Characterisation of recharge processes and groundwater flow mechanisms in weathered-fractured granites of Hyderabad (India) using isotopes

In order to address the problem of realistic assessment of groundwater potential and its sustainability, it is vital to study the recharge processes and mechanism of groundwater flow in fractured hard rocks, where inhomogeneties and discontinuities have a dominant role to play. Wide variations in chloride, δ¹⁸O and ¹⁴C concentrations of the studied groundwaters observed in space and time could only reflect the heterogeneous hydrogeological setting in the fractured granites of Hyderabad (India). This paper, based on the observed isotopic and environmental chloride variations of the groundwater system, puts forth two broad types of groundwaters involving various recharge processes and flow mechanisms in the studied granitic hard rock aquifers. Relatively high ¹⁴C ages (1300 to ～6000 yr B.P.), δ¹⁸O content (?3.2 to ?1.5‰) and chloride concentration (<100 mg/l) are the signatures that identified one broad set of groundwaters resulting from recharge through weathered zone and subsequent movement through extensive sheet joints. The second set of groundwaters possessed an age range Modern to ～1000 yr B.P., chloride in the range 100 to ～350 mg/l and δ¹⁸O from ?3.2 to +1.7‰. The δ¹⁸O enrichment and chloride concentration, further helped in the segregation of the second set of groundwaters into three sub-sets characterized by different recharge processes and sources. Based on these processes and mechanisms, a conceptual hydrogeologic model has evolved suggesting that the fracture network is connected either to a distant recharge source or to a surface reservoir (evaporating water bodies) apart from overlying weathered zone, explaining various resultant groundwaters having varying ¹⁴C ages, chloride and δ¹⁸O concentrations. The surface reservoir contribution to groundwater is evaluated to be significant (40 to 70%) in one subset of groundwaters. The conceptual hydrogeologic model, thus evolved, can aid in understanding the mechanism of groundwater flow as well as migration of contaminants to deep groundwater in other fractured granitic areas.     

Groundwater-recharge estimation using a surface electrical resistivity method in the Himalayan foothill region, India

A new method for the estimation of groundwater recharge is presented using a surface resistivity method and isotope technique. A linear relationship was obtained between the resistivity of the unsaturated top layer and the recharge estimated using a tritium tagging technique for the piedmont zone in the Himalayan foothill region, India. The relation can be used for the estimation of recharge using surface electrical resistivity measurements for the same geological formation. The data used for the study are 32 vertical electrical resistivity sounding measurements at a station interval of 2 km, tritium tagging studies at six selected sites and pre- and post-monsoon water-level monitoring in the piedmont zone of the Himalayan foothill region (India). The results of this study were mapped using GIS techniques. In the study area, a well-defined empirical relationship between unsaturated zone resistivity and recharge per cent was obtained. The method suggests a new application of surface electrical resistivity data in determining recharge per cent due to infiltration. The technique of estimating groundwater recharge using surface electrical resistivity measurement is efficient, economic, less time consuming and easy to use compared with other methods used for this purpose.

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Resumen Se presenta un método nuevo para estimar recarga de agua subterránea utilizando un método superficial de resistividad y una técnica de isótopos. Se ha obtenido una relación linear entre la resistividad de la capa superior no saturada y la recarga estimada utilizando la técnica de tritio marcado etiquetado para la zona de piedemontes en la región de colinas al pie del Himalaya, India. La relación puede utilizarse para estimar recarga usando mediciones superficiales de resistividad eléctrica para la misma formación geológica. Los datos utilizados en el estudio consisten de treinta y dos mediciones de sondeos eléctricos verticales de resistividad en un intervalo de estaciones de dos km, estudios de tritio marcado en seis sitios seleccionados y monitoreo de niveles de agua, pre-monzón y post-monzón, en la zona piedemontes de la región de colinas al pie del Himalaya (India). Se mapearon los resultados de este estudio utilizando técnicas SIG. Se obtuvo para el área una relación empírica bien definida entre la resistividad de la zona no saturada y el porcentaje de recarga. El método sugiere una aplicación nueva de los datos superficiales de resistividad eléctrica en la determinación del porcentaje de recarga ocasionado por infiltración. La técnica de estimar recarga de agua subterránea utilizando mediciones superficiales de resistividad eléctrica es eficiente, económica, demanda poco tiempo, y fácil de utilizar en comparación con otros métodos que se utilizan para este propósito.

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Resumé Une nouvelle méthode permettant destimer la recharge des eaux souterraines a été présentée, utilisant une méthode de résistivité de surface et des méthodes isotopiques. Une relation linéaire a été obtenue entre la résistivité de la zone non saturée et la recharge estimée grâce au Tritium dans la zone du Piedmont au pied de lHimalaya, Inde. La relation peut être utilisée pour lestimation de la recharge en utilisant la méthode de résistivité de surface dans la même formation géologique. Les données utilisées pour létude sont vingt-deux sondages électriques réalisés tous les deux kilomètres, létude de la signature du tritium en six endroits sélectionnés, et la comparaison des niveaux piézométriques pré et post moussons. Les résultats de cette étude ont été cartographiés en utilisant les techniques SIG. Dans la zone détude une relation très bien définie entre la recharge (%) et la résistivité de la zone non saturée a été obtenue. La méthode suggère une nouvelle application de la résistivité de surface, pour déterminer le pourcentage de la recharge due à linfiltration. Cette technique est efficace, économique, rapide et facile à mettre en oeuvre, en comparaison dautres techniques utilisées pour atteindre le même objectif.

     

Resolution of MRS applied to the characterization of hard-rock aquifers

The performance of the Magnetic Resonance Sounding (MRS) method applied to the investigation of heterogeneous hard-rock aquifers was studied. It was shown using both numerical modeling and field measurements that MRS could be applied to the investigation of the weathered part of hard-rock aquifers when the product of the free water content multiplied by the thickness of the aquifer is >0.2 (for example, 10-m-thick layer with a 2% water content). Using a currently available one-dimensional MRS system, the method allows the characterization of two-dimensional subsurface structures with acceptable accuracy when the size of the subsurface anomaly is equal to or greater than the MRS loop. However, the fractured part of hard-rock aquifers characterized by low effective porosity (<0.5%) cannot be resolved using currently available MRS equipment. It was found that shallow water in the weathered part of the aquifer may screen MRS signals from deeper water-saturated layers, thus further reducing the possibility of investigating deeper fractured aquifers. A field study using the NUMIS(plus) MRS system developed by IRIS Instruments was carried out on an experimental watershed in southern India. A heterogeneous unconfined aquifer in a gneissic formation was successfully localized, and MRS results were confirmed by drilling shortly after the geophysical study. The top of the aquifer revealed by MRS was found to be in a good agreement with observed static water level measurements in boreholes.     

Chandra and XMM–Newton observations of the low-luminosity X-ray pulsators SAX J1324.4−6200 and SAX J1452.8−5949

We present results from our Chandra and XMM–Newton observations of two low-luminosity X-ray pulsators  SAX J1324.4−6200  and  SAX J1452.8−5949  which have spin periods of 172 and 437 s, respectively. The XMM–Newton spectra for both sources can be fitted well with a simple power-law model of photon index,  Γ∼ 1.0  . A blackbody model can equally well fit the spectra with a temperature,   kT ∼  2 keV, for both sources. During our XMM–Newton observations,  SAX J1324.4−6200  is detected with coherent X-ray pulsations at a period of 172.86 ± 0.02 s while no pulsations with a pulse fraction greater than 18 per cent (at 95 per cent confidence level) in 0.2–12 keV energy band are detected in  SAX J1452.8−5949  . The spin period of  SAX J1324.4−6200  is found to be increasing on a time-scale of     which would suggest that the accretor is a neutron star and not a white dwarf. Using subarcsec spatial resolution of the Chandra telescope, possible counterparts are seen for both sources in the near-infrared images obtained with the son of infrared spectrometer and array camera (SOFI) instrument on the New Technology Telescope. The X-ray and near-infrared properties of  SAX J1324.4−6200  suggest it to be a persistent high-mass accreting X-ray pulsar at a distance  ≤8 kpc  . We identify the near-infrared counterpart of  SAX J1452.8−5949  to be a late-type main-sequence star at a distance ≤10 kpc, thus ruling out  SAX J1452.8−5949  to be a high-mass X-ray binary. However, with the present X-ray and near-infrared observations, we cannot make any further conclusive conclusion about the nature of  SAX J1452.8−5949  .     

Influence of natural and anthropogenic activities on UV Index variations – a study over tropical urban region using ground based observations and satellite data

Measurements of total ozone column and solar UV radiation under different atmospheric conditions are needed to define variations of both UV and ozone and to study the impact of ozone depletion at the Earth’s surface. In this study, spectral and broadband measurements of UV-B irradiance were obtained along with total ozone observations and aerosol optical depth measurements in the tropical urban region of Hyderabad, south India. We specifically used an Ultra-Violet Multifilter Rotating Shadow band Radiometer (UVMFR-SR), to measure UV irradiance in time and space. To assess the aerosol and O₃ effects on ground-reaching UV irradiance, we used measurements from a Microtops II sun photometer in addition to the Tropospheric Ultraviolet Visible radiation (TUV) model. We also assessed the Defense Meteorological Satellite Program – Operational Line Scanner (DMSP-OLS) night time satellite data for inferring biomass burning fires during the study period. Results clearly suggested a negative correlation between the DMSP-OLS satellite derived fire count data and UVMFR-SR data suggesting that aerosols from biomass burning are directly attenuating UV irradiance in the study region. Also, correlation analysis between UV index and ozone measurements from sun photometer and TOMS-Ozone Mapping Instrument (OMI) indicated a clear decrease in ground reaching UV-B irradiance during higher ozone conditions. The higher levels are attributed to photochemical production of O₃ during the oxidation of trace gases emitted from biomass burning. Results also suggested a relatively high attenuation in UV irradiance (~6% higher) from smoke particles than dust. We also found a relatively good agreement between the modeled (TUV) and measured UV irradiance spectra for different atmospheric conditions. Our results highlight the factors affecting UV irradiance in a tropical urban environment, south India.     

Chemical characterization of wet precipitation events and deposition of pollutants in coal mining region,India

The present study investigated the chemical composition of wet atmospheric precipitation in India’s richest coal mining belt. Total 418 samples were collected on event basis at six sites from July to October in 2003 and May to October in 2004 and analysed for pH, EC, F⁻, Cl⁻, , , Ca²⁺, Mg²⁺, Na⁺, K⁺ and . The average pH value (5.7) of the rainwater of the investigated area is alkaline in nature. However, the temporal pH variation showed the alkaline nature during the early phase of monsoonal rainfall but it trends towards acidic during the late and high rainfall periods. The rainwater chemistry of the region showed high contribution of Ca²⁺ (47%) and (21%) in cations and (55%) and Cl⁻ (23%) in anionic abundance. The high non seas salt fraction (nss) of Ca²⁺ (99%) and Mg²⁺ (96%) suggests crustal source of the ions, while the high nss (96%) and high ratio signifying the impact of anthropogenic sources and the source of the acidity. The ratio of varies from 0.03 to 3.23 with the average value of 0.84 suggesting that Ca²⁺ and play a major role in neutralization processes. The assessment of the wet ionic deposition rates shows no any specific trend, however Ca²⁺ deposition rate was highest followed by and _.     

Mass balance and morphological evolution of the Dokriani Glacier,central Himalaya,India during 1999–2014

Glaciological mass balance(MB)is considered the most direct,undelayed and unfiltered response of the glaciers to climatic perturbations.However,it may inherit errors associated with stake underrepresentation,averaging over the entire glacier and human bias.Therefore,proper validation of glaciological MB with geodetic MB is highly recommended by the World Glacier Monitoring Service(WGMS).The present study focuses on the Dokriani Glacier,central Himalaya which is one of the bench-mark glaciers in the region and has glaciological MB records from 1993 to 2013 with intermittent gaps.In the present study,firstly the glaciological MB series is extended to 2014 i.e.,field-based MB for one more year is computed and,to compare with it,the geodetic MB is computed for the 1999–2014 period using high resolution Cartosat-1 digital elevation model(DEM)and SRTM DEM.Finally,the study assesses the regional representation of the Dokriani Glacier in terms of MB and evaluates the influence of the MB regime on its morphological evolution.Results show that the average glaciological MB(-0.34±0.2 m water equivalent(w.e.)y-1)is more negative than the geodetic MB(-0.23±0.1 m w.e.y-1)for the 1999–2014 period.This is likely because of the partial representation of glacier margins in the glaciological MB,where melting is strikingly low owing to thick debris cover(>30 cm).In contrast,geodetic MB considers all marginal pixels leading to a comparatively low MB.A comparative assessment shows that the MB of Dokriani Glacier is less negative(possibly due to its huge accumulation area)than most other glacier-specific and regional MBs,restricting it to be a representative glacier in the region.Moreover,continuous negative MB has brought a peculiar change in the epiglacial morphology in the lower tongue of the glacier as differential debris thickness-induced differential melting has turned the glacier surface into a concave one.This concavity has led to development of a large(10–20 m deep)supraglacial channel which is expanding incessantly.The supraglacial channel is also connected with the snout wall and accelerates terminus disintegration.Given the total thickness of about 30–50 m in the lower glacier tongue,downwasting at its current pace,deepening/widening of supraglacial channel coupled with rapid terminus retreat may lead to the complete vanishing of the lower one km glacier tongue.     

Street Versus Rooftop Level Concentrations of Fine Particles in a Cambridge Street Canyon

Dispersion of particles, as evidenced by changes in their number distributions (PNDs) and concentrations (PNCs), in urban street canyons, is still not well understood. This study compares measurements by a fast-response particle spectrometer (DMS500) of the PNDs and the PNCs (5–1000 nm, sampled at 1 Hz) at street and rooftop levels in a Cambridge UK street canyon, and examines mixing, physical and chemical conversion processes, and the competing influences of traffic volume and rooftop wind speed on the PNDs and the PNCs in various size ranges. PNCs at street level were ≈6.5 times higher than at rooftop. Street-level PNCs followed the traffic volume and decreased with increasing wind speed, showing a larger influence of wind speed on 30–300 nm particles than on 5–30 nm particles. Conversely, rooftop PNCs in the 5–30 nm size range increased with wind speed, whereas those for particles between 30 and 300 nm did not vary with wind speed.     

Variations in CO,O<Subscript>3</Subscript> and black carbon aerosol mass concentrations associated with planetary boundary layer (PBL) over tropical urban environment in India

Carbon monoxide (CO), Ozone (O₃) and Black Carbon (BC) aerosol mass concentrations in relation to planetary boundary layer (PBL) height measurements were analyzed from January–December, 2008 over tropical urban environment of Hyderabad, India. DMSP-OLS night-time satellite data were analyzed for fire occurrence over the region and its correlation with pollution concentrations over the urban region. Results of the study suggested considerable increase in CO and BC concentrations during early morning hours. Higher concentration of BC, CO and ozone was observed during pre-monsoon, post-monsoon and winter and lowest concentrations exhibited during monsoon season. NCEP/NCAR reanalysis winds suggested long range transport of aerosols and trace gases from forest fires are enhancing the pollutant concentrations over the study area.