Measurement of trace nitrate concentrations in seawater by ion chromatography with valve switching

An ion chromatographic method with a valve switching facility was developed to determine trace nitrate concentrations in seawater using two pumps, two different suppressors, and two columns. A carbohydrate membrane desalter was used to reduce the high concentrations of sodium salts in samples. In this method, trace nitrate was eluted from the concentrator column to the analytical columns, while the matrix flowed to waste. Neither chemical pre-treatment nor sample dilution was required. In the optimized separation conditions, the method showed good linearity （R〉0,99） in the 0.05 and 50 mg/L concentration range, and satisfactory repeatability （RSD〈5%, n=6）. The limit of detection for nitrate was 0.02 mg/L. Results showed that the valve switching system was suitable and practical for the determination of trace nitrate in seawater.     

Chemical characteristics and environmental significance of fresh snow deposition on Urumqi Glacier No. 1 of Tianshan Mountains, China

Ice and snow chemistry of alpine glaciers is crucial for the research of regional atmospheric environment change. Fresh snow samples were weekly collected from Urumqi Glacier No.1 in the Tianshan Mountains, Xin- jiang, China, and the chemical characteristics and seasonal variations of major ions, mineral dust, δ18O and trace metals were measured. Results show that the concentrations of major ions in the snow are Ca2+ SO42- NH4+ NO3- Cl- Na+ Mg2+ K+, in which Ca2+ is the dominant cation, and SO42-is the dominant anion. All major ions have close positive correlations with each other except NO3-. δ18O shows positive correlation with air temperature change during the study period. Mineral dust particle and major ionic concentrations in fresh snow have obvious seasonal change, with high concentration in spring but low concentration in summer and autumn, which indicates that the chemical mass input from Asian dust activity to snow is very significant. Temporal changes of trace metals in fresh snow, e.g., Cd, Pb, Zn, Al, Fe, have shown that human-induced pollution of central Asian region also has large contribution to the snow chemistry on alpine glaciers of the Tianshan Mountains.     

生活百科

<正>不吃主食藏危机谷类食物含有大量碳水化合物,除了能为人体提供能量,还是维生素B的主要来源,缺乏维生素B,对肝脏不利,而摄入动物脂肪时,如碳水化合物摄入不足,     

蓟县山前土壤氡浓度与断裂和地热关系研究

作者通过对天津蓟县山前地段土壤氡浓度的测量,对土壤氡-断裂-地热三者关系进行了研究,判明了这三者之间的物理相关性和形成机理的内在联系,其主要结论是:氡浓度异常与断裂构造的走向、地热异常的范围具有一致性,且氡浓度异常与地热异常具有正相关性;地下水的运移是产生氡浓度异常及地热异常的充分条件,构造破碎带是导通和富集氡浓度异常及地热异常的必要条件.在不同的构造单元中,可产生不同的热储类型.本方法可以确定地热资源的勘查方向,为地热资源的开发利用提供旁证依据.     

体积排阻高效液相色谱-电感耦合等离子体质谱法同时测定印度芥菜(Brassica Juncea)中镉铜锌形态

螯合作用是植物对细胞内重金属耐受的主要方式之一,植物中螯合肽(PCs)在植物耐重金属毒害中的作用己有许多报道,但作用程度并未得出一致的结论,关于PCs是在镉刺激下直接合成还是以谷胱甘肽为底物合成同样存在争议。本文研究了胁迫浓度和胁迫时间对超积累植物印度芥菜(Brassica juncea)中镉形态分布的影响。印度芥菜幼苗分别用0.5、1.0、3.0、5.0、10.0 mg/L镉标准溶液胁迫24 h、48 h、72 h、96 h后收获,用体积排阻高效液相色谱-电感耦合等离子体质谱技术测定植物体根部和叶部中镉形态的含量。结果表明,在低胁迫浓度下(≤3.0 mg/L),植物叶中PCs-Cd的含量与胁迫浓度成正比;在高胁迫浓度下,PCs-Cd含量反而降低,根中PCs-Cd的含量持续增加,但叶中PCs-Cd总量高于根部,说明PCs在植物体内会由根部向叶部转移,从而提高了镉耐受性。在持续长时间胁迫下,PCs-Cd含量也降低,表明PCs在镉解毒机制中仅有短暂的作用;持续高浓度胁迫下,植物会引发其他机制来抵制Cd的毒性。研究认为PCs在镉解毒机制中的作用需要考虑胁迫时间和胁迫浓度这两个重要参数。     

户县热电厂污染气象条件和大气环境质量分析

计算、分析了户县热电厂地区污染气象条件特征和ＳＯ＿２浓度，为该地大气污染治理提供了依据。     

Spatial Disparity of Slope Farmland and Food Security in Three Gorges Area

As an important measure of ecoenvironmental construction, the process of de-farming in slope farmland is being undertaken gradually in the whole China. Meanwhile, the problem of reducing in food yield in de-farming areas can not be neglected any more. It is especially the case in areas with concentrated slope farmland and inconvenient transportation. In this paper, we analyze the causes of hidden troubles in food security, and the spatial relationship between farmland and slope farmland in the reservoir area of Three Gorges, and unveil the spatial disparity of contradictions between food supply and demand. Finally, combining the accessibility of areas, three different spatial types of food security, food security area, food alert area, and food crisis area, are divided.