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991.
A successful application of reaction transport algorithms to calculate the chemical evolution of natural systems requires accurate methods to compute the rates of mineral/fluid surface reactions. Regarding the transport of radio-nuclides in mining dumps the dissolution of minerals is of special importance. Using a kinetic rate law of the mineral dissolution verified for unsaturated conditions will allow a realistic modelling of the mineral weathering in the environment. Dissolution rates of minerals in an aqueous solution are determined by several characteristics. These are surface reaction rates, morphology of the mineral's surface and, in case it is the unsaturated zone, the degree of the water saturation. For this process, the quantity of the particle surfaces which are in contact with percolating water is most decisive. In order to study the differences of mineral dissolution under saturated and unsaturated conditions batch and column experiments were carried out with a pyrite-calcite mixture. The experimental results were verified by calculations. Comparing the dissolution in batch with those in the column experiment, which was performed with a water flow velocity of 0.64 cm/day and was analyzed in the region of a water saturation of 0.11, one can conclude that only a small portion of about 5% of the grain surface is chemically reactive in this unsaturated flow.  相似文献   
992.
Polychlorinated biphenyls (PCBs) were measured in sediment cores from ponds located near a large seabird colony at Cape Vera, Devon Island, Arctic Canada. Surface sediment PCB concentrations were ∼5× greater in seabird-affected sites relative to a nearby control pond and were correlated with independent indicators of seabird activity including, sedimentary δ15N and lakewater chlorophyll a and cadmium concentrations. PCB fluxes were amongst the highest recorded from the High Arctic, ranging from 290 to 2400 ng m−2 yr−1. Despite a widespread ban of PCBs in the mid-1970s, PCB accumulation rates in our cores increased, with the highest values recorded in the most recent sediments. Possible mechanisms for the recent PCB increases include a vertical flux step driven by seabird-delivered nutrients and/or delayed loading of PCBs from the catchment into the ponds. The high PCB levels recorded in the seabird-affected sites suggest that seabird colonies are exposing coastal ecosystems to elevated levels of contaminants.  相似文献   
993.
The contribution of ZAMG to MONAROP consists of special weather forecasts to control the SOCs sampling procedure and of the analysis of the specific transport processes for SOCs, which is still in progress.In this paper, air pollutant transport into the Alps is demonstrated by examples of inorganic pollutants: Measurements of NOx and ozone provide evidence for air pollutant transport by local wind systems (valley and slope winds), especially at low elevated sites of the Alps. In addition, trajectory analyses for the high elevation sites demonstrate the importance of large scale synoptic air pollutant transport. The effects of these transport processes with different spatial and temporal scales are governed by the physical and chemical properties of the particular pollutant.First results for the high alpine MONARPOP stations show that air masses from east Europe influence mostly Sonnblick (Austria), whereas the influence of the Po basin is strongest at Weissfluhjoch (Switzerland).  相似文献   
994.
A popular method for the treatment of aquifers contaminated with chlorinated solvents is chemical oxidation based on the injection of potassium permanganate (KMnO4). Both the high density (1025 gL− 1) and reactivity of the treatment solution influence the fate of permanganate (MnO4) in the subsurface and affect the degree of contaminant treatment. The MIN3P multicomponent reactive transport code was enhanced to simulate permanganate-based remediation, to evaluate the pathways of MnO4 utilization, and to assess the role of density contrasts for the delivery of the treatment solution. The modified code (MIN3P-D) provides a direct coupling between density-dependent fluid flow, solute transport, contaminant treatment, and geochemical reactions. The model is used to simulate a field trial of TCE oxidation in a sandy aquifer that is underlain by an aquitard. Three-dimensional simulations are conducted for a coupled reactive system comprised of ten aqueous components, two mineral phases, TCE (dissolved, adsorbed, and NAPL), reactive organic matter, and including ion exchange reactions. Model parameters are constrained by literature data and a detailed data set from the field site under investigation. The general spatial and transient evolution in observed concentrations of the oxidant, dissolved TCE, and reaction products are adequately reproduced by the simulations. The model elucidates the important role of density-induced flow and transport on the distribution of the treatment solution into NAPL containing regions located at the aquifer–aquitard interface. Model results further suggest that reactions that do not directly affect the stability of MnO4 have a negligible effect on solution density and MnO4 delivery.  相似文献   
995.
This study deals with two-dimensional solute transport in an aquifer–aquitard system by maintaining rigorous mass conservation at the aquifer–aquitard interface. Advection, longitudinal dispersion, and transverse vertical dispersion are considered in the aquifer. Vertical advection and diffusion are considered in the aquitards. The first-type and the third-type boundary conditions are considered in the aquifer. This study differs from the commonly used averaged approximation (AA) method that treats the mass flux between the aquifer and aquitard as an averaged volumetric source/sink term in the governing equation of transport in the aquifer. Analytical solutions of concentrations in the aquitards and aquifer and mass transported between the aquifer and upper or lower aquitard are obtained in the Laplace domain, and are subsequently inverted numerically to yield results in the real time domain (the Zhan method). The breakthrough curves (BTCs) and distribution profiles in the aquifer obtained in this study are drastically different from those obtained using the AA method. Comparison of the numerical simulation using the model MT3DMS and the Zhan method indicates that the numerical result differs from that of the Zhan method for an asymmetric case when aquitard advections are at the same direction. The AA method overestimates the mass transported into the upper aquitard when an upward advection exists in the upper aquitard. The mass transported between the aquifer and the aquitard is sensitive to the aquitard Peclet number, but less sensitive to the aquitard diffusion coefficient.  相似文献   
996.
Colloids and bacteria (microorganisms) naturally exist in groundwater aquifers and can significantly impact contaminant migration rates. A conceptual model is first developed to account for the different physiochemical and biological processes, reaction kinetics, and different transport mechanisms of the combined system (contaminant–colloids–bacteria). All three constituents are assumed to be reactive with the reactions taking place between each constituent and the porous medium and also among the different constituents. A general linear kinetic reaction model is assumed for all reactive processes considered. The mathematical model is represented by fourteen coupled partial differential equations describing mass balance and reaction processes. Two of these equations describe colloid movement and reactions with the porous medium, four equations describe bacterial movement and reactions with colloids and the porous medium, and the remaining eight equations describe contaminant movement and its reactions with bacteria, colloids, and the porous medium. The mass balance equations are numerically solved for two-dimensional groundwater systems using a third-order, total variance-diminishing scheme (TVD) for the advection terms. Due to the complex coupling of the equations, they are solved iteratively each time step until a convergence criterion is met. The model is tested against experimental data and the results are favorable.  相似文献   
997.
坡耕地薄层紫色土-岩石系统中氮磷的迁移特征   总被引:5,自引:0,他引:5  
鲜青松  唐翔宇  朱波 《环境科学》2017,38(7):2843-2849
于2015年两场代表性降雨事件下研究了紫色土坡耕地(1 500 m~2)水文过程驱动的氮磷地表和地下迁移特征.结果表明:(1)前期土壤水饱和度和降雨量决定地表径流和裂隙潜流的产流深度和胶体浓度的基本水平;降雨强度则控制产流量的变化趋势和胶体浓度的峰值水平.(2)氮素主要以溶解态随裂隙潜流迁移;磷素则主要以细颗粒结合态通过地表径流流失.(3)氮磷迁移过程的水文驱动特征明显,氮素迁移主要受裂隙潜流的驱动作用影响,而磷素迁移则主要受地表径流的驱动作用影响.该研究结果丰富了对坡耕地薄层土壤-裂隙母岩二元系统中氮磷迁移对降雨响应规律的认识,可为农业氮磷非点源污染防治提供可靠的田间数据支持并明确关键的水文调控环节.  相似文献   
998.
利用耦合了污染源在线追踪模块的化学传输模式NAQPMS (Nested Air Quality Prediction Model System),结合地面细颗粒物(PM2.5)的小时观测数据,模拟了2014年1、4、7、10月4个月份武汉地区PM2.5浓度时空分布特征,量化了本地、武汉城市圈及远距离地区对武汉PM2.5浓度贡献.研究发现,2014年武汉市PM2.5年均浓度为85.3 μg·m-3,污染天(PM2.5日均值≥75 μg·m-3)占全年总天数的47.9%.细颗粒物的月均值呈现出季节性特征,即冬季污染最为严峻,1月均值为199.1 μg·m-3,PM2.5浓度超标持续一整月;夏季空气质量最好,春秋介于两者之间.模拟的PM2.5平均浓度在空间上大致呈现"城区高,郊区低"的分布态势.污染物区域来源解析发现,武汉市本地排放源贡献在1月最低,为34.1%,表明外来源贡献对长期灰霾的形成起决定性作用.7月本地源影响最显著(65.7%),和毗邻城市源(23.1%)一起成为夏季污染物的主要来源.4月和10月本地排放贡献比分别为49.1%和42.1%.4个月份,武汉城市圈对该市PM2.5浓度的贡献差异不大,范围在20.8%~24.1%.受大尺度天气系统的影响,远距离传输贡献率趋势与本地来源相反,占10.6%~35.3%.研究结果表明污染气团跨界输送对武汉不同季节PM2.5浓度有重要贡献.在冬季大范围污染背景下,污染物区域大范围协同控制才能有效减缓武汉PM2.5污染问题;而夏季对本地及近周边城市的减排措施可以有效改善武汉的空气质量.  相似文献   
999.
Bioremediation of hydrophobic organic compounds (HOCs) contanlinated soils involves several physicochemical and microbiological interracial processes among the soil-water-microorganism interfaces. The participation of surfactants facilitates the mass transport of HOCs in both the physicochemical and microbiological interfaces by reducing the interfacial tension. The effects and underlying mechanisms of surfactants on the physi-cochemical desorption of soil-sorbed HOCs have been widely studied. This paper reviewed the progress made in understanding the effects of surfactant on microbiological interlhcial transport of HOCs and the underlying mechanisms, which is vital for a better understanding and control of the mass transfer of HOCs in the biodegradation process. In summary, surfactants affect the microbiological interfacial behaviors of HOCs during three consecutive processes: the soil solution-microorganism sorption, the transmembrane process, and the intracellular metabolism. Surfactant could promote cell sorption of HOCs depending on the compatibility of surfactant hydrophile hydrophilic balance (HLB) with cell surface properties; while the dose ratio between surfactant and biologic mass (membrane lipids) determined the transmembrane processes. Although surfactants cannot easily directly affect the intracellular enzymatic metabolism of HOCs due to the steric hindrace, the presence of surfactants can indirectly enhanced the metabolism by increasing the substrate concentrations.  相似文献   
1000.
任肖敏  张连营  郭良宏 《环境化学》2014,(10):1662-1671
多溴联苯醚(PBDEs)和全氟烷基酸(PFAAs)是两类使用量大、环境污染广泛、人体暴露严重的新型有机污染物,2009年已纳入《斯德哥尔摩公约》持久性有机污染物(POPs)名单,但其毒性效应及作用机制并不明确.本文综述了本课题组近几年针对多溴联苯醚PBDEs和全氟烷基酸PFAAs的分子毒理机制研究工作,主要集中在这两类污染物对甲状腺系统、雌激素系统和肝脏脂肪酸代谢系统干扰效应的分子机制研究.本文分别从分子、细胞和活体三个层面,研究了污染物与核受体的直接结合作用、结合后受体的构象变化、细胞内受体的转录活性、以及活体暴露后受体调控基因的表达变化,由此阐明了污染物通过与受体直接作用导致细胞和活体生物功能改变的分子机制.同时结合计算模拟,探讨了污染物生物效应与其化学结构之间的关系,发现污染物的受体活性取决于它们与受体结合的空间构型,而其活性强度基本与二者的结合能力一致,主要受疏水作用和氢键的影响.此外,还通过研究污染物与天然配体转运蛋白的相互作用,明确了各个污染物与转运蛋白的结合能力,探讨了其构效关系,并评估了污染物对天然配体在体内转运过程的潜在干扰效应.通过上述研究工作,提出了多层面、多靶点研究环境污染物分子毒理机制的新思路,建立和引进了研究污染物与生物靶分子相互作用的新方法,发现了PBDEs、PFAAs与TR、ER、PPARγ核受体结合的新模式,为深入了解这些污染物的分子毒理机制提供了有用的信息和有效的研究手段.  相似文献   
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