镍超积累植物布氏香芥——一种镍的植物补救和植物潜在采矿介质

在意大利进行了关于超积累植物布氏香芥（Ａｌｙｓｕｍｂｅｒｔｏｌｏｎｉｉ）对超镁南土壤中镍的植物潜在采矿作用的实验,在托斯卡钠区穆洛（Ｍｕｒｌｏ）特定的现场实验小区,在两年内以不同的方式施肥,最优化的化肥处理方式（Ｎ＋Ｋ＋Ｐ）使可再生产的生物量增加了两倍,增至９．０ｔ／ｈａ（吨／公顷）,未施肥时的镍含量没有稀释,于物质中０．８％（灰分中１１％）的镍含量在不需重播而收获的情况下将会产生７２ｋｇ／ｈａ的     

On the use and error of approximation in the Domenico (1987) solution

A mathematical solution for solute transport in a three-dimensional porous medium with a patch source under steady-state, uniform ground water flow conditions was developed by Domenico (1987). The solution derivation strategy used an approximate approach to solve the boundary value problem, resulting in a nonexact solution. Variations of the Domenico (1987) solution are incorporated into the software programs BIOSCREEN and BIOCHLOR, which are frequently used to evaluate subsurface contaminant transport problems. This article mathematically elucidates the error in the approximation and presents simulations that compare different versions of the Domenico (1987) solution to an exact analytical solution to demonstrate the potential error inherent in the approximate expressions. Results suggest that the accuracy of the approximate solutions is highly variable and dependent on the selection of input parameters. For solute transport in a medium-grained sand aquifer, the Domenico (1987) solution underpredicts solute concentrations along the centerline of the plume by as much as 80% depending on the case of interest. Increasing the dispersivity, time, or dimensionality of the system leads to increased error. Because more accurate exact analytical solutions exist, we suggest that the Domenico (1987) solution, and its predecessor and successor approximate solutions, need not be employed as the basis for screening tools at contaminated sites.     

Hydraulic displacement of dense nonaqueous phase liquids for source zone stabilization

Hydraulic displacement is a mass removal technology suitable for stabilization of a dense, nonaqueous phase liquid (DNAPL) source zone, where stabilization is defined as reducing DNAPL saturations and reducing the risk of future pool mobilization. High resolution three-dimensional multiphase flow simulations incorporating a spatially correlated, heterogeneous porous medium illustrate that hydraulic displacement results in an increase in the amount of residual DNAPL present, which in turn results in increased solute concentrations in groundwater, an increase in the rate of DNAPL dissolution, and an increase in the solute mass flux. A higher percentage of DNAPL recovery is associated with higher initial DNAPL release volumes, lower density DNAPLs, more heterogeneous porous media, and increased drawdown of groundwater at extraction wells. The fact that higher rates of recovery are associated with more heterogeneous porous media stems from the fact that larger contrasts in permeability provide for a higher proportion of capillary barriers upon which DNAPL pooling and lateral migration can occur. Across all scenarios evaluated in this study, the ganglia-to-pool (GTP) ratio generally increased from approximately 0.1 to between approximately 0.3 and 0.7 depending on the type of DNAPL, the degree of heterogeneity, and the imposed hydraulic gradient. The volume of DNAPL recovered as a result of implementing hydraulic displacement ranged from between 9.4% and 45.2% of the initial release volume, with the largest percentage recovery associated with 1,1,1 trichloroethane, the least dense of the three DNAPLs considered.     

Matrix diffusion-derived plume attenuation in fractured bedrock

Matrix diffusion can attenuate the rate of plume migration in fractured bedrock relative to the rate of ground water flow for both conservative and nonconservative solutes of interest. In a system of parallel, equally spaced constant aperture fractures subject to steady-state ground water flow and an infinite source width, the degree of plume attenuation increases with time and travel distance, eventually reaching an asymptotic level. The asymptotic degree of plume attenuation in the absence of degradation can be predicted by a plume attenuation factor, beta, which is readily estimated as R' (phi(m)/phi(f)), where R' is the retardation factor in the matrix, phi(m) is the matrix porosity, and phi(f) is the fracture porosity. This dual-porosity relationship can also be thought of as the ratio of primary to secondary porosity. Beta represents the rate of ground water flow in fractures relative to the rate of plume advance. For the conditions examined in this study, beta increases with greater matrix porosity, greater matrix fraction organic carbon, larger fracture spacing, and smaller fracture aperture. These concepts are illustrated using a case study where dense nonaqueous phase liquid in fractured sandstone produced a dissolved-phase trichloroethylene (TCE) plume approximately 300 m in length. Transport parameters such as matrix porosity, fracture porosity, hydraulic gradient, and the matrix retardation factor were characterized at the site through field investigations. In the fractured sandstone bedrock examined in this study, the asymptotic plume attenuation factors (beta values) for conservative and nonconservative solutes (i.e., chloride and TCE) were predicted to be approximately 800 and 12,210, respectively. Quantitative analyses demonstrate that a porous media (single-porosity) solute transport model is not appropriate for simulating contaminant transport in fractured sandstone where matrix diffusion occurs. Rather, simulations need to be conducted with either a discrete fracture model that explicitly incorporates matrix diffusion, or a dual-continuum model that accounts for mass transfer between mobile and immobile zones. Simulations also demonstrate that back diffusion from the matrix to fractures will likely be the time-limiting factor in reaching ground water cleanup goals in some fractured bedrock environments.     

Numerical examination of the factors controlling DNAPL migration through a single fracture

The migration of five dense nonaqueous phase liquids (DNAPLs) through a single fracture in a clay aquitard was numerically simulated with the use of a compositional simulator. The effects of fracture aperture, fracture dip, matrix porosity, and matrix organic carbon content on the migration of chlorobenzene, 1,2-dichloroethylene, trichloroethylene, tetra-chloroethylene, and 1,2-dibromoethane were examined. Boundary conditions were chosen such that DNAPL entry into the system was allowed to vary according to the stresses applied. The aperture is the most important factor of those studied controlling the migration rate of DNAPL through a single fracture embedded in a clay matrix. Loss of mass to the matrix through diffusion does not significantly retard the migration rate of the DNAPL, particularly in larger aperture fractures (e.g., 50 microm). With time, the ratio of diffusive loss to the matrix to DNAPL flux into the fracture approaches an asymptotic value lower than unity. The implication is that matrix diffusion cannot arrest the migration of DNAPL in a single fracture. The complex relationships between density, viscosity, and solubility that, to some extent, govern the migration of DNAPL through these systems prevent accurate predictions without the use of numerical models. The contamination potential of the migrating DNAPL is significantly increased through the transfer of mass to the matrix. The occurrence of opposite concentration gradients within the matrix can cause dissolved phase contamination to exist in the system for more than 1000 years after the DNAPL has been completely removed from the fracture.     

用于公路滑溜状况预测的数值预报系统

该文论述对丹麦公路站点滑溜路面状况进行自动预测的一个数值预报系统。该系统建立在由大气有限区域业务模式输入的路面状况模式的基础之一。在经过改进的、包括能对每个测站的通量资料进行订正的初始化程序中，使用了各公路站点观测的云量、温度和温度等观测资料。该系统在丹麦气象研究所答询业务中投入运行。目前２００个公路站点每小时的新的预报，可在５ｈ前作出，两个选定时段的模式预报和业务运动结果表明，该系统具有潜在的优     

GPS测量中存在的问题

有关ＧＰＳ方面的许多文章都以极大的热情报道ＧＰＳ是如何给定位技术带来了一场革命，毫无凝问，总的说这是没有错。但是无论如何，在应用ＧＰＳ方面仍然存在一些问题，本文将对这些进行讨论。为了使用户便于理解，这里将这些问题分为两类。一类可看成是人为造成的，如选择可用笥（ＳＡ），抗窃密（Ａ－Ｓ）等，其中大部分均可通过过政策的调整加以消除；另一类则是ＧＰＳ系统本身所固有的在任何情况下都不可避免的问题，其中之一就