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501.
Christine Wallgren 《Local Environment》2013,18(2):233-251
Abstract This study compares energy use for food transport to a farmers' market in Sweden with energy use for transport in the conventional food system. The farmers' market was investigated through data sampling from on-site investigations. The conventional food system was studied with the aid of life cycle assessments reported in the literature. Overall, the study found no significant differences in levels of energy use for transport to the farmers' market compared with the conventional food system. For certain products, such as fresh fruits and vegetables, transport-related energy use was much lower in the local system although the season in Sweden for this kind of product is restricted to two or three months at the end of the summer. However, there is considerable potential to increase energy efficiency in local food systems by organizing the selling in new ways and by using more energy efficient vehicles. 相似文献
502.
Abstract The forests of Nepal, which in the past were at least nominally under the direct control of the state, are today increasingly entrusted to local people in the name of community forestry (CF). CF is considered a successful endeavour in managing forest resources, conserving biodiversity and supplying people with basic economic needs. In order to assess to what extent the two goals of biodiversity conservation and meeting economic needs of people have been integrated through CF, four community forestry user groups (CFUGs) were studied in the Mid-hills ecological zone. Based on a participatory survey and a critical review of the statutes and operational plans of these CFUGs, it was found that integration of biodiversity conservation was still insufficient, and that improvements in the policy and management regimes of CF are necessary to achieve a balance between biodiversity conservation and economic use of the forest resources. 相似文献
503.
为准确评价城轨信号系统安全保障能力及影响因素,基于云理论对定性与定量因素的良好融合优点,构建城轨信号系统安全保障能力评价云模型及评价指标体系,采用组合赋权法对各指标赋予权重,并基于专家意见,利用正向云发生器生成标准云。结果表明:该云模型具有一定稳定性和可靠性,可对城轨信号系统安全保障能力进行有效测评,同时能够发现安全运营中的缺陷,有助于协助管理方进行针对性改善,以提高城轨信号系统的安全保障能力。 相似文献
504.
以广东省佛山市甲、乙两间污水处理厂为例,从工艺特征、工艺参数、水质特点、存在问题及相应措施几个方面介绍了两种改良型A2/O工艺在不同进水条件下的运行情况。 相似文献
505.
惠阳城区降雨径流重金属污染特征研究:Ⅰ.地表堆积物重金属含量分析 总被引:2,自引:0,他引:2
以惠阳城区为研究对象,选取4种具有代表性的典型城市功能区类型:工业区、商业区、住宅区、交通区,对其地表堆积物进行样品采集和实验分析.结果表明:地表堆积物细粒部分(粒径<149舯)所占比例为51%,粗粒部分(粒径>2 000um,)所占比例仅4.1%;重金属含量的粒径分级特性和质量分数相似,即粒径越细的部分重金属含量越高;Pb,Zn,Cu.Cr之间的相关系数较高;重金属的浸出浓度在不同的功能区基本遵循同样的规律,即细粒部分重金属浸出浓度最高,随粒径的增大浸出浓度逐减,细粒部分重金属的浸出浓度:w(Pb)为59.1 rag/kg/kg,w(Zn)为93.5 mg/kg,w(Cu)为37.7 ms/ks,w(Cr)为23.9 ms/kg,w(Cd)为0.07 mg,kg. 相似文献
506.
城市生态系统承载机制初步研究 总被引:1,自引:0,他引:1
文章分析了城市生态系统组成、结构及功能流,立足于资源承载力、环境承载力的角度,探讨了城市生态系统内部资源、环境对人类社会经济活动的承载约束机制,从城市生态系统客观存在性、弹性与扩展性、递阶性及相对性等方面,总结了城市生态系统承载机制的特点,在建立承载机制评价指标框架的基础上,初步提出了承载机制的定量研究方法。 相似文献
507.
508.
城市间空气污染控制的马氏链模型 总被引:1,自引:0,他引:1
根据城市间空气污染物相互扩散和无后效性的特点,应用马尔可夫随机过程理论,先建立各城市污染物浓度状态转移方程,再由城市间污染物浓度状态形成一个吸收链。建立城市间污染物排放控制的马氏链模型。通过模型求解,得出了城市间空气污染物浓度达到国家排放标准的条件,最后应用数值计算软件MAT-LAB,编写了一个城市间空气污染控制的通用程序,它能在保证城市空气质量的前提下,快速准确地计算出控制区内各污染源污染物的最大允许排放量,这对环保部门进行城市空气污染物排放量控制工作具有实际意义。 相似文献
509.
510.
Qihua Shan Yuanchun Yu Jian Yu Jinchi Zhang 《Frontiers of Environmental Science & Engineering in China》2008,2(2):218-223
To reveal the biological characteristics of urban forest soil and the effects of soil enzyme on soil fertility as well as
the correlation between physicochemical properties and enzyme activities, 44 urban forest soil profiles in Nanjing were investigated.
Basic soil physicochemical properties and enzyme activities were analyzed in the laboratory. Hydrogen peroxidase, dehydrogenase,
alkaline phosphatase, and cellulase were determined by potassium permanganate titration, TTC (C19H15N4·Cl) colorimetry, phenyl phosphate dinatrium colorimetry, and anthrone colorimetry, respectively. The result showed that soil
pH, organic carbon (C), and total nitrogen (N) had great effects on hydrogen peroxidase, dehydrogenase, and alkaline phosphatase
activities in 0–20 cm thick soil. However, pH only had great effect on hydrogen peroxidase, dehydrogenase, and alkaline phosphatase
activities in 20–40 cm thick soil. Hydrogen peroxidase, dehydrogenase, and alkaline phosphatase were important biological
indicators for the fertility of urban forest soil. Both in 0–20 cmand 20–40 cmsoil, soil enzyme system (hydrogen peroxidase,
dehydrogenase, alkaline phosphatase, and cellulase) had a close relationship with a combination of physicochemical indicators
(pH, organic C, total N, available K, available P, cation exchange capacity (CEC), and microbial biomass carbon (Cmic)). The more soil enzyme activities there were, the higher the fertility of urban forest soil.
__________
Translated from Urban Environment & Urban Ecology, 2007, 20(4): 4–6, 9 [译自: 城市环境与城市生态] 相似文献