Historical pollution variability from abandoned mine sites,Greater Blue Mountains World Heritage Area,New South Wales,Australia     

Jennifer Harrison  Hendrik Heijnis  Graziella Caprarelli 《Environmental Geology》2003,43(6):680-687

Core and surface sediments from the Tonalli River, a tributary of the artificial lake, Lake Burragorang, in the Blue Mountains National Park, New South Wales, Australia, were studied to evaluate the spatio-temporal distribution of pollutants from the Yerranderie silver-lead-zinc mine site, abandoned in the late 1920s. A sediment core was collected in the mouth of the Tonalli River, at its junction with Lake Burragorang, and surface sediment samples were collected in the Tonalli River and its tributaries. The concentrations of Pb, As, Zn, Cu, Cd, Hg and Ag in the sediments were determined by ICP-MS and ICP-AES techniques. Temporal variability of metal concentrations was established through ²¹⁰Pb dating of the core sediments and compared with published historical records, rainfall records and bushfire data. Metal concentrations in core sediments showed an overall increase around the year 1950 as well as increases coincident with heavy rainfall. Spatially, metal concentrations were up to 400 times the guideline limit around mine sites but decreased rapidly with distance downstream of the mines.  相似文献   

Engineering a Remote Survey of Jet's Divertor Structure Under Conditions of Restricted Access Using Digital Photogrammetry     

B. Macklin  R. Brade  F. Hurd  S. F Mills  S. Sanders  R. Stokes  & J. Tait 《The Photogrammetric Record》1998,16(92):213-223

JET (Joint European Torus) Joint Undertaking is currently planning to install its new Gasbox Divertor remotely. In line with JET's policy and philosophy, it was decided to survey the divertor structure remotely to confirm its position, shape and integrity prior to installing the new tile configuration. A survey to metrology standards with sub-millimetre accuracy is required. While remote surveys have been carried out in the past, they have not been to this level of accuracy. Digital photogrammetry (the evolution of photogrammetry, using CCD cameras) in conjunction with “targetless” software was selected as being the most suitable technique. It was seen as the natural evolution of the survey techniques already developed for use at JET, as well as having the potential to assist in preparations for future remote handling operations. Photogrammetry requires a large number of retroreflective targets to ensure accurate results. Clearly it would not be practical to fit targets remotely to the divertor structure. However, a technique has been developed at JET which uses a combination of targeted and targetless photogrammetry. A number of frames fitted with targets will be remotely positioned on the divertor structure. When surveyed these targets allow accurate determination of camera positions. Specially developed software allows the selection of untargeted features of components in the digital pictures. Their co-ordinates can be determined by triangulation from the known camera positions. Trials have shown that accuracy of ±0.6 mm is achievable. This paper will describe the development of this concept, the design of the necessary equipment, the testing to prove the accuracy and feasibility and the trials carried out in JET's In-vessel Training Facility. These included remote handling of the six million pixel camera and other equipment, data handling and download via an ethernet link through the remote handling articulated boom, development of survey techniques, optimization of analysis techniques using coded targets for fast processing and finally the engineering assessment of the divertor structure based on survey results.  相似文献   

In situ measurements of sound velocities and densities across the orthopyroxene → high-pressure clinopyroxene transition in MgSiO₃ at high pressure     

Jennifer Kung  Baosheng Li  Yanbin Wang  Robert C. Liebermann 《Physics of the Earth and Planetary Interiors》2004,147(1):27-44

Using acoustic measurement interfaced with a large volume multi-anvil apparatus in conjunction with in situ X-radiation techniques, we are able to measure the density and elastic wave velocities (V_P and V_S) for both ortho- and high-pressure clino-MgSiO₃ polymorphs in the same experimental run. The elastic bulk and shear moduli of the unquenchable high-pressure clinoenstatite phase were measured within its stability field for the first time. The measured density contrast associated with the phase transition OEN → HP-CEN is 2.6-2.9% in the pressure of 7-9 GPa, and the corresponding velocity jumps are 3-4% for P waves and 5-6% for S waves. The elastic moduli of the HP-CEN phase are K_S=156.7(8) GPa, G = 98.5(4) GPa and their pressure derivatives are K_S′=5.5(3) and G′ = 1.5(1) at a pressure of 6.5 GPa, room temperature. In addition, we observed anomalous elastic behavior in orthoenstatite at pressure above 9 GPa at room temperature. Both elastic wave velocities exhibited softening between 9 and 13-14 GPa, which we suggest is associated with a transition to a metastable phase intermediate between OEN and HP-CEN.  相似文献   

Social Attitudes Predict Biases in Geographic Knowledge*     

Dennis D. Kerkman  David Stea  Karen Norris  Jennifer L. Rice 《The Professional geographer》2004,56(2):258-269

Three principal components were found to underlie Texas university students' experiences with and attitudes toward Canada, the United States, and Mexico: diversity orientation, Mexican experiences, and Canadian experiences. Diversity orientation included positive attitudes toward Hispanics, Canadians, minorities, interethnic friendships, and dating and was negatively correlated with natio‐centrism (e.g., believing U.S. citizens receive the world's best education). Diversity orientation and natio‐centrism were not related to experiences with Mexico or Canada. Students estimated the locations of Canadian cities too far north and Mexican cities too far south. Biased estimates for Mexican cities were negatively correlated with diversity orientation, not experience with Mexico.  相似文献   

Response of Nebraska Sand Hills Natural Vegetation to Drought, Fire, Grazing, and Plant Functional Type Shifts as Simulated by the Century Model     

Jennifer M. Mangan  Jonathan T. Overpeck  Robert S. Webb  Carol Wessman  Alexander F. H. Goetz 《Climatic change》2004,63(1-2):49-90

The Nebraska Sand Hills exist in a semi-arid climatic environment and the land surface is grassland growing on sandy soils. These soils have been periodically active throughout the Holocene, but are currently stabilized by the vegetation. However, a shift in climate could cause grassland death and eventual sand dune remobilization. Our studies used the CENTURY nutrient cycling and ecosystem model to investigate the impacts of drought, plant functional type, fire, grazing, and erosion on Nebraska Sand Hills vegetation and dune stability. Fire and grazing alone had little impact on the vegetation, but when combined with mild drought, biomass decreased. Overall biomass increased if one plant functional type was allowed to dominate the ecosystem. Addition of as little as 1 mm of erosion per year under current climate conditions decreases vegetation as much as a drought 20 percent drier than the worst of the 1930s drought years in Nebraska.  相似文献   

Business and Bludgeon at the Border: A transnational political economy of human displacement in Thailand and Burma     

Jennifer Hyndman 《GeoJournal》2002,56(1):39-46

Transnational economic integration between Thailand and Burma is intimately linked to protection for Burmese refugees in Thailand. In the case of Burmese nationals who seek safety in Thailand, their protection becomes more negotiable as economic integration with Thailand proceeds. Since 1988, hundreds of thousands of Burmese citizens have fled beyond the borders of their state, fearing both human rights abuses and successive offensives by a military junta intent on its own survival. Critical analysis of the dynamic of human displacement and bi-national economic cooperation between the governments of Thailand Burma grounds this study. The story is one of transnational trade across one border, where people's labour, homes, and passports are exchanged – in an obscured fashion – for investment, natural resources, and economic cooperation. The Thai-Burmese border proves to be a flexible concept that can be invoked to produce refugees or blurred to promote binational economic infrastructure and trade. Despite economic booms and busts in Southeast Asia, economic integration in the region is on-going. At the same time, Burma's government – the State Peace and Development Council – and its military force more and more citizens into neighbouring countries. Their reception in Thailand, however, is increasingly chilly. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

A new interpretation of the structure of disordered α-cristobalite     

M. J. Wilson  J. D. Russell  J. M. Tait 《Contributions to Mineralogy and Petrology》1974,47(1):1-6

Disordered -cristobalite which occurs extensively in bentonites, opals and particularly deep-sea cherts, has been previously interpreted in terms of a unidimensionally disordered structure in which cristobalite is interstratified with two-layer tridymite-like sheets. An alternative interpretation is that the structure is essentially tridymitic but that the sheets are stacked with random transverse displacement normal to the c axis, an arrangement similar to the translational, turbostratic stacking postulated for smectites. This interpretation was arrived at after a comparitive study of a silica phase in an Italian bentonite and a deep-sea chert, material which yielded an X-ray powder pattern almost identical with that of disordered -cristobalite, but electron diffraction patterns and infrared spectra more consistent with tridymite. It is suggested that this type of silica, which has been described almost universally as cristobalite, is more appropriately referred to as disordered -tridymite.Thanks are due to Mr R. H. S. Robertson, Pitlochry for the sample of bentonite and Mr D. S. Cassidy, Associate Curator, Antarctic Research Facility, Florida State University, U.S.A. for the sample of deep-sea chert.  相似文献   

Hydrogeologic controls on groundwater recharge and salinization: a geochemical analysis of the northern Hueco Bolson aquifer, Texas, USA     

Jennifer L. Druhan  James F. Hogan  Christopher J. Eastoe  Barry J. Hibbs  William R. Hutchison 《Hydrogeology Journal》2008,16(2):281-296

Identification of hydrogeologic controls on groundwater flowpaths, recharge, and salinization is often critical to the management of limited arid groundwater resources. One approach to identifying these mechanisms is a combined analysis of hydrogeologic and hydrochemical data to develop a comprehensive conceptual model of a groundwater basin. To demonstrate this technique, water samples were collected from 33 discrete vertical zone test holes in the Hueco Bolson aquifer, located within the Trans-Pecos Texas region and the primary water resource for El Paso, Texas, USA and Juárez, Mexico. These samples were analyzed for a suite of geochemical tracers and the data evaluated in light of basin hydrogeology. On the basis of δ²H and δ¹⁸O data, two regional recharge sources were recognized, one originating from western mountain-fronts and one from through-flow of the adjacent Tularosa aquifer. Chloride concentrations were strongly correlated with lithologic formations and both Cl/Br and ³⁶Cl ratios suggested the primary chloride source is halite dissolution within a specific lithologic unit. In contrast, sulfur isotopes indicated that most sulfate originates from Tularosa basin Permian gypsum sources. These results yielded a more comprehensive conceptual model of the basin, which suggested that chloride salinization of wells is the result of upconing of waters from the Fort Hancock formation.  相似文献   

Seston Removal by Natural and Constructed Intertidal Eastern Oyster (<Emphasis Type="Italic">Crassostrea virginica</Emphasis>) Reefs: A Comparison with Previous Laboratory Studies,and the Value of in situ Methods     

Raymond E. Grizzle  Jennifer K. Greene  Loren D. Coen 《Estuaries and Coasts》2008,31(6):1208-1220

An important ecological role ascribed to oysters is the transfer of materials from the water column to the benthos as they feed on suspended particles (seston). This ecosystem service has been often touted as a major reason for many oyster restoration efforts, but empirical characterization and quantification of seston removal rates in the field have been lacking. Changes in chlorophyll a (chl a) concentrations in the water column were measured in May 2005 and June 2006 in South Carolina using in situ fluorometry and laboratory analysis of pumped water samples taken upstream and downstream as water flowed over natural and constructed intertidal oyster reefs. Both methods gave similar results overall, but with wide variability within individual reef datasets. In situ fluorometer data logged at 10 to 30-s intervals for up to 1.3 h over eight different reefs (three natural and five constructed) showed total removal (or uptake) expressed as % removal of chl a ranging from −9.8% to 27.9%, with a mean of 12.9%. Our data indicate that restored shellfish reefs should provide water-quality improvements soon after construction, and the overall impact is probably determined by the size and density of the resident filter feeder populations relative to water flow characteristics over the reef. The measured population-level chl a removal was converted to mean individual clearance rates to allow comparison with previous laboratory studies. Although direct comparisons could not be made due to the small size of oysters on the study reefs (mean shell height, 36.1 mm), our calculated rates (mean, 1.21 L h⁻¹) were similar to published laboratory measured rates for oysters of this size. However, the wide variability in measured removal by the oyster reefs suggests that individual oyster feeding rates in nature may be much more variable than in the laboratory. The proliferation of ecosystem-level models that simulate the impacts of bivalves on water quality based only on laboratory-feeding measurements underscores the importance of further research aimed at determining ecologically realistic feeding rates for oysters in the field. Because in situ methods provide many replicate measurements quickly, they represent a potentially powerful tool for quantifying the effects of oyster reefs, including all suspension-feeding taxa present, on water quality.  相似文献   

The drying up of Britain? A national estimate of changes in seasonal river flows from 11 Regional Climate Model simulations     

Christel Prudhomme  Andy Young  Glenn Watts  Tracey Haxton  Sue Crooks  Jennifer Williamson  Helen Davies  Simon Dadson  Stuart Allen 《水文研究》2012,26(7):1115-1118

As climate change may modify the hydrological cycle significantly, understanding the impact on river flow is important because it affects long‐term water resources planning. Here, we describe a high‐resolution British assessment of changes in river flows in the 2050s under 11 different realisations of HadRM3. In winter, river flows may either increase or decrease, with a wide range of possible decreases in summer flow. These results should encourage adaptation that copes with a broad range of future hydrological conditions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献