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。     

Influence of Water Content and Plants on the Dissipation of Chlorinated Volatile Organic Compounds in Soil

To devise effective procedures for the remediation of soil contaminated by VOCs, an improved understanding of their fate and transport mechanisms in soil is essential. To show the effect of plants on the dissipation of 1,1,1-trichloroethane (TCA), trichloroethylene (TCE) and tetrachloroethylene (PCE), two types of experiments, vial and column, were conducted. The results suggested that keeping the soil moisture content at field capacity is desirable for VOCs dissipation. All VOCs were dissipated quickly in unplanted columns than planted conditions in early periods of the experiment because more volatilization occurred in unplanted conditions. The plants could take up and retard volatile contaminants, and prevent contamination of ambient air. Although the time for acclimation for microbial communities to contaminants for enhanced biodegradation should be considered, phytoremediation is potentially a cost-effective remediation technique for soils contaminated by volatile organic compounds (VOCs).     

Effects of Grasses on the Fate of VOCs in Contaminated Soil and Air

Plant toxicity and chemical removal tests were conducted to investigate the remediation ability of grasses with respect to volatile organic contaminants (VOCs) in contaminated soil and air. Eastern gamagrass (Tripsacum dactyloides) and annual ryegrass (Lolium rigidum) were exposed to artificially contaminated soil or air containing a mixture of 1,1,1-trichloroethane (TCA), trichloroethylene (TCE), and tetrachloroethylene (PCE) under controlled laboratory conditions. The results showed that the grasses are more severely affected in hydroponics than potted soil contaminated with a mixture of these contaminants. It was observed from the results that more contaminants were detected in the shoot and root of plants grown in a closed system with contaminated air than in an open system with contaminated soil. It is suggested from the results that grasses can be used for purification of VOCs from contaminated air especially in a closed system, but the purification effects are likely to be low. The results also suggested that the concentration level of VOCs in shoot, root, and soil could be used as contamination indicator at contaminated sites.     

Availability of Aged Toluene and Decane for Biodegradation in Soil

Toluene and decane which are common volatileorganic compounds (VOCs) found in natural gas spills, have beentested for their availability to biodegradation in soil aftervarious times of aging. For this purpose, single compounds wereadded to sterile soil in three concentrations of up to 1000 ppmand aged for 0, 35, and 70 days. After aging, soils were vented,inoculated and then incubated for 31 days. Both compounds wererapidly biodegraded reaching final soil concentrations below 1 ppm, regardless of the aging time. However, some sequestration ofsmall amounts of aged chemical in soil was evident for decane (up to 0.7 ppm), especially when the compound was added in largeramounts of 1000 ppm.     

非反应性物质在土壤中的迁移及其参数确定

采用一维对流－水动力弥散方程研究了非反应性化学物质在土壤中的迁移行为。通过实验研究了土壤团聚体大小和孔隙水流速对非反应物质在土壤中迁移的影响。结果表明,对流－水动力弥散方程能较好地预报氚（＾３Ｈ２Ｏ）的穿透英线和迁移行为,随着团聚体由小变大,＾３Ｈ２Ｏ在其土柱中的穿透曲线的溶质出流提前,而淋洗结果推迟,峰值变小,最佳拟合Ｄ值由小变大。流速增加,Ｄ值增大,扩散现象加剧,Ｄ和流速呈正比。这为进一步研究     

Determination of effective release rates of polycyclic aromatic hydrocarbons and dissolved organic carbon by column outflow experiments

Risk assessment of groundwater pollution requires quantitative information on the release kinetics of pollutants and organic matter from contaminated soil. We applied a new experimental design for column outflow experiments to investigate the release of polycyclic aromatic hydrocarbons (PAHs) and dissolved organic matter under water-saturated flow conditions. We used materials originating from a soil contaminated with non-aqueous phase liquids. To distinguish between release at equilibrium and release limited by mass transfer, we used two flow velocities and multiple interruptions to the flow. We quantified release and transport parameters by inverse numerical simulation of the individual breakthrough curves, applying a model based on the advection–dispersion equation including non-equilibrium and non-linear sorption. Release of the dissolved organic C takes place in two steps. Initially, a large amount of readily available organic matter is released. This first flush is followed by an outflow with typical characteristics of rate-limited release: larger concentrations in slower flow and increased concentrations after interruptions. The breakthrough of PAHs responds neither to the different flow velocities nor to the interruptions. We hypothesize that release of PAHs from the contaminated material is governed by dissolution at equilibrium according to Raoult's law. The boundary conditions of the experimental design, i.e. the flow velocities and multiple interruptions, enable us to distinguish between release at equilibrium and that which is rate-limited. Also, the response of the breakthrough behaviour to the boundary conditions can be used to estimate inversely effective release parameters.     

Produced Water Surface Spills and the Risk for BTEX and Naphthalene Groundwater Contamination

The widespread use of unconventional drilling involving hydraulic fracturing (“fracking”) has allowed for increased oil-and-gas extraction, produced water generation, and subsequent spills of produced water in Colorado and elsewhere. Produced water contains BTEX (benzene, toluene, ethylbenzene, xylene) and naphthalene, all of which are known to induce varying levels of toxicity upon exposure. When spilled, these contaminants can migrate through the soil and contaminant groundwater. This research modeled the solute transport of BTEX and naphthalene for a range of spill sizes on contrasting soils overlying groundwater at different depths. The results showed that benzene and toluene were expected to reach human health relevant concentration in groundwater because of their high concentrations in produced water, relatively low solid/liquid partition coefficient and low EPA drinking water limits for these contaminants. Peak groundwater concentrations were higher and were reached more rapidly in coarser textured soil. Risk categories of “low,” “medium,” and “high” were established by dividing the EPA drinking water limit for each contaminant into sequential thirds and modeled scenarios were classified into such categories. A quick reference guide was created that allows the user to input specific variables about an area of interest to evaluate that site’s risk of groundwater contamination in the event of a produced water spill. A large fraction of produced water spills occur at hydraulic-fracturing well pads; thus, the results of this research suggest that the surface area selected for a hydraulic-fracturing site should exclude or require extra precaution when considering areas with shallow aquifers and coarsely textured soils.     

土壤-地下水中微塑料迁移的影响因素及机制研究进展

微塑料在环境中广泛分布,世界范围内的农业土壤及地下水中都已发现微塑料污染,生态环境和人体健康受到严重威胁。研究土壤-地下水中微塑料迁移的影响因素及机制,对于准确评价其分布归趋及环境风险具有重要意义。该研究通过文献调研,对土壤-地下水环境中微塑料的来源、团聚及迁移研究进行梳理、归纳和总结,系统阐明了土壤-地下水中微塑料迁移的影响因素,剖析了影响微塑料迁移的机制,并对未来研究进行展望。土壤中微塑料的来源可分为原位型微塑料和外源输入型微塑料2种,地下水中的微塑料一般源自于土壤中微塑料的垂直迁移及地表-地下水微塑料交换。水体中微塑料的团聚受多种水环境因素的影响,其团聚程度与迁移能力密切相关,是迁移行为的基础和前提。土壤-地下水中影响微塑料迁移的因素可分为化学、物理、生物3类。水化学条件、介质成分、水流条件、介质物理条件、植物生长发育、小型动物及微生物的生命活动均会影响土壤-地下水中微塑料的迁移行为,且影响机制各不相同。目前,土壤-地下水中微塑料的迁移研究处于起步阶段,在进一步的研究中,野外尺度微塑料迁移、多元化微塑料迁移、微塑料特性对其迁移行为影响、微塑料迁移过程中的转化等研究值得重点关注。     

土壤容重对红壤水分溶质运移特征影响的试验研究

通过测定南方第四纪红壤不同土壤容重条件下,土壤水分水平入渗过程和溴化钾溶液穿透曲线,分析了土壤容重对入渗速率、土壤饱和导水率的影响;根据CDE模型、运用CXTFIT软件对溴离子的穿透曲线(BTC)进行拟合.并求其运移参数.结果表明:土壤水分运移速率和土壤饱和导水率随着红壤容重增大而减少;随着容重增大,Br-的水动力弥散系数D增大,阻力因子R也增大.     

A transfer-function method for analysing breakthrough data in the time domain of the transport process

A transfer‐function method is proposed to determine transport parameters from solute breakthrough data. The method is based on the assumptions that a linear process governs the transport of solute through soil and that the soil is homogeneous. It needs breakthrough data at two different vertical locations from a pulse input of solute to the soil. The method predicts the response by convoluting the input with the transfer function in the time domain. Solute breakthrough data were measured in unsaturated soil columns by time‐domain reflectometry (TDR). An experimental soil column was placed over a supporting column filled with sandy soil. A constant hanging water table, maintained in the lower column, created suction in the upper column and maintained unsaturated conditions. A solution of calcium chloride (CaCl₂) was spread over the soil in the upper column during steady flow of water in the column. Resident concentrations of solute in terms of electrical conductivity were measured at two depths by TDR sensors. We analysed breakthrough curves of CaCl₂ in 81 experiments to determine the transport parameters in coarse sand, sandy loam soil and clay loam soil by the transfer‐function method. The transport parameters obtained were compared with those determined by the widely used deterministic equilibrium model of the CXTFIT program. The transfer‐function method provided a better fit between the measured and estimated breakthrough curves in almost all cases and resulted in stable values of the parameters. The method is robust against small errors in measurements. It is a mathematically sound and efficient method for analysing breakthrough data.     

Modeling gas migration through unsaturated soils from waste disposal sites

The movement of gases away from waste disposal sites and hazardous waste spills through soils can result in serious safety and health hazards. As in the analogous problem of contaminant transport in groundwater, mathematical models are useful in predicting future gas excursion distances at existing sites and evaluating gas migration control alternatives. This paper presents a mathematical model for simulating the migration of gases from waste disposal sites through the unsaturated zone. The system equations used to represent gas migration through the unsaturated zone are an amalgam of the traditional groundwater flow-contaminant transport equations with the representation of gaseous flows in molar quantities. The model accounts for gas migration due to gas pressure, concentration and velocity gradients. The system equations are solved with the Galerkin finite element technique. The mathematical model successfully reproduced observed historical gas pressure and concentration data at two landfill sites. These two applications tested the mathematical model for both summer and winter flow conditions and under both natural and forced gas potential gradients.     

不同土壤玉米根际挥发性有机物组成和微生物群落特征

【目的】土壤理化性质和微生物群落的差异显著影响玉米根际挥发性有机物 (volatile organic compounds,VOCs) 的产生和释放。对根际VOCs的深入研究有望为充分挖掘根际生物学潜力和根际调控做出积极贡献。【方法】采集山东德州、河北涞水、河北保定、江西南昌、河南孟津、河南商丘等6个地区的旱地耕层土壤进行为期两个月的玉米盆栽试验,利用顶空固相微萃取联合气相色谱–质谱联用检测技术对根际土壤挥发性有机物进行了分析鉴定,利用实时荧光定量PCR技术对根际细菌和真菌进行了定量分析,利用高通量测序技术对根际细菌16S和真菌ITS进行了测序。【结果】从6个旱地土壤中共检测出44种VOCs,主要是烷烃、烯烃、酯类、胺类、有机酸和芳香类化合物,其中多种化合物与植物或微生物的生长代谢密切相关。胺类化合物N-Benzyl-N-ethyl-p-isopropylbenzamide和D-2-Bromolysergic acid diethylamide在6个土壤中均被检出,占总量的54.2%;其次检出最多的是烷烃和烯烃,占总量的31.1%和7.6%。江西南昌土壤释放的VOCs在数量和丰富度上均显著高于其他土壤,且大部分为烷烃和烯烃类化合物;从河北保定土壤中检出了6种特有的有机酸和酯类化合物。供试6种土壤中,河南商丘和河北保定的细菌数量显著高于其他四个地方。南昌土壤真菌数量显著较高,但其细菌数量、丰富度和多样性均显著低于其他土壤。6种土壤中的主要细菌依次为Thaumarchaeota(奇古菌门)、Actinobacteria(放线菌门)、Proteobacteria(变形菌门)、Chloroflexi(绿弯菌门)、Acidobacteria(酸杆菌门)、Firmicutes(厚壁菌门) 和 Unclassified(未分类门),占总细菌群落的92.1%;主要真菌依次为Ascomycota(子囊菌门)、Basidiomycota(担子菌门) 和 Chytridiomycota(壶菌门),占总真菌群落的98.3%。绿弯菌门仅在南昌土壤中占绝对优势,而南昌土壤中奇古菌门和变形菌门的相对丰度显著比其他地区少;子囊菌门在6种土壤中均为绝对优势真菌门。玉米根际释放的VOCs数量和丰富度与pH、硝态氮、细菌多样性和真菌多样性呈显著负相关 (P < 0.05),与铵态氮和真菌数量呈极显著正相关 (P < 0.01);与主要细菌门中的奇古菌门、变形菌门和酸杆菌门呈显著负相关 (P < 0.05),与绿弯菌门呈极显著正相关 (P < 0.01),但是与主要真菌门相关性不显著。【结论】理化性质不同的玉米根际土壤中,微生物群落结构与组成存在显著差异。pH是影响微生物生长的重要因素,酸性土壤中的真菌数量显著高于中性土壤,但是其细菌数量、微生物群落丰富度和多样性均显著小于中性土壤。VOCs的产生和释放受土壤、微生物和植物等众多因素的影响,土壤有机质含量越高、透气性越好、微生物数量越多时,释放的VOCs越丰富。     

Retention and Transport of PAH-Degrading Bacterium <Emphasis Type="Italic">Herbaspirillum chlorophenolicum</Emphasis> FA1 in Saturated Porous Media Under Various Physicochemical Conditions

Dispersal of functional microorganisms is a rate-limiting process during in situ bioremediation of contaminated soil and groundwater. In this work, series of column experiments were conducted to investigate the retention and transport behaviors of Herbaspirillum chlorophenolicum FA1, a promising bacterial agent for bioremediation, in saturated porous media under conditions of different combinations of grain size, solution pH, solution ionic strength (IS), and humic acid (HA) concentration. Experimental data showed that the mobility of FA1 in saturated porous media was strongly dependent on the physicochemical conditions. The breakthrough curves (BTCs) indicated that the amounts of FA1 in the effluent increased with increasing in sand size, solution pH, and HA concentration, but decreased with increase of solution IS. The shape of retention profiles (RPs) was hyper-exponential. The amounts of retained bacteria in the media also varied with the experimental conditions with opposite trends to that of effluent. Both experimental BTCs and RPs were simulated by a mathematical model that accounted for deposition kinetics to better interpret the effects of physicochemical conditions on FA1 deposition dynamics. Findings from this study showed that fate and transport of the functional bacterium FA1 in porous media strongly relied on the environmental conditions. Both experimental and modeling results can provide guidelines for field application of functional bacteria for soil and groundwater remediation.     

Vertical transport of a field-released genetically engineered microorganism through soil

The vertical movement of a genetically-engineered bacterium released into a sub-surface soil contained within a lysimeter was investigated. The strain used was Pseudomonas fluorescens HK44, a lux-based microbe capable of bioremediating specific polyaromatic hydrocarbons (PAHs). Strain HK44 was inoculated into a 4 m deep by 2.5 m diameter soil lysimeter outfitted with a hydraulic assembly to control groundwater levels. After 230 days, the lysimeter was subjected to a water table manipulation that resulted in significant transport of HK44 cells to depths 60 cm below the original inoculation zone within 20 days. A lysimeter not exposed to water level fluctuations exhibited no significant vertical transport. These results demonstrate the potential distribution of genetically engineered microorganisms in subsurface soil due to groundwater effects.     

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。     

重非水相流体在砂壤中驱替与残留试验研究

通过对PCE在砂壤土中的人渗再分布以及水分驱替和残留的试验研究,结果表明:PCE在砂壤中的人渗与再分布深度和时间的关系可以很好地用对数函数来描述.水分驱替后被置换区域土壤内PCE的饱和度明显降低,向下迁移并累积,达到一定含量后,PCE向下运动锋面速率增大.被水置换后,PCE在土体内将残留一小部分,残留饱和度为4%～15%,多小于10%,随着容重增大残留量将增加,残留的PCE在土体中缓慢溶解,随水分类似于溶解的溶质进行对流和扩散,向上可能到达地表,挥发进入大气;向下则可能进入地下水体,成为长期的潜在污染源.     

洛克沙胂在土壤柱中的淋溶迁移

畜禽粪便中残留的兽药进入土壤后的移动性是评价其淋溶能力（对地下水的污染风险）的重要信息。通过土壤柱稳定流实验,考察了不同淋溶剂、粪浸液等对洛克沙胂在不同深度（0～20、20～50、50～80 cm）灰潮土中的迁移行为影响。结果表明,水、0.01mol.L^-1 CaCl2、0.01 mol.L^-1 EDTA-Na2淋溶剂,对不同深度土壤柱中洛克沙胂的淋溶穿透曲线（BTCs）呈现不同程度的不对称性,在不同深度土壤柱中对洛克沙胂的淋出率分别为：水为92.3%～97.1%,0.01 mol.L^-1 CaCl2为71.0%～84.9%,0.01 mol.L^-1 EDTA-Na2为75.4%～91.2%;土壤柱先用粪浸液通过后,洛克沙胂的穿透曲线峰时间均有不同程度的提前,淋出率均有增加,在不同深度土壤柱中的淋出率分别为：水为96.4%～110.4%,0.01 mol.L^-1 CaCl2为94.5%～106.8%,0.01 mol.L^-1 EDTA-Na2为90.8%～103.2%。说明洛克沙胂随粪便进入土壤后可较快地淋溶迁移,可进入地表水和地下水中,对水环境质量的影响较大。     

石灰土壤原状土柱上硼和锌的迁移

Leaching of boron （B） and zinc （Zn） can be significant in some pedomorphic conditions, which can cause contamination of shallow groundwater and economic losses. Boron and Zn adsorption and transport was studied using 8.4 cm diameter × 28 cm long intact columns from two calcareous soil series with differing clay contents and vadose zone structures： Lyallpur soil series, clay loam （fine-silty, mixed, hyperthermic Ustalfic Haplargid）, and Sultanpur soil series, sandy loam （coarse-silty, mixed, hyperthermic Ustollic Camborthid）. The adsorption isotherms were developed by equilibrating soil with 0.01 tool L^-1 CaCl2 aqueous solution containing varying amounts of B and Zn and were fitted to the Langmuir equation. The B and Zn breakthrough curves were fitted to the two-domain convective-dispersive equation. At the end of the leaching experiment, 0.11 L 10 g L^-1 blue dye solution was also applied to each column to mark the flow paths. The Lyallpur soil columns had a slightly greater adsorption partition coefficient both for B and Zn than the Sultanpur soil columns. In the Lyallpur soil columns, B arrival was immediate but the peak concentration ratio （the concentration in solution at equilibrium/concentration applied） was lower than that in the Sultanpur soil columns. The breakthrough of B in the Sultanpur soil columns occurred after about 10 cm of cumulative drainage in both the columns; the rise in effluent concentration was fast and the peak concentration ratio was almost 1. Zinc leaching through the soil columns was very limited as only one column from the Lyallpur soil series showed Zn breakthrough in the effluent where the peak concentration ratio was only 0.05. This study demonstrates the effect of soil structure on B transport and has implications for the nutrient management in field soils.     

Solute transport in aggregated porous media: Comparing model independent and dependent parameter estimation

In many studies on solute transport soil column experiments arc used to obtain the transport characteristics for Convection-Dispersion-Models. Early breakthrough of the solute pulse has been attributed to a non-equilibrium in phase exchange. It is a standard procedure to determine several model parameter values from such breakthrough curves (BTC). This investigation is focused on the physical significance of simultaneously fitted parameter values used in the convection and diffusion-controlled mass transfer model (mobile — immobile phase concept). Saturated column experiments were conducted with solid phases consisting of porous and solid glass beads. One set of model parameter values was obtained from the breakthrough curves by simultaneous optimization and a second set was determined by independent measurements of individual parameter values. Both sets of parameter values described the BTCs equally well but deviated substantially from each other. These discrepancies were analysed in terms of local parameter sensitivities.     

宁夏黄灌区灌淤土硝态氮运移规律研究

为研究硝态氮在宁夏黄灌区灌於土中的基本运移规律,采用水平土柱进行硝态氮水平运移规律研究,并采用自制垂直土柱完成了硝态氮垂直运移规律研究。硝态氮水平运移规律研究表明：硝态氮运移与水分湿润峰迁移具有很好的一致性,随着硝态氮运移距离的增加,硝态氮浓度升高,并在湿润峰处累积;硝态氮浓度随含水量的增加而减少,并呈幂函数关系;硝态氮运移速率随运移距离增加而减小,且呈冥函数关系。硝态氮垂直运移实验表明：由于有机质和粘粒含量不同,各土层硝态氮穿透曲线差异较大;CXTFIT模型的拟合结果与实测结果相关性很好,说明可以使用CXTFIT模型进行土壤硝态氮运移预测和土壤硝态氮运移参数的测定。