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981.
982.
Biodiversity declines and ecosystem decay follow forest fragmentation; initially, abundant species may become rare or be extirpated. Underlying mechanisms behind delayed extirpation of certain species following forest fragmentation are unknown. Species declines may be attributed to an inadequate number of breeding adults required to replace the population or decreased juvenile survival rate due to reduced recruitment or increased nest predation pressures. We used 10 years of avian banding data, 5 years before and 4 years after fragment isolation, from the Biological Dynamics of Forest Fragments Project, carried out near Manaus, Brazil, to investigate the breeding activity hypothesis that there is less breeding activity and fewer young after relative to before fragment isolation. We compared the capture rates of active breeding and young birds in 3 forest types (primary forest, fragment before isolation, and fragment after isolation) and the proportion of active breeding and young birds with all birds in each unique fragment type before and after isolation. We grouped all bird species by diet (insectivore or frugivore) and nesting strategy (open cup, cavity, or enclosed) to allow further comparisons among forest types. We found support for the breeding activity hypothesis in insectivorous and frugivorous birds (effect sizes 0.45 and 0.53, respectively) and in birds with open-cup and enclosed nesting strategies (effect sizes 0.56 and 0.44, respectively) such that on average there were more breeding birds in fragments before isolation relative to after isolation. A larger proportion of birds in the community were actively breeding before fragment isolation (72%) than after fragment isolation (11%). Unexpectedly, there was no significant decrease in the number of young birds after fragment isolation, although sample sizes for young were small (n = 43). This may have been due to sustained immigration of young birds to fragments after isolation. Together, our results provide some of the strongest evidence to date that avian breeding activity decreases in response to fragment isolation, which could be a fundamental mechanism contributing to ecosystem decay. 相似文献
983.
北京市大气中CO的浓度变化监测分析 总被引:18,自引:5,他引:13
CO是城市大气中一种重要的污染物,在城市和区域的光化学反应中起着重要的作用.用装配氢火焰离子化检测器(FID)的HP5890II气相色谱(GC)方法,以每10min的采样频率,在北京中科院大气物理研究所325m气象环境观测铁塔上(39°9′N,116°4′E),对北京城市大气CO浓度进行了连续监测,时间为2004-01~2004-12.结果显示北京城市大气CO浓度日变化呈双峰型,1d之中出现2个高峰期,早晨07:00~08:00和夜晚22:00~23:00,最高浓度值分别达到13.8mg·m-3,17.1mg·m-3.不同季节CO的日变化存在差异:冬季、秋季的日变化幅度大,而夏季、春季的日变化幅度小.秋季、冬季早晨上班高峰期后CO浓度下降快,春季、夏季上班高峰期后CO浓度下降慢.CO的这种日变化是由地表排放源和气象条件共同决定的.另外,CO存在明显的季节变化,总的表现为浓度最高值出现在冬季12月份(4.0±3.4)mg·m-3,浓度最低值出现在5月份(1.7±0.7)mg·m-3.整个观测期间1a的平均浓度为(2.6±1.9)mg·m-3,采暖期平均浓度为(3.5±2.6)mg·m-3,非采暖期平均浓度为(2.2±1.2)mg·m-3. 相似文献
984.
利用被称为战略与策略实验室的系统动力学方法,建立了城市生活垃圾问题的系统动力学研究模型;以北京市为实例,探讨了垃圾排放及污染随人口和经济发展的变化,以及污染和占地损失、绿色GDP核算、居民家庭、企事业单位生活垃圾与建筑垃圾组合收费方案等问题. 相似文献
985.
986.
为有效防治油液在储运过程中易发生火灾问题,针对油液储运火灾特点,研发1种PFC-APG-SA水成膜泡沫材料。基于发泡性能、表面张力、pH值和抗烧性能,对复配的8种水成膜泡沫液开展性能测试实验,优选出最佳配方。结合分子动力学模拟,探究复配表面活性剂在模拟体系界面中分子排布作用的微观机理。研究结果表明:新型水成膜泡沫液发泡倍数为9.5,泡沫形态稳固,表面张力为17.521 mN/m,抗烧时间约为784 s,用量小且可以有效抑制油液燃烧;在分子动力学模拟中,复配的表面活性剂分子在油表面排列更为紧密,与油之间的相互作用能绝对值为8 210.238 kJ/mol,相互作用强且结构稳定。研究结果可为水成膜泡沫在油液储运火灾防治中的应用提供一定参考。 相似文献
987.
David L. MacIntosh Susan A. Zimmer-Dauphinee Randall O. Manning Phillip L. Williams 《Environmental monitoring and assessment》2000,63(3):409-429
Aldehydes are an airborne byproduct of many industrialprocesses, vehicle transportation, and emissions fromnumerous natural sources. To characterize aldehydeconcentrations in ambient air of the Savannah, Georgiaarea, air samples for 3 aldehydes (formaldehyde,acetaldehyde, and propionaldehyde) were collected atfive sites on a monthly basis over a 12-month periodfrom December of 1995 through November 1996. Four ofthe sites were in central Savannah and the fifth sitewas located in a rural area about 56 km south ofSavannah. During each 24-hr sampling episode, sampleswere collected in two 12-hr periods approximatingdaylight and nighttime hours, following U.S. EPAMethod TO-11. Formaldehyde concentrations ranged from0.17 to 6.80 g m-3, acetaldehydeconcentrations ranged from 0.07 to7.60 g m-3, and propionaldehyde levels rangedfrom 0.02 to 9.10 g m-3. On average, thefour sites in Savannah had higher aldehydeconcentrations than the rural site (2.0 versus1.2 g m-3 for formaldehyde, 2.3 versus1.7 g m-3 for acetaldehyde, and 1.2 versus1.0 g m-3 for propionaldehyde). The daytimeconcentrations for formaldehyde and acetaldehyde werehigher than the nighttime levels. The data from allthe sites were within published worldwide backgroundvalues for aldehydes. 相似文献
988.
Russian Journal of Ecology - 相似文献
989.
Jeroen C. van den Bergh 《Regional Environmental Change》2001,2(1):13-23
This article provides a short overview of the main themes of ecological economics (EE). It is argued that EE provides a platform
that fosters multidisciplinary environmental research by bringing together the core contributing disciplines – economics and
ecology. In addition, EE is regarded as a pluralistic approach to environmental research that can be set opposite to, and
has indeed developed as a response to, traditional environmental and resource economics. A comparison of the two fields is
presented to clarify the essential differences between them. In addition, specific themes are examined in more detail. These
include: sustainable development; the growth debate; international trade; dynamic processes; and behaviour and policy.
Electronic Publication 相似文献
990.
The geysers panic grass [Dichanthelium lanuginosum Spellenberg var. thermale (Bol.) Spellenberg or DILA] is exclusively associated with surface geothermal manifestations in Sonoma County, California,
USA (38°46′N, 122°38′W). Steam extraction by power plants could alter the subsurface distribution of heat and water to the
site, potentially impacting subpopulations of this rare plant. The purpose of this study was to use demographic monitoring
to determine: (1) temporal and spatial patterns of soil temperature in relation to the distribution of established DILA individuals
at Little Geysers, (2) in situ response of experimental populations of DILA to spatial variations in soil temperature, and
(3) habitat requirements of DILA as an indicator of its tolerance to variations in surficial geothermal features. Thermocouple
transects and a datalogger provided data for characterizing the spatial and temporal patterns of soil temperature in four
microhabitats (fumarole, DILA stand, Andropogon stand, and cleared). Experimental populations were established by precisely sowing and monitoring DILA seeds in these microhabitats.
The results indicated that spatial and temporal variations in soil temperature had significant effects on the processes of
germination, growth, survivorship, and reproduction, thus producing a readily observed metapopulation patch dynamic in relation
to geothermal activity. Seasonal depressions of soil temperature near the fumaroles by cold air and prolonged rainfall events
also promoted the emergence and survival of DILA seedlings in a microhabitat that was previously too hot to occupy. Over longer
periods of time, DILA metapopulation dynamism reflected climatic and geothermal variation. Drought years inhibited germination
for lack of water, but more importantly for the lack of requisite soil temperature depressions in the fumarole microhabitat.
Wet years promoted subpopulation expansion into transition areas that were once too hot and dry. There have also been shifts
in the underground distribution of steam into areas distant from known geothermal features. The demographic responses of DILA
to spatial and temporal variations in soil temperature indicate that heat is an absolutely essential component of the steam
resource. In its absence, germination, seeding survivorship, growth, and maturation are significantly inhibited even if soil
conditions are favorable and potential competitors are controlled. Ultimately, persistence of the species depends on maintaining
the ecosystem dynamic of colonization and extirpation in response to variations in surficial geothermal features over long
spatial and temporal scales. This should shift management perspective from its narrow focus on individual plants to a wider
focus on monitoring the essential habitat component of steam. 相似文献