ARIMA时间序列分析模型在臭氧浓度中长期预报中的应用

近年来,京津冀地区近地面臭氧浓度呈现上升趋势,臭氧污染超标情况严重.目前由于前体物源排放清单、臭氧生成和扩散的物理和化学过程机制存在不足等原因,导致了数值模型在预报夏季臭氧浓度时仍然存在较大偏差,而时间序列分析方法由于具有建模简单、计算成本低的特点,在臭氧污染预报中具有很好的应用前景.本研究利用华北区域大气本底站上甸子站点和环境监测总站天津和保定站点的臭氧观测数据,采用ARIMA时间序列分析模型开展臭氧浓度中长期预报研究.结果表明,季节性ARIMA模型在预报臭氧长期月均值时,预测值和观测值的相关系数R可达0.951,均方根误差RMSE仅为10.2 μg·m^-3.加入了日最高气温及二次项作为协变量的动态ARIMA模型,对臭氧日最大8 h滑动平均值的预报效果得到了很大提升,预测值和观测值的相关系数由0.296~0.455提升至0.670~0.748,RMSE得到了有效降低.     

Seasonal and interannual variation of soil respiration in four vegetation types in the loess hilly region北大核心CSCD

Soit carbon (C) stock is the largest C pool in terrestrial ecosystems, and the emission of CO2 through soil respiration contributes to the majority of soil C expenditure and atmospheric C. Soil respiration is also one of the major processes controlling the C budget of terrestrial ecosystems. A slight change in soil CO2 emission might cause drastic variations in global C balance. Therefore, it is of great significance to investigate the characteristics of soil respiration of soils growing different types of vegetation over a long period, and determine its relationship with variables such as soil temperature and moisture. The rate of soil respiration was measured each month in the growing seasons (from April to October) of 2011, 2013, and 2014 using the Li-8100 CO2 flux measurement system in the central Loess Plateau. Four types of vegetation (Quercus liaotungensis, Platycladus orientalis, Robinia pseudoacacia, and a natural shrub) were chosen for the periodical measurements. A permanent sample plot was established for each type of vegetation, and five polyvinyl chloride (PVC) collars were placed in each plot for the measurements. The temperature and water content of the soil in the upper 12 cm near the collar were measured using a digital soil temperature probe and a TDR 200 soil moisture meter at the same time when the soil respiration was measured. The soil respiration rates were fitted to the soil temperature and moisture with an exponential function, power function, linear function, and an equation combining the two variables. The results showed that: (1) the seasonal variation in the rates of soil respiration in the soils growing the four types of vegetation were almost the same, and were lower in the earlier period and then increased to high levels in the middle and later periods; (2) the rates of soil respiration in the same month varied with the type of vegetation grown, and were in the descending order: Q. liaotungensis > P. orientalis > shrub > R. pseudoacacia; (3) the average values of the rates of soil respiration in 2011, 2013, and 2014 were 2.77, 3.48, and 5.08 μmol m-2 s-1, respectively. The variation in soil respiration was higher across the three years than the variation for the types of vegetation grown; and (4) the rate of soil respiration was positively correlated to soil temperature and moisture for all the types of vegetation. A better fit was obtained by using the equation that included both the variables, soil temperature and moisture, than by an equation that included a single factor. Our results suggested that both seasonal and inter-annual variations of soil respiration occurred in the soils growing the four types of vegetation in the region. The temperature and water content of soils are the major regulating factors, and soil respiration in the Loess Plateau is more greatly affected by environment factors than by the type of vegetation. © 2018 Science Press. All rights reserved.     

Advances in research of airborne microbes in subway systems北大核心CSCD

Subway systems are indispensable for transportation in modern cities, with the air being easily polluted by microbes owing to the enclosed and crowded environment. The microbiological characteristics of subway aerosols have attracted the attention of researchers worldwide during recent years. This review aimed to evaluate the sampling and analyzing methods suitable for detecting airborne microbes in subway systems. Active air sampling methods and molecular biology techniques based on polymerase chain reaction (PCR) such as 16S rRNA gene sequencing, metagenomics, and quantitative PCR demonstrated great potential in microbial analysis of aerosols because they can provide accurate and comprehensive information. Temporal and spatial distributions of airborne microbes, as well as the factors influencing their distribution characteristics, were also discussed by critically reviewing worldwide literature on subway microbiome studies. The concentration and composition of airborne bacteria and fungi in subway can vary dramatically with time and space. The critical factors determining microbial community structure and composition include temperature, relative humidity, carbon dioxide concentration, number of passengers, presence of platform screen door, ventilation systems, and so on. The review suggests that future studies on standardized sampling and analyzing protocols are required to obtain contamination levels of subway airborne microbes and to establish the relationship between microbial monitoring data and public health risks. © 2018 Science Press. All rights reserved.     

准东煤矿区土壤镉污染风险评价及敏感性分析

镉是一种毒性很强的重金属元素,易通过食物链进入人体,对人体健康产生影响。新疆地区的煤炭资源开发已引起重金属污染问题,但目前有关镉污染风险评价的研究相对不足。本研究采用地质累积指数法、潜在生态危害指数法、美国环保局(US EPA)健康风险评估方法和缓冲区分析方法,对准东红沙泉和北山煤矿土壤中镉的污染现状、生态风险水平和健康风险水平做了分析与评价。结果显示:1)研究区土壤镉含量普遍超过国家土壤环境质量Ⅱ级标准,处于重污染水平;2)研究区的镉污染具有极高生态风险;3)镉污染水平和生态风险系数具有明显空间性,它们在研究区的强度排序为堆煤场矿区生活区芨芨湖雀仁乡;4)手-口途径是最主要的健康风险暴露途径,所有人群中儿童暴露风险最高;5)准东煤矿区镉污染水平较高,但其非致癌水平和致癌水平均未超过风险限值;6)矿区周边0~30 km区域内属于健康风险高敏感区域。综上可知:准东地区煤矿开采引起了周边环境镉污染。镉污染对人类健康,特别是儿童的健康具有较高的暴露风险。当地镉污染虽未达到致病水平,但也应引起足够重视。     

热重实验条件下不同氧气浓度对煤自燃反应能级的实验研究

为研究不同氧气浓度对煤自燃反应能级的影响,基于热重实验分别得到6个不同氧气浓度下的煤自燃特征温度点,通过计算不同阶段内煤自燃的反应动力学参数分析氧气浓度与煤自燃反应能级关系。实验结果表明:n≠1时,氧气浓度对煤自燃反应能级(n)的影响在不同温度段内的影响不同;氧气浓度与T1,T2,T3特征温度点的关系曲线变化趋势不明显,T4~T8温度点与氧浓度的关系呈现先增大后减小的趋势。     

延龙图地区城市土地生态适宜性评价

土地是人类生存、发展的物质基础,但是快速的城市化和城镇化每年使得很多生态用地转化为建设用地,结果导致一系列严峻的生态环境问题。在生态文明建设背景下,城市发展需合理规划以减少城市发展对生态环境造成的影响,而城市合理规划的前提是认清土地生态适宜性及其等级。鉴于此,论文从自然地理、社会经济、生态限制三方面选取了12个评价因子构建阻力评价体系,运用“阻力模型”和“最小累积阻力模型”相结合的方法,并借助GIS空间分析技术对延龙图地区城市土地生态适宜性及其等级进行了评价。结果表明：延龙图地区城市土地生态适宜性可分为重点建设区（538.55 km²）、优化建设区（743.53 km²）、限制建设区（1 887.46 km²）和禁止建设区（1 919.16 km²）。论文明确各区空间分布并提出相对应的发展建议,以期为延龙图地区城市土地规划布局提供理论、技术、决策支撑与参考。     

多方法研究呼伦湖表层沉积物有机质的赋存特征及来源

湖泊沉积物有机质是全球碳循环的重要组成部分之一.寒旱区湖泊由于地理位置和气候条件的特殊性,其沉积物有机质的赋存和迁移转化特征更容易受到气候变化的影响.以我国寒旱区典型代表湖泊——呼伦湖为例,采用连续提取法、C/N（碳氮比值）、δ13C（碳稳定同位素）、三维荧光光谱技术对呼伦湖表层沉积物有机质的含量和组分的时空分布特征、污染来源及稳定性进行了研究.结果表明:①2018年10月（秋季）、2019年3月（冬季）、2019年5月（春季）、2019年7月（夏季）,呼伦湖表层沉积物中w（TOC）的平均值分别为（25.05±9.73）（26.92±11.60）（24.68±10.19）（24.36±10.01）g/kg,呈冬季高、夏季低,由西北部向东南部递减的时空分布趋势.②w（WEOM）（WEOM为水提态有机质）、w（FA）（FA为富里酸）、w（HA）（HA为胡敏酸）和w（HM）（HM为胡敏素）的年均值分别为（0.63±0.33）（2.31±1.26）（3.42±1.49）（19.21±7.83）g/kg,w（WEOM）:w（FA）:w（HA）:w（HM）为1.0:3.7:5.5:30.7,其中HM为有机质的优势组分.③WEOM包括类富里酸组分C1,类腐殖酸组分C2和C3,以及类色氨酸组分C4共4个荧光组分,其中,类腐殖质组分（C1+C2+C3）贡献了总荧光强度的79.2%,为优势荧光组分.④沉积物有机质主要来自于陆源,陆源有机质的平均贡献率在80%左右.⑤沉积物PQ值（胡敏酸占腐殖酸的比例）和WEOM的HIX（腐殖化指数）年均值分别为0.55和6.39,表明现阶段呼伦湖表层沉积物有机质腐殖化程度较高且相对稳定.研究显示:呼伦湖表层沉积物有机质含量较高,表现出季节和空间分布差异性;有机质主要来自陆源,以类腐殖质为主,具有腐殖化程度高和相对稳定的特点.      

基于DEM的地形指数提取方法及应用

在水文模拟中,地形指数ln(α/tan β) 作为反映地形信息的物理指标具有很高的应用价值。应用基于DEM的River Tools软件和GRIDATB程序,对红壤丘陵区地形起伏平缓的小流域进行地形指数的提取。 River Tools软件和GRIDATB程序分别使用目前常用的D8方法（单流向法）和多流向法。结果表明：与多流向法相比,D8方法的计算值较为离散,分布曲线较粗糙,平均值略高,方差和偏态系数也较大;但是,两种方法计算的ln(α/tan β) 的分布曲线大致相似。对于仅需要ln(α/tan β) 频率分布的水文模型（如TOPMODEL）来说,可以用单流向法取代多流向法来计算ln(α/tan β) 的频率分布。     

近15年来长江源区土地利用变化及其生态环境效应

长江源区是我国重要的水源涵养区,也是高海拔地区生物多样性最集中的地区和生态变化最为敏感的地区。基于1986年TM和2000年ETM+卫星遥感数据和野外实地调查,采用GIS软件和景观生态空间分布格局分析方法,对长江源区近15年来土地利用类型的时空变化进行了研究。结果表明：1986～2000年,源区林地和湿地面积减少54.2 %和42.69 %,建设用地、耕地和未利用土地面积分别增加120 %、43.83 %和21.1 %。全区土地利用的空间位置转换面积大于其数量变化,土地利用类型总变化的面积大小依次是草地＞未利用土地＞湿地＞水域＞林地＞耕地＞建设用地。土地利用动态转化过程以草地转化为未利用土地、湿地转化为草地和未利用地逆转为草地为主要特征。15年里景观破碎化程度加剧,分维数和多样性指数增加,优势度降低,景观异质性增强。长江源区脆弱的生态体系对土地利用变化响应强烈,造成水土流失与沙漠化程度加剧,导致大范围高寒草甸、草原植被退化,湿地萎缩。气候变化和人类经济活动是导致研究区土地利用变化的主要因素。     

Arctic Wilderness Policy in the United States and Finland

The United States and Finland have passed laws to classify and manage Arctic wilderness areas, but their national policies are based on different nature ideologies. Finns tend to perceive wilderness as a human-centered idea, while Americans are inclined to see the same land from a nature-based point of view. Rural residents in the Arctic, and especially indigenous peoples, use motorized vehicles for hunting and gathering in wilderness areas. Attempts of southern-based environmental groups to restrict motor use by imposing a nature-based ideology on rural residents in northern Alaska will result in high levels of political conflict. Alaska land managers need to respect the minority rights of rural residents and a study of wilderness policies in Finnish Lapland is instructive toward this end.