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11.
Small-scale vegetation dynamics were followed for ecotones and in uniform stands inArtemisia-dominated steppe vegetation under grazing and when recovering from heavy grazing. Species composition was followed annually for 5 years in 1 m2and 0·25 m2plots for (1) presence–absence; (2) density; and (3) biomass.More rapid vegetation dynamics, in terms of change of type of vegetation and distance moved in DCA species space between sampling occasions, were observed in smaller plots and in early seral stages, where species were few and alpha diversity low. Only the plots recently protected from grazing showed a directional vegetation change; those protected for more than 3 years and those under continued grazing showed, at this scale, non-directional dynamics. 相似文献
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乌鲁木齐西山断层新构造运动特征 总被引:4,自引:0,他引:4
展布于哈萨克斯坦—准噶尔亚板块南缘西山南麓的乌鲁木齐西山断层,构造地貌发育,航卫片上线性影象清晰,呈舒缓波状。断面倾向NWW,倾角60°~83°。破碎带宽约100m,内含多个断面,构成叠瓦状构造,逆冲量颇大。在走向近NE区段有一定左行走滑活动分量。新构造运动使侏罗系逆冲到中更新统之上,断层断错了全新统的冲积层。由中强地震沿西山断层分布资料显示,现今仍为粘滑活动。经14C测年确定,最近两次明显粘滑活动时间为4759a和493a,其时间间隔为4266a,其中一个断面的逆冲量分别为1.0m和0.25m。 相似文献
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西秦岭铀矿床含矿热液物理化学条件改变对铀沉淀影响 总被引:2,自引:0,他引:2
本文研究了西秦岭铀矿床含矿热液物理化学条件的改变对铀沉淀富集的影响。研究表明,铀在相对还原条件下迁移,而在相对氧化条件下沉淀富集。铀的沉淀富集主要发生在含矿热液的温度、压力和氧逸度大幅度降低,酸性增强及氧化-还原电位增高的物理化学条件下。 相似文献
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G. C. Poole J. A. Stanford S. W. Running C. A. Frissell W. W. Woessner B. K. Ellis 《地球表面变化过程与地形》2004,29(10):1259-1274
Geomorphology interacts with surface‐ and ground‐water hydrology across multiple spatial scales. Nonetheless, hydrologic and hydrogeologic models are most commonly implemented at a single spatial scale. Using an existing hydrogeologic computer model, we implemented a simple hierarchical approach to modeling surface‐ and ground‐water hydrology in a complex geomorphic setting. We parameterized the model to simulate ground‐ and surface‐water ?ow patterns through a hierarchical, three‐dimensional, quantitative representation of an anabranched montane alluvial ?ood plain (the Nyack Flood Plain, Middle Fork Flathead River, Montana, USA). Comparison of model results to ?eld data showed that the model provided reasonable representations of spatial patterns of aquifer recharge and discharge, temporal patterns of ?ood‐water storage on the ?ood plain, and rates of ground‐water movement from the main river channel into a large lateral spring channel on the ?ood plain, and water table elevation in the alluvial aquifer. These results suggest that a hierarchical approach to modeling ground‐ and surface‐water hydrology can reproduce realistic patterns of surface‐ and ground‐water ?ux on alluvial ?ood plains, and therefore should provide an excellent ‘quantitative laboratory’ for studying complex interactions between geomorphology and hydrology at and across multiple spatial scales. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
15.
After the 1995 Kobe earthquake, the expressway structures in Japan were retrofitted and they will not now be seriously damaged under a certain level of strong earthquake motion. However, the stability of a moving vehicle has not been investigated yet. It has been reported that drivers feel seismically induced vibrations, especially in the transverse direction of vehicles. Owing to this phenomenon, drivers have some difficulty in controlling the vehicles during strong shaking. For further safety promotion of the expressway networks, it is important to understand the drivers' reactions to seismic motion. The present authors have performed a series of seismic response analyses of a moving vehicle to investigate its response characteristics based on numerical simulation. However, the responses of the driver were not considered in the simulation process. In order to investigate the drivers' reactions during an earthquake, a series of virtual tests were conducted using a driving simulator. This driving simulator has six servomotor‐powered electric actuators that control its motions. Several types of tests were carried out for different examinees to investigate drivers' responses while controlling the simulator under seismic motion. The results of this study showed that a larger response time lag to strong shaking and over turning of the steering wheel may shift the vehicle into the next lane. According to this finding, trafficaccidents could possibly occur under strong ground shaking in the case of heavy traffic. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
新近系地下淡水是下辽河三角洲地区的盘锦市和辽河油田主要供水水源。地下水处于封闭到半封闭环境,包括明化镇组(Nm)和馆陶组(Ng)两个含水岩组。天然状态下,地下水位接近或高于地表;开采条件下,地下水位逐年下降,形成区域性降落漏斗,地下水流场均发生显著变化,形成汇向开采区的向心流场。开采明化镇组地下水为主的盘东水源地,开采初期水位下降速率为1.61~5.19m/a,至1996年降至0.63~1.03m/a;馆陶组地下水为主的各水源地,开采初期水位下降速率为2.10~4.21m/a,至1996年减至1.49~2.05m/a。这是由于地下水流场变化,导致明化镇成水体内侵和下移所致,该地地下水中Cl^-的不断增高也证明了这一点。至1998年。平面上,成水体每年增加3.18km^2,盘东水源南部,成水体内侵速率已达每年220m。垂向上成水体年下移速率一般每年0.5~1.67m。进行新近系地下水动态特征和演化趋势研究,将为合理开发利用宝贵的淡水资源提供科学依据。 相似文献
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Edith L Gego P. Steven Porter John S. Irwin Christian Hogrefe S. Trivikrama Rao 《Pure and Applied Geophysics》2005,162(10):1919-1939
Airborne fine particulate matter across the United States is monitored by different networks, the three prevalent ones presently being the Clean Air Status and Trend Network (CASTNet), the Interagency Monitoring of PROtected Visual Environment Network (IMPROVE) and the Speciation and Trend Network (STN). If combined, these three networks provide speciated fine particulate data at several hundred locations throughout the United States. Yet, differences in sampling protocols and samples handling may not allow their joint use. With these concerns in mind, the objective of this study is to assess the spatial and temporal comparability of the sulfate, nitrate and ammonium concentrations reported by each of these networks. One of the major differences between networks is the sampling frequency they adopted. While CASTNet measures pollution levels on seven-day integrated samples, STN and IMPROVE data pertain to 24-hour samples collected every three days. STN and IMPROVE data therefore exhibit considerably more short-term variability than their CASTNet counterpart. We show that, despite their apparent incongruity, averaging the data with a window size of four to six weeks is sufficient to remove the effects of differences in sampling frequency and duration and allow meaningful comparison of the signals reported by the three networks of concern. After averaging, all the sulfate and, to a lesser degree, ammonium concentrations reported are fairly similar. Nitrate concentrations, on the other hand, are still divergent. We speculate that this divergence originates from the different types of filters used to collect particulate nitrate. Finally, using a rotated principal component technique (RPCA), we determined the number and the geographical organization of the significant temporal modes of variation (clusters) detected by each network for the three pollutants of interest. For sulfate and ammonium, the clusters’ geographical boundaries established for each network and the modes of variations within each cluster seem to correspond. RPCA erformed on nitrate concentrations revealed that, for the CASTNet and IMPROVE networks, the modes of variation do not correspond to unified geographical regions but are found more sporadically. For STN, the clustered areas are unified and easily delineable. We conclude that the possibility of jointly using the data collected by CASTNet, IMPROVE and STN has to be weighed pollutant by pollutant. While sulfate and ammonium data show some potential for joint use, at this point, combining the nitrate data from these monitoring networks may not be a judicious choice. 相似文献
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