Application of HYDRUS 1D model for assessment of phenol–soil adsorption dynamics

Laboratory-scale batch, vertical, and horizontal column experiments were conducted to investigate the attenuative capacity of a fine-grained clayey soil of local origin in the surrounding of a steel plant wastewater discharge site in West Bengal, India, for removal of phenol. Linear, Langmuir, and Freundlich isotherm plots from batch experimental data revealed that Freundlich isotherm model was reasonably fitted (R ²?=?0.94). The breakthrough column experiments were also carried out with different soil bed heights (5, 10, and 15 cm) under uniform flow to study the hydraulic movements of phenol by evaluating time concentration flow behavior using bromide as a tracer. The horizontal migration test was also conducted in the laboratory using adsorptive phenol and nonreactive bromide tracer to explore the movement of solute in a horizontal distance. The hydrodynamic dispersion coefficients (D) in the vertical and horizontal directions in the soil were estimated using nonlinear least-square parameter optimization method in CXTFIT model. In addition, the equilibrium convection dispersion model in HYDRUS 1D was also examined to simulate the fate and transport of phenol in vertical and horizontal directions using Freundlich isotherm constants and estimated hydrodynamic parameters as input in the model. The model efficacy and validation were examined through statistical parameters such as the coefficient of determination (R ²), root mean square error and design of index (d).     

Simulation of boundary layer trajectory dispersion sensitivity to soil moisture conditions: MM5 and Noah-based investigation

In this study, the sensitivity of trajectory paths to anomalous soil moisture was analyzed during three different synoptic episodes in June 2006. The MM5 and Noah land surface models were used to simulate the response of the planetary boundary layer. The HYSPLIT model was used for trajectory analysis. It was found that the response in horizontal lower-level wind field was larger at regions where vertical wind velocity changes were also large. In addition, the sensitivity to soil moisture changes was significant and localized where convective activity was well developed and synoptic effects did not dominate. A non-local effect was felt over the rest of the domain where convection was not present since the model atmosphere reacted as a whole to compensate for induced changes in vertical velocity. This finding was supported by the fact that domain averaged vertical velocities changes were of the order of 0.2 cm s^?1 or less at about 650 hPa and about 200 times smaller than modeled local vertical velocity changes. The largest change in horizontal wind field near the surface was found for weak synoptic events on June 11–12 and June 22–23 while the stronger synoptic event of June 17–18 showed smaller differences. These changes in wind field conditions impacted the transport and dispersion of pollutants. To quantify the sensitivity of air quality estimates to soil moisture uncertainty, we have used three well known measures of trajectory differences: the absolute horizontal transport deviation (AHTD), the relative horizontal transport deviation (RHTD) and the absolute vertical transport deviation (AVTD) for an ensemble of 98 trajectories departing from a region well within the computational domain. For the June 11–12 event it was found that for wet and dry soil moisture experiments, AHTD, RHTD, and AVGTD can reach values in the range 60–100 km, 10–20% and 500–900 m at 24 h run time, respectively. For the June 17–18 and June 22–23 events these values of trajectory differences were reduced more than half. These differences in behavior between time periods are largely attributed to the combined effects of synoptic forcing and the sensitivity of planetary boundary layer to soil moisture changes during well developed convection. The implication for air quality studies is that the soil moisture anomaly and related uncertainty in planetary boundary layer response needs to be incorporated in order to construct an ensemble of the most probable scenarios in which pollutants are released and transported throughout a given target region.     

江阴某场地土壤及地下水环境风险管控与修复项目工程案例

通过对江阴某地块土壤及地下水环境风险管控与修复项目的工程实施过程介绍,重点针对柔性垂直/水平阻隔技术、水处理高级氧化技术在污染土壤及地下水风险管控项目应用中的技术原理、施工流程进行了分析与探讨,可为后续采用柔性垂直阻隔技术的风险管控项目提供参考。     

Breakthrough adsorption study of migratory nickel in fine-grained soil.

The present study was conducted to evaluate the breakthrough curve for nickel adsorption in fine-grained soil from a nearby ash pond site of a thermal power plant. Nickel was found to be the major polluting solute in the ash sluicing wastewater. The adsorption of nickel by vertical soil column batch test and horizontal migration test was carried out in the laboratory. Field investigation was conducted also, by installing test wells around the ash pond site. Experimental results showed a good adsorptive capacity of soil for nickel ions. The breakthrough curves showed a reasonable fitting with a one-dimensional mathematical model. The breakthrough curves yielded from field test results showed good agreement with a two-dimensional mathematical model.     

Characteristics of nitrate horizontal transport in a paddy field of the Tai Lake region,China

The characteristics of nitrate horizontal transport in a major paddy soil, Wu Shan soil in the Tai Lake region, were studied. The concentration of nitrate during horizontal movement decreased with the increasing in distance from the tracer source, the change following a logarithmic function. The concentration of the nitrate was strongly correlated with the soil moisture content, as an exponential function. The horizontal transport velocity of nitrate was significantly correlated with the distance of the tracer source as power function. Therefore, the velocity of nitrate horizontal transport was controlled by the concentration gradient of nitrate, and soil water potential gradient from beginning to the 20 cm mark in the horizontal column. However, the velocity of nitrate horizontal was stable beyond 20 cm, where it was controlled by soil matric potential.     

Distribution and mobility of metals in contaminated sites. chemometric investigation of pollutant profiles

The distribution and mobility of heavy metals in the soils of two contaminated sites in Piedmont (Italy) was investigated, evaluating the horizontal and vertical profiles of 15 metals, namely Al, Cd, Cu, Cr, Fe. La, Mn, Ni, Pb, Sc, Ti, V, Y, Zn and Zr. The concentrations in the most polluted areas of the sites were higher than the acceptable limits reported in Italian and Dutch legislations for soil reclamation. Chemometric elaboration of the results by pattern recognition techniques allowed us to identify groups of samples with similar characteristics and to find correlations among the variables. The pollutant mobility was studied by extraction with water, dilute acetic acid and EDTA and by applying Tessier's procedure. The fraction of mobile species, which potentially is the most harmful for the environment, was found to be higher than the one normally present in unpolluted soils, where heavy metals are, to a higher extent, strongly bound to the matrix.     

A field study of the ecotoxicology of copper to bryophytes

The impact of particulate copper, emitted from a copper rod-rolling plant, on the distribution of common grassland bryophytes has been investigated. Several areas of managed grassland, differing in total and water-extractable soil copper content, surrounding the factory were surveyed to establish species composition and distribution of the bryophyte flora. Clear differences emerged in the distribution patterns of the main acrocarpous (upright/tufted growth form) and pleurocarpous (horizontal/spreading growth form) species present, with some species being more or less confined to soils with elevated copper (Pohlia nutans), whilst others were absent from such sites. The distribution of acrocarpous species was not related to increasing soil copper concentrations, whereas pleurocarpous species showed considerable sensitivity. This may not be a simple reflection of sensitivity to copper; ecological factors such as differences in patterns of water and soluble copper uptake between the different growth forms may be significant factors, as may be changes in the vascular plant flora giving rise to differences in population densities of potential competitors between sites. Pleurocarpous species are absent from grassland where total soil copper >550 microg g(-1) dry weight, whilst the less sensitive acrocarpous species occur at total soil copper levels in excess of 2000 microg g(-1) dry weight.     

Theory and laboratory study of a tall passive chamber for measuring gas fluxes at soil surface

A tall passive flux chamber with a height significantly greater than its horizontal dimensions is proposed for measuring fluxes of volatile organic compounds (VOCs) at the soil surface. The main feature of this tall chamber is the presence of a vertical concentration gradient of the target gas in the chamber. The emission and transport behavior of the target gas in the soil-chamber system are analyzed using the diffusion theory. A mathematical model is developed to estimate the flux from the soil into the tall chamber, providing the target gas establishes a detectable vertical concentration gradient in the chamber. To obtain the data required for calculating flux, only two gas concentrations (C1 and C2) at two heights (h1 and h2) within the chamber need to be measured at the end of a short chamber placement time (tp). To evaluate the applicability of the tall chamber for measuring flux, several laboratory tests have been conducted, using CH2Cl2 and CH3Br as the target gases. The results indicate that the proposed tall chamber has promising potential as a method for measuring fluxes of VOCs at the soil surface.     

Vertical and horizontal distributions of microbial abundances and enzymatic activities in propylene-glycol-affected soils

The natural microbial activity in the unsaturated soil is vital for protecting groundwater in areas where high loads of biodegradable contaminants are supplied to the surface, which usually is the case for airports using aircraft de-icing fluids (ADF) in the cold season. Horizontal and vertical distributions of microbial abundance were assessed along the western runway of Oslo Airport (Gardermoen, Norway) to monitor the effect of ADF dispersion with special reference to the component with the highest chemical oxygen demand (COD), propylene glycol (PG). Microbial abundance was evaluated by several biondicators: colony-forming units (CFU) of some physiological groups (aerobic and anaerobic heterotrophs and microscopic fungi), most probable numbers (MPN) of PG degraders, selected catabolic enzymatic activities (fluorescein diacetate (FDA) hydrolase, dehydrogenase, and β-glucosidase). High correlations were found between the enzymatic activities and microbial counts in vertical soil profiles. All microbial abundance indicators showed a steep drop in the first meter of soil depth. The vertical distribution of microbial abundance can be correlated by a decreasing exponential function of depth. The horizontal trend of microbial abundance (evaluated as total aerobic CFU, MPN of PG-degraders, and FDA hydrolase activity) assessed in the surface soil at an increasing distance from the runway is correlated negatively with the PG and COD loads, suggesting the relevance of other chemicals in the modulation of microbial growth. The possible role of potassium formate, component of runway de-icers, has been tested in the laboratory by using mixed cultures of Pseudomonas spp., obtained by enrichment with a selective PG medium from soil samples taken at the most contaminated area near the runway. The inhibitory effect of formate on the growth of PG degraders is proven by the reduction of biomass yield on PG in the presence of formate.     

Risk based characterisation of contaminated industrial site using multivariate and geostatistical tools

Human and ecological risk assessment requires the sources, distribution, mobility and environmental behaviour of contaminants to be investigated on a site-specific basis. It often deals with data sets which are relatively small and affected by sampling gaps. In the case of a polycyclic aromatic hydrocarbon (PAH) contaminated industrial site, Kriging interpolation of spatial data and principal component analysis (PCA) proved useful for extracting additional value from the data set. Kriging was adopted for assessing the horizontal and vertical distribution and transport of PAHs in soil. PCA was applied to PAH concentration and relative abundance in soil samples and interpreted on the basis of the PAH physico-chemical and bio-degradation properties. It revealed correlation with the products of a neighbouring factory and the weathering of the lighter PAHs. The geo- and multivariate statistical results were coupled with the previous hydrogeological characterisation of the site to develop a site-conceptual model for use in the exposure scenario modelling for risk assessment.     

Harmonic analysis of flow in open boreholes due to barometric pressure cycles

Barometric pressure changes can induce airflow in an open borehole or well screened in the vadose zone, thereby ventilating the soil surrounding the borehole. This paper presents an analytic model of the induced airflow and compares the predictions of the model with experimental measurements. This model may be useful for the design of passive soil vapor extraction as applied to the remediation of soil contaminated by volatile organic compounds (VOCs). Based on harmonic analysis, the model predicts the time-dependent flow in agreement with measurements at a borehole in strata of differing permeability. The model uses no adjustable parameters, but proceeds from first principles based upon known or estimated values of soil properties as a function of depth. In an approximation, the calculated flow is determined by the difference between barometric pressure and the attenuated pressure that would propagate vertically into the vadose zone in the absence of an open borehole. The attenuated vertical propagation of pressure can be calculated by a corresponding harmonic method presented previously. The model reveals that the flow in the borehole is approximately proportional to the horizontal permeability in the formation, and depends only weakly on the soil porosity and borehole radius.     

Vertical distributions of aerosols under different weather conditions: Analysis of in-situ aircraft measurements in Beijing,China

In this study, aerosol vertical distributions of 17 in-situ aircraft measurements during 2005 and 2006 springs are analyzed. The 17 flights are carefully selected to exclude dust events, and the analyses are focused on the vertical distributions of aerosol particles associated with anthropogenic activities. The results show that the vertical distributions of aerosol particles are strongly affected by weather and meteorological conditions, and 3 different types of aerosol vertical distributions corresponding to different weather systems are defined in this study. The measurement with a flat vertical gradient and low surface aerosol concentrations is defined as type-1; a gradual decrease of aerosols with altitudes and modest surface aerosol concentrations is defined as type-2; a sharp vertical gradient (aerosols being strongly depressed in the PBL) with high surface aerosol concentrations is defined as type-3. The weather conditions corresponding to the 3 different aerosol types are high pressure, between two high pressures, and low pressure systems (frontal inversions), respectively. The vertical mixing and horizontal transport for the 3 different vertical distributions are analyzed. Under the type-1 condition, the vertical mixing and horizontal transport were rapid, leading to strong dilution of aerosols in both vertical and horizontal directions. As a result, the aerosol concentrations in PBL (planetary boundary layer) were very low, and the vertical distribution was flat. Under the type-2 condition, the vertical mixing was strong and there was no strong barrier at the PBL height. The horizontal transport (wind flux) was modest. As a result, the aerosol concentrations were gradually reduced with altitude, with modest surface aerosol concentrations. Under the type-3 condition, there was a cold front near the region. As a result, a frontal inversion associated with weak vertical mixing appeared at the top of the inversion layer, forming a very strong barrier to prevent aerosol particles being exchanged from the PBL height to the free troposphere. As a result, the aerosol particles were strongly depressed in the PBL height, producing high surface aerosol concentrations. The measured vertical aerosol distributions have important implications for studying the effects of aerosols on photochemistry. The J[O₃] values are reduced by 11%, 48%, and 50%, under the type-1, type-2, and type-3 conditions, respectively. This result reveals that atmospheric oxidant capacity (OH concentrations) is modestly reduced under the type-1 condition, but is significantly reduced under the type-2 and type-3 conditions. This result also suggests that the effect of aerosol particles on surface solar flux is an integrated column effect, and detailed vertical distributions of aerosol particles are very important for assessing the impacts of aerosol on photochemistry.     

Distribution patterns of lead accumulation in roadside soils: a case study from Erzurum, Turkey

Surface soils along roadsides or near to industrial areas may contain high concentrations of lead that adversely affect plant production. Lead contamination of roadside soils is generally attributed to the exhaust emissions of automobiles operating with leaded gasoline. The objectives of this study were to determine the relationships between lead accumulation in soils and the distance from the road edge, predominant wind direction and soil depth, and to define vertical and horizontal distribution patterns of lead accumulation within the study area. The lead content of soil decreased rapidly with the distance from the road, and the relationship was described by a power function. The contamination was more dependent on the predominant wind direction. Our results indicated that lead that had accumulated within the top few centimetres of soil had been mixed throughout the ploughing layer in cultivated lands. Soils within 40 m of the motorway had at least 2 to 6 times higher amounts of lead than the background level.     

A novel sigma coordinate system to simulate abrupt changes of underwater terrain in a hydrodynamic model: application to Lake Mead,USA

The sigma (SIG) coordinate system in ocean circulation simulation models results inevitably in horizontal pressure gradient error. This problem also emerges in models of deep lakes or reservoirs with the same characteristics of underwater terrain mutation. SIG coordinates reflect vertical relative stratification but cannot be used to calculate horizontal pressure gradient force in places with drastic topographic changes; this results in vertical water temperature and circulation errors. In deep lakes or reservoirs, differences in water density caused by the temperature difference between upper and lower water bodies is the primary cause of thermal stratification phenomena. Lake Mead was used as a case study on steep topography based on Environmental Fluid Dynamics Code (EFDC) model in this study. SIG coordinates result in close agreement between the calibrated temperature time series at the top and middle water layers, but disparity in the bottom water layer. The error emerges in the horizontal pressure gradient error due to the SIG coordinate transformation. Neither increasing the vertical resolution nor adjusting the horizontal viscosity coefficient resolve this error. We test the sigma-zed (SGZ) coordinate which combines Z coordinate and SIG coordinate as a replacement for the SIG coordinate to find that they effectively reduce the model’s runtime and simulation efficiency. The vertical temperature distribution in SGZ coordinate mode is more accurate than the distribution in SIG coordinate mode. The Navier-Stokes horizontal gradient and advection diffusion equation results under SIG coordinates are very sensitive to the pressure gradient. The replacement also enhances resolution near the thermocline, facilitates reclosing of the water bottom and the equal sigma surface, lends significant advantages in terms of vertical temperature in the simulation for local deep water with steep terrain, and shortens runtime for 0.14 h. SGZ mixed coordinates are recommended in the simulation of deep lakes or reservoirs wherein the underwater topography is large (with abundant continuous deep trenches or reefs).

     

Probing the distribution and contamination levels of 10 trace metal/metalloids in soils near a Pb/Zn smelter in Middle China

The horizontal and vertical distribution patterns and contamination status of ten trace metal/metalloids (Ag, Bi, Co, Cr, Ge, In, Ni, Sb, Sn, Tl) in soils around one of the largest Chinese Pb–Zn smelter in Zhuzhou City, Central China, were revealed. Different soil samples were collected from 11 areas, including ten agricultural areas and one city park area, with a total of 83 surface soil samples and six soil cores obtained. Trace metal/metalloids were determined by inductively coupled plasma–mass spectrometry after digestion by an acid mixture of HF and HNO₃. The results showed that Ag, Bi, In, Sb, Sn, and Tl contents decreased both with the distance to the Pb–Zn smelter as well as the soil depth, hinting that these elements were mainly originated from the Pb–Zn smelting operations and were introduced into soils through atmospheric deposition. Soil Ge was influenced by the smelter at a less extent, while the distributions of Co, Cr, and Ni were roughly even among most sampling sites and soil depths, suggesting that they were primarily derived from natural sources. The contamination status, as revealed by the geo-accumulation index (I _geo), indicated that In and Ag were the most enriched elements, followed by Sb, Bi, and Sn. In general, Cr, Tl, Co, Ni, and Ge were of an uncontaminated status.     

煤矿复垦区土壤重金属分布特征与质量评价

为保证煤矿复垦区种植农作物的充填复垦土壤的生态安全,以淮南矿区煤矸石充填复垦地为研究对象,通过对研究区内Cd、Cr、Ni、Pb、Cu、Zn和Hg 7种重金属不同深度含量分析,总结其纵向分布特征,并将研究区土壤重金属含量与淮南市土壤背景值、《土壤环境质量标准》(GB 15618-1995)作比较,分析这7种重金属的污染程度.结果表明,这7种重金属都有不同程度的污染,其中土壤受Cd污染最严重,土壤中重金属垂直方向上无确定分布规律.总体而言,土壤重金属潜在生态风险属于强生态危害.从垂直方向来看,重金属潜在生态风险指数(RD随着深度的增加出现先下降后升高的趋势,其中40～60 cm深度的RI最大.重金属生态危害程度依次为Cd＞ Hg＞ Ni＞ Cu＞ Cr＞ Pb＞ Zn,其中Cd为矿区土壤中最主要的重金属污染生态风险因子.     

多菌群污水生物处理反应器中污泥分布的试验研究

在多菌群污水生物处理反应器处理城市污水的试验中,对反应器主反应区内水平中线及垂直中线上所布设取样点位的混合液悬浮固体(MLSS)、混合液挥发性悬浮固体(MLVSS)、污泥沉降比(SV30)及污泥容积指数(SVI)进行了检测分析。结果表明,MLSS与MLVSS分布趋势大致相同,在水平方向与垂直方向污泥浓度总体呈现大小交替型分布;SV30与SVI在水平方向总体呈现出周边大、中心小的非对称分布,而在垂直方向由上到下呈现出先增大后减小再增大的分布趋势。污泥浓度与污泥沉降性能的差异分布,对将反应器进水点分布在污泥浓度高值区域、污泥回流点布置在污泥浓度低值区域及出水点选定在污泥浓度较低且沉降性能较好区域有着重要的指导作用,为反应器的优化控制提供了理论依据。     

Observations of winds above and below a forest canopy located near a clearing

Measurements of wind movements have been made within and above a forest canopy located near a 0.5 km² clearing. They showed the existence of complex wind systems characterized by strong horizontal jets of air and large vertical velocities beneath the canopy during unstable atmospheric conditions. Under stable situations wind flows seemed to be less complex with both horizontal and vertical winds being greater above the canopy than below.     

白洋淀北岸农田土壤特性的表征

本文采用标准方法,测定了白洋淀北岸部分农田土壤的粒度组成、ｐＨ和有机碳含量等指标,对该地区土壤的特性进行了表征分析。结果表明,土壤的平均粒度分布大于２０μｍ的占５２．７３％,主要属于砂壤土。与１０年前相比,ｐＨ值变化不大;而有机碳含量是１０年前的１．２６倍。ｐＨ随土壤的垂直深度而略有增加,而有机碳含量则随土壤的垂直深度而减少。     

Chelator induced phytoextraction and in situ soil washing of Cu

In a soil column experiment, we investigated the effect of 5 mmol kg(-1) soil addition of citric acid, ethylenediamine tetraacetate (EDTA), diethylenetriamine-pentaacetate (DTPA) and [S,S]-stereoisomer of ethylenediamine-disuccinate (EDDS) on phytoextraction of Cu from a vineyard soil with 162.6 mg kg(-1) Cu, into the test plant Brassica rapa var. pekinensis. We also examined the use of a horizontal permeable barrier, composed of layers of nutrient enriched sawdust and apatite, for reduction of chelator induced Cu leaching. The addition of all chelators, except citric acid, enhanced Cu mobility and caused leaching of 19.5-23% of initial total Cu from the soil column. However, Cu plant uptake did not increase accordingly; the most effective was the EDDS treatment, in which plant Cu concentration reached 37.8 +/-1.3 mg kg(-1) Cu and increased by 3.3-times over the control treatment. The addition of none of the chelators in the concentration range from 5 to 15 mmol kg(-1) exerted any toxic effect on respiratory soil microorganisms. When EDDS was applied into the columns with horizontal permeable barriers, only 0.53 +/- 0.32% of the initial total Cu was leached. Cu (36.7%) was washed from the 18 cm soil layer above the barrier and accumulated in the barrier. Our results indicate that rather than for a reduction of Cu leaching during rather ineffective chelate induced Cu phytoextraction, horizontal permeable barriers could be more effective in a new remediation technique of controlled in situ soil washing of Cu with biodegradable chelates.