Deeper groundwater chemistry and geochemical modeling of the arsenic affected western Bengal basin,West Bengal,India

A regional scale hydrogeochemical study of a ∼21,000-km² area in the western Bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers. Spatial trends of solutes and geochemical modeling indicate that carbonate dissolution, silicate weathering, and cation exchange control the major-ion chemistry of groundwater and river water. The main aquifer water has also evolved by mixing with seawater from the Bay of Bengal and connate water. The isolated aquifers contain diagenetically altered water of probable marine origin. The postoxic main aquifer water exhibits overlapping redox zones (metal-reducing, sulfidic and methanogenic), indicative of partial redox equilibrium, with the possibility of oxidation in micro-scale environments. The redox processes are depth-dependent and hydrostratigraphically variable. Elevated dissolved As in the groundwater is possibly related to Fe(III) reduction, but is strongly influenced by coupled Fe–S–C redox cycles. Arsenic does not show good correlations with most solutes, suggesting involvement of multiple processes in As mobilization. The main river in the area, the Bhagirathi–Hoogly, is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry. Arsenic in water of smaller streams (Jalangi and Ichamati) is probably introduced by groundwater discharge during the dry season.     

Upper gondwana succession of the Rewa Basin,India: Understanding the interrelationship of lithologic and stratigraphic variables

The current work attempts to address a century old problem regarding the stratigraphic disposition of the Upper Gondwana succession of the Rewa basin based on geological mapping and litholog preparation along well exposed transects. The proposed Upper Gondwana stratigraphy of the Rewa basin comprises a continuous and thick package of Triassic sediments unconformably overlain by the Jurassic Parsora Formation. The Triassic succession consists of a basal Pali Formation, an intermediate and newly designated Karki Formation and the overlying mud-dominant Tiki Formation. These formations are well defined based on physical attributes such as lithology, textures and sedimentary structures, and are easily distinguishable in the field. Based on stratigraphic correlation and fossil content, a Lower-Middle Triassic age has been assigned for the Pali and Karki formations, while the Tiki Formation is Upper Triassic (Carnian) in age. Preliminary observations based on lithological characteristics, sand body geometry and sand: mud ratios suggest that within a fluvial setting there were considerable changes in environments of deposition through time, especially during Triassic to Jurassic transition.     

Observed seasonal and intraseasonal variability of the East India Coastal Current on the continental slope

We present data from three acoustic Doppler current profilers (ADCPs) moored off Cuddalore (12^°N), Kakinada (16.5^°N), and Gopalpur (19^°N) on the continental slope of the western Bay of Bengal and one mooring on the slope of the northern bay (89^°E, 19^°N; referred to as being located at Paradip). The data were collected during May 2009 to March 2013 and the observations show that the seasonal cycle, which includes the annual cycle, the semi-annual cycle, and a peak around 120 days, dominates the observed variability of the East India Coastal Current (EICC). Spectral analysis suggests that the 120-day peak dominates the seasonal variability at Paradip and is strong at Gopalpur and Kakinada. The annual cycle is coherent along the western boundary of the bay, i.e., the east coast of India, but with significant phase differences between moorings. At the semi-annual and 120-day periods, the alongshore coherence is weaker. Intraseasonal variability is weaker than the seasonal cycle, particularly at Cuddalore and Paradip, and it exhibits seasonality: the strongest intraseasonal variation is during spring (February–April). Peaks around 12 and 20–22 days are also seen at Gopalpur, Kakinada, and Cuddalore. A striking feature of the currents is the upward phase propagation, but there are also instances when phase propagates downward. The much lower vertical phase speed in the top ～100 m at Cuddalore leads to a distinct undercurrent at this location; at other locations, the undercurrent, though it exists often, is not as striking. During spring, however, the EICC tends to flow poleward (eastward) at Cuddalore, Kakinada, and Gopalpur (Paradip) over the top ～300 m, which is the maximum depth to which observations were made. The cross-shore component of the EICC is much weaker than the alongshore component at Cuddalore and, except for a few bursts during spring, at Kakinada and Gopalpur. It is only at Paradip, on the slope of the northern boundary, that significant cross-shore flows are seen during spring and the summer monsoon (June–August) and these flows are seen to be associated with eddy-like circulations in the altimeter data. We use the ADCP data to validate popular current data products like OSCAR (Ocean Surface Currents Analyses Real-time), ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II), and GODAS (Global Ocean Data Assimilation System). The OSCAR currents at Paradip match the observed currents well, but the correlation is much weaker at the other three locations. Both ECCO2 and GODAS fair poorly, particularly the latter because its variability in this boundary-current regime is extremely weak. Though it performs badly at Paradip, ECCO2 does capture the observed variability on occasions at the other locations.     

Forest cover change prediction using hybrid methodology of geoinformatics and Markov chain model: A case study on sub-Himalayan town Gangtok,India

In the Himalayan states of India, with increasing population and activities, large areas of forested land are being converted into other land-use features. There is a definite cause and effect relationship between changing practice for development and changes in land use. So, an estimation of land use dynamics and a futuristic trend pattern is essential. A combination of geospatial and statistical techniques were applied to assess the present and future land use/land cover scenario of Gangtok, the subHimalayan capital of Sikkim. Multi-temporal satellite imageries of the Landsat series were used to map the changes in land use of Gangtok from 1990 to 2010. Only three major land use classes (built-up area and bare land, step cultivated area, and forest) were considered as the most dynamic land use practices of Gangtok. The conventional supervised classification, and spectral indices-based thresholding using NDVI (Normalized Difference Vegetation Index) and SAVI (Soil Adjusted Vegetation Index) were applied along with the accuracy assessments. Markov modelling was applied for prediction of land use/land cover change and was validated. SAVI provides the most accurate estimate, i.e., the difference between predicted and actual data is minimal. Finally, a combination of Markov modelling and SAVI was used to predict the probable land-use scenario in Gangtok in 2020 AD, which indicted that more forest areas will be converted for step cultivation by the year 2020.     

Kinematics of horizontal simple shear zones of concentric arcs (Taylor–Couette flow) with incompressible Newtonian rheology

We present preliminary kinematic analyses of Taylor–Couette flow. We consider deformation of a Newtonian incompressible ductile material inside rotating horizontal listric (concentric circular) boundaries. The velocity profile is curved indicating non-uniform shear strain but leads to the same shear sense. Each material point on progressive shear keeps increasing shear strain linearly with time. A curve of no movement, the ‘neutral curve’, may exist inside the shear zone. Irregular geometries of initially regular markers and their individual non-matching strain paths indicate inhomogeneous deformaion in such Taylor–Couette flow.     

Neoproterozoic diamictite in the Eastern Desert of Egypt and Northern Saudi Arabia: evidence of ~750 Ma glaciation in the Arabian–Nubian Shield?

The Neoproterozoic Atud diamictite in Wadi Kareim and Wadi Mobarak in the Eastern Desert of Egypt and the Nuwaybah formation in NW Saudi Arabia consist of poorly sorted, polymictic breccia, with clasts up to 1 m of granitoid, quartz porphyry, quartzite, basalt, greywacke, marble, arkose, and microconglomerate in fine-grained matrix. Stratigraphic relations indicate that the diamictite was deposited in a marine environment. Integrated field investigation, petrographic study and U–Pb SHRIMP zircon ages demonstrate that the Atud and Nuwaybah are correlative. The distribution of zircon ages indicate that ~750 Ma ages are dominant with a significant component of older materials, characterized by minor Mesoproterozoic and more abundant Paleoproterozoic and Neoarchean ages. Some matrix and metasedimentary clast zircons yield ages that are a few 10s of Ma younger than the age of the youngest clast (754 ± 15 Ma), suggesting Atud/Nuwaybah diamictite deposition ~750 Ma or slightly later, broadly consistent with being deposited during the Sturtian glaciation (740–660 Ma). The Paleoproterozoic and Neoarchean clasts have no source within the ensimatic Arabian–Nubian Shield. The distribution of the pre-Neoproterozoic ages are similar to the distribution of the pre-Neoproterozoic ages in Yemen and Saharan Metacraton, suggesting that these clasts have been transported hundreds of kilometers, maybe by ice-rafting. The Atud diamictite may represent important evidence for Cryogenian “Snowball Earth” in the Arabian–Nubian Shield.     

Variable Quasi Periodic Oscillations during an outburst of the transient X-ray pulsar XTE J1858 + 034

We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858 + 034 during the second outburst of this source in April–May 2004. We have used observations made with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14–18, 2004, in the declining phase of the outburst. We detected the presence of low frequency QPOs in the frequency range of 140–185 mHz in all the RXTE-PCA observations. We report evolution of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with pulse fraction increasing from 20% at 3 keV to 45% at 30keV. We found that, similar to the previous outburst, the energy spectrum is well fitted with a model consisting of a cut-off power law along with an iron emission line.     

Higher dimensional inhomogeneous cosmological models in Lyra geometry

We have presented in homogeneous cosmological models within the framework of Lyra geometry. We have considered an inhomogeneous spherically symmetric higher dimensional model in presence of a mass less scalar field whose potential has a flat part. The scalar field is considered to be inhomogeneous. Also an inhomogeneous cosmological model is derived in a Kaluza-Klein type of space time. The matter field is taken as an inhomogeneous distribution of fluid. It is observed that there is no singularity at finite past in our model and the desirable feature of dimensional reduction is also possible for the extra space. This revised version was published online in July 2006 with corrections to the Cover Date.     

Integrating multivariate statistical analysis with GIS for geochemical assessment of groundwater quality in Shiwaliks of Punjab,India

The dependency of people on groundwater has increased in the past few decades due to tremendous increase in crop production, population and industrialization. Groundwater is the main source of irrigation in Shiwaliks of Punjab. In the present study the samples were collected from predetermined location as was located on satellite image on basis of spectral reflectance. Global positioning system was used to collect samples from specific locations. Principal components analysis (PCA) together with other factor analysis procedures consolidate a large number of observed variables into a smaller number of factors that can be more readily interpreted. In the present study, concentrations of different constituents were correlated based on underlying physical and chemical processes such as dissociation, ion exchange, weathering or carbonate equilibrium reactions. The PCA produced six significant components that explained 78% of the cumulative variance. The concentration of the few trace metals was found to be much higher indicating recharge due to precipitation as main transport mechanism of transport of heavy metals in groundwater which is also confirmed by PCA. Piper and other graphical methods were used to identify geochemical facies of groundwater samples and geochemical processes occurring in study area. The water in the study area has temporary hardness and is mainly of Ca–Mg–HCO₃ type.     

Assessment of Hurricane Ivan impact on chlorophyll-a in Pensacola Bay by MODIS 250 m remote sensing

The impact of Hurricane Ivan on water quality in Pensacola Bay was investigated by MODIS 250 m remote sensing of chlorophyll-a concentrations at different time slots before and after the hurricane event. Before the hurricane, the mean chlorophyll-a in the Bay was 5.3 μg/L. Heavy rainfall occurred during the hurricane landfall. The 48 h rainfall reached 40 cm and the peak storm surge reached 3 m on 9/16. After the rainstorm and during the storm surge on 9/17/2004, the mean chlorophyll-a concentration substantially increased to 14.7 μg/L. 26.3% water area was in the poor-water-quality condition (chl-a > 20 μg/L). This indicates that heavy nutrient loads from urban stormwater runoff and storm-surge inundation simulated chlorophyll bloom. After the end of the storm surge on 9/18/2004, the mean chlorophyll dropped to 2.0 μg/L, suggesting the effective flushing of polluted water from the bay to the Gulf of Mexico by the storm-surge. The good water quality condition lasted for almost several weeks after the storm surge. The peak river flow, arriving on the 4th day after the peak storm surge, did not alter the good water quality situation in the bay. This indicates that urban stormwater runoff rather than the river inflow is the major pollutant source for water quality in Pensacola Bay during the hurricane.