Origin and evolution of closed depressions in central Belgium,European loess belt     

T. Vanwalleghem  J. Poesen  I. Vitse  H. R. Bork  M. Dotterweich  G. Schmidtchen  J. Deckers  A. Lang  B. Mauz 《地球表面变化过程与地形》2007,32(4):574-586

Closed depressions (CDs) are lower lying areas where the sediment eroded from the surrounding soil surfaces draining towards the CD is trapped in the system. CDs have been reported in several regions of the European loess belt and are attributed either to natural processes (e.g. dissolution of subsurface horizons) or to human intervention (e.g. quarrying). Previous studies focussed mainly on cropland areas where, however, only few and largely filled in CDs remain. The objectives of this study were to i) assess the spatial distribution of CDs under forest and cropland, ii) to determine and compare the morphology of CDs under forest and under cropland, and iii) to determine the origin and age of these CDs under forest. In a study area located partly in ancient forest (13 km²) and partly in cropland (29 km²), a systematic survey revealed the presence of 71 CDs under forest (5·3 CD.km^?2) and 30 CDs under cropland (1 CD.km^?2). Comparison of their morphology showed that CDs under forest were significantly deeper, with steeper sidewalls and a smaller surface area because of the erosion and deposition processes acting on the CDs under cropland. By comparing CDs that had been under cropland for different time intervals, the rate of this morphological evolution could be reconstructed. Analysis of the soil stratigraphy of two representative CDs in the ancient forest area confirmed their origin as quarries. Most probably, calcareous loess was excavated since this soil horizon, about two to five meters thick, was completely absent within the CDs. Dating of the infilling of one CD by optically stimulated luminescence (OSL) shows that the CD filled in between the first century BC and the fourth century AD. This dating corresponds to the dating of sediment deposits in nearby, human‐induced gullies that were attributed to an agricultural land use phase between the 18th century BC and the third century AD.  相似文献   

Numerical modelling of chloride propagation in the quaternary aquifer of the southern Upper Rhine Graben     

U. Lang  T. Gudera  P. Elsass  G. Wirsing 《International Journal of Earth Sciences》2005,94(4):550-564

The deep groundwater in the quaternary gravel sequence of the southern Upper Rhine Graben locally contains high chloride concentrations near the river Rhine between Fessenheim (France) in the South and Breisach (Germany) in the North. This historical pollution is mainly due to past infiltration from the former brine storage basins of the French potash mines on the Fessenheim Island and—to a lesser extent—from the leaching of the salt dumps of the German potash mines in Buggingen and Heitersheim. The spreading of the salt plume was investigated by means of a groundwater model. The aim of the model was to understand the brine movement, the present distribution of chloride as defined by recent hydrochemical investigations, and to select locations for new reconnaissance boreholes. The geological structure was reproduced by a three layer model, which was calibrated for steady state flow conditions. The hydraulic conductivity of the first layer was determined by comparing measured and calculated heads in the model area. The vertical resolution was refined to simulate the density-dependent salt transport processes. The transport of the salt plumes was simulated over a 40-year period, starting at the beginning of brine storage in the 1950s. The relevant transport parameters have been estimated in a sensitivity analysis, where the simulated breakthrough curves of chloride concentration have been compared with the measured data. The results of the groundwater model indicate that brines containing approximately 1 million tons of chloride are still present at the bottom of the aquifer. These highly concentrated salt brines mix with fresh water from the upper part of the aquifer. This dispersive process leads to the formation of a plume of chloride-rich water extending downstream, where pumping wells for several local water supplies are located.  相似文献   

A multibeam H i survey of the Virgo cluster – two isolated H i clouds?     

J. Davies  R. Minchin  S. Sabatini  W. van Driel  M. Baes  P. Boyce  W. J. G. de Blok  M. Disney  Rh. Evans  V. Kilborn  R. Lang  S. Linder  S. Roberts  R. Smith 《Monthly notices of the Royal Astronomical Society》2004,349(3):922-932

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Carbon biogeochemistry of ground water, Guiyang, southwest China   总被引：4，自引：0，他引：4  

Li SL  Liu CQ  Tao FX  Lang YC  Han GL 《Ground water》2005,43(4):494-499

Variations in the concentrations and isotopic compositions (delta13C(DIC)) of dissolved inorganic carbon (DIC) reflect contamination and biogeochemical cycling of the carbon in ground water. In order to understand contamination and biogeochemical cycling of DIC, we carried out research on the geochemistry of ground water of Guiyang, the capital city of Guizhou Province, China. Results show that ground water is mainly characterized by SO4.HCO3-Ca.Mg and HCO3-Ca.Mg chemical compositions. The hydrochemical characteristics of these types of water are mainly controlled by lithology of the aquifers. HCO3- is the dominant species of DIC in ground water and has lower concentrations and more negative values of delta13C(DIC) in the high-flow (summer monsoon) season, as compared to the low-flow season. This indicates that DIC is relatively enriched in carbon of biological origin in the high-flow season as compared to the low-flow season and that biological activities are the predominant control on shifts of stable carbon isotope values. The evidence that the delta13C(DIC) values of ground water decrease with increasing concentrations of anthropogenic species shows that the carbon isotopic composition of DIC can be a useful tracer of contamination, in addition to biogeochemical cycling of inorganic carbon in ground water. Results from this study show that ground water is impacted by significant levels of contamination from human activities, especially in the urban areas, as well as the northeast and west suburbs, in Guiyang city, southwest China.  相似文献   

The Use of Dual-Doppler Radar Data in the Study of 1998 Meiyu Frontal Precipitation in Huaihe River Basin     

Xu Hui  Zhang Weiping  Lang Xuxing  Guo Xi  Ge Wenzhong  Dang Renqing  TakaoTakeda 《大气科学进展》2000,17(3):403-412

During the Meiyu period in June and July of 1998, intensified field observations have been carried out for the project “Huaihe River Basin Energy and Water Cycle Experiment (HUBEX)”. For studying Meiyu front and its precipitation in Huaihe River basin, the present paper has performed analysis on the middle and lower level wind fields in the troposphere by using the radar data obtained from the two Doppler radars located at Fengtai district and Shouxian County. From June 29 to July 3 in 1998, the continuous heavy precipitation occurred in Huaihe River basin around Meiyu front. The precipitation process on July 2 occurred within the observation range of the two Doppler radar in Fengtai district and Shouxian County. The maximum rainfall of the Meiyu front was over 100 mm in 24 h, so it can be regarded as a typical mesoscale heavy precipitation process related to Meiyu front. Based on the wind field retrieved from the dual Doppler radar, we find that there are meso-γ scale vertical circulations in the vertical cross-section perpendicular to Meiyu front, the strong upward motion of which corresponds to the position of the heavy rainfall area. Furthermore, other results obtained by this study are identical with the results by analyzing the conventional synoptic data years ago. For example: in the vicinity of 3 km level height ahead of Meiyu front there exists a southwest low-level jet; the rainstorm caused by Meiyu front mainly occurs at the left side of the southwest low-level jet; and the Meiyu front causes the intensification of the low-level convergence in front of it.  相似文献   

Time of emergence of climate signals over China under the RCP4.5 scenario   总被引：1，自引：0，他引：1  

Yue Sui  Xianmei Lang  Dabang Jiang 《Climatic change》2014,125(2):265-276

The signal of climate change is emerging against a background of natural internal variability. The time of emergence (ToE) is an indicator of the magnitude of the climate change signal relative to this background variability and may be useful for climate impact assessments. In this work, we examined the ToE of surface air temperature and precipitation over China under a medium mitigation scenario Representative Concentration Pathway 4.5 based on 30 satisfactory global climate models that are chosen from the Coupled Model Intercomparison Project Phase 5. Major conclusions are: the earliest ToE of annual and seasonal temperature occurs in the eastern Qinghai-Tibetan Plateau between 2006 and 2012 for S/N?>?1.0 and between 2020 and 2030 for S/N?>?2.0, which is 10–20 years sooner than in Northeast China where the latest ToE appears in the country. Consistent with previous studies at the global scale, the median ToE for most of China occurs sooner in summer (2008–2020 for S/N?>?1.0 and 2020–2045 for S/N?>?2.0), while for Northeast and North China the median ToE occurs sooner in autumn (2015–2025 for S/N?>?1.0 and 2040–2050 for S/N?>?2.0). For the ToE of temperature, the inter-model uncertainty is at least 24 years in all five regions of concern and more than 85 years in some seasons, and the inter-model uncertainty in one season for which the earliest median ToE occurs is the smallest among the seasons. For precipitation, the early ToE occurs in the northeastern Qinghai-Tibetan Plateau for the annual mean, and seasonally it occurs first in winter in northern Northeast China and southwestern Northwest China and in winter and spring in the northeastern Qinghai-Tibetan Plateau. For southern China, the median ToE will not occur until 2090.  相似文献   

基于AutoLISP的数字地形图塔基断面自动提取程序设计     

周浪  赵胜其  杨春燕  刘海军 《测绘工程》2014,23(11):74-77

随着电力事业的发展,架空送电线路电力勘测塔基断面显得十分重要,同时也是结构专业塔基基础设计的参考依据.文中分析目前电力勘测塔基断面获取的方法和DXF文件的编码格式,利用实测的大比例尺数字塔基地形图,基于AutoLISP编程实现数字塔基、地形图塔基断面自动提取存储的方法.提取的塔基断面数据与实测数据对比,证明方法具有可靠性、准确性、自动化程度高等特点,满足设计要求,弥补传统塔基断面数据获取的不足,提高数据处理效率.  相似文献   

Vegetation feedback under future global warming   总被引：2，自引：0，他引：2  

Dabang Jiang  Ying Zhang  Xianmei Lang 《Theoretical and Applied Climatology》2011,106(1-2):211-227

It has been well documented that vegetation plays an important role in the climate system. However, vegetation is typically kept constant when climate models are used to project anthropogenic climate change under a range of emission scenarios in the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios. Here, an atmospheric general circulation model, and an asynchronously coupled system of an atmospheric and an equilibrium terrestrial biosphere model are forced by monthly sea surface temperature and sea ice extent for the periods 2051?C2060 and 2090?C2098 as projected with 17 atmosphere?Cocean general circulation models participating in the IPCC Fourth Assessment Report, and by appropriate atmospheric carbon dioxide concentrations under the A2 emission scenario. The effects of vegetation feedback under future global warming are then investigated. It is found that the simulated composition and distribution of vegetation during 2051?C2060 (2090?C2098) differ greatly from the present, and global vegetation tends to become denser as expressed by a 21% (36%) increase in global mean leaf area index, which is most pronounced at the middle and high northern latitudes. Vegetation feedback has little effect on globally averaged surface temperature. On a regional scale, however, it induces statistically significant changes in surface temperature, in particular over most parts of continental Eurasia east of about 60°E where annual surface temperature is expected to increase by 0.1?C1.0?K, with an average of about 0.4?K for each future period. These changes can mostly be explained by changes in surface albedo resulting from vegetation changes in the context of future global warming.  相似文献   

利用VB控件监视与管理时间服务器     

蔡菲菲  刘爱民  郎宏山 《气象科技》2011,39(6):818-822

在极轨气象卫星数据接收系统中,时间统一性对气象卫星资料接收质量有着重要影响。因此需要时间服务器为系统提供统一的时间基准,从而保证卫星资料的完整按时接收。由于GPS时钟具有稳定、准确的特点,将其作为时间服务器的信号源。为了保证GPS时间服务器正常工作,有必要对其进行状态监视。在VB60环境下,利用串口通信成功实现了对时间服务器的监视、管理功能。监视功能为时间服务器故障的发现、定位与记录提供了重要依据。管理功能包括参数查询、功能设置等,方便用户对时间服务器的操作。  相似文献   

北京及附近地区地壳速度结构与构造   总被引：2，自引：0，他引：2  

王帅军  王夫运  张成科  黄灿  杨雅琼  齐浪 《华北地震科学》2011,29(2):6-12

利用研究区多条地震测深剖面段观测资料解释及多条剖面段的模型数据计算出了研究区结晶基底及莫霍面深度等深线结果,对该地区地壳深部速度结构与构造进行了较详细研究.结果表明,地壳深部速度结构与构造在纵向和横向上具有明显的不均一性,浅部基底断裂发育;研究区莫霍面等深线总体特征显示出从东向西逐渐加深趋势,局部区域显示异常变化,变化...  相似文献