降水变化、氮添加对鼎湖山主要森林土壤有机碳矿化和土壤微生物碳的影响

全球变化对土壤有机碳(SOC)存贮与分解的影响在全球碳(C)循环中具有重要地位.分别通过室内土壤培养法和氯仿熏蒸法,研究了降水变化和氮(N)添加处理对鼎湖山3种不同演替阶段的季风常绿阔叶林、针阔混交林和马尾松针叶林SOC矿化和土壤微生物量碳(SMBC)的影响.结果表明:1)降水量增加能够提高森林演替晚期SOC累积矿化量和矿化速率,而对森林演替早期SOC累积矿化量和矿化速率没有显著影响(P>0.05).2)干旱条件(降水量减少)降低森林SMBC含量,且在鼎湖山季风林表层土壤(0～10 cm)中SMBC的减少达到显著水平(P<0.05).3)N添加处理对鼎湖山3种森林类型SOC累积矿化量、矿化速率以及SMBC都没有显著影响(P>0.05).未来关于SOC矿化对全球变化响应的研究,要综合考虑土壤有机质质量、C/N比例、外源性氮输入等因素的作用.图4表2参37     

基于宏基因组技术获得的对厌氧氨氧化菌代谢的新理解

厌氧氨氧化菌(Anaerobic ammonium oxidation bacteria,AAOB)是化能自养菌,由于其生理代谢的奇异性、细胞结构的特殊性以及对氮素循环的重要性,已成为环境工程、微生物以及海洋生物学等领域的研究热点.然而,AAOB未能实现纯培养的现状已成为AAOB代谢途径研究的巨大障碍.近年来兴起的宏基因组技术(Metagenomics)为AAOB代谢途径的研究提供了新手段.采用宏基因组技术,可直接研究微生物群体中某特定微生物基因组的结构与功能,摆脱了传统微生物学研究对纯培养的依赖,使未培养微生物的认识和开发成为可能.本文首先简述获取AAOB宏基因组信息的过程,然后通过比较由传统代谢研究方法和宏基因组技术获得的AAOB代谢途径的研究成果,论述基于宏基因组技术获得的对AAOB代谢的新理解,得出以下结果和结论:1)AAOB的碳素固定途径为乙酰辅酶A途径,碳素固定的还原力来自NADH或者QH2;2)AAOB氮素转化的重要中间产物是NO,而非NH2OH,并提出了以NO为核心的AAOB代谢的改进模型;3)AAOB的ATP合成途径为氧化磷酸化,推测的电子传递途径为N2H4—QH2—细胞色素bc1复合体;细胞色素bc1复合体再将电子用于NO2-还原和N2H4合成.AAOB的宏基因组技术使AAOB代谢途径的研究更具方向性.随着分子生物学理论和技术的不断发展,宏基因组学的升级技术(如宏转录组学、宏蛋白质组学)将为AAOB代谢途径的研究提供新的方法与平台.图3表1参51     

仿生植物附着微生物膜对污染水体氮素迁移转化效能分析

通过室外及室内控制试验,研究5种常见填料作为原材料制成的仿生植物对污染水体氮素的去除性能,结果表明,仿生植物原材料的差异将直接影响其附着生物膜特性,其附着生物膜量、硝化强度、反硝化强度以及硝化细菌、反硝化细菌均表现为：软性填料﹥组合填料﹥悬浮填料﹥立体弹性填料﹥半软性填料。水深对仿生植物附着生物膜亦有不同程度的影响,其中生物膜量随水深的增加并未表现出明显的分层效应,而生物膜硝化作用强度、硝化细菌随水深的增加逐渐降低,但生物膜反硝化作用强度、反硝化细菌则随水深的增加则呈现出逐渐增加的趋势。5种不同材质的仿生植物对水体TN、NH4＋-N、NO3--N具有较好的去除效果,去除率表现为：软性填料﹥组合填料﹥悬浮填料﹥立体弹性填料﹥半软性填料﹥对照系统。同时,仿生植物种植密度也影响其对水体氮素的去除效果,表现为CK〈7株·m-3〈13株·m-3〈20株·m-3,研究结果将为仿生植物的野外实际应用及我国城市重污染河道水质原位修复提供技术支持。     

亚硝酸盐氮胁迫对罗非鱼（GIFTOreoohromisniloticus）血清非特异性免疫酶活性的影响

试验设置了不同浓度亚硝酸盐氮（空白对照、0．75mg·L-1、1．50mg-L-1、3．00mg·L-1和5．00mg·L-1）,研究了亚硝酸盐氮胁迫对罗非鱼（GIFTOreochromisniloticus）血清非特异性免疫酶（溶菌酶、碱性磷酸酶、补体c3）活性的影响。结果表明：罗非鱼血清碱性磷酸酶、溶菌酶、补体C3活性均呈现出随亚硝酸盐氮浓度升高而降低的趋势,且当亚硝酸盐氮浓度小于1．50mg·L-1时,罗非鱼血清碱性磷酸酶、溶菌酶、补体C3活性与对照组相比差异不显著（P〉0．05）,说明低于1．50mg·L-1的亚硝酸盐氮不会对罗非鱼机体免疫力产生显著影响;而高于3．00mg·L-1的亚硝酸盐氮胁迫能够显著（P〈O．05）降低罗非鱼血清碱性磷酸酶、溶菌酶、补体C3活性,最大下降率分别达到31．75％、27．40％、14．43％,从而显示出高浓度亚硝酸盐氮（〉3．00mg·L-1）能够对罗非鱼机体产生强烈的氧化胁迫和免疫损伤,导致机体免疫力下降,增加罗非鱼对致病菌的易感性。本研究认为,3．00mg·L-1可能是亚硝酸盐氮胁迫引起罗非鱼机体免疫力显著降低的阈值。     

三江平原农田源头排水沟渠截留排水中氮素动态

通过小尺度野外原位试验,研究排水沟渠水体、底泥和植物中氮含量的变化规律.结果表明,随水体停留时间增加,沟渠对水体氮素的净化能力增强,认为停留8d左右较适宜.沟渠对NH4-N的截留率大于TN和NO3--N.渠水停留11d时,4条试验沟渠[氮浓度高、磷浓度低(NHPL),氮浓度高、磷浓度高(NHPH),氮浓度低、磷浓度低(NLPL),氮浓度低、磷浓度高(NLPH)]对NH4+-N的截留率均达100％,对NO3--N的截留率分别为84.63％、84.35％、75.67％和76.14％,对TN的截留率分别为88.02％、89.89％、90.88％和88.53％.试验结束时沟渠表层(0～15 cm)底泥氮含量降低,植物氮累积量远大于进水TN总量,说明植物生长同时吸收了水体、土壤和底泥中的氮,建议在秋季适时收割植物,以避免植物分解导致二次污染.     

啤酒废水同步脱氮除磷工艺启动研究

为了将短程硝化反硝化与A/O法除磷同时应用于SBR工艺处理啤酒废水,通过改变序批式反应器(SBR)工艺运行方式,使活性污泥依次经历厌氧、好氧、缺氧3个阶段,控制ρ(MLSS)=4 700 mg/L、pH=7.5～8.0、DO=0.3～0.5 mg/L(好氧阶段)。反应器内短程硝化反硝化同步除磷效果明显,氨氮去除率大于90%,亚硝酸盐积累率大于85%,磷去除率大于98%。试验结果表明短程硝化反硝化与A/O法除磷可同时应用于SBR工艺处理啤酒废水。     

我国电解锰行业氨氮污染分析与控制

我国"十二五"期间将氨氮纳入总量控制指标,电解锰行业氨氮污染控制变得非常紧迫。介绍了电解锰氨氮污染的现状,分析了电解锰氨氮污染的产生途径以及电解锰生产中的氨氮平衡,依据"源头消减、过程控制、末端循环"的清洁生产理念,提出了电解锰氨氮污染的控制措施。     

Validation of liquid nitrogen vaporisation rate by small scale experiments and analysis of the conductive heat flux from the concrete

The vaporisation of a liquid nitrogen pool spilled on concrete ground was investigated in small scale field experiments. The pool vaporisation rate and the heat transfer from the concrete ground were measured using a balance and a set of embedded heat flux sensors and thermocouples. The ability to predict the concrete's thermal properties based on these measurements was investigated. This work showed that a simple, one-dimensional theoretical model, assuming heat conduction through a semi-infinite ground with ideal contact between the cryogenic liquid and the ground, commonly used to describe the heat transfer from a ground to the LNG, can be used to match the observed vaporisation rate. Though estimated parameters, thermal conductivity and thermal diffusivity, do not necessary represent real values. Although the observed vaporization rate follows a linear trend, and thus can be well represented by the model, the overall model prediction seems to be overestimated. The temperature profile inside the concrete is slightly over-predicted at the beginning and under-predicted at later stage of the spill. This might be an effect of the dependence of the concrete's thermal properties on the temperature or may indicate an incorrect modelling and a varying temperature of the ground surface.     

Nitrogen budget and its environmental loading in an urban ecosystem with the rapid urbanisation of China

A detailed nitrogen (N) budget has been developed for an urban ecosystem based on the method of material flow analysis. How increased human activity and urbanisation influences N cycling have also been analysed. Total N input and output in the urban ecosystem of Zhengzhou City (ZUE) was calculated at 304.8?Gg was 275.3?Gg year^?1, resulting in an N accumulation of 29.5?Gg year^?1. Industry and human life activities, which respectively accounted for 43.8% and 34.2% of total N inputs and 52.6% and 29.1% of total N outputs, were the core of N flow in the urban ecosystem. Humans activities mediated more than 98% N inputs into the ZUE, 73.2% of N was released into the atmosphere and 11.7% into hydrosphere. This very large volume of released N could contribute to regional problems. High energy consumption, insufficient wastewater treatment facility practices, and low N use efficiency are the primary causes of pollution. The major challenge ahead for the urban ecosystem is how to manage high-intensity N pollutant inputs to the urban ecosystems coupled with incomplete N cycling and removal. Based on the analysis of the N budget and loading, this study also proposes an N management strategy for the ZUE.     

Effects of different mowing frequencies on soil carbon and nitrogen changes in leymus chinensis steppe of Hulun Buir北大核心CSCD

Mowing is the main management of Hulun Buir grasslands in Inner Mongolia; therefore, understanding the changes of soil organic carbon (SOC), total nitrogen (TN), and carbon sequestration under different mowing frequencies will provide an important scientific basis for grassland carbon sink management in Inner Mongolia. Three treatment plots were devised in the study area, including enclosed sample (Y), mowing every other year (2G), and mowing once a year (1G), where SOC, TN content and storage were investigated. The results showed that with increased mowing frequency, the SOC and TN content showed a decreasing trend in the 0-30 cm depth soil layer. The SOC and TN content were different in each soil layer, which decreased gradually with increasing soil depth in Y and 2G plots, whereas increased gradually in 1G plots. The soil carbon storage was significantly correlated with the soil nitrogen storage, and both showed a significant linear decrease with increased mowing frequency, which showed as carbon and nitrogen loss. In 2G plots, the soil carbon storage decreased by 17.1% and soil nitrogen storage decreased by 20.8%. In 1G plots, the soil carbon storage decreased by 21.6% and soil nitrogen storage decreased by 29.3%. The results showed that the change of soil carbon and nitrogen was sensitive to mowing frequency for the Hulun Buir grassland. It is possible to reduce the loss of carbon and nitrogen by reasonably controlling mowing frequency, and the sustainable use of grassland could be achieved with appropriate fertilization. Keywords. © 2018 Science Press. All rights reserved.