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  • 期刊名称:

    Journal of Contaminant Hydrology

  • 中文名称: 污染水文学
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  • ISSN: 0169-7722
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  • 机译 通过分区示踪剂测试对NAPL进行表征以量化分区非线性的影响
    • 作者:William R. Wise;
    • 刊名:Journal of Contaminant Hydrology
    • 1999年第1/2期
    摘要:The inherent nonlinearity in the equilibrium interphase distribution of a partitioning tracer between a NAPL and water affects the manner in which the partitioning tracer moves throughout a region of the subsurface contaminated with the NAPL. A semi-analytic solution is developed to describe this behavior. Analysis of a breakthrough curve of the partitioning tracer in such a system using a linear partitioning based model results in systematic overestimation of the NAPL present in the region swept during the test.
  • 机译 停留时间和水饱和度对吸附非平衡参数的影响
    摘要:This study reports the impact of the degree of water saturation on sorption nonequilibrium parameters. Two nonionic organic compounds (benzene and dimethylphthalate) and three nonag- gregated sandy soils were utilized. Local equilibrium assumptions were found to be invalid for describing the transport of these compounds even at pore-water velocities as low as 0.7 cm/h. Sorption nonequilibrium appeared to be of a diffusive nature rather than due to a slow chemical reaction. Sorption mass-transfer coefficients varied proportionally with pore-water velocity. A strong correlation between the mass-transfer coefficient and residence time was found utilizing present and previously reported laboratory data. A similar relationship was also found for the mass-transfer coefficient between mobile and immobile water regions. Field data indicate that the sorption mass--transfer coefficient may continue to decrease in a consistent way even at residence times as large as 5 × 10~3 h. Variations in the degree of water saturation had no impact on the value of the sorption mass-transfer coefficient other than what would be expected due to changes in the residence time. This suggested that movement into the solid grains of the large emptied pores through diffusion from the water-filled pores into stagnant water covering these grains was relatively fast compared to the sorption rate.
  • 机译 气相萃取估算层状土壤中的净化时间
    摘要:Soil vapor extraction (SVE) is a standard remediation technique for cleaning up soils contaminated by volatile organic compounds (VOCs). A key parameter for planning SVE operations is the time required to reach the desired cleanup standard. In this paper, an approximate analytical solution is developed, which allows the fast estimation of cleanup times in layered unsaturated zones. The contaminants are assumed to be dissolved in the pore water, sorbed on the soil matrix and mixed with the soil air. Liquid organic phase is absent. For partitioning between gas and water and water and solid, local--equilibrium is assumed. The analytical solution is based on the well mixed reservoir model and on the plug flow model. It is shown that, for a number of scenario cases, the results of the analytical solution are, for practical purposes, in reasonable agreement with a numerical solution of the partial differential equations for the local-equilibrium advection--dispersion model of mass transport in porous media by Fickian diffusion and Darcian air flow. The results are displayed in terms of Peclet number of molecular diffusion (PNMD). In the analytical solution three different approximations are used. The PNMD range is divided into three intervals, representing different transport regimes. At low PNMD, molecular diffusion dominates transport in both layers. In this interval cleanup time is estimated by the average of the plug flow time for one pore volume through the layer of higher permeability, and the cleanup time estimated by the mixed reservoir model. At intermediate PNMD values, advective transport dominates in the more permeable layer and molecular diffusion in the less permeable. Conse- quently, cleanup time is limited by diffusive mass transfer from the less to the more permeable layer. In this interval, the estimation of cleanup time is entirely based on the mixed reservoir model. At high PNMD values, transport is governed in both layers by advection. Here, cleanup time is estimated by applying the plug flow model to the layer of lower permeability. The range of soil permeability values, for which such high PNMD values can be achieved, as well as the range of the actual air flow rates, are identified. The limitations of the validity of local-equilibrium assumption at high PNMD values are discussed using the relationship between desorption rates and gas advection fluxes. Further, the sensitivity of cleanup time estimates with respect to the independent dimensionless parameters characterizing the SVE configuration considered, is studied.
  • 机译 通过分配示踪剂测试对非水相液体进行表征,并利用改进的Langmuir关系描述了分配非线性
    摘要:The equilibrium interphase behaviors of alcohol partitioning tracers between NAPL and water are inherently nonlinear in nature. This nonlinearity may be described using an unfavorable form of the Langmuir partitioning relation with a good degree of agreement up to tracer mole fraction values of 0.3. The presence of co--tracers tends to move the equilibrium partitioning closer to Raoult's law. It may be possible to manipulate tracer tests systems to minimize the effects of nonlinearities through the use of co-tracers.
  • 机译 荧光假单胞菌菌株P17通过石英砂柱的迁移与水分含量的关系
    摘要:Porous media column experiments were used to investigate Pseudomonas fluorescens strain P17 transport as a function of water content and the influences of the solid--liquid and gas--liquid interfaces. Retention of radiolabeled P17 in washed quartz sand was evaluated at 100, 84, and 46/100 water saturation. At the completion of each experiment, the porous medium was extruded and sampled directly for cell retention on the basis of a radiolabel mass balance. Maximum cell retention occurred in the top centimeter of porous media at all three water contents and decreased with depth in the column. The total fraction of cells retained (R_t) was inversely proportional to water content, with nearly twice the cell retention at 46/100 saturation (R_t = 0.95) compared to retention in 100/100 water-saturated experiments (R_t = 0.50). Total retained cells were further divided into strongly and weakly attached fractions by settling a sample of the porous medium through groundwater to dislodge loosely adhering cells. Cells that became suspended in the solution represented the fraction retained at the gas-liquid interface or weakly attached to the solid-liquid interface (R_g). Those that remained attached to the porous medium were defined as cells strongly attached to the solid--liquid interface (R_s). Values of R_g/R_t were inversely related to water content, while R_s/R_t decreased with decreasing saturation. Bacteria thus preferentially accumulated at the gas--liquid interface with total cell removal inversely proportional to water content. The increased retention of bacteria at the gas--liquid interface indicates the presence of the interface is an important factor in limiting pathogen migration, evaluating biocolloid-facilitated transport of pollutants, and developing bioremediation strategies for unsaturated porous media.
  • 机译 戊唑醇中阿特拉津吸附参数和其他土壤性质的空间变异性
    摘要:The spatial variability of the K_f and n parameters of the Freundlch sorption isotherm for atrazine and their correlation with soil textural variables, cation exchange capacity and organic carbon content were studied in a stagnic podzoluvisol. Ninety-three sample points were organized on an irregular three--dimensional grid to a depth of 3.2 m. A trend in the vertical direction explains, for most variables, about 85% of the observed variance. This trend also significantly influences the observed correlation structure between the variables. The horizontal and vertical trends were removed from the data set with the median polish algorithm. The residuals resulting from this technique obey the intrinsic hypothesis. Organic carbon content, cation exchange capacity and n revealed spatial structure. The estimated correlation length scales in the vertical direction were between 0.63--0.8l m for n and the organic carbon content, and between 0.25--0.40 m for the cation exchange capacity. The variograms of sand, loam, clay and K_f exhibited pure nugget. The correlation structures between the variables differ for different spatial increments. Variables appeared correlated at small spatial increments whereas they are not correlated if the spatial location of the sample points is neglected.
  • 机译 低水溶性电子给体,用于减少厌氧沉积物中的硝基芳烃
    摘要:Studies are presented investigating the ability to enhance aryl nitro--reduction processes in sediments through electron donor addition. In particular, high molecular weight (starch and guar gum) and/or low aqueous solubility electron donors (oleic acid) were studied, since they should be less prone to diffusive loss to the water column after addition to contaminated areas. For comparison, complimentary studies were conducted with water-soluble electron donors (acetate and dextrose). The ability to enhance activity was measured by methane production and reduction of either nitrobenzene or 1,3,5--trinitrobenzene to aniline or dinitroaniline. The results demonstrate that all electron donors resulted in increased methane production after a lag phase. The highest level of methane production and the shortest lag phase in uncontaminated sediment microcosms was observed in acetate-fed systems. Sorption studies of all electron donors showed that starch was partitioning the least into the water phase. In microcosms containing nitrobenzene, trini- trobenzene and acetate, methane production did not occur and nitro--reduction was not observed. Conversely, the addition of dextrose or starch yielded methane production and aryl nitro--reduction with each contaminant tested. Neither nitrobenzene nor trinitrobenzene was significantly reduced in HgCl_2-killed controls. From these studies, it appears that starch may be well suited for applications of in-place, anaerobic sediment bioremediation.
  • 机译 冲积砾石中镉的非平衡迁移
    摘要:The transport of Cd in alluvial gravels was investigated using batch tests and miscible displacement experiments with large and small columns. Batch tests indicates that Cd adsorption fitted the Freundlich isotherm reasonably well and was highly nonlinear. The sorption of Cd under batch conditions was essentially complete within a few minutes, followed by a time-dependent slow sorption in weeks. A large column (200 cm long, 19 cm diameter) was injected with pulse solutions containing Cd, Br, Cl, and rhodamine WT at pore--water velocities of 20 and 61 m/day; while the small column (18 cm long, 10 cm diameter) was injected with Br and Cd pulses at pore--water velocities of 18 and 58 m/day. Breakthrough curves (BTCs) of Cd were highly asymmetric while those of other solutes were essentially symmetric, suggesting the presence of a non--equilibrium component for the Cd transport. This was further evidenced by decreases in Cd concentrations when flow was interrupted. Under all conditions investigated, asymmetry in Cd BTCs essentially resulted from chemical non-equilibrium as physical non-equilibrium was not present. Both equilibrium and non-equilibrium models, as incorporated in CXTFIT, were used to describe observed BTCs of Cd. Dispersivity was obtained from the nonreactive solute Br data, and it was then held constant for the other solutes. The retardation factor (R) vales were estimated based on results from batch tests and the time moment method. For comparison purposes, the R values of the Cd data were also simulated from the two-site models. The values of the partitioning coefficient (β) and the mass transfer coefficient (ω) were estimated from two-region/site models. Modelling results suggest that (1) Cd transport was mainly controlled by rate--limited sorption; (2) the scale effect on Cd transport was minor for the reasonably well sorted material investigated, with a slight increase in the degree of equilibrium in the large column. Small columns may be used to obtain fast experimental results for homogeneous medium. However, if heterogeneity and preferential flow is important, larger columns are recommended. (3) it was evidenced that the degree of chemical non--equilibrium increased with increasing pore--water velocities, however the change was not major for the flow rates investigated (18--61 m/day); and (4) equilibrium models could provide apparently good fits to skewed BTCs by overestimating dispersivity, which incorporates all the effects from the dispersion and diffusion within both mobile and immobile liquid phases and/or type--1 and type-2 sorption sites. Comparatively, non--equilibrium models described the Cd data better and provided a more correct explanation for the spreading and asymmetry of the Cd BTC.
  • 机译 氟在粘土中扩散和吸附的实验分析
    摘要:Double reservoir diffusion cell tests were employed to estimate parameters for fluoride sorption and diffusion through porous clay media. Tests were conducted on both commercial kaolin and bentonite clays. The bentonite was found to be a better fluoride barrier than kaolin, especially when volumetric changes from swelling were minimised by clamping. Modelled values of effective diffusion in kaolin were typically around 0.015 m~2/yr, which are nearly three times lower than the molecular diffusion in free solution and 10 times greater than the value obtained for clamped bentonite (constant volume and constant confining pressure). Optimised sorption parame- ters obtained by fitting both linear and non--linear sorption models to diffusion cell breakthrough data were compared with equivalent parameters from batch sorption tests. Both models were equally capable of accurately fitting all experimental data. However, in cases of highly non--linear sorption, care must be taken with the linear model as the sorption parameter depends on the concentration range. Sorption parameters from t1uoride batch tests and clay tortuosities from chloride diffusion tests were found to adequately predict fluoride diffusion results. It was found that the modelled parameters for diffusion and partition did not depend significantly on the initial moisture content at compaction of the clay plug. Clay plugs formed through consolidation of a slurry, however, appear to provide more tortuous barriers than compacted clay plugs. Some decline in fluoride retention was observed with increasing ionic strength of solution.
  • 机译 特内里费岛的农用化学品浸出潜力评估
    摘要:This paper reports an index-based regional-scale characterization of non--point source ground- water contamination potential for the agricultural areas on the Canary Island of Tenerife. The relative leaching potential for 24 pesticides was quantitatively assessed and ranked using the Leaching index (Li) for the soil, landcover, and recharge conditions in Tenerife. The uncertainty in the Li estimates, due to uncertainties in the soil, recharge, and chemical data, were accounted for using first--order uncertainty analysis. Several of the pesticides considered in this study were assessed to be potential leachers. The soil insecticide Carbofuran (2,3--dihydro-2,2--dimethyl-7-be zofuranyl--n--methylcarbamate) was found to have the greatest leaching potential for the soil, landcover, and recharge conditions across Tenerife.
  • 机译 DNAPL的随机聚集模型(SAM)-多孔介质中的水置换
    摘要:Source zone characterization of DNAPL in the subsurface is a necessary part of managing environmental risks. Modeling DNAPL--water displacement processes at the pore-scale can lead to greater insight and understanding of lateral spreading, the extent of vertical migration, and the final fluid distributions of dense non--aqueous phase liquids. A two-dimensional stochastic aggregation model is developed to study DNAPL--water displacement in porous media. The model is a modified diffusion limited aggregation model, and uses essential properties governing front stability as model input : DNAPL--water viscosity differences, DNAPL--water density differences, intrinsic permeability of the porous media, flow rate, and the inclination angle of the porous media from the horizontal. Due to the simplicity of the algorithm, this modeling technique can produce realistic DNAPL--water configurations much faster than conventional continuum approaches and allows for a Monte Carlo approach to be utilized. The model is validated through comparison to laboratory experiments involving 1,2-Dichloroethane, carbon tetrachloride, tetrachloroethylene, and mobile pyrogard 53. These experiments were performed at varying flow rates and angles of inclination from the horizontal.
  • 机译 电迁移的评估作为研究放射性核素在黏性土壤中扩散的新技术
    摘要:For the performance assessment study of a geological disposal of High Level Waste (HLW) in clayey formations, migration studies are essential. For low permeability soils (clays), classical diffusion studies take a very long time. In order to reduce the experimental time, we propose an electrical field as driving force to accelerate the migration of ionic species. This paper reports the assessment of the electromigration technique as a powerful new and fast technique for migration studies. The apparent molecular diffusion coefficient can be derived by two independent methods using the migration parameters obtained from an electromigration experiment, namely the apparent dispersion coefficient and the apparent convection velocity. First, it can be calculated from the velocity of the migrating species by the Einstein relation. But, corrections are necessary for electroosmotic flow. The apparent electroosmotic mobility is experimentally determined as 2.2 ·10~(-9) m~2/Vs. Second, it can be calculated from the relation between the apparent dispersion coefficient and the total apparent convection velocity. But it is necessary to know the dispersion length of the medium. The dispersion length for Boom Clay is experimentally determined as 8· 10~(-5) m. Because of the serious reduction in time, it becomes possible to run series of experiments at different electrical fields to obtain averaged values for the apparent molecular diffusion coefficient according to the two methods. Experiments at different electrical fields have another advantage f the intercept of the linear relationship between the total apparent convection velocity and the apparent dispersion coefficient gives the apparent molecular diffusion coefficient. The apparent molecular diffusion coefficients obtained for ~85S, ~131I and HTO are respectively 0.8. 10~(-11), 15· 10~(-11), and 24· 10~(-11) m~2/s. These values are confirmed by pure diffusion experiments. The excellent agreement with the apparent molecular diffusion coefficients obtained by classical diffusion tests clearly demonstrates the feasibility of the electromigration technique for the determination of diffusion coefficients.
  • 机译 表面活性剂对土壤吸附阿特拉津的影响
    摘要:This study investigates the effect of synthetic wastewater containing surfactants on the sorption of atrazine using an equilibrium batch technique. Laboratory experiments were conducted on three soils with two non-ionic (Rexol and Rexonic) surfactants and one anionic (Sulphonic) surfactant, specifically manufactured for the detergent industry. Four sets of experiments were conducted to examine the influence of surfactants on the equilibrium time of atrazine sorption, to explore the effect of surfactant concentration, pH and type of surfactant on the amount of atrazine sorbed and to determine sorption isotherms of atrazine in the presence of surfactants. The results indicate that the application of Sulphonic results in dramatic increase in the adsorption of atrazine on to soils, the increase being directly proportional to the concentration of the surfactant. Application of the Sulphonic surfactants with a concentration of 3000 mg/l can result in a significant increase in K_d values of atrazine for loam and sandy loam soils. On the other hand, the effect of non-ionic surfactants depends on their concentration. Generally, non-ionic surfactants can result in a slight increase in atrazine sorption at high concentration, an exception being Rexol on sandy loam soil. At low concentrations, non-ionic surfactants have shown a tendency to decrease atrazine sorption.
  • 机译 玻璃微珠溶质运移的微观模型研究
    摘要:This study presents solute transport experiments and simulations conducted in a horizontally- mounted glass bead micromodel. The glass bead micromodel of novel design, with one layer of glass beads fused between two glass plates, simulates an ideal porous medium. Various scale levels of solute transport through the micromodel were observed experimentally and recorded on video tape for use with image analyzers. Results were analyzed with image analyzers to obtain relative concentration plots for the bulk micromodel and at various points in the model. The results show favorable comparisons of experimental and numerical data. The glass bead micro- model study was a feasible procedure for quantifying micromodel experiments.
  • 机译 CHEMFRONTSf一个耦合的地球化学和运输模拟工具
    摘要:A computer program to calculate coupled mass transport and fluid rock interactions has been developed. CHEMFRONTS is based on the quasi-stationary state approximation and it uses a kinetic expression to describe mineral dissolution and precipitation rates. It simulates the chemical evolution of the mineral and aqueous phases over time along a streamline. For fast kinetics, local equilibrium conditions are approached. In the aqueous phase, complexation and redox reactions are included. Reactions with gas phases such as carbonation may also be handled by the program in some special cases. The quasi-stationary state approximation makes it possible to solve problems that would require an extremely large computer effort with conventional models. Such problems arise when the mass of minerals is large compared to the concentrations in the water. The program is especially suited to handle sharp reaction fronts. As the program does not use spatial discretization, the separation between closely located fronts can be resolved and the movements of the fronts may be computed with high spatial resolution. Sharp fronts are usual in the ground and typical examples are redox fronts and dissolution and precipitation fronts. The capabilities of the program are shown in the interpretation of two field--scale processes.
  • 机译 富含厌氧硫酸盐的地下水中BTEX羽的变异性和内在修复
    摘要:Data from long--term groundwater sampling, limited coring, and associated studies are synthe- sised to assess the variability and intrinsic remediation/natural attenuation of a dissolved hydrocarbon plume in sulphate-rich anaerobic groundwater. Fine vertical scale (0.25-- and 0.5-m depth intervals) and horizontal plume--scale (> 400 m) characteristics of the plume were mapped over a 5-year period from 1991 to 1996. The plume of dissolved BTEX (benzene, toluene, ethylbenzene, xylene) and other organic compounds originated from leakage of gasoline from a subsurface fuel storage tank. The plume was up to 420 m long, less than 50 m wide and 3 m thick. In the first few years of monitoring, BTEX concentrations near the point of leakage were in approximate equilibrium with non-aqueous phase liquid (NAPL) gasoline. NAPL composition of core material and long-term trends in ratios of BTEX concentrations in groundwater indicated significant depletion (water washing, volatilisation and possibly biodegradation) of benzene from residual NAPL after 1992. Large fluctuations in BTEX concentrations in individual boreholes were shown to be largely attributable to seasonal groundwater flow variations. A combination of temporal and spatial groundwater quality data was required to adequately assess the stationarity of plumes, so as to allow inference of intrinsic remediation. Contoured concentration data for the period 1991 to 1996 indicated that plumes of toluene and o-xylene were, at best. only partially steady state (pseudo--steady state) due to seasonal groundwater flow changes. From this analysis, it was inferred that significant remediation by natural biodegradation was occurring for BTEX component plumes such as toluene and o-xylene, but provided no conclusive evidence of benzene biodegradation.
  • 机译 在传质受限条件下从残留的截留非水相液体中溶解苯,甲苯,间二甲苯和萘
    摘要:The results of dissolution experiments for benzene, toluene, m-xylene and naphthalene (BTXN) from a relatively insoluble oil phase (tridecane), residually trapped in a non-sorbing porous medium, are described. This mixture was chosen to simulate dissolution of soluble aromatic compounds from a petroleum hydrocarbon mixture, e.g., crude oil, for which a large fraction of the mixture is relatively insoluble. The experiments were carried out at a small source length to interstitial velocity ratio, L/v, so that dissolution would be mass transfer limited (MTL). When fitted to data for toluene, a multiregion mass transfer model was found to predict the experimental data satisfactorily for the other components without adjustment of the mass transfer rate parameters. These results indicate that the dissolution process can be generalized for various hydrophobic organic compounds present in a multicomponent non--aqueous phase liquid (NAPL) when mass transfer limitations are present. This also suggests that dissolution data obtained for one compound can be useful for predicting the dissolution histories for other compounds from petroleum hydrocarbon mixtures.
  • 机译 纳瓦霍砂岩上沉淀的尿素的氧化溶解
    摘要:Column and batch experiments were conducted with sandstone and ground water samples to investigate oxidation of uraninite precipitated by microbially mediated reduction of U(VI), a contaminant in ground water beneath a uranium mill tailings site near Tuba City, AZ, USA. Uraninite precipitated together with mackinawite (FeS_0.9) because Fe(III) from the sandstone and sulfate, another contaminant in the water were reduced together with U(VI). After completion of U(Vl) reduction, experiments were conducted to find out whether uraninite is protected by mackinawite against reoxidation. Uncontaminated ground water from the same site, containing 7 mg/l of dissolved oxygen, was passed through the columns or mixed with sandstone in batch experiments. The results showed that small masses of uraninite, 0.1 μg/g of sandstone, are protected by mackinawite from reoxidation. Uraninite masses on the order of 0.1μ g/g corre- spond to U(VI) concentrations of 0.5 mg/l, typically encountered in uranium contaminated ground waters. Mackinawite is an effective buffer and is formed in sufficient quantity to provide long-term protection of uraninite. Uranium concentrations in ground water passed through the columns are too low (4 μg/l) to distinguish between dissolution and oxidative dissolution of uraninite. However, batch experiments showed that uraninite oxidation takes place.
  • 机译 挥发性有机化合物在粘土矿物上的吸附/解吸动力学
    摘要:Soils surrounding industrial sites or at locales where industrial chemicals are utilized, fre- quently become contaminated through unsuitable discharge of potentially hazardous organic compounds. The fate and transport of these chemicals must be sufficiently understood to predict detrimental environmental impacts and to develop technically and economically appropriate remedial action to minimize environmental degradation. Improving our understanding of the processes involved in organic pollutant vapor transport is important because the gas phase is often the most mobile, and therefore most potentially hazardous phase. In order to gain a better understanding of the basic kinetic processes affecting soil adsorption/desorption of volatile organic compounds (VOC's) in the vapor phase, we conducted VOC adsorption/desorption experiments using oven-dry clay minerals. Transient, isothermal, gravimetric sorption experiments using volatile organic compounds (VOC's) acetone, benzene and toluene onto pure clay minerals obtained from Ward's Scientific (kaolinite, illite, and Ca-montmorillonite) suggest a biphasic sorption mechanism on these minerals. Experimental results indicate that hydrophobic sorption onto oven-dry clay minerals with negligible soil organic matter is controlled by rates of inter--particle Fickian diffusion mechanisms, intra-particle Fickian diffusion mechanisms, and sorption kinetics. Using an analytical solution to Fick's Second Law where sorption is partitioned into macroscopic and microscopic domains, each with unique diffusion time constants, enables precise prediction of experimental sorption observations. Correlation coefficients of 0.999 were found between the parameter optimized analytical solution and very large sets of experimental data. Macroscopic diffusion coefficients ranged from 10~(-2) to 10~(-4) cm~2/min, while microscopic diffusion coefficients ranged from 10~(-12) to 10~17 cm~2/min. Sorption rates suggest that signifi- cant fractions of VOC's adsorb onto surfaces other than the external mineral surfaces. The fraction of mass sorbed on the mineral surface ranged from 30/100 to 75/100 of the equilibrium sorbed mass.
  • 机译 分层裂缝含水层中污染物的运移方式
    摘要:We investigated patterns of contaminant transport within the layered and fractured aquifer of a 7.3-km~2 upland agricultural watershed in east--central Pennsylvania, USA. Geometry and hy- draulic properties of the aquifer had been characterized by field testing and model calibration. These results were extended to simulate flow pathways and patterns of contaminant transport in both areal and cross--section formats within the watershed. The analyses indicated that the ground water flow system at the larger watershed scale is comprised of smaller units of subsurface flow which are self-contained at the scale of first-- or second--order streams. For this scale subwatershed or larger, contaminant inputs to ground water from the mix of land use within the subwatershed should translate directly to the quality of nonstorm streamflow. For illustration, recharge water quality from typical land--use distributions were combined with a simple model of contaminant transport to simulate nitrate concentration patterns in ground water in a cross--section format. Land use in the vicinity of the drainage divides between streams was found to control ground water quality within the deeper layers of the aquifer, while land use over the remainder of the watershed area affected water quality only within the shallower layers of the aquifer. Streamflow nitrate data collected during a baseflow survey on the watershed were examined in context of these simulations and found to support the conclusions. Results of the study demonstrate the potential for localized contamination of ground water and nonstorm streamflow by agricultural land use, as well as the potential for managing stream quality and minimizing contamination within targeted zones of the ground water by controlling land use position.
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