Spatial and temporal variation of below-ground N transfer from a leguminous tree to an associated grass in an agroforestry system

Nitrogen (N) transfer from leguminous trees can be a major N source for the associated crop in low-input agroforestry systems. The aim of this study was to identify the main climatic and soil factors controlling N transfer from the leguminous tree Gliricidia sepium (Jacq.) Walp to the associated grass Dichanthium aristatum (Poir.) C.E. Hubb, in a 16-year-old tropical agroforestry system. Nitrogen transfer was estimated using the natural ¹⁵N abundance method. Before tree pruning, total N transfer represented 57% of the N uptake of the grass, including 31% coming from N₂ fixation. The spatial variation induced by the tree was well described by soil organic N content (ON). In this system, ON is an index of soil available N as well as of tree root density. Rainfall (R) and evapotranspiration (ETP) were the main climatic factors controlling N transfer. Multiple regression analysis indicated that R, ETP and ON explained 79% of the temporal and spatial variation of N transfer. Transferred N cannot be estimated after pruning because of the change in the isotopic signature of the soil N source. This was related to N release from root turnover. The results suggest that grass showed a preferential uptake of N coming from the tree, which could be due to a lower energy cost compared to obtaining absorbed N from the clayey soil used in this work.     

氨基改性SBA-15有序介孔材料对Cd(Ⅱ)的吸附热力学特征研究

以硅酸钠为硅源,三嵌聚合物Pluronic P123为模板剂,采用水热-后期接枝的合成方法,制备出氨基改性SBA-15.用透射电镜、X射线衍射、氮气吸附-解吸和红外光谱等手段对其结构进行了表征.在此基础上,以改性SBA-15为吸附剂,通过批实验讨论了吸附时间、体系初始pH值和温度等对水溶液中Cd2+吸附的影响,并讨论了...     

Photocatalytic degradation of paraquat using nano-sized Cu-TiO2/SBA-15 under UV and visible light

Photocatalytic degradation of paraquat using mesoporous-assembled Cu-TiO₂/SBA15 under UV and visible light was investigated. The catalyst was synthesized by impregnation of Cu-TiO₂ colloids onto SBA-15. The colloids of Cu-TiO₂ were prepared via sol-gel method while the mesoporous support was prepared using hydrothermal technique. The catalyst was characterized using X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV diffuse reflectance spectroscopy, Zeta potential and X-ray adsorption spectroscopy. Results from characterizations showed that Cu doped TiO₂ had a small crystalline size and was well-dispersed on SBA-15. The inclusion of SBA-15 significantly enhanced the photocatalytic activity of the catalyst. Among the three types of undoped catalyst in this study (P25, TiO₂, TiO₂/SBA-15), TiO₂/SBA-15 yielded the highest degradation of paraquat for all pH under UV illumination. Meanwhile 2 wt.% Cu-TiO₂/SBA-15 yielded the highest activity under visible light.     

Methodological approach for metal pollution evaluation in sediments collected from the Taranto Gulf

The concentrations of Hg, Cd, Pb, Cu, Ni, V, and Sn were determined in marine sediments collected from Taranto Gulf (Ionian Sea, Southern Italy). The aim of this article is to study the methodological approach in order to evaluate total metal levels determined in marine sediments of a contaminated area (Taranto Gulf, Southern Italy), to identify contaminated areas and to predict adverse biological effects based on Sediment Quality Guidelines (SQGs). The results are discussed in relation to geological characteristics of sediments in order to define background levels and anthropogenic input. Experimental results were elaborated by multivariate statistical techniques and Geographical Information System (GIS) software. The geoaccumulation index I _geo and two sets of SQGs (in particular (a) the threshold effect level (TEL), the probable effect level (PEL) and (b) the effect range-low (ERL) and the effect range median (ERM)) have been used for environmental evaluation of metal concentrations. Results show that in Taranto coastal area, Mar Piccolo basin represents the most contaminated area. A comparison with results from other Mediterranean areas demonstrates that for some metals (such as Cd, Pb, and Hg) Taranto seas represent one of the most polluted areas in the Mediterranean Sea. A comparison of metal levels with SQGs also suggests an ecotoxicological risk for benthic organisms mainly in the first inlet of Mar Piccolo.     

Natural resource dependence and the accumulation of physical and human capital in Latin America

In a simultaneous model of human and physical capital accumulation for 17 Latin American countries from 1975 to 2004, we show that overall resource dependence has no significant direct effect on physical and human capital. When disaggregating the natural resource variable into sub-categories, we find that petroleum export dependence has a significant positive direct effect on physical capital, but a significant negative direct effect on human capital. Agricultural export dependence shows a significant negative direct effect on physical capital. Petroleum exports have a long run positive effect on physical capital but a negative long run effect on human capital. Agricultural exports have a negative long run effect on physical and human capital.     

Bioaccumulation, depuration and biotransformation of 4,4'-dibromodiphenyl ether in crucian carp (Carassius auratus)

Polybrominated diphenyl ethers (PBDEs) are extensively used as a class of flame retardants and have become ubiquitous environmental pollutants. Significant biotransformation of some PBDEs via reductive debromination has been observed. However, little is known about the fate of lower brominated BDEs in fish. In this study, the tissue distribution, excretion, depuration and biotransformation of 4,4′-dibromodiphenyl ether (BDE 15) were investigated in crucian carp (Carassius auratus) which were exposed to spiked water solution at different concentrations for 50 d, followed by a 14-d depuration period. Bioaccumulation parameters were calculated and the results showed that BDE 15 was mainly concentrated in the gill and liver. In particular, five biotransformation products of BDE 15 in carp were identified using GC-MS/MS. Besides two debrominated metabolites, three of the metabolites were mono-OH-BDE 15, diOH-BDE 15 and bromophenol. Our results unequivocally suggested that BDE 15 oxidation did occur via the formation of hydroxylated (OH-) metabolites in crucian carp exposed in vivo. These findings will be useful for determination of the metabolic pathways of PBDEs in freshwater fish, especially about their oxidation metabolism.     

电动力学作用下多溴联苯醚在土壤中的迁移特性

以4,4′-二溴联苯醚(BDE-15)为研究对象,探讨了电极电压、初始土壤pH、β-环糊精加入量、NaCl加入量等工艺条件对多溴联苯醚在土壤中迁移效果的影响。实验结果表明:在电极电压为5~15V范围内,随着电极电压的升高,土壤中BDE-15的迁移效果增强;初始土壤为酸性时、加入β-环糊精或NaCl后,土壤中BDE-15的迁移效果均增强。本实验选择的最佳工作条件为:电极电压15V,初始土壤pH3,β-环糊精的加入量3g,NaCl加入量5g。     

Cu-SBA-15催化湿式过氧化氢氧化水溶液中罗丹明B

采用水热晶化法合成了不同含铜量的Cu—SBA-15介孔分子筛,并且用XRD、N2吸附、TEM以及uV—vis对所合成的样品进行表征。以Cu—SBA-15为催化剂,H2O2为氧化剂,催化湿式过氧化水溶液中的罗丹明B,主要考察H2O2浓度、催化剂用量、处理温度、初始pH等因素对罗丹明B氧化效果的影响。结果表明,在同样的处理条件下罗丹明的脱色率明显高于TOC去除率,处理温度、初始pH对罗丹明B的脱色与氧化有重要影响。在罗丹明B初始浓度100mg／L,H2O2初始浓度1．8g／L,催化剂量0．3g／L,温度60℃,pH为7．0,处理时间100min时,罗丹明B的脱色率为98．6％,TOC去除率为62．8％。     

Biodiesel production from a free fatty acid containing Karanja oil by a single-step heterogeneously catalyzed process

Karanja oil, containing 6.2% free fatty acids (FFAs), was considered for biodiesel production using a single-step solid-phase acid catalyzed process. Different types of zeolites and Amberlyst15 catalysts were tested and biodiesel was produced. Under similar conditions, the highest biodiesel yield was achieved using an Amberlyst15 catalyst, which contained 3–5% of moisture. The effects of operating parameters of the reaction such as reaction temperature, catalyst amount, and methanol-to-oil ratio were studied. An increase of methanol:oil ratio revealed a non-monotonic increase in biodiesel yields. Similar non-monotonic behavior was observed when Jatropha oil was used. Leaching and catalyst reusability were also considered. No significant effects of leaching were observed and catalyst reusability appeared to be affected by methanol interactions. The presence of a co-solvent, Tetrahydrofuran (THF), increased the biodiesel yield. Furthermore, an optimum amount of THF (THF:methanol volume ratio of 1:2) gave rise to the highest biodiesel yield. A biodiesel yield of 93% was achieved at 120 °C using a single-step process with Amberlyst15 as a catalyst, THF as a co-solvent, and a methanol:oil ratio of 30:1.     

有序介孔材料过滤脱除纳米颗粒物

多孔材料过滤去除环境纳米颗粒物(nanoparticles,NPs)是空气净化治理的重要方法之一.本文采用介孔分子筛(MCM-41、SBA-15)和有序介孔碳(CMK-3)这3种典型介孔材料对2~20 nm的NPs进行过滤脱除研究,旨在探索介孔材料在NPs过滤方面的应用可行性与相关理论基础.基于3种介孔材料的物理化学性质表征结果,通过本实验发现介孔材料孔道的最可几孔径以及一定量的介孔孔容是吸附NPs的关键,而微孔分布对去除NPs贡献不大.进一步对SBA-15在不同流量及不同颗粒床厚度下对NPs的去除进行了分析,发现纳米颗粒物的最易穿透粒径(most penetrating particle size,MPPS)随着流量的增大而减小,同时MPPS颗粒物的去除效率随之降低,且MPPS基本不受颗粒床厚度变化的影响.本研究为介孔材料过滤脱除NPs提供了技术依据.