Design and Performance of a Channel Reconstruction Project in a Coastal California Gravel-Bed Stream

A 0.9 km-reach of Uvas Creek, California, was reconstructed as a sinuous, meandering channel in November 1995. In February 1996, this new channel washed out. We reviewed project documents to determine the basis for the project design and conducted our own historical geomorphological study to understand the processes operating in the catchment and project reach. The project was designed using a popular stream classification system, based on which the designers assumed that a "C4" channel (a meandering gravel-bed channel) would be stable at the site. Our historical geomorphological analysis showed that the reach had been braided historically, typical of streams draining the Franciscan Formation in the California Coast Ranges, with episodic flows and high sand and gravel transport. After the project washed out, Uvas Creek reestablished an irregular, braided sand-and-gravel channel, although the channel here was narrower than it had been historically, probably due to such factors as incision caused by gravel mining. Our study casts doubt on several assumptions common in many stream restoration projects: that channel stability is always an appropriate goal; that channel forms are determined by flows with return periods of about 1.5 years; that a channel classification system is an easy, appropriate basis for channel design; and that a new channel form can be imposed without addressing the processes that determine channel form.     

固体微粒气溶胶灭火剂的改性研究

固体微粒气溶胶灭火剂作为一种新型灭火剂具有优越的抑制火灾的性能,但其应用和推广的关键在于降低灭火气溶胶形成时的温度.本文利用TG方法分析了灭火剂的热分解过程,并通过测定固体微粒气溶胶灭火剂的释放速度、释放区温度分布及灭火性能,研究了固体微粒气溶胶灭火剂的降温消焰技术.同时对气溶胶的成分和固体粒子粒度分布进行了分析.     

火灾中温度升高对蛋白质构象影响的计算机模拟(Ⅰ)

应用分子力学原理进行了温度对肽链构象影响的计算机模拟,模拟结果显示,火灾中环境温度升高对生物分子的结构和功能是一个很敏感的因素之一,天然生物分子因吸热而使自身构象发生异常变化,进而与特定构象紧密联系的生物活性丧失,发生变性,模拟结果对于从分子水平上揭示火灾对生物体的危害具有重要意义.     

乌鲁木齐市大气污染成因分析及防治对策

乌鲁木齐市大气污染十分严重,并已被列入世界十大污染城市之一。乌鲁木齐所处山口地形、三面环山的特殊地理条件所形成的逆温层是造成大气严重污染的主要原因。本文就逆温层形成、污染源排放特点等影响因素进行分析,以提出切实可行的防治方法及解决途径,以达到明显改善乌鲁木齐大气环境质量的目的。     

Ecophysiological Responses of Larix sibiricaLedeb. and Pinus sibiricaDu Tour Undergrowth to Climate Change

The effects of probable climate change—an increase in atmospheric CO₂(by two times), air temperature, precipitation—on CO₂exchange and temperature dependence of net photosynthesis in the larch and Siberian stone pine undergrowth formed in the light larch forests of West Siberia were studied in chambers with an artificial climate. The change of the aforementioned ecological factors caused an increase in the temperature optima of photosynthesis and the range of optimum temperatures (in the case of Siberian stone pine, to a slightly greater degree). Therefore, the ranges of both species may broaden, and the Siberian stone pine can expand to the north, displacing larch tree stands.     

压缩空气对井下热环境的降温效果研究

压缩空气是矿山井下常用动力,它具有膨胀吸热的特性,因而可用于改善井下作业环境与气候条件。通过对矿井压缩空气吸热量的计算,分析了压气对井下热工作面的降温影响,并获得了压气与工作面降温效果的数学关系。还对井下采用压气降温进行了经济评价,指出了压气降温仍为我国深井局部降温的一种可供选择的好方法。     

Spatially Disaggregated Inventories of Soil NO and N2O Emissions for Great Britain

Estimates of soil N₂O and NOemissions at regional and country scales arehighly uncertain, because the most widely usedmethodologies are based on few data, they do notinclude all sources and do not account forspatial and seasonal variability. To improveunderstanding of the spatial distribution of soilNO and N₂O emissions we have developedsimple multi-linear regression models based onpublished field studies from temperate climates.The models were applied to create spatialinventories at the 5 km² scale of soil NOand N₂O emissions for Great Britain. The N₂O regression model described soilN₂O emissions as a function of soil N input,soil water content, soil temperature and land useand provided an annual N₂O emission of 128 kt N₂O-N yr^-1. Emission rates largerthan 12 kg N₂O-N ha^-1 yr^-1 werecalculated for the high rainfall grassland areasin the west of Great Britain.Soil NO emissions were calculated using tworegression models, which described NO emissionsas a function of soil N input with and without afunction for the water filled pore space. Thetotal annual emissions from both methods, 66 and7 kt NO-N yr^-1, respectively, span the rangeof previous estimates for Great Britain.     

环境因子对长江口潮滩沉积物中NH+4的释放影响

以长江口潮滩沉积物湿样进行模拟实验,研究盐度、pH和温度等环境因子对沉积物中NH₄+释放的影响.结果表明,随着盐度和温度的上升,沉积物中NH₄+释放量都显著增加;由于潮滩沉积物缓冲性能较好,pH的影响不太明显.此外,NH₄+的释放与沉积物类型有关,沙性物质含量高的低潮滩沉积物NH₄+的释放量明显低于沙性物质低的高、中潮滩沉积物.      

环境因子对红斑顠体虫生长的影响

讨论了环境中氨氮的浓度、pH值、盐度、温度对红斑顠体虫生长的影响.结果表明,在pH值为7时,氨氮对红斑顠体虫的急性毒性半致死浓度为264mg/L;红斑顠体虫对氨氮长期接触时的最大可接受浓度在20～50mg/L;氨氮对红斑顠体虫的毒性随pH值的增加而增加;盐度在1000mg/L以下,对红斑顠体虫的死亡没有影响;温度在15～30℃,红斑顠体虫的表观增长速率满足Arrhenius拟合,其表观增长率随温度增加而增大,但35℃时红斑顠体虫的生长减缓.     

Comparing environmental influences on coral bleaching across and within species using clustered binomial regression

Differential susceptibility among reef-building coral species can lead to community shifts and loss of diversity as a result of temperature-induced mass bleaching events. We evaluate environmental influences on coral colony bleaching over an 8-year period in the Florida Keys, USA. Clustered binomial regression is used to develop models incorporating taxon-specific responses to the environment in order to identify conditions and species for which bleaching is likely to be severe. By building three separate models incorporating environment, community composition, and taxon-specific responses to environment, we show observed prevalence of bleaching reflects an interaction between community composition and local environmental conditions. Environmental variables, including elevated sea temperature, solar radiation, and reef depth, explained 90% and 78% of variability in colony bleaching across space and time, respectively. The effects of environmental variables were only partially explained (33% of variability) by corresponding differences in community composition. Taxon-specific models indicated individual coral species responded differently to local environmental conditions and had different sensitivities to temperature-induced bleaching. For many coral species, but not all, bleaching was exacerbated by high solar radiation. A 25% reduction in the probability of bleaching in shallow locations for one species may reflect an ability to acclimatize to local conditions. Overall, model results indicate predictions of coral bleaching require knowledge of not just the environmental conditions or community composition, but the responses of individual species to the environment. Model development provides a useful tool for coral reef management by quantifying the influence of the local environment on individual species bleaching sensitivities, identifying susceptible species, and predicting the likelihood of mass bleaching events with changing environmental conditions.