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Field observations of flow and sediment transport in a tributary channel through intertidal mudflats indicate that suspended sediment was closely linked to advection and dispersion of a tidal salinity front. During calm weather when tidal forcing was dominant, high concentrations of suspended sediment advected up the mudflat channel in the narrow region between salty water from San Francisco Bay and much fresher runoff from the small local watershed. Salinity and suspended sediment dispersed at similar rates through each tidal inundation, such that during receding ebbs the sediment pulse had spread spatially and maximum concentrations had decreased. Net sediment transport was moderately onshore during the calm weather, as asymmetries in stratification due to tidal straining of the salinity front enhanced deposition, particularly during weaker neap tidal forcing. Sediment transport by tidal forcing was periodically altered by winter storms. During storms, strong winds from the south generated wind waves and temporarily increased suspended sediment concentrations. Increased discharge down the tributary channels due to precipitation had more lasting impact on sediment transport, supplying both buoyancy and fine sediment to the system. Net sediment transport depended on the balance between calm weather tidal forcing and perturbations by episodic storms. Net transport in the tributary channel was generally off-shore during storms and during calm weather spring tides, and on-shore during calm weather neap tides. 相似文献
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实现资源信息GIS辅助决策系统方案的探讨 总被引：1，自引：0，他引：1
GIS技术和网络技术的发展，为资源信息海量数据管理、资源信息共享的社会化服务和综合利用提供了技术保障，建立一个以国家资源信息基础数据库建设为依托的，集海量资源信息管理、查询、应用、服务为一体的计算机应用系统，对全国或区域性资源信息进行管理和监控，提高处理效率，为多尺度、多类型的资源信息提供海量存储工具，为资源评价多目标综合分析和管理提供网络操作对资源信息的空间特征，阐述资源信息GIS系统运行机制、空间数据库数据模型、专业空间分析GIS集成技术、资源信息可视化的实现方案。 相似文献
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A discharge flow apparatus with chemiluminescence detector has been used to study the reaction O + ClO --> Cl + O2, where O2 = O2(a1 delta g) or O2(b1 sigma+ g). The measured quantum yields for producing O2(a1 delta g) and O2(b1 sigma+ g) in the above reaction are less than 2.5 x 10(-2) and equal to (4.4 +/- 1.1) x 10(-4), respectively. The observed O2(a1 delta g) airglow of Venus cannot be explained in the context of standard photochemistry using our experimental results and those reported in recent literature. The possibility of an alternative source of O atoms derived from SO2 photolysis in the mesosphere of Venus is suggested. 相似文献
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Mossello MT 《Rivista geografica italiana》1986,93(3):285-298
Migration trends in Italy since the early 1970s are reviewed. The author notes that a change occurred during the 1970s away from south-north migration and migration to the largest cities toward migration to the northeast and center of the country and toward medium-sized cities. Furthermore, overall mobility declined, and short-range migration as a percentage of overall migration increased. The implications of these trends for spatial policy and the implications of a growth of immigration are considered. (SUMMARY IN ENG AND FRE) 相似文献
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Lake Bonney, a permanently ice-covered Antarctic lake, has a middepth maximum N2O concentration of 41.6 micromoles N (>580,000% saturation with respect to the global average mixing ratio of N2O) in its east lobe, representing the highest level yet reported for a natural aquatic system. Atmospheric N2O over the lake was 45% above the global average, indicating that this lake is an atmospheric source of N2O. Apparent N2O production (ANP) was correlated with apparent oxygen utilization (AOU), and denitrification was not detectable, implying that nitrification is the primary source for this gas. The slope of a regression of ANP on AOU revealed that potential N2O production per unit of potential O2 consumed in the east lobe of Lake Bonney is at least two orders of magnitude greater than reported for the ocean. The maximum yield ratio for N2O [ANP/(NO2(-) + NO3-)] in Lake Bonney is 26% (i.e. 1 atom of N appears in N2O for every 3.9 atoms appearing in oxidized N), which exceeds previous reports for pelagic systems, being similar to values from reduced sediments. Areal N2O flux from the lake to the atmosphere is >200 times the areal flux reported for oceanic systems; most of this gas apparently enters the atmosphere through a small moat that occupies approximately 3% of the surface of the lake and exists for approximately 10 weeks in summer. 相似文献