of dewatered and liquid sludges, either in the presence or absence of barley. The HAs isolated were characterized comparatively for their compositional, structural, and chemical properties by use of elemental analysis and by Fourier Transform infrared (FT IR), fluorescence, and electron spin resonance spectroscopies. The sludge HA was predominantly aliphatic and, therefore, markedly different from the nonamended soil HA and was characterized by a low oxygenated functional group content, high contents of S- and N-containing groups and polysaccharide components, very low free radical concentration, high molecular heterogeneity, low ring polycondensation and polymerization, and low humification degree. The application of the dewatered sludge induced only limited modifications in the structural and chemical properties of HAs from amended soils, which were only partially affected by the amendment rate used. However, marked modifications of HAs did occur in soils amended with liquid sludge, especially at high rates. The absence or presence of barley cultivation did not show any measurable effect on the composition and properties of sludge-amended soil HAs.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The distribution of various forms of heavy metals after addition to soils needs study to improve predictions of metal solubility, especially when the metal is added to soils with large quantities of organic carbon that oxidize over time. The extractability of added zinc (Zn) was determined in a laboratory study using sequential extractions as a function of pH and organic matter (OM as biosolids) additions to A and B horizon samples of three soils from the Coastal Plain of Maryland. The study used Galestown loamy sand (Psammentic Hapludults), Bertie silt loam (Typic Hapludults), and Othello silt loam (Typic Endoaquults), chosen to represent a typical toposequence in this physiographic province. Watersoluble Zn in the six horizons, with and without biosolids added, decreased with increasing pH from 4.0 to 7.0 and increasing cation exchange capacity (CEC) from 2.2 to 106 mmolc/kg soil. Although this decrease with increasing pH was expected, exchangeable levels of Zn were positively correlated with the CEC only up to pH 5.8 but were negatively correlated at pH > 5.8 in all the soils, suggesting that CEC was not a major contributor to Zn exchangeability at pH > 5.8. The biosolids amendment increased the solubility of Zn in all soils at pH < 5.0, and this effect of organic matter on the solubility of Zn was more pronounced in the coarse-textured Galestown sandy soil (both horizons) than it was in the finer-textured soils. The biosolids addition, compared with no biosolids addition, lowered the exchangeability of Zn and favored partitioning into the nonexchangeable Zn forms at pH values > 5.8 in all of the soils. The results indicate that pH was a controlling variable for the redistribution of water-soluble, exchangeable, and nonexchangeable Zn affected by biosolids addition. The higher level of nonexchangeable Zn in the Bertie soil compared with other soils, about 0.80 mmol/kg soil for the biosolids treatments and 0.47 mmol/kg soil for the soils without biosolids at pH 7.0, was attributed to the presence of higher native organic C levels and Fe(III) and Mn(III, IV)(hydr) oxide contents that enhance surface-induced hydrolysis and chemisorption of Zn. The effect of biosolids addition on nonexchangeable Zn retention was more pronounced in B horizons of all the soils, especially at pH > 5.8. The results have implications for predicting the mobility and bioavailability of Zn in soils in which pH and organic C levels are modified purposefully for the disposal of heavy metal and C-rich wastes.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Numerous studies have been reported regarding atrazine (2-chloro-4-isopropyl-6 ethyl-diamino-triazine) sorption/desorption and mobility in soil using the pure atrazine compound. Relatively little research has been carried out on atrazine behavior in soil minerals in the presence of surfactants. We hypothesized that clay mineralogy and surfactants may influence sorption/mobility of atrazine. In this study, we conducted miscible displacement experiments to elucidate the influence of the surfactant Brij 35 (C12H25[C2H4O]23OH), clay mineral type, and exchange phase composition on atrazine mobility in mixtures of specially prepared 2:1 clays. Chromatography columns were packed in duplicate with sand and Na- or Ca-saturated illite or mixtures of Na- or Ca-bentonite (0:1, 1:1, 9:1). The columns were presaturated with defined CaCl2(154 mmolCL−1) or CaCl2plus NaCl (SAR = 75 (mmol L−1)−1/2) solutions and adjusted to pH 6.3. Columns were later eluted with a pulse of a 6 mg L−1atrazine solution with or without 0.1% Brij 35, incubated for 48 h after atrazine breakthrough, and then washed with d-H2O. Results showed that atrazine breakthrough was incomplete (max C/Co < 1.0) in all systems. In the bentonite systems, the atrazine breakthrough curve (BTC) in the presence of Brij 35 was shifted to the left of the atrazine BTC in the absence of Brij 35 (at one pore volume) when the Na- to Cabentonite ratio = 9:1, suggesting that the surfactant enhanced atrazine mobility. In contrast, surfactant was shown to reduce atrazine mobility with a diminishing Na- to Ca-bentonite ratio. Similar results were found in the illite systems, but in reverse order with respect to Na- and Ca-clay exchange phase composition. Based on our work, we concluded that the exchange phase composition impacted the surfactant’s ability to mobilize atrazine in soils.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Chelation and complexation of uranium (U) and soil acidification were evaluated as practical ways to solubilize, detoxify, and enhance U accumulation by plants. Sunflower (Helianthus annuus) and Indian mustard (Brassica juncea) were selected as potential U accumulators for U phytoextraction in one U mine tailing soil (469 mg U kg−1) and nine acid and calcareous soils (pH 4.7 to 8.1) contaminated with different rates (100 to 600 mg U(VI)kg−1) of uranyl nitrate (UO2(NO3)2·6H2O). To enhance U phytoextraction, organic chelates were added to soils alone or as complexed-U forms of CDTA, DTPA, EDTA, and HEDTA, and citric and oxalic acids at rates of 1 to 25 mmol kg−1, to soils with 4-week old seedlings. Dry matter production, U concentration in shoots and roots, and soil pH were measured. Contaminated soils were also evaluated for U desorption and by fractionation. Uranium desorption was performed with 2 to 20 mmol kg−1of citric acid, CDTA, DTPA, and HEDTA. Uranium fractions [(exchangeable, carbonate, manganese (Mn), iron (Fe), organic, and residual)] were determined after 4 weeks of incubation. Plant dry matter production and U accumulation varied with soil contamination rate, chelate, organic acid form and rate, and soil type. The highest U concentration was in plants growing in calcareous soils and the lowest in clayey acid soils with high Fe and Mn oxides and organic matter content. Addition of citric and oxalic acids increased U accumulation and U translocation to the shoots significantly. Addition of 20 mmol of citric acid kg−1to loamy acid soils reduced the soil pH to below 5.0 and increased U concentration in shoots to 1400 mg U kg−1or by 150-fold, but addition of complexed-U forms had little effect on U translocation to shoots. Citric acid was the most effective chelate in desorption and plant accumulation of U. Uranium phytoacumulation was limited to acid soils with low adsorptive potential and to alkaline soils with carbonate minerals.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The objective of this work was to determine the effects of sample diversity on mid-infrared diffuse reflectance spectroscopic calibrations for biological measures in soils. A total of 136 soil samples representing a landscape within a small watershed were taken from a 20-ha field. The samples were obtained in a grid pattern from the first 10 centimeters. Soil samples were analyzed by mid-infrared diffuse reflectance spectroscopy and by conventional methods for total C and N, biomass C and N, acid and alkaline phosphatase, and arylsulfatase. Dried and ground samples, non-KBr diluted, were scanned from 4000 to 400 cm−1(4 cm−1resolution, 64 co-added scans) on a DigiLab FTS-60 Fourier transform spectrometer using a custom made sample transport that allowed a sample area of 50 by 2-mm to be scanned. Results using partial least squares regression showed that diffuse reflectance infrared fourier transform spectroscopy was capable of determining, to some degree, compositional parameters (total C and N) and biological activity as reflected by three enzymes. Based on calibration errors relative to the mean analyte values, the results for the measures of biological activity were as good as those found in previous studies using a less diverse (mineralogically) set of samples, although calibrations for biomass C and N were not feasible. In general, the results using mid-infrared spectra were also more accurate than those found using near-infrared spectra for the same samples.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Site-specific forestry requires detailed characterization of the spatial distribution of forest soil properties and the magnitude of harvesting impacts in order to prescribe appropriate management schemes. Furthermore, evaluation of the effects of timber harvesting on soil properties conducted on a landscape scale improves the interpretive value of soil survey data. Questions exist regarding the extent and spatial distribution of the effects of timber harvesting on eroded soils of the Alabama Piedmont. We evaluated the impacts of clear-cut harvesting on the temporal and spatial variability of bulk density (ρb), soil strength, and water content (&thetas;g) at three sites in the Alabama Piedmont where timber was predominantly mature plantation stands of loblolly pine (Pinus taedaL.). Pre-harvest spatial variability of texture, surface horizon thickness, and soil organic carbon (SOC) within single soil mapping delineations was also evaluated. Soils were moderately to severely eroded and classified in fine, kaolinitic, thermic Typic and Rhodic Kanhapludult and Kandiudult families. Although significant increases (P< 0.05) in ρbwere observed after timber harvesting for some of the trafficking class-depth interval combinations at all sites, the largest increases were observed at the moderately eroded site. Harvesting timber increased soil strength by 25.1% on the moderately eroded site, with increases occurring to a 40-cm depth in skid trails. Results suggested the degree of harvesting impacts were erosion phase dependent, with greater impacts on moderately versus severely eroded soils. Geostatistical analyses indicated that pre-harvest % clay and surface thickness were more highly spatially correlated than pre-harvest SOC, which may be related to erosion processes. Analyses also suggested harvesting slightly increased the overall spatial variablity of ρb, soil strength, and &thetas;g. These results suggest that the establishment of site-specific forest tillage zones to ameliorate compaction may be impractical to implement because of the increases in spatial variability of these properties.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID