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41.
Desert pavements (DPs) are critical for maintaining ecological stability and promoting near-surface hydrological cycling in arid regions. However, few studies have focused on eco-hydrological processes of DPs in the ecological systems of fluvial fans. Although DP surfaces appear to be barren and flat, we found that the surfaces are characterized by surface mosaic patterns of desert pavement (mosaic DP) and bare ground (mosaic BG). We investigated the effects of mosaic DP on water infiltration and vegetation distribution at six sites in fluvial fans (one on a hillside and five within the sectors of fans) along a southwest belt transect in northern Linze County, in the central Hexi Corridor (China). We found significant differences in mosaic DP between the hillside and sector sites in terms of pavement thickness and vesicular horizon thickness (Av thickness), particle composition, and bulk density, although significant differences were absent for mass soil water content, gravel coverage, and surface gravel size. The mosaic DP inhibited water infiltration by the pavement layer, where the sorptivity (S), initial infiltration rate (iint), steady-state infiltration rate (isat) and infiltration time (T) averaged 1.19 cm/min-0.5, 0.64 cm/min, 0.13 cm/min and 12.76 min, respectively. Where the pavement layer was scalped, the S, iint, and isat increased by 0.27 cm/min-0.5, 0.52 cm/min, and 0.40 cm/min, respectively, and the T reduced by 7.42 min. Water infiltration was mainly controlled by the pavement layer thickness (+), Av thickness (−), surface gravel coverage (−), fine earth (+) and fine gravel (−) in the pavement layer. The DP surfaces only had a sparse covering of shrubs, but an abundance of herbs. Few shrubs were present on the mosaic DP, but a greater number of shrubs and herbs grew on the mosaic BG. It can be concluded that DPs can maintain vegetation stability for different surface mosaic patterns. This study deepens our understanding of the eco-hydrological cycle of DP landscapes in arid regions. 相似文献
42.
Soil nails have been widely used to stabilize slopes and earth retaining structures in many countries and regions, especially, in Hong Kong. The analysis of the interaction between a soil nail and the surrounding soil is of great interests to both design engineers and researchers. In this paper, authors present a simple mathematical model for the interaction analysis of a soil nail and the surrounding soil considering a few key factors which are soil dilation, bending of the soil nail, vertical pressure, and non-linear subgrade reaction stiffness. The lateral subgrade reaction between the soil and the soil nail is assumed to obey a hyperbolic relation. Reported test data in the literature are used to verify the present model. The contributions of the soil-nail bending on the pull-out resistance are evaluated in two case studies. 相似文献
43.
本文研究了以磷酸三丁酯为固定相,大孔聚乙烯苯(X-5型)为担体的浸渍树脂、垂直型反相色谱柱,对铀分离富集的基本性能,以及铀(Ⅳ)-间硝基苯基萤光酮(m-NPF)一氨三乙酸(NTA)-吐温-80显色体系的反应条件,提出了TBP(X-5)分离,m-NPF-NTA-吐温-80光度法测定铀,经标准样品验证,结果满意。 相似文献
44.
光度法测定痕量钛的研究 总被引:6,自引:1,他引:6
基于痕量Ti(Ⅳ)在稀H2SO4介质中对EDTA还原Cr2O2-7褪色反应的抑制作用,建立了测定痕量Ti(Ⅳ)的光度法。测定范围为24~24μg/L,检出限为106×10-7g/LTi(Ⅳ)。结合萃取分离富集技术,方法用于测定人发及茶叶样品中的痕量Ti(Ⅳ),结果与标准值相符,加标回收率在95%~100%,RSD(n=6)为11%~20%。 相似文献
45.
扇三角洲沉积体系及其与油气聚集关系 总被引:21,自引:2,他引:21
扇三角洲沉积体系是断陷盆地中极为发育的一种沉积体系,主要由扇三角洲平原组合、扇三角洲前缘组合和前三角洲沉积构成,可识别出9种成因相。受沉积物供给速率、可容空间增长速率及盆缘断裂产状等因素控制可划分出退积型、加积型、前积型、陡坡型和缓坡型5种扇三角洲类型。位于扇三角洲平原的辫状分流河道砂体及其位于扇三角洲前缘的与之有成因联系的水下分流河口坝、洪水型重力流砂体等物性好,可以构成优质储层。含油性勘探成果亦证实各主力油层段平面上主要分布于扇三角洲前缘及分流间湾区,小部分位于扇三角洲平原区。受埋藏深度和成岩场的影响,不同地区、不同层位主力油层段的物性与岩性相关性各异。因此,应用沉积体系分布与油气聚集规律挖掘剩余油层及进行远景区预测是有效的与可行的。 相似文献
46.
通过1∶5万区调填图(1988~1990),笔者将蛤蟆塘盆地白垩纪地层划分为大拉子组、富兴屯砾岩、龙井组。其中大拉子组下部为山麓冲积扇沉积,上部为湖相沉积;富兴屯砾岩为河流—扇三角洲相沉积;龙井组为浅盆广湖相沉积,其中产有Nigerestheriasp等化石,属早白垩世,与延吉盆地等有明显时代差异,具有穿时性。 相似文献
47.
48.
Competition within the marine microalgae over the polar dark period in the Greenland Sea of high Arctic 总被引:2,自引:0,他引:2
Abstract-With the onset of winter, polar marine microalgae would have faced total darkness for aperiod of up to 6 months. A natural autumn community of Arctic sea ice microalgae was collected fordark survival experiments from the Greenland Sea during the ARKTIS-XI/2 Expedition of RV Po-larstern in October 1995. After a dark period of 161 days, species dominance in the algal assemblagehave changed from initially pennate diatoms to small phytoflagellates (<20μm). Over the entire darkperiod, the mean algal growth rate was-0.01 d~(-1). Nearly all diatom species had negative growthrates, while phytoflagellate abundance increased. Resting spore formation during the dark period was ob-served in less than 4.5% of all cells and only for dinoflagellates and the diatom Chaetoceros spp. We as-sume that facultative heterotrophy and energy storage are the main processes enabling survival during thedark Arctic winter. After an increase in light intensity, microalgal cells reacted with fast growth withindays. Phytoffa 相似文献
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