A study of arsenic,iron and other dissolved ion variations in the groundwater of Bishnupur District,Manipur, India   总被引：1，自引：1，他引：0  

Jayalakshmi Devi Oinam  AL. Ramanathan  Anurag Linda  Gurmeet Singh 《Environmental Earth Sciences》2011,62(6):1183-1195

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.  相似文献   

Swashed away? Storm impacts on sandy beach macrofaunal communities     

Linda Harris  Ronel Nel  David Schoeman 《Estuarine, Coastal and Shelf Science》2011,94(3):210-221

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The origin of eucrites,diogenites, and olivine diogenites: Magma ocean crystallization and shallow magma chamber processes on Vesta     

Ben E. Mandler  Linda T. Elkins‐Tanton 《Meteoritics & planetary science》2013,48(11):2333-2349

The asteroid 4 Vesta is one of the very few heavenly bodies to have been linked to samples on Earth: the howardite‐eucrite‐diogenite (HED) meteorite suite. This large and diverse suite of meteorites provides a detailed picture of Vesta's igneous and postigneous history. We have used the range of igneous rock types and compositions in the HED suite to test a series of chemical models for solidification processes following peak melting (magma ocean) conditions on Vesta. Fractional crystallization cannot have been a dominant early process in the magma ocean because it leads to excessive Fe‐enrichment in the melt. Models that are dominated by equilibrium crystallization cannot produce orthopyroxene cumulates (diogenites). Our best models invoke 60–70% equilibrium crystallization of a magma ocean followed by continuous extraction of the residual melt into shallow magma chambers. Fractional crystallization in these magma chambers combined with continuous or periodic addition of more melt from the slowly compacting crystal mush (magmatic recharge) can produce all of the igneous HED lithologies (noncumulate and cumulate eucrites, diogenites, dunites, harzburgites, and olivine diogenites). Magmatic recharge can also explain the narrow range in eucrite compositions and the variability of incompatible trace element concentrations in diogenites. We predict an internal structure for Vesta that permits excavation of the HEDs during the formation of the Rheasilvia basin, while remaining consistent with observations from the Dawn mission and most impact models.  相似文献   

Delineating and defining the boundaries of an active landslide in the rainforest of Puerto Rico using a combination of airborne and terrestrial LIDAR data   总被引：1，自引：0，他引：1  

Guoquan Wang  James Joyce  David Phillips  Ramesh Shrestha  William Carter 《Landslides》2013,10(4):503-513

Light detection and ranging (LIDAR) is a remote sensing technique that uses light, often using pulses from a laser to measure the distance to a target. Both terrestrial- and airborne-based LIDAR techniques have been frequently used to map landslides. Airborne LIDAR has the advantage of identifying large scarps of landslides covered by tree canopies and is widely applied in identifying historical and current active landslides hidden in forested areas. However, because landslides naturally have relatively small vertical surface deformation in the foot area, it is practically difficult to identify the margins of landslide foot area with the limited spatial resolution (few decimeters) of airborne LIDAR. Alternatively, ground-based LIDAR can achieve resolution of several centimeters and also has the advantages of being portable, repeatable, and less costly. Thus, ground-based LIDAR can be used to identify small deformations in landslide foot areas by differencing repeated terrestrial laser scanning surveys. This study demonstrates a method of identifying the superficial boundaries as well as the bottom boundary (sliding plane) of an active landslide in National Rainforest Park, Puerto Rico, USA, using the combination of ground-based and airborne LIDAR data. The method of combining terrestrial and airborne LIDAR data can be used to study landslides in other regions. This study also indicates that intensity and density of laser point clouds are remarkably useful in identifying superficial boundaries of landslides.  相似文献   

The use of tracers to assess drill-mud penetration depth into sandstone cores during deep drilling: method development and application     

Linda Pellizzari  Dominik Neumann  Mashal Alawi  Dieter Voigt  Ben Norden  Hilke Würdemann 《Environmental Earth Sciences》2013,70(8):3727-3738

For the utilization of deep saline aquifers in the frame of geotechnical use, such as geological sequestration of CO₂, H₂ or energy storage, a baseline characterization of pristine reservoir rock cores is required to monitor changes in the indigenous microbial communities and pore fluids, and to study alterations in rock characteristics resulting from interaction with geological storage technologies. However, drilling procedures and technical fluids, particularly drill mud, are sources of core contamination. To measure the penetration of drill mud into the cores, three tracers (fluorescein, microspheres, and 4′,6-diamidino-2-phenylindole stained bacteria) were tested under laboratory conditions. The flow of drill mud into core samples was induced by applying uniaxial pressure differentials to the core, and the penetration depth was microscopically determined for each tracer. Fluorescein was extracted from the rock samples and quantified fluorometrically. The results indicate that all tested tracers are suitable for tracking drill-mud penetration. The actual penetration depth seems to be related to differences in mineral composition and texture as well as microfractures. Among all tested tracers, fluorescein labelling is the simplest, cheapest and most accurate method for analyzing the contamination of rock cores by technical fluids. The application of this tracer was successfully applied during two deep drilling campaigns at the CO₂ storage pilot site in Ketzin, Germany. The results highlight that the use of tracers is indispensable to ensure the quality of core samples for microbiological and biogeochemical analysis.  相似文献   

New challenges in biogeography     

Chris Joyce 《Area》2009,41(3):354-357

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Decolonizing Development: Colonial Power and the Maya – By Joel Wainwright     

Linda A  Newson 《The Geographical journal》2009,175(3):240-241

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The influence of dimensionality on simulations of mass recovery from nonuniform dense non-aqueous phase liquid (DNAPL) source zones     

John A. Christ  Lawrence D. Lemke  Linda M. Abriola 《Advances in water resources》2009

The influence of model dimensionality on predictions of mass recovery from dense non-aqueous phase liquid (DNAPL) source zones in nonuniform permeability fields was investigated using a modified version of the modular three-dimensional transport simulator (MT3DMS). Thirty-two initial two- (2D) and three-dimensional (3D) tetrachloroethene–DNAPL source zone architectures, taken from a recent modeling study, were used as initial conditions for this analysis. Commonly employed source zone metrics were analyzed to determine differences between 2D and 3D predictions: (i) down-gradient flux-averaged contaminant concentration, (ii) reductions in contaminant mass flux through a down-gradient boundary, (iii) source zone ganglia-to-pool (GTP) ratio, and (iv) time required to achieve a remediation objective. 3D flux-averaged contaminant concentrations were approximately 3.5 times lower than concentrations simulated in 2D. This difference was attributed to dilution of the contaminant concentrations down gradient of the source zone. Contaminant flux reduction predictions for a given mass recovery were generally 5% higher in 3D simulations than in 2D simulations. The GTP ratio declined over time as mass was recovered in both 2D and 3D simulations. Although the source longevity (i.e., time required to achieve 99.99% mass recovery) differed between individual 2D and 3D realizations, the mean source longevity for the 2D and 3D simulation ensembles was within 2%. 2D simulations tended to over-predict the time required to achieve lower mass recovery levels (e.g. 50% mass recovery) due to a smaller contaminated area exposed to uncontaminated water. These findings suggest that ensemble averages of 2D numerical simulations of DNAPL migration, entrapment, dissolution, and mass recovery in statistically homogenous, nonuniform media may provide reasonable approximations to average behavior obtained using simulations conducted in fully three-dimensional domains.  相似文献   

Climate Change and the Disappearance of Malaria from England     

Steve Lindsay  Andy Joyce 《Global Change & Human Health》2000,1(2):184-187

As the world's climate continues to change there is concern that this may cause malaria to spread to new areas. Here we examine whether past changes in temperature, in addition to social changes, may have affected malaria in England. Our analysis indicates that cold summers experienced during the 1800s may have contributed to the disappearance of this disease from the country. As our summers become progressively warner it is unlikely that malaria will become firmly re-established on these shores, although the possibility of future outbreaks should not be ignored.  相似文献   

A Nondimensional Evaluation of Tracer Sensitivity to Density Effects     

Marc Jalbert  Jacob H. Dane  Linda M. Abriola  Kurt D. Pennell 《Ground water》2000,38(2):226-233

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