摘要:

We considered the adsorption of ions onto surfaces of soil particles to be a three-step mechanism, namely, diffusion of ions from the bulk solution in the soil pores to a subsurface layer around the soil particles, diffusion across the subsurface layer, and finally a surface reaction. Diffusion across the subsurface layer was assumed to be at a constant rate. Adsorption onto the surfaces of soil particles was described by a kinetic reaction at the surface.Based on the assumption that, for adsorbing surfaces that obey the Freundlich isotherm, the activation energies of adsorption and desorption relate to the heat of adsorption in a linear manner, the surface reaction process was found to be described bywhereS(±g/g soil) is the amount adsorbed per unit mass of soil, &thetas;′(ml/cm3) is the normalized form ofS(dimensionless),C‘(±g/ml) is the concentration, &thetas;’(ml/cm3) is the volumetric water content of the subsurface layer, ρb(g soil/cm3) is the bulk density of the soil,t(s) is time,k1andk2(1/s) are surface reaction constants, andb(dimensionless) is a constant associated with the rate of change of energy of adsorption as a function of surface coverage. By also considering lateral diffusion from the bulk solution to the surfaces of soil particles, we found the rate of adsorption to be described bywhereKd(1/s) is the diffusive conductance of the subsurface layer, and (&thetas;/ρb)C(±g/g soil) is the amount of ions in the bulk liquid phase. The magnitudes ofKd,k1andk2are functions of pore water velocity.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

The effect of the initial soil water content prevailing in a porous column before the initiation of an infiltration-redistribution cycle on the redistribution rate is studied both theoretically and experimentally. I point out that the initial water content may vary following either the drying boundary or the wetting boundary curve of the hysteresis loop involved in the infiltration-redistribution process, and I argue on theoretical grounds that the redistribution rate for initial states on the drying curve is greater than that for states on the wetting boundary curve. I also argue that an increase of the initial water content along the drying curve may result in an increase of the redistribution rate, though an increase along the wetting curve may result in a decrease of the redistribution rate. Experimental results presented support the theoretical conclusions.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We developed a three-dimensional mechanistic model describing soil-atmosphere energy exchange and water transport in an effort to account for the effect of time-varying and space-variable shading on evaporation from a bare soil. During the course of a day, the effect of a canopylike shading body was to create a west-to-east shaded band in which soil surface temperature and evaporation were reduced (in comparison with a continuously sunlit surface) and soil moisture was enhanced. The possibilities inherent in the use of orthographic fisheye view factors are demonstrated.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

cis-4-Hydroxycinnamic acid was distributed in 23 peat soil samples in three different forms: A, B, and C. Average contents of the A form (the free form), B form (a combined form extractable with the organic solvent), and C form (another combined form unextractable with the organic solvent) were 18, 7.5, and 280 ±g/g soil, respectively. The acid was detected in all the samples except those in various forms from one soil. The frequencies of detection in the A and C forms were 83 and 92 percent, respectively, but that of the B form was lower (42 percent). The correlation coefficient (r) between the amount and the mean depth of the samples taken was very low in any given case. The ratios of the acid to the correspondingtrans-isomer in the A, B, and C forms were 0.90, 0.21, and 0.20, respectively. It certainly is interesting that the ratio was apparently different from the free form (the A form) and both combined forms (the B and C forms).

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We determined the mineralogy and chemistry of spodosols in three Adirondack lake-watersheds by x-ray and electron microprobe analysis and by optical microscopy. The major minerals present in the soils are quartz, K-feldspar, plagioclase feldspar, and hornblende. Accessory minerals identified with the petrographic microscope include magnetite, ilmenite, hypersthene, garnet, tourmaline, epidote, and zircon. Vermiculite is the dominant clay mineral in the <2-μm fraction. Illite, kaolinite, mixed-layer illite/ vermiculite, smectite, and chlorite are also present, but are less abundant.Vermiculite in the soil profiles contains aluminum interlayer contaminants that prevent the mineral from collapsing to 10 A upon K-saturation. The data suggest that vermiculite in the soil horizons is derived mainly from the weathering of hornblende. The high content of extractable iron in these Adirondack soils (up to 6 wt% Fe) results from the chemical dissolution of iron-rich (ferrohastingsitic) hornblende.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

The effects of solution composition, electrolyte concentration, and exchangeable ions on Sr2+adsorption by noncalcareous soils at low levels of Sr2+loading were studied, and the distribution coefficients of Sr2+and the selectivity coefficient for Sr-Ca adsorption were calculated. The distribution coefficient was independent of Sr2+loading, whereas this coefficient was strongly dependent on salt concentration, cation species (Na versus Ca), and pH. The selectivity coefficient, KCaSr, was less than 1 for wide ranges of pH and ionic strength and increased with pH. The data suggest that both H+and Ca2+exert specific depressing effects on Sr2+adsorption. The data presented are supports for the existence of specific adsorption sites for Sr on hydrous oxides and clay mineral edges.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We studied the alteration of silicic volcanic glass of recent Towada ash in the different soil environments by means of electron-microprobe analysis. Two types of glass alteration (tentatively named α and β types) were established and were distinguished on the basis of potassium and calcium contents of the glass samples.The α type glass alteration was characterized by a very large gain of potassium and a large loss of sodium. This alteration was explained by the ion exchange reaction between Na+and H+plus K+without significant change in the glass structure. The β type alteration characteristically showed a significant loss of potassium and a large gain of calcium and some other elements. The behaviors of alkalies and alkaline earths in the β type glass could not be interpreted by the stoichiometry of exchange processes of these elements. Changes of glass structure during weathering were suggested for the β type glass.There were close relationships between the mode of glass alteration, clay mineralogy of ash-derived soils, and soil environments. Only α type glass alteration was observed in the 2:1 mineral soils that showed the very low pH, very low contents of exchangeable bases, but relatively high content of exchangeable potassium. In contrast the β type glass alteration was the most intense in the allophanic Ando soil, which showed a relatively high content of exchangeable bases and a high pH.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

In earlier papers, we showed the applicability of a power-form equation to describe the kinetics of soil P desorption for several soils in laboratory batch experiments and in a rainfall-runoff processwherePdis the amount of P desorbed in timetat a water: soil ratio ofW, withPobeing the initial amount of desorbable P present in the soil, andK, α, and β constants for a given soil. In this note, we have attempted to explain the above equation in terms of diffusion-controlled desorption. The development utilized some empirical deductions from the literature. The basic desorption rate equation is formulated as a diffusion equation, with the diffusion coefficient taken as a power function of the fraction ofPoyet to be desorbed. This basic formulation is tested on experimental data for different levels ofPoandt, at a large value ofW. The basic equation is integrated and the results are simplified to derive the equation forPdgiven above.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID