活性氮和世界:200年的变化

本文通过将19世纪后期和20世纪后期的氮流动情况进行对比,分析了食物和能源生产对全球氮循环的影响.我们虽然对人类产生的活性氮的数量及其释放到环境所产生的主要影响有了充分的认识,但是,我们对于环境库中氮的累积速度缺乏了解,由于积累在环境中的氮具有阶式效应,因此,对其在环境中的积累尚有不明之处.未来活性氮的产生、分布状况及其形成速度增加的可能性(尤其是在亚洲)存在巨大的区域性差异,因而需要制定"总活性氮措施",以优化食物和能源生产,保护环境系统.     

Effects of marine biofouling on gas sensor membrane materials

The use of underwater gaseous sensors has increased rapidly in the last 10 years. The majority of such sensors employ a thin membrane through which the gas diffuses. These sensors are potentiometric gas-sensing probes and essentially they are ion-selective electrodes. The deployment time of these membranes is curtailed by the formation of biofouling on the membrane leading to erroneous results. The physical properties of a variety of commonly used membranes were investigated using SEM and AFM. This showed that there were differences in topography between the PTFE membranes, such as pore sizes and surface roughness, which may be attributed to the manner in which they are manufactured. The pore size of the PTFE membranes varied greatly, ranging from circular pores with a diameter of 500 nm to elongated pores measuring 1 x 22 microm. The contact angle of each membrane showed that they were all hydrophobic. The amount of fouling on each was also observed and its affect on oxygen diffusion was monitored. Fouling slowed down the response of the instrument and caused reduced diffusion through the membranes. The amount of fouling varied between the membranes with the YSI membrane fouling least. Some of the membranes tested did foul less than others and there could be lifetime advantages of choosing a membrane with a smoother surface and a small pore size.     

The Effects of Precipitation on Aquatic and Terrestrial Ecosystems: A Proposed Precipitation Chemistry Network

Precipitation is one of the most important factors determining the nature and productivity of terrestrial and aquatic ecosystems. Detailed historical and contemporary records are available indicating the amount of water deposited at thousands of locations throughout the world. Comparatively, however, knowledge of the changing chemistry of precipitation has developed only recently and is still very fragmentary. Our present ignorance of the total impact of changes in precipitation quality on the productivity and stability of ecosystems is especially profound. This paper has a fourfold purpose: (1) to describe the myriad of trace chemical constituents transferred from the atmosphere into the biosphere of the earth; (2) to define the range of beneficial and injurious ecological effects of perturbations in atmospheric deposition; (3) to explain the concepts of sensitive areas, life stages, and life forms; and (4) to describe briefly plans for a National Deposition Network and associated research on the terrestrial and aquatic ecosystems of the United States.     

Reactive nitrogen and public policies for environmental protection

A core goal of both US and European pollution control policies has been to establish rules and regulations pertaining to the movement of reactive-nitrogen (Nr) through the environment. This is manifest in US federal legislation such as the Clean Air Act Amendments and the Clean Water Act Amendments and in various protocols of the United Nations Economic Commission for Europe (UNECE) and its Convention on Long-Range Transboundary Air Pollution (CLRTAP). In this paper, we begin by reviewing the two US laws and their effectiveness and make some comparisons with the approaches used mainly in Europe by the UNECE and CLRTAP. Next we use the Mississippi drainage/Gulf of Mexico hypoxia case study to highlight the importance of applying a "systems approach" to address the reactive nitrogen problem at the regional scale. After briefly posing a number of unanswered questions related to nitrogen control policies, we conclude by sketching a blueprint for future actions related to the development of improved policies to regulate reactive nitrogen.     

活性氮:多多益善?

尺度和范围 1790年,Jean Claude Chaptal将元素周期表中的第14个元素命名为"氮"[1].两个世纪后,氮在生物地球化学过程中的作用和其作为一种必需营养元素的重大功能得到了很好的理解.我们知道,人类(以及植物和动物)的生存离不开氮;大气中大量存在的氮气(N2)是植物和动物不能直接利用的一种化学形式;只有少数特殊的微生物能够将大气中的氮转化("固定")为植物、动物可以利用的活性氮(活性氮)[2];另一小群体的微生物能够将活性氮转化(反硝化)为氮气.     

活性氮与环保公共政策

美国和欧洲污染治理政策的一个核心目标,是建立环境中活性氮运移的相关法规和条例.这表现在美国联邦政府的立法上(例如<清洁空气法修正案>和<清洁水法修正案>),以及联合国欧洲经济委员会的各种议定书及其<远程跨边界空气污染公约>上.本文中我们首先回顾一下美国的这两部法规及其实施效果,并将它们与联合国欧洲经济委员会和<远程跨边界空气污染公约>主要在欧洲采用的一些方法进行对比.然后利用密西西比河流域和(或)墨西哥湾氧过少的案例研究结果,重点讨论运用"系统分析方法"处理区域性活性氮问题的重要性.在列举了与氮治理政策有关的一些无法回答的问题后,我们在文末简要描述了在制定完善的活性氮管理政策过程中将要实施的行动计划.     

Meeting report

SUMMARY

In many developing countries, the determination of a ranking of investments designed to improve and extend the road system is a commonplace prerequisite of planning for the transport sector as a whole and the road sub-sector within it. A major objective of determining investment priorities is to secure the greatest efficiency in the use of resources allocated to the sector and, for this reason, any system of assigning priorities must rely upon conventional investment appraisal techniques producing quantifiable measures of worth. Exercises of this kind, in which road investments are identified and ranked, are usually undertaken to produce a road sector investment plan. The implementation of such plans is, however, often compromised because of perceived deficiencies with a methodology which places undue reliance on investment appraisal and fails to properly address the issue of public interest and sustainability. This paper attempts to produce a pragmatic set of ground rules which, while mindful of the need to promote economic efficiency, allow for other factors to be embraced in a more holistic methodology.