浙江北部海域春季浮游动物的群落结构研究

根据2007年春季在浙江北部海域所采集的浮游动物样品,对该调查海域浮游动物的种类组成、丰度、生物量和生物多样性进行了探讨,采用多元统计软件PRIMER 5分析了该海域浮游动物的群落结构。研究结果表明,调查海域共鉴定各类浮游动物62种、浮游幼虫12种,合计74种。经统计共有2种优势种,分别是中华哲水蚤(Calanus sinicus)和五角水母(Muggiaea atlantica)。浮游动物生物量和丰度的平面分布比较相似,主要分布在调查海域的东部和东南部,并存在着向东南方向呈递增的趋势,而在杭州湾内的值比较小。调查海域浮游动物生物多样性比较低,平均值为1.54。根据对本次调查获得的浮游动物群落结构的聚类分析,主要存在着两个生态类群,群落Ⅰ为沿岸低盐群落,群落Ⅱ为暖温带近海群落。     

图们市大气颗粒物中重金属含量及分布特征

采集了图们市2006年秋、冬两季的TSP和PM10样品,采用湿法消解-原子吸收分光光度法测定了其中的铅、镉、饲、锌、铬、铁、锰7种重金属.结果表明,图们市大气颗粒物中重金属含量由高到低的顺序是Fe>Cr>Zn>Pb>Mn>Cu>Cd.多数重金属元素含量冬季高于秋季,在一天之内早晨的重金属浓度也往往高于晚上争中午,说明大气颗粒物的来源包括天然源和人为源.     

Perfluoroalkyl acids(PFAAs) in urban surface water of Shijiazhuang,China: Occurrence,distribution,sources and ecological risks

It is extremely important to analyze the contaminative behaviors of Perfluoroalkyl acids(PFAAs) due to their serious threats to urban environments which are closely related to humans. Current study aimed to explore the distribution, source apportionment and ecological risk assessment of PFAAs in surface water from Shijiazhuang, China. The concentrations of ΣPFAAs ranged from 19.5 to 125.9 ng/L in the investigation area. Perfluorobutanesulfonic acid(PFBS) and perfluoropentanoic acid(PFPeA) were t...     

辽宁省降水化学组份分析

对辽宁省１９９１～１９９５年期间五城市降水中的化学组份进行了八种离子分析，研究了其时空分布，组成特征及变化规律．得出辽宁省存在降水污染的结论     

河流水体中直链烷基苯磺酸钠(LAS)含量水平调查

对盐河中水体直链烷基苯磺酸钠（ＬＡＳ）在水体中的分布状况、自净和迁移转化规律进行了调查研究．结果表明，污水中ＬＡＳ主要迁移到底泥中，底泥中ＬＡＳ同系物在各个时期中含量和波动幅度的顺序是：Ｃ１２＞Ｃ１１＞Ｃ１３＞Ｃ１０．     

甘肃省土壤农业水文特性的研究

本文在研究甘肃省土壤容重、土壤凋萎湿度和田间持水量的时空分布规律及其相关因素的基础上,根据占田间持水量40％(严重干旱)、60％(轻度干旱)和80％(最适宜)时的土壤湿度标准,计算出5种地域类型26个代表点的不同土壤湿度标准的土壤水分界限值,为各地采取不同的农业耕作和管理措施提供依据。最后以凋萎湿度为主导指标,以容重和田间持水量为辅助指标,建立甘肃省土壤农业水文特性分区指标系统,把全省划分为5个大区12个副区,对各大区土壤农业水文特性值进行了评述,并提出土壤改良措施和相应的办法。     

Distributions of personal VOC exposures: a population-based analysis

Information regarding the distribution of volatile organic compound (VOC) concentrations and exposures is scarce, and there have been few, if any, studies using population-based samples from which representative estimates can be derived. This study characterizes distributions of personal exposures to ten different VOCs in the U.S. measured in the 1999-2000 National Health and Nutrition Examination Survey (NHANES). Personal VOC exposures were collected for 669 individuals over 2-3 days, and measurements were weighted to derive national-level statistics. Four common exposure sources were identified using factor analyses: gasoline vapor and vehicle exhaust, methyl tert-butyl ether (MBTE) as a gasoline additive, tap water disinfection products, and household cleaning products. Benzene, toluene, ethyl benzene, xylenes chloroform, and tetrachloroethene were fit to log-normal distributions with reasonably good agreement to observations. 1,4-Dichlorobenzene and trichloroethene were fit to Pareto distributions, and MTBE to Weibull distribution, but agreement was poor. However, distributions that attempt to match all of the VOC exposure data can lead to incorrect conclusions regarding the level and frequency of the higher exposures. Maximum Gumbel distributions gave generally good fits to extrema, however, they could not fully represent the highest exposures of the NHANES measurements. The analysis suggests that complete models for the distribution of VOC exposures require an approach that combines standard and extreme value distributions, and that carefully identifies outliers. This is the first study to provide national-level and representative statistics regarding the VOC exposures, and its results have important implications for risk assessment and probabilistic analyses.     

哈尔滨市土壤中PCBs的污染现状研究

采用GC／MS法对哈尔滨市18个表层土壤及1个深层土壤中PCBs的浓度进行了测定,并讨论了PCBs在土壤中的分布特征及同族体的组成情况。结果表明,该市表层土壤中∑PCBs浓度分布在0．025-1．795ng／g之间,平均值为0．545ng／g,深层土壤中未能检测到目标物,土样中共有18种同系物有不同程度的检出,主要以五氡联苯为主,其中工业区的土壤样品中∑PCBs含量最高。     

X~2分布、t分布和F分布的近似计算

当自由度很大时,三大抽样分布的P值无表可查,而且如果编程计算P值时,需要计算一个无穷区间上的广义积分,还会面临数值溢出的问题,解决这些问题需要较高的计算机编程技巧,这些不利于开发实用程序,限制了它们的实际应用。本文利用χ^2分布、一元t分布和一元F分布的一致渐进正态性、标准正态分布的分布函数近似计算公式和软件Mathematica 5．0,通过计算机仿真,指出当自由度较大时,可以用正态分布进行近似计算,避免了数值溢出和无穷区间的积分问题,为使用常用开发语言编程解决实际问题提供了一种可行方案,具有一定的应用价值。     

Comparative performance of generalized additive models and multivariate adaptive regression splines for statistical modelling of species distributions

Two statistical modelling techniques, generalized additive models (GAM) and multivariate adaptive regression splines (MARS), were used to analyse relationships between the distributions of 15 freshwater fish species and their environment. GAM and MARS models were fitted individually for each species, and a MARS multiresponse model was fitted in which the distributions of all species were analysed simultaneously. Model performance was evaluated using changes in deviance in the fitted models and the area under the receiver operating characteristic curve (ROC), calculated using a bootstrap assessment procedure that simulates predictive performance for independent data. Results indicate little difference between the performance of GAM and MARS models, even when MARS models included interaction terms between predictor variables. Results from MARS models are much more easily incorporated into other analyses than those from GAM models. The strong performance of a MARS multiresponse model, particularly for species of low prevalence, suggests that it may have distinct advantages for the analysis of large datasets. Its identification of a parsimonious set of environmental correlates of community composition, coupled with its ability to robustly model species distributions in relation to those variables, can be seen as converging strongly with the purposes of traditional ordination techniques.