不同CDE模型对硒在黄绵土中运移特性的模拟研究

污染物在土体运移是影响土体和地下水污染的一个重要的因素。为了研究不同因素对亚硒酸根离子在土体中运移的影响,在室内不同实验条件下,采用垂直土柱易混置换法对亚硒酸根离子在黄绵土土柱中的运移进行了研究,获得了不同容重及不同土柱高度条件下亚硒酸根离子的穿透曲线,通过STANMOD软件,应用确定性平衡CDE数学模型和确定性非平衡两区模型对穿透曲线进行拟合,研究结果表明:容重增大,阻滞因子R值减小,弥散系数D值则是先增大后减小;随着土柱高度的增加,弥散系数D值减小,而阻滞因子R变化不大。非平衡两区模型对于亚硒酸根离子运移参数的拟合优于平衡模型。穿透曲线能较好地反映出离子在土壤中运移的参数值,曲线越靠近y轴、初始穿透时间越小则弥散系数D越大;曲线越平缓则R值越大。     

阿特拉津在饱和砂质壤土中非平衡运移的模拟

针对农药阿特拉津在稳定流场饱和砂质壤土中的运移 ,根据平衡与非平衡假设条件下对流—弥散方程数学模型的解析解 ,基于易混合置换实验获得的阿特拉津和示踪溶质Br- 的穿透曲线及批量平衡法求得的阻滞因子 ,应用CXTFIT 2 .0软件 ,通过拟合土柱实验中溶质的出流浓度变化 ,估算了模型的有关参数 ,在此基础上模拟分析了实验土柱不同埋深处阿特拉津的出流浓度和累积淋溶量动态 ,结果表明 ,化学非平衡的两点模型对本文实验条件下阿特拉津运移的仿真具有较高的精度     

阿特拉津在饱和砂质壤土中非平衡运移的模拟

针对农药阿特拉津在稳定流场饱和砂质壤土中的运移 ,根据平衡与非平衡假设条件下对流—弥散方程数学模型的解析解 ,基于易混合置换实验获得的阿特拉津和示踪溶质Br- 的穿透曲线及批量平衡法求得的阻滞因子 ,应用CXTFIT 2 0软件 ,通过拟合土柱实验中溶质的出流浓度变化 ,估算了模型的有关参数 ,在此基础上模拟分析了实验土柱不同埋深处阿特拉津的出流浓度和累积淋溶量动态 ,结果表明 ,化学非平衡的两点模型对本文实验条件下阿特拉津运移的仿真具有较高的精度     

大肠杆菌在饱和砂质壤土中非平衡运移的CDE数学模型模拟

稳态、饱和条件下，以速度u=0．214cm min^-1和0．470cm min^-1进行混合置换实验，研究大肠杆菌在砂质壤土中的运移，并根据平衡与非平衡假设下，对流一弥散方程数学模型进行数值模拟。结果表明，含非平衡的双点吸附、且含有不可逆滞留项的模型能够较好地模拟大肠杆菌在砂质壤土中的运移。模拟和实验结果均表明，大肠杆菌的BTC（Breakthrough Curve穿透曲线）与示踪剂相比峰值明显降低，拖尾明显，且出现延迟，总的流出量也明显少于示踪剂；当水流速度由0．214cm min^-1增至0．470cm min^-1时。大肠杆菌BTC峰值由0．05增至0．2，且随速度的增加，滞留系数减小。     

土壤离子吸附：3.离子吸附的动力学

介绍了土壤离子吸附研究的一次平衡法，混合置换技术和压跳法，论述了主要动力学方程的适用条件及其在离子吸附方面的应用。     

不同质地土壤中镉运移的数值模拟与预测

通过室内土柱实验,采用溶质运移的对流-弥散方程,模拟了饱和条件下重金属镉在不同质地土壤中的运移.结果表明,化学非平衡单点模型(One-site model,OSM)能较好地模拟镉在粉壤土、壤砂土中的运移(R2分别为0.810和0.901),而对镉在砂壤土中运移的模拟效果较差(R2=0.542).OSM模型准确地模拟了土柱中镉运移的穿透时间,但是对穿透曲线拖尾部分的拟合效果欠佳.土壤对镉运移的阻滞作用与土壤理化性质有关,但是其机理还需要进一步研究.由于上层砂壤土对镉的强烈吸附,使镉的穿透时间较晚(10 pv),且不同土层界面处镉的浓度和吸附量变化明显.     

土壤胶体在不同饱和度土壤介质中的释放与淋溶行为研究

采用饱和与非饱和填充土柱纵向淋溶研究方法,结合对流弥散模型方程（CDE）对穿透曲线的拟合计算,全面考察了土壤介质水饱和度、土壤水pH/离子强度、土壤孔隙水流速和土壤胶体颗粒大小对天然土壤胶体在实际土壤介质中释放、沉积迁移行为的影响。分别获取胶体扩散系数和阻滞因子值,定量说明实验中水化学、水动力学等条件的作用影响力。结果显示,介质不饱和条件不利于胶体的释放和淋溶;高pH和低离子强度条件对土壤胶体释放与迁移有利;淋溶过程的间断干扰,可以促使土壤胶体的增量淋溶释放;淋溶强度及胶体颗粒粒径大小,能够影响胶体穿透时间和穿透浓度峰值大小。     

Cu/Pb/Zn/Cd在石英砂中的迁移实验及模拟

通过稳定流混合置换实验,研究了孔隙水流速和pH变化对Cu/Pb/Zn/Cd在石英砂中迁移行为的影响,获得了示踪剂Br-和Cu/Pb/Zn/Cd的穿透曲线(BTCs);并通过室内批量平衡实验获得吸附系数,进而计算出阻滞因子Rd。基于这些实验结果,借助CXTFIT2.1软件,用平衡CDE模型拟合了Br-的BTCs,得到了弥散系数D;在此基础上应用CDE非平衡模型拟合Cu/Pb/Zn/Cd在不同流速和pH条件下的BTCs,并预测了平行实验和不同埋深处Cu/Pb/Zn/Cd浓度的动态变化。结果表明,Cu/Pb/Zn/Cd的迁移能力随流速的增大而增强,而随pH的增大而降低;化学非平衡的两点模型能较好地模拟本文实验条件下Cu/Pb/Zn/Cd的迁移过程。     

黄土高原土壤物理性质对养分迁移速率的影响

采用一维饱和稳定流易混置换试验,用Cl-和K 为对象模拟黄土高原地区4种典型土壤对养分运移阻滞因子R的影响。试验结果表明对于不同质地的土壤,随着土壤质地变细,运移阻滞因子增大;对于同种质地土壤,随着容重增加,运移阻滞因子增大;对于同种质地而粒级不同的土壤,运移阻滞因子随着粒级的增大而增大;受土壤排斥的离子较受土壤吸引的离子容易穿透土壤。     

重金属离子在土壤中的竞争吸附动力学初步研究Ⅱ.铜与镉在褐土中竞争吸附动力学

用液流法研究了重金属离子铜与镉的在褐土中的竞争吸附动力学特性,用LJ吸附动力学方程结合竞争系数对铜与镉的竞争吸附动力学过程进行了描述.竞争性弱的镉离子吸附曲线出现"过饱和点",镉在开始时占据的吸附位量的一部分,随着吸附过程的延续被铜逐渐交换占据,镉的吸附量由"过饱和点"逐渐下降,最后趋于竞争平衡;在试验温度区间内,单一离子及竞争离子在褐土中的吸附量均随温度的升高而增大;吸附速率随温度的升高而减小,阿仑尼乌斯经验方程不能符合本试验结果,显示出铜及镉在供试褐土中的吸附动力学有其特殊性.温度和pH值的升高对镉的竞争有利,但镉在褐土中的吸附竞争能力远小于铜.     

Measured and predicted transport of two S-triazine herbicides through soil columns

Effluent concentration of chloride and two pesticides (prometon and atrazine) were measured during column displacement experiments at two water flow rates. A constant suction of approximately 1300 Pa was maintained in the packed soil columns which were positioned vertically on top of a vacuum chamber enclosing an automatic fraction collector. Measured breakthrough curves (BTC's) were analyzed in terms of two solute transport models: the standard two-parameter convection-dispersion equation (CDE), and a four-parameter two-site/two-region nonequilibrium model (TRM). Calculations obtained with the TRM model were found to be in better agreement with measured BTC's than predictions using the CDE model. Column retardation factors for prometon and artrazine calculated from equilibrium batch sorption coefficients were comparable to those estimated from the observed BTC's only when the nonequilibrium TRM model was used.     

非均质饱和土壤盐分优先运移的随机模拟

在室内使用特殊形状的土柱隔板成功地填装了在水平横截面上呈“川”字型分布、由质地相差较大的两种土壤相间构成的非均质土柱。当土柱出流达到稳态后，灌入CaCl2溶液，监测土柱出流液的浓度动态。通过计算表征氯离子迁移时间随机特征的概率密度函数，对出流盐分的优先运移采用传递函数模型进行仿真，并对构成非均质土柱的两种均质土壤分别进行了条件类似的水盐入渗实验和模拟。在此基础上获得了参与氯离子输运的土壤水运移体积和可动体积以及土壤溶液中氯离子的体积平均驻留浓度。     

棕壤对铜的吸附特性研究

棕壤对铜的吸附特性以及土壤条件对吸附的影响进行了研究，结果表明，棕壤对铜的吸附随溶液中铜的平衡浓度增加而增加，但在高浓度时增幅渐缓，与处于相同地区的褐土相比棕壤的吸附相对较弱，其吸附可用Langmiur、Frundlich、Temkin及米氏方程进行描述。土壤酸度增强，棕壤对铜的吸附降低，用H^＋浓度对Frundlich方程进行修饰，能更好地描述铜的吸附状况。此外，离子强度、陪伴离子对吸附都有影响，随离子强度增加及高价陪伴离子比例的上升吸附减弱。     

一种耦合化学反应的溶质运移模型的应用

土壤中的化学作用对溶质运移具有重要影响．离子交换和络合反应是土壤中常见的化学反应。利用室内土柱出流实验对这两种作用下的土壤溶质运移进行了探讨，用CXTFIT软件模拟了不考虑化学反应时的常规溶质运移；用水文地球化学模拟软件PHREEQC进行了耦合离子交换和络合反应运移模型的模拟。结果表明，耦合模型的模拟精度更高，从而也初步证明了耦合模型是成功的。     

Modelling Multi-Ion Transport in Saturated Soil and Parameter Estimation. I: Theory

A coupled convective-dispersive model was developed to describe the solute movement of four ionic species (Ca²⁺, Na⁺, SC₄² and CI) through soil. The model considers precipitation and dissolution of calcium sulfate as well as cation exchange or adsorption during steady-state water flow in saturated soil columns. With the model hypothetical miscible displacement experiments were carried out. The governing partial differential equations were solved numerically with an implicit Crank-Nicolson scheme. With the use of obtained results the effect of various model parameters on the shape of the calculated breakthrough curves was investigated. It was found that the processes of dissolution and precipitation, cation exchange or adsorption do have a definite influence on the shape of the breakthrough curves.     

农药草甘膦在砂质潮土上的迁移行为及其影响因素

化学物质在土壤中的移动性是人们精确评价其潜在淋溶能力(即对地下水的污染风险)的必要信息。通过一次平衡法和饱和土柱稳定流混合置换实验,来阐明环境pH变化和磷酸盐施用对草甘膦在砂质潮土中的吸附和迁移行为的影响。结果表明,草甘膦在砂质潮土上的吸附量随着pH的增大而降低,在pH4~6的范围内吸附量变化最明显;其穿透曲线(BTCs)均呈现不同程度的不对称性,加入的草甘膦浓度越低这种不对称性越明显;在本实验条件下,施用磷酸盐有抑制草甘膦迁移的趋势,但其抑制趋势并非随磷酸盐施用量的增加而持续增加。如加入草甘膦浓度为500 mg L-1,不加磷酸盐P0时,流出液中草甘膦峰值为459.8mg L-1,而加入磷酸盐P1和P2时,其峰值分别为147.3 mg L-1和373.6 mg L-1。推测其原因可能与磷酸盐施用导致环境pH降低及磷酸盐在加草甘膦前已经占据过多的吸附位点有关。     

Cation transport during unsaturated flow through two intact soils

In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl₂ and Ca(NO₃)₂ of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h^?1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg²⁺ and Ca²⁺ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha^?1 of native potassium was leached from the alluvial soil, but only about 10 kg ha^?1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily.     

Simulating nitrogen dynamics in soils using a deterministic model

Abstract. LEACHN is a deterministic model for simulating nitrogen dynamics in soil. Transport processes are based upon numerical solutions to the Richards equation for water flow and the convection-dispersion equation for solute transport. Transformations of urea, ammonium, nitrate and three organic pools are included, and the influence of water content and temperature can be reflected. Lack of measured input data sometimes limits the more general use of models such as these. Approaches to estimating data values using soil survey information and a limited number of measured data are discussed. Simple model sensitivity studies and a limited number of field measurements can guide the choice of input data values and lead to simulations that reflect the main features of the field soil nitrogen regime. Such an approach provides initial values for a modelling exercise, and improves intuition regarding the relative importance of processes and interactions in the field nitrogen cycle.     

Modelling water and solute transport in macroporous soil. I. Model description and sensitivity analysis

A detailed mechanistic model of water movement and transport of non-reactive solute in a macroporous soil is described. One important feature of the model is that it may be run in either one or two flow domains using the same values for the hydraulic properties characterizing the soil. Water and solute movement in the micropores is calculated with the Richards and convection-dispersion equations and, in two domains, this is coupled to fluxes of water and solute in the macropores by empirical interaction terms. These interaction terms are redundant in the one-domain model, which simply reduces to the non-steady state convection-dispersion equation. A sensitivity analysis is presented showing how it is possible to identify conditions under which a macropore flow domain may need to be considered. In part II (Jarvis et al., 1991), the model is evaluated under field conditions in chloride breakthrough experiments in soil monolith lysimeters.