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991.
Subsurface dams to harvest rainwater— a case study of the Swarnamukhi River basin, Southern India 总被引:2,自引:0,他引:2
Declining water level trends and yields of wells, deterioration of groundwater quality and drying up of shallow wells are common in many parts of India. This is mainly attributed to the recurrence of drought years, over exploitation of groundwater, increase in the number of groundwater structures and explosion of population. In this subcontinent, the saving of water has to be done on the days it rains. India receives much of its rainfall in just 100 h in a year mostly during the monsoon period. If this water is not captured or stored, the rest of the year experiences a precarious situation manifest in water scarcity. The main objective behind the construction of subsurface dams in the Swarnamukhi River basin was to harvest the base flow infiltrating into sandy alluvium as waste to the sea and thereby to increase groundwater potential for meeting future water demands. An analysis of hydrographs of piezometers of four subsurface dams, monitored during October 2001–December 2002, reveals that there is an average rise of 1.44 m in post-monsoon and 1.80 m in the pre-monsoon period after the subsurface dams were constructed. Further, during the pre-monsoon month of June, much before construction of subsurface dams in October 2001, the water level was found fluctuating in the range of 3.1–10 m, in contrast to the fluctuation ranging from 0.4 to 3.1 m during the period following the construction of dams. Hence, the planning of rainwater harvesting structures entails thorough scientific investigations for identifying the most suitable locations for subsurface dams. 相似文献
992.
993.
994.
V. V. Egorova N. I. Volkova R. A. Shelepaev A. E. Izokh 《Mineralogy and Petrology》2006,88(3-4):419-441
Summary Ultramafic and mafic xenoliths in Ordovician Agardag alkaline basalt dikes from the Sangilen Plateau, southeastern Siberia,
provide samples from the upper mantle and crust beneath central Asia. Three major groups were distinguished among the xenoliths:
Group I xenoliths are spinel lherzolites, Group II xenoliths are spinel-garnet clinopyroxenites, and Group III comprises gabbroic
xenoliths with two subgroups: Group IIIa comprises garnet bearing gabbroids and Group IIIb is represented by garnet-free gabbroids.
The spinel lherzolite xenoliths represent the uppermost lithospheric mantle beneath the Sangilen Plateau and have geochemical
characteristics similar to those of primitive mantle. Spinel-garnet clinopyroxenite and gabbroic xenoliths are of igneous
origin and represent fragments of intrusive bodies crystallized at depths close to the mantle-crust boundary, as well as in
the lower and the upper crust. The gabbroic xenoliths are evidently the crystallization products of melts similar in major
and trace element composition to parental magma of the Bashkymugur gabbronorite-monzodiorite intrusion. Gabbroic xenoliths
from the Ordovician Agardag alkaline basalt dikes demonstrate the presence of intermediate magmatic chambers within the crust
beneath the Sangilen Plateau during the Early Palaeozoic. The relatively high equilibration temperatures of the mantle and
lower crust xenoliths in the Agardag alkaline basalt dikes are largely attributable to a plume occurring beneath the Sangilen
Plateau during the Ordovician. 相似文献
995.
I. N. Demidov 《Doklady Earth Sciences》2006,407(2):213-216
996.
Palaeoproterozoic A-type felsic magmatism in the Khetri Copper Belt, Rajasthan, northwestern India: petrologic and tectonic implications 总被引:1,自引:0,他引:1
Summary A number of small Palaeoproterozoic granitoid plutons were emplaced in the Khetri Copper Belt, which is an important Proterozoic
metallogenic terrane in the northeastern part of Aravalli mountain range. Contiguous Biharipur and Dabla plutons are located
about 15 km southeast of Khetri, close to a 170 km long intracontinental rift zone. The plutons are composed of amphibole-bearing
alkali-feldspar granites, comprising microcline-albite granite, albite granite and late-stage microgranite. The albite granite
in Biharipur is confined to the margins of the pluton, and shows extensive commingling with the synchronous mafic plutonics.
Geochemically, the albite granites are characterised by low K2O (∼0.5 wt.%) and elevated Na2O (∼7.0 wt.%) abundances. By contrast, the microcline-albite granite does not show any significant mafic-granite interactions
and shows normal concentrations of alkali elements. The granitoids display high concentrations of the rare earth (except Eu)
and high field strength elements, high values of Ga/Al (>2.5), agpaitic index and Fe*-number. These features together with their alkaline metaluminous and ferroan nature classify the rocks as typical A-type
within-plate granites. All the granitoid facies display similar REE and incompatible element profiles indicating their cogenetic
nature. These granitoids were emplaced in a shallow crustal chamber under relatively low pressures, high temperature (≥850 °C)
and relatively oxidising conditions. The oxidised nature, HFSE concentrations and Nd isotope data (ɛNd = −1.3 to −2.9) favour
derivation of these granitoid rocks from crustal protoliths. The generation of albite granite is attributed to the replacement
of alkali feldspar and plagioclase of the original granite by pure albite as a consequence of pervasive infiltration of a
high Na/(Na + K) fluid at the late-magmatic stage. This model may have wider significance for the generation of albite granites/low-K
granites or albitites in other areas. The A-type plutonism under consideration seems to be an outcome of ensialic rifting
of the Bhilwara aulacogen. 相似文献
997.
998.
The contents of regurgitated Long-eared Owls (Asio otus) pellets collected in Minqin Desert Experimental Research Station of northwestern China were analysed. A total of 303 individuals representing five species of rodents and one of bird were identified in the pellets. By frequency, the most common species taken by Long-eared Owls was Meriones meridianus, followed by Cricetulus barabensis and Phodopus roborovskii. By biomass, Meriones meridianus was the most important species taken, followed by C. barabensis and Rhombomys opimus. Our results suggest that the Long-eared Owls were nocturnal hunters and fed on a wide range of animals with respect to their habitats. 相似文献
999.
I. D. L. Foster T. M. Mighall H. Proffitt D. E. Walling P. N. Owens 《Journal of Paleolimnology》2006,35(4):881-895
We present 137Cs profiles for three low lying coastal lagoons in Southwest England that show a decline in activity with sediment depth.
137Cs inventories are lower than expected by comparison with local reference inventories despite the fact that sampling was undertaken
in the deep-water zone of each lake where sediment and 137Cs focusing would be expected. At all three locations, lake sediment 7Be and unsupported 210Pb (210Pbun) inventories are not significantly lower than the local reference inventory. 137Cs inventories in the study cores range from 38 to 95% of local reference inventories. The standing water level and mud: water
interface at two sites are below maximum tide level and, at all three sites, salinity increases significantly in the water
columns between low and high tide and in the pore waters of the underlying sediments. We suggest that the difference in hydrostatic
pressure between sea level and standing water levels in the lagoons forces salt water up through the sediment column and that
monovalent cations (especially Na+ and K+) replace 137Cs on exchange sites leading to the upward migration and loss of 137Cs. Rising sea levels may therefore contribute to remobilisation and release of 137Cs to the aquatic environment from the sediments of coastal lagoons. 相似文献
1000.
Miriam Dühnforth Andreas G. N. Bergner Martin H. Trauth 《Journal of Paleolimnology》2006,36(3):281-294
The Nakuru-Elmenteita basin in the Central Kenya Rift, contains two shallow, alkaline lakes, Lake Nakuru (1770 m above sea level) and Lake Elmenteita (1786 m). Ancient shorelines and lake sediments at 1940 m suggest that these two lakes formed a single large and deep lake as a result of a wetter climate during the early Holocene. Here, we used a hydrological model to compare the precipitation–evaporation balance during the early Holocene to today. Assuming that the Nakuru-Elmenteita basin was hydrologically closed, as it is today, the most likely climate scenario includes a 45% increase in mean-annual precipitation, a 0.5°C decrease in air temperature, and an increase of 9% in cloud coverage from the modern values. Compared to the modeling results from other East African lake basins, this dramatic increase in precipitation seems to be unrealistic. Therefore, we propose a significant flow of water from the early Holocene Lake Naivasha in the south towards the Nakuru-Elmenteita basin to compensate the extremely negative hydrological budget of this basin. Since we did not find any field evidence for a surface connection, as often proposed during the last 70 years, the hydrological deficit of the Nakuru-Elmenteita basin could have also been compensated by a subsurface water exchange. 相似文献