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The middle class in metropolitan Chinese cities has become an important social group. With the rapid development of urbanization and constant advancement of suburbanization, the middle class has increasingly come to influence city traffic. Research into middle-class commuting activities thus has practical significance for improving traffic congestion and reducing the commuting burden in metropolitan cities. Based on a dataset formed by 816 completed surveys, this paper analyzes the commuting mode, time and distance of middle-class residents in Guangzhou City using the descriptive statistical method. The results indicate that private cars are the main commuting mode, followed by public transport. Meanwhile, middle-class residents mainly undertake medium-short time and medium- short distance commuting. The study subsequently uses multilevel logistic regression and multiple linear regression models to analyze the factors that influence commuting mode choice, time and distance. The gender, age, number of family cars, housing source and jobs-housing balance are the most important factors influencing commuting mode choice; housing, population density, jobs-housing balance and commuting mode significantly affect commuting time; and transport accessibility, jobs-housing balance and commuting mode are the notable factors affecting commuting distance. Finally, this paper analyzes what is affecting the commuting activities of middle-class residents and determines the differences in commuting activity characteristics and influence factors between middle-class and ordinary residents. Policy suggestions to improve urban planning and urban management are also proposed. [ABSTRACT FROM AUTHOR]

Environmental pollution from industrialization, urbanization and agriculture is a serious issue facing all countries during economic development. The Pearl River Delta in Southern China offers a unique case for study and documentation on the ecosystem changes during the fast economic development and urbanization over the past 40 years. This collection of papers from a conference on marine coastal pollution and ecotoxicology held in Guangzhou of China provide the current status on the environmental and ecological processes from the intensive urbanization and development. The research information available from this special issue can be used for both a comparison over time and with other locations and countries, and, in addition, for policy making to serve the long-term sustainable development of the region and the world. [ABSTRACT FROM AUTHOR]

Anthropogenic factors resulted from the urbanization may affect the groundwater As in urbanized areas. Groundwater samples from the Guangzhou city (South China) were collected for As and other parameter analysis, in order to assess the impact of urbanization and natural processes on As distribution in aquifers. Nearly 25.5 % of groundwater samples were above the WHO drinking water standard for As, and the As concentrations in the granular aquifer (GA) were generally far higher than that in the fractured bedrock aquifer (FBA). Samples were classified into four clusters by using hierarchical cluster analysis. Cluster 1 is mainly located in the FBA and controlled by natural processes. Anthropogenic pollution resulted from the urbanization is responsible for high As concentrations identified in cluster 2. Clusters 3 and 4 are mainly located in the GA and controlled by both natural processes and anthropogenic factors. Three main mechanisms control the source and mobilization of groundwater As in the study area. Firstly, the interaction of water and calcareous rocks appears to be responsible for As release in the FBA. Secondly, reduction of Fe/Mn oxyhydroxides and decomposition of organic matter are probably responsible for high As concentrations in the GA. Thirdly, during the process of urbanization, the infiltration of wastewater/leachate with a high As content is likely to be the main source for groundwater As, while NO contamination diminishes groundwater As. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition in subtropical metropolitan regions has increased greatly because of rapid urbanization, and such increase could lead to N-related changes in soil properties and plant diversity in remnant forests of urban ecosystems. To investigate the pattern of atmospheric N deposition along an urban-rural gradient in metropolitan Guangzhou, southern China, and to assess the potential influence of N deposition on soil properties and understory plant diversity in remnant forests, precipitation, and soil samples were collected and vegetation was surveyed from four forest sites between March 2010 and March 2011. The atmospheric inorganic nitrogen deposition (DIN) decreased with increasing distance from the urban center: DIN inputs were 43.3, 41.2, 35.2, and 30.1 kg N ha year in two urban sites, a suburban site and a rural site, respectively. However, forest soil N status (NH-N, NO-N, and total nitrogen) showed the opposite pattern. Understory herb-layer diversity was negatively correlated to DIN input and positively correlated to soil calcium (Ca) and potassium (K) concentrations and pH; with highest herb-layer diversity found in the rural site receiving the lowest amount of DIN input. These results indicated that higher DIN along with soil acidification and leaching of base cations (Ca and K) might change the current N status and increase nutrients leaching and thereby cause reductions in understory plant diversity. A regional policy linking atmospheric pollution and land protection is needed to protect the most N-sensitive herb species (e.g., forbs and ferns) in these remnant forests. [ABSTRACT FROM AUTHOR]