An Efficient ELLAM Implementation for Modeling Solute Transport in Fractured Porous Media

The goal of this study is to introduce an adaptation of the Eulerian-Lagrangian localized adjoint method (ELLAM) for the simulation of mass transport in fractured porous media, and to evaluate the performance of ELLAM in such a case. The fractures are represented explicitly using the discrete fracture model. The velocity field was calculated using the mixed hybrid finite element method. A sound ELLAM implementation is developed to address numerical artifacts (spurious oscillations and numerical dispersion) arising from the presence of fractures. The efficiency of the developed ELLAM implementation was further improved by taking advantage of the parallel computing on shared memory architecture for the tasks related to particles tracking and linear system resolving. The performance of ELLAM was tested by comparing its results with the Eulerian discontinuous Galerkin method based on several benchmark problems dealing with different fracture configurations. The results highlight the robustness and accuracy of ELLAM, as it allows the use of large time steps, and overcomes the Courant-Friedrichs-Lewy (CFL) restriction. The outcome also shows that ELLAM is more efficient when fracture density is increased.     

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。     

Column Holdup Formula of Soil Solute Transport

The shortcomings of the present two formulae for describing column holdup are analyzed and deductions are made to find a new formula. The column holdup, Hw, described by the new formula is dimensional,and related to soil solute transport kinesis and column physical properties. Compared with the other two column holdups, Hw is feasible to describe dimensional column holdup during solute transport process. The relationships between Hw and retardation factor, R, in different solute transport boundary conditions are established.     

土壤溶质迁移的柱滞留方程

The relationship between magnetic properties and particle size of soils derived from metamorphic rock,basalt,granite,Quaternary red clay,limestone and mudstone from Zhejiang Province,East China was studied,Based on the variations of the mass magnetic susceptibility (χ),anhysteretic remanent magnetization (ARM),and saturation isothermal remanent magnetization (SIRM) with soil particle size,the relationship could be classfied into three groups.For the soils derived from metamorphic rock and basalt,magnetic values were the highest in the gravel and coarse sand fractions and decreased with decreasing soil particle size.The soils derived from sedimentary rock had a bimodal distribution of magnetic values.with peaks in 1-0.5 and 0.005-0.0005mm fractions.The soil developed on granite was characterized by a peak of magnetic value in 0.001-0.0005mm fractions.The soil developed on granite was characterized by a peak of magnetic value in 0.001-0.0005 mm fractions.Frequency-dependent susceptibility(χfd)and ratios of magnetic parameters (ARM/χ,SIRM/χand SIRM/ARM) of soil particle fractions showed that variations in ferrimagnetic grain size paralleled those in particle size,χfd peaked in caly fraction and decreased with increasing particle size,irrespective of soil parent materials.The acquisition curves of IRM and demagnetization paramenter of different soil particles indicated that there were different magnetic minerals assemblages in different particle fractions.     

Clumn Holdup Formula of Soil Solute Transport

The shortcomings of the present two formulae for describing column holdup are analyzed and deductions are ade to find a new formula,The column holdup,Hw,described by the new formula is dimensional,and related to soil soulte transport kinesis and column physical properties,Compared with the other two column holdups,Hw is feasible to describe dimensional column holdup during solute transport process,The relationships between Hw and retardation factor,R,in different solute transport boundary conditions are established.     

柑橘地土壤溶质优先运移研究

通过室内原状土柱与重塑土柱对比实验,应用溶质穿透曲线研究柑橘地土壤优先流及溶质优先运移的特征。结果表明:柑橘地原状土柱土壤穿透曲线表现出了上升阶段的拐点现象,是优先流与基质流共同作用的结果。原状土柱土体穿透曲线下降初期较陡,并表现出了较长的拖尾特征,重塑土柱下降趋势相对稳定。存在优先路径的土体出流速率稳定性较差,变异系数较大,其平均出流速率是重塑土柱出流速率的3.5倍。优先流作用使溶质相对浓度到达峰值的时间缩短了37.7%,此时造成的溶质运移量却是平衡基质流所造成的溶质运移量的2.5倍,因此优先流能够导致土壤溶质的快速大量迁移。     

溶质施放部位对红壤坡面溶质迁移特征的影响

以非吸附性溴离子为示踪剂,采用室内模拟降雨方法研究间歇降雨和施肥部位对红壤坡面产流、产沙以及溴离子迁移特征的影响。结果表明,降雨特征相同条件下,3次降雨的总径流量无明显差异,但第3次降雨形成的产沙量分别是第1次和第2次的7倍和2.2倍,这表明因前期含水量的提高而降低了土壤抗冲性是红壤侵蚀的主要原因之一;径流溴离子浓度随时间变化均呈幂函数衰减,与施肥部位无关;施肥部位越靠近坡底,径流溴离子初始浓度越高且衰减速度越快;溴离子流失数量与施肥距离呈显著正线性关系。通过估算3次间歇降雨径流中溶质流失数量的来源发现,淋溶到坡面土壤中的溴离子再次参与径流流失的数量,其平均比重从81.61%提高到了93.76%,这表明施加在上坡部位的肥料被淋溶后对后期径流养分流失的贡献十分显著。     

基于GLUE的土壤溶质运移参数反演及不确定性

溶质运移模型参数的识别结果常存在较高的不确定性,制约了模型的实际应用。以土壤中Cu2+运移过程为例,采用广义似然不确定性估计(Generalized likelihood uncertainty estimation,GLUE)并引入最大似然值(MaximumNash-Sutcliffe,MNS)等三种定量指标,探讨了数值反演估计弥散系数等参数的不确定性。结果表明,非线性最小二乘法(Nonlinear least squares,NLLS)得到的唯一"最优"参数组合对Cu2+出流曲线拟合效果很好(R20.937),但因"异参同效",无法刻画预测结果的不确定性。GLUE则可明确溶质运移参数及其响应界面的不确定性,MNS对应的参数组合对Cu2+出流曲线拟合R20.937,效果与NLLS的拟合结果高度一致。GLUE计算的95%置信区间覆盖了80%以上的观测点(NLLS为46.3%),其反演参数的取值范围也远大于NLLS的结果。在模型参数及响应界面不确定性分析两方面GLUE方法均优于NLLS方法。     

黄土区农田溶质径流过程模拟方法分析

根据黄土区土壤溶质向地表径流传递并随地表径流迁移的具体特点,结合室内模拟实验研究分析结果,探讨了土壤溶质随地径流迁移的影响因素和建立模拟模型的方式。同时传递了质量传递模型,并对模型中的参数确定方法进行了分析。利用室内模拟结果,对模型进行了初步验证。     

采用通气堆沤对石油烃污染土壤进行生物修复

Laboratory simulation studies and a composting pilot study were conducted to evaluate the capacity of three strains of fungi, indigenous fungus Fusarium sp. and Phanerochaete chrysosporium and Coriolus Versicolor, to remediate petroleum-contaminated soils. In laboratory, the fungi were inoculated into a liquidculture medium and the petroleum-contaminated soil samples for incubation of 40 and 50 days 5 respectively. In the 200-day pilot study, nutrient contents and moisture were adjusted and maintained under aerobiccondition in composting units using concrete container (118.5 cm × 65.5 cm × 12.5 cm) designed specially for this study. The laboratory simulation results showed that all the three fungi were effective in degrading petroleum in the liquid culture medium and in the soil. At the end of both the laboratory incubations, the degradation rates by Phanerochaete chrysosporium were the highest, reaching 66% after incubation in liquid culture for 50 days. This was further demonstrated in the composting pilot study where the degradation rate by P. chrysosporium reached 79% within 200 days, higher than those of the other two fungi (53.1% and 46.1%), indicating that P. chrysosporium was the best fungus for bioremediation of soil contaminated with petroleum. Further research is required to increase degradation rate.     

Effectiveness of Bioremediation Processes of Hydrocarbon Pollutants in Weathered Drill Wastes

The aim of this article is to present the problem of purification of 50-year-old weathered wastes (soil) from waste pits—the result of oil drilling. The soil was deeply contaminated with petroleum hydrocarbons—total petroleum hydrocarbon (TPH) level: 85,654–101,842 mg kg dry mass. This work presents results of waste pit material purification with the use of stage technology: initial reclamation, basic bioremediation, and bioaugmentation (inoculation with indigenous microorganisms). The whole process was controlled with the use of gas chromatography/flame ionization detector. This analytical method enables observation of alternation in n-alkanes content during the consecutive stages of purification. According to this method, estimation of oil hydrocarbon biodegradation degree with the use of n-C₁₇/Pr and n-C₁₈/F indicators can be done. The use of biomarker C₃₀-17α(H)21β(H)-hopane to normalize the TPH concentration in laboratory research enabled the creation of the first-order mathematical model of biodegradation. It is possible to recognize the dynamics of the following purification stages due to the calculated first-order biodegradation constants. Decrease in the TPH content (63.8–65.1%) was a result of laboratory tests led in 130 days of basic bioremediation. The next stage of soil purification (130 days) included inoculation with biopreparation based on indigenous microorganisms—TPH decrease in 80.7–81.7%. Laboratory tests results enabled elaboration of purification methods applied in tested waste pits in industrial conditions (in situ). The technology of the G-44 and G-12 waste pits purification from huge petroleum hydrocarbons content, consisting of stage purification process, enables the TPH decrease to the satisfactory level in 3 years.     

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。     

土壤容重对溶质迁移过程的影响

土壤在径流作用下发生流失、土壤溶质迁移等现象,是一个受径流、土壤性质、下垫面特性、土地利用方式等多种因素综合影响的复杂过程.利用斜坡土槽,采用一定的坡度和实验流量,对不同容重的土样进行了室内放水实验,研究了在土壤饱和条件下,土壤容重对土壤溶质迁移过程的影响.实验结果表明:(1)随径流作用时间的增加,单位时间内土壤溶质迁移量逐渐减少,其关系可用幂函数来描述;(2)土壤溶质发生迁移是受地表径流和壤中流共同作用的结果;(3)土壤容重对土壤溶质迁移过程影响总体表现为土壤容重越大,随径流迁移的土壤溶质量越少;(4)土壤容重增加相同幅度,但同时刻随径流迁移的土壤溶质递减量逐渐减少.     

土壤溶质运移特性研究进展

可溶性化学物质(土壤溶质)在土壤中的运移和分布已成为近年来研究的热点。本文综述了近年来土壤溶质运移机理、吸附模型、溶质运移数学模型等方面的研究进展。     

Bioremediation in Field Box Plots of a Soil Contaminated with Wood-Preservatives: A Comparison of Treatment Conditions using Toxicity Testing as a Monitoring Technique

A soil contaminated with polycyclic aromatic hydrocarbons, petroleum hydrocarbons and chlorophenols was bioremediated in field box plots. Three different bioremediation treatments (tillage and irrigation alone (box plot 2) or in addition to amendment with nitrogen and phosphorus (box plots 3 and 4) and additional organic amendment composed ofagricultural crop residues (box plot 4)) were comparedusing chemical analysis for target contaminants andsix toxicity tests (seed germination, earthwormsurvival, SOS Chromotest, Toxi-Chromotest, solid-phaseMicrotox® andred blood cell (RBC) haemolysisassay). Degradation was enhanced, and toxicity wasgenerally the most reduced, in box plots 3 and 4. Although chemical analysis indicated that the twoamendment protocols were equally effective, soiltoxicity was generally the most reduced in box plot 4. The earthworm survival and seed germination assayswere the most reliable and relevant toxicity tests. Difficulties arising with the other tests includedinsensitivity to changes in soil contaminant levels,inconsistency and interference by soil particles andother soil constituents. Because of the lack ofagreement between toxicity tests, these resultssupport the use of a battery of toxicity tests inconjunction with chemical analysis, when assessing theefficacy of bioremediation.     

Characterizing Uncertainties Associated with Contaminant Transport Modeling through a Coupled Fuzzy-Stochastic Approach

Water, Air, & Soil Pollution - Historic lead mining, milling and smelting on the floodplain soils of the upper reaches of the Vils River, Eastern Bavaria, Germany has led to heavy metal...     

纳米碳对黄绵土水分运动及溶质迁移特征的影响

以黄绵土为研究对象,均匀添加不同含量纳米碳(质量含量分别为0,0.001,0.005,0.01,0.05g/g),采用室内土柱试验分别测定土壤累积入渗量曲线、溶质穿透曲线及水分特征曲线,初步研究了纳米碳含量对黄绵土水分运动及溶质迁移过程的影响。结果表明:(1)纳米碳的存在对土壤水分入渗过程产生阻碍作用,入渗率随着纳米碳含量增加而减小,Philip方程能较好地描述添加纳米碳的黄绵土入渗过程;(2)纳米碳可以提高土壤的持水能力,随着纳米碳含量增加,土壤饱和含水量增加,相同土壤水吸力下的土壤含水量增大,van Genuchten模型可较好拟合含有纳米碳的黄绵土水分特征曲线,进气吸力随纳米碳含量增加而减小,形状参数(n)随之减小;(3)纳米碳可以有效提高土壤吸持溶质能力,随纳米碳含量增加,初始穿透时间提前,完全穿透时间延长,弥散度增大;土柱被置换液完全穿透后,土样中Cl-平均含量随纳米碳含量增加而变大。     

大孔隙分布对坡地产汇流及溶质运移的影响

以室内土槽为平台,采用人工模拟降雨试验,研究了粉砂壤土中两种不同大孔隙分布情况下,土槽中土壤含水量、坡面流速、地面径流、地下径流及溶质运移的变化。结果表明,相对于面大孔隙度为19%,容积大孔隙度为0.095%的未加密型的土槽,面大孔隙度为57%,容积大孔隙度为0.285%的大孔隙加密型土槽中各层土壤含水量增加幅度、平均坡面流速及地面径流量相对偏小,地下流出现时间较早且径流量较大,地面径流中溴离子、铵根离子浓度、硝酸根离子浓度偏小。在地下水出流前期,大孔隙加密型土槽中的铵根离子浓度和浓度变化幅度都偏小,但溴离子、硝酸根离子浓度则偏大。     

Atmospheric Stability and Meteorological Scenarios as Inputs to Air Pollution Transport Modeling

Meteorological scenarios concerning the data required for engineering applications of pollutant transport modeling in the low layers of troposphere are defined through a simple methodology. This involves only data at soil surface and substantially relies on the determination of atmospheric stability carried out through fictitious vertical profiles of air temperature considered as representative of the actual vertical profiles in a study area. This assumption is supported by comparisons of fictitious vertical profiles, obtained by measurements of air temperature at soil surface but at different heights above sea level, and the temperature vertical profiles observed by the radio-sounding station closer to the study area. The fictitious profiles are first used to derive the usual classes of atmospheric stability as unstable atmosphere, neutral atmosphere, stable atmosphere, thermal inversion at the surface and thermal inversion in the upper layers. Then, each scenario is determined through the classes of atmospheric stability observed at 06.00 GMT and 15.00 GMT together with the experimental data of air temperature, relative humidity, wind speed, wind direction, and cloud cover, all averaged in the period of investigation of a few years. An area of Central Italy, where the meteorological measurements for a period of 7 years were available, has been selected for this study.