共查询到20条相似文献，搜索用时 15 毫秒
1.
The transport processes of solutes in two soil columns filled with undistrubed soil material collected from an unsaturated sandy aquifer formation in Belgium subjected to a variable upper boundary condition were identified from breakthrough curves measured by means of time domain reflectometry(TDR),Solute breakthrough was measured with 3 TDR probes inserted into each soil column at three different depths at a 10 minutes time interval.In addition,soil water content and pressure head were measured at 3 different depths.Analyteical solute transport models were used to estimate the solute disperison coefficient and average pore-water velocity from the observed breakthrough curves,the results showed that the analytical solutions were suitable in fitting the observed solute transport,The dispersion coefficient was found to be a function of the soil depth and average proe-water velocity,imposed by the soil water flux.the mobile moistrue content on the other hand was not correlated with the average pore-water velocity and the dispersion coefficient. 相似文献
2.
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
3.
JENS RAUNSØ 《European Journal of Soil Science》1983,34(2):249-262
Chloride transport was investigated in four columns packed with glass spheres, spheres of a cation exchange resin, a loamy sand and a sandy loam, respectively. Using step input, vertical downward flow and relatively high flow-rates, 0.01 m KCl displaced water in the column packed with glass spheres, otherwise 3.33 × 10?4m CaCl2 displaced or was displaced by 3.33 × 10?3m CaCl2. The breakthrough curves of chloride were analysed to give dispersion coefficients and mobile volumes. It was found that (i) chloride exchanged between mobile and immobile region in the sandy loam, (ii) the dispersion coefficient (K) was linearly related to pore flow velocity (U) for the individual columns, and that (iii) the ratio of dispersivity (dK/dU) to median grain diameter increased with increasing standard deviation of the logarithmicnormal grain size distribution. 相似文献
4.
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
5.
6.
《Communications in Soil Science and Plant Analysis》2012,43(22):2935-2946
The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg?1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θim), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (Dh). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl?1) in disturbed soil column. Cl?1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θim+ θm) and real pore water velocity calculated based on the mobile water content (θm) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg?1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg?1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg?1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θim and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater. 相似文献
7.
The potential effect of acidification of contaminated sandy soils on Cd transport in the unsaturated zone was assessed. Forty‐eight soil profiles were sampled at five depths in a polluted field that was set aside in 1992. The Cd concentration in the top 30 cm of this field was, on average, 10 mg kg−1. A column experiment was carried out with one of the topsoil samples. Homogeneously packed columns were leached with 0.001 m CaCl2, adjusted to pH 3 or pH 5.7, at a pore water velocity of 6 cm day−1. The Cd and proton transport was predicted with coupled transport equations. The Cd transport was modelled by assuming local equilibrium and by using sorption parameters derived from batch experiments, while acidification was modelled with a kinetic approach, on the assumption that proton buffering was due to cation exchange and mineral weathering. Organic matter was the main contributor to the cation exchange capacity of these soils. Observed and predicted pH and Cd profiles in the columns agreed well. With the same model, the proton and Cd transport at field scale was calculated for each of the 48 profiles sampled (‘grid model’). It was predicted that the field‐averaged Cd concentration in the seepage water will increase from 6 μg litre−1 at present to 200 μg litre−1 over 260 years, which greatly exceeds the maximum permissible concentration (MPC) in groundwater of 5 μg litre−1. Predictions of Cd transport using field‐averaged soil properties yielded a later breakthrough time and a larger peak Cd concentration than predicted with the grid model, which illustrates the impact of spatial variability on solute transport. Continuation of liming practices is a possible solution to prevent breakthrough of Cd at concentrations far in excess of the MPC. 相似文献
8.
Preferential flow in soil can enhance the leaching of agricultural chemicals. In a number of studies it has been shown that the mobile‐immobile solute transport model (MIM) is a useful tool to characterize preferential flow. In the present study, a new laboratory method for determining the MIM parameters θm and θim (mobile and immobile water content), as well as α (mass transfer coefficient), is developed. The computations are uncomplicated and the method requires only simple equipment. It is applied to short, undisturbed soil columns. Measured values ranged from 0.11 to 0.27 for θim θ—1 and from 0.015 h—1 to 0.034 h—1 for α for an Iowan soil (Nicollet silt loam). For two sandy Eutric Gleysols from Germany, low values for θim θ—1 from 0.04 to 0.07 and from 0.001 h—1 to 0.008 h—1 for α were determined. Although the new method is a flow‐interruption technique, values for the Nicollet silt loam compare well with those from conventional leaching experiments. Values for the Eutric Gleysols agree with the observation that these soils were poorly structured. Because the new method does not assume negligible dispersion, it is applicable to a wider range of soils and boundary conditions than comparable approaches. We conclude that the new method provides parameter values that are suited to describe non‐equilibrium solute transport. 相似文献
9.
I. VOGELER D. R. SCOTTER B. E. CLOTHIER R. W. TILLMAN 《European Journal of Soil Science》1997,48(3):401-410
In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl2 and Ca(NO3)2 of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h?1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg2+ and Ca2+ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha?1 of native potassium was leached from the alluvial soil, but only about 10 kg ha?1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily. 相似文献
10.
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
11.
低频探地雷达地波法测定土壤含水量的可行性研究 总被引：4，自引：0，他引：4
利用地波法来探讨低频探地雷达(GPR)在土壤含水量测定方面的可行性。分别采用50 MHz和100 MHz天线的探地雷达地波法对黄淮海平原潮土地区砂壤土和砂土中的含水量进行了探测研究。结果表明,50 MHz天线GPR分辨率过低,在砂土和砂壤土中均无地波信号。100 MHz天线在砂壤土中无地波信号,但在砂土中可清晰读取出空气波和地波。TDR测得含水量为6.3%的砂土,用100 MHz天线地波法3次测定结果分别为5.9%,6.2%和6.5%,绝对误差均在0.4%以内。采用共中点法(CMP)和固定间距法(FO)相结合探测土壤含水量,在FO最佳天线间距1 m时测得灌水前后的砂土含水量分别为6.5%和20.2%,与TDR测定结果6.3%和19.7%相比,绝对误差在0.5%以内。100 MHz天线CMP和FO相结合的方法兼顾了CMP法读取地波的精确和FO法的快速便捷,在砂土的含水量测定应用中是可信、可行的。 相似文献
12.
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
13.
在室内使用特殊形状的土柱隔板成功地填装了在水平横截面上呈“川”字型分布、由质地相差较大的两种土壤相间构成的非均质土柱。当土柱出流达到稳态后，灌入CaCl2溶液，监测土柱出流液的浓度动态。通过计算表征氯离子迁移时间随机特征的概率密度函数，对出流盐分的优先运移采用传递函数模型进行仿真，并对构成非均质土柱的两种均质土壤分别进行了条件类似的水盐入渗实验和模拟。在此基础上获得了参与氯离子输运的土壤水运移体积和可动体积以及土壤溶液中氯离子的体积平均驻留浓度。 相似文献
14.
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
15.
Thomas H. Christensen 《Water, air, and soil pollution》1984,21(1-4):105-114
Sorption of Cd at low concentrations onto two Danish soils (loamy sand, sandy loam) was examined in terms of kinetics and governing factors. From an environmental point of view soil sorption of Cd is a fast process: More than 95% of the sorption takes place within 10 min, equilibrium is reached in 1 hr, and exposures up to 67 wk did not reveal any long term changes in Cd sorption capacities. The soils have very high affinity for Cd at pH = 6.00 (10?3 M CaCl2) exhibiting distribution coefficients in the order of 200 to 250 (soil Cd concentration/solute Cd concentration). However, the sorption isotherms describing the distribution of Cd between soil and solute are slightly curvelinear. In the pH-interval 4 to 7.7, the sorption capacity of the soil approximately increases 3 times for a pH increase of one unit. Increasing the Ca concentration from 10?3 to 10?2 M reduces the sorption capacity of the sandy loam to one third. 相似文献
16.
土壤溶质锋运移的解析解 总被引：5，自引：0，他引：5
为了推求土壤溶质锋运移与时间的关系 ,假设土壤溶质运移发生在溶质输入内边界至溶质锋之间 ,应用拉普拉斯变换方法求解输入内边界到溶质锋边界的对流—弥散方程 ( CDE)。溶质锋浓度解与半无限精确解的比较表明 ,在内边界至溶质锋边界内具有良好的一致性。溶质锋运移解的一个重要应用是估计实验室和田间条件的溶质运移参数。这个新的参数估计方法要求土壤中溶质锋随时间运移数据。如果应用有色示踪剂 ,溶质锋运移可以目测 ;如果应用其他示踪剂 ,可以通过 TDR或其它仪器测量示踪剂通量或体积浓度 ,确定溶质锋的深度。这个新的方法简单易行、节省时间 ,而且能够应用到实验和田间条件。 相似文献
17.
透射式探地雷达探测土壤含水率 总被引：1，自引：1，他引：1
探地雷达可以进行土壤含水率的快速探测,但普通反射式雷达容易受反射层位难确定的影响造成探测误差。该研究使用透射式探地雷达对不饱和含水壤土及砂土所构建的物理模型进行透射式探测,通过起跳时间对比标定的方法,精确计算了介质中雷达波波速和土壤的相对介电常数。最后通过统计分析,发现以Topp模型公式形式为基础的三次多项式具有最高拟合优度,并修正了Topp公式中的参数后,分别建立起非饱和壤土和砂土体积含水率与介电常数的经验公式及其适用范围。最后,通过试验对比验证了该方法对砂土含水率的测量相对误差为13.20%,较时域反射TDR(time domain reflectometry)方法低14.34%,壤土为9.48%,较TDR方法低15.79%,测量精度明显高于TDR方法。因此该方法可替代TDR方法用于特定条件下土壤含水率的准确检测。 相似文献
18.
19.
推求土壤水分运动参数的简单入渗法──Ⅱ.实验验证 总被引：18，自引：0，他引：18
预报土壤中水分流动需要的土壤导水特性可通过观察水平土柱的入渗过程来确定,这一观测过程的分析是基于对Ｒｉｃｈａｒｄｓ方程求积分解。土壤水分特征曲线中的参数由观测的水平土柱和特征湿润长度和吸力为确定,非饱和土壤导水率由已确定的特征曲线中的参数和测定的饱和导水率导出。供试土壤有三种,它们的质地从砂壤到粘壤。由这种方法所确定的这三种土壤的水分特征曲线与实测的特征曲线符合良好,所确定的砂壤的非饱和导水率与实 相似文献
20.
Modelling soil water flow and solute transport under field conditions requires the knowledge of many parameters that are difficult to determine directly. Values determined on small isolated samples in the laboratory are often not representative of field situations. We investigated the applicability of inverse modelling to a soil–plant system in lysimeter experiments. We also tested whether parameters obtained from one experiment could be applied to another with the same soil. In a lysimeter planted with young trees, we first did a multistep drainage experiment and then a long‐term bromide tracer experiment with atmospheric boundary conditions at the soil surface. To estimate the unsaturated hydraulic properties, we linked the inverse program SUFI (Sequential Uncertainty FItting) to the flow and transport model HYDRUS5. A comparison of several scenarios showed that the resulting values of parameters depended strongly on the data used for calibration and the formulation of the objective function. The results suggested that inverse modelling could be used to identify important processes. Inversely obtained parameters gave better predictions for a second experiment when more variables were considered in the objective function and when the range of hydraulic conditions was wider. Furthermore, with retention curves directly fitted to measured water retention data we achieved acceptable results. Despite some limitations, the inverse approach was found to be a sound and useful procedure for estimating parameters of a complex system involving water uptake by roots, solute transport and unsaturated flow. 相似文献