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971.
B. J. M. Goes 《Hydrogeology Journal》1999,7(3):294-304
The Hadejia–Nguru Wetlands are annually inundated flood plains in semi-arid northeastern Nigeria. The area has a unique ecosystem
that forms a natural barrier against the encroachment of the Sahara desert. Both the rich wetland vegetation and local farmers
using shallow tube wells depend on a groundwater mound (with a water table less than 6 m below the surface) that is present
in the unconfined aquifer under the flood-plain area. Using well records (1991–97) and a hydrogeologic profile based on piezometers
that were monitored for two years, it is shown that recharge through the annually inundated flood plains is the source of
the groundwater mound. Maintenance of the groundwater-recharge function of the flood plains depends on wet-season releases
from two large upstream dams. On the basis of a water-budget method, the mean (1991–97) wet-season unconfined groundwater
recharge in the flood-plain area between Hadejia and Nguru and in the immediate vicinity (1250 km2) is estimated to be 132 mm (range, 73–197 mm). Outflow from the unconfined flood-plain aquifer to the unconfined upland aquifer
is approximately 10% of the wet-season flood-plain recharge. The unconfined groundwater outflow from the flood-plain area
can provide a significant contribution to the present-day rural water supply in the surrounding uplands, but it does not offer
much potential for additional groundwater abstraction. In addition to outflow to the upland aquifer (∼14 mm), the distribution
of the annually recharged water volume of the shallow flood-plain aquifer is (1) domestic uses (3 mm), (2) small-scale irrigation
(∼15 mm), and (3) evapotranspiration ( 1 100 mm). Along the hydrogeologic profile, the recharge in the upland (i.e., outflow
from the unconfined flood-plain aquifer and possibly diffuse rain-fed recharge) is in balance with the water uses (i.e., domestic
uses, groundwater outflow, and evapotranspiration). The absence of a seasonal water-level trend in the two piezometers in
the upland indicates that no rain-fed recharge occurs through preferential path-way (macropore) flow.
Received, June 1998 / Revised, November 1998, January 1999 / Accepted, January 1999 相似文献
972.
The aim of the study is to investigate the interaction between waters of Lake Girdev and groundwater in the allochthonous
limestone units exposed in the area between Lake Girdev and Kazanpınarı Spring, southwestern Turkey. The features analyzed
include the flow direction and apparent groundwater velocity, their relationship with Lake Girdev, and the effect of lithological
and structural features on the groundwater circulation. The results of a fluorescein tracer test indicate that groundwater
flows east-northeast and the apparent flow velocity ranges from 26.2 to 35.6 m h–1 between the injection site and various observation points. Tritium data suggest that the water of Lake Girdev and groundwater
are probably similar in age, and oxygen-18 isotope data indicate that water derived from Lake Girdev is the main source of
recharge to the aquifer. The aquifer is fed not only by Lake Girdev but also by rainfall percolating through allochthonous
limestones; together, these provide the discharge of springs in Elmalı Polje. The permeability of the allochthonous limestone
aquifer has been enhanced as a result of jointing and faulting.
Received, June 1997 / Revised, June 1998, March 1999 / Accepted, July 1999 相似文献
973.
Relation of streams, lakes, and wetlands to groundwater flow systems 总被引:24,自引:10,他引:14
Thomas C. Winter 《Hydrogeology Journal》1999,7(1):28-45
Surface-water bodies are integral parts of groundwater flow systems. Groundwater interacts with surface water in nearly all
landscapes, ranging from small streams, lakes, and wetlands in headwater areas to major river valleys and seacoasts. Although
it generally is assumed that topographically high areas are groundwater recharge areas and topographically low areas are groundwater
discharge areas, this is true primarily for regional flow systems. The superposition of local flow systems associated with
surface-water bodies on this regional framework results in complex interactions between groundwater and surface water in all
landscapes, regardless of regional topographic position. Hydrologic processes associated with the surface-water bodies themselves,
such as seasonally high surface-water levels and evaporation and transpiration of groundwater from around the perimeter of
surface-water bodies, are a major cause of the complex and seasonally dynamic groundwater flow fields associated with surface
water. These processes have been documented at research sites in glacial, dune, coastal, mantled karst, and riverine terrains.
Received, April 1998 · Revised, July 1998, August 1998 · Accepted, September 1998 相似文献
974.
975.
Deng Jinfu Mo Xuanxue Zhao Hailing LuoZhaohua Zhao GuochunDepartment of Geology Mineral Resources China University of Geosciences Beijing 《中国地质大学学报(英文版)》1999,10(1)
Yanshanianmagma-tectonic-metalogenicbeltoftheEastChinaisapartofthecircum-Pacificdomain.Alotofpapershavebeenpublishedtodiscuss... 相似文献
976.
动态追踪了云南地区第4 强震活跃期6 .3 级以上强震前波速比异常图像,显示出明显的南北差异:滇西南的1988 年11 月6 日澜沧- 耿马7 .6 、7 . 2 级和1993 年1 月27 日普洱6 .3 级强震发生在低波速比异常区内; 中缅边境上的1992 年4 月23 日6 .7 、6 .8 级和1995 年7 月12 日孟连西7 .2 级强震发生在低波速比异常区边缘;而滇西北的1996 年2 月3 日丽江7 .0 级、1976 年11 月7 日、12 月14 日宁蒗6 .7 、6 .4 级和滇东的1995 年10 月24 日武定6 .5 级强震却都发生在高波速比异常区内.强震前近震震级 ML 与持续时间震级 MD 的震级差的南北差异也进一步证实了波速比异常的差别. 相似文献
977.
The crystal structures, lattice dynamics and magnetic properties of synthetic Co-cordierite, Co2Al4Si5O18, and Mn-cordierite, Mn2Al4Si5O18 have been studied by neutron powder diffraction, infrared spectroscopy and magnetisation measurements. Due to different synthesis
conditions, the Co-cordierite used here crystallised in the hexagonal α-cordierite structure with a disordered Si/Al distribution
in the framework, while for the Mn-cordierite the orthorhombic β-structure has been determined. The experimentally determined
paramagnetic moments,
exp
(Mn) = 5.47(6)
B
and
exp
(Co) = 3.88(4)
B
, are in good agreement with theoretical predictions for octahedrally coordinated Mn2+ and Co2+, respectively. In both compounds there is no magnetic long-range order down to at least 1.5 K. However, the onset of an anti-ferromagnetic
short-range correlation of magnetic moments along [001] has been observed for Mn-cordierite by magnetisation and neutron diffraction
measurements. This short-range magnetic correlation becomes evident from diffuse scattering observed at 2 K. The diffuse scattering
has been interpreted in terms of a Blech-Averbach function.
Received: 30 June 1998 / Revised, accepted: 3 March 1999 相似文献
978.
P. A. van Aken V. J. Styrsa B. Liebscher A. B. Woodland G. J. Redhammer 《Physics and Chemistry of Minerals》1999,26(7):584-590
The Fe M
2,3-edge spectra of solid solutions of garnets (almandine-skiagite Fe3(Al1–xFex)2[SiO4]3 and andradite-skiagite (Fe1–xCax)3Fe2[SiO4]3), pyroxenes (acmite-hedenbergite (Ca1–xNax)(Fe2+
1−xFe3+
x)Si2O6), and spinels (magnetite-hercynite Fe(Al1–xFex)2O4) have been measured using the technique of parallel electron energy-loss spectroscopy (EELS) conducted in a transmission
electron microscope (TEM). The Fe M
2,3 electron energy-loss near-edge structures (ELNES) of the minerals exhibit a characteristic peak located at 4.2 eV and 2.2 eV
for trivalent and divalent iron, respectively, prior to the main maximum at about 57 eV. The intensity and energy of the pre-edge
feature varies depending on Fe3+/ΣFe. We demonstrate a new quantitative method to extract the ferrous/ferric ratio in minerals. A systematic relationship
between Fe3+/ΣFe and the integral intensity ratio of the main maximum and the pre-edge peak of the Fe M
2,3 edge is observed. Since the partial cross sections of the Fe M
2,3 edges are some orders of magnitude higher than those of the Fe L
2,3 edges, the Fe M
2,3 edges are interesting for valence-specific imaging of Fe. The possibility of iron valence-specific imaging is illustrated
by Fe M
2,3-ELNES investigations with high lateral resolution from a sample of ilmenite containing hematite exsolution lamellae that
shows different edge shapes consistent with variations in the Fe3+/ΣFe ratio over distances on the order of 100 nm.
Received: 14 April 1998 / Revised, accepted: 8 March 1999 相似文献
979.
Sven O. Egenhoff Arndt Peterhänsel Thilo Bechstädt Rainer Zühlke & Jürgen Grötsch 《Sedimentology》1999,46(5):893-912
The 720-m-thick succession of the Middle Triassic Latemàr Massif (Dolomites, Italy) was used to reconstruct the lagoonal facies architecture of a small atoll-like carbonate platform. Facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations, which reflect a syndepositional palaeorelief. Based on tracing of lagoonal flooding surfaces, the metre-scale shallowing-upward cycles are interpreted to be of allocyclic origin. Short-term sea-level changes led to subaerial exposure of wide parts of the marginal zone, resulting in the development of a tepee belt of varying width. Occasional emergence of the entire lagoon produced lagoon-wide decimetre-thick red exposure horizons. The supratidal tepee belt in the backreef area represented the zone of maximum elevation, which circumscribed the sub- to peritidal lagoonal interior during most of the platform's development. This tepee rim, the subtidal reef and a sub- to peritidal transition zone in between stabilized the platform margin. The asymmetric width of facies belts within individual metre-scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present-day south and west. The overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit, overlain by three tepee-rich intervals, separated by tepee-poor units composed of subtidal to peritidal facies. This stacking pattern reflects two third-order sequences during the late Anisian to early middle Ladinian. 相似文献
980.
In this paper an attempt has been made to search a new parameter for the prediction of the Indian summer monsoon rainfall.
For this purpose the relationship of the global surface-air temperature of four standard seasons viz., Winter (December-January-February),
Spring (March-April-May), Summer (June-July-August), Autumn (September-October-November) with the Indian summer monsoon rainfall
has been carried out. The same analysis is also carried out with surface-air temperature anomalies within the tropical belt
(30°S to 30°N) and Indian summer monsoon rainfall. For the present study data for 30 years period from 1958 to 1988 have been
used. The analysis reveals that there is a strong inverse relationship between the monsoon activity and the tropical belt
temperature. 相似文献