Hydrogeological processes controlling the release of arsenic in parts of 24 Parganas district,West Bengal     

Neha Singh  Ravi Prakash Singh  Saumitra Mukherjee  Kyle McDonald  K. J. Reddy 《Environmental Earth Sciences》2014,72(1):111-118

A study was conducted to understand the hydrogeological processes dominating in the North 24 Parganas and South 24 Parganas based on representative 39 groundwater samples collected from selected area. The abundance of major ions was in the order of Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ > Fe²⁺ for cations and HCO₃ ^? > PO₄ ^3? > Cl^? > SO₄ ^2? > NO₃ ^? for anions. Piper trilinear diagram was plotted to understand the hydrochemical facies. Most of the samples are of Ca-HCO₃ type. Based on conventional graphical plots for (Ca + Mg) vs. (SO₄ + HCO₃) and (Na + K) vs. Cl, it is interpreted that silicate weathering and ion exchange are the dominant processes within the study area. Previous studies have reported quartz, feldspar, illite, and chlorite clay minerals as the major mineral components obtained by the XRD analysis of sediments. Mineralogical investigations by SEM and EDX of aquifer materials have shown the occurrence of arsenic as coating on mineral grains in the silty clay as well as in the sandy layers. Excessive withdrawal of groundwater for irrigation and drinking purposes is responsible for fluctuation of the water table in the West Bengal. Aeration beneath the ground surface caused by fluctuation of the water table may lead to the formation of carbonic acid. Carbonic acid is responsible for the weathering of silicate minerals, and due to the formation of clay as a product of weathering, ion exchange also dominates in the area. These hydrogeological processes may be responsible for the release of arsenic into the groundwater of the study area, which is a part of North 24 Parganas and South 24 Parganas.  相似文献   

Spatial heterogeneity in near surface aerosol characteristics across the Brahmaputra valley     

Binita Pathak  Arup Borgohain  Pradip Kumar Bhuyan  Shyam Sundar Kundu  S Sudhakar  Mukunda M Gogoi  Toshihiko Takemura 《Journal of Earth System Science》2014,123(4):651-663

In order to examine the spatial variability of the aerosol characteristics across the Brahmaputra valley, a land campaign was conducted during late winter (February 3–March 2) 2011. Measurements of particulate matter (PM, PM₁₀, PM_2.5) and black carbon (BC) concentrations were made onboard an interior redesigned vehicle. The length of the campaign trail stretched about 700 km, covering the longitude belt of 89.97°–95.55°E and latitude belt of 26.1°–27.6°N, comprising 13 measurement locations. The valley is divided into three sectors longitudinally: western sector (R1: 89.97°–91.75°E), middle sector (R2: 92.5°–94.01°E) and eastern sector (R3: 94.63°–95.55°E). Spatial heterogeneity in aerosol distribution has been observed with higher PM₁₀ and PM_2.5 concentrations at the western and middle sectors compared to the eastern sector. The locations in the western sector are found to be rich in BC compared to the other two sectors and there is a gradual decrease in BC concentrations from west to east of the Brahmaputra valley. Two hotspots within the western and middle sectors with high PM and BC concentrations have been identified. The associated physico-optical parameters of PM reveal abundance of PM_2.5 aerosols along the entire valley. High population density in the western and middle sectors, together with the contribution of remote aerosols, leads to higher anthropogenic aerosols over those regions. Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) slightly underestimates the measured PM₁₀ and PM_2.5 at the eastern sector while the model overestimates the measurements at a number of locations in the western sector. In general, BC is underestimated by the model. The variation of BC within the campaign trail has not been adequately captured by the model leading to higher variance in the western locations as compared to the middle and eastern locations.  相似文献   

Estimation of sedimentary thickness in the Godavari basin     

K. Sushini  G. Srijayanthi  P. Solomon Raju  M. Ravi Kumar 《Natural Hazards》2014,71(3):1847-1860

A major portion of the southern part of the Indian subcontinent is classified as a stable continental region. However, a few segments in this region are punctuated by rifts and shear zones that are seismically active. The Godavari rift that sutures the eastern Dharwar and the Bastar cratons is one such region, prone to seismic hazard. Estimation of the sedimentary thickness in these seismically active regions assumes importance since locales of thick and soft sediments are vulnerable to destruction due to surface waves generated by earthquakes. In the present study, data from five broadband seismological stations are utilized to estimate the average sedimentary thickness of the Godavari region using the difference in travel times of the direct S and converted Sp phases from local earthquakes. The thickness of sediments varies between 0.32 and 4.32 km. Also, the site-specific response in terms of the fundamental resonance frequency and the corresponding amplifications are estimated using the well-established Nakamura technique. The predominant frequencies are in the range of 1.3–4.61 Hz, and the amplifications are higher (>1.5) for the stations inside the Godavari basin. Both the thickness and amplification values clearly indicate that the sediments tend to get thicker toward the center of the basin, in good agreement with the geological distribution of the sedimentary units.  相似文献   

Voids in a ΛCDM universe     

Jörg M. Colberg  Ravi K. Sheth  Antonaldo Diaferio  Liang Gao  Naoki Yoshida 《Monthly notices of the Royal Astronomical Society》2005,360(1):216-226

We study the formation and evolution of voids in the dark matter distribution using various simulations of the popular Λ cold dark matter cosmogony. We identify voids by requiring them to be regions of space with a mean overdensity of −0.8 or less – roughly the equivalent of using a spherical overdensity group finder for haloes. Each of the simulations contains thousands of voids. The distribution of void sizes in the different simulations shows good agreement when differences in particle and grid resolution are accounted for. Voids very clearly correspond to minima in the smoothed initial density field. Apart from a very weak dependence on the mass resolution, the rescaled mass profiles of voids in the different simulations agree remarkably well. We find a universal void mass profile of the form  ρ(< r )/ρ( r _eff) ∝ exp[( r / r _eff)^α]  , where r _eff is the effective radius of a void and  α∼ 2  . The mass function of haloes in voids is steeper than that of haloes that populate denser regions. In addition, the abundances of void haloes seem to evolve somewhat more strongly between redshifts ∼1 and 0 than the global abundances of haloes.  相似文献   

Investigation of Soil Suction Characteristics Induced by the Degradation of Organic Matter     

Dubey  Anant Aishwarya  Borthakur  Annesh  Ravi  K. 《Geotechnical and Geological Engineering》2022,40(4):2371-2378

Geotechnical and Geological Engineering - Total soil suction is considered to be the accumulative influence of matric and osmotic suction, assuming that the soil is biologically inert. However,...  相似文献   

Trends and fluctuations of rainfall regime in the Brahmaputra and Barak basins of Assam, India   总被引：2，自引：1，他引：1  

R. L. Deka  C. Mahanta  H. Pathak  K. K. Nath  S. Das 《Theoretical and Applied Climatology》2013,112(1-2):61-71

Severe weather conditions create negative impacts on humans. One of the severe weather conditions is storms. In the scope of this study, the storm effects on the Marmara Region were investigated using data for the period 2000 to 2010 giving the hourly averaged wind direction and speed in the Marmara Region, as provided by the Turkish Meteorological Service. The monthly distribution of storms has been estimated and their daily variability has been investigated. Additionally, air masses that cause storms have been determined by using NCEP/NCAR re-analysis data. Other than this, by studying the storms, extreme values have been ascertained and northerly values from these storm values (since in percentage terms they are larger) and hourly variability in a single day for 17 weather stations have been depicted graphically. The days that northerly storms reached extreme values are shown with the meteorological maps (surface chart, 850, 700, 500, and 300 hPa) and the temperature diagrams for Istanbul in the Marmara Region have been examined and analysed.  相似文献   

Modulations in the radio light curve of the Type IIb supernova 2001ig: evidence for a Wolf–Rayet binary progenitor?     

Stuart D. Ryder  Elaine M. Sadler  Ravi Subrahmanyan  Kurt W. Weiler  Nino Panagia  Christopher Stockdale 《Monthly notices of the Royal Astronomical Society》2004,349(3):1093-1100

  相似文献   

VLF radiation from lightning     

P. P. Pathak  J. Rai †  N. C. Varshneya 《Geophysical Journal International》1982,69(1):197-207

Summary. Electrical and magnetic fields due to arbitrarily oriented lightning over an imperfectly conducting ground have been obtained. The theory has been applied to K -changes, return strokes and horizontal lightning. The results are in good agreement with the experimental observations previously reported by many workers.  相似文献   

Climate change and crop yields in the Indian Cardamom Hills, 1978–2007 CE     

Muthusamy Murugan  Paddu Krishnappa Shetty  Raju Ravi  Aavudai Anandhi  Arulappan Joseph Rajkumar 《Climatic change》2012,110(3-4):737-753

In this study we analyzed climate and crop yields data from Indian cardamom hills for the period 1978–2007 to investigate whether there were significant changes in weather elements, and if such changes have had significant impact on the production of spices and plantation crops. Spatial and temporal variations in air temperatures (maximum and minimum), rainfall and relative humidity are evident across stations. The mean air temperature increased significantly during the last 30?years; the greatest increase and the largest significant upward trend was observed in the daily temperature. The highest increase in minimum temperature was registered for June (0.37°C/18?years) at the Myladumpara station. December and January showed greater warming across the stations. Rainfall during the main monsoon months (June–September) showed a downward trend. Relative humidity showed increasing and decreasing trends, respectively, at the cardamom and tea growing tracts. The warming trend coupled with frequent wet and dry spells during the summer is likely to have a favorable effect on insect pests and disease causing organisms thereby pesticide consumption can go up both during excess rainfall and drought years. The incidence of many minor pest insects and disease pathogens has increased in the recent years of our study along with warming. Significant and slight increases in the yield of small cardamom (Elettaria cardamomum M.) and coffee (Coffea arabica), respectively, were noticed in the recent years.; however the improvement of yield in tea (Thea sinensis) and black pepper (Piper nigrum L.) has not been seen in our analysis.  相似文献   

Quantitative evaluation of climatic variability and risks for wheat yield in India     

H. Pathak  R. Wassmann 《Climatic change》2009,93(1-2):157-175

This study comprises (1) an analysis of recent climate trends at two sites in north-west India (Ludhiana in Punjab and Delhi) and (2) an impact and risk assessment for wheat yields associated with climatic variability. North-west Indian agriculture is dominated by rice-wheat rotation in which the wheat season (‘rabi’, November to March) is characterized by predominantly dry conditions—superimposed by very high inter-annual variability of rainfall (17 to 260 mm in Ludhiana and <1 to 155 mm in Delhi). While rainfall remained without discernable trend over the last three decades, minimum and average temperatures showed increasing trends of 0.06 and 0.03°C year^???1, respectively, at Ludhiana. The site in (metropolitan) Delhi was apparently influenced by city-effects, which was noticeable from the decrease in solar radiation of 0.09 MJ m^???2 day^???1 year^???1. The CERES-wheat model was used to calculate yields of rainfed wheat that were at both locations highly correlated with seasonal rainfall. An assessment framework was developed to quantify yield impacts due to rainfall variability in three steps: (1) data from different years were aggregated into four classes, i.e., years with scarce, low, moderate, and high rainfall, (2) yield records of each rainfall class were ranked according to yield to facilitate (3) a comparison of yields with identical rank, i.e. among the best yield of each class, the second-best, etc. The class with moderate rainfall was taken as baseline yield to compute yield impacts of other rainfall scenarios. Years with scarce rainfall resulted in only 34% (Ludhiana) and 35% (Delhi) of the baseline yield. The yields in years with low rainfall accounted for 61% (Delhi) and 49% (Ludhiana) of the baseline yields. In Ludhiana, high rainfall years resulted in 200% yield as compared to the baseline yield, whereas they reached only 105% in Delhi. Low-intensity (1× and 3×) irrigation decreased the relative yield losses, but entailed a higher vulnerability in terms of absolute yield losses. Only high-intensity (4×) irrigation buffered wheat yields against adverse rainfall years. Early sowing was beneficial for wheat yields under all rainfall scenarios. The framework could be a valuable decision-support tool at the farm level where seasonal rainfall variability is high.  相似文献