华北土石山区森林土壤中石砾分布特征对土壤大孔隙及导水性质的影响

为了探究土壤中石砾对大孔隙形成的作用及对饱和导水率的影响,研究京郊密云水库水源涵养林内土壤石砾分布特征、大孔隙分布特征以及与饱和导水率之间的关系。结果表明:(1)林区0—30cm土壤层内石砾体积含量范围为7.10%~22.05%,质量含量范围为10.76%~38.20%,且石砾多集中分布于5~10mm粒径范围内;石砾含量随坡向呈现阳坡阴坡半阴半阳坡的规律;(2)石砾含量与当量孔径1.5mm的孔隙密度呈现极显著相关关系(p0.01),粒径5mm的石砾体积含量与大孔隙密度具有显著相关性(p0.05),说明砾石主要影响较大孔隙,特别是粒径5mm的石砾对大孔隙的形成影响较大;(3)当量孔径1.5mm的孔隙数量仅占总孔隙数量的1.41%,但对导水速率的贡献率为54.44%;饱和导水率与其呈线性关系。     

六盘山叠叠沟小流域的土壤石砾含量坡面分布特征

山区土壤石砾含量经常很高,这对土壤水文功能具有不可忽视的作用.为了解六盘山区土壤石砾含量的空间分布特征.在叠叠沟小流域调查研究了土壤石砾含量随坡向、坡位和土层深度的变化规律.结果表明,土壤(以表层0-20 cm为例)石砾体积含量的坡向顺序为阳坡(3.07%)>阴坡(2.89%)>半阴半阳坡(1.99%),坡位顺序为下部(3.46%)>中上部(3.05%)>坡顶(2.46%)>中部(2.20%)>上部(2.08%).在受侵蚀影响导致表层土壤石砾富集的同时,石砾含量主要受离开母岩距离的影响,因而表现为随土壤加深而增加的趋势,基于此提出了不同坡向坡位时石砾体积含量随土壤深度变化的模型,与实际数据吻合较好.     

土壤溶质运移研究动态及展望

土壤溶质运移的研究是目前土壤物理学、环境科学和农业灌溉学的重要研究领域 ,本文根据国内外学者对土壤溶质运移转化方面的研究成果 ,综述了土壤溶质运移研究中的优势流、模型的建立、新的研究手段的采用以及方程参数的确定 ,并简要讨论了土壤溶质运移的发展趋势。     

基于Visual Modflow的某油库地下水污染模拟

[目的]对陕西省黄陵县某油库地下水污染状况进行模拟,为油库区地下水污染的辅助预测和防治提供科学指导。[方法]通过野外调查试验获得初始参数,应用Visual Modflow软件建立了地下水水流模型,进行模型识别验证,获得最终水文地质参数。耦合水流方程与污染物迁移方程,得到地下水溶质运移模型。[结果]模拟了两种假设情形下运移情况:正常工况和油罐漏油。数值模拟预测了污染的范围和程度。到预测时间20a,污染物影响范围最大。[结论]污染物主要沿水流方向运移,对水环境的影响随时间逐渐增大,污染浓度随距离增大而减小;两种情况下,油罐漏油时对水环境造成的影响更加恶劣,污染范围远超出油库区。     

考虑尺度效应的土壤溶质运移动力学特征分析

[目的]为了了解土壤环境中弥散尺度效应、动力学吸附等作用对溶质运移过程的影响。[方法]应用Laplace变换方法和复变函数理论推得溶质运移动力学模型的解析解。利用De Hoog数值反演方法,验证解析解的正确性,利用解析解分析溶质在土壤中的运移特征。[结果]解析解的计算结果与反演函数Fourier级数项数2 N较大(N=500)时的De Hoog数值计算结果吻合很好;土壤溶质浓度随尺度效应的增强、吸附作用及生物降解作用的减弱而增大;分子扩散、一阶动力学吸附以及吸附相溶质降解作用对溶质运移变化影响较小。[结论]所推求解析解是正确的;土壤溶质运移的弥散尺度效应,溶质在液相和吸附相间的线性分配作用及溶质在液相中的降解作用是影响土壤溶质运移过程的主要因素。     

固体废物处理厂地下水污染预测及控制模拟

[目的]以江苏省镇江市新区大港片区某固体废物处理厂为研究对象,对地下水污染情况进行模拟研究,为同类建设项目及企业的地下水污染预测和防治提供参考。[方法]通过系统分析该固体废物处理厂野外水位和水质观测数据以及水文地质条件等资料,利用Visual Modflow软件构建了地下水水流和溶质运移模型。[结果]对厂区污水处理站防渗破损后特征污染物CODMn和氨氮运移情况以及地表硬化污染控制措施对污染物的阻隔效果进行预测评价,数值模拟预测污染物的影响范围、超标范围和最大运移距离。预测时间20a后,污染物影响范围最大,运移距离最远,且CODMn影响范围较氨氮大,运移距离较远;地表硬化后,20a后污染羽未超出评价范围。[结论]污染物主要沿水流方向迁移,对水环境的影响随时间逐渐增大,污染物浓度随着迁移距离的增加而减小,不同污染物在地下水含水层中的溶质运移范围和迁移距离不同。地表硬化措施能有效控制污染物扩散。     

土壤溶质迁移的指数函数模型

边界层方法是描述土壤溶质迁移的简单方法,通过边界层距离与时间的关系可以估计溶质迁移参数。基于边界层方法,研究了土壤溶质迁移的数学模拟及相应参数估计问题。假定土壤溶质浓度剖面为指数函数,得到了描述溶质浓度分布的指数函数模型。各参数对边界层距离的影响分析表明,应选取较小的孔隙水流速度、短历时推求土壤溶质迁移参数;对不同模型预测土壤溶质分布进行比较,结果表明,在短距离处指数型解与精确解的误差比其它都要小。误差分析表明了指数函数模型的有效性和实用性。     

考虑尺度效应的瞬时输入溶质运移模型及解析解

为探索土壤环境中尺度效应对溶质运移的影响,建立了瞬时输入条件下考虑尺度效应的溶质运移模型。通过Laplace变换和复变函数理论得到了模型的解析解,并利用解析解分析了弥散尺度效应对溶质运移过程的影响。结果表明：随着土壤弥散尺度效应的增强,土壤中溶质浓度分布范围越广,浓度峰运移的距离越大,但浓度峰值越小;随着入口弥散系数（D0）的增加,溶质运移的范围更大,溶质浓度峰值越小,但浓度峰运移的距离几乎没有变化;随着入口孔隙水流速度（v0）的增加,溶质浓度峰运移的距离越大,溶质的运移锋面越远,而溶质浓度峰值及溶质浓度分布范围几乎没有变化。用一维8 m 长土柱中的溶质运移试验资料对所推解析解进行验证,模拟结果与试验结果吻合较好,决定系数可达0.95以上。结果表明所推得的解析解可用来模拟预测较大尺度上溶质运移过程,为土壤环境治理等实际工程提供理论依据。     

基于分形理论的土壤优先流运动控制方程

为表征土壤优先流的快速非平衡运动、更准确地预测非饱和带土壤中的水流运动和溶质运移过程,该文在活动流场模型基本理论和土壤优先流表现出的分形特征的基础上,将分形理论引入到连续性模型,根据质量守恒原理建立了描述土壤优先流形式下水流运动和溶质运移过程的控制方程,发展和完善了活动流场模型理论;对比分析了活动流场模型理论与二域模型理论和活动裂隙模型理论之间的联系和区别。研究成果为运用活动流场模型解决优先流条件下土壤水流运动和溶质运移等相关问题提供了参考。     

体积置换法测量土石混合物组分含量

土石混合物组分含量测量在农业生产、建筑施工及水利工程等方面都有重要的意义。该文根据体积置换原理测量土石混合物比例、土壤含水率、容重、孔隙度/孔隙比等一系列土壤物理参数。给出了测量原理、设备、试验方法与过程。采用陕西杨凌的黏黄土、吉林黑土以及粒径为5~10 mm的石砾,预制不同体积含水率(10%、15%、20%)、石砾体积比例(10%、15%、20%)和土壤颗粒体积比例(40%、45%、50%)的土样。首先采用体积置换法测得土样中石砾、土壤颗粒和土壤水的总体积,随后取出土样中的石砾,用体积置换法测得石砾体积,进而得到土壤颗粒和土壤水的体积,并据此得到土壤含水率、土壤容重、土中气体含量、土壤孔隙度和孔隙比。用烘干法测量得到土壤容重和含水率,将2种方法测得的结果对比分析表明,使用体积置换法测得的土壤含水率比烘干法测量的结果大,相对误差在5%左右,测量的土壤容重偏小约1%,土壤气体含量的测量相对误差约为2%。测量土壤孔隙度的相对误差约为1%,土壤孔隙比的测量误差为1%~1.5%。表明体积置换法可以较为准确地测量土石混合物中各组分的相对含量,具有操作便捷、测量精度高、有普遍适用性等优点,可以为相关研究和测量提供参考。     

土壤中优势流的几个基本问题研究

优势流是指土壤在整个入流边界上接受补给,但只通过少部分土体的快速运移.优势流是一种普遍存在的现象,而不是一种特例.它受许多因素的控制,如土壤中的大空隙、土壤结构、土壤质地、土壤水分含量、土壤初始水分含量、水和溶质的施加速率及溶质的施加方法等.优势流的产生机理主要有2种:一种是由土壤介质的非均质性所驱动的优势流;另一种是由湿润锋的不稳定性所驱动的优势流.目前,优势流的监测方法主要有取土壤原状土、实验室内的土柱出流试验及染色示踪试验.尽管优势流的模拟非常困难,但人们仍提出了许多模型来描述它.今后优势流研究的重点应放在进行大量的综合性野外试验,以获取足够的数据资料来确切地刻划优势流;发展新的观测技术以便在时间和空间上监测优势流;建立新的模型来模拟优势流,从而进一步解决与土壤和地下水污染有关的环境问题.     

土壤优先流研究现状与发展趋势

优先流是近年来针对土壤水运动所提出的术语,是土壤中水运动机制研究由均匀走向非均匀领域的标志,是指在土壤各向异性的情况下,水分和溶质在多重因素的共同作用下,沿着特定的路径向下发生非稳定渗流的现象.优先流是造成降雨型滑坡、泥石流等地质灾害以及地下水质污染、农业土壤中养分流失等现象的主要诱因之一,所以深入开展优先流的研究显得尤为重要.本文从优先流的界定出发,主要介绍回顾了优先流数学模型的发展和研究优先流所采用的技术手段和方法,最后总结并探讨了优先流研究中存在的问题和发展趋势.     

Solute leaching in a sandy soil with a water-repellent surface layer: A simulation

Many sandy soils in the Netherlands have a water-repellent surface layer covering a wettable soil with a shallow groundwater table. Fingers form in the water-repellent surface layer and rapidly transport water and solutes to the wettable soil in which the streamlines diverge. Although several field observations are available, this system has not yet been studied systematically. In this paper, we present a model with a steady-state water flow to which solutes are added as a pulse. The model predicts the flow through the distribution zone and through the finger in the water-repellent surface layer with a closed form solution and transport in the wettable subsoil numerically. Model calculations show that the travel time through the water-repellent surface layer and the thickness and hydraulic conductivity of the wettable soil have the strongest effect on the arrival time of the solute pulse at groundwater level. The calculations also show that, assuming transport in the wettable subsoil to take place in fingers, the travel time is considerably shorter than when the diverging flow in the wettable soil is included.     

地下水浅埋条件下包气带水和溶质运移数值模拟研究述评

地下水浅埋条件下包气带水和溶质运移规律是解决土壤盐渍化、地下水污染等环境与生态问题的基本理论基础，基于多孔介质水和溶质运移基本方程的数值模型是研究包气带物质运移的重要手段。通过深入分析土壤水和地下水之间的相互关系，强调在地下水埋深小于其极限埋深的情况下应把地下水作用耦合到包气带水和溶质运移模型中。该文概括总结了现有研究把地下水作用与土壤水模型相耦合的方法，并分析了各种方法的优缺点。在回顾现有土壤水分运动参数和溶质运移参数确定方法的基础上，归纳了包气带水和溶质运移模型从“点”尺度向“田块”尺度扩展的途径，随机方法仍将是今后的研究热点，并有望应用于实践。     

Short‐term transport of cadmium during a heavy‐rain event simulated by a dual‐continuum approach

The transport of solutes in soils, and its intensification due to preferential flow, plays crucial role when problems related to the groundwater pollution are dealt with. The objective of this study was to examine transport of cadmium (Cd) in response to an extreme rainfall event for three different soils using numerical modeling. The ^115mCd²⁺ concentration profile had been measured in the Bodiky reference site (Danubian Lowland, Slovakia) by the radioactive‐tracer technique and used for the calibration of the dual‐continuum model S1D. The Cd transport during a single rain event was predicted with the S1D model for light, medium‐heavy, and heavy soil in the same region. The Cd transport through the soil profile was simulated by the one‐dimensional dual‐permeability model, which assumes the existence of two pore domains: the soil‐matrix domain and the preferential‐flow domain. The model is based on Richards' equation for water flow and advection‐dispersion equation for solute transport. A modified batch technique enables to distinguish process of adsorption in the matrix domain and the preferential pathways. Modeling with classical single‐permeability approach and dual‐continuum approach without considering the particle‐facilitated transport led to negligible Cd penetration. The rainfall event with extremely high rainfall intensity induced deep penetration of Cd in the medium‐heavy and heavy soil, which may indicate increased vulnerability to shallow groundwater pollution for the respective sites in Danubian Lowland region. The highest Cd leaching was predicted for heavy clay soil, where the preferential particle‐facilitated transport of Cd through the soil profile was significant due to the contrasting properties of the soil‐matrix domain and the preferential‐flow domain. The results of the sensitivity analysis suggested only slight effect of the transfer rate coefficients on simulated Cd leaching.     

Effects of Different Factors on Water Flow and Solute Transport Investigated by Time Domain Reflectometry in Sandy Clay Loam Field Soil

Factors affecting preferential flow and transport in the vadose zone need to be investigated by experiments and simulations to protect groundwater against surface applied chemicals. The objectives of this study were to investigate the effects of several factors (soil structure, initial soil water content (SWC), and application rate) and their interactions on the extent of preferential flow and transport in a sandy clay loam field soil using the time domain reflectometry (TDR) for measuring SWC and electrical conductivity (EC) in 12 treatments, modeling (by HYDRUS-1D and VS2DTI) the measured SWC and EC, and conducting statistical tests for comparing the means of the measured and modeled SWC and EC and solute transport parameters (pore water velocity and dispersion coefficient) obtained by inversely fitting in the CXTFIT program. The study results showed that the applied solution moved faster in the undisturbed, wet initial SWC, and higher application rate experimental conditions than in the disturbed, dry initial SWC, and lower application rate, respectively, based on the analysis of the changes in TDR measured SWC and EC with depth at 1, 2, 5, and 15?h of the experiments. However, the effects of interactive factors or treatments on water flow and solute transport were not clear enough. The modeling results showed that HYDRUS-1D was better than VS2DTI in the estimation of EC and especially SWC, but overall the models had relatively low performances in the simulations. Statistical test results also showed that the treatments had different flow and transport characteristics because they were divided into different groups in terms of the means of SWC and EC and solute transport parameters. These results suggest that similar experiments with more distinct interactions and modeling studies with different approaches need to be considered for better understanding the complex flow and transport processes in the vadose zone.     

A usable mechanistic model of nitrate leaching I. The model

A mechanistic model to simulate the leaching of nitrate in soil is described. Three flow patterns are accommodated: conventional convective-dispersion; preferential flow, in which water and solute moving in the larger water-filled pores fails to equilibrate with that in the smaller pores; and by-pass flow, in which water (and solute) moves rapidly down cracks and fissures without displacing the soil water. The pattern of flow depends on the rainfall intensity and the hydraulic conductivity of the water-filled pore space. The performance of the model is examined in terms of its ability to reproduce solute profiles calculated from analytical solutions to transport equations, and in the sensitivity of the output to changes in the main parameters. A second paper (Barraclough, 1989) illustrates the use of the model to reproduce nitrate leaching patterns observed in the field.     

干旱区绿洲农业生态系统土壤优先流量化方法可行性综述

归因于多孔介质的空间变异性和各向异性,非饱和带中土壤水流运动与溶质运移对优先流响应机制的研究十分具有挑战性。绿洲农业生态系统作为新疆主要经济支柱,如果忽略土壤优先流现象,可能会降低灌溉用水利用效率,减少土壤吸附污染物时间,进而导致地下水污染,最终制约农业发展。因此,该研究以新疆干旱绿洲区121团场的棉花种植区作为研究对象,旨在探明与探究在干旱绿洲区中可能导致优先流发生的潜在因素以及适合该地区观测优先流现象的量化技术。总体而言,在121团场,冻融循环,残膜现象,深耕棉秆还田的耕作方式以及土壤盐渍化会影响并改变土壤耕层孔隙度与结构,形成大孔隙式的优先入渗路径,进而引发大孔隙流。与此同时,因为该地区的主要土壤类型为壤土,其斥水性驱动着水流不稳定运动,导致指流或漏斗流的发生。通过对量化技术的总结与评估,染色示踪成像方法由于其能直观表述土壤水的非均匀运动,在121团场具有能很好地评价土壤优先流的潜力与实用性。其他的量化技术虽然具有各自的优势,但相较于染色示踪成像试验成本高,前期准备工作量大,评价尺度不统一,因此不适用于干旱绿洲区优先流的量化评价。在未来的研究中,需要适当地采用将微尺度观察与大尺度调查相结合的方法来对优先流现象进行全面评估。该研究有望为新疆及世界其他类似地区干旱绿洲生态系统优先流的研究提供理论参考。     

土壤优先流模型理论与观测技术的研究进展

优先流是土壤中常见的和重要的水流运动和溶质运移形式。由于土壤优先流的形成和影响因素众多、表现形式多样,加之土壤优先流的快速非平衡特征明显以及土壤高度的空间变异性,准确描述和模拟土壤优先流的时空变化特征一直以来都是土壤水文学界的热点问题和难点问题。该文从优先流的定义、表现类型、形成和影响因素、模型理论与观测技术等5个方面综述了土壤优先流的研究进展,指出该领域今后的主要研究方向为建立土壤优先流的统一判别标准、提升优先流模型理论的有效性、发展优先流的专用观测技术设备。文章对深入研究土壤优先流具有参考价值。