Existence of impervious surface areas (ISA) in cities strongly influences the physical and chemical characteristics of regional soil, therefore, has profound impact on ecosystem carbon cycle at multiple scales. However, due to the inaccessibility of soil sample beneath urban ISA, we know little about the biochemical properties and distribution pattern as well as the importance of soil organic carbon under urban ISA (SOCISA). To clarify this issue, 100-cm-depth soil profiles from 27 paired ISA and pervious surface areas (PSA) sites in northern Tianshan urban cluster in a dryland environment of northwestern China were taken. In order to estimate total soil carbon storage, urban land cover was retrieved from cloud-free Landsat8 images. Based on the data of land cover area and SOC, the soil carbon storage of this urban cluster was calculated. (1) averaged 100-cm-depth SOCISA of the northern Tianshan urban cluster is 5.74±0.39 kgC·m-2, which is significantly lower than the paired soil organic carbon of PSA (SOCPSA) of 8.69±0.75 kgC·m-2, about 52% of the latter (p<0.01); averaged soil bulk density (BD) under ISA BDISA=1.58±0.02 g·cm-3, which is significantly higher than its paired BD of PSA of 1.51±0.02 g·cm-3, about 5% of the latter (p<0.01). (2) SOC and BD of both ISA and PSA declines with depth. The results of linear fitting between SOC, BD, and depth show that SOCISA and BDISA have significantly declining trends, however, SOCPSA and BDPSA does not show such clear trend. In addition, SOCPSA at the 60~100 cm soil layers is significantly higher than SOCISA but there is no stable correlation between them. (3) Carbon storage hidden under ISA of northern Tianshan urban cluster is 68% of the total urban carbon storage and for individual cities this percentage is higher than 50%, therefore, SOCISA is the main part of the urban SOC storage. By revealing the SOCISA and its distribution, this study can facilitate the understanding of biochemical characteristics of soils beneath urban ISA, which is significance for estimating carbon cycling in both urban and global ecosystems.
Desertification is a serious problem worldwide that has environmental and socioeconomic consequences. Desertification research has important significance for protecting the environment and for regional sustainable development. Based on an examination of the connotation of desertification we suggest that desertification not only are caused by human disturbance superimposing on climatic drought in dryland areas of the north, but also can be a result of extreme land degradation due to soil erosion superimposing on physical drought effect in southern humid areas. This study compared different aspects of the desertification processes in dry and humid areas, including material base, climatic conditions, influencing factors, formation forces, core functions, and land surface processes. Finally, we used red beds area of southern China as an example to analyze red beds land degradation by combining on-the-spot investigation and vegetation cover (VFC) data derived from Landsat TM images in 1992-2013. The results show that under the impact of repeated human interference and natural factors, there is a clear trend of vegetation change, topsoil loss, and rock weathering, which produce desert-like landscape. The degradation process in red beds is similar to the Karst rocky desertification and land degradation of red soil in hilly areas, but whether this type of extreme land degradation that took place in the humid area of southern China is "desertification" needs further studying.
Understanding the complexity of spatiotemporal variations of sudden environmental pollution incidents and quantifying the contribution of their driving factors are important for effective environmental management in China. In this study, we analyzed the spatiotemporal patterns of sudden environmental pollution incidents and influencing factors in China for the period of 1995-2012 based on the Exploratory Spatial Data Analysis (ESDA) and Spatial Econometric Panel Model. The results indicate that: the frequency of environmental pollution incidents was gradually declining after the initial fluctuating growth and the high-frequency areas were mainly concentrated in eastern and southwestern China; ESDA analysis revealed that China's environmental pollution incidents were random distributed from 1995 to 2000 and agglomerated after 2001; in recent years the high-frequency area focused on the Pan-Yangtze River Delta region; the high-frequency center moved rapidly in 1998-2001 and 2004-2007 as a consequence of the regional industrial transfer and high pollution discharge pressure, toward southwest and northeast. Environmental pollution incident was different from pollutant emissions and is not an inevitable outcome of economic development. It is mainly related to the level of pollution control, government environmental supervision ability, spatial effect, and other factors. As one of the most important factors influencing environmental pollution incidents, spatial effect mainly included the spatial proximity effect and spillover effect. In order to control environmental pollution incidents effectively, the government should formulate joint transboundary pollution incidents emergency response mechanisms within regions based on regional pollution diffusion and transfer.
The spatial characteristics of Regional Plan Environmental Impact Assessment (RPEIA) determine its sensitivity to spatial scale. Spatial scale of RPEIA is not only a technical issue, but also related to the important questions that RPEIA needs to answer and elaborate. This article discusses the relationship between spatial scale and basic data, the screening of significant environmental factors, and evaluation indicators, as well as the relationship between spatial scale and prediction of atmospheric environmental impact. It then examines two cases: the RPEIA of
Gaoqiao Town (2005)
and the Strategic Environmental Impact Assessment of the economic and social development plan of Pudong New District,
for further elaboration. This article concludes that data collection and integration is a very important step in RPEIA. Different types of basic data posses different spatial characteristics, their spatial scope and resolution should be determined according to the requirements of the RPEIA and regional conditions. The main environmental concerns vary considerably at different spatial scales and they affect the selection of significant environmental factors directly, which in turn affects the corresponding evaluation indicator system. This article also indicates that atmospheric environmental impact prediction and evaluation at large spatial scale focus on the macroscopic description, revealing the general spatial patterns and trends of the spread of air pollutants, while at the local scale is more conducive to explain localized pollution patterns. Emission inventory also emphasizes different spatial characteristics for prediction and evaluation at different scales.
Nitrogen (N) cycle has been poorly characterized in urban ecosystems. In China, urbanization is an important process that alters urban ecosystem and urban nitrogen biogeochemical cycle. Human activities have more than doubled the nitrogen inputs to urbanized areas, and the sources, magnitude, spatiotemporal patterns, and drivers of N fluxes have been mediated by human activities. The imbalance of nitrogen cycle has far exceeded the safe limits of urban sustainable development in some urban areas in China. The urbanized areas are facing a series of environmental problems induced by excessive emission and deposition of reactive nitrogen. Urban smog is becoming very serious in a large number of Chinese cities. However, owing to the limited knowledge on the role of humans in the N biogeochemical cycle and the complexity and uncertainty of urban ecosystems, ecological research of nitrogen emission, deposition, transformation, removal, and retention in urban areas is relatively weak. Thus, comprehensively quantifying changes of nitrogen cycle in urbanized areas and understanding the effects of human activities, such as urbanization and economic development, on the variations of reactive nitrogen fluxes, have been a crucial topic in urban ecological research. This article reviews the state-of-the-art research in this field on the basis of comparison and analysis of Chinese and international studies. The problems exist in current research were summarized and future areas of research aiming at a much improved understanding of the scope of the anthropogenic N problem are discussed. With serious nitrogen pollution and environmental effects in urban areas, it is essential to carry out a long-term study of nitrogen flux and nitrogen budget to investigate the problem of nitrogen imbalance. It is necessary to think beyond the control of pollutant emissions and approach the issue and solution from an urban planning perspective and conduct comprehensive studies to understand the variation of nitrogen input and output trends and driving mechanisms.