Dissociation Constants of Protonated Oxidized Glutathione in Seawater Media at Different Salinities

Oxidized glutathione (GSSG), which has four carboxylic and two amino groups, interacts with metal ions and may affect the bioavailability and geochemistry of metals in natural waters. In the present paper, six stepwise protonation constants K^\textH_i K^{\text{H}}_{i} for GSSG were measured as a function of salinity, S = 5–35‰ at t = 25°C (and in NaCl/MgCl₂ mixtures at different ionic strengths), in order to provide thermodynamic data for their acid base properties, which are useful for studying the interaction with metals in these media. The protonation enthalpies (ΔH _i /kJ mol⁻¹) were also determined at t = 25°C. The results were interpreted using the SIT model and Pitzer equations. The seawater model with the interaction parameters accounts for the differences between the values in NaCl and seawater. The results suggest that it is important to consider all of the ionic interactions in natural waters in examining the proton dissociation of GSSG.     

Landslide susceptibility zonation of the Chamoli region, Garhwal Himalayas, using logistic regression model

A remote sensing and Geographic Information System-based study has been carried out for landslide susceptibility zonation in the Chamoli region, part of Garhwal Himalayas. Logistic regression has been applied to correlate the presence of landslides with independent physical factors including slope, aspect, relative relief, land use/cover, lithology, lineament, and drainage density. Coefficients of the categories of each factor have been obtained and used to assess the landslide probability value to ultimately categorize the area into various landslide susceptibility zones; very low, low, moderate, high, and very high. The results show that 71.13% of observed landslides fall in 21.96% of predicted very high and high susceptibility zone, which in fact should be the case. Furthermore, lineament first buffer category (0–500 m) and the east and south aspects are the most influential in causing landslides in the region.     

Numerical model and flume experiments of single- and two-layered hillslope flow related to slope failure

A hillslope flow model is developed considering 3D saturated and unsaturated flow of water during rainfall events. A finite difference-based numerical model of hillslope flow processes is developed. Four different experiments are done to see the effects of a single- and double-layered soil in pore-water pressure dynamics and slope failure. Results from the numerical model are verified with experimental results. The numerical and experimental values of the pore-water pressure and moisture contents are in good agreement. The results show that the hillslope heterogeneity caused by multiple layers of soil has greater influence on hillslope pore-pressure dynamics and slope failure patterns. The depth of slope failure shows high dependency on layering characteristics of the soil slope and pattern of rainfall. The proposed model provides a perspective on failure mechanism of a single- or double-layered slope under rainfall infiltration.     

Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India

Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this high-altitude mountainous terrain. VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the slide parallel to the geological gneiss–schist contact within the Lanta Khola slide. This indicates that the conductive feature correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide.     

Reaction textures and P–T conditions of Opx-Crd gneisses from Karimnagar, Andhra Pradesh, India

Summary The Karimnagar granulite terrain is an integral part of the Eastern Dharwar Craton (EDC). It has received much interest because of the only reported granulite facies rocks in the EDC. These granulites contain quartz-free sapphirine-spinel-bearing granulites, kornerupine – bearing granulites, mafic granulites, orthopyroxene-cordierite gneisses, charnockites, amphibolites, dolerite dykes, granite gneisses, quartzites and banded magnetite quartzite. The orthopyroxene-cordierite gneisses occur as enclaves within granite-gneiss in association with banded magnetite quartzites, charnockites and amphibolites. The observed reaction textures, spectacular as they are, have an extraordinary information content within a tiny domain. Coronas, symplectites and resorption textures are of particular interest as they reflect discontinuous or continuous reactions under changing physical conditions. The main mineral assemblages encountered in these gneisses are orthopyroxene – cordierite – biotite – plagioclase – perthite – quartz and garnet – orthopyroxene – cordierite – biotite – quartz – plagioclase – perthite ± sillimanite. Multiphase reaction textures in conjunction with mineral chemical data in the KFMASH system indicate the following reactions: Based on chemographic relationships and petrogenetic grids in the K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O (KFMASH) system, a sequence of prograde (early stage), isothermal decompression (middle stage) and retrograde (late stage) reactions (‘back reactions’ and hydration reactions) are inferred. Relatively lower P–T estimates (0.35 GPa/550–750 °C) obtained from the different geothermobarometers are attributed to late Fe–Mg re-equilibration during cooling. Therefore, the convergence method has been applied to retrieve simultaneously the P–T conditions of the thermal peak of metamorphism. The near thermal peak condition of metamorphism estimated by the convergence method are 850 °C/0.62 GPa. The P–T estimates define a retrograde trajectory with substantial decompression.     

A multi-isotope approach for understanding sources of water,carbon and sulfur in natural springs of the Central Appalachian region

Natural springs have been reliable sources of domestic water and have allowed for the development of recreational facilities and resorts in the Central Appalachians. The structural history of this area is complex and it is unknown whether these natural springs receive significant recharge from modern precipitation or whether they discharge old water recharged over geological times scales. The main objective of this study was to use stable isotopes of water ( $\delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}}$ and $\delta^{2} {\text{H}}_{{{\text{H}}_{2} {\text{O}}}}$ ), dissolved inorganic carbon ( $\delta^{13} {\text{C}}_{\text{DIC}}$ ) and dissolved sulfate ( $\delta^{34} {\text{S}}_{{{\text{SO}}_{4} }}$ and $\delta^{18} {\text{O}}_{{{\text{SO}}_{4} }}$ ) to delineate sources of water, carbon and sulfur in several natural springs of the region. Our preliminary isotope data indicate that all springs are being recharged by modern precipitation. The oxygen isotope composition indicates that waters in thermal springs did not encounter the high temperatures required for O isotope exchange between the water and silicate/carbonate minerals, and/or the residence time of water in the aquifers was short due to high flow rates. The carbon isotopic composition of dissolved inorganic carbon and sulfur/oxygen isotopic composition of dissolved sulfate provide evidence of low-temperature water–rock interactions and various biogeochemical transformations these waters have undergone along their flow path.     

Genesis of some tertiary Indian coals from the chemical composition of ash – a statistical approach: Part 1

In the present investigation, 37 numbers of high sulphur tertiary coal samples from Meghalaya, India have been studied on the basis of proximate and ash analysis. Various statistical tools like Bivariant Analysis, Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA), and also the geochemical indicators were applied to determine the dominant detrital or authigenic affinity of the ash forming elements in these coals. The genetic interpretation of coal as well as the coal ash has been carried out based on chemical compositions of high temperature ash (HTA) by using Detrital/Authigenic Index. X-Ray Diffraction (XRD) analysis was also carried out to study the mineralogy of the studied coal ashes. Both statistical tools and geochemical indicators have confirmed the detrital nature of these coals as well as the ash forming elements.     

Mineralogy,petrography and micro-chemical characteristics of enclaves of mylonitic BIFs within Sukinda ultramafic complex,Odisha

Elongated NE-SW trending bodies of iron-rich rock are exposed adjacent to pyroxenite dyke within Sukinda ultramafic complex, Odisha. Field study followed by optical and electron microscopy, XRD and EPMA investigation reveal the rocks to be fine grained, weathered, limonitised; containing quartz, magnetite, hematite/martite and goethite. The rock has suffered from deformation during intrusion of chromiferous magma. It rarely shows banding/lamination, but largely exhibits mylonitic fabric, resulting from magmatic intrusion. The stronger deformation is evident from sub-grain formation, deformed mineral grains; often with orientation, stretching (boudinage) and shortening (folding); presence of porphyroclasts, pull-apart structure, undulose extinction, dynamic recrystallisation etc. From the microstructure and mineral abundance, the rock is designated as “Mylonitic Magentite Quartzite” (MMQ).Enrichment of some elements like Ni, Mg, Cr in the magnetite phase of MMQ is attributed to solid state diffusion of these elements from chromiferous mafic magma during thermal metamorphism. This is determined from electron probe microanalysis of iron-rich phase in MMQ, which is found to contain 88-90 wt% of FeO^(t) with ~1%, NiO, ~1%, MgO and 0.1% Cr₂O₃ having around 3 mole% of trevorite; 4-6% of magnesioferrite; 0.15-0.3% of chromite; 86-87% of magnetite and 3-4% of wustite. Considering presence of wustite as temperature indicator, the temperature of magma envisaged to be around 950-1100°C.In a later period, the MMQ has undergone oxidation and lateritisation owing to its prolonged exposure. During this process, new minerals like hematite and goethite substituted magnetite, resulting leaching of iron (FeO: 62-68%) and magnesium (MgO: 0.1-0.35) and enrichment of chromium (Cr₂O₃:4-7%) and nickel (NiO: 1.6-2.3%). The silica (SiO₂: 4-5%), alumina (Al₂O₃:~1%) are contributed by kaolinite, formed during lateritisation.The field and laboratory studies confirm these iron-rich exposures to be enclaves of BIFs, banded magnetite quartzite (BMQ) in particular, within the Sukinda chromiferous ultramafic complex. Micro-structural features and microchemical composition of iron minerals in these exposures are interpreted as the influence of forceful ultramafic intrusion into the existing BMQ and effect of thermal metamorphism followed by oxidation, weathering/lateritisation.     

Characteristics of ambient ammonia over Delhi,India

In the present paper, we have characterized the ambient ammonia over Delhi along with other trace gases (NH₃, NO, NO₂, SO₂ and CO) and particulates (PM_2.5 and PM₁₀) measured during December 2011 to June 2012. The average mixing ratios of ambient NH₃, NO, NO₂, SO₂ and CO were recorded as 21.2 ± 5.4, 19.5 ± 4.9, 17.4 ± 1.4, 1.7 ± 0.5 ppb and 1.6 ± 0.7 ppm, respectively, during winter, whereas the average mixing ratios of ambient NH₃, NO, NO₂, SO₂ and CO were recorded as 20.8 ± 4.7, 21.7 ± 6.3, 16.8 ± 3.1, 2.2 ± 0.8 ppb and 1.8 ± 0.9 ppm, respectively, during summer. In the present case, non-significant seasonal and diurnal variations of NH₃, NO, NO₂, SO₂ and CO were observed during both the seasons. The average monthly NH₃/NH₄ ⁺ ratios varied from 0.28 to 2.56 with an average value of 1.46 in winter. The higher NH₃/NH₄ ⁺ ratio (3.5) observed in summer indicates the abundance of NH₃ in the atmosphere during summer. The higher fraction of particulate NH₄ ⁺ observed in winter than summer attributes to the conversion of gaseous NH₃ into NH₄ ⁺. The results emphasized that the traffic could be one of the significant sources of ambient NH₃ at the urban site of Delhi as illustrated by positive correlations of NH₃ with traffic-related pollutants (NO, NO₂ and CO). Surface wind analysis and wind directions also support the roadside traffic and agricultural activities at the nearby area indicating possible major sources of ambient NH₃ at the study site.     

Evaluation of TRMM multi-satellite precipitation analysis (TMPA) against terrestrial measurement over a humid sub-tropical basin,India

To support the GPM mission which is homologous to its predecessor, the Tropical Rainfall Measuring Mission (TRMM), this study has been undertaken to evaluate the accuracy of Tropical Rainfall Measuring Mission multi-satellite precipitation analysis (TMPA) daily-accumulated precipitation products for 5 years (2008–2012) using the statistical methods and contingency table method. The analysis was performed on daily, monthly, seasonal and yearly basis. The TMPA precipitation estimates were also evaluated for each grid point i.e. 0.25° × 0.25° and for 18 rain gauge stations of the Betwa River basin, India. Results indicated that TMPA precipitation overestimates the daily and monthly precipitation in general, particularly for the middle sub-basin in the non-monsoon season. Furthermore, precision of TMPA precipitation estimates declines with the decrease of altitude at both grid and sub-basin scale. The study also revealed that TMPA precipitation estimates provide better accuracy in the upstream of the basin compared to downstream basin. Nevertheless, the detection capability of daily TMPA precipitation improves with increase in altitude for drizzle rain events. However, the detection capability decreases during non-monsoon and monsoon seasons when capturing moderate and heavy rain events, respectively. The veracity of TMPA precipitation estimates was improved during the rainy season than during the dry season at all scenarios investigated. The analyses suggest that there is a need for better precipitation estimation algorithm and extensive accuracy verification against terrestrial precipitation measurement to capture the different types of rain events more reliably over the sub-humid tropical regions of India.