Evaluation of vegetative criteria for near-surface groundwater detection using multispectral mapping and GIS techniques in semi-arid Botswana     

Susan Ringrose  Cornelis Vanderpost  Wilma Matheson 《Applied geography (Sevenoaks, England)》1998,18(4):331-354

The critical need to consider all options in the search for groundwater in semi-arid areas has promoted work on the possible association of near-surface groundwater and vegetation characteristics using a combination of remote-sensing data and geographic information systems (GIS) techniques. Two vegetative criteria (dense woody cover and abundance of deep-rooting species) are identified as being indicative of near-surface groundwater, and their spatial distribution is tested against the location of aquifers in southeast Botswana. Vegetative criteria classes were combined in a GIS environment with the distribution of geomorphic units and bedrock geology to determine the degree of coincidence with assumed or known aquifers. Results indicate that the distribution of dense woody vegetation as mapped from Thematic Mapper imagery has some potential in identifying especially surficial but also bedrock near-surface groundwater sources in mostly naturally vegetated semi-arid areas. Dense woody cover classes tend to select aquifers in topographically higher areas while classes comprising some deep-rooting species tend to select low-lying aquifers such as those occurring in fossil valleys. Deep-rooting species, however, are less successful as a vegetative criterion. Although various technical refinements are suggested, this work shows that vegetative criteria mapping can however be used in conjunction with conventional geological/geophysical techniques to enhance the prospects for groundwater location in relatively undisturbed semi-arid areas.  相似文献   

Modern diatom, cladocera, chironomid, and chrysophyte cyst assemblages as quantitative indicators for the reconstruction of past environmental conditions in the Alps. II. Nutrients   总被引：5，自引：0，他引：5  

André F. Lotter  H. John B. Birks  Wolfgang Hofmann  Aldo Marchetto 《Journal of Paleolimnology》1998,19(4):443-463

Surface sediments from 68 small lakes in the Alps and 9 well-dated sediment core samples that cover a gradient of total phosphorus (TP) concentrations of 6 to 520 g TP l^-1 were studied for diatom, chrysophyte cyst, cladocera, and chironomid assemblages. Inference models for mean circulation log₁₀ TP were developed for diatoms, chironomids, and benthic cladocera using weighted-averaging partial least squares. After screening for outliers, the final transfer functions have coefficients of determination (r², as assessed by cross-validation, of 0.79 (diatoms), 0.68 (chironomids), and 0.49 (benthic cladocera). Planktonic cladocera and chrysophytes show very weak relationships to TP and no TP inference models were developed for these biota. Diatoms showed the best relationship with TP, whereas the other biota all have large secondary gradients, suggesting that variables other than TP have a strong influence on their composition and abundance. Comparison with other diatom – TP inference models shows that our model has high predictive power and a low root mean squared error of prediction, as assessed by cross-validation.  相似文献   

Three-dimensional waveform sensitivity kernels   总被引：2，自引：0，他引：2  

Henk Marquering  Guust Nolet  & F.A. Dahlen 《Geophysical Journal International》1998,132(3):521-534

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Anisotropy in the Indian Ocean upper mantle from Rayleigh- and Love-waveform inversion   总被引：3，自引：0，他引：3  

J.J. Lévêque  E. Debayle  & V. Maupin 《Geophysical Journal International》1998,133(3):529-540

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Relationship between global seismicity and solar activities     

Gui-Qing Zhang 《地震学报(英文版)》1998,11(4):495-500

The relations between sunspot numbers and earthquakes (M≧6), solar 10.7 cm radio flux and earthquakes, solar proton events and earthquakes have been analyzed in this paper. It has been found that: (1) Earthquakes occur frequently around the minimum years of solar activity. Generally, the earthquake activities are relatively less during the peak value years of solar activity, some say, around the period when magnetic polarity in the solar polar regions is reversed. (2) the earthquake frequency in the minimum period of solar activity is closely related to the maximum annual means of sunspot numbers, the maximum annual means of solar 10.7 cm radio flux and solar proton events of a whole solar cycle, and the relation between earthquake and solar proton events is closer than others. (3) As judged by above interrelationship, the period from 1995 to 1997 will be the years while earthquake activities are frequent. In the paper, the simple physical discussion has been carried out. These results supported the exploration and studies of some researchers to a certain extent. This work is supported by Foundation of the Chinese Academy of Sciences (major item).  相似文献   

上海旱地农田氮磷随地表径流流失研究   总被引：14，自引：0，他引：14  

黄宗楚  郑祥民  姚春霞 《云南地理环境研究》2007,19(1):6-10

选择上海宝山罗店镇具有代表性的旱地蔬菜农田生态系统，从2004年3月到8月的近半年时间里，通过对径流及径流中侵蚀泥沙的氮磷流失情况的连续监测，研究了旱地农田施肥与氮磷流失污染之间的关系，探讨了农田氮磷的迁移特征及环境效应，主要结果表明：当季施用化肥的地表径流总流失量，总氮为32．77kg/hm^2，总磷为8．1kg／hm^2，随径流排出农田的氮素中有37．7％是当季施用的氮素化肥，磷素中有26．9％是当季施用的磷素化肥；从过量施肥与环境污染之间的“因”与“果”来看，减量15％施肥区相比常规施肥区的茄子的产量减少2．7％，但是其污染负荷却减少了13．4％，表明在化肥利用的有效性上或增施化肥与控制环境污染之间，应该寻找一个最佳的平衡点。  相似文献   

Structure of the crust in the Black Sea and adjoining regions from surface wave data     

T. B. Yanovskaya  E. S. Kizima  L. M. Antonova 《Journal of Seismology》1998,2(4):303-316

Group velocities of Rayleigh and Love waves along the paths across the Black Sea and partly Asia Minor and the Balkan Peninsula are used to estimate lateral variations of the crustal structure in the region. As a first step, lateral variations of group velocities for periods in the range 10–20 s are determined using a 2D tomography method. Since the paths are oriented predominantly in NE–SW or N–S direction, the resolution is estimated as a function of azimuth. The local dispersion curves are actually averaged over the extended areas stretched in the predominant direction of the paths. The size of the averaging area in the direction of the best resolution is approximately 200 km. As a second step, the local averaged dispersion curves are inverted to vertical sections of S-wave velocities. Since the dispersion curves in the 10–20 s period range are mostly affected by the upper crustal structure, the velocities are estimated to a depth of approximately 25 km. Velocity sections along 43° N latitude are determined separately from Rayleigh and Love wave data. It is shown that the crust under the sea contains a low-velocity sedimentary layer of 2–3 km thickness, localized in the eastern and western deeps, as found earlier from DSS data. Beneath the sedimentary layer, two layers are present with velocity values lying between those of granite and consolidated sediments. Velocities in these layers are slightly lower in the deeps, and the boundaries of the layers are lowered. S-wave velocities obtained from Love wave data are found to be larger than those from Rayleigh wave data, the difference being most pronounced in the basaltic layer. If this difference is attributed to anisotropy, the anisotropy coefficient = (SH - SV)/Smean is reasonable (2–3%) in the upper layers, and exceeds 9% in the basaltic layer.  相似文献   

氧化铬柱支撑蒙脱石的制备研究   总被引：4，自引：1，他引：3  

田淑贵  王冠鑫 《矿物学报》1998,18(4):390-395

以浙江和新疆的膨润土为原料合成了氧化铝柱支撑蒙脱石,成柱溶液以Na2CO3为碱水解铝盐溶液制得。因为制备含有大聚羟基铬阳离子的成柱溶液是获得具有大的基面间距的柱支撑粘土的关键,我们详细研究了CO32-／Cr3＋值、水解温度和水解时间对所得柱支撑蒙脱石性质的影响。聚羟基铬阳离子通过阳离子交换引入蒙脱石,所得产物用X射线衍射分析和BET氮比表面等方法研究。所得氧化铝柱支撑蒙脱石（简称Cr－mont）的基面间距为2．55nm,BET氮比表面积为190～230m2／g。  相似文献   

硬质合金钎头胎体表面渗硼强化实验研究          下载免费PDF全文

王树理  张拔川  李功伯  树玉秀 《探矿工程》1998,(5):34-35

对钎头胎体表面渗硼方法和工艺进行了实验研究,给出了有关工艺参数与方法。它对提高硬质合金钎头胎体表面和耐磨性,延长钎头的使用寿命具有积极的意义。  相似文献   

Experimental study on the mechanism of non-synchronism of seismo-electromagnetic radiation precursors   总被引：1，自引：0，他引：1  

钱书清  吕智  任克新 《地震学报(英文版)》1998,11(5):623-629

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