Change detection study of islands in Hooghly estuary using multidate satellite images

River estuarine environment constitutes a highly dynamic fluvio-morphological setting where processes of accretion and deposition are active. Hooghly estuary, being one of the largest of estuaries in the east coast of India, needs constant monitoring. Multidate satellite images of IRS-1A L1SS-I and Landsat MSS for 1975–1991 period are studied to detect long term morphological changes in this estuary. The study reveals that the estuarine islands like Sagar, Ghorarmara and Suparbhanga are eroding whereas Lohachara islands has completely eroded off Nayachara island near Haldia due to its shape and size bifurcates the river into two channels. The island as revealed from Satellite images is in accretional phase where the total surface area has increased. The study, therefore, indicates that constant monitoring of spatial and temporal changes in this type of environment would help to understand physical processes.     

Recent Trends of Arctic and Antarctic Summer Sea-Ice Cover Observed from Space-Borne Scatterometer

Long term variations in Sea ice distribution strongly influence the atmosphere and ocean in the polar regions. In the recent period significant variations in sea ice cover have been observed in both the hemispheres. In the past, studies have been carried out that report the trends either at the Arctic/Antarctic level or at sector level. However, only a few studies have concentrated on the investigation of trends at grid level using scatterometer data. The present study focuses on the investigations of the sea ice trend at 1 × 1 degree grid level over the period 2000–2007 using QuickSCAT 0.2-degree resolution Scatterometer data. It was observed that in the Arctic overall monthly trend is negative in all the sectors, with the Arctic level decline of 3.26% per year. In the Antarctic, region-wise different trends have been observed. Negative trend is observed in the Amundsen- Bellingshausen Seas and also in the Indian Ocean sector near the continental Ice shelves. It was highlighted that significant trends exists within the pockets of marginal seas.     

Predicting dam-related downstream geomorphic response with widely available stream gauge data: A case study of the Godavari River Basin,India

Dam-related downstream adjustments of riverbeds are normally investigated by analysing the trend in sediment supply and high flow events during the pre- and post-dam periods. The required data for existing predictive models is not measured at river gauges, which limits the application of these tools. We derived the frequency of sediment-transporting streamflow events (T*) and upstream sediment supply (S*) in the pre- and post-dam periods with widely available gauged records and predicted changes in the downstream riverbed by adapting an existing model. Ten gauging stations in the Godavari River Basin, India, located downstream of dams, were chosen as study sites. Annually surveyed cross-sections at each site validated the accuracy of the predicted dam-related downstream changes. Then, a regression equation (R² = 0.75) was established between T*/S* (independent variable) and changes in the downstream bed elevation (dependent variable) for the Godavari Basin. We recommended that similar local empirical equations be formulated for larger river basins. Models of large-scale rainfall-runoff and sediment transport processes that can account for the influence of dams, such as the Soil & Water Assessment Tool, can be paired with the proposed regression equation to estimate dam-related downstream erosion and deposition with globally available data.     

Heterogeneous agglutinitic glass and the fusion of the finest fraction (F3) model

Abstract— Evidence in favor of the model fusion of the finest fraction (F³) for the origin of lunar agglutinitic glass has been accruing. They include (1) theoretical expectations that shock pulses should engulf and melt smaller grains more efficiently than larger grains, (2) experimental results of impact shock, albeit at lower than presumed hypervelocity impacts of micrometeorites on the lunar regolith, and (3) new analyses confirming previous results that average compositions of agglutinitic glass are biased towards that of the finest fraction of lunar soils from which they had formed. We add another reason in support of the F³ model. Finer grains of lunar soils are also much more abundant. Hence, electrostatic forces associated with the rotating terminator region bring the finest grains that are obviously much lighter than courser grains to the surface of the Moon. This further contributes to the preferential melting of the finest fraction upon micrometeoritic impacts. New backscattered electron imaging shows that agglutinitic glass is inhomogeneous at submicron scale. Composition ranges of agglutinitic glass are extreme and deviate from that of the finest fraction, even by more than an order of magnitude for some components. Additionally, we show how an ilmenite grain upon impact would produce TiO₂‐rich agglutinitic glass in complete disregard to the requirements of fusion of the finest fraction. We propose an addition to the F³ model to accommodate these observations (i.e., that micrometeorite impacts indiscriminately melt the immediate target regardless of grain size or grain composition). We, therefore, suggest that (1) agglutinitic glass is the sum of (a) the melt produced by the fusion of the finest fraction of lunar soils and (b) the microvolume of the indiscriminate target, which melts at high‐shock pressures from micrometeoritic impacts, and that (2) because of the small volume of the melt and incorporating cold soil grains, the melt quenched so rapidly that it did not mix and homogenize to represent any preferential composition, for example, that of the finest fraction.     

Regional hydrostratigraphy and groundwater flow modeling in the arsenic-affected areas of the western Bengal basin, West Bengal, India

The first documented interpretation of the regional-scale hydrostratigraphy and groundwater flow is presented for a ～21,000-km² area of the arsenic-affected districts of West Bengal [Murshidabad, Nadia, North 24 Parganas and South 24 Parganas (including Calcutta)], India. A hydrostratigraphic model demonstrates the presence of a continuous, semi-confined sand aquifer underlain by a thick clay aquitard. The aquifer thickens toward the east and south. In the south, discontinuous clay layers locally divide the near-surface aquifer into several deeper, laterally connected, confined aquifers. Eight 22-layer model scenarios of regional groundwater flow were developed based on the observed topography, seasonal conditions, and inferred hydrostratigraphy. The models suggest the existence of seasonally variable, regional, north–south flow across the basin prior to the onset of extensive pumping in the 1970s. Pumping has severely distorted the flow pattern, inducing high vertical hydraulic gradients across wide cones of depression. Pumping has also increased total recharge (including irrigational return flow), inflow from rivers, and sea water intrusion. Consequently, downward flow of arsenic contaminated shallow groundwater appears to have resulted in contamination of previously safe aquifers by a combination of mechanical mixing and changes in chemical equilibrium.     

Stable isotope dynamics of groundwater interactions with Ganges river

Groundwater depletion has been an emerging crisis in recent years, especially in highly urbanized areas as a result of unregulated exploitation, thus leaving behind an insufficient volume of usable freshwater. Presently Ganges river basin, the sixth largest prolific fluvial system and sustaining a huge population in South Asia, is witnessed to face (i) aquifer vulnerability through surface waterborne pollutant and (ii) groundwater stress due to summer drying of river as a result of indiscriminate groundwater abstraction. The present study focuses on a detailed sub-hourly to seasonally varying interaction study and flux quantification between river Ganges and groundwater in the Indian subcontinent which is one of the first documentations done on a drying perennial river system that feeds an enormous population. Contributing parameters to the total discharge of a river at its middle course on both temporal and spatial scale is estimated through three-component hydrograph separation and end-member mixing analysis using high-resolution water isotope (δ¹⁸O and δ²H) and electrical conductivity data. Results from this model report groundwater discharge in river to be the highest in pre-monsoon, that is, 30%, whereas, during post-monsoon the contribution lowers to 25%; on the contrary, during peak monsoon, the flow direction reverses thus recharging the groundwater which is also justified using annual piezometric hydrographs of both river water and groundwater. River water-groundwater interaction also shows quantitative variability depending on river morphometry. The current study also provides insight on aquifer vulnerability as a result of pollutant mixing through interaction and plausible attempts towards groundwater management. The present study is one of the first in South Asian countries that provides temporally and spatially variable detailed quantification of baseflow and estimates contributing parameters to the river for a drying mega fluvial system.     

Holocene climate variability from lake sediment core in Larsemann Hills,Antarctica

A sediment core (L2) from Larsemann Hills, Antarctica was analyzed for Biogenic Silica (BSi), Sand (%) and Total Organic Carbon (TOC). The 78 cm core length represents the time span of ∼8.3 cal ka BP. The values of BSi from the core show prominent high productivity from ∼8.3 to ∼6 cal ka BP in comparison to less productivity in mid-late Holocene (∼6 cal ka BP to recent). Moreover, high sand (%) infers the glacio-fluvial deposition from ∼8.3 to ∼5 cal ka BP TOC shows little variation through out the core, except in the upper ∼10 cm (∼4 cal ka BP) part wherein it is comparatively high. The increased TOC in the upper part of the core possibly indicates presence of algal mat due to exposure of the lake to the ice free (glacier free) conditions.     

Physical properties of sediment from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope

This study characterizes cored and logged sedimentary strata from the February 2007 BP Exploration Alaska, Department of Energy, U.S. Geological Survey (BPXA-DOE-USGS) Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope (ANS). The physical-properties program analyzed core samples recovered from the well, and in conjunction with downhole geophysical logs, produced an extensive dataset including grain size, water content, porosity, grain density, bulk density, permeability, X-ray diffraction (XRD) mineralogy, nuclear magnetic resonance (NMR), and petrography.This study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate. Gas hydrate (GH) occurs in three unconsolidated, coarse silt to fine sand intervals within the Paleocene and Eocene beds of the Sagavanirktok Formation: Unit D-GH (614.4 m-627.9 m); unit C-GH1 (649.8 m-660.8 m); and unit C-GH2 (663.2 m-666.3 m). These intervals are overlain by fine to coarse silt intervals with greater clay content. A deeper interval (unit B) is similar lithologically to the gas-hydrate-bearing strata; however, it is water-saturated and contains no hydrate.In this system it appears that high sediment permeability (k) is critical to the formation of concentrated hydrate deposits. Intervals D-GH and C-GH1 have average “plug” intrinsic permeability to nitrogen values of 1700 mD and 675 mD, respectively. These values are in strong contrast with those of the overlying, gas-hydrate-free sediments, which have k values of 5.7 mD and 49 mD, respectively, and thus would have provided effective seals to trap free gas. The relation between permeability and porosity critically influences the occurrence of GH. For example, an average increase of 4% in porosity increases permeability by an order of magnitude, but the presence of a second fluid (e.g., methane from dissociating gas hydrate) in the reservoir reduces permeability by more than an order of magnitude.