A study of arsenic,iron and other dissolved ion variations in the groundwater of Bishnupur District,Manipur, India

The presence of arsenic (As) in groundwater and its effect on human health has become an issue of serious concern in recent years. The present study assessed the groundwater quality of the Bishnupur District, Manipur, with respect to drinking water standards. Higher concentrations of pH, iron and phosphate were observed at several locations. Phosphate and iron levels were highest in the pre-monsoon, followed by monsoon and post-monsoon seasons. The arsenic concentrations were highest during post-monsoon (1–200 μg L⁻¹) as compared to pre-monsoon (1–108 μg L⁻¹) and monsoon (2–99 μg L⁻¹). Kwakta and Ngakhalawai show higher levels of arsenic concentration as compared to the prescribed World Health Organization (WHO) and Bureau of Indian Standards (BIS) norms. Arsenic showed a strong positive correlation with phosphate and negative correlation with sulphate, suggesting a partial influence of anthropogenic sources. The study suggests that the Bishnupur area has an arsenic contamination problem, which is expected to increase in the near future.     

The formation of boundary clinopyroxenes and associated glass veins in type B1 CAIs

Abstract— We used focused ion beam thin section preparation and scanning transmission electron microscopy (FIB/STEM) to examine the interfacial region between spinel and host melilite for spinel grains in type B1 inclusions from the Allende and Leoville carbonaceous chondrites. Boundary clinopyroxenes decorating spinel surfaces have compositions similar to those of coarser clinopyroxenes from the same region of the inclusion, suggesting little movement after formation. Host melilite displays no anomalous compositions near the interface and late‐stage minerals are not observed, suggesting that boundary pyroxenes did not form by crystallization of residual liquid. Allende spinels display either direct spinel‐melilite contact or an intervening boundary clinopyroxene between the two phases. Spinel‐melilite interfacial regions in a Leoville B1 are more complex, with boundary clinopyroxene, as observed in Allende, but also variable amounts of glass, secondary calcite, perovskite, and an Mg‐, Al‐, OH‐rich and Ca‐, Si‐poor crystalline phase that may be a layered double hydrate. One possible scenario of formation for the glass veins is that open system alteration of melilite produced a porous, hydrated aggregate of Mg‐carpholite or sudoite + aluminous diopside that was shock melted and quenched to a glass. The hydrated crystalline phase we observed may have been a shocked remnant of the precursor phase assemblage, but is more likely to have formed later by alteration of the glass. In the mantle, boundary clinopyroxenes may have been crystallized from Ti‐rich liquids formed by the direct dissolution of perovskite and an associated Sc‐Zr‐rich phase or as a reaction product between dissolving perovskite and liquid. In the core, any perovskite and associated Ti‐enriched liquids that may have originally been present disappeared before the growth of boundary clinopyroxene, and the observed boundary clinopyroxene may have nucleated and grown from the liquid, along with the larger core clinopyroxene.     

DIAGNOSIS OF WAVE ACTIVITY OVER RAINBAND OF LANDFALL TYPHOON

A generalized wave-activity density, which is defined as an absolute value of production of three-dimensional vorticity vector perturbation and gradient of general potential temperature perturbation, is introduced and its wave-activity law is derived in Cartesian coordinates. Constructed in an agoestrophic and nonhydrostatic dynamical framework, the generalized wave-activity law may be applicable to diagnose mesoscale weather systems leading to heavy rainfall. The generalized wave-activity density and wave-activity flux divergence were calculated with the objective analysis data to investigate the character of wave activity over heavy-rainfall regions. The primary dynamical processes responsible for disturbance associated with heavy rainfall were also analyzed. It was shown that the generalized wave-activity density was closely correlated to the observed 6-h accumulative rainfall. This indicated that the wave activity or disturbance was evident over the frontal and landfall-typhoon heavy-rainfall regions in middle and lower troposphere. For the landfall-typhoon rainband, the portion of generalized wave-activity flux divergence, denoting the interaction between the basic-state cyclonic circulation of landfall typhoon and mesoscale waves, was the primary dynamic process responsible for the evolution of generalized wave-activity density.     

Weathering and biokarst development on marine terraces,northwest Morocco

Weathering features are described from an arid coastal area in northern Morocco which are indicative of invasive chasmolithic and endolithic microbial communities. Active weathering of marine terraces and karst development is associated with endolithic and epilithic algae responsible for boring, disintegration of matrix and mineral fabrics, solution and biomineralization that undermines the marine carbonate platform. Evidence of a range of biological weathering agents remains preserved, speci?cally calci?ed ?laments and sporangial material. An abundance of ?laments and spores representative of a consortium of algae, fungi, cyanobacteria and lichens is associated with the most denuded outcrops. The array of microbes contributes to the formation of the stromatolites to depths of 0·5 m within the limestone substrate. The preservation of stromatolites is supported by calci?cation of spores and ?laments, with trapping and binding of carbonate held in suspension by vadose waters. The pervasive weathering on this sector of coastline has important practical implications for coastal planning and development authorities in Morocco. Copyright © 2003 John Wiley & Sons, Ltd.     

Rare earth element variations resulting from inversion of pigeonite and subsolidus reequilibration in lunar ferroan anorthosites

We present results of a secondary ion mass spectrometry study of the rare earth elements (REEs) in the minerals of two samples of lunar ferroan anorthosite, and the results are applicable to studies of REEs in all igneous rocks, no matter what their planet of origin. Our pyroxene analyses are used to determine solid-solid REE distribution coefficients (D = C_REE in low-Ca pyroxene/C_REE in augite) in orthopyroxene-augite pairs derived by inversion of pigeonite. Our data and predictions from crystal-chemical considerations indicate that as primary pigeonite inverts to orthopyroxene plus augite and subsolidus reequilibration proceeds, the solid-solid Ds for orthopyroxene-augite pairs progressively decrease for all REEs; the decrease is greatest for the LREEs. The REE pattern of solid-solid Ds for inversion-derived pyroxene pairs is close to a straight line for Sm-Lu and turns upward for REEs lighter than Sm; the shape of this pattern is predicted by the shapes of the REE patterns for the individual minerals.Equilibrium liquids calculated for one sample from the compositions of primary phases, using measured or experimentally determined solid-liquid Ds, have chondrite-normalized REE patterns that are very slightly enriched in LREEs. The plagioclase equilibrium liquid is overall less rich in REEs than pyroxene equilibrium liquids, and the discrepancy probably arises because the calculated plagioclase equilibrium liquid represents a liquid earlier in the fractionation sequence than the pyroxene equilibrium liquids. “Equilibrium” liquids calculated from the compositions of inversion-derived pyroxenes or orthopyroxene derived by reaction of olivine are LREE depleted (in some cases substantially) in comparison with equilibrium liquids calculated from the compositions of primary phases. These discrepancies arise because the inversion-derived and reaction-derived pyroxenes did not crystallize directly from liquid, and the use of solid-liquid Ds is inappropriate. The LREE depletion of the calculated liquids is a relic of formation of these phases from primary LREE-depleted minerals. Thus, if one attempts to calculate the compositions of equilibrium liquids from pyroxene compositions, it is important to establish that the pyroxenes are primary. In addition, our data suggest that experimental studies have underestimated solid-liquid Ds for REEs in pigeonite and that REE contents of liquids calculated using these Ds are overestimates.Our results have implications for Sm-Nd age studies. Our work shows that if pigeonite inversion and/or subsolidus reequilibration between augite and orthopyroxene occurred significantly after crystallization, and if pyroxene separates isolated for Sm-Nd studies do not have the bulk composition of the primary pyroxenes, then the Sm-Nd isochron age and ε_Nd will be in error.     

Suspended sediment dynamics in the meltwater of Chhota Shigri glacier,Chandra basin,Lahaul-Spiti valley,India

Present study shows suspended sediment dynamics in the meltwater of Chhota Shigri glacier, Himachal Pradesh, India for different melt seasons during the period 2011-2014. Maximum suspended sediment concentration in the meltwater was found during the month of July 2011, 2012 and 2014 constituting to 55.2%, 48.3% and 46.9%, respectively. Whereas in 2013, maximum suspended sediment concentration was observed in August accounting for 46.1% of the total. On the other hand, maximum suspended sediment load was monitored in the month of July 2011, 2012 and 2014 constituting 59.5%, 63% and 55.7% of the total, respectively. Whereas in 2013, maximum suspended sediment load was observed in the month of August accounting for 49.8% of the total suspended sediment load. Annual distribution of suspended sediment concentration (SSC) and suspended sediment load (SSL) in the Chhota Shigri glacier shows higher value of SSC and SSL during the study period 2012 and 2013, which may be due to the presence of high glacial runoff and negative mass balance of the studied area during these time periods. Marked diurnal variation has been observed in the SSC of meltwater. Strong correlation was observed between SSC and SSL with discharge. On the other hand, SSC and SSL also showed strong exponential correlation with air temperature of the studied area. Sediment yield from the catchment of Chhota Shigri glacier is high during the peak melt season (July and August) and low during the late melt season (September and October). The average value of erosion rate for Chhota Shigri glacier basin during the study period 2011-2014 was calculated to be 1.1 mm/yr, which is lower than the average erosion rate of other Himalayan glaciers such as Rakiot, Chorabari and Gangotri glaciers, which may be caused by its geological setting containing high erosion resistant rocks such as granite, granite gneiss and porphyritic granite.     

Major ion composition and seasonal variation in the Lesser Himalayan lake: case of Begnas Lake of the Pokhara Valley, Nepal

The Begnas Lake in the Pokhara Valley is one of the threatened habitats in Nepal. The major ion chemistry explains the status of most of the inorganic nutrients and their possible sources. However, the earlier studies mostly cover limnological investigations, and phytoplankton and zooplankton diversity. Thus, the present study has been conducted to investigate the geochemical processes and to examine the seasonal variation of chemical composition within Begnas Lake. The results showed that SO ₄ ^2- , PO ₄ ^3- , and NO ₃ ^- increased compared with the previous values. The domination of Ca²⁺, Mg²⁺, and HCO ₃ ^- explains the influence of carbonate weathering on the major ion concentration. In general, pH and dissolved oxygen decreased with the depth of water-column, while electric conductivity, total dissolved solids, HCO ₃ ^- , Cl^-, H₄SiO₄, K⁺, Mg²⁺, Ca²⁺, Mn²⁺, and Fe increased. Among the cations, the predominance of Ca²⁺ and Mg²⁺ as characterized by high (>0.6) (Ca²⁺ + Mg²⁺)/(Tz⁺) and (>0.8) (Ca²⁺ + Mg²⁺)/(Na⁺ + K⁺) equivalent ratios, also suggests prevalence of carbonate weathering. The low value of (Na⁺ + K⁺)/Tz⁺ ratio shows deficiency of Na⁺ and K⁺, suggesting low contribution of cations via aluminosilicate weathering. The C-ratio suggests a proton source derived both from oxidation of sulfide and dissolution and dissociation of atmospheric CO₂ during different seasons. Though the major hydro-chemical parameters are within permissible limit, the increase in trophic state of the lake suggests that inherent biogeochemical processes make the limiting nutrients available, rendering eutrophic effect. Therefore, further comprehensive studies incorporating sediment–water interaction ought to be carried out to explain the ongoing phenomena and curb the eutrophication process in the lake.     

Osmium isotope and highly siderophile element systematics of the lunar crust

Coupled ¹⁸⁷Os/¹⁸⁸Os and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data are reported for pristine lunar crustal rocks 60025, 62255, 65315 (ferroan anorthosites, FAN) and 76535, 78235, 77215 and a norite clast in 15455 (magnesian-suite rocks, MGS). Osmium isotopes permit more refined discrimination than previously possible of samples that have been contaminated by meteoritic additions and the new results show that some rocks, previously identified as pristine, contain meteorite-derived HSE. Low HSE abundances in FAN and MGS rocks are consistent with derivation from a strongly HSE-depleted lunar mantle. At the time of formation, the lunar floatation crust, represented by FAN, had 1.4 ± 0.3 pg g^? 1 Os, 1.5 ± 0.6 pg g^? 1 Ir, 6.8 ± 2.7 pg g^? 1 Ru, 16 ± 15 pg g^? 1 Pt, 33 ± 30 pg g^? 1 Pd and 0.29 ± 0.10 pg g^? 1 Re (～ 0.00002 × CI) and Re/Os ratios that were modestly elevated (¹⁸⁷Re/¹⁸⁸Os = 0.6 to 1.7) relative to CI chondrites. MGS samples are, on average, characterised by more elevated HSE abundances (～ 0.00007 × CI) compared with FAN. This either reflects contrasting mantle-source HSE characteristics of FAN and MGS rocks, or different mantle–crust HSE fractionation behaviour during production of these lithologies. Previous studies of lunar impact-melt rocks have identified possible elevated Ru and Pd in lunar crustal target rocks. The new results provide no supporting evidence for such enrichments.If maximum estimates for HSE in the lunar mantle are compared with FAN and MGS averages, crust–mantle concentration ratios (D-values) must be ≤ 0.3. Such D-values are broadly similar to those estimated for partitioning between the terrestrial crust and upper mantle, with the notable exception of Re. Given the presumably completely different mode of origin for the primary lunar floatation crust and tertiary terrestrial continental crust, the potential similarities in crust–mantle HSE partitioning for the Earth and Moon are somewhat surprising. Low HSE abundances in the lunar crust, coupled with estimates of HSE concentrations in the lunar mantle implies there may be a ‘missing component’ of late-accreted materials (as much as 95%) to the Moon if the Earth/Moon mass-flux estimates are correct and terrestrial mantle HSE abundances were established by late accretion.     

A study on the hydrogeology and hydrogeochemistry of groundwater from different depths in a coastal aquifer: Annamalai Nagar,Tamilnadu, India

Chemical characterization of groundwater is essential to bring out its nature and utility. Samples from shallow and deep ground water of the same location were collected and studied for their geochemical characteristics following standard procedures (APHA 1998). Sediment samples from different depths were collected and analysed for minerals using FTIR and SEM. Resisitivity logging was carried out in the bore well to understand the variations in depth to fresh water potential. The shallow ground water is dominated by Na–Cl–HCO₃–SO₄ and deeper groundwater by Na–HCO₃–SO₄–Cl types. It is observed that there is a significant ionic variation with depth. The ionic strength of the deeper samples is lesser than in the shallower samples. Wide pH variations in the shallow water samples are due to ion exchange process. Thermodynamic stability plot was used to identify the state of stability. It is inferred that there is no major significant difference in the thermodynamic state of stability in the shallow and the deeper aquifers as the aquifer matrix for the shallow and deeper aquifers are almost similar. Saturation index of Gibbsite, Kaolinite, Calcite, Dolomite and anhydrite, were studied for shallow and deep aquifers, to identify the difference in hydro chemical signatures. The Si/Al ratios of shallow samples are less when compared with the deeper samples. Leaching of secondary salts was the chief mechanism controlling the ground water chemistry of the region.