不同消解方法测定土壤中汞的方法研究

应用氢化物发生—原子荧光光谱法,测定土壤中汞的技术,用不同消解方法测定土壤中总汞的差异。结果发现,利用硫硝混酸-高锰酸钾法测得的标准样的总汞接近实际值。分析了土壤标样Ess-3、Ess-4,进行了方法精密度和回收率试验。在经过优化的试验条件下,硫硝混酸-高锰酸钾法测得汞的检出限：0.002μg/L,回收率在98.7%～101.6%之间,相对标准偏差≤1.94%。     

Electrokinetic remediation: The use of mercury speciation for feasibility studies applied to a contaminated soil from Almadén

We have chosen the BCR (Bureau Communautaire de Référence) sequential extraction procedure as a speciation analysis to determine the mobility of mercury in the contaminated soil of the Almadén (Spain) mining district. This soil has a high mercury concentration (1000 mg kg⁻¹) in some areas. In previous works, the relationship between the weak-acid soluble fraction and the amount of contaminant recoverable by acid-enhanced electrokinetic remediation (EKR) was shown. In this study, after testing that this relationship is maintained, we test if similar relationships with chelating agents could be established. Recently, several chelating agents were tried and iodide was shown to be quite efficient for the removal of mercury. Thus we have carried out iodide-enhanced EKR experiments at the lab (16 g of soil) and semi-pilot (2 kg) scales. From these experiments it can be concluded that the amount of mercury recoverable by this technique is similar to the one recovered in the batch extraction experiments. Thus, this is another evidence that this kind of experiments can be used for the feasibility studies of the remediation technique. It is also shown that, although the removal efficiency is similar to the one obtained previously for in situ flushing, the time required to achieve this efficiency would be several orders of magnitude shorter for this soil.Nevertheless, the residual Hg present in the weak-acid soluble fraction of the speciation analysis of the soil after the EKR treatment increases with respect to the original contaminated soil, indicating a possible increase of the risks associated to the contaminated site. Therefore, a second EKR treatment is applied to the same soil, this time using acid-enhanced EKR. It is shown that, although almost no Hg was recovered with this technique for the original soil, an important amount can be recovered after the first treatment (iodide-enhanced EKR). Also it is shown that the design and operation of this second technique should be studied carefully due to the rather complex chemistry of the species involved.     

Transformations of soil and manure phosphorus after surface application of manure to field plots

Transfer of phosphorus (P) from surface-applied manures to runoff is an important source of pollution, but few studies have closely monitored P dynamics in manure, soil, and runoff through time. We monitored manure and soil P over 14 to 17 months in field experiments in Texas and Pennsylvania, USA following dairy and poultry manure surface application. Manure was applied to porous fabric that enabled discrete sampling of both manure and underlying soil. Manure mass consistently decreased while manure total P was essentially constant through time. Manure water extractable P decreased rapidly for the first two months, likely due to rainfall leaching, but then maintained stable concentrations thereafter, with other forms of manure P gradually transformed to water extractable forms. Soil P from the upper 2 cm rapidly increased after manure application in association with manure leaching by rain. After 2 to 3 months, soil P peaked and either remained constant or gradually declined. Similar trends occurred at 2–5 and 5–10 cm, but with lesser magnitudes. At 10–15 cm, soil P changed little over time. In Pennsylvania, naturally occurring runoff from 0.7-m × 1.3-m plots without and without manure was also monitored. Runoff dissolved P concentrations were greatest for the first event after manure application and decreased steadily through time, but remained greater than P concentrations from control plots, and were always well related to manure water extractable P. This study reveals that management practices for water quality protection must consider the potential for manure P transformations to contribute dissolved P to runoff long after manure is applied.     

The synthesis of salt-resistant emulsion and its application in ecological sand-fixing of high salt-affected sandy land

For the first time, the salt-resistant emulsion was applied as an ecological sand-fixing material to enhance the sand-fixing ability in salty desert. This study started from the synthesis of the novel salt-resistant poly(vinyl acetate-dibutyl maleate-acyclic acid-sodium p-styrene sulphonate) copolymer emulsion. Then, the structure, composition and thermal property of the emulsion were characterised. The sand-fixing properties and ecological effect of the emulsion were evaluated. The experimental results showed that the emulsion has been successful synthesised and could be used as an ecological sand-fixing material. The related reason is that, first, the emulsion could significantly visibly enhance the sand-fixing ability in high salt-affected sand land. Second, the prepared emulsion had good thermal aging resistance and freeze-thaw stabilities to withstand the changes in the temperature of salty desert, and the test of the influence of the emulsion on the growth of microbe of sand showed a favourable ecological effect.     

Oven-Drying Characteristics of Soils of Different Origins

Abstract

The accurate measurement of the moisture content of a soil is an important step in characterizing its engineering behavior. However, the oven-drying method can cause some chemical reaction (oxidation or loss of water of crystallization) to occur in certain soil types. The level of oxidation of the solid particles was studied over the drying temperature range of 60 to 140°C for different soils. The period of oven drying necessary for the specimen mass to equilibrate was also examined. The standard practice of oven drying the soil specimens at 110 ± 5°C or 105±5°C over a period of 24 h was confirmed as giving accurate moisture content values for inorganic soils. Oven drying of peat and other highly organic soils over a period of 24 h at 80°C produced similar levels of accuracy in the moisture content measurements as that for inorganic soils at the standard oven drying temperatures of 105 or 110°C. Some oxidation of the organic fraction commenced at between 80 and 90°C.     

HIGH WATER ABSORBENTS FROM LIGNOCELLULOSES. I. EFFECT OF REACTION VARIABLES ON THE WATER ABSORBENCY OF POLYMERIZED LIGNOCELLULOSES

Hydrogels of 350 water-absorbency (g H₂O₂/g sample) and 900 water-keeping capacity (mL H₂O₂/g sample) were prepared from local lignocellulosic wastes. The wastes used are rice straw, sugar-cane bagasse, and cotton stalks. These hydrogels were prepared via graft–polymerization reaction using some vinyl monomers, followed by alkali hydrolysis. The effects of grafting parameters (concentration of both initiator and monomer, temperature, and time), purity of lignocellulose sample, type of monomer, pretreatment of lignocellulose, and manner of saponification reaction were examined.

The application of such polymeric materials as soil conditioners, by following the pore size distribution of sand soil, in comparison with conventional soil conditioners (e.g., natural organic fertilizer and clay), were also evaluated.     

Sugarcane residue management and grain legume crop effects on N dynamics,N losses and growth of sugarcane

To reduce greenhouse gas emissions farmers are being encouraged not to burn sugarcane residues. An experiment was set up in NE Thailand, where sugarcane residues of the last ratoon crop were either burned, surface mulched or incorporated and subsequently the field left fallow or planted to groundnut or soybean. The objectives of the current experiment were to evaluate the residual effects of these treatments during the following new sugarcane crop on (i) microbial and mineral N dynamics, (ii) performance of sugarcane and (iii) effectiveness of recycled legume residues compared to mineral N fertilizer on N use efficiencies, ¹⁵N recovery in the system and in soil particle size and density fractions (using ¹⁵N labelled legume residues and fertilizer). The millable cane and sugar yield were positively affected by sugarcane residue mulching and incorporation compared to burning suggesting microbial remobilization of previously immobilized N. Residual effects of legumes increased sugarcane tillering and yield (127 and 116 Mg ha⁻¹ for groundnut and soybean, respectively) compared to the fallow treatment without N fertilizer (112 Mg ha⁻¹). Soybean residues of higher C:N ratio (33:1) and lignin content (13%) compared to groundnut residues (21:1 C:N, 5% lignin) decomposed slower and improved N synchrony with cane N demand. This led to a better conservation of residue N in the system with proportionally less ¹⁵N losses (15–17%) compared to the large losses from groundnut residues (50–57%) or from mineral N fertilizer (50–63%). ¹⁵N recoveries in soil were larger from residues (41–80%) than from fertilizer (30%) at final harvest. Recycled legume residues were able to substitute basal fertilizer N application but not topdressing after 6 months.     

Long-term impact of chronosequential land use change on soil carbon stocks on a Swedish farm

Agricultural practices and land use significantly influence soil carbon storage. The processes that are affected by land use and management are generally understood, but uncertainties in projections are high. In this paper, we investigate the long-term effects of chronosequential land use change from grassland to cropland and vice versa on soil carbon stock dynamics in four fields on a Swedish farm. Between 1850 and 1920, three of the fields were converted from grassland into cropland, and one was converted back to grassland in 1971. The fourth (control) field is a grassland that has never been ploughed. In 1937, the four fields were sampled at 111 points in a regular grid (25 or 50 m) and the dried soil samples were stored at our Department. In 1971 and 2002, the original grid points were revisited and re-sampled. Land use changes affected the soil C stock significantly. In 1937, carbon stocks were significantly smaller in the arable fields than in the grassland soil. In the field that was converted from arable back to grassland, soil C increased significantly at an average rate of about 0.4 Mg ha⁻¹ year⁻¹. A soil C balance model (ICBM) driven by standard meteorological data and soil carbon input estimated from yield records described soil carbon dynamics reasonably well, although the range of simulated relative changes in C stocks between 1937 and 2002 in the four fields (from −7.4 to +8.8%) was narrower than those measured (from −19.5 to +16.5%). There are only few long-term studies in Northern Europe available for quantifying the effect of land use change on soil carbon stocks and the results presented here are therefore useful for improving predictions of changes in soil carbon driven by land use change.     

绿色马铃薯栽培技术

马铃薯是临县的主要农作物。文章从种薯选择、测土配方施肥、田间管理等方面,介绍了绿色马铃薯栽培技术,为农户生产提供借鉴。     

A critical analysis of the performance of plate- and point-electrodes for determination of electrical properties of the soil mass

In the recent past, researchers have started utilizing electrical properties of the soil mass for its characterization by employing either plate- or point electrodes. Though, plate-electrodes are easy to use for laboratory experiments, and quantification of geometrical characteristics of the electric field generated within them is easy to quantify, their application for in-situ experiments and for samples of cylindrical shape becomes difficult. On the other hand, usage of point-electrodes which are cylindrical in shape, are used for moisture content determination of the soil or migration of contaminants in it, for coarse-grained soils and fine-grained soils might yield erroneous results, due to the presence of inter particle voids and presence of cavities & anomalies, respectively. Furthermore, quantification of geometrical parameters of the electric field of point-electrodes is quite difficult which results erroneous measurements in determination of electrical properties of the material, in which they are installed. Hence, establishment of the uniqueness of electrical properties obtained from the plate- and point-electrodes, for identical samples becomes utmost important. With this in view, COMSOL Multiphysics® was employed to simulate the electrical response of various geomaterials in their uncontaminated and contaminated states and results were critically evaluated vis-à-vis those obtained from the impedance analysis (1 Hz to 40 MHz). Efforts have also been made to relate the geometrical dimensions of electrodes and electric field generated across the point electrodes, which would facilitate proper design and installation of sensors in a material to achieve the desired output. This study demonstrates the suitability and versatility of the point-electrodes for various (field and laboratory) applications where in moisture profiling and contaminant transport is to be established.