Speciation analysis and significance of ecological geochemistry

Different species of one element have different activities, so it has different effects on environment and human health. To analyze qualitatively and quantitatively the speciation of a special element in sample, which is the important basis for appraising the toxicity and studying the rule of transfer and translation of elements. Since the 1970＇s, the scheme of sequential extraction has already been used at many laboratories both at home and abroard, to get the information about heavy metals＇ activity in polluted soils. Because this method has the experimental nature, many schemes of problem has taken place, the absence of consistency of these sequential extraction have been formed. Thus the complexity of the schemes, the lack of selectivity of reagent, the lack of quality control, the result mainly related to the extraction scheme used, and so on. In the face of these problems, the study of experimental methods of sequential extraction on three different soils, sediment in Dongting Lake, soil in Jiangsu Province and loess in Shanxi Province was made. Reference materials of heavy metal speciation following sequential extraction in soil and sediment had been developed. Nowadays two kinds of sequential extraction methods which are widely used are BCR （three steps） and improved Tessier methods （seven steps）. Based on three steps of BCR, water-soluble speciation and the residual speciation were increased in our research. BCR701 was determined eight times at different laboratories using BCR three steps. The results showed that determined data obtained eight times were identical to the standard value, and it is indicated that this method has good reproducibility. The stability and homogeneity experiments indicated that the preparation of three types of candidates accorded with our requirements. Eight laboratories had afforded the determined values of 12 heavy metal elements （Cu, Pb, Zn, Mn, Co, Ni, Cd, Cr, Mo, As, Sb, Hg, Se et al.） using BCR three steps. Also, these three candidates afforded the determined values by seven steps, and 12 laboratories had participated.     

Total gaseous mercury emissions from mercury-enriched soil in Guizhou, China

Guizhou is located in the Circum-Pacific Global Mercuriferous Belt, and mercury concentrations in soil in this area are enriched. In-situ total gaseous mercury （TGM） exchange fluxes between air and soil surface were intensively measured at four sampling sites in Guiyang from 21 May to 16 June, 2003, and five sites in the Lanmuchang mercury mining area in December 2002 and May 2003, respectively. The in-situ Hg flux measurement was conducted with a dynamic flux chamber （DFC） of quartz. Overall, net emissions were obtained from all sampling sites. Soil mercury concentration and solar radiation have been proved to be the two most important parameters to control mercury emissions from soil. Meanwhile, rain events can enhance mercury emission rate significantly.     

Study on Kailyard soil amendment by adding compost of sludge

Mixture of municipal sewage sludge and organic garbage, which was alternatively treated by aerobic and anaerobic composting technologies for 60 days. The characteristics of the compost are as follows： the total nitrogen （TN）, total phosphors （TP） and total potassium （TK） are 1.40%, 0.101% and 1908.32 mg/kg on dry weight basis, the contents of Cu, Ni, Cd, Cr, Pb and Zn are 131.23, 21.49, 1.31, 35.49, 72.50 and 616.76 mg/kg on dry weight basis. A basin-scale experiment was carded out by planting watercress with kailyard soil fertilizing with the compost, the results showed that the municipal sewage sludge and organic garbage compost could promote the production of watercress to different degrees, the crop biomass increased from 74.46% to 312.00% with the amount of compost fertilizing on the kaliyard soil while the amount of compost fertilizing on the kaliyard soil below 150 g per 3.75 kg kaliyard soil and decreased from 312.00% to 102.29% while the amount of compost fertilizing on it over 150 g per 3.75 kg kaliyard soil, so the optimal addition of compost in the watercress and soil was 150 g compost per 3.75 kg kailyard soil. Furthermore,     

The structure and dynamics of 2-dimensional fluids in swelling clays

The interlayer pores of swelling 2:1 clays provide an ideal 2-dimensional environment in which to study confined fluids. In this paper we discuss our understanding of the structure and dynamics of interlayer fluid species in expanded clays, based primarily on the outcome of recent molecular modelling and neutron scattering studies. Counterion solvation is compared with that measured in bulk solutions, and at a local level the cation-oxygen coordination is found to be remarkably similar in these two environments. However, for the monovalent ions the contribution to the first coordination shell from the clay surfaces increases with counterion radius. This gives rise to inner-sphere (surface) complexes in the case of potassium and caesium. In this context, the location of the negative clay surface charge (i.e. arising from octahedral or tetrahedral substitution) is also found to be of major importance. Divalent cations, such as calcium, eagerly solvate to form outer-sphere complexes. These complexes are able to pin adjacent clay layers together, and thereby prevent colloidal swelling. Confined water molecules form hydrogen bonds to each other and to the clays' surfaces. In this way their local environment relaxes to close to the bulk water structure within two molecular layers of the clay surface. Finally, we discuss the way in which the simple organic molecules methane, methanol and ethylene glycol behave in the interlayer region of hydrated clays. Quasi-elastic neutron scattering of isotopically labelled interlayer CH₃OD and (CH₂OD)₂ in deuterated clay allows us to measure the diffusion of the CH₃- and CH₂-groups in both clay and liquid environments. We find that in both the one-layer methanol solvates and the two-layer glycol solvates the diffusion of the most mobile organic molecules is close to that in the bulk solution.     

Analysis of a rigid footing lying on three-layered soil using the finite difference method

A numerical procedure is described for the analysis of the vertical deformation and the stress distribution of the strip footings on layered soil media. Three layers of soil with different stiffness are considered with the middle soil layer the thinnest and most stiff layer. The soil media is discretized and using the theory of elasticity, the governing differential equations are obtained in terms of vertical and horizontal displacements. These equations along with appropriate boundary and continuity conditions are solved by using the finite difference method. The vertical and horizontal displacements, strains and stresses are found at various nodes in the soil media. Parametric studies are carried out to study the effect of the placement depth of the middle soil layer, the relative ratios of the moduli of deformation of the soil layers on the vertical displacement of the footing and the vertical stress distribution. These studies reveal that the middle thin but very stiff layer acts like a plate and redistributes the stresses on the lower soft soil layer uniformly. The displacement on the top and bottom of the middle soil layer is almost the same showing that the compression of the middle layer is negligible as it is very stiff.     

Break out resistance of inclined anchors in sand

Inclined anchors are widely used in a variety of civil engineering problems to resist oblique loads, most relevant being in transmission towers and in rocks and dams for structural strengthening. In the present study, the breakout resistance of the inclined anchors in sand has been worked out using limit equilibrium approach. The breakout resistance has been calculated for different soil friction angles with varying relative depth ratio and anchor inclination. The break out factor increases continuously with the inclination of the anchor. A comparison of predicted values of break out resistance of anchors by the proposed analysis with the experimental values as reported by the other researchers showed reasonably good agreement.     

The log-normal distribution for hydraulic conductivity of compacted clays: Two or three parameters?

Risk and uncertainty assessments for waste containment systems employing clay barriers often include spatial variability in the hydraulic conductivity as part of the analysis. The two-parameter log-normal distribution is often used to describe the spatial variability, but for compacted clays the three-parameter form can be more appropriate. A statistical hypothesis test was developed that can be used to determine if the two- or three-parameter form of the log-normal distribution is more appropriate. The test is based on a likelihood ratio, comparing likelihood functions for the two- and three-parameter forms at their maximums. Likelihood functions are used assuming that a data set can be segregated into a set of distinct groups of hydraulic conductivities. A step-by-step calculation procedure is described and the test is applied to data collected from 45 sites.     

紫色丘陵区水土保持林低效化的土壤成因

四川盆地紫色丘陵区的水土保持林低效化问题已较严重。研究了其土壤方面的成因。通过对土壤构造、土壤肥力特性、土壤结构性评价等研究，指出该区人工林地的土壤构造发育不正常，土壤腐殖质胶体积累量低。土壤结构质量差等林地土壤退化是土壤水土保持功能降低的主要原因。根据研究的初步结果，提出了相应的对策建议。