【作者】 常静；

【导师】 刘敏； 许世远；

【作者基本信息】 华东师范大学 ， 自然地理学， 2007， 博士

【摘要】 城市作为一个受人类活动影响的地域综合体,其自然地理过程、机制与范式等极为复杂,是人地关系演变新阶段的重要表现,也是当前自然地理学与全球变化研究的典型区域,倍受人们关注。有关城市环境问题的研究已成为当前多学科联合攻关研究的核心问题之一。IHDP(全球环境变化人文因素计划)于2004年提出了两项新的IGBP-IHDP联合研究计划,其中之一即为“城市化与全球环境变化(Urbanization and Global Environmental Change)”。城市第二自然地理格局的出现使不透水地面成为下垫面格局的主要单元和影响物质循环的重要因素,越来越多的地理学者开始思考有关“城市自然地理学”的议题。近年来,本课题组已就城市自然地理系统的主要物质循环和环境过程进行了一系列初步的、探索性的理论和实证研究,取得了诸多可借鉴的成果。论文在前人及原有研究成果的基础上,尝试进一步从物质循环的角度,对城市自然要素开展系统性研究,丰富自然地理学内容,探讨城市自然地理研究方法学,为城市自然地理与全球变化区域响应提供实证。物质尤其是污染物质在城市环境系统多介质、多界面的循环是城市自然地理过程研究的关键切入点。论文以上海中心城区为例,从多介质的角度开展典型污染物(营养盐、重金属)在城市地表灰尘-降雨径流系统内的时空格局、迁移过程与环境效应研究,重点探讨了以不透水地面为特征的城市地表环境对污染物迁移转化的影响与控制,初步建立了城市“第二自然格局”背景下的物质循环研究框架。论文主要认识与结论如下:(1)初步建立了污染物在以“不透水地面”为主要特征的城市地表环境系统迁移循环模式。提出了“城市地表灰尘—降雨径流”的系统概念,认为城市汇水域(Urban Catchment)是物质循环的基本单元,不透水地面的累积和冲刷是污染物迁移转化的关键过程,颗粒物是影响污染物整个迁移过程的主要因子。(2)研究了城市地表灰尘负荷量及其污染物的时空分布特征,发现上海地表灰尘累积量无明显的季节性变化,与国内外研究比较属于中等水平。地表灰尘重金属含量在国内城市中较高,显示出冬春季节较高,夏秋季节较低的特征。(3)研究了城市地表灰尘污染粒级效应及其生物有效性。发现地表灰尘污染物粒级效应显著,低于75μm是其主要的污染粒径级别,重金属粒级效应顺序为Cr>Pb>Cd>Zn>Ni>Cu。通过地表灰尘重金属赋存形态研究表明,Zn、Cd和Ni主要以碳酸盐结合态存在,Pb主要为铁锰氧化物结合态,Cu主要为有机结合态存在,Cr主要以残渣态存在,地表灰尘重金属非稳定形态含量由大到小顺序依次为Zn>Pb>Ni>Cd>Cu>Cr。(4)研究了地表灰尘污染物累积过程的输入-输出机制。发现地表灰尘对大气环境污染的贡献率不可忽视,低于75μm粒径级别颗粒物是地表灰尘与大气悬浮物进行物质交换的主要来源,应用美国EPA道路颗粒物排放因子方法,计算出上海城市地表灰尘对PM2.5、PM10和TSP的排放因子为0.99、7.64和9.17 g/VKT,排放量分别为1.7、13.1和69.6万吨/年。(5)在国内首先开展了地表污染物累积过程的实证研究。揭示了土地利用类型和道路交通行为是影响地表灰尘大气环境“源-汇”效应的重要因素。在高交通流量地区,地表灰尘重金属表现出对大气悬浮颗粒物的“源”效应,而交通流量相对较低的区域则显示出其对大气悬浮物的“汇”效应。对地表污染物累积过程研究表明,随着无雨期天数增加,地表灰尘负荷量总体上表现出增大趋势,颗粒物粒径逐渐增大;持续时间长、雨强较大的降雨对颗粒物和污染物负荷有明显的削减作用;重金属负荷累积过程符合S型增长曲线。(6)对污染物径流冲刷过程研究表明,径流粒径曲线多呈双峰或多峰分布。降雨类型是影响污染物冲刷过程的重要因素。不同土地利用类型冲刷过程研究表明,Zn和Cu,Pb和Cd,Cr和Ni在EMC值空间分异特征上都显示出了较明显的一致性。不同降雨事件冲刷过程研究表明,Zn,Pb和Cu表现出了相似的环境行为,Cd与其相差不大,Cr和Ni也比较相似,认为这种比较固定的组合特征在一定程度上反映出了重金属来源和环境行为的相似性。(7)提出了初始冲刷效应的定量表征方法,发现上海城市径流初始冲刷属于中等强度,强度指数b值在0.185～0.896之间。重金属总量初始冲刷强度顺序为Ni>Pb>Zn>Cd>Cu>Cr,溶解态重金属初始冲刷强度不明显。最大雨强及出现时间是影响污染物初始冲刷强度的重要因素。(8)提出径流水体“固-液”界面过程的重要性,认为“固-液”界面过程对于污染物在径流水体中存在相态的改变和量的时空分布具有重要影响。径流冲刷过程中,颗粒物是控制污染物迁移转化的重要因素,重金属Zn、Pb和Cu与颗粒物相关性最大,Cd和Cr相关性依次降低,Ni不显著相关。在溶解态重金属含量比值的空间分异上,Pb和Cu,Ni和Cr,Zn和Cd各表现出相似的分布趋势。重金属分配系数从大到小依次为Pb>Cd>Zn>Ni>Cu>Cr。(9)污染物“地表灰尘—降雨径流”多介质系统分配特征研究表明,上海城市大气湿沉降对径流污染的贡献不可忽视,雨水中重金属Zn浓度达到了国外研究的上限值,值得关注。对地表灰尘和径流水体重金属含量因子分析表明,由于干湿沉降过程影响,径流水体的因子分析对重金属来源解释得更全面,而地表灰尘因子分析则要相对散乱,更多反映了其污染物粒级效应的相关。径流水体因子分析中,Pb、Zn和Cu明显聚为一类,Cd处于外围,Cr和Ni则距离较远。排水系统特征是影响污染物在雨水管道中物理化学变化的重要因素,分流制排水系统初始冲刷效应不明显。(10)研究了重金属在“地表灰尘-径流悬浮物-雨水口沉积物-河流沉积物”系统中的分配特征和生物有效性。发现径流悬浮颗粒物和河流沉积物是重金属迁移过程中“非稳定形态”比例最高的环节,一定程度上增加了降雨径流污染的水体毒性和潜在生态风险。Zn和Cd在径流颗粒物中都占有最高的含量浓度和非稳定态比例,Pb、Cu、Cr和Ni则在河流沉积物占有较高的非稳定形态比例。(11)应用美国EPA人体暴露风险评价方法对上海城市地表灰尘重金属进行健康风险评价。发现手-口接触行为是儿童摄入地表灰尘重金属的最主要途径,其次为皮肤吸收量和吸入空气量。总体而言,重金属非致癌危害指数和致癌因子指数都在控制范围内,不会对人体造成健康危害。在六种重金属中,Pb的非致癌因子排在首位,其次为Cr和Ni;在三种致癌重金属中,Cr和Ni致癌因子也排在Cd之前,其潜在生态危害值得重视。对污染物在“地表灰尘—降雨径流”系统中环境生态效应作出总体评价,指出要特别关注低于75μm粒径级别灰尘颗粒物的环境效应和健康安全。更多还原

【Abstract】 By the end of this decade, more than half of the world’s population will live in cities. It is clear that the development of urban areas hold the key of many of the challenges we face in our interactions with the environment. Urban areas are complex and dynamic systems that reproduce within their territory the interactions, among geographical and environmental processes on a local, regional, and global scale. This is one of the reasons why urban areas have become an increasing focus for the IGBP and IHDP.Aiming to discuss the research framework and methods of Urban Physical Geography, this paper presents the main findings of a study carried out in Shanghai （China）, during June 2005 to July 2006 with two main purposes: to discuss the pollutants transport processes and mechanisms in rrban surface environmental system; and to evaluate, by means of risk assessment strategies, the potential adverse health effects of the exposure of children living in Shanghai to surface dust.（1） Particles play a role in virtually every process of pollutant behaviors in urban environment by ①deliveringthe contaminants to roadway surfaces as dust and dirt, ②affecting howreadily the contaminants are mobilized during storms, and ③influencing thephysical, chemical and biological transformations that contaminants undergo as they aretransported to receiving waters through sanitary and roadway runoff sewer systems. ④In receiving waters, particles modulate the biological impact that contaminants haveon aquatic and benthic organisms.（2） An understanding of pollutant characteristics on impervious surfaces is essential to estimate pollutant wash off characteristics and to design methods to minimize the impacts of pollutants on the environment. This paper presents data on surface pollutant characteristics on different urban road surfaces in Shanghai city, from samples collected over one year period at weekly interval. Result shows that particle size distribution has the important influence on pollutant concentrations. The <75μm fraction dominates throughout the cascade since it contains the highest levels of all of the heavy metals, and the order refers to Cr>Pb>Cd>Zn>Ni>Cu.（3） A five-step sequential extraction of roadside sediments showed that Zn, Cd and to a lesser degree Ni occur predominantly in the carbonate bound fraction, while Pb is highest in the reducible fraction, Cu in the organic fraction, and Cr in the residual fraction. It was found that the concentrations in the readily available exchangeable fraction were generally low for most metals examined, except for Ni whose exchangeable fraction was appreciable. Considering the proportion of metals bound to the exchangeable and carbonate fractions, the comparative mobility of metals probably decreases in the order of Zn>Pb>Ni>Cd>Cr>Cu.（4） The surface pollutant load data collected in this experimental study on an urban road surface indicate that pollutant buildup occurs over the dry days. The surface pollutant also becomes coarser over the dry days as it is disintegrated by traffic and other factors. The washoff of surface pollutant is dependent on the rainfall and runoff characteristics, but the results here show that common storms only remove a small proportion of the total surface pollutant load. The results also suggest that the rainfall and runoff disintegrates and dissolves more surface pollutant that they can actually remove.（5） Particulate emissions occur whenever vehicles travel over a paved surface such as a road or parking lot. Dust emissions from paved roads have been found to vary with what istermed the "silt loading" present on the road surface as well as the average weight of vehicles traveling the road. The term silt loading （sL） refers to the mass of silt-size material （equal to or less than 75 micrometers [μm] in physical diameter） per unit area of the travel surface. Emission factors of Shanghai surface dust of PM2.5、PM10 and TSP refer to 0.99, 7.64 and 9.17 g/VKT, emission quantities are 1.7,13.1 and 696 thousand t/a. High traffic volμmes in urban areas are responsible for increased Particulate contents within the breathing zone, due to the turbulence in the near-surface atmosphere and suspension of particles from the road surface.（6） Increased stormwater flow and the companying runoff pollution are a direct result of urbanization and the consequent increase in the proportion of land area under impervious surface. Runoff from urban areas is often presumed to be a significant contributor to nonpoint source （NPS） water pollution and has been identified as one of the major causes of the deterioration of the quality of receiving waters. And so, the objectives of this study were to investigate the characteristics of pollutants in storm events, and the relationships between pollutant load and flow-runoff patterns, and to analyze EMCs loadings of pollutants, then revealed "First Flush effect" of road runoff in different functions in Shanghai City.（7） Stormwater quality and quantity were investigated in urbanized catchments in the Central Shanghai city in order to characterize Temporal-spatial distribution and First Flush Effect of stormwater runoff pollution. Sampling locations selected can be grouped into at four sites with different land use categories （traffic, commercial and residential areas）. The result indicates that concentration of contaminants decrease with the increasing of rainfall time. A single index known as event mean concentrations （EMC） can be used to characterize runoff constituents. Several heavy metals such as Pb-Zn-Cu and Cd, Cr-Ni groups show similar environmental behaviors during the runoff process, which reflect their sources in urban environment.（8） Dimensionless cumulative curves of First Flush Effect from four watershed sampling sites for selected storm events, and the magnitude of the first flush phenomenon is calculated using a method of M （V） fitting power curves, parameter b and MFF30 depending M （V） curves are used to illuminate strength of FFE. Result indicates that the magnitude of the first flush phenomenon was found to be greater for high intensity rainfall events and less for low-intensity ones, and strength of FF refers to Ni>Pb>Zn>Cd>Cu>Cr. Compared with total heavy metals, Dissolved heave metals show a less distinctive first flush phenomena（9） The maximum rainfall intensity, Imax, and the time between the start of the event and the occurrence of I_max, T_max, have the most important influence on FFE. The association between MFF30 of heavy metals and Tmax is negative and strongly linear. If rainfall intensity maximum appears earlier (T_max is smaller) it would cause a more distinctive first flush phonomina and therefore a negative correlation between MFF₃₀ of pollutants and T_max is found.（10） The examination of the movement of sediment in the urban environment in terms of the four compartments has proven an effective tool in establishing some trends in the contamination of the urban environment by heavy metals. The overall trend is for the deposits to contain the highest concentrations of Ni, Cu, Cr and Pb, whilst the highest concentrations of Zn and Cd and are found in the transported sediments. Different trends in concentrations are shown by some of the heavy metals such that Cu increases in concentration from source to deposit, Cd decreases in concentration, whilst Ni peaks in value in the transported material. This may reflect the growth of antigenic material such as organic matter diluting the concentration or addition of contaminated material, which would increase it.（11） The use of risk assessment strategies has proved helpful in identifying the routes of exposure to urban surface dust and the trace elements therein of most concern in terms of potential adverse health effects. In Shanghai city, the highest levels of risk seem to be associated with route of ingestion of dust particles, for all the elements included in the study presents a slightly higher risk than ingestion. It appears that the exposure pathway which results in the highest levels of risk for children exposed to street dust is ingestion of this material, and that three elements — Pb, Cr and Ni—are of most concern regarding the potential occurrence of health effects. However, given the large uncertainties associated with the estimates of toxicity values and exposure factors, and the absence of site-specific biometric factors, these results should be regarded as preliminary and further research should be undertaken before any definite conclusions regarding potential health effects are drawn.更多还原