Advancements in hydrochemistry mapping: methods and application to groundwater arsenic and iron concentrations in Varanasi,Uttar Pradesh,India     

Ricardo?A.?OleaEmail author  N.?Janardhana?Raju  Juan?José?Egozcue  Vera?Pawlowsky-Glahn  Shubhra?Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(1):241-259

The area east of Varanasi is one of numerous places along the watershed of the Ganges River with groundwater concentrations of arsenic surpassing the maximum value of 10 parts per billion (ppb) recommended by the World Health Organization in drinking water. Here we apply geostatistics and compositional data analysis for the mapping of arsenic and iron to help in understanding the conditions leading to the occurrence of elevated level of arsenic in groundwater. The methodology allows for displaying concentrations of arsenic and iron as maps consistent with the limited information from 95 water wells across an area of approximately 210 km²; visualization of the uncertainty associated with the sampling; and summary of the findings in the form of probability maps. For thousands of years, Varanasi has been on the erosional side in a meander of the river that is free of arsenic values above 10 ppb. Maps reveal two anomalies of high arsenic concentrations on the depositional side of the valley, which has started seeing urban development. The methodology using geostatistics combined with compositional data analysis is completely general, so this study could be used as a prototype for hydrochemistry mapping in other areas.  相似文献   

On the formation of diaplectic glass: Shock and thermal experiments with plagioclase of different chemical compositions     

Jrg Fritz  Vera Assis Fernandes  Ansgar Greshake  Andreas Holzwarth  Ute Bttger 《Meteoritics & planetary science》2019,54(7):1533-1547

This contribution addresses the role of chemical composition, pressure, temperature, and time during the shock transformation of plagioclase into diaplectic glass—i.e., maskelynite. Plagioclase of An_50‐57 and An₉₄ was recovered as almost fully isotropic maskelynite from room temperature shock experiments at 28 and 24 GPa. The refractive index (RI) decreased to values of a quenched mineral glass for An_50‐57 plagioclase shocked to 45 GPa and shows a maximum in An₉₄ plagioclase shocked to 41.5 GPa. The An₉₄ plagioclase experiments can serve as shock thermobarometer for lunar highland rocks and howardite, eucrite, and diogenite meteorites. Shock experiments at 28, 32, 36, and 45 GPa and initial temperatures of 77 and 293 K on plagioclase (An_50‐57) produced materials with identical optical and Raman spectroscopic properties. In the low temperature (<540 K) region, the formation of maskelynite is entirely controlled by shock pressure. The RI of maskelynite decreased in heating experiments of 5 min at temperatures of >770 K, thus, providing a conservative upper limit for the postshock temperature history of the rock. Although shock recovery experiments and static pressure experiments differ by nine orders of magnitude in typical time scale (microseconds versus hours), the amorphization of plagioclase occurs at similar pressure and temperature conditions with both methods. The experimental shock calibration of plagioclase can, together with other minerals, be used as shock thermobarometer for naturally shocked rocks.  相似文献   

A steep-fronted Carboniferous carbonate platform: clinoformal geometry and lithofacies (Picos de Europa, NW Spain)     

Juan R. Bahamonde  Carmen Vera  & Juan R. Colmenero 《Sedimentology》2000,47(3):645-664

A steep‐margined carbonate platform is developed in the Carboniferous synorogenic foreland basin of northern Spain. Dips of 60–90° produced during Late Carboniferous thrusting enable cross‐sections of a 4‐km‐wide portion of the marginal area of this platform (Las Llacerias outcrop) to be studied in aerial photographs at a seismic scale. Three stratal domains are observed: (1) a horizontal‐bedded platform; (2) a clinoformal‐bedded margin with a relief of up to 500 m; and (3) a low‐angle toe‐of‐slope, where slope beds interfinger with basin sediments. The slope shows well‐bedded sigmoidal clinoforms with depositional dips ranging from 15° to 32°. Based on lithology and stratal patterns, four facies groups have been recognized: (1) a flat‐topped platform, in which thick algal boundstone, skeletal packstone–grainstone and peloidal micrite wackestone with a poorly rhythmic character prevail; (2) the platform margin and upper slope, characterized by microbial boundstone spanning a bathymetric range of ≈150 m measured from the break of slope; (3) a slope, predominantly composed of margin‐derived rudstones and breccias; and (4) a toe‐of‐slope to basin zone, where a cyclic alternation of spiculitic siltstones, packstone to grainstone calciturbidites and rudstone/breccia is visible. Five successive stages of platform development are deduced: (1) Bashkirian: flooding of the pre‐existing Serpukhovian platform giving rise to the nucleation of a low‐angle ramp to the south‐east of the study area with microbial mud‐mound accumulations, and breccias and calciturbidites on the margins; (2) Early Moscovian: an influx of siliciclastic sediment buried part of the platform and reduced the area of carbonate sedimentation; (3) Moscovian: aggradation and progradation of the carbonate system produced an extensive steep‐margined and flat‐topped shallow‐water platform (shelf system); (4) Latest Moscovian–earliest Kasimovian: drowning of the platform; and (5) Kasimovian: covering of the platform by marly calcareous ramp sediments.  相似文献   

Late Quaternary vegetation and fire history in the northernmost Nothofagus forest region: Mallín Vaca Lauquen,Neuquén Province,Argentina     

Vera Markgraf  Cathy Whitlock  R. Scott Anderson  Adriana García 《第四纪科学杂志》2009,24(3):248-258

The last 16 000 cal. a of vegetation, fire and limnological history are described from the steppe‐forest ecotone in the northernmost Nothofagus forest region east of the Andes (Mallín Vaca Lauquen, Neuquén Province, Argentina, latitude 36° 51.336′ S, longitude 71° 02.538′ W). Between 16 000 and 14 800 cal. a BP, scrub steppe with substantial open ground expanded in formerly glaciated valleys, whereas Nothofagus–Prumnopitys andina woodland covered mountain slopes. The site was a relatively deep and unproductive small lake at this time. After 14 800 cal. a BP, both steppe and woodland vegetation became denser, indicating increased moisture and temperatures, although not to present levels. The lake was still relatively deep and dystrophic, but became more alkaline by 10 000 cal. a BP. Between 8900 and 5500 cal. a BP, conditions were markedly drier than before; a Cyperaceae marsh developed and disturbance taxa increased. After 5500 cal. a BP, moisture increased but varied greatly, as evidenced by fluctuating water levels and high fire activity from 5500 to 4400 cal. a BP and from 2300 to 1000 cal. a BP. Human activity, in terms of forest clearance and livestock grazing, is documented in the uppermost levels. The evidence of high environmental variability in the middle and late Holocene is consistent with the onset or strengthening of the El Niño–Southern Oscillation, but differences in the timing of fire activity among sites on the west and east sides of the Andes suggest that fuel conditions were important in determining the local occurrence of fire. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The Quaternary glacial sequence in Ecuador: a reinterpretation of the work of Walter Sauer     

Chalmers M. Clapperton  Ramon Vera 《第四纪科学杂志》1986,1(1):45-56

The Quaternary glacial sequence proposed for the Ecuadorian Andes by Walter Sauer is critically reviewed. Examination of his field evidence at sections exposing Quaternary sediments east of Quito has led to a fundamental reinterpretation. Deposits which Sauer considered as glacial, glacio-fluvial, glacio-lacustrine and pluvio-glacial in origin appear to have been formed mainly by volcanic, volcano-loessic, laharic, fluvial, colluvial and pedogenic processes.  相似文献   

Effect of organic acids and fluoride on the dissolution kinetics of hydrous alumina. A model study using the rotating disc electrode     

Vera Žutić  Werner Stumm 《Geochimica et cosmochimica acta》1984,48(7):1493-1503

The dissolution of aluminium oxide was studied with an oxide film covered rotating disc aluminium electrode. This allows us to make measurements under conditions of well defined mass transport under conditions representative of those found in natural waters (conc. of Al, organic acids and fluoride), and permits us to distinguish between surface-controlled and transport-controlled rates.Under steady-state conditions, the dissolution current is a direct measure of the flux of dissolving Al ions at the aqueous interface of the amorphous hydrous oxide film.At pH 3–6 and in presence of organic ligands, dissolution is controlled by a surface process, i.e. the rate of detachment of surface complexes. Fluoride ions in concentrations ≥ 10^?6 M increase dramatically the dissolution rate: at pH = 4 the process is controlled by convertive diffusion of F^? from the solution to the surface (k_F- = (3.6 ± 0.5) × 10^?2cms^?1). Competitive and reversible adsorption of organic ligands (10^?6 ? 10^?2M) displacing fluoride slows down the rate of detachment of the surface complex which becomes the rate-limiting step. The affinity of ligands for the Al₂O₃ surface sites increases in the sequence: formate ~ chloride ~ carbonate < acetate < sulphate < salicylate < fumarate < maleate < malonate ? oxalate ? fluoride ≤ citrate.The results are compared with simulated weathering experiments and interpreted in terms of the surface complexation model.  相似文献   

Boost for Bulgarian anti-pollution research     

Vera Rich 《Marine pollution bulletin》1982,13(11):373-374

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Funds setback for Hudson River project     

Vera Rich 《Marine pollution bulletin》1983,14(5):161-162

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Bulgaria     

Vera Rich 《Marine pollution bulletin》1983,14(5):162-165

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Norway     

Vera Rich 《Marine pollution bulletin》1983,14(9):325-334

This section of a two-part report is introduced by Drs Ehler and Basta of NOAA. It deals with operational discharges of oil from marine transportation sources and was compiled by Virgil F. Keith, Robert A. Mondor and Nannette J. Goldberg, of Engineering Computer Optecnomics, Inc., Annapolis, MD 21401, and Charles N. Ehler, Daniel J. Basta and Thomas F. LaPointe of the Ocean Assessments Division, Office of Oceanography and Marine Services, National Ocean Service, National Oceanic and Atmospheric Administration, Rockville, MD 20852. Charles Ehler is the Acting Chief of the division; Daniel Basta is the Acting Chief of its Strategic Assessment Branch. The second part of the report on predicting surface transport of pollutants in the Gulf will form next month's Viewpoint.  相似文献