共查询到10条相似文献，搜索用时 187 毫秒
1.
The aim of the study was to evaluate effects of mobile and immobile water and diffusion‐limited transport on the binding and release of ions in soils. The desorption and leaching of calcium in a humic layer of a densely rooted acid forest soil under a beech stand was studied in laboratory experiments by leaching soil columns with a desorption solution and recycling the leachate through the columns. Radioactive tracers were added and monitored in the leachate to evaluate desorption and leaching characteristics of the soil. Parallel experiments were conducted with chloride and calcium to determine transport and desorption parameters independently. The experimental data were then analysed with a transport model, taking into account effects of mobile and immobile soil water fractions, and in the case of calcium assuming an equilibrium Langmuir adsorption isotherm. The transport was highly dependent on the mobility of the soil water, and in particular the fraction of the soil water to which the chemical was confined as a result of ionic properties. For chloride an excluded soil water phase had to be taken into account to explain the experimental findings. Immobile or mobile water and solute transfer and transport properties were not sufficient to explain non‐equilibrium effects in the adsorption reactions. Desorption curves agreed with results from batch experiments, provided the leaching experiments were done in such a way that equilibration between the soil solution and the solid matrix adsorption sites was reached, otherwise desorption was delayed and the calculated isotherms do not represent actual equilibrium adsorption–desorption conditions. 相似文献
2.
本文对渗灌条件下的非饱和土壤水二维流动问题进行了探讨。对水平二维流及垂直二维流均进行了重复实验,并建立了相应的非饱和土壤水二维流的数学模型。按有限差分的计算方法求到数学解且与实验结果相符合,验证了该数学模型的可行性。同时应用数学模型对田间渗灌在不同条件下(如不同初始含水量、不同的土质、不同的密实度及不同直径供水管等几个主要因素)的非饱和土壤水二维流进行了模拟计算。根据计算结果分别就上述各影响因素对田间渗灌的非饱和二维流动的差异性进行了分析,由此对田间渗灌中若干问题提出初步看法。 相似文献
3.
Jan Ilsemann Rienk&#x;R. van der Ploeg Robert Horton Dirk Hermsmeyer 《植物养料与土壤学杂志》2006,169(6):754-761
The vulnerability of groundwater from chemical leaching through soil is a concern at some locations. Because measurements are laborious, time‐consuming, and expensive, simulation models are frequently used to assess leaching risks. But the significance of simulated solute movement through a layered soil is questionable if vertical homogeneity of physical soil properties has been assumed. In the present study, a semi‐analytical model for solute leaching in soils is presented. The model is relatively simple, but it does account for soil layers having different physical properties. The model includes the mobile‐immobile model (MIM) to describe one‐dimensional (1‐D) nonequilibrium, transient solute transport under steady‐state flow conditions. The MIM is rewritten as a second‐order differential equation and solved by a numerical scheme. Differing from fully analytical or fully numerical solutions, the new approach solves the differential equation numerically with respect to time and analytically with respect to distance. Numerical experiments for a single layered soil profile show that the semi‐analytical solution (SA‐MIM) is numerically stable for a wide range of parameter values. The accuracy of SA‐MIM predictions is comparable to that of analytical solutions. Numerical experiments for a multilayered profile indicate that the model correctly predicts effluent curves from finite layered soil profiles under steady‐state flow conditions. The SA‐MIM simulations with typical parameter values suggest that neglecting vertical heterogeneity of flow paths in a layered soil can lead to inaccurate prediction of soil‐solute leaching. The quality of predictions is generally improved if parameter estimates for the different soil layers are considered. However, the mobile‐immobile‐parameter estimates obtained in a number of previous studies may not be transferable to a field situation that is characterized by a slow and steady flow of water. Further field experiments to determine mobile‐immobile parameters under such conditions are desirable. 相似文献
4.
细菌和病毒等致病微生物广泛存在于化粪池、污水污泥、废水等源头。由于病毒比细菌和原生动物包囊小得多，在通过多孔土壤时不容易被过滤净化，地下水资源的病毒污染已引起各国科学家的高度关注，在过去的几十年间已经进行了较多的研究工作。也有了一些有关病毒在土壤中迁移行为及其影响机理的文献报道。本文的主要目的是在对过去国内外的一些研究结果作一综述，重点探讨影响病毒在土壤中迁移的主要因素，包括（1）影响病毒迁移的水动力学因素；（2）病毒吸附机理及其影响因素；（3）影响病毒生存或死亡的因素。土壤物理性质的不均一性是导致微生物和非反应物质之间的迁移行为差异的主要因素。影响病毒在土壤中吸附和死亡的因素很多，比如：土壤类型、病毒类型、pH、离子强度和多价阳离子、有机质、温度、土壤含水量、微粒、微生物活动等，对它们的影响机理进行了一一描述和解释。在指示病毒的选择上，噬菌体（比如MS2、PRD1、ФX174）已经被广泛用来研究病毒在土柱和田间条件下的迁移行为，并认为它们比较吻合指示病毒所需的各种条件。根据上述综述资料，在文章的最后对病毒迁移的进一步研究提出了一些建议。 相似文献
5.
An amended functional leaching model applicable to structured soils. I. Model description 总被引：1，自引：0，他引：1
D. G. M. HALL 《European Journal of Soil Science》1993,44(4):579-588
A functional model designed to simulate the transport of non-interactive solutes through macroporous soil is described. The concept of mobile and immobile water is used but the pore volume available for mobile water is partitioned to allow for flow through smaller water-filled pores and rapid preferential flow through larger macropores and fissures. The general performance of the model under steady infiltration following an injection of solute is presented. The sensitivity of the output to variations in the model parameters is also discussed. A second paper compares the model with bromide and chloride leaching data on two texturally contrasting soils. 相似文献
6.
7.
《Communications in Soil Science and Plant Analysis》2012,43(22):2935-2946
The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg?1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θim), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (Dh). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl?1) in disturbed soil column. Cl?1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θim+ θm) and real pore water velocity calculated based on the mobile water content (θm) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg?1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg?1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg?1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θim and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater. 相似文献
8.
9.
10.
盐分再分配条件下河套灌区冲洗水量的数值模拟 总被引：7，自引：6，他引：7
该文旨在探讨干旱缺水地区长期灌溉条件下,合理解决节水灌溉与冲洗灌溉间矛盾的途径,为在该地区实施节水灌溉战略提供理论依据。采用修正的对流扩散模型(SOTR)及特征有限元方法对中国内蒙古河套灌区冲洗—蒸发条件下的冲洗定额进行数值模拟研究。并用γ射线测定土柱土壤水盐运移结果标定了数值模拟结果。重点分析了基于土壤水动力学与溶质动力学原理,再灌溉冲洗与再分配条件下,均质垂直剖面上溶质运移过程;长期灌溉条件下,干旱地区土壤盐分布与冲洗定额、初始土壤盐分含量、地下水位埋深及地下水矿化度间的内在联系;在此基础上,确定节水灌溉条件下河套灌区最优的冲洗定额。该成果对于促进该地区农业可持续发展具有一定的指导意义 相似文献