岩石圈内部第二深度空间金属矿产资源形成与集聚的深层动力学响应   总被引：9，自引：1，他引：8       下载免费PDF全文

滕吉文  杨立强  刘宏臣  闫雅芬  杨辉  张洪双  张永谦  田有 《地球物理学报》2009,52(7):1734-1756

中国的快速工业化发展和经济腾飞必须有大量金属矿产资源的支撑,在共享世界资源的同时,其根本出路在于立足本土．因此提出第二深度空间（500～2000 m）金属矿产资源的找矿勘探新理念．通过对国内外金属矿产资源地球物理勘探发展的概况分析和研究提出：①金属矿产资源的集聚和分布受控于地壳内部物质与能量的交换和其深层动力过程;②在地壳内部第二深度空间存在着丰富的矿产资源,包括大型和超大型矿床;③必须充分发挥高精度地球物理探测方法的效能,并进行综合技术集成．  相似文献   

The causes and processes responsible for rocky desertification in karst areas of southern China   总被引：2，自引：0，他引：2  

Sen Li  XingHu Wei  JinGuo Huang  XiZhi Wang  GuanYao Lu  HuiXia Li 《寒旱区科学》2009,1(1):0080-0090

The karst region of southern China is a fragile ecological zone with widespread rocky desertification. This paper describes the rocky desertification occurring in this region in terms of both natural and anthropogenic factors. During geological time periods, the region’s changing environment governed the natural rocky desertification processes, whereas during historical and modern times, anthropogenic processes have been superimposed on these natural processes. Human activities have accelerated and exacerbated rocky desertification. The period from the beginning to the middle of the Qing dynasty was an important transitional period in which human activities began to exert a particularly strong influence on rocky desertification. Since then, the effect of anthropogenic factors has increasingly exceeded the effect of natural factors. The rocky desertification process in southern China’s karst region combines surface ecological processes (including vegetation degradation and loss, soil erosion, surface water loss, and bedrock solution) with a reduction of the land’s biological productivity, leading to degradation that produces rocky desert. Controlling rocky desertification requires comprehensive development of sustainable agriculture and economic development that provides employment alternatives to agriculture and thereby promotes the rehabilitation of rocky desertified land.  相似文献   

The sensitivity of ground surface temperature prediction to soil thermal properties Using the Simple Biosphere Model (SiB2)   总被引：1，自引：0，他引：1  

张晓惠  高志球  魏东平 《大气科学进展》2012,29(3):623-634

Using the Simple Biosphere Model (SiB2), soil thermal properties (STP) were examined in a Tibetan prairie during the monsoon period to investigate ground surface temperature prediction. We improved the SiB2 model by incorporating a revised force-restore method (FRM) to take the vertical heterogeneity of soil thermal diffusivity (k) into account. The results indicate that (1) the revised FRM alleviates daytime overestimation and nighttime underestimation in modeled ground surface temperature (T_g), and (2) its role in little rainfall events is significant because the vertical gradient of k increases with increasing surface evaporation. Since the original formula of thermal conductivity (λ) in the SiB2 greatly underestimates soil thermal conductivity, we compared five algorithms of λ involving soil moisture to investigate the cause of overestimation during the day and underestimation at night on the basis of the revised FRM. The results show that (1) the five algorithms significantly improve T_g prediction, especially in daytime, and (2) taking one of these five algorithms as an example, the simulated T_g values in the daytime are closer to the field measurements than those in the nighttime. The differences between modeled T_g and field measurements are mostly within the margin of error of ±2 K during 3 August to 4 September 1998.  相似文献   

On Methods of Teaching Geography     

《The Journal of geography》2012,111(2):70-76

This study investigates the location and varying spatiality of questions in geography textbooks. The results show that study questions posed in page margins address the three components of spatial thinking—concepts of space, using tools of representation, and processes of reasoning—more than questions in other locations within the text. Three practices are particularly recommended to help students develop spatial thinking skills through answering textbook questions: (1) utilize page-margin questions; (2) select questions around spatial representations; and (3) focus on higher-level cognitive processes.  相似文献   

An Evaluation of University World Geography Textbook Questions for Components of Spatial Thinking     

《The Journal of geography》2012,111(5):208-219

ABSTRACT

Geography textbooks contain chapter or review questions that may engage students in spatial thinking. This research used Jo and Bednarz’s (2009) Taxonomy of Spatial Thinking to evaluate the percentage of spatial thinking questions in four university-level world geography course textbooks. The results from this study were then compared to the findings in Jo and Bednarz’s (2009) analysis of high school geography textbooks. Thirty-five percent of university level textbook questions are related to spatial thinking compared to twenty-four percent in high school geography textbooks. The results provide information useful to stakeholders, such as teachers, administrators, and textbook writers and may help these stakeholders to consciously incorporate the three components of spatial thinking as defined by the National Research Council (2006). A simplified taxonomy for identifying spatial-thinking concepts in textbook review questions is also suggested.  相似文献   

LABORATORY OBSERVATIONS OF SEDIMENT ENTRAINMENT BY FREEZING SUPERCOOLED WATER     

SIMON J. COOK  PETER G. KNIGHT  DEBORAH A. KNIGHT  RICHARD I. WALLER 《Geografiska Annaler: Series A, Physical Geography》2012,94(3):351-362

Debris in basal ice produced by glaciohydraulic supercooling is typically characterized by high proportions of silt. A prominent hypothesis for this silt‐dominance is that frazil ice growing in supercooled water preferentially traps silt from sediment‐laden water percolating through it. It has therefore been suggested that silt‐dominance may be diagnostic of glaciohydraulic supercooling. The aim of our work is to test this hypothesis that freezing sediment‐laden supercooled water necessarily produces ice dominated by silt. We do this by simulating two freezing processes under laboratory conditions: (1) percolation of sediment‐laden water through frazil ice; (2) turbulent supercooling and subsequent freezing of sediment‐laden water. In experiments repeated using different particle sizes (sand, silt and clay in individual experiments) both processes entrained sand most effectively and silt least effectively. In experiments using a sediment mixture dominated by medium to coarse silt, both processes produced ice facies dominated by particle sizes between fine sand and coarse silt. These results suggest that silt‐dominance should therefore not be expected for supercooled freeze‐on, and is not a reliable diagnostic signature for supercooling. The silt‐dominated character of basal ice types associated with supercooling may result from other controls such as a silt‐dominated sediment supply or subglacial water flow rates, rather than the freezing process.  相似文献   

Sediment yield of the lower Tana River,Kenya, is insensitive to dam construction: sediment mobilization processes in a semi‐arid tropical river system          下载免费PDF全文

Naomi Geeraert  Fred Ochieng Omengo  Fredrick Tamooh  Paolo Paron  Steven Bouillon  Gerard Govers 《地球表面变化过程与地形》2015,40(13):1827-1838

Dam construction in the 1960s to 1980s significantly modified sediment supply from the Kenyan uplands to the lower Tana River. To assess the effect on suspended sediment fluxes of the Tana River, we monitored the sediment load at high temporal resolution for 1 year and complemented our data with historical information. The relationship between sediment concentration and water discharge was complex: at the onset of the wet season, discharge peaks resulted in high sediment concentrations and counterclockwise hysteresis, while towards the end of the wet season, a sediment exhaustion effect led to low concentrations despite the high discharge. The total sediment flux at Garissa (c. 250 km downstream of the lowermost dam) between June 2012 and June 2013 was 8.8 Mt yr^‐1. Comparison of current with historical fluxes indicated that dam construction had not greatly affected the annual sediment flux. We suggest that autogenic processes, namely river bed dynamics and bank erosion, mobilized large quantities of sediments stored in the alluvial plain downstream of the dams. Observations supporting the importance of autogenic processes included the absence of measurable activities of the fall‐out radionuclides ⁷Be and ¹³⁷Cs in the suspended sediment, the rapid lateral migration of the river course, and the seasonal changes in river cross‐section. Given the large stock of sediment in the alluvial valley of the Tana River, it may take centuries before the effect of damming shows up as a quantitative reduction in the sediment flux at Garissa. Many models relate the sediment load of rivers to catchment characteristics, thereby implicitly assuming that alterations in the catchment induce changes in the sediment load. Our research confirms that the response of an alluvial river to external disturbances such as land use or climate change is often indirect or non‐existent as autogenic processes overwhelm the changes in the input signal. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Tectonics,sedimentation and surface processes: from the erosional engine to basin deposition          下载免费PDF全文

Sébastien Castelltort  Alex Whittaker  Jaume Vergés 《地球表面变化过程与地形》2015,40(13):1839-1846

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Impact of model development,calibration and validation decisions on hydrological simulations in West Lake Erie Basin   总被引：1，自引：0，他引：1       下载免费PDF全文

Prasad Daggupati  Haw Yen  Michael J. White  Raghavan Srinivasan  Jeffrey G. Arnold  Conor S. Keitzer  Scott P. Sowa 《水文研究》2015,29(26):5307-5320

Watershed simulation models are used extensively to investigate hydrologic processes, landuse and climate change impacts, pollutant load assessments and best management practices (BMPs). Developing, calibrating and validating these models require a number of critical decisions that will influence the ability of the model to represent real world conditions. Understanding how these decisions influence model performance is crucial, especially when making science‐based policy decisions. This study used the Soil and Water Assessment Tool (SWAT) model in West Lake Erie Basin (WLEB) to examine the influence of several of these decisions on hydrological processes and streamflow simulations. Specifically, this study addressed the following objectives (1) demonstrate the importance of considering intra‐watershed processes during model development, (2) compare and evaluated spatial calibration versus calibration at outlet and (3) evaluate parameter transfers across temporal and spatial scales. A coarser resolution (HUC‐12) model and a finer resolution model (NHDPlus model) were used to support the objectives. Results showed that knowledge of watershed characteristics and intra‐watershed processes are critical to produced accurate and realistic hydrologic simulations. The spatial calibration strategy produced better results compared to outlet calibration strategy and provided more confidence. Transferring parameter values across spatial scales (i.e. from coarser resolution model to finer resolution model) needs additional fine tuning to produce realistic results. Transferring parameters across temporal scales (i.e. from monthly to yearly and daily time‐steps) performed well with a similar spatial resolution model. Furthermore, this study shows that relying solely on quantitative statistics without considering additional information can produce good but unrealistic simulations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Application of Advanced Oxidation Processes for Polycyclic Aromatic Hydrocarbons Removal from Municipal Treatment Sludge          下载免费PDF全文

Gizem Karaca  Yücel Tasdemir 《洁净——土壤、空气、水》2015,43(2):191-196

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