草酸活化磷矿粉对砖红壤中外源铅的钝化效果

磷矿粉被广泛用于固定污染土壤中的重金属,然而施用草酸活化磷矿粉后对土壤中铅形态的研究非常有限。该文采用Tessier连续提取法分析砖红壤中施加未活化和经草酸活化的磷矿粉后,砖红壤中外源铅形态的变化。结果表明:随着磷矿粉施加量的增加,各处理中交换态铅质量分数比对照(64.1mg/kg)显著下降,未活化磷矿粉处理(PR)的交换态铅质量分数为0.1mg/kg,而草酸活化磷矿粉处理(APR)中未检出;醋酸盐提取态铅质量分数除草酸活化磷矿粉2000mg/kg处理为24.5mg/kg(APR3)减少外,其他处理均高于对照(27.2mg/kg),在未活化磷矿粉500mg/kg(PR2)处理时达到最大值41.8mg/kg;铁锰氧化物结合态除未活化磷矿粉50mg/kg(PR1)处理为69.5mg/kg低于对照(74.2mg/kg)外,其余均高于对照,在APR3处理时达最大值117.2mg/kg;有机物结合态铅质量分数除PR1处理为20.7mg/kg,其余均高于对照处理(21.8mg/kg),在APR3处理时达到最大值46.5mg/kg;PR处理残渣态铅与对照相比(44.2mg/kg)显著增加至60.6mg/kg,对APR处理其变化范围为42.7～43.5mg/kg,各处理稍低于对照,但差异不显著(p<0.05)。显然,磷矿粉的施加可有效降低砖红壤中交换态铅质量分数,增加稳定态铅质量分数,且草酸活化磷矿粉的效果更佳。同时,草酸活化后磷矿粉的释磷能力增加,除草酸活化磷矿粉最高施磷量处理外(5000mg/kg),施入磷矿粉和草酸活化磷矿粉后释放的磷对环境构成风险可能性极小。X-射线衍射光谱(X-ray diffraction,XRD)和扫描电镜(scaning electron microscope,SEM)结果分析也表明草酸活化磷矿粉的释磷能力增加,更有利于固定土壤中的铅。该研究可为草酸活化磷矿粉固定土壤中的铅提供参考依据。     

Relationship between mycorrhizal dependency and rate variables associated with P uptake,utilization and growth

Abstract

A greenhouse investigation was undertaken to determine the relationship between mycorrhizal dependency of host species and rate variables associated with their P uptake, P utilization and growth. The results indicated that species that are marginally dependent on VAM fungi tend to have lower P utilization efficiency, higher P absorption rate and higher growth rates compared to moderately or highly VAM dependent species when they are not colonized by mycorrhizal fungi. The results also demonstrated that species differing in growth rates could differ in their mycorrhizal dependency even when they have similar root morphological characteristics.     

Characteristics and potential pedogenetic processes of a Technosol developing on iron industry deposits

Purpose

Technosols include soils dominated or strongly influenced by human-made materials. Similarly to natural soils, technogenic parent materials submitted to environmental factors undergo weathering and transformation processes. But the pedogenesis of Technosols remains little known. With this aim in view, a Technosol developing on purely technogenic materials resulting from an iron industry was thoroughly characterized in order to discuss the pedogenetic evolution of this Technosol using knowledge about the pedogenesis of natural soils.

Materials and methods

The studied site was a former settling pond where mainly sludge generated by wet cleaning of blast furnace fumes was dumped probably until the mid-twentieth century. Thereafter, the pond has been colonized by vegetation and is covered by a diversified forest. The soil was composed of contrasted layers. A 20-cm organic layer has developed at the surface. Samples were collected in the first 2 m which are under root influence. Elemental composition, agronomic parameters, mineralogy, as well as the physical and hydraulic properties of the soil materials were characterized.

Results and discussion

Some characteristics of the Technosol, e.g. elemental composition, mineralogy or profile stratification, resulted mainly from industrial processes. However, some properties of the Technosol can be compared with natural soils. Particularly, the presence of low periodic order minerals and physical and hydraulic properties were analogous to the properties of Andosols. However, alkaline pH and the carbonate contents made the Technosol closer to carbonated soils. Moreover, the presence of Mn oxides, high porosity and water retention were also encountered in Mn-bearing soils. Early pedogenic processes, e.g. development of organic surface layer and signs of mineral weathering, were observed. But transfers seemed to be rather limited and/or slow in the profile. However, the physical and chemical properties, e.g. high water retention and high pH, were rather favourable to element retention.

Conclusions

The evolution of the Technosol seems to be still limited in the profile, which could be explained by the high retention capacity of the soil. The presence of highly reactive mineral phases, such as low periodic order Mn oxides or allophane-like minerals, with high contents of carbonates is rarely encountered in the natural environment and may suggest an important potential for pedogenic evolution, which could be directed by the balance between the weathering processes of these phases.     

Early transformation and transfer processes in a Technosol developing on iron industry deposits

Large surface areas covered with man‐made materials are subject to pedogenetic evolution. However, pedogenetic processes in the resulting Technosols are seldom fully assessed. This work was conducted to identify and characterize the processes occurring on deposits of industrial technogenic materials. A former settling pond of the iron and steel industry where a forest has established since termination of the industrial activity approximately 50 years ago was chosen. A 2‐m deep pit was opened, and a series of layers of the soil profile were sampled. The macro‐ and micro‐structure were studied, and soil samples were analysed for structural, chemical and mineralogical assessment (chemical analyses, X‐ray diffraction, infrared and Mössbauer spectroscopies, scanning and transmission electron microscopies coupled with energy dispersion spectrometry). Results showed that the profile was composed of a succession of sub‐horizontal layers arranged in two groups according to their structure and composition, linked to the composition of the industrial effluent. Group 1 was composed of iron‐, carbonate‐ and aluminosilicate‐rich layers exhibiting a compact structure. Group 2 contained manganese‐rich layers with a friable structure. Pedogenetic processes of various intensities were detected at different depths. Besides an accumulation of organic matter at the surface, transformations of minerals were recorded all along the soil profile, with weathering, leaching and precipitation of new phases. Phenomena occurred primarily in specific zones, such as cracks and interfaces between two layers. In conclusion, the soil maintained characteristics of the original industrial material and displayed several stages of pedogenesis, which were controlled chronologically by climatic and biological factors.     

Aggregation and availability of phosphorus in a Technosol constructed from urban wastes

Purpose

To preserve natural soil resources and in order to create fertile constructed Technosols for plant cultivation, wastes and by-product mixtures were studied in relation to their pedogenic properties and especially soil organic matter contents. We assessed interactions between aggregation and nutrient availability, focusing on phosphorus (P) transfer in the soil-water-plant system.

Materials and methods

Four typical urban wastes, dried and sieved to pass 2 mm, were mixed selectively to mimic a fertile topsoil material: excavated subsoil AE, compost from sludge and green wastes CO, green wastes GW, and bricks BR. After characterization of the wastes for physico-chemical and toxicological parameters, we focused on four mixtures: AE/CO, AE/GW, BR/CO, and BR/GW. The mixtures were tested in a 55-day long pot experiment under controlled conditions in a climate chamber. Pots were bare and planted with Lolium perenne (ryegrass) and Brassica napus (rape). The two plant species were selected for contrasting root activities and architectures and phosphorus (P) acquisition strategies. The aggregate formation was tested using the mean weight diameter method at the end of the experiment.

Results and discussion

We have measured intense aggregation in mixture AE/GW, low aggregation in AE/CO, and no aggregation in BR/CO and BR/GW. After 55 days, neither Technosol aggregation nor aggregate stability was significantly affected by plant development. Available phosphorus (P_Olsen) content was sufficient for plant development in all the mixtures (from 0.28 to 0.58 g kg^?1). The P_Olsen/P_total ratio was higher in mixtures with GW, even if the mixtures with compost (AE/CO and BR/CO) induced the highest biomass production for ryegrass and rape.

Conclusions

The nutrient availability in constructed Technosols and the transfer of P to plant were highly dependent on organic matter type, with high or low delivery of P_Olsen linked to the mineralization potential and the size and distribution of aggregates. Therefore, pedological engineering processes can be improved by the selection of adapted constitutive wastes and by-products to create a fertile substrate allowing high biomass production.

     

The effect of phosphate deficiency on the kinetics of phosphate absorption by sterile excised barley roots,and some factors affecting the ion uptake efficiency of roots

Abstract

The influence of phosphate nutrition on the kinetics of phosphate absorption by sterile excised barley roots was examined. The roots of seedlings grown in dilute CaSO₄ showed uptake kinetics similar to roots grown in phosphate deficient nutrient culture. The absence of microorganisms did not abolish the dual form of the absorption isotherm at pH 4.0

The most important effect of phosphate deficiency for uptake at low phosphate concentration was a marked decrease in the apparent dissociation constant of the ion‐carrier complex postulated to be involved in the uptake process. The results are discussed in relation to kinetic factors which may influence the efficiency of ion uptake by roots of different species of plants, including the apparent dissociation constant, the rate constant for uptake and the concentration of the ion‐carrier system.     

Effects of environmental and biological variables on the toxicity of mercuric chloride

This study evaluated the effects of environmental and biological variables on the toxicity (LC₅₀) of mercuric chloride on the fish Notopterus notopterus. The results reveal that the change in temperature, dissolved oxygen, pH and fish size in experiments is highly significant both at 1 and 5% levels except in size, where it is insignificant at 1% level.     

Effect of water content on aggregation and contaminant leaching: the study of an urban Technosol

Background, aim, and scope  

Natural porous material structure is a key parameter in the transport of particles and associated contaminants towards groundwater, and it is a dynamic property that evolves with water content. This study investigates the relationship between aggregation–potential leaching and moisture content.     

The kinetics of phosphate removal in small alkaline lakes by natural and artificial processes

Two small lakes in Southeast Florida were observed to have intermittently high P concentrations as a result of surface runoff from fertilized drainage areas. Simulation of this phenomenon was effected through direct fertilization of a lake with high phosphate fertilizer (0 - 46 - 0), and phosphate levels were monitored with time. Removal rates were observed to adhere closely to two consecutive first-order reactions. The components of the total rate of removal were identified as hydraulic flushing (HF), primary productivity (PP) and physicochemical processes (PCP). Of the P applied, PCP were found to remove 79.7 to 97.6% during the first stage (phase 1) of each experiment, however the highest per diem removal by natural processes was 11.1%. Adsorption and subsequent nucleation on calcite were thought to be the predominant mechanisms governing orthophosphate concentrations in the water column. The second phase of phosphate removal was accounted for primarily through HF and PP. Decreasing high levels of P in the water column by precipitation with Al was found to have a high per diem efficiency (40.8%). This effectively reduced the high potential yield of macrophyte biomass experienced with natural phosphate limiting mechanisms.     

A note on the description of the kinetics of phosphate sorption

Summary Observations on the rate of sorption of phosphate by four samples of Danish soils have been re‐examined. A previously reported lag phase in plots of log concentration against log time could be ascribed to the use of large solution:soil ratios rather than to the inclusion of short periods of reaction.     

Desorption of phosphate from iron oxides in relation to equilibrium pH and porosity

Reactions of phosphated lepidocrocites and geothites with 0.1 M NaCl, 0.1 M NaOH and 0.5 M NH₄F solutions have been studied. Solutions of indifferent electrolyte (0.1 M NaCl) at the same pH as used during adsorption of P were used to desorb P so that new apparent equilibria were reached, but a slow readsorption was also observed. Strongly alkaline solutions seemed to cause some breakdown of the solid surface and part of the adsorbed P became occluded.Desorption and isotopic exchange data have been related to porosity of the two oxides, and presence of a component of the exchangeable P released very slowly, has been attributed to P adsorbed on surfaces of micropores.     

Oxidation of diazinon by aqueous chlorine: kinetics, mechanisms, and product studies

The oxidation kinetics and mechanisms of diazinon, an organophosphorus pesticide, by aqueous chlorine were studied under different conditions. The oxidation is of first order with respect to both diazinon and chlorine. The oxidation rate is found to increase with decreasing pH. The second-order rate constants at pH 9. 5, 10.0, 10.5, and 11.0 are determined to be 1.6, 0.64, 0.43, and 0. 32 M(-)(1) s(-)(1), respectively. Based on the rate constants at different temperatures, the activation energy is calculated to be 30 kJ/mol at pH 10.0 with a chlorine-to-diazinon ratio of 11:1, 33 kJ/mol at pH 11.0 with a 11:1 ratio, and 36 kJ/mol at pH 11.0 with a 5:1 ratio, respectively. Diazoxon is identified as the oxidation product by GC-MS. Ion chromatography analysis shows an increase of sulfate concentration as the reaction proceeds, indicating that sulfur is being oxidized to sulfate. This study indicates that oxidation by aqueous chlorine can significantly affect the fate of diazinon in the environment.     

Effects of soil properties on the kinetics of desorption of phosphate from Alfisols by anion‐exchange resins

Phosphorus‐desorption rates by anion‐exchange resins were best described by three empirical kinetic models: Elovich equation, the parabolic diffusion equation, and the fractional power equation in that order. The objective of this study was to determine the relationship between kinetic rate constants from Elovich, fractional power, and parabolic rate equations and soil physical and chemical properties from soils of different lithogenic origins from the Nigerian savanna. Phosphorus‐desorption patterns included an initial fast reaction, followed by a slow release that continued up to 20 h. Particle diffusion was observed to be the rate‐limiting step in the kinetic desorption of native P in the soils studied as opposed to ligand exchange or surface reaction. The influence of parent material is not prominent due to long history of pedogenesis over the soils. The rate coefficients from the Elovich equation, parabolic diffusion equation, and the fractional power model were best predicted from clay, pH, and extractable Al and Fe oxides and therefore exert a profound influence on the rate of P release from the soils. These soil properties together explained between 93% and 99% of the variance in the rate coefficients of P desorption from the soils.     

Characterization of a Technosol developed from deposited flue‐dust slurry and release of inorganic contaminants

A flue dust originaly enriched in metal sulfides evolved as a by‐product of Cu smelting. The dust was deposited as slurry in unsealed heaps. It is characterized by very high contents of toxic metals such as Pb and Zn. The slurry is a source of soil, sediment, and water contamination. We studied a Technosol profile developed from deposited flue‐dust slurry by means of chemical and mineralogical characterization (SEM‐EDX, XRD, FTIR, DTA‐MS, XRF, Pb isotopes), by open‐flow and closed‐flow column experiments on contaminant release under water‐saturated conditions, and by geochemical modeling to evaluate release processes and to quantify aqueous contaminant concentrations. Besides ash particles and quartz, the flue‐dust slurry contains Fe oxides, silicates, sulfates, and sulfides (in varying states of weathering). In both column approaches, metal concentrations exceed inspection values. The concentration patterns in both experimental column approaches indicate near‐equilibrium mineral dissolution. Geochemical modeling reveals partial dissolution of sulfates and precipitation of secondary carbonates. Their precipitation prevents complete sulfate dissolution, which would have led to even higher aqueous metal concentrations and contaminant export. The combination of detailed material characterization, column experiments, and modeling allows for quantitative and qualitative estimation of contaminant release into the soil solution.     

The effects of phosphate on zinc sorption by a soil

Zinc sorption curves were obtained after treatment of a soil with several rates of phosphate and with two rates of lime. The lime permitted evaluation of the effects of phosphate on Zn sorption via its effects on pH. The phosphate was either incubated with the soil at a high temperature before reaction with Zn or was supplied at the same time as the Zn. This produced treatments with similar concentration of phosphate in solution but different amounts of sorbed phosphate.
Two distinct effects of phosphate addition on Zn sorption were detected. One arose from effects of phosphate on pH. This effect could be large and could either increase or decrease Zn sorption depending on the direction of the pH effect. A second effect was correlated with the amount of sorbed phosphate and was assumed to operate through the effects of phosphate on charge. The effects were small at low levels of Zn but larger at higher levels. This suggested that Zn and phosphate were sorbed at opposite ends of a spectrum of electrostatic potentials and overlap only occurred when the level of application was high. A third possible effect, due to reaction of the soil with zinc phosphate complexes in solution, was not proved.     

Tillage, mineralization and leaching: phosphate

Phosphate is usually the limiting nutrient for the formation of algal blooms in freshwater bodies, so tillage practices must minimize phosphate losses by leaching and surface run-off from cultivated land. Mineral soils usually contain 30–70% of their phosphate in organic forms, and both organic and inorganic phosphate are found in the soil solution. Some organic phosphates, notably the inositol phosphates, are as strongly sorbed by soil as inorganic phosphates, and this decreases their susceptibility to mineralization. The strength with which both categories are sorbed lessens the risk of their being leached as solutes but makes it more likely that they will be carried from the soil on colloidal or particulate matter, and the greatest losses of phosphate from the soil usually occur by surface run-off and erosion. Recent studies at Rothamsted have, however, shown substantial concentrations of phosphate in drainage from plots that have long received more phosphate as fertilizer than is removed in crops. These losses probably occurred because preferential water flow carried the phosphate rapidly from the surface soil to the field drains. For lessening losses of phosphate by leaching and run-off, the prime requirement of tillage is that it should encourage flows of water through the soil that help it to retain phosphate. Primary and secondary tillage should ensure that the surface roughness and porosity of the top-soil encourage the flow of water into the soil matrix where it will move relatively slowly and allow phosphate to be sorbed, thereby avoiding problems from run-off and preferential flow. Inversion tillage can be useful for lessening the loss of phosphate by run-off and erosion. Secondary tillage could be used to decrease the size of the aggregates and increase the surface area for sorption. Although tillage will increase the mineralization of organic phosphate, pulses of mineralization are unlikely to be so rapid or to lead to such large losses as with nitrate. The strength with which phosphate is sorbed also lessens the problem. As with nitrate, the key to managing phosphate is basically good husbandry.     

Prediction of soil depth using environmental variables in an anthropogenic landscape, a case study in the Western Ghats of Kerala, India

Soil (regolith) depth is a crucial input for modeling earth surface phenomena. However, most studies ignore its spatial variability. Techniques that map the spatial variability of soil depth are of three types: (1) physically-based; (2) empirico-statistical from environmental correlates; and (3) interpolation from point observations. In an anthropogenic landscape, soil depth does not depend primarily on natural processes, making it difficult to apply a physically-based approach. The present study compares empirico-statistical methods with geostatistical methods for predicting soil depth in such a landscape: Aruvikkal catchment (9.5 km²) in the Western Ghats of Kerala, India. Regression kriging applied on blocks of 20 m by 20 m using the environmental covariates elevation, slope, aspect, curvature, wetness index, land use and distance from streams, proved to be the best predictor of soil depth. This model explains 52% of the variability of soil depth in the catchment; with a prediction variance of 0.05 to 0.19. A Gaussian simulation was attempted for a more realistic visualization of the depth, as opposed to the smooth kriging prediction. The most important explanatory variable of soil depth in this landscape is land use, as expected from the strong human intervention.