Leaf litter decomposition and soil microarthropods affected by sulphur dioxide fallout

A field experiment was set up in northeastern Italy to investigate the effects of sulphur dioxide fallout on leaf litter decomposition rates and soil microarthropods. The pollution fallout, which affected part of the Po River delta, originated from the activity of an oil-fired power plant located at Isola Camerini (Porto Tolle, Rovigo). Four sampling sites, exposed to different amounts of pollutant fallout, were selected along the river bank. Two sites, located 1·5 km from the power-plant stack, received minimum sulphur dioxide fallout and were used as controls; two high-deposition sites were about 13 km away from the power-plant settlement. Soil cores were taken to compare sulphur concentrations in the upper layers of the sampling site soil profiles. Litter bags filled with plant material of various types, laid down over two consecutive sampling periods, were used to study leaf litter decomposition and sulphur accumulation on plant tissues. Microarthropods were extracted from the litter bags by means of a modified Tullgren apparatus. Soil chemical analysis showed the highest sulphur concentrations at the high pollutant deposition sites along the plume path. Litter bag dry weight loss over time was reduced by sulphur accumulation in plant tissues. Sulphur accumulation in litter bags gave an indirect measure of the differential pollutant deposition over the land. High-deposition sampling sites showed a significant reduction in the total number of some decomposers. Collembola, in particular, appeared to be a robust bio-indicator of pollutant fallout. Conclusions were drawn about the possible detrimental effects of sulphur compounds on soil and leaf chemistry, litter decomposition and microarthropod decomposer populations.© 1997 John Wiley & Sons, Ltd.     

Kinetics of heterogeneous photocatalytic decomposition of 2,4-dichlorophenoxyacetic acid over titanium dioxide and zinc oxide in aqueous solution

The photocatalytic transformation of 2,4-D in aqueous solution containing a suspension of titanium dioxide or zinc oxide leads to the formation of intermediates which are totally mineralised to carbon dioxide and hydrogen chloride (2,4-dichlorophenol and chlorohydroquinone are the major intermediates). The products at the initial stage of the reaction were 2,4-dichlorophenol (2,4-DCP), chlorohydroquinone, 4-chloropyrocatechol, 2,4-dichloropyrocatechol and 1,4-chlorobenzoquinone. The initial rate of photodegradation was studied as a function of the initial concentration of reactants by the linearised form of the Langmuir–Hinshelwood equation, by which rate constants k and equilibrium adsorption constants K were evaluated. These constants were calculated at different temperatures between 25 and 60°C. The photodegradation rate increased with increase of pH. The photocatalytic transformation of 2,4-D over titanium dioxide or zinc oxide in solution containing hydrogen peroxide was studied. The latter accelerated the reaction rate of 2,4-D significantly. It was found that chloride or bicarbonate ions slowed down the photodegradation rate of 2,4-D by scavenging hydroxyl radicals. Partial inhibition by ethanol is attributed to scavenging of the OH radicals involved in the first step of the reaction. © 1998 Society of Chemical Industry     

农业温室二氧化碳模糊控制系统算法

利用BP神经网络模糊控制器对农业温室二氧化碳进行控制.详细介绍了模糊规则表的生成及神经网络模糊控制器的设计,并使用Mablab进行了仿真学习,仿真结果表明该设计能够有效的对温室二氧化碳进行控制.     

CO2超临界流体法提取银杏叶黄酮工艺的研究

通过正交试验对二氧化碳超临界流体法提取银杏叶中黄酮工艺进行研究。正交实验结果分析表明超临界流体萃取最佳工艺条件为：萃取压力35MPa,萃取温度50℃,萃取时间1．5h,夹带剂浓度90％。     

二氧化锗对共培养萱藻丝状体和硅藻生长的影响

为抑制萱藻丝状体保存和扩增过程中出现的小伪菱形藻与碎片菱形藻的生长,本实验应用实验生态学方法,分别建立了丝状体与小伪菱形藻、丝状体与碎片菱形藻、丝状体与小伪菱形藻和碎片菱形藻的共培养体系,研究了1.00～4.00μg/mL二氧化锗(GeO_2)对共培养条件下丝状体生长发育及附生硅藻生长的影响。结果显示:(1)处理萱藻丝状体和硅藻共培养体系的适宜GeO_2浓度为1.00～2.50μg/mL,各实验组14 d的硅藻抑制率均高于67.33%±5.18%,且丝状体生长发育良好,2.00μg/mL为最适浓度,此浓度下丝状体日均增长率最高,在各培养体系中均大于11.00%,且诱导后孢子囊枝比例和孢子囊直径分别为57.47%±5.31%和(24.55±1.01)μm,与对照组差异不显著;(2) 3.50和4.00μg/mL GeO_2虽对硅藻抑制效果更佳,但同时也会抑制丝状体生长和后期孢子囊的形成与发育,其中4.00μg/mL GeO_2可导致丝状体死亡;(3)碎片菱形藻较小伪菱形藻对GeO_2更敏感。实验14 d,各浓度GeO_2对碎片菱形藻的抑制率为(82.10%±2.40%)～(96.35%±0.79%),均高于同浓度GeO_2对小伪菱形藻的抑制率;同时在丝状体与小伪菱形藻和碎片菱形藻的共培养体系中,碎片菱形藻占硅藻比例随GeO_2浓度升高而相应下降。     

苦楝素提取方法的比较研究

对比研究了从苦楝树皮中提取苦楝素的几种方法,通过实验,得出了不同提取方法的最佳条件。超临界CO2萃取在萃取温度45℃、压力20MPa、夹带剂为60%乙醇的情况下萃取2h,苦楝素的萃取率为0.850%;微波辅助提取法,以60%乙醇为溶剂,料液比为1∶9(g∶mL,下同),微波功率340W,辐射时间40s×3次,苦楝素的提取率为0.693%;超声波提取法,以60%乙醇为溶剂,料液比为1∶9,超声波作用时间为30min,超声波功率为200W,苦楝素的提取率为0.715%。将上述3种提取方法与传统的有机溶剂提取法进行详细的比较,结果表明:对于苦楝素提取,超声波提取法最好。     

A device that converts aqueous ammonia into nitrogen gas

A photoelectrocatalytic oxidation (PECO)³ device was developed for converting aqueous ammonia into nitrogen gas. The device uses a germicidal UV lamp to activate a titania (TiO₂)-coated anode (photoanode) that is connected to a titanium or platinum wire cathode to form an electrolytic cell. When a small bias (2 V DC) was applied between the anode and cathode, ammonia (−3 oxidation state) was oxidized primarily into nitrogen gas (0 oxidation state) rather than nitrite (+3 oxidation state) or nitrate (+5 oxidation state). The ammonia oxidation rate changed as a function of the crystalline structure of the titania coating on the anode, the salinity of the water, the applied voltage, and the disruption of boundary layers near the photoanode surface. There was no ammonia removal in water without at least some NaCl in solution, suggesting that the device works by converting chloride ions into chlorine and hypochlorous acid, which then react with ammonia to form nitrogen gas. Varying the pH between pH = 5 and pH = 10 had no effect on the rate of ammonia removal. A continuous flow-through PECO reactor was tested using aquariums spiked with ammonium chloride or stocked with seawater-adapted tilapia fed a high protein diet, and found to effectively remove ammonia and limit nitrite and nitrate accumulation in the tanks.     

加工方式对海水虾及其制品中SO2含量的影响

亚硫酸盐(以SO_2残留量计)超标是目前影响虾类及其制品质量安全的主要因素之一。本文研究了水煮、蒸、微波烘烤、油炸、风干等加工方式对海水虾中二氧化硫(SO_2)残留量的影响。结果显示,水煮、蒸、微波烘烤和油炸等加工方式可有效降低虾肉中SO_2残留量,降低效果从高到低依次为水煮、蒸、微波烘烤和油炸。在风干过程中,虾肉中SO_2残留量呈先升高后降低的趋势,温度越高,对SO_2的脱除效果越好。在20℃、40℃、60℃、80℃条件下风干加工虾米,当水分含量达到成品要求时,虾米中SO_2残留率分别为132.00%、146.70%、78.25%和48.90%。常温风干方式不利于海米中SO_2消除。脱壳处理可有效降低虾米和烤虾中SO_2残留量。本研究结果将为海水虾中SO_2残留量的控制和限量指标制定提供科学依据,对消费者和生产者利用加工手段降低海水虾中SO_2残留量也具有借鉴意义。     

橡胶林土壤呼吸研究概述及展望

橡胶林生态系统是热带地区重要的人工生态系统,为热带地区的生态服务和经济发展做出了重要贡献,在世界森林生态系统中占有重要的位置。橡胶林土壤呼吸对调控大气CO2有着重要的作用,是全球变化背景下碳循环过程研究的一个重要环节。系统概述了橡胶林土壤呼吸的研究意义、研究方法、影响因素、时空变化以及对干扰的响应和组分区分,指出橡胶林土壤呼吸研究中存在的不确定性,并对后续研究的热点与方向进行展望。     

城市园林对大气颗粒物的消减与大气中二氧化硫和氮氧化物的浓度变化

研究了昆明市城市园林对大气颗粒物的消减量和大气中二氧化硫和氮氧化物浓度的年内动态变化及其两者之间相关性。结果表明,昆明市大气中二氧化硫和氮氧化物的浓度随季节有明显的变化,氮氧化物、二氧化硫的含量变化范围分别为0.149~0.175 mg·m^-3与0.226~0.252 mg·m^-3,含量高低顺序均为:春季>冬季>秋季>夏季。植被对大气颗粒物的消减量的高低顺序为:春季>冬季>秋季>夏季,与二氧化硫和氮氧化物浓度变化一致。大气颗粒物对有毒有害气体具有一定的吸附性,植被对大气颗粒物的消减量与二氧化硫和氮氧化物的浓度具有负相关性,其中二氧化硫和氮氧化物的浓度与PM₁₀极显著负相关,通过3次曲线模型对两者之间的关系进行拟合表明,植被对大气颗粒物的滞留作用间接减少了大气中二氧化硫和氮氧化物的含量,可为地方和区域环境监测评价提供参考。