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排序方式: 共有75条查询结果,搜索用时 15 毫秒
1.
Manish Kumar M. Someshwar Rao Bhishm Kumar Algappan Ramanathan 《Hydrogeology Journal》2011,19(2):463-474
Recharge zones and sources in an urban setup (NCT of Delhi, India) were identified using environmental isotopes (2H, 3H, 18O); they were then correlated with hydrogeological conditions. The isotopic results showed that groundwater is being recharged by surface water during the dry season, while recharge associated with local precipitation becomes prominent during the monsoon. The effect of source-water evaporation and altitude on the isotopic characteristics of groundwater was clearly noted. A gradual increase in groundwater age, i.e. decrease in tritium content, while moving away from the river/canals/drains, suggests a degree of mixing of old-aged groundwater with relatively young recharging water. Further, to substantiate the findings of isotopic investigations, surface recharge conditions were differentiated into potential pervious (recharge prone) and impervious (recharge resistant) surfaces through mapping of potential recharge areas based on soil type and water-table depth, to depict a three-dimensional illustration of hydrogeologically mediated recharge zones of the area. The hydrogeological evidence thus obtained about the spatial distribution of permeable zones, slope and boundary conditions, aptly substantiates the isotopic findings. The study seeks its impact by correlation of the isotopic findings with the regional groundwater flow regime which has been altered by the urban development. 相似文献
2.
A study of arsenic,iron and other dissolved ion variations in the groundwater of Bishnupur District,Manipur, India 总被引:1,自引:1,他引:0
Jayalakshmi Devi Oinam AL. Ramanathan Anurag Linda Gurmeet Singh 《Environmental Earth Sciences》2011,62(6):1183-1195
The presence of arsenic (As) in groundwater and its effect on human health has become an issue of serious concern in recent
years. The present study assessed the groundwater quality of the Bishnupur District, Manipur, with respect to drinking water
standards. Higher concentrations of pH, iron and phosphate were observed at several locations. Phosphate and iron levels were
highest in the pre-monsoon, followed by monsoon and post-monsoon seasons. The arsenic concentrations were highest during post-monsoon
(1–200 μg L−1) as compared to pre-monsoon (1–108 μg L−1) and monsoon (2–99 μg L−1). Kwakta and Ngakhalawai show higher levels of arsenic concentration as compared to the prescribed World Health Organization
(WHO) and Bureau of Indian Standards (BIS) norms. Arsenic showed a strong positive correlation with phosphate and negative
correlation with sulphate, suggesting a partial influence of anthropogenic sources. The study suggests that the Bishnupur
area has an arsenic contamination problem, which is expected to increase in the near future. 相似文献
3.
Particle Filter-based assimilation algorithms for improved estimation of root-zone soil moisture under dynamic vegetation conditions 总被引:1,自引:0,他引:1
Karthik Nagarajan Jasmeet JudgeWendy D. Graham Alejandro Monsivais-Huertero 《Advances in water resources》2011,34(4):433-447
In this study, we implement Particle Filter (PF)-based assimilation algorithms to improve root-zone soil moisture (RZSM) estimates from a coupled SVAT-vegetation model during a growing season of sweet corn in North Central Florida. The results from four different PF algorithms were compared with those from the Ensemble Kalman Filter (EnKF) when near-surface soil moisture was assimilated every 3 days using both synthetic and field observations. In the synthetic case, the PF algorithm with the best performance used residual resampling of the states and obtained resampled parameters from a uniform distribution and provided reductions of 76% in root mean square error (RMSE) over the openloop estimates. The EnKF provided the RZSM and parameter estimates that were closer to the truth than the PF with an 84% reduction in RMSE. When field observations were assimilated, the PF algorithm that maintained maximum parameter diversity offered the largest reduction of 16% in root mean square difference (RMSD) over the openloop estimates. Minimal differences were observed in the overall performance of the EnKF and PF using field observations since errors in model physics affected both the filters in a similar manner, with maximum reductions in RMSD compared to the openloop during the mid and reproductive stages. 相似文献
4.
The chemical compositions of various ions in meltwater of the Chhota Shigri glacier were analysed during the observation period from May to October 2010. Total 164 samples of meltwater were collected in two times a day at 8.0 a.m and 6.0 p.m. Bicarbonate and calcium were the dominant anion and cation in meltwater of the investigation area. High ratios of (Ca + Mg) versus TZ+ and (Ca + Mg) versus (Na + K) demonstrate that hydrogeochemistry of the study area was mainly governed by carbonate type weathering. The average sulphate mass fraction of meltwater was computed to be 0.31 ± 0.12, showing dominancy of bicarbonate over sulphate. This excess bicarbonate would be generated by an alternative proton supply mechanism due to biological activities in the bed rock lithology and sulphide oxidation may be about the same as carbonation as a driver of chemical weathering at Chhota Shigri glacier. In general, major ions and total dissolved solid concentrations showed decreasing trend with increasing discharge from the study area. The average daily mean dissolved load of this glacier was much lower than that of the Gangotri glacier, which may be due to low meltwater runoff and lithology of the investigation area. The cation weathering rates of study area for early, peak and late melt seasons were computed to be 694, 1631 and 481 meq m?2 a?1, respectively. The average value of chemical denudation rates of the Chhota Shigri glacier meltwater was found lower than that of the Dokriani glacier. 相似文献
5.
Evaluation of geochemical impact of tsunami on Pichavaram mangrove ecosystem,southeast coast of India 总被引:1,自引:0,他引:1
The 26 December 2004-tsunami has deposited sediments in the Pichavaram mangrove ecosystem, east coast of India. Ten surface
and three core sediment samples were collected within 30 days of the event and analyzed for nutrients. Water samples were
also analyzed to see the impact of tsunami on the geochemical behavior of nutrients. An increase in the concentration of various
nutrients namely nitrate and phosphate was observed. The geochemistry of the mangrove forest was observed to be influenced
by a number of factors like rapid increase of aquaculture farms, agricultural practices and the anthropogenic discharge from
the nearby-inhabited areas. Further the sediment column was disturbed due to energetic tsunami waves, which has caused a sheer
increase in the dissolved oxygen in water. As a result, the change in the redox potential has resulted in change in the nutrients
absorbed/associated with the sediments. In addition, role of retreating water after tsunami on the nutrient geochemistry was
also evaluated. 相似文献
6.
D. P. sharma A. K. Jain S. C. Chakravarty K. Kasturirangan K. R. Ramanathan U. R. Rao 《Astrophysics and Space Science》1972,17(2):409-425
The electron production rates in the night-time D-region arising from the transit of strong celestial X-ray sources Sco X-1,
Tau X-1 and Galactic Center are estimated and compared with the ambient electron production rates resulting from other known
stable agencies. Using the experimentally measured values of the night-time electron densities, the number of additional electrons/cc
expected from the passage of these sources is computed. For the 164 kHz transmission from Tashkent, received at Ahmedabad,
the associated enhancement in the attenuation is calculated using the full wave admittance technique of Barron and Budden.
Reasonable agreement is shown to exist between the calculated values of the attenuation and those of direct observations. 相似文献
7.
Manish Kumar Bhawna Sharma AL. Ramanathan M. Someshwar Rao Bhishm Kumar 《Environmental Geology》2009,56(6):1171-1181
Present study is an effort to distinguish between the contributions of natural weathering and anthropogenic inputs towards
high salinity and nutrient concentrations in the groundwater of National Capital Territory (NCT) Delhi, India. Apart from
the source identification, the aquifer of entire territory has been characterized and mapped on the basis of salinity in space
and water suitability with its depth. Major element chemistry, conventional graphical plots and specific ionic ratio of Na+/Cl−, SO4
2−/Cl−, Mg2+/Ca2+ and Ca2+/(HCO3
− + SO4
2−) are conjointly used to distinguish different salinization sources. Results suggest that leaching from the various unlined
landfill sites and drains is the prime cause of NO3
− contamination while study area is highly affected with inland salinity which is geogenic in origin. The seasonal water level
fluctuation and rising water level increases nutrients concentration in groundwater. Mixing with old saline sub-surface groundwater
and dissolution of surface salts in the salt affected soil areas were identified as the principle processes controlling groundwater
salinity through comparison of ionic ratio. Only minor increase of salinity is the result of evaporation effect and pollution
inflows. The entire territory has characterized into four groups as fresh, freshening, near freshening and saline with respect
to salinity in groundwater. The salinity mapping suggests that in general, for drinking needs, groundwater in the fresh, freshening
and near freshening zone is suitable up to a depth of 45, 20 and 12 m, respectively, while the saline zones are unsuitable
for any domestic use. In the consideration of increasing demand of drinking water in the area; present study is vital and
recommends further isotopic investigations and highlights the need of immediate management action for landfill sites and unlined
drains. 相似文献
8.
Anna Mani C. R. Sreedharan B. B. Huddar Y. Ramanathan 《Pure and Applied Geophysics》1972,100(1):101-108
Summary Results of measurements of the atmospheric electrical conductivity and potential gradient made during the sixth Scientific Cruise of the Indian Oceanographic Ship INS Kistna in the Bay of Bengal during February–March 1963 are presented. Observations were made when the skies were generally clear and the sea calm, in the geographical area 8°N to 17°N and 80°E to 95°E, on the outward journey of INS Kistna from Madras (80°E, 13°N) to Port Blair (93°E, 12°N) and on the return journey to Madras.Over the ocean where there are no local sources of pollution, the measured values of conductivity and potential gradient are in agreement with theoretical values, assuming that an ion equilibrium exists, that ions are destroyed primarily by collision with small ions of opposite sign and that small ions are produced only by cosmic radiation. The values of electrical conductivity obtained are generally of the same order as those to be expected from theoretical considerations and in general agreement with those obtained during the Carnegie cruises in the Indian Ocean in 1920. There are, however, significant variations near the coast where the electric structure above the ocean is affected by continental sources of pollution. Conductivity values near the land are about half that in the unpolluted air over the ocean but prevailing winds prevent the extension of pollution beyond 100–200 km from the coast in this season.
Zusammenfassung Es wird über Messungen der luftelektrischen Leitfähigkeit und des Potentialgefälles berichtet, welche während der Sechsten Wissenschaftlichen Kreuzfahrt des indischen Ozeanographischen Forschungsschiffes Ins Kistna in der Bengalischen Bucht im Februar und März 1963 ausgeführt wurden. Die Beobachtungen sind im allgemeinen bei klarem Himmel und ruhiger See gemacht worden, und zwar in dem geographischen Bereich zwischen 8 und 17°N und 80 und 95°E während der Ausfahrt der INS Kistna von Madras (80°E, 13°N) nach Port Blair (93°E, 12°N) und auf der Rückreise nach Madras. In den Bereichen des Ozeans, in denen keine örtlichen Pollutionsquellen bestehen, stimmen die gemessenen Werte der Leitfähigkeit und des Potentialgefälles mit den theoretischen Werten überein, die man erhält, wenn man annimmt, dass ein Ionengleichgewicht besteht, dass die schnellen Ionen vorwiegend durch Zusammenstoss mit schnellen Ionen des entgegengesetzten Vorzeichens vernichtet werden, und dass die schnellen Ionen nur durch die kosmische Höhenstrahlung erzeugt werden. Die Werte der Leitfähigkeit stimmen mit denen überein, die man aus theoretischen Überlegungen gewinnt, und auch mit denen, die während der Kreuzfahrten des Forschungsschiffes Carnegie im Indischen Ozean im Jahre 1920 gemessen Küste sind jedoch bedeutsame Abweichungen festzustellen, wo die elektrischen Verhältenisse über dem Ozean durch Pollutionsquellen auf dem Lande beeinflusst werden. Die Leitfähigkeitswerte nahe dem Land sind nur ungefähr halb so gross wie die in der pollutionsfreien Luft des offenen Ozeans-jedoch haben die während der Mess-Jahreszeit vorherrschenden Winde eine Ausbreitung der Pollutionszone auf einen Bereich von 100 bis 200 km von der Küste beschränkt.相似文献
9.
The paper presents the results of a photometric study of the hydroxyl bands (7–2) and (8–3) in the night airglow spectrum at Mt. Abu in the winter and spring of 1966–1972. The observed nocturnal variation differs from the variation expected from the theoretical studies of Hesstvedt, Hunt, Shimazaki and others. Instead of a gradual fall in intensity after sunset to shortly before sunrise, a peak in intensity is found at a time which changes from month to month and roughly coincides with the transit times of the X-ray star TAU (XR-1)-Crab Nebula. Anexplanation of the observed phenomenon is offered in terms of the increased energy output into the D and E regions of the atmospheres, increased eddy diffusion, and production, of additional O(3P) and O3 in the region 80–95 km. O3 reacting with H gives rise to OH*. 相似文献
10.
The characteristics of simulated air flow over Andaman Islands are studied with a two-dimensional version of the University
of Virginia meso scale model (UVMM). Using the observed synoptic data as initial conditions, 24 hr simulations are obtained
for a day each in April and November. These days are chosen to study the variations in the simulated flow pattern under different
synoptic conditions including precipitation effects. A large scale condensation scheme is employed to consider the effect
of latent heat release on the perturbations. The results show that the latent heat released by condensation strengthens the
intensity of perturbations and the topography accelerates the arrival of sea breeze by about an hour. The model-simulated
results, given in graphical form, are discussed and compared with available observations. 相似文献