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SK Nag 《Journal of the Indian Society of Remote Sensing》1998,26(1-2):69-76
Remote sensing techniques using satellite imagery have proved to be an indispensible tool in morphometric analysis and groundwater studies. In the present area, morphometric analysis using temote sensing techniques have been carried out in Chaka river sub-basin of Manbazar Block, Purulia district, West-Bengal, which is one of the most drought affected area in West-Bengal. The parameters worked out include Bifurcation ratio (Rb), Stream length (Lu). Form factor (Rf), Circulatory ratio (Rc), and Drainage density. The morphometric analysis suggests that the area is covered by fractured, resistant, permeable rocks, the drainage network not so affected by tectonic disturbances. Using satellite imageries of LANDSAT and IRS, different hydrogeomorphological units have been delineated. The study shows that moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration. 相似文献
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Sudarsana Rao Pandi Rayaprolu Kiran Nittala S. Sarma A. S. Srikanth V. V. S. S. Sarma M. S. Krishna D. Bandyopadhyay V. R. Prasad T. Acharyya K. G. Reddy 《Ocean Dynamics》2014,64(1):89-101
Absorption spectra, particulate pigments, and hydrochemical constituents were measured in the western Bay of Bengal (BoB) during July-August 2010 when influence of river discharge is at peak. Chromophoric dissolved organic matter (CDOM) absorption coefficient (aCDOM(440)) displayed a significant inverse linear relationship with salinity in the surface waters implying conservative mixing of marine and terrestrial end members. The northern part of the study area is influenced by discharge from the river Ganga and a dominant terrestrial CDOM signal is seen. The southern part receives discharge from peninsular rivers with corresponding signals of higher CDOM than the linear model would indicate and higher UV-specific absorption coefficient (SUVA) indicating more aged and humified DOM. Lower contribution of CDOM to total non-water absorption and higher phytoplankton biomass (chlorophyll a absorption coefficient, aph(440)) but lower chlorophyll a specific phytoplankton absorption coefficient (a ph * (440)) characterize the northern part, compared to the southern part. Chlorophyll b had a distinct linear relationship with chlorophyll a in the latter. The size index (SI) indicated dominance of microphytoplankton in the northern and nano and picophytoplankton in the southern parts. Chlorophyll a is significantly related to a ph * (440) by an inverse power model in the northern part but by an inverse linear model in the southern part. Our study suggests that knowledge of the phytoplankton community structure is essential to improve chlorophyll a algorithm in the coastal Bay of Bengal. 相似文献
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V. V. S. S. Sarma M. S. Krishna R. Viswanadham G. D. Rao V. D. Rao B. Sridevi B. S. K. Kumar V. R. Prasad Ch. V. Subbaiah T. Acharyya D. Bandopadhyay 《Journal of Oceanography》2013,69(1):45-55
A study on biogeochemical cycling in the west coastal Bay of Bengal was undertaken during the peak discharge period to understand the influence of enhanced stratification and primary production on the possible intensification of the oxygen minimum zone (OMZ). Our study reveals that oxygen concentrations were below the detection limits in the northwestern (NW) coastal Bay of Bengal between 100 and 500 m associated with strong stratification and high phytoplankton biomass. Such low oxygen concentrations have never been reported so far from the coastal Bay of Bengal. Despite the existence of an environment conducive to denitrification in the coastal Bay of Bengal, accumulation of neither secondary nitrite nor nitrous oxide (N2O) was observed. The absence of denitrification was reported to be caused by faster scavenging of organic matter and low bacterial respiration rates; in contrast, our results suggest that neither of these factors are potential reasons for the absence of denitrification in the coastal Bay of Bengal. 相似文献
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Sediment resuspension during and after mechanical excavation of macrophytes may have a significant impact on resident fish populations. Unfortunately, little is known about the influence of this sediment on the respiratory performance and feeding abilities of fishes in New Zealand waterways. We examined the effects of suspended sediment (SS) concentrations previously observed after a large-scale macrophyte removal operation on oxygen consumption (MO2) and feeding rates of brown trout (Salmo trutta). MO2 at 0 mg L?1, 150 mg L?1, 300 mg L?1, 450 mg L?1 and 600 mg L?1 of SS was measured using semi-closed respirometry. Feeding rates at the same SS concentrations were also measured using laboratory tank experiments. Results suggest that SS concentrations up to 600 mg L?1 have no effect on MO2. Conversely, feeding rates were significantly reduced at 450 mg L?1 (22% reduction) and 600 mg L?1 (31% reduction), indicating that sediment concentrations above 450 mg L?1 may negatively affect brown trout populations. 相似文献
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Mafic-ultramafic rocks of Archaean age constitute a significant component of the Eastern Indian Craton. These occur in two
different modes. In the eastern belt these occur as a long, linear enclave within the Singhbhum granite and the primary banding
in them is subvertical. In the more extensive western belt along the periphery of the Singhbhum granite, the disposition of
the primary banding is subhorizontal.
The major rock type in both the belts is meta-basalt with minor peridotitic komatiite and basaltic komatiite occurring in
the eastern belt. Rare ultramafic rocks with cumulate textures are present in both the belts. The larger volume of the basaltic
rocks preclude the possibility of their being derived by fractional crystallization of the high-MgO components.
On the basis of trace element and REE characters the rocks may be classified into three groups. One of the groups shows a
tholeiitic trend and include samples mostly from the eastern belt while the second consisting mostly of samples from the western
belt shows a calc-alkaline trend. The third group includes samples having elemental ratios intermediate between these two
groups. Zr/Nb ratios for the tholeiitic and calc-alkaline samples are different suggesting their sources to be different.
The tholeiitic samples have been generated from a source having chondritic REE characters, while the calc-alkaline samples
have been generated from a source with LREE enriched character. The high-MgO components in both the groups are suggested to
represent high degrees of melting compared to the basalts in each group.
It is further suggested that the tholeiitic basalts have been generated relatively early from a chondritic source. Down-buckling
of this material has added LREE enriched melts to the source, thereby changing its character into a LREE enriched one. Melting
of a source with such changed character has subsequently produced the calc-alkaline melts. Rocks with variable but intermediate
characters between these two groups have been generated as a result of contamination between these two groups. 相似文献
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S.K. Acharyya 《Tectonophysics》1979,56(3-4)
The fit and configuration of India and Southeast Asia vis-à-vis Australia—Antarctica are critically analysed together with the evolutionary history of the Himalaya. Peninsular India, Himalaya, Tibet and Southeast Asia appear to be tied up with the development of Paleozoic-Mesozoic peripheral “Gondwanide” and Mesozoic-Cenozoic Alpine-Himalayan-Indonesian orogenic belts. Southeast Asia and Tibet are usually included within Cathaysia-Laurasia. The extent of the Tethys, separating Gondwanaland from the latter, thus appears to be much narrower than commonly believed. An alternative Gondwanaland reconstruction is proposed, placing India amidst a proto-Indian Ocean adjacent to Africa, but separated from Antarctica-Australia. 相似文献
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S.K. Acharyya 《Gondwana Research》2005,8(1):55-66
Late Quaternary stratigraphy and sedimentation in the Ganga Alluvial Plain and the Bengal Basin have influenced arsenic contamination of groundwater. Arsenic contaminated aquifers are pervasive within lowland organic rich, clayey deltaic sediments in the Bengal Basin and locally within similar facies in narrow, entrenched river valleys within the Ganga Alluvial Plain. These were mainly deposited during early-mid Holocene sea level rise. Arsenic was transported from disseminated sources as adsorbed on dispersed phases of hydrated-iron-oxide. These were preferentially entrapped as sediment coatings on organic-rich, fine-grained deltaic and floodplain sediments. Arsenic was released later to groundwater mainly by reductive dissolution of hydrated-iron-oxide and corresponding oxidation of sediment organic matter. Strong reducing nature of groundwater in the Bengal Basin and parts of affected middle Ganga floodplains is indicated by high concentration of dissolved iron (maximum 9-35 mg/l). Groundwater being virtually stagnant under these settings, released arsenic accumulates and contaminates groundwater. The upland terraces in the Bengal Basin and in the Central Ganga Alluvial Plain, made up of the Pleistocene sediments are free of arsenic contamination in groundwater. These sediments are weakly oxidised in nature and associated groundwater is mildly reducing in general with low concentration of iron (<1 mg/l), and thus incapable to release arsenic. These sediments are also flushed free of arsenic, released if any, by groundwater flow due to high hydraulic head, because of their initial low-stand setting and later upland terraced position. 相似文献
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