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1.
2002年9月16日—11月28日和2003年9月9日—11月26日,在云南南涧凤凰山共网捕秋季迁移鸟176种6 677只,分属13目29科。凤凰山鸟类夜间迁移时间开始于8月上旬,至11月中旬结束,可分为开始期、高峰期和结束期。高峰期出现于9月中旬—10月上旬,迁移波峰出现在10月初;高峰期间受圆月影响,中间出现2个网捕低谷。候鸟夜间迁移在日落后约1小时开始,在20:30—24:00出现第1个迁移高峰;随后鸟类迁移数量逐渐减少;到次日4:00左右又开始增多,出现当夜的第2个高峰;在凌晨5:30左右再度减少直到日出前为止。白天迁移主要出现在迁移后期,开始于10月中旬左右,10月下旬、11月中旬达到白天迁移高峰,随后逐渐减少,一直持续到11月下旬,1甚至到12月上旬。白昼迁移鸟在日出前约1小时开始迁过,8:30左右达到白昼迁移高峰,11:00后停止。凤凰山秋季迁移鸟的迁徙期持续约100天。夜间迁徙鸟在西南风无月有雾之夜在22:00过境高峰后,还会在午夜、凌晨和黎明前出现另外3个过境高峰,而其他天气仅在22:00出现1次过境高峰。  相似文献   

2.
云南南涧凤凰山秋季夜间迁移鸟类多样性分析   总被引:6,自引:4,他引:2  
2002年9月16日至11月28日、2003年4月6日至26日、2003年9月9日至11月26日,对云南南涧凤凰山秋季夜间迁移鸟类进行了研究。共网捕迁移鸟176种6677只,分属13目29科,其中红喉姬、红点颏、蓝歌鸲等雀形目鸟类数量优势度十分显著,表明该地迁移鸟类以雀形目等中小型鸟类为主。对网捕迁移鸟进行多样性分析,Shannon-Weaner指数为3·89,G指数为4·13,总的F指数为25·56,表明该地迁移鸟在种、属、科等分类阶元的多样性均较丰富。2002和2003年迁移鸟类多样性t检验结果表明,年间、月份间的多样性差异明显,即凤凰山迁移鸟类动态变化明显。  相似文献   

3.
在鸟类迁徙季节,夜间鸟击事故频发是机场鸟击发生的一个显著特点.了解鸟类的夜间迁徙规律对于改进夜间鸟击防范措施具有重要的指导意义.本研究综合采用网捕法和声音记录法对沈阳桃仙机场夜间鸟类迁徙物种组成和迁徙规律进行研究.结果表明: 56种鸟类(占比88.9%)具有夜间迁徙习性,且以后半夜迁徙为主;鸟类夜间迁徙具有明显的时间动态和迁徙次序,春季鸟类迁徙较为集中,迁徙高峰在5月中旬,主要鸟类由鹌鹑、红尾伯劳、栗耳鹀、黑喉石鵖、普通夜鹰、黄眉柳莺等组成,秋季迁徙较为分散,迁徙高峰出现在9月下旬至10月上旬,主要由鹌鹑、灰背鸫、红喉鹨、丘鹬、矛斑蝗莺和灰头鵐等组成.对夜间迁徙鸟类的危险等级评估发现,春季严重危险物种是鹌鹑和红尾伯劳,秋季严重危险物种是鹌鹑、纵纹腹小鸮、灰背鸫和丘鹬.分别从夜间迁徙鸟类组成、迁徙动态、时间节律和物种危险等级等角度提出了相应的鸟击防范对策,为桃仙机场鸟击防范提供参考.  相似文献   

4.
2002年9月16日至11月28日、2003年4月6日至26日、2003年9月9日至11月26日,对云南南涧凤凰山秋季夜间迁移鸟类进行了研究。共网捕迁移鸟176种6 677只,分属13目29科,其中红喉姬weng、红点颏、蓝歌鸲等雀形目鸟类数量优势度十分显著,表明该地迁移鸟类以雀形目等中小型鸟类为主。对网捕迁移鸟进行多样性分析,Shannon-Weaner指数为3.89,G指数为4.13,总的F指数为25.56,表明该地迁移鸟在种、属、科等分类阶元的多样性均较丰富。2002和2003年迁移鸟类多样性t检验结果表明,年间、月份间的多样性差异明显,即凤凰山迁移鸟类动态变化明显。  相似文献   

5.
云南新平哀牢山夜间捕获鸟类的多样性   总被引:1,自引:0,他引:1  
2007-09-05—2007-11-05和2008-09-03—2008-11-07期间,在云南省新平县哀牢山金山丫口用灯光诱捕对秋季夜间迁徙鸟类组成进行了调查。共捕获鸟类129种,7943只,分属于14目23科。雀形目鸟类为网捕主要鸟类,占总网捕数量的58.9%。其中红尾伯劳(Lanius cristatus)、小杜鹃(Cuculus poliocephalus)和红喉歌鸲(Luscinia calliope)3种是该地夜间网捕优势种鸟类,三者数量皆超过网捕鸟类总数的5%。每天夜间20:00—22:00和次日凌晨04:00—06:00是捕获鸟类数量的高峰时段。网捕期间,早期Shannon-Wiener指数和Pielou指数最低,优势指数C最高;中期Shannon-Wiener指数和Pielou指数最高,优势度指数C最低。2008与2007年相比, 优势指数C和G-F指数较低, 但Shannon-Wiener指数和Pielou指数较高。云南省不同“打雀山”夜间捕获鸟类的种类和数量存在差异。地理和气候可能是造成这些差异的主要因素。  相似文献   

6.
北京西山典型游憩林空气颗粒物不同季节的日变化   总被引:5,自引:0,他引:5  
以百望山森林公园为例,对北京西山3种典型游憩林一年四季空气颗粒物浓度进行了昼夜观测,结果发现:(1)北京西山3种典型游憩林4种粒径空气颗粒物日变化整体上在4个季度均近似呈"双峰双谷"型,两个高峰时段分别出现在5:00~9:00和19:00之后到凌晨3:00,低谷出现时间是15:00左右和5:00左右,不同季节之间峰、谷出现时间稍有差异.(2)3种游憩林相比较,侧柏林空气颗粒物夜间高峰出现迟,高峰值大,且高峰期持续时间长,故夜间低谷出现时间也延迟.所以郁闭度较大的侧柏林夜间空气颗粒物浓度高于其他两种林型,且在夏、秋季表现得越来越明显.(3)同一游憩林不同粒径空气颗粒物相比,细粒径颗粒物白天高峰和夜间低谷出现时间提前,而白天低谷和夜间高峰却有所滞后.  相似文献   

7.
为了解鸟击规律,作者收集了重庆江北机场2009—2013年的鸟击事件信息并对鸟击残骸进行送检,共收集鸟击事件信息189起,其中白天77起,占40.74%,夜间112起,占59.26%。鸟击数据显示:春、夏、秋季是鸟击高发季节;8月和11月为白天鸟击高发月份;夜间鸟击高发在春季(4、5月)和秋季(8、9、10月);鸟击多发种类有小云雀、家鸽、家燕、金腰燕、白鹡鸰、池鹭、大杜鹃及蝙蝠等。结合江北机场鸟类群落调查数据分析发现:在飞行区集群活动的鸟种容易成为鸟击的高危物种,鸟击发生频率与鸟类生活习性关系密切;迁徙鸟类是江北机场鸟击的最大威胁。本文根据分析结果提出了一些相应的预防措施。  相似文献   

8.
2006年10月28日凌晨3点,笔者在位于云南省新平县哀牢山的金山丫口鸟类环志站进行夜间鸟类环志工作时,用灯光诱捕到一只鹭科鸟类,经鉴定为海南(开鸟) (Gorsachius magnificus),为云南省鸟类物种新记录.  相似文献   

9.
鄱阳湖越冬水鸟种群变化动态   总被引:7,自引:0,他引:7  
鄱阳湖是东亚-澳大利西亚候鸟迁徙路线上重要的越冬地,开展鄱阳湖越冬水鸟种群变化动态研究,对指导鄱阳湖湿地生境管理,尤其是水位管控具有重要意义。2005~2007年的越冬季节,我们对鄱阳湖国家级自然保护区内3个重要湖泊(大湖池、沙湖和梅西湖)的越冬水鸟种群变化动态进行了调查,调查时间为每年10月至次年4月。3年共记录到水鸟53种,隶属于7目13科。3个越冬季节中单个调查日种类的最低值为9种,最高为31种。鄱阳湖越冬水鸟从10月上旬开始出现,在11月份鸟类数量急剧增加,在12月上旬和中旬达到数量峰值,然后开始缓慢减少,至4月初仅有少于1%的鸟类还停留在监测区域。在鄱阳湖要继续深入开展越冬候鸟空间分布动态变化的研究,分析水文节律变化对越冬鸟类生境的潜在影响,并深入研究气候因子与鄱阳湖越冬水鸟迁徙的关系。  相似文献   

10.
2007年7月-2010年11月,对杭州湾曹娥江口至甬江口间潮间带及其附近海涂水库的水鸟群落进行定期监测,共记录9目18科128种.其中,候鸟119种,占总数的93%;而国家重点保护鸟类11种.对13种鸻鹬类和9种鸭类进行种群数量随时间变化的种间相关性分析,两个类群各有21对和23对显著相关.通过对水鸟季节动态及其迁徙模式分析,将其迁徙过程分为6个阶段,即:4月上旬-5月中旬、7月下旬-9月下旬(旅鸟迁徙高峰期)、2月下旬-3月下旬、10月上旬-12月中旬(冬候鸟迁徙高峰期)、12月下旬-次年2月中旬(越冬期)和5月下旬-7月中旬(繁殖期).种间吸引作用可能是影响该区域迁徙季节鸻鹬类和越冬地鸭类群落组成的重要原因,而该区域特殊地理位置和水鸟群落构成可能是造成鸻鹬类春秋季迁徙高峰数量巨大差异的主要因素.  相似文献   

11.
The temporal relationships between follicle deviation and systemic hormone concentrations were studied in mares. Blood samples were obtained at 01:00, 07:00, 13:00, and 19:00 h from nine mares throughout an interovulatory interval. Diurnal variation in progesterone occurred on Days 4-12 and in LH on Days 4 and 5; the lowest concentration for both hormones was at 13:00 h. Ultrasonically observed deviation in the ovulatory follicular wave began on Day 15.7+/-0.5 (ovulation=Day 0). An increase (P<0.002) in LH began on Day 14 before the beginning of deviation, and an increase (P<0.05) in estradiol began at the beginning of deviation. Testosterone concentrations began to increase (P<0.05) 2 days after the beginning of deviation and reached maximum 1 day before the next ovulation. The beginning of deviation was encompassed by a decline (P<0.003) in cortisol concentrations, and the concentrations remained low during the preovulatory period.  相似文献   

12.
2002年我国华北三代粘虫大发生的虫源分析   总被引:5,自引:0,他引:5  
潘蕾  翟保平 《生态学报》2009,29(11):6248-6256
华北平原地区三代粘虫的大发生是一小概率事件,对其虫源问题尚无确切回答.应用HYSPLIT 4.8轨迹分析平台对2002年华北平原地区三代粘虫主要迁入峰期进行轨迹回推以确定此次迁入的虫源区,同时对东北地区虫源在迁出期的去向进行了模拟;并运用GrADS气象图形软件对华北地区和东北地区迁飞期天气学背景和风场的时空分布进行了分析.结果表明:2002年华北平原地区大发生的三代粘虫主要虫源来自陕西、山西二省;东北地区虫源对本次华北平原地区的迁入无影响.  相似文献   

13.
The purpose of this study was to determine whether the occurrence of accidental blood-borne pathogen exposure incidents in medical students and residents in training varies during the 24 h. A retrospective review of reported exposures was conducted in a large urban teaching institution--the University of Texas Health Science Center in Houston--between November 1993 and July 1998. Professional level (year of student or level of resident), time of exposure, means/route of exposure (needle stick, laceration, or splash), and type of medical service were recorded. Analysis of the clock time of the 745 reported blood-borne pathogen exposures showed they occurred more frequently during the day than night. Over the nearly 5-year span, 531 incidents took place between 06:00 and 17:59 in comparison to only 214 between 18:00 and 05:59. To account for the day-night difference in medical student and resident hospital staffing, the data were reexpressed as exposure rates, that is, in terms of the number of events per hour per 1000 medical students and residents. Based on the total number of reported exposures over the almost 5-year span of data collection, the average rate was 40 accidents per hour per 1000 doctors in training during the 12 h daytime span (6:00-17:59). It was 50% greater at night (18:00-05:59), with 60 incidents per hour per 1000 doctors in training. The day-night difference in rate of exposures was statistically significant (p < .04). The relative risk ratio for residents and students when working during the day shift compared to working the night shift was 0.67. This means that doctors in training are at a 1.50 higher risk of sustaining a blood-borne pathogen exposure when working nights than when working days.  相似文献   

14.
Night shift work is associated with a myriad of health and safety risks. Phase-shifting the circadian clock such that it is more aligned with night work and day sleep is one way to attenuate these risks. However, workers will not be satisfied with complete adaptation to night work if it leaves them misaligned during days off. Therefore, the goal of this set of studies is to produce a compromise phase position in which individuals working night shifts delay their circadian clocks to a position that is more compatible with nighttime work and daytime sleep yet is not incompatible with late nighttime sleep on days off. This is the first in the set of studies describing the magnitude of circadian phase delays that occurs on progressively later days within a series of night shifts interspersed with days off. The series will be ended on various days in order to take a "snapshot" of circadian phase. In this set of studies, subjects sleep from 23:00 to 7:00 h for three weeks. Following this baseline period, there is a series of night shifts (23:00 to 07:00 h) and days off. Experimental subjects receive five 15 min intermittent bright light pulses (approximately 3500 lux; approximately 1100 microW/cm2) once per hour during the night shifts, wear sunglasses that attenuate all visible wavelengths--especially short wavelengths ("blue-blockers")--while traveling home after the shifts, and sleep in the dark (08:30-15:30 h) after each night shift. Control subjects remain in typical dim room light (<50 lux) throughout the night shift, wear sunglasses that do not attenuate as much light, and sleep whenever they want after the night shifts. Circadian phase is determined from the circadian rhythm of melatonin collected during a dim light phase assessment at the beginning and end of each study. The sleepiest time of day, approximated by the body temperature minimum (Tmin), is estimated by adding 7 h to the dim light melatonin onset. In this first study, circadian phase was measured after two night shifts and day sleep periods. The Tmin of the experimental subjects (n=11) was 04:24+/-0.8 h (mean+/-SD) at baseline and 7:36+/-1.4 h after the night shifts. Thus, after two night shifts, the Tmin had not yet delayed into the daytime sleep period, which began at 08:30 h. The Tmin of the control subjects (n=12) was 04:00+/-1.2 h at baseline and drifted to 4:36+/-1.4 h after the night shifts. Thus, two night shifts with a practical pattern of intermittent bright light, the wearing of sunglasses on the way home from night shifts, and a regular sleep period early in the daytime, phase delayed the circadian clock toward the desired compromise phase position for permanent night shift workers. Additional night shifts with bright light pulses and daytime sleep in the dark are expected to displace the sleepiest time of day into the daytime sleep period, improving both nighttime alertness and daytime sleep but not precluding adequate sleep on days off.  相似文献   

15.
【目的】明确稻飞虱迁飞种群的上灯行为节律,以指导其大田迁入种群和迁出种群的发生预测与灾变预警。【方法】本研究运用逐时自动灯诱装置对2010和2011连续两年稻飞虱迁飞种群的上灯行为节律进行了系统研究。【结果】灰飞虱Laodelphax striatellus迁飞种群上灯始见期和灯诱虫量年际间差异不明显,白背飞虱Sogatella furcifera和褐飞虱Nilaparvata lugens迁飞过境种群上灯始见期和灯诱虫量年际间差异较大。此外,灰飞虱迁飞种群的特大高峰期和高峰期逐时灯诱虫量百分比与一般上灯期和零星上灯期相比突出了晨暮双峰型中的暮峰型上灯行为特点;白背飞虱迁飞种群特大高峰期逐时灯诱虫量百分比与高峰期和一般期相比突出了晨暮双峰型中的晨峰型生物学特性。【结论】稻飞虱迁飞种群的上灯行为节律存在种的特异性,这一行为节律除了受环境因素的影响外主要与其生物学特性有关。  相似文献   

16.
Night shift work is associated with a myriad of health and safety risks. Phase‐shifting the circadian clock such that it is more aligned with night work and day sleep is one way to attenuate these risks. However, workers will not be satisfied with complete adaptation to night work if it leaves them misaligned during days off. Therefore, the goal of this set of studies is to produce a compromise phase position in which individuals working night shifts delay their circadian clocks to a position that is more compatible with nighttime work and daytime sleep yet is not incompatible with late nighttime sleep on days off. This is the first in the set of studies describing the magnitude of circadian phase delays that occurs on progressively later days within a series of night shifts interspersed with days off. The series will be ended on various days in order to take a “snapshot” of circadian phase. In this set of studies, subjects sleep from 23:00 to 7:00 h for three weeks. Following this baseline period, there is a series of night shifts (23:00 to 07:00 h) and days off. Experimental subjects receive five 15 min intermittent bright light pulses (~3500 lux; ~1100 µW/cm2) once per hour during the night shifts, wear sunglasses that attenuate all visible wavelengths—especially short wavelengths (“blue‐blockers”)—while traveling home after the shifts, and sleep in the dark (08:30–15:30 h) after each night shift. Control subjects remain in typical dim room light (<50 lux) throughout the night shift, wear sunglasses that do not attenuate as much light, and sleep whenever they want after the night shifts. Circadian phase is determined from the circadian rhythm of melatonin collected during a dim light phase assessment at the beginning and end of each study. The sleepiest time of day, approximated by the body temperature minimum (Tmin), is estimated by adding 7 h to the dim light melatonin onset. In this first study, circadian phase was measured after two night shifts and day sleep periods. The Tmin of the experimental subjects (n=11) was 04:24±0.8 h (mean±SD) at baseline and 7:36±1.4 h after the night shifts. Thus, after two night shifts, the Tmin had not yet delayed into the daytime sleep period, which began at 08:30 h. The Tmin of the control subjects (n=12) was 04:00±1.2 h at baseline and drifted to 4:36±1.4 h after the night shifts. Thus, two night shifts with a practical pattern of intermittent bright light, the wearing of sunglasses on the way home from night shifts, and a regular sleep period early in the daytime, phase delayed the circadian clock toward the desired compromise phase position for permanent night shift workers. Additional night shifts with bright light pulses and daytime sleep in the dark are expected to displace the sleepiest time of day into the daytime sleep period, improving both nighttime alertness and daytime sleep but not precluding adequate sleep on days off.  相似文献   

17.
Wildlife-related accidents are a serious problem in different countries and describing their temporal pattern allows for the development of measures to mitigate them. We described the temporal pattern of wild ungulate-related accidents occurring between January 2006 and December 2010 in the Autonomous Region of Galicia, northwest of Spain. We examined the temporal distribution of the accidents according to months, phenological and hunting seasons, days of the week and time of the day. From the 6,255 wild ungulate-related traffic accidents analysed, 36.5% were related to roe deer Capreolus capreolus and 62.8% were related to wild boar Sus scrofa. The monthly distribution of accidents was not random but follows a characteristic pattern for each species. Roe deer-related accidents have their maximum in April and May, coinciding with the breeding season, followed by July, coinciding with the rut. Wild boar-related accidents have their maximum between October and January, coinciding with the hunting season but also with months with the longest nights. Both roe deer- and wild boar-related accidents showed an increase at weekends, specially on Sundays. During the hunting season, the wild boar-related accidents showed a marked peak on the same day. This weekly pattern was explained by drivers’ behaviour and by hunting. For roe deer, peaks of accidents occurred between 19:00 and 22:00 (about dusk) and between 05:00 and 08:00 (about dawn). For wild boar, 69% of accidents occurred between 18:00 and 23:00, coinciding with dusk and night. This daily pattern of accidents was explained by the behaviour of the species.  相似文献   

18.
We investigated the influence of Swedish recommended vitamins A, D3 and E supplementation levels on muscle tenderness and fatty acid (FA) composition under indoor or outdoor finishing programmes. Swedish Red breed steer calves were divided into vitamin supplemented (n = 12) and non-supplemented (n = 15) groups while on pasture prior to the finishing period. This trial began at the beginning of the winter housing period during which the steers were fed a 55 : 45 dry matter barley : grass silage diet indoors. The indoor finished group was comprised of vitamin supplemented (n = 6) and non-supplemented (n = 8) steers slaughtered after about 155 days on feed. Vitamin supplemented steers were provided with 100 g mineral supplement providing 400 000 IU vitamin A, 100 000 IU D3 and 3000 IU E daily as recommended for Swedish production practices. In spring, outdoor finished vitamin supplemented (n = 6) and non-supplemented (n = 7) steers grazed semi-natural grassland for an additional 120 days before slaughter. During pasture, vitamin supplemented steers had free-choice access to a mineral supplement containing vitamins A, D3 and E. The mineral supplement for the non-supplemented steers did not contain vitamins A, D3 and E and was provided at the same amount as the vitamin supplemented steers. Shear force values were similar between vitamin supplemented and non-supplemented steers after ageing 2, 7 and 14 days within indoor and outdoor finishing programmes. The shear force values had decreased by 14 days of ageing within all programmes. The μ- and m-calpain activity did not differ between vitamin supplemented and non-supplemented steers for either the indoor or outdoor finishing programmes. The calpastatin activity was higher for the indoor, vitamin supplemented steers. Indoor finished vitamin supplemented steers had a greater proportion of C18:1c-9 and total monounsaturated fatty acids, whereas the non-supplemented steers had a greater proportion of total saturated fatty acids. We concluded that the meat quality from steers not receiving vitamin supplementation was similar to that of steers receiving vitamins A, D3 and E supplementation at Swedish recommended levels under indoor and outdoor finishing programmes.  相似文献   

19.
A recent worldwide trend in chemical and petrochemical industries is to extend the duration of shifts. Optimization of the labor force to reduce costs is one reason to increase the length of working time in a shift. Implementation of 12h shifts is a controversial decision for managers and scientists. Literature reviews show alertness is lower during the nighttime hours, and sleep duration is reduced and worse during the daytime. The main objective of this study was to evaluate the impacts of 12h shifts on alertness and sleep. To evaluate the duration and quality of sleep and alertness during work, 22 male shift workers on a continuous rotating schedule at a petrochemical plant completed activity logs and estimated alertness using analog 10-cm scales for 30 consecutive days, three times (at 2h, 6h, and 10h of the shift) every work shift. Statistical tests (analysis of variance [ANOVA] and Tukey) were performed to detect differences between workdays and off days. The shift schedule was 2 days/3 nights/4 off days, followed by 3 days/2 nights/5 off days, followed by 2 days/2 nights/5 off days. Sleep duration varied significantly (p < .001) among the work shifts and off days. Comparing work nights, the shortest mean sleep occurred after the second night (mean = 311.4 minutes, SD = 101.7 minutes), followed by the third night (mean = 335.3 minutes, SD = 151.2 minutes). All but one shift (sleep after the first work night) were significantly different from sleep after the first 2 workdays (p < .002). Tukey tests showed no significant differences in sleep quality between workdays and nights, with the exception of sleep after the third day compared to sleep after night shifts. However, significant differences were detected between off days and work nights (p < .01). ANOVA analysis showed borderline differences among perceived alertness during day shifts (p = .073) and significant differences among the hours of the shifts (p = .0005), especially when comparing the 2nd hour of the first day with the 10th hour of all the day shifts. There were no significant differences in perceived alertness during night work among the first, second, and third nights (p = .573), but there were significant differences comparing the times (2nd, 6th, 10th hour) of the night shifts (p < .001). The evaluation of sleep (duration and quality) and level of alertness have been extensively used in the literature as indicators of possible performance decrements at work. The results of this study show poorer sleep after and significantly decreased alertness during night work. Shifts of 12h are usually implemented for technical and economic reasons. These results point out the necessity of a careful trade-off between the financial and technical gains longer shifts might bring and the possible losses due to incidents or accidents from performance decrements during work.  相似文献   

20.
北京西山典型城市森林内PM_(2.5)动态变化规律   总被引:11,自引:0,他引:11  
王成  郭二果  郄光发 《生态学报》2014,34(19):5650-5658
城市森林内PM2.5浓度的状况可以直接反映城市森林对PM2.5的净化效果,也是居民休闲游憩关心的森林环境问题。选择北京西山3种典型的游憩型城市森林,通过对林内PM2.5浓度一年四季昼夜24h内变化的同步观测,分析了不同类型城市森林内PM2.5浓度的季节变化、日变化以及影响因素,结果表明:(1)北京西山3种游憩林内PM2.5浓度多数时候远低于城区对照值,在春、夏、秋三季都达到了国家城市化地区的标准,甚至在春季、秋季还达到了国家一类地区的标准。(2)城市森林在不同季节对PM2.5的净化效果存在差异,林内PM2.5浓度总体上呈现冬季夏季秋季春季的规律。(3)林内PM2.5浓度在一天24h内有很大变化波动,夜间浓度总体上高于白天,日变化曲线近似呈"双峰双谷"型,两个高峰出现在夜晚和早上,两个低谷出现在凌晨和中午前后。一年四季白天低谷出现时间有所不同,春季15:00左右、夏季13:00—17:00、秋季13:00—15:00、冬季9:00—11:00。(4)PM2.5在不同类型游憩林内的变化趋势和浓度值存在一定差异。郁闭度较大的侧柏林夜间PM2.5浓度总体上高于其它两种林型,其高峰和低谷出现时间延迟,高峰值大,高峰期持续时间长,且这种规律在秋季表现得更明显。(5)基于上述研究认为,北京西山城市森林为居民在PM2.5污染比较突出的都市背景下提供了一个相对清洁、健康的森林游憩环境,春季、夏季、秋季全天以及冬季9:00—11:00均是森林中PM2.5状况健康而适宜外出游憩的时段。  相似文献   

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