Yuqun Xue

Responses of the antioxidant defenses of the Goldfish Carassius auratus, exposed to 2,4-dichlorophenol

Goldfish Carassius auratus were exposed to 0.1mg/l of 2,4-dichlorophenol (2,4-DCP), widely used as transportation power in China, for 2, 5, 10, 20 and 40 days, while one control group was designated for each exposure group. Antioxidant defenses consisting of contents of reduced glutathione (GSH) and glutathione disulfide (GSSG) and activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), selenium-dependent glutathione peroxidase (Se-GPx) and glutathione S-transferase (GST) in liver of freshwater fish were determined and the GSH-GSSG ratio and content of tGSH (total glutathione) were calculated. In the present study, the role of hepatic antioxidant defenses was evaluated and the possible poisoning mechanism of fish can be explained as an oxidative stress mechanism. In addition, hepatic SOD and GSH, especially tGSH, were sensitive to 2,4-DCP contamination and thus, can possibly be used in early assessment of 2,4-DCP-dominant polluted aquatic ecosystems.

A Three-Dimensional Miscible Transport Model For Seawater Intrusion in China

A three-dimensional miscible transport model for seawater intrusion in a phreatic aquifer with a transition zone is presented. This model considers many important factors, such as the effect of variable density on fluid flow, the effect of precipitation infiltration and phreatic surface fluctuation on the process of seawater intrusion, the existence of great discharge pumping wells, etc. The difficulty in solving this problem can be tackled by the presented numerical method and iteration technique. This model is used to describe seawater intrusion in Huangheying, Longkou, Peoples Republic of China. The simulated values agree very well with the field data (e.g., the total mean values of the absolute error of Cl− concentration are 46.13 mg/L and 55.67 mg/L, respectively, and those of the water head are 0.24 m and 0.08 m, respectively).

Numerical Simulation of Viscoelastoplastic Land Subsidence due to Groundwater Overdrafting in Shanghai, China

Land subsidence caused by groundwater overpumping in Shanghai is becoming a serious geological hazard. Due to its important economic position, the field data, including compression of individual stratum from extensometer groups and the groundwater levels from observation wells, have been collected over the past 45 years. Considering the fact that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics, such as elasticity, elastoplasticity, and viscoelastoplasticity, at different sites of the cone of depression or in different periods, a nonlinear coupled regional land subsidence model is developed. The coupled model consists of a three-dimensional groundwater flow model and a one-dimensional vertical deformation model, both based on a viscoelastoplastic constitutive laws (called modified Merchant model), and then solved using a multiscale iterative finite-element method. The model is calibrated using 28,184 hy...

Land subsidence and uplift due to long-term groundwater extraction and artificial recharge in Shanghai, China

Increasing artificial water recharge and restriction on groundwater pumpage have caused land displacements in Shanghai (China) to shift from subsidence to uplift. On the basis of field and laboratory data, the characteristics and mechanism of land subsidence and uplift are analyzed and discussed. Under the condition of long-term groundwater extraction, the deformation of aquifer and aquitard units consists of elastic, plastic, visco-elastic, and visco-plastic components. The recoverable elastic and visco-elastic deformation is only a small portion of the total deformation for both aquitard and aquifer units, especially when the groundwater level in the units is lower than the historically lowest values. When the groundwater level in aquifer and aquitard units rises, whether their expansion occurs immediately or not, depends on the changing modes of groundwater level they have experienced. Even aquifer units do not always rebound closely following the rise of groundwater level in them. The lagging of the occurrence of arrested land subsidence and uplift, clearly behind the rise of groundwater level in aquifer units, can be attributed to the visco-plastic deformation of all units and the consolidation deformation of aquitard units. Artificial recharge and limitation of pumpage are efficient measures for controlling land subsidence, but earlier actions are necessary to keep groundwater levels in all aquifer units above their historically lowest values all the time, if a more effective outcome is expected.RésuméL’augmentation de la recharge artificielle des aquifères et la restriction de la sollicitation des eaux souterraines par pompage ont causé des déplacements des terrains à Shanghai (Chine) passant de la subsidence au soulèvement. Sur la base de données de terrain et de laboratoire, les caractéristiques et mécanismes de la subsidence et du soulèvement des terrains sont analysés et discutés. En condition d’exploitation des eaux souterraines sur le long terme, la déformation de l’aquifère et des formations aquitards repose sur les composantes suivantes : élasticité, plasticité, visco-élasticité et visco-plasticité. La déformation élastique et visco-élastique réversible constitue seulement une faible proportion de la déformation totale pour les deux unités aquifères et aquitards, en particulier lorsque le niveau piézométrique dans ces unités est inférieur aux valeurs historiques les plus basses. Lorsque les niveaux piézométriques dans les unités aquifères et aquitards augmentent, si le développement de l’influence se produit immédiatement ou non, cela est dû au changement de régime des niveaux piézométriques. Les unités aquifères également ne subissent pas toujours des mouvements verticaux immédiatement après une augmentation des niveaux piézométriques en leur sein. Le retard de l’apparition d’un arrêt de subsidence et de soulèvement des terrains juste après une augmentation du niveau piézométrique dans les unités aquifères peut être attribué à la déformation visco-plastique de toutes les unités et à la déformation de la consolidation des unités aquitards. La recharge artificielle et la limitation des pompages sont des mesures efficaces pour contrôler la subsidence des terrains, mais des actions préalables sont nécessaires pour maintenir de manière permanente les niveaux piézométriques dans toutes les unités aquifères au-dessus des valeurs historiques les plus basses, si un résultat plus efficace est attendu.ResumenEl aumento de la recarga artificial de agua y la restricción en el bombeo de agua subterránea han causado movimientos del terreno en Shanghai (China) lo cual ha significado un desplazamiento desde la subsidencia a la elevación. Sobre la base de los datos de campo y de laboratorio se analizan y discuten las características y el mecanismo de la subsidencia y la elevación del terreno. La deformación de las unidades acuíferas y acuitardas consta de las componentes elásticas, plásticas, visco-elásticas y visco-plásticas en condiciones de extracción de agua subterránea a largo plazo. La deformación elástica y visco-elástica recuperable es sólo una pequeña parte de la deformación total para las unidades acuíferas y acuitardas, especialmente cuando el nivel de las aguas subterráneas en las unidades es inferior a los valores históricamente más bajos. Cuando el nivel de las aguas subterráneas en las unidades acuíferas y acuitardas asciende, si la expansión se produce en forma inmediata o no, depende del modo en que los cambios se han experimentado en el nivel de las aguas subterráneas. Incluso las unidades acuíferas no siempre se recuperan siguiendo de cerca el ascenso del nivel del agua subterránea en ellas. El retraso en la ocurrencia de la subsidencia y de la elevación del terreno retenido, claramente detrás del ascenso del nivel del agua subterránea en las unidades de acuíferas, puede ser atribuida a la deformación visco-plástico de todas las unidades y la consolidación de la deformación de las unidades acuitardas. La recarga artificial y la limitación de bombeo son medidas eficientes para controlar la subsidencia del terreno, pero son necesarias las acciones previas para mantener los niveles de agua subterránea en todas las unidades del acuífero por encima de sus valores históricamente más bajos durante todo el tiempo, si se espera un resultado más efectivo.摘要不断增加的人工回灌量和对地下水开采量的限制使得上海的地面从下沉转变为上升。根据现场和室内试验资料,本文分析和讨论了上海地面下沉和上升的特征和机理。在长期开采地下水条件下,含水层和弱透水层的变形包括弹性、塑性、粘弹性和粘塑性变形。无论对含水层还是弱透水层,可恢复的弹性和粘弹性变形仅占总变形的一小部分,特别是当地下水位低于含水层、弱透水层所经历的历史上的最低水位时。含水层和弱透水层在其中地下水位升高的情况下是否立即回弹取决于它们所经历的地下水位变化模式,即使含水砂层也不总是随着其中的地下水位回升而立即回弹。地面沉降及回升的明显滞后可归因于含水层和弱透水层的粘塑性变形以及弱透水层的固结。人工回灌和限制地下水开采量是控制地面沉降的有效措施,但是要获得更好的控沉效果,需要尽早采取行动以使含水层和弱透水层中的水位高于其历史上的最低水位。ResumoAumentos na recarga artificial e restrições no bombeamento das águas subterrâneas tem causado deslocamentos de terreno em Xangai (China) a fim de alterar subsidência para soerguimento. Com base nos dados de campo e de laboratório, as características e mecanismos de subsidência e soerguimento de terreno são analisados e discutidos. Sob a condição de extração de águas subterrâneas em longo prazo, a deformação dos aquíferos e unidades aquitardes consiste componentes elásticos, plásticos, visco-elásticos, e visco-plásticos. A deformação elástica e visco-elástica recuperável é apenas uma pequena parte da deformação total para ambas as unidades aquitardes e aquíferos, especialmente quando o nível das águas subterrâneas nas unidades é mais baixo que seus os menores valores históricos. A elevação das águas subterrâneas em aquíferos e aquitardes depende dos modos de mudança de níveis por onde elas passaram, quer sua expansão ocorra imediatamente ou não. Mesmo unidades aquíferas nem sempre acompanham o recuo a ascensão de seus níveis freáticos. O atraso encontrado na ocorrência de subsidência e soerguimento, visto claramente por trás da ascensão do nível do lençol freático em unidades aquíferas, pode ser atribuído à deformação visco-plástica de todas as unidades e à deformação/consolidação de unidades aquitarde. A recarga artificial e limitação do bombeamento são medidas eficientes para controlar a subsidência de terreno, mas ações prévias são necessárias para manter os níveis de águas subterrâneas em todas as unidades aquíferas acima de seus valores históricos mais baixos o tempo todo, caso se espere um resultado eficaz.

Modeling visco-elastic–plastic deformation of soil with modified Merchant model

Eighty-four to ninety-eight percent of land subsidence in Shanghai City is caused by the visco-elastic–plastic deformation of sediments. Numerical experiments are done on the sediments with visco-elastic–plastic deformation in Shanghai to verify the modified Merchant model (MM model) and land subsidence model based on the modified Merchant (LS-MM) model. There are two advantages of the MM model and the LS-MM model. One is that only a few parameters are involved. There are three parameters in the MM model and four parameters in the LS-MM model. The other one is that both models can describe elastic, elastic–plastic and visco-elastic deformation in addition to visco-elastic–plastic deformation. The corresponding models are developed by setting proper values of the three parameters of μ, α1 and α2. The two advantages make the LS-MM model flexible and applicable to the simulation of the large regional land subsidence with visco-elastic–plastic deformation and other different kinds of deformation. The results can be improved by variable parameters, especially specific storage.

Antioxidant response of Daphnia magna exposed to no. 20 diesel oil

Abstract This is the first report of the antioxidant response of Daphnia magna following a short-term response to the water soluble fractions of no. 20 diesel oil. Daphnia magna was exposed for 24h to nominal concentrations of 0, 0.005, 0.01, 0.05, 0.1, 0.5 or 1.0 mg/L diesel oil. Following this exposure, the activities of catalase (CAT) and glutathione S-transferase (GST) were induced significantly on the whole compared to control group; the activity of selenium-dependent glutathione peroxidase (Se-GPx) were inhibited significantly on the whole; the activity of superoxide dismutase (SOD) only responded to diesel oil exposure at the two highest exposure concentrations; the activity of glutathione reductase (GR) and the content of reduced glutathione (GSH) were greatly activated in Group 4; and the content of oxidized glutathione (GSSG) were induced at two different concentrations. Total glutathione (tGSH) and GSH/GSSG ratio were also calculated to analyze the occurrence of oxidative stress. In conclusion, CAT, GST and tGSH could be potential early warning signals for short-term effects of diesel oil in aquatic ecosystems, and further studies are needed.

A cubic‐spline technique to calculate nodal Darcian velocities in aquifers

A continuous and reliable velocity field is required for the simulation of mass and heat transport in an aquifer system. In this paper, a cubic-spline technique is proposed to calculate nodal Darcian velocities after the flow field is obtained. With this technique, a continuous velocity field is produced, and mass conservation is satisfied to an acceptable degree. Its requirements for computer storage are very small, and the calculation speed is very fast; it can be implemented in parallel. A synthetic diffusion problem is used to examine the accuracy of this technique. The results agree very well with the analytical solution. Application to another problem shows that this technique can be applied to any heterogeneous and anisotropic aquifer. The results of the two sample problems are also compared with the Galerkin finite element method [Yeh, 1981] and the dual mesh method [Batu, 1984]. It is observed that its agreement with the Galerkin method is much better than the dual mesh method.

Modified Multiscale Finite-Element Method for Solving Groundwater Flow Problem in Heterogeneous Porous Media

AbstractThe purpose of this paper is to modify the multiscale finite-element method (MSFEM) to solve groundwater flow problems in heterogeneous porous media, such as large-scale problems, long-term prediction problems, and nonlinear problems. The MSFEM has been developed to deal with flows in heterogeneous porous media. Many practical works and numerical simulations have been done to show its accuracy. However, for the large-scale or long-term prediction problems, the MSFEM needs a great amount of computational cost in constructing base functions, which is not efficiency. The primary feature of our modified MSFEM (MMSFEM) is to use a new coarse element subdivision to reduce the number of the interior nodes, thus to decrease the unknowns in the reduced elliptic problems to save much computational cost while ensuring computational accuracy. Some numerical experiments in this paper indicate that the MMSFEM can reduce more than 90% of CPU time of the MSFEM.

Mechanisms for earth fissure formation due to groundwater extraction in the Su-Xi-Chang area, China

Excessive groundwater withdrawal has caused many earth fissures in the cities of Suzhou, Wuxi, and Changzhou (i.e., the Su-Xi-Chang area or “SXC area”) in Jiangsu Province, China. The appearance of these fissures is closely associated with groundwater withdrawal both temporally and spatially. Based on field investigations, three models of the earth fissures in the SXC area were conceptualized. The changes in and distributions of normal and shear stress in hydrostratigraphic units due to groundwater extraction were analyzed numerically for each conceptualized model. Results from these numerical simulations indicated that geological conditions play a crucial role in the occurrence and distribution of earth fissures. Earth fissures are much more likely to initiate in areas where the depth of the bedrock below the ground surface is small, the thickness of the exploited aquifer unit changes abruptly, and the surface of the bedrock undulates dramatically. Earth fissures are also likely to occur in the vicinity of a distant restricted boundary. In addition, very stiff topsoil is more prone to cracking, and the locations of discharge wells also influence the occurrence of earth fissures.

Compaction of aquifer units under complex patterns of changing groundwater level

Long-term groundwater withdrawal has caused severe land subsidence in Shanghai, in which compaction of aquifer units has taken an important role. The compaction characteristics of aquifer units are closely related to the changing patterns of groundwater levels the units have experienced. They may be elastic, elasto-plastic, visco-elastic, or visco-elasto-plastic. Several compaction models are discussed and used to calculate the compaction of the aquifer units in Shanghai. Compared with other models, it is found that double-yielding visco-elasto-plastic model can capture the compaction characteristics of aquifer units and more reasonably simulate the compaction of aquifer unit under complex changing patterns of groundwater level. In particular, the double-yielding model can describe the plastic compaction when the average groundwater level declines but is higher than the historically lowest level and the obvious visco-plastic compaction when the groundwater level is lower than the historically lowest level, which is a popular deformation characteristic for aquifer units in Shanghai.