Rate and historical change of direct recharge from precipitation constrained by unsaturated zone profiles of chloride and oxygen‐18 in dry river bed of North China Plain     

Ruiqiang Yuan  Xianfang Song  Dongmei Han  Yinghua Zhang  Liang Zhang  Bing Zhang  Xiting Long  Yilei Yu 《水文研究》2012,26(9):1291-1301

Quantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well‐irrigated agriculture. In the North China Plain, the land use is dominated by groundwater‐irrigated farmland where the direct recharge derived from precipitation and irrigation. To characterize the mean rate and historical variance of direct recharge derived from precipitation, unsaturated zone profiles of chloride and δ¹⁸O in the dry river bed of the Beiyishui River were employed. The results show that archival time scale of the profile covers the duration from 1980 to 2002 (corresponding to depths from 5 to 2 m) which is indicated by matching the δ¹⁸O peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation. Using the chloride mass balance method, the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3·8 ± 0·8 mm year^?1, which accounts for about 0·7% of the long‐term average annual precipitation. Further, the direct recharge rates vary from 2·1 to 6·8 mm year^?1 since 1980. Despite the subhumid climate, the estimate of recharge rates is in line with other findings in semiarid regions. The low rate of direct recharge is considered as a result of the relative dry climate in recent decades. In dry river bed, unsaturated zone profiles of chloride and δ¹⁸O combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Experiments on steady buoyancy transfer through turbulent fluid layers separated by density interfaces     

Harindra J.S. Fernando  Robert R. Long 《Dynamics of Atmospheres and Oceans》1988,12(3-4)

A laboratory experiment was performed to investigate mixing across a density interface which separates two turbulent fluid layers and coexists with a stabilizing buoyancy flux. It was found that the buoyancy flux (q₀) across the interface and through the turbulent layers (of depth D) becomes steady and constant in magnitude in the vertical direction, only when , where u is the horizontal r.m.s. velocity at the base of the mixed layers. The results suggest that mixing across the density interface is controlled by a dynamically important buoyancy gradient induced in the turbulent layers and that parameters such as the bulk Richardson number, , where Δb is the interfacial buoyancy jump, are of secondary importance. Measurements are used to infer the mixing mechanism at the interface, the mixing efficiency of stratified fluids and the entrainment law. Some geophysical applications of the results are also discussed.  相似文献   

El Chichón火山的太阳辐射效应          下载免费PDF全文

金龙 《气象学报》1988,46(3):333-340

利用1964—1983年冬季无云条件下的太阳辐射资料分析发现,1982年3月底至4月初,墨西哥El Chichón(厄·奇冲)火山爆发后,对到达地球表面的太阳直接辐射、散射辐射以及总辐射产生了显著和持续的影响。这种影响特征与近百年来的几次巨大火山爆发所引起的辐射效应是一致的,这主要是因为火山气溶胶对太阳辐射的强大反向散射和吸收作用,改变了大气透明度所造成的。  相似文献   

Generation of Hydrogen Gas as a Result of Drilling Within the Saturated Zone   总被引：1，自引：0，他引：1  

Bruce N. Bjornstad  James P. McKinley  Todd O. Stevens  Shirley A. Rawson  James K. Fredrickson  Philip E. Long 《Ground Water Monitoring & Remediation》1994,14(4):140-147

Hydrogen gas was discovered within the steel casing above standing water in a percussion-drilled borehole on the Hanlord Site in south-central Washington state. In situ measurements of the borehole fluids indicated anoxic, low-Eh (<-400 mV) conditions. Ground water sampled from adjacent wells in the same formation indicated that the ground water was oxygenated. H₂ was generated during percussion drilling, due to the decomposition of borehole waters as a result of aqueous reactions with drilled sediment and steel from the drilling tools or casing. The generation of H₂ within percussion-drilled boreholes that extend below the water table may be more common than previously realized. The ambient concentration of H₂ produced during drilling was limited by microbial activity within the casing-resident fluids. H₂ was generated abiotically in the laboratory, whereby sterilized borehole slurry samples produced 100 times more H₂ than unsterilizcd samples. It appears that H₂ is metabolized by microorganisms and concentrations might be significantly greater if not for microbial metabolism.  相似文献   

Statistical distribution of natural fractures and the possible physical generating mechanism     

F. K. Boadu  L. T. Long 《Pure and Applied Geophysics》1994,142(2):273-293

We have fitted field measurements of fracture spacings (from the vicinity of Lake Strom Thurmond, Georgia, U.S.A.) to the Weibull, Schuhmann and fractal distributions. The fracture spacings follow a fractal and Weibull distribution which implies that they were formed as a result of a repetitive fragmentation process. The limited variation of the fracture density with orientation in the study area suggests that the stress distribution generating these fractures may be uniform.  相似文献   

α径迹的试验研究及其与地震关系的初步探讨          下载免费PDF全文

倪明康  龙明  林思诚  李彤起 《地震工程学报》1987,9(4):39-47

本文在大量试验的基础上对α径迹法在径迹蚀刻、判定、读数方法、误差来源等方面作了讨论,並做了一些相应规定,使α径迹法在地震预报中取得了一定效果。本文还对陇西3.6级地震前α径迹法的观测结果作了讨论。  相似文献   

The Chemical Composition of Global Subducting Sediments and Its Geological Significance     

Renjie Zhao  Quanshu Yan  Haitao Zhang  Yili Guan  Zhenmin Ge  Long Yuan  Shishuai Yan 《地球科学进展》1986,35(8):789-803

Subducted sediments play an important role in crust-mantle interaction and deep mantle processes, especially for subduction zone magmatism and mantle geochemistry. The current rate of Global Subducting Sediments (GLOSS) is 0.5~0.7 km³/a. The GLOSS are composed of terrigenous material(76 wt.%), calcium carbonate(7 wt.%), opal(10 wt.%) and mineral-bound H₂O⁺(7 wt.%). The chemical compositions of GLOSS are similar to those of upper continental crust which is mainly controlled by the terrigenous materials, and yet the materials formed by marine processes will dilute the terrigenous materials. The components of subducted sediments are different among trenches. In the accretionary margin, the components of subducted sediments are similar to those of the upper crust, while in the non-accretionary margin the components are terrigenous materials plus those produced by marine processes. During subduction, subducted sediments will released fluids, melt or supercritical fluid to affect island arc/back-arc basin magmatism by means of aqueous fluid or sediment melt. In addition, a part of subducted sediments, together with underlying altered oceanic crust/lithosphere, recycle into the mantle and contribute to the mantle heterogeneity. Geochemical tracers indicate that subducted sediments play variable contributions to the magmatic processes in different tectonic setting. Thus, subducted sediments play an important role in two relatively independent dynamics systems (plate tectonics and mantle plume), as well as related mantle evolution models. As a result, by accurately calculating the compositions of subduction sediments and using various geochemical indicators, we can further limit the input and output fluxes of various elements or isotopes, and then obtain more accurately residual subducted components, which can provide us some important clues for geodynamic process.  相似文献   

Origin of granite at Cabo de Santo Agostinho,Northeast Brazil     

Leon E. Long  Alcides N. Sial  Hanna Nekvasil  Glicia S. Borba 《Contributions to Mineralogy and Petrology》1986,92(3):341-350

A 4 km² exposure of shallowly-emplaced leucogranite on the Atlantic coast at Cabo de Santo Agostinho, 30 km south of Recife, Brazil has been extensively studied chemically and isotopically. Twenty-three major-element analyses indicate that the Cabo granite ranges from peralkaline to peraluminous; Na₂O+K₂O is very high (7.4 to 10.4 wt.%), with CaO low (0.3%) and MgO vanishing (<0.06%). Microprobe analyses confirm the presence of arfvedsonite (biotite absent), and nearly total absence of plagioclase. The rocks are moderately to highly enriched in LREE (La 45 to 350 times chondritic), with extremely pronounced negative Eu anomalies (Eu/Eu^*=0.02 to 0.07). Whole-rock ¹⁸O is consistent at +8.5±0.3%._oSMOW A Rb-Sr isochron age of isotopically slightly disturbed samples is 104.8±1.8 Ma, with initial⁸⁷Sr/⁸⁶Sr=0.7084±0.0011. Sr is depleted (2–20 ppm) but Ba is 200–750 ppm.Crystallization path calculations and petrographic observations suggest that magma formed at a pressure close to 6 kbar but rose to a crustal level equivalent to roughly 1 kbar. Quartz, the liquidus phase at moderate H₂O concentrations and pressures above 2 kbar, was resorbed during decompression as the magma moved upwards. Ultimately, quartz and alkali feldspar coprecipitated. Feldspar was not retained in the source rock nor removed early from the fractionating magma. Therefore the strong negative Eu anomaly and low Sr abundance are characteristics inherited from the source. A high H₂O concentration necessary for a large degree of melting was lacking, hence the Cabo magma composition must reflect a small degree of partial melting of a rather quartz-rich rock such as a feldspathic arenite.In a pre-drift reconstruction of Gondwanaland, the Cabo granite fits on the southernmost and youngest end of the trend of the Niger-Nigerian igneous centers with which it has close affinity. The Cabo granite occupies the western end of the trace of the ancestral Ascension mantle plume which presumably served as the heat source.  相似文献   

临涣矿区水化学特征及在矿井水源判别中的意义   总被引：4，自引：1，他引：4  

成春奇  徐龙 《煤田地质与勘探》1995,23(1):43-47

通过分析、比较临涣矿区三个地下水子系统的水文地球化学特征得出，这三个子系统在水溶标型发及少、微量元素的含量上无明显差别，表明各子系统间存在水力联系，而环境同位素氘和＾１８Ｏ分析则是解决矿井水来源判别的有效方法。  相似文献   

滇西实验场两次中强地震前后尾波衰减的区域特征分析   总被引：9，自引：0，他引：9  

秦嘉政  刘祖荫 《中国地震》1995,11(3):212-221

本文在地方震尾波散理论模式的基础上，研究了１９９２年１２月发生在滇西地震预报实验场永胜期纳地区的两次Ｍｓ５．４，５．１地震前后的序列地震尾波振幅衰减率β和尾波Ｑ＾－１值随时间和空间变化的衰减特征。结果表明，尾波衰减率在空间分布上表现出明显的小区域范围的非均匀性，在主震震中附近的近场区内，主震期间的β值是０．００７６ｓ＾－１，相应的Ｑｃ＾－１值是０．００５６；余震期间的β值是０．０２０９ｓ＾－１，相  相似文献