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51.
The nitrogen (N) distribution and cycling of atmosphere-plant-soil system in the typical meadow Calamagrostis angustifolia wetland (TMCW) and marsh meadow Calamagrostis angustifolia wetland (MMCW) in the Sanjiang plain were studied by a compartment model. The results showed that the N wet deposition amount was 0.757 gN/(m2·a), and total inorganic N (TIN) was the main body (0.640 gN/(m2·a)). The ammonia volatilization amounts of TMCW and MMCW soils in growing season were 0.635 and 0.687 gN/m2, and the denitrification gaseous lost amounts were 0.617 and 0.405 gN/m2, respectively. In plant subsystem, the N was mainly stored in root and litter. Soil organic N was the main N storage of the two plant-soil systems and the proportions of it were 93.98% and 92.16%, respectively. The calculation results of N turnovers among compartments of TMCW and MMCW showed that the uptake amounts of root were 23.02 and 28.18 gN/(m2·a) and the values of aboveground were 11.31 and 6.08 gN/(m2·a), the re-translocation amounts from aboveground to root were 5.96 and 2.70 gN/(m2·a), the translocation amounts from aboveground living body to litter were 5.35 and 3.38 gN/(m2·a), the translocation amounts from litter to soil were larger than 1.55 and 3.01 gN/(m2·a), the translocation amounts from root to soil were 14.90 and 13.17 gN/(m2·a), and the soil (0-15cm) N net mineralization amounts were 1.94 and 0.55 gN/(m2·a), respectively. The study of N balance indicated that the two plant-soil systems might be situated in the status of lacking N, and the status might induce the degradation of C. angustifolia wetland. 相似文献
52.
沿海发达地区土地利用研究新进展与方向 总被引:5,自引:2,他引:5
土地资源的短缺、质量退化与低效利用.已成为影响沿海发达地区生态安全与可持续发展的重要制约因素,也是土地利用管理与规划决策所面临的现实难题。我国沿海经济发达地区作为人地矛盾激化和经济快速转型背景下特殊的人文生态脆弱区,受到了包括地理学、生态学、经济学和社会学等多学科学者的密切关注,尤其是近10多年来在沿海土地利用变化及其效应研究方面取得了丰硕成果。主要以土地科学研究新方向和沿海地区经济社会发展态势为基本背景.从土地利用类型及其转换格局、驱动力因素辨识与驱动机制、土地利用转换的效应、区域土地可持续利用.以及土地利用优化配置与调控等方面,对沿海地区土地利用研究进行了初步梳理和评述,并指出今后应重视深化沿海发达地区土地利用研究的9个重点问题。 相似文献
53.
基于效果-效率-适应性的养殖废弃物资源化利用管理模式评价框架构建及初步应用 总被引:4,自引:0,他引:4
由于产业发展正处于转型阶段,我国畜禽养殖污染治理中的管理问题比技术问题更加突出,选择适宜的组织管理模式尤其重要。融合了效果分析、效率评价和适应性分析,尝试构建一个养殖废弃物资源化利用管理模式综合评价框架,并选择太湖流域4个不同类型的典型案例进行方法例证。研究表明,传统的养殖企业主导型管理模式应用于小型、分散养殖废弃物资源化利用时面临着经济效率低、适应性差难题;农村废弃物处理中心、种植企业和有机肥企业的参与可以改善小型、分散养殖废弃物资源化利用的经济效率;综合考虑效果、效率与适应性,种植企业、有机肥企业主导型模式的适宜推广范围更广。应根据不同地区种植-养殖产业关系、污染治理需求、经济发展水平与政府投入能力等,灵活组合应用不同管理模式。 相似文献
54.
The study aims to compare the detection of 16S rRNA gene of Dehalococcoides species and the microcosm study for biotransformation in predicting reductive dechlorination of chlorinated ethenes in ground water at hazardous waste sites. A total of 72 ground water samples were collected from 12 PCE or TCE contaminated sites in the United States. The samples were analyzed and used to construct microcosms in the laboratory. The results showed that the presence of Dehalococcoides DNA was well associated with dechlorination to ethene in the field. Nearly half of the wells where Dehalococcoides DNA was detected had ethene as a dechlorination end product. In comparison, for ground water samples of 16 wells where ethene was detected, ethene was produced in 11 of the corresponding microcosms. For most microcosms, during two years of incubation, dechlorination was less extensive than that observed in the field. 相似文献
55.
国民信息素养的高低已成为一个国家在全球竞争中获得优势地位的关键,信息素养教育在全世界范围内备受重视。本文以信息素养为出发点,以当今高校对在校大学生信息素养培训的新要求为依据,通过信息的选择、检索、利用,个人创新和文化素养等五个方面的教育,论述了如何培养高校学生信息素养,使学生养成终身学习的习惯。 相似文献
56.
57.
Problem
To simplify the computation of the variance in before-after studies, it is generally assumed that the observed crash data for each entity (or observation) are Poisson distributed. Given the characteristics of this distribution, the observed value (xi) for each entity is implicitly made equal to its variance. However, the variance should be estimated using the conditional properties of this observed value (defined as a random variable), that is, f(xi|μi), since the mean of the observed value is in fact unknown.Method
Parametric and non-parametric bootstrap methods were investigated to evaluate the conditional assumption using simulated and observed data.Results
The results of this study show that observed data should not be used as a substitute for the variance, even if the entities are assumed to be Poisson distributed. Consequently, the estimated variance for the parameters under study in traditional before-after studies is likely to be underestimated.Conclusions
The proposed methods offer more accurate approaches for estimating the variance in before-after studies. 相似文献58.
59.
职业安全绩效指标研究 总被引:3,自引:2,他引:1
为了建立企业安全生产长效机制,提高安全管理水平,预防事故的发生,笔者在研究国内外企业安全绩效要素及分类方法的基础上,提出了包含10个一级要素及50个二级要素的企业安全绩效指标体系,并就指标的设立原则、定义、权重的确定和应用进行了阐述示例。同时,也为政府安全监管部门提供了科学决策的依据。 相似文献
60.
K. Pritsch D. Ernst F. Fleischmann S. Gayler T. E. E. Grams A. Göttlein W. Heller N. Koch H. Lang R. Matyssek J. C. Munch M. Olbrich H. Scherb S. Stich J. B. Winkler M. Schloter 《Water, Air, & Soil Pollution: Focus》2008,8(2):139-154
A lysimeter study was performed to monitor effects of elevated ozone on juvenile trees of Fagus sylvatica L. as well as on the plant–soil system. During a fumigation period over almost three growing seasons, parameters related
to plant growth, phenological development and physiology as well as soil functions were studied. The data analyses identified
elevated ozone to delay leaf phenology at early and to accelerate it at late developmental stages, to reduce growth, some
leaf nutrients (Ca, K) as well as some soluble phenolics (hydroxycinnamic acid derivatives, total flavonol glycosides). No
or very weak ozone effects were found in mobile carbon pools of leaves (starch, sucrose), and other phenolic compounds (flavans).
Altered gene expression related to stress and carbon cycling corresponded well with findings from leaf phenology and chemical
composition analyses indicating earlier senescence and oxidative stress in leaves under elevated ozone. Conversely in the
soil system, no effects of ozone were detected on soil enzyme activities, rates of litter degradation and lysimeter water
balances. Despite the fact that the three reported years 2003–2005 were climatically very contrasting including a hot and
dry as well as an extremely wet summer, and also mild as well as cold winters, the influence of ozone on a number of plant
parameters is remarkably consistent, further underlining the phytotoxic potential of elevated tropospheric ozone levels. 相似文献