Critical velocity in phosphorus exchange processes across the sediment-water interface

Sediments are ultimate sinks of nutrients in lakes that record the pollution history evolutionary processes, and anthropogenic activities of a lake. However, sediments are considered as inner sources of environmental factor changes such as the variation in hydrodynamic conditions because of the nutrients they release. How does this process happen？ This study investigates a typical nutrient phosphorus （P） exchange among sediment, suspended particle matter （SPM）, and water. Compared with numerical and experimental studies, this study confirms that the critical velocity that occurs at a lower flow rate state exists in the range of 7 to 15 crn/sec. Critical velocity below the critical flow rate promotes the migration of particulate phosphorus （PP） to the SPM. On the other hand, critical velocity above the critical flow rate promotes the release of PP in water.     

Cumulative impact assessment in environmental planning: A coastal wetland watershed example

Several theoretical, analytical, and institutional difficulties have impeded the development and application of the assessment of cumulative environmental impacts. Watershed development on coastal wetlands offers an ideal context for evaluating the land disturbance target approach to cumulative impact assessment. A model land use planning system involving a time series approach was developed for Elkhorn Slough in California. The approach included four major components: evaluation of erosion susceptibility, measurement of land disturbance, establishment of a land disturbance target, and a comparison of existing and target land disturbance values. Further research is needed to test the transferability of the approach in a wide range of coastal watersheds and to verify the applicability of the methods to other cumulative impact problems.     

城市火灾中飞火蔓延距离计算方法研究

飞火是城市火灾特别是城市震后火灾的重要蔓延方式之一,它可以使火灾在相距较远的离散可燃物之间进行跳跃式蔓延,从而增加了扑救难度,威胁扑救人员的安全。因此,对飞火蔓延现象的认识和飞火蔓延距离的计算是降低飞火危险性的前提。基于Baum-McCaffrey火焰羽流模型,重点研究在城市火灾羽流中球形飞火颗粒的上升行为和环境风影响...     

杭州市城郊土壤重金属含量和形态的研究

研究了杭州市城郊文教居民区、风景旅游区、市郊农业区、市内商业区和市郊工业区等5种土地利用背景下的32个土样中8个重金属元素（Cd、Co、Cr、Cu、Ni、Pb、Zn、Mn）的含量和形态。结果表明，杭州市城郊土壤已受重金属的明显污染，其中以Pb的污染最为严重。污染程度为：市郊工业区＞市内商业区＞风景旅游区＞文教居民区＞市郊农业区。用连续提取方法对重金属分级表明，Cd、Co、Cr和Ni主要以残余态为主，平均占总量的60％以上，而Cu、Pb、Zn和Mn主要以酸可提取态、氧化物结合态和有机结合态存在，有较大的释放潜力和生物有效性。     

Urbanization and its impact on groundwater: a remote sensing and GIS-based assessment approach

The perils of unplanned urbanization and increasing pressure of human activities on hydro-geomorphologic system often result in modification of the existing recharge mechanism, which leads to many environmental consequences. In the present research, an attempt has been made to investigate the applicability of remote sensing and geographical information system (GIS) in dealing with spatial and temporal variability of dynamic phenomena, like urbanization and its impact on groundwater. This paper covers primarily, quantitative and qualitative impacts of urban growth on the behavior of aquifer in Ajmer city (India). Urban growth of the Ajmer city in last 17 years has been estimated from the satellite images. Database related to urbanization and groundwater has been created in GIS. Groundwater recharge has been computed using a water balance approach known as Water Level Fluctuation Methodology. Recharge estimation methodology has been implemented in GIS to introduce the spatial variability of hydro-geological characteristics. Further, temporal and spatial variations in groundwater quality and quantity have been correlated with urban growth using overlay analysis in GIS. The study reveals a general decline in water table and quality with urbanization. Further, remote sensing and GIS technologies have been found useful in assessment of spatial and temporal phenomena of urbanization and its impact on groundwater system.     

Cooperative Game Among Cities in Urban Agglomerations and Economical Sustainable Development

This paper analyses redounded profits of cooperation and non-cooperation among cities in urban agglomerations based on game theory. It discusses the problems of economical development among cities with feeble cooperation, and deduces the conclusion that only cooperation of cities produces the maximum profits and realizes Pareto efficiency for cities and urban agglomerations. The paper states that cooperation is the cornerstone of economic sustainable development in urban agglomerations in profits produced by cooperation among cities. Some suggestions to accelerate cooperation among cities are proposed.     

Impact of urbanization on hydrochemical evolution of groundwater and on unsaturated-zone gas composition in the coastal city of Tel Aviv, Israel

The coastal city of Tel Aviv was founded at the beginning of the 20th century. The number of its inhabitants and its water consumption increased rapidly. This study analyses a 15-year record (1934-1948) of pre-industrial development of groundwater chemistry in the urban area. Archive data on concentrations of major ions, dissolved gases (CO2 and O2), organic matter, and pH were available for each half-year during the period of 1934-1948. The major factors causing changes in the chemistry of groundwater flowing in three sandy sub-aquifers have been seawater encroachment due to overpumping, and infiltration of effluents from pit-latrine collectors. Influence of these factors decreases with depth. Landward-penetrating seawater passed through clayey coastal sediments, interbedded among sands and calcareous sandstones, and spread into the Kurkar Group aquifer. This has led to exchange of sodium (dominant in seawater) with calcium adsorbed on clay particles, enriching groundwater with calcium. Intensity of cation exchange decreases inland and with depth. Infiltration of pit-latrine effluents has introduced large amounts of ammonium into the unsaturated zone. Its rapid oxidation in unsaturated sediments has caused massive nitrate production, accompanied by pore-water acidification. This process induces dissolution of vadose carbonate, resulting in enrichment of groundwater recharge in calcium. Anthropogenically induced dissolution of calcite in the unsaturated zone has been the major factor for the increase of Ca2+ concentration in groundwater, accounting for about 80% of this increase. In the interface zone, an additional 20% of calcium has been supplied by cation exchange. Owing to pH increase caused by denitrification in the aquifer, Ca(2+)-rich waters supersaturated with calcite could be formed, especially in the capillary fringe of the uppermost sub-aquifer, which could induce calcite precipitation and ultimately lead to the cementation of sandy aquifers. Urban development has caused drastic changes in the gas content in the unsaturated zone and in groundwater. Carbon dioxide was intensively generated by nitrification-denitrification processes, by hydration of urea, to a lesser degree by oxidation of organic matter, and probably by anoxic biodegradation of organics. Between 1934 and 1948, concentrations of CO2 in unsaturated sediment air rose from 3.2% to 7.6%. In the unsaturated zone, oxygen consumption for oxidation of ammonium and organic matter lowered O2 concentrations in sediment air to unusually low values of 3.9-12.9%. Nitrification in the urban unsaturated zone could thus serve as a pump, sucking in atmospheric oxygen at a rate of about 0.3-0.5 g m-2 day-1. The extreme concentrations of CO2 and O2 in unsaturated sediments have been preserved due to production and consumption of gas under conditions of diminishing areas open to the atmosphere, uncovered by buildings and by roads.     

武汉城市圈城市用地扩张对经济增长贡献度的动态研究——“两型社会”试验区设置前后的比较

运用索洛余值法量化测度武汉城市圈"两型社会"试验区设置前后(2000~2006年和2007~2012年)各县区的TEP以及资本、劳动、土地、中间投入品等生产要素供给对经济增长的贡献度,为促进武汉城市圈供给侧结构性改革及提升土地要素产出效率提供参考。结果显示:武汉城市圈经济发展主要依靠资本、劳动等生产要素的投入以及技术进步,土地扩张对经济增长的影响相对较低,中间投入品的影响微弱;武汉城市圈"两型社会"实验区的规划设置提升了土地要素供给对经济发展的贡献率,城市土地扩张的产出效率有所增强,但在要素投入中仍显微弱、增幅较小,ΔES与ΔTEP的差距与对应区域产业结构对土地投入的依赖性呈反比。研究发现:武汉城市圈在经济发展中需要继续推进技术革新,加大对劳动力素质的培训及优质人才的吸引,促进经济增长方式由粗放转向集约;大力推行政策扶持以提高土地对经济的参与程度,以城市圈为整体统筹规划城市用地的供给,根据区域产业结构和资源优势制定差别化的土地供给与经济发展政策,从"供给侧改革"出发在作用原理及机制上集约利用土地。     

ALAWAT: A spatially allocated watershed model for approximating stream,sediment, and pollutant flows in Hawaii,USA

The Ala Wai Canal Watershed Model (ALAWAT) is a planning-level watershed model for approximating direct runoff, streamflow, sediment loads, and loads for up to five pollutants. ALAWAT uses raster GIS data layers including land use, SCS soil hydrologic groups, annual rainfall, and subwatershed delineations as direct model parameter inputs and can use daily total rainfall from up to ten rain gauges and streamflow from up to ten stream gauges. ALAWAT uses a daily time step and can simulate flows for up to ten-year periods and for up to 50 subwatersheds. Pollutant loads are approximated using a user-defined combination of rating curve relationships, mean event concentrations, and loading/washoff parameters for specific subwatersheds, land uses, and times of year. Using ALAWAT, annual average streamflow and baseflow relationships and urban suspended sediment loads were approximated for the Ala Wai Canal watershed (about 10,400 acres) on the island of Oahu, Hawaii. Annual average urban suspended sediments were approximated using two methods: mean event concentrations and pollutant loading and washoff. Parameters for the pollutant loading and washoff method were then modified to simulate the effect of various street sweeping intervals on sediment loads.     

Urbanisation and greening of Indian cities: Problems,practices, and policies

Progress of the Indian economy is threatened by the impact of climate change. Generation of urban heat islands (UHIs), waning of urban green cover, increase in carbon emissions and air pollution deteriorate the living environment. Rise in urban temperatures and heat stress induced mortality remain major concerns. Although the National Action Plan on Climate Change emphasises the national missions of ‘enhanced energy efficiency’, and ‘green India’, little research has been devoted to explore the passive cooling potential of urban greenery in India, thus lending uniqueness to this study. The manifestations of unplanned urban development (UHIs, escalated carbon emissions, air pollution) are discussed and corroborated with identification of contributory factors. Contemporary greening practices and bye-laws in four major Indian cities (New Delhi, Pune, Chennai, and Visakhapatnam) are analysed and compared with global best practices. The findings are used to propose planning guidelines which are expected to assist in consolidating natural sustainability of emerging economies.