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941.
Stable isotope evidence of dual (Arabian Sea and Bay of Bengal) vapour sources in monsoonal precipitation over north India 总被引:2,自引:0,他引:2
High resolution time series data of hydrogen (δD) and oxygen (δ18O) isotope values of precipitation have been generated for the first time at Kolkata, eastern India where the summer monsoon clouds from Bay of Bengal (BOB) commence their journey over India. Use of a Rayleigh cum two component mixing model and comparison of Kolkata data with the International Atomic Energy Agency (IAEA)–Global Network of Isotopes in Precipitation (GNIP) data base of New Delhi suggest that the precipitation at New Delhi cannot be explained by simple continental effect of a BOB vapour source alone, traveling and raining successively along Kolkata–New Delhi route. It is necessary to invoke an admixture of 20% vapour originating from the Arabian sea with the vapour coming from BOB and finally causing summer monsoon rains at New Delhi. The findings have major implications to the regional water vapour budget over India. 相似文献
942.
The dytiscid beetle Rhantus sikkimensis, Regimbart, 1899 (Coleoptera: Dytiscidae), a member of the freshwater insect communities of the Darjeeling Himalayas, were noted to predate on the coexisting larvae of Chironomus sp. Meigen. Evaluation of predation by R. sikkimensis on Chironomus sp. larvae, in the laboratory, revealed that a single adult morph of R. sikkimensis could kill and consume on an average 10–90 and 10–78 numbers of small and large Chironomus sp. larvae, respectively, per day, depending on the prey density. The attack rate ranged between 520 and 537, and the handling time ranged between 4.3 and 8.6 depending on the size of the preys. The predation varied with respect to predator density also, with a maximum of 151 larvae killed by three predators per day. Two indices of predation, ingestion rate (IR) ranging between 13.33 and 74.15 larvae/day/predator and clearance rate (CR) ranging between 19.67 and 39.99 L prey/day/predator, varied with the prey size and predator density, significantly, when the predation was observed for 9 consecutive days, at two predator densities. It was also noted that R. sikkimensis predated on an average 9.8 larvae of Chironomus sp. and 1 larva of Culex sp., when the larvae of both the species are present together as preys, showing a preference for the Chironomus sp. larvae. 相似文献
943.
944.
Arsenic contamination in groundwater affecting West Bengal (India) and Bangladesh is a serious environmental problem. Contamination
is extensive in the low-lying areas of Bhagirathi–Ganga delta, located mainly to the east of the Bhagirathi River. A few isolated
As-contaminated areas occur west of the Bhagirathi River and over the lower parts of the Damodar river fan-delta. The Damodar
being a Peninsular Indian river, the arsenic problem is not restricted to Himalayan rivers alone. Arsenic contamination in
the Bengal Delta is confined to the Holocene Younger Delta Plain and the alluvium that was deposited around 10,000–7,000 years
bp, under combined influence of the Holocene sea-level rise and rapid erosion in the Himalaya. Further, contaminated areas are
often located close to distribution of abandoned or existing channels, swamps, which are areas of surface water and biomass
accumulation. Extensive extraction of groundwater mainly from shallow aquifers cause recharge from nearby surface water bodies.
Infiltration of recharge water enriched in dissolved organic matter derived either from recently accumulated biomass and/or
from sediment organic matter enhanced reductive dissolution of hydrated iron oxide that are present mainly as sediment grain
coatings in the aquifers enhancing release of sorbed arsenic to groundwater. 相似文献
945.
南岭以南东江流域临江地层剖面LJ3层位是一套红色沙质沉积物,经TL年代测定其形成于(9 500±800)—(19 600±1 800) a BP的MIS2阶段。根据对该层16个样品(LJ3\|100到LJ3-85)的粒度分析结果,发现:①各个粒组配置给不同样品具有大致相同的含量;②)Md、Mz、σ、Sk和Kg从LJ3\|100到LJ3\|85摆动在一个狭窄的区间;③诸样品在概率累积曲线上的各个段落以基本相同的斜率平行延展。经研究,这三个方面都共同的反映了LJ3的风成特征。据此认为,该层是发生在岭南MIS2阶段内的红色沙质沉积物,反映了当时干旱的气候。 相似文献
946.
南疆铁路沿线风沙危害与工程防治 总被引:4,自引:0,他引:4
文章通过对南疆铁路沿线的概况、地质地貌、植被分布及气象状况,特别是风信状况的调查,阐明了沿线的自然状况。20世纪90年代,研究工作者在沿线风沙活动最为剧烈的巴楚地区设置定位观测站,对典型的活动沙丘特征进行观测,获得了沙丘移动的定量数据。同时在各种类型典型戈壁地段,设置积沙仪,在不同的风速情况下收集动态流沙,总结出当地的输沙率公式,为风沙防护提供了直接的设计依据。通过对各种工程防治措施的调查研究、特别是新材料试验,归纳出各种工程防沙结构的功能效果,提出适宜当地条件的新工程防沙结构模式。 相似文献
947.
The Palaeoproterozoic Aravalli Supergroup in Salumber region includes a basal unit of metabasic volcanic rocks (Salumber volcanic
rocks) overlain by a volcaniclastic/conglomerate one. Although these volcanic rocks have been metamorphosed to green-schist
facies, some primary volcanic features are still preserved. This metabasic volcanic sequence can be further differentiated
on the basis of textural variations, and the mineral assemblages are: (a) oligoclase + actinolite + chlorite + epidote; and
(b) oligoclase + hornblende+ chlorite + biotite + Fe-Ti oxides. The SiO2 content ranges from ∼47.7 to 55.8% and MgO from ∼4.2 to 12.8%. Geochemical characteristics allow their subdivision into high
Mg and Fe tholeiites. Inverse relationship of MgO with silica, alkalis and Zr is generally consistent with fractionation mechanism,
also suggested by a change in colour of the rocks from dark greenish to light greenish towards the upper parts of the sequence.
These metabasic volcanic rocks are enriched in incompatible trace elements and LREE (La = 30 − 40 × chondrite, Lu = 2 − 5
× chondrite), and demonstrate affinity mainly with MORB and within plate settings in geochemical tectonic discrimination schemes.
The geochemical characteristics suggest a complex evolutionary history envisaging derivation of the melt from an enriched
heterogeneous lithospheric source. 相似文献
948.
V. Purnachandra Rao Pratima M. Kessarkar R. Nagendra E. V. S. S. K. Babu 《Journal of Earth System Science》2007,116(6):525-536
Cretaceous phosphorites from the onshore of Tamil Nadu have been investigated for their origin and compared with those in
the offshore. Cretaceous phosphorites occur as light brown to yellowish brown or white nodules in Karai Shale of the Uttatur
Group in the onshore Cauvery basin. Nodules exhibit phosphatic nucleus encrusted by a chalky shell of carbonate. The nucleus
of the nodules consists of light and dark coloured laminae, phosphate peloids/coated grains and detrital particles interspersed
between the laminae. Scanning electron microscope (SEM) studies reveal trapping and binding activity of microbial filaments.
A mat structure with linearly arranged microbial filaments and hollow, cell-based coccoid cyanobacterial mat are present.
Nodules contain abundant carbonate fluorapatite, followed by minor calcite, quartz and feldspar. The P2O5 content of the phosphorites ranges from 18 to 26%. The CaO/P2O5, Sr and F contents are higher than that of pure carbonate fluorapatite. Concentrations of Si, Al, K, Fe, and Ti are low.
We suggest that the nuclei of the nodules represent phosphate clasts related to phosphate stromatolites formed at intertidal
conditions. At high energy levels the microbial mats were disintegrated into phosphate clasts, coated with carbonate and then
reworked into Karai Shale. On the other hand, Quaternary phosphorites occur as irregular to rounded, grey coloured phosphate
clasts at water depths between 180 and 320m on the continental shelf of Tamil Nadu. They exhibit grain-supported texture.
Despite Quaternary in age, they also resemble phosphate stromatolites of intertidal origin and reworked as phosphate clasts
onto the shelf margin depressions. Benthic microbial mats probably supplied high phosphorus to the sediments. Availability
of excess phosphorus seems to be a pre-requisite for the formation of phosphate stromatolites. 相似文献
949.
Estimation of seismic spectral acceleration in Peninsular India 总被引:6,自引:0,他引:6
Peninsular India (PI), which lies south of 24°N latitude, has experienced several devastating earthquakes in the past. However,
very few strong motion records are available for developing attenuation relations for ground acceleration, required by engineers
to arrive at rational design response spectra for construction sites and cities in PI. Based on a well-known seismological
model, the present paper statistically simulates ground motion in PI to arrive at an empirical relation for estimating 5%
damped response spectra, as a function of magnitude and source to site distance, covering bedrock and soil conditions. The
standard error in the proposed relationship is reported as a function of the frequency, for further use of the results in
probabilistic seismic hazard analysis. 相似文献
950.
《The Professional geographer》1983,35(2):230-260
Book Reviewed in this article: Rabat: Urban Apartheid in Morocco . Janet Abu -Lughod . Marketplaces in a Developing Country: The Case of Western Nigeria . Isaac Ayinde Adalemo . Farming Development and Space: A World Agricultural Geography . Bernd Andreae . Section and Party: A Political Geography of American Presidential Elections, from Andrew Jackson to Ronald Reagan . J. Clark Archer and Peter J. Taylor . Women and Space: Ground Rules and Social Maps . Shirley Ardener , ed. European Progress in Spatial Analysis . R. J. Bennett , ed. The Origins of Academic Geography in the United States . Brian W. Blouet Geographic Perspectives on Global Problems . Ronald Reed Boyce . Seasonal Dimensions to Rural Poverty . Robert Chambers , Richard Longhurst and Arnold Pacey eds. The New Nationalism and the Use of Common Spaces: Issues in Marine Pollution and the Exploitation of Antarctica . Jonathan I. Charney , ed. Communications Tomorrow: The Coming of the Information Society . Edward Cornish , ed. The Design of Suburbia . Arthur Edwards . Explorer on the Northern Plains: Lieutenant Gouverneur K. Warren's Preliminary Report of Explorations in Nebraska and Dakota in the Years 1855–56–57. With an Introduction by Frank N. Schubert . The Changing Climate: Responses of the Natural Flora and Fauna . Michael J. Ford . Essentials of Physical Geography . Robert E. Gabler , Robert J. Sager , Sheila Brazier , and Daniel L. Wise. The Road to Jaramillo . William Glen . Valued Environments . John R. Gold and Jacquelin Burgess , eds. Proximity and Preference: Problems in the Multidimensional Analysis of Large Data Sets . Reginald G. Golledge and John N. Rayner , eds. A Search for Common Ground . Peter Gould and Gunnar Olsson , eds. Geography: Its History and Concepts . Arild Holt -Jensen . A Population Geography . Huw R. Jones . The Human Mosaic: A Thematic Introduction to Cultural Geography, 3rd ed. Terry G. Jordan and Lester Rowntree . Urban Social Geography: An Introduction . Paul Knox . The Anatomy of Job Loss: The How, Why and Where of Employment Decline . Doreen Massey and Richard Meegan . The Information Society as Post-Industial Society . Yoneji Masuda . Map Librarianship, 2nd ed. Harold Nichols . India: Cultural Patterns and Processes . Allen G. Noble and Ashok K. Dutt , eds. The God that Limps: Science and Technology in the Eighties . Colin Norman . Geography: An Introductory Perspective . Robert E. Norris , Keith D. Harries and John D. Vitek . The Politics of Technology Assessment . David M. O'Brien and Donald A. Marchand . Ethnic Segregation in Cities . Ceri Peach , Vaughan Robinson and Susan Smith , eds. Churches and Church Membership in the United States, 1980 . Bernard Quinn , Herman Anderson , Martin Bradley , Paul Goetting and Peggy Shriver . Energy in Australia: Politics and Economics . Hugh Saddler . Development from Above or Below? The Dialectics of Regional Planning in Developing Countries . Walter B. Stóuhr and D. R. Fraser Taylor , eds. Human Impact on the Ecosystem . Joy Tivy and Greg O'Hare . Plants and People: Vegetation Change in North America . Thomas R. Vale . The Mapmakers: The Story of the Great Pioneers in Cartography from Antiquity to the Space Age . John Noble Wilford . 相似文献