Inter-comparison of model-predicted wave heights with satellite altimeter measurements in the north Indian Ocean

A numerical model based on a wind-wave energy transport formulation of Toba is developed to generate hindcast wave height data for the equatorial and the north Indian Ocean, which is otherwise a data-sparse region. The intercomparison between model-predicted wave heights for three years (1987–1989) obtained utilising analysed surface wind fields' data, and model grid averaged GEOSAT Altimeter significant wave height data showed moderate match, particularly for H_S greater than 1 m.     

Inorganic arsenic sorption by drinking-water treatment residual-amended sandy soil: effect of soil solution chemistry

Previous studies in our laboratory have demonstrated that drinking-water treatment residuals are effective sorbents of arsenic V. However, the effect of soil solution chemistry on arsenic V sorption by drinking-water treatment residuals-amended soils remains to be explored. The current study uses a batch incubation experimental set up to evaluate the effect of soil solution pH, competing ligands, and complexing metal on arsenic V sorption by a sandy soil (Immokalee series) amended with two rates (25 and 50 g kg^?1) of aluminum and iron-based drinking-water treatment residuals. Experiments were conducted at three initial arsenic loads (125, 1,875, 3,750 mg kg^?1) and a constant solid: solution ratio of 200 g L^?1. An optimum equilibration time of 8 days, obtained from kinetic studies, was utilized for sorption experiments with both aluminum and iron drinking-water treatment residual-amended soil. Presence of phosphate decreased arsenic V sorption by both aluminum and iron drinking-water treatment residual amended soils, with a strong dependence on pH, drinking-water treatment residual types, drinking-water treatment residual application rates, and phosphate concentrations. Addition of sulfate had no effect on arsenic V sorption by aluminum or iron drinking-water treatment residual-amended soil. A complementing effect of calcium on arsenic V sorption was observed at higher pH. Results elucidating the effect of soil solution chemistry on the arsenic V sorption will be helpful in calibrating drinking-water treatment residual as a sorbent for remediation of arsenic-contaminated soils.     

Effects of soil types and forms of arsenical pesticide on rice growth and development

For decades, repeated and widespread use of arsenical pesticides has significantly contributed to arsenic contamination in soils. Residues from the overuse of these arsenicals may result in phytotoxicity to crops, which will depend on soil types, plant species and the toxicity of arsenical pesticides. A greenhouse column study was conducted to evaluate the effect of two pesticides, i.e. one organic (dimethylarsinic acid) and one inorganic (sodium arsenate), on the vegetative response of rice as a function of soil properties. Four soils with varying arsenic retention capabilities at two different pesticide amendment rates (675 and 1500 mg/kg) representing the worst case scenarios in superfund sites were used. Results showed that arsenic availability to rice was mainly influenced by soil physicochemical properties. The soil with the lowest arsenic retention capacity had the highest arsenic concentration in the leachate as well as in the plant tissue. In contrast, for soils with higher arsenic retention capacity, higher concentrations of arsenic were found in the surface soil which resulted in the inhibition of plant growth. There was no significant difference between labile arsenic / plant-available arsenic irrespective of the form of arsenical pesticide used. Plant growth parameters such as biomass, shoot height, root length decreased with increased arsenic concentrations in all soils. A significant negative correlation (P<0.05) was observed between the phytoavailable arsenic and plant growth response. Interestingly, the form of arsenical pesticide used did not impact arsenic uptake or shoot growth but significantly impacted root growth.     

Late Archaean mantle metasomatism below eastern Indian craton: Evidence from trace elements,REE geochemistry and Sr—Nd—O isotope systematics of ultramafic dykes

Trace, rare earth elements (REE), Rb-Sr, Sm-Nd and O isotope studies have been carried out on ultramafic (harzburgite and lherzolite) dykes belonging to the newer dolerite dyke swarms of eastern Indian craton. The dyke swarms were earlier considered to be the youngest mafic magmatic activity in this region having ages not older than middle to late Proterozoic. The study indicates that the ultramafic members of these swarms are in fact of late Archaean age (Rb-Sr isochron age 2613 ± 177 Ma, Sri ∼ 0.702 ± 0.004) which attests that out of all the cratonic blocks of India, eastern Indian craton experienced earliest stabilization event. Primitive mantle normalized trace element plots of these dykes display enrichment in large ion lithophile elements (LILE), pronounced Ba, Nb and Sr depletions but very high concentrations of Cr and Ni. Chondrite normalised REE plots exhibit light REE (LREE) enrichment with nearly flat heavy REE (HREE; (ΣHREE)_N ∼ 2–3 times chondrite, (Gd/Yb)_N ∼ 1). The ε^Nd(t) values vary from +1.23 to -3.27 whereas δ¹⁸O values vary from +3.16‰ to +5.29‰ (average +3.97‰±0.75‰) which is lighter than the average mantle value. Isotopic, trace and REE data together indicate that during 2.6 Ga the nearly primitive mantle below the eastern Indian Craton was metasomatised by the fluid (± silicate melt) coming out from the subducting early crust resulting in LILE and LREE enriched, Nb depleted, variable ε^Nd, low Sr_i(0.702) and low δ¹⁸O bearing EMI type mantle. Magmatic blobs of this metasomatised mantle were subsequently emplaced in deeper levels of the granitic crust which possibly originated due to the same thermal pulse.     

Electric and magnetic field perturbations recorded by DEMETER satellite before seismic events of the 17th July 2006 M 7.7 earthquake in Indonesia

Seismo-electromagnetic phenomena refers to the electric and magnetic field perturbations that may be caused due to geophysical activities like earthquakes and volcanic eruptions. Due to the existence of such phenomena before earthquakes they may be regarded as short term precursors to earthquakes. Keeping in mind the in situ measurements for detection of such phenomena, the satellite based techniques are of great interest because they keep a constant track of the seismically active zones globally. With the objective of detecting the electromagnetic emissions in the ionosphere, the DEMETER satellite has been launched on 29th June 2004 from Baikonour in order to study the ionospheric perturbations associated with seismic activities. In this paper, we discuss some interesting results of electromagnetic emissions that are observed before a series of recent Indonesian earthquakes in the Jawa region with a major shock measuring 7.7 magnitude on Richter scale which occurred on 17 July 2006. The emissions have been observed in the Ultra Low Frequency (ULF)/Extremely Low Frequency (ELF) range of electromagnetic spectra.     

Morphological signatures of fault lines in an earthquake prone zone of southern Baromura hill,north-east India: a multi sources approach for spatial data analysis

This paper aims to assess the morphological signatures of tectonic features (faults) on the basis of multi sources spatial data analysis. For that purpose, the present authors selected the southern part of Baromura hill of Tripura, which has been discussed very little in the scientific literatures. An extensive field work was done in the assumed faulted areas to understand the geomorphic signatures of faulting. In the field, GPS was used for fixing the ground control points. Scanned Survey of India (SOI) topographical sheets, SPOT PAN and Land sat band-5 was used for digital analysis. An old DEM on IRS LISS-III FCC was also consulted for final mapping. Two clear lineaments (Faults) were detected from field observation on southern Baromura hill. Apart from these, another one was found in the outer part of this hill range. An attempt was made to explain the morphological signatures of those faults by density slicing on radiometric data based on emittance of different physical components. Finally a geomorphic map with main tectonic features of Baromura was prepared for future disaster management planning.     

Validation of IRI-2007 against TEC observations during low solar activity over Indian sector

Published values of Total Electron Content (TEC) measured by ATS-6 are used to assess the latest available IRI-2007 model during solar minimum over Indian sector covering equatorial to low-mid-latitudes stations. The study reveals that during all seasons and at all locations, in general, the TEC predicted by NeQuick and IRI01-corr options provided in the IRI-2007 model shows much better agreement with the TEC observations as compared to those generated by IRI-2001.option. TEC predicted using NeQuick option found to be little more closer to the observation except at equatorial station during daytime, while IRI-2001 option highly overestimates the TEC in all seasons and times.     

Microbial mat structures in profile: The Neoproterozoic Sonia Sandstone,Rajasthan, India

Ubiquitous microorganisms, especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats. In the absence of grazers and bioturbators, microbial mat is a unique feature of the Proterozoic. Most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding. Nonetheless, bed surface exposures are relatively rare in rock records. This limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed-across sections is needed. The 60 m thick coastal marine interval of the Sonia Sandstone Formation is bounded between two terrestrial intervals, a transgressive lag at the base and an unconformity at the top, and has been chosen for exploration of microbial mat structures in bed-across sections. A wide variety of microbial mat-induced structures in bed-across sections are preserved within the coastal interval of the Sonia Sandstone. Though many of these structures are similar in some aspects with bed surface structures, some of those presented here are new. The palaeogeographic range of these microbial structures extends from supralittoral to neritic. Diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains. SEM and EDAX analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the Sonia Sandstone. Effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous. The mat-cover on sediment surfaces hinders reworking and/or erosion of the sediments thereby increases the net sedimentation rate. Successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these Proterozoic formations could be a target for exploration.     

Ecological consideration of trace element contamination in sediment cores from Sundarban wetland,India

This article reports on the concentration of selected trace elements (Mn, Zn, Cr, Cu, Ba, As, B, V, and Hg) and major elements (Fe and Al) from the intertidal sediment cores from Sundarban wetland, India. This is a typical meso-macrotidal estuarine area affected by domestic and industrial activities located upstream. The overall concentrations range is low to moderate, indicating the environmental conditions in the outfall zone (grain size, hydrodynamic regime, and confinement), which favors the in situ accumulation of pollutants. The extent of contamination from trace elements in Sundarban core sediments is evaluated through a two-pronged approach: (i) by determining the metal enrichment in the sediments through the calculation of Pollution Load Index (PLI), Enrichment Factor (EF) and Index of Geoaccumulation (I _geo), and (ii) by defining a potential level of biological risk by the use of quality criteria such as Threshold Effect Level (TEL) and Effects Range-Low (ERL) benchmarks. On the basis of the calculated indices, sediments are particularly enriched with Cr, Cu, B, V, and As. Those enrichments seem to be due to the fine granulometry of the regions with Fe and Mn oxi-hydroxides being the main metal carriers. Trace Elements input to the Sundarban wetland need to be kept under strict control in future specially with reference to As since, according to TEL and ERL benchmarks, it already appears to be associated with a potential biological risk.     

Heavy metal pollution assessment through comparison of different indices in sewage-fed fishery pond sediments at East Kolkata Wetland,India

The sediments of the raw sewage-fed fishpond system at East Kolkata Wetland (EKW) were analyzed for heavy metal content in a comprehensive way. Various indices of contamination like enrichment factor (EF), geo-chemical index (I _geo), modified degree of contamination (mD_C), and pollution load index (PLI) were assessed. In all cases, instead of literature values, the metal concentrations of less contaminated sites, separated by the statistical approach of the hierarchical cluster analysis, were used as baseline values. In the present study, about 70% of the pond sediments are found uncontaminated, 5% display low degree of contamination and 25% are designated as moderate degree of contamination. Both the EF and I _geo indices highlighted that the metals lead (Pb), cadmium (Cd), and chromium (Cr) are responsible for the contamination while there is little anthropogenic input in cases of Cu, Zn, and Ni. Most of the ponds situated near the main sewage flowing canals as well as the main traffic highway and close to the solid waste dumping areas recorded higher degree of metal contamination as evident from spatial variation of mD_C and PLI indices in the study area. Indices comparison study clearly indicates that although these are calculated using different methods, these may or may not produce the same indices values and hence the values should neither be compared nor be averaged. But all the above indices are directly related to a common term contamination factor (CF). Classification of contamination levels based on these CF values is found to be similar and this classification is only valid up to the level of high degree of contamination. Thus, the use of any one of these indices is sufficient to classify the degree of contamination of an area. However, to evaluate the contamination per metal, both I _geo and EF are effective while, to assess the composite effect of all the metals, PLI is preferable to mD_C.