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1.
镉在中性和碱性土柱中不同深度处的运移模拟 总被引：2，自引：0，他引：2
Human health has been potentially threatened by cadmium (Cd) contained in sewage irrigation water.Previous studies of Cd transport in soils were mainly conducted using small soil cores with pH values less than 6.The objectives of this study were to determine the parameters of the convection-dispersion equation (CDE) for Cd transport in relatively larger columns with neutral and alkaline soils,and to investigate the parameters' variability with depth.The soil columns were 50 cm in length and 12.5 cm in diameter.Ceramic suction lysimeters were buried at depths of 2.5,7.5,17.5,27.5,and 37.5 cm to abstract soil solution.Cd concentration in the soil solution samples were subsequently analyzed to obtain breakthrough curves (BTCs).Equilibrium and nonequilibrium models in CXTFIT program were used to estimate parameters of the CDE.The results suggested that both equilibrium and non-equilibrium models performed well in modeling Cd transport.The hydrodynamic dispersion coefficient (D) ranged from 0.18 to 10.70 cm 2 h 1,showing large differences among different depths.The retardation factor (R d) ranged from 25.4 to 54.7 and the standard deviation of R d value was lower than 30% of the mean value.Precipitation coefficient (R p) decreased consistently with increasing depth,varying from 1.000 × 10 10 to 0.661 h 1.Sensitivity tests showed that D was less sensitive than R d.These results would be helpful in understanding the transport and retention of Cd in non-acidic soils. 相似文献
2.
A combined model of solute transport and water flow was developed to simulate the migration of methanol, a soluble organic chemical, in unsaturated soil zone. The solute transport equation considered convective-dispersive transport in the liquid phase as well as diffusion in the gas phase. The effect of rainfall and evapotranspiration on transport was considered at the boundary conditions of the governing equations. Data on the characteristics of a loam soil and the climatic conditions in southern California were also introduced to compare the results with those from a study in the USA in which the profiles of methanol distribution and water content in the soil zone at different times had been depicted. This comparison showed that there was good agreement between the two studies. The results showed that methanol contamination reached a depth of about 250 cm after 8 760 h. In contrast, if rainfall and evapotranspiration were not considered, the depth was only about 140 cm. The model therefore confirmed that rainfall strongly affected solute transport. 相似文献
3.
红壤中水热耦合转化的实验和数值模拟研究 总被引：1，自引：0，他引：1
Coupled transfer of soil water and heat in closed columns of homogeneous red soil was studied under laboratory conditions.A coupled model was constructed using soil physical theory,empirical equations and experimental data to predict the coupled transfer.The results show that transport of soil water was affected by temperaature gradient,and the largest net water transport was found in the soil column with initial water content of 0.148m^3m^-3,At the same time,temperature changes with the transport of soil water was in a nonlinear shape as heat parameters wre function of water content,and the changes of temperature were positively correlated with the net amount of water transported.Numerical modelling results show that the predicted values of temperature distribution were close to the observed values,while the predicted values of water content exhibited limited deviation at both ends of the soil column due to the slight temperature changes at both ends .It WAS indicated that the model proposed here was applicable. 相似文献
4.
放牧强度对中国内蒙古草原土壤水分状况与通量的影响 总被引：1，自引：0，他引：1
In the past few decades,the increase in grazing intensity has led to soil degradation and desertification in Inner Mongolia grassland,China,due to population growth and shift in the socio-economic system.Two sites with different grazing intensities,continuous grazing site(CG) with 1.2 sheep ha 1 year 1 and heavy grazing site(HG) with 2.0 sheep ha 1 year 1,were investigated at the Inner Mongolia Grassland Ecosystem Research Station(43 37 50 N,116 42 18 E) situated in the northern China to i) characterize the temporal distribution of soil water content along soil profile;and ii) quantify the water fluxes as affected by grazing intensity.Soil water content was monitored by time domain reflectometry(TDR) probes.Soil water retention curves were determined by pressure membrane extractor,furthermore processed by RETC(RETention Curve) software.Soil matric potential,plant available water and water flux were calculated using these data.Both sites showed an identical seasonal soil water dynamics within four defined hydraulic periods:1) wetting transition coincided with a dramatic water increase due to snow and frozen soil thawing from March to April;2) wet summer,rainfall in accordance with plant growth from May to September;3) drying transition,a decrease of soil water from October to November due to rainfall limit;and 4) dry winter,freezing from December to next February.Heavy grazing largely reduced soil water content by 43%-48% and plant available water by 46%-61% as compared to the CG site.During growing season net water flux was nearly similar between HG(242 mm) and CG(223 mm) sites between 5 and 20 cm depths.However,between 20 and 40 cm depths,the upward flux was more pronounced at HG site than at CG site,indicating that water was depleted by root uptake at HG site but stored at CG site.In semi-arid grassland ecosystem,grazing intensity can affect soil water regime and flux,particularly in the growing season. 相似文献
5.
An analytical solution for advance of solute front in soils 总被引：3，自引：0，他引：3
Based on the assumption that solute transport in a semi-infinite soil column or in a field soil profile can be described by the boundary-layer method, an analytical solution is presented for the advance of a solute front with time. The traditional convection-dispersion equation (CDE) subjected to two boundary conditions: 1) at the soil surface (or inlet boundary) and 2) at the solute front, was solved using a Laplace transformation. A comparison of resident concentrations using a boundary-layer method and an exact solution (in a semi-infinite-domain) showed that both were in good agreement within the range between the two boundaries. This led to a new method for estimating solute transport parameters in soils, requiring only observation of advance of the solute front with time. This may be corroborated visually using a tracer solution with marking-dye or measured utilizing time domain reflectometry (TDR). This method is applicable to both laboratory soil columns and field soils. Thus, it could be a step forward for modeling solute transport in field soils and for better understanding of the transport processes in soils. 相似文献
6.
江西省雨水、灌溉水及渗漏水中的硫对土壤硫的影响 总被引：1，自引：0，他引：1
Ten rainfall and irrigation water-collecting posts were set up in different ecotype districts of Jiangxi Province,China,to quarterly measure S content in rainfall and irrgation water.A rasinwater chemical composition-collecting device was used to collect the sulphur in rainfall,and the amount of sulphur adsorbed on the resin column in the device was determined.The soil percolating water was gathered using 6 lysimeters built up according to the profile sequence of the red soil derived from red sandstone and the red soil derived from Quaternary red clay,separately.On the lysimeters peanuts,soybean and radish were grown in rotation.Two treatments were designed:without S addition and with S additin at a rate of 14kg S ha^-1,The SO4^2- contents in rainfall,irrigation water and soil percolating water were determined by the turbidimetry.The results in 1997 showed that the average annual S content in rainwater ws 28.13kg S ha^-1.the average S content in irrigation water was 1.7mg S L^-1,and the average content of SO4^2- in soil percolation water was 2.30kg Sha^-1 year^-1 and 4.70 kg Sha^-1 year^-1 in treatments without and with sulphur application,respectively,In Jiangxi Province,apart from the losses by runoff and leaching,the sulphur in rainfall avaliable to crops is 7.3kg S ha^-1 year^-1 and additional S application is required.When rice is grown.however,irrigation water can suply 6.9kg S ha^-1,which,along with the sulphur in rainfall,cal almost meet the S requirement of one cropping of rice. 相似文献
7.
Soil water-retention characteristics at measurement scales are generally different from those at application scales, and there is scale disparity between them and soil physical properties. The relationships between two water-retention parameters, the scaling parameter related to the inverse of the air-entry pressure (αvG, cm-1) and the curve shape factor related to soil pore-size distribution (n) of the van Genuchten water-retention equation, and soil texture (sand, silt, and clay contents) were examined at multiple scales. One hundred twenty-eight undisturbed soil samples were collected from a 640-m transect located in Fuxin, China. Soil water-retention curves were measured and the van Genuchten parameters were obtained by curve fitting. The relationships between the two parameters and soil texture at the observed scale and at multiple scales were evaluated using Pearson correlation and joint multifractal analyses, respectively. The results of Pearson correlation analysis showed that the parameter αvG was significantly correlated with sand, silt, and clay contents at the observed scale. Joint multifractal analyses, however, indicated that the parameter αvG was not correlated with silt and sand contents at multiple scales. The parameter n was positively correlated with clay content at multiple scales. Sand content was significantly correlated with the parameter n at the observed scale but not at multiple scales. Clay contents were strongly correlated to both water-retention parameters because clay content was relatively low in the soil studied, indicating that water retention was dominated by clay content in the field of this study at all scales. These suggested that multiple-scale analyses were necessary to fully grasp the spatial variability of soil water-retention characteristics. 相似文献
8.
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. 相似文献
9.
Diffusion coefficients of chlorde ions in four soils of different exture with varying effective moisture content and varying bulk density from 1.1 to 1.6 g cm^3 under three different temperatures were determined by the diffusion-cell method using ^36Cl-labelled CaCl2 solution.The result showed that activation energy decreased with water content,which indicated that the threshold fro diffusion was lower at a higher soil moisture rate .Therefor,the diffusion coefficient(D) of chloride ions in soil increased consistently with soil moisture,Although a near linear increase in the diffusion coefficient with increasing soil moisture or bulk density in all the soils was observed,the increase rate in different soils was not the same.The D value increased with teperature,and with temperature increased by 10℃ in the range from 5℃to 45℃ the D valve increased by 10%-30%,averaging about 20%. 相似文献
10.
公路旁土壤中水分和重金属的迁移 总被引：14，自引：0，他引：14
Roads with very high traffic loads in regions where soils are low in both pH and sorption capacity might be a source of percolation water loaded with heavy metals. Looking at some ＂worst case＂ scenarios, this study focused on the input of traffic related pollutants and on Pb, Cd, Cu, Zn, Ni and Cr concentrations in the soil matrix and soil solution, respectively. The analysis also included pH and electrical conductivity and at some sites DOC. The investigations were carried out on sandy soils with more or less low pH values at four motorway sites in Germany. The average of daily traffic was about 50 000 up to 90 000 vehicles. Soil pore water was collected in two soil depths and at four distances from the road. The pH in general decreased with increasing distance from the roadside. The elevated pH near the roadside was presumably caused by deposition of dust and weathering residues of the road asphalt, as well as by infiltration of salt that was used during winter time. At these road sites, increased heavy metal concentrations in the soil matrix as well as in the soil solution were found. However, the concentrations seldom exceeded reference values of the German Soil Protection Act. The soil solution concentrations tended to increase from the road edge to 10 m distance, whereas the concentration in the soil matrix decreased. Elevated DOC concentrations corresponded with elevated Cu concentrations but did not substantially change this tendency. High soil water percolation rates were found near the roads. Thus, even low metal concentrations of percolation water could yield high metal loads in a narrow area beside the road. 相似文献
11.
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. 相似文献
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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。 相似文献
15.
Hasan Merdun 《Water, air, and soil pollution》2012,223(8):4905-4923
Factors affecting preferential flow and transport in the vadose zone need to be investigated by experiments and simulations to protect groundwater against surface applied chemicals. The objectives of this study were to investigate the effects of several factors (soil structure, initial soil water content (SWC), and application rate) and their interactions on the extent of preferential flow and transport in a sandy clay loam field soil using the time domain reflectometry (TDR) for measuring SWC and electrical conductivity (EC) in 12 treatments, modeling (by HYDRUS-1D and VS2DTI) the measured SWC and EC, and conducting statistical tests for comparing the means of the measured and modeled SWC and EC and solute transport parameters (pore water velocity and dispersion coefficient) obtained by inversely fitting in the CXTFIT program. The study results showed that the applied solution moved faster in the undisturbed, wet initial SWC, and higher application rate experimental conditions than in the disturbed, dry initial SWC, and lower application rate, respectively, based on the analysis of the changes in TDR measured SWC and EC with depth at 1, 2, 5, and 15?h of the experiments. However, the effects of interactive factors or treatments on water flow and solute transport were not clear enough. The modeling results showed that HYDRUS-1D was better than VS2DTI in the estimation of EC and especially SWC, but overall the models had relatively low performances in the simulations. Statistical test results also showed that the treatments had different flow and transport characteristics because they were divided into different groups in terms of the means of SWC and EC and solute transport parameters. These results suggest that similar experiments with more distinct interactions and modeling studies with different approaches need to be considered for better understanding the complex flow and transport processes in the vadose zone. 相似文献
16.
利用两区和两流区模型模拟氯离子在黑垆土中的迁移过程 总被引：1，自引：0，他引：1
以原状长武黑垆土为研究对象,针对不同输入方式、不同孔隙水流速条件下的氯离子溶质迁移过程,分析原状土壤中大孔隙存在条件下溶质迁移的特征,对两区模型和两流区模型的各拟合参数进行对比和分析。结果表明:大小脉冲输入条件下,氯离子浓度在试验土柱中均随穿透试验的进行呈现先增加而后降低的趋势,其峰值大小及其出现位置随孔隙水流速变化差异显著,且小脉冲输入时溶质穿透曲线较大脉冲时的不对称和拖尾现象更为显著;两流区模型相对于两区模型可较好描述氯离子的穿透曲线;两模型所得模拟参数随孔隙水流速的变化差异性较大。两模型拟合所得弥散度(λ)随孔隙水流速的变化趋势相同,但两流区模型拟合的弥散度大两区模型拟合值2个数量级。两模型拟合所得可动水含量(β)均随孔隙水流速的增加相应增加,而质量交换系数(α)值均极小。 相似文献
17.
Cu/Pb/Zn/Cd在石英砂中的迁移实验及模拟 总被引：4，自引：0，他引：4
通过稳定流混合置换实验,研究了孔隙水流速和pH变化对Cu/Pb/Zn/Cd在石英砂中迁移行为的影响,获得了示踪剂Br-和Cu/Pb/Zn/Cd的穿透曲线(BTCs);并通过室内批量平衡实验获得吸附系数,进而计算出阻滞因子Rd。基于这些实验结果,借助CXTFIT2.1软件,用平衡CDE模型拟合了Br-的BTCs,得到了弥散系数D;在此基础上应用CDE非平衡模型拟合Cu/Pb/Zn/Cd在不同流速和pH条件下的BTCs,并预测了平行实验和不同埋深处Cu/Pb/Zn/Cd浓度的动态变化。结果表明,Cu/Pb/Zn/Cd的迁移能力随流速的增大而增强,而随pH的增大而降低;化学非平衡的两点模型能较好地模拟本文实验条件下Cu/Pb/Zn/Cd的迁移过程。 相似文献
18.
A series of miscible-displacement experiments was conducted to examine the impact of experiment conditions (detection limit, input pulse size, input concentration, pore-water velocity, contact time) on the performance of a mathematical solute transport model incorporating nonlinear, rate-limited sorption/desorption described by a continuous distribution reaction function. Effluent solute concentrations were monitored over a range of approximately seven orders of magnitude, allowing characterization of asymptotic tailing phenomenon. The model successfully simulated the extensive elution tailing observed for the measured data. Values for the mean desorption rate coefficient (ln k 2) and the variance of ln k 2 were obtained through calibration of the model to measured data. Similar parameter values were obtained for experiments with different input pulse size, input concentration, pore-water velocity, and contact time. This suggests that the model provided a robust representation of sorption–desorption for this system tested. The impact of analytical detection limit was examined by calibrating the model to subsets of the breakthrough curves wherein the extent of the elution tail was artificially reduced to mimic a poorer detection limit. The parameters varied as a function of the extent of elution tail used for the calibrations, indicating the importance of measuring as full an extent of the tail as possible. 相似文献
19.
两流区模型为描述优先流情况下的溶质穿透曲线提供了新的方法。但两流区模型的所有参数目前仅能通过反推参数法获得，限制了其应用。近年来，毛管理论和土壤水力特性模型的发展使得有可能从更加微观的角度来揭示土壤水分和溶质运动的机理，同时也为对流弥散模型参数的确定提出了新的思路。本研究在Brooks—Corey模型的基础上，推求了土壤中的孔隙流速分布；以平均孔隙流速为两流区的临界流速，得到了两流区模型参数与Brooks-Corey水分特征曲线模型形状系数之间的简单关系；提出了由土壤水分特征曲线确定两流区模型参数的方法。用实测资料对考虑和不考虑不动水体情况下这种方法的可靠性进行了验证。结果表明，不考虑不动水体，上述方法可靠性较差；考虑不动水体，用上述方法预测两流区模型参数有一定精度，不会对模型的预测结果产生太大的误差。 相似文献
20.
获取土壤溶质迁移参数是利用数学模型预测土壤溶质迁移过程的前提。本文根据对流弥散方程（Convective-dispersive equation，CDE）的一级近似解，建立了土壤溶质迁移过程中溶质锋随时间变化的函数关系，并以时域反射仪（Time domain reflectometry，TDR）为手段、Cl-为对象，通过与土壤溶质穿透曲线（Breakthrough curve，BTC）拟合法相比较，研究了利用该函数关系确定溶质迁移参数的可行性。研究结果表明，两种方法估计的R比较接近，而溶质锋信息法估计的水动力弥散系数D小于穿透曲线拟合法。TDR探测的溶质锋滞后于理论溶质锋，是导致利用溶质锋信息估计水动力弥散系数D偏小的原因之一。将溶质锋信息法估计的迁移参数代入CDE计算的土壤溶质穿透曲线与实测土壤溶质穿透曲线比较发现，风沙土中计算的穿透曲线整体滞后于实测穿透曲线，但两者的穿透过程基本一致，蝼土中计算的初始、完全穿透时间与试验穿透曲线一致，但穿透过程有所差异，说明溶质锋信息法估计的迁移参数具有一定的可应用性，在估计水动力弥散系数的精度方面有待提高。 相似文献