Organic litter: dominance over stones as a source of interrill flow roughness on low‐gradient desert slopes at Fowlers Gap,arid western NSW,Australia     

David Dunkerley 《地球表面变化过程与地形》2003,28(1):15-29

Thirty‐six runoff plot experiments provide data on flow depths, speeds, and Darcy–Weisbach friction coefficients (f) on bare soil surfaces, and surfaces to which were added sufficient extra plant litter or surface stones to provide projected cover of 5, 10 and 20 per cent. Precision flow depth data were derived with a computer‐controlled gantry and needle gauge for two different discharges for each plot treatment. Taking a fixed flow intensity (Reynolds number, Re = 150) for purposes of comparison shows means of f = 17·7 for bare soil surfaces, f = 11·4 for added stone treatments, and f = 23·8 for added litter treatments. Many individual values of f for stone treatments are lower than for the bare soil surface, but all litter treatments show increases in fcompared to bare soil. The lowering of f in stone treatments relates to the submerged volume that the stones occupied, and the associated concentration of flow onto a smaller part of the plot surface. This leads to locally higher flow intensities and lower frictional drag along threads of flow that the obstacles create. Litter causes higher frictional drag because the particles are smaller, and, for the same cover fraction, are 100 times more numerous and provide 20 times the edge or perimeter length. Along these edges, which in total exceed 2·5 m g^?1 (equivalent to 500 m m^?2 for a loading of 2 t ha^?1), surface tension draws up water from between the litter particles. This reduces flow depth there, and as a consequence of the lower flow intensity, frictional drag rises. Furthermore, no clear passage remains for the establishment of flow threads. These findings apply to shallow interrill flows in which litter is largely immobile. The key new result from these experiments is that under these conditions, a 20 per cent cover of organic litter can generate interrill frictional retardation that exceeds by nearly 41 per cent that of a bare soil surface, and twice that contributed by the same cover fraction of surface stones. Even greater dominance by litter can be anticipated at the many dryland sites where litter covers exceed those tested here. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

杭州市化工园区选址的气象环境与评估的数值模拟研究          下载免费PDF全文

徐集云  顾骏强陈燕 吴涧 《气象科技》2003,31(6):334-339344

城市化是国家社会发展的必然趋势，为了在新一轮城市总体规划中能保证杭州市的大气环境质量，优化不同空间尺度的城市规划，协调城市发展与保护环境的关系，本文利用一个三维非静力区域边界层数值模式，对一些典型天气条件下杭州地区的风场和气温的空间分布特征进行模拟分析，并以此为依据，给出选取化工园区的位置的评估意见。模拟结果表明，化工园区的选址宜考虑在杭州市的西南方向。  相似文献   

沈阳2×200兆瓦低温核供热站厂址基准地面运动参数的确定   总被引：2，自引：0，他引：2  

吴明大  钟以章  高静 《地震工程与工程振动》2003,23(4):78-82

本文在综合厂址、近区域及区域地震地质资料的基础上,根据有关规范的要求,采用地震构造法、最大历史地震法和概率法分别计算了沈阳2×200兆瓦低温核供热站厂址的极限安全地震动SL-2,计算结果分别为200Gal、125Gal和170Gal。取三者最大值,厂址SL-2应当是200gal。厂址基岩地面运动SL-2水平向加速度反应谱取确定性法和概率法计算曲线的外包线作为用于厂址的基岩加速度反应谱。  相似文献   

超积累植物与找矿   总被引：13，自引：0，他引：13  

唐世荣  黄昌勇  朱祖祥 《物探与化探》1997,21(4):263-268

本文介绍了超积累植物的概念和它在地质找矿中的意义,回顾了国外超积累植物的研究历史,并对应用超积累植物进行找矿的发展方向进行了讨论。  相似文献   

Hydrologic and climatic implications of a multidisciplinary study of late Holocene sediment from Kenosee Lake, southeastern Saskatchewan, Canada     

R. E. Vance  W. M. Last  A. J. Smith 《Journal of Paleolimnology》1997,18(4):365-393

Sediment lithology and mineralogy, as well as ostracode, plant macrofossil and stable isotope stratigraphies of lake sediment cores, are used to reconstruct late Holocene hydrologic changes at Kenosee Lake, a relatively large, hyposaline lake in southeastern Saskatchewan. Chronological control is provided by AMS radiocarbon ages of upland and shoreline plant macrofossils. All indicators outline an early, low-water, saline phase of lake history (4100–3000 BP), when the basin was occupied by a series of small, interconnected, sulfate-rich brine pools, as opposed to the single, topographically-closed lake that exists today. A rapid rise in lake-level (3000–2300 BP) led to the establishment of carbonate-rich, hyposaline lake conditions like those today. Lithostratigraphic data and ostracode assemblages indicate peak salinities were attained early in this period of lake infilling, suggesting that the lake-level rise was initially driven by an influx of saline groundwater. Lake-level and water chemistry have remained relatively stable over the last 2000 years, compared to earlier events. Because of a lack of datable organic material in sediments deposited during the last 2000 years, the chronology of recent events is not well resolved. Plant macrofossil, lithostratigraphic and ostracode evidence suggests that lake draw-down, accompanied by slightly higher than present salinites, occurred sometime prior to 600 BP, followed by peak lake-level and freshwater conditions. This most recent high lake stand, indicative of a high water table on the surrounding upland, may also have led to the establishment of an extensive cover of Betula in the watershed, possibly in response to paludification. Ostracode assemblages indicate that peak freshwater conditions occurred within the last 100 years. Since historically documented lake-level fluctuations correlate with decadal scale climatic fluctuations in the meteorological record, and late-Holocene hydrologic dynamics correspond to well documented climatic excursions of the Neoglacial and Little Ice Age, Kenosee Lake dynamics offer insight into the susceptibility of the region's water resources to climate change.  相似文献   

Ibex diggings in the Negev Desert highlands of Israel as microhabitats for annual plants. Soil salinity, location and digging depth affecting variety and density of plant species   总被引：1，自引：0，他引：1  

Yitzchak Gutterman 《Journal of Arid Environments》1997,37(4):665-681

About 400 Nubian ibex (Capra ibex nubiana) dig many hundreds of temporary night beds, approximately 80 cm × 110 cm and 15 cm deep, on slopes near the edges of the cliffs bordering the Zin valley. The beds are used according to the wind direction and the size of the ibex group, which depends on the ibex social behaviour during the year.The diggings are gradually abandoned and become important microhabitats for seed accumulation and germination, seedling development and annual plant establishment. These are influenced by soil salinity, slope direction and angle, digging depth, and the time since the diggings were abandoned. A greater variety of plant species and plant density were found in these diggings than upslope from the diggings.  相似文献   

湖南省珍稀濒危植物及其特征     

包维楷 《山地学报》1997,(4)

首批中国珍稀濒危植物分布于湖南的有65种4变种。从区系组成、植物地理分布、在自然森林群落中的生态地位,以及利用价值等方面分析了它们的特征,并对湖南珍稀濒危植物就地保护的有效性和措施进行了讨论。  相似文献   

Effect of environmental factors on the flora of alluvial fans in southern Sinai     

Abd El-Raouf A. Moustafa  A. Zayed 《Journal of Arid Environments》1996,32(4):431-443

The purpose of this study was to elucidate the floristic and structural characteristics of simple alluvial fan vegetation of southern Sinai and to relate them to environmental variation. The main question addressed was: how does the floristic composition of fan habitats, species richness and life-form vary in relation to environmental change? Thirty-seven alluvial fans, randomly selected in two mainwadis(WadiFeiran andWadiDahab) were analysed quantitively. Two-way Indicator Species Analysis (TWINSPAN) classification and Canonical Correspondence Analysis (CCA) were applied in successive stages of the data analysis to describe vegetational variation in relation to physical gradients. Seven main clusters of fans were defined on the basis of environmental variation. These clusters are divided into three main groups of species richness. Species richness varied along a moisture gradient. The richest fans were the driest habitats, indicating that maximum species richness did not occur at high moisture availability. The moisture gradient is a complex gradient correlated with elevation, slope, climatic aridity, soil texture and the nature of the soil surface. Fine sand, silt plus clay and calcium carbonate showed significant differences between the internal groups and subgroups of the first and second level of the TWINSPAN classification.  相似文献   

吐哈盆地西南缘水西沟群古气候演变特征及其层序地层学意义     

吴伯林  徐高中 《华东地质学院学报》2004,27(2):135-140

通过对水西沟群(J1-2sh)古植物、古孢粉化石组合特征等系统的研究，对八道湾组(J1b)、三工河组(J1s)、西山窑组(J1x)古气候类型进行了区分；并据此认为西山窑组(J1x)为一套气候地层层序，相应划分为四个体系域：即低水位、湖泊扩张，高水位及湖泊收缩体系域。再结合一些岩性岩相等特殊标志，对十红滩东部外围地层层序进行了划分，结果与十红滩矿区地层层序本质是一致的。  相似文献   

金沙江下游白鹤滩水电站岩体结构的建造特征     

王奖臻  黄润秋  许模 《地球科学进展》2004,(Z1)

拟建的白鹤滩水电站的坝基为峨眉山玄武岩。峨眉山玄武岩由火山熔岩类、火山碎屑熔岩类、火山碎屑岩类和沉积火山碎屑岩类所组成。火山熔岩又可划分为斜斑玄武岩、块状玄武岩和杏仁状玄武岩;火山碎屑岩包括集块岩、火山角砾岩以及凝灰岩;而沉积火山碎屑岩类则由沉火山角砾岩和沉凝灰岩所组成。不同类型岩石的结构构造、矿物成分和形成环境不同,导致它们的岩石力学性质和工程性能也不相同。块状玄武岩、斜斑玄武岩和沉积火山碎屑熔岩的抗压强度和抗风化能力都比较大,因而具有很好的工程地质稳定性;杏仁状玄武岩、火山碎屑熔岩的抗压强度稍低,但抗风化能力很好,因此也具有较好的工程地质稳定性;而火山碎屑岩包括火山角砾岩、凝灰岩的抗压强度和抗风化能力都很低,往往形成岩体中的软弱夹层,工程地质稳定性较差。  相似文献