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751.
The concentration of gaseous elemental mercury (GEM) in the atmosphere of urban Beijing was measured from October 2003 to September 2004 to investigate the origins and spatial-temporal variations of atmospheric Hg. The mean value of Hg concentration is 17.1 ng·m-3 (n=653). The atmospheric Hg data showed spatial-temporal variations throughout the duration of our observation. The maximum GEM concentration (53.7 ng·m-3) was observed at Gucheng in the western area of urban Beijing. The GEM concentrations increased from the north to the south of the studied area, and were higher in winter than in summer. The highest and lowest monthly averages of GEM concentrations were measured to be 23.3 and 4.1 ng·m-3 in January and July, respectively. In addition, GEM concentrations are higher in the daytime than at night in Autumn and from 14 March to 15 April, but daily GEM variation showed an inverse pattern from 22 April to 22 May. In winter, two peak values of GEM concentrations occurred at 13:30 and 21:30. Daily variation of GEM concentrations in summer was the lowest in the four seasons. Mercury from coal combustion was estimated to be the main source of anthropogenic emissions in Beijing from October 2003 to September 2004. Additionally, Hg emission from natural gas burning was estimated to be another dominant source of atmospheric Hg in Beijing. 相似文献
752.
Based on the results of previous studies and under the direction of the theory of “ore deposit genesis”, the authors made
use of high temperature and high pressure experimental facilities and conditions at the Tectono-geochemistry Research Room
under the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, and put
the focus on the multi-source of tectonically controlling ore-forming materials, the characteristics of multi-stage and multi-episode
hydrothermal activities and mineralization and the characteristics of multi-genesis and multi-ore deposition so as to shed
light on the metallogenic mechanisms of super-large Cu and Au deposits. In addition simulating experiments were made on multi-stage
and multi-episode tectonic activities and rock and ore deformation, multi-stage and multi-episode tectonic activities and
mobilization and migration of ore-forming materials, and multi-stage and multi-episode tectonic activities and superimposition
and enrichment of ore-forming materials. The experimental results showed that under the action of multi-stage and multi-episode
tectonic stress the deformation and fragmentation of not only rocks and ores have been intensified, and but also the ore-forming
materials originally disbursed in the rocks and ores have been mobilized and migrated and superimposed and enriched. The experimental
results also provided the scientific experimental data and grounds for deep-going research on the rules of metallogenesis
and geneses of super-large ore deposits in the Dexing region, Jiangxi Province. 相似文献
753.
Shangyue Shen Qinglai Feng Wenqian Yang Zhibin Zhang Chonglakmani Chongpan 《中国地球化学学报》2010,29(3):255-260
On the basis of the petrographic characteristics, rock assemblages, petrochemistry, REEs, trace elements and geotectonic settings, the authors described the characteristics of continental marginal arc-volcanic rocks in the Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of the ocean-ridge/oceanic island basalts in the Chiang Mai belt. The volcanic rock assemblage is basaltic andesite-andesite-rhyolite. The volcanic series is dominated by the calc-alkaline series, with the tholeitic series coming next. The chemical composition of the volcanic rocks is characterized by high Al2O3; the REE distribution patterns are of the LREE-enrichment rightward incline type; the large cation elements are highly enriched, and the volcanic rocks are generally enriched in U and Th and depleted in Ti, Cr and P. The petrochemical plot falls within the field of island-arc volcanic rocks, in consistency with the projected points of continental marginal arc-volcanic rocks in the Lancangjiang belt. These continental mar-ginal arc-volcanic rocks, together with ocean-ridge/oceanic island-type volcanic rocks in the Chiang Mai belt, con-stitute the ocean-ridge volcanic rock-arc magmatic rock belts distributed in pairs, indicative of eastward subduction of the oceanic crust in the Chiang Mai belt. This result is of great importance in exploring the evolution of the pa-leo-Tethys in the Chiang Mai belt. 相似文献
754.
Debris and mudflows are some of the main geological hazards in the mountain foothills of the Chilean capital city of Santiago.
There, the risk of flows triggered in the basins of ravines that drain the range into the city increases with time due to
the city growth. A multivariate statistical study based on the logistic regression method is presented. The model provides
equations that allow the computation of combined meteorological triggering factors associated with a probability of rain-induced
flow occurrence. Daily rainfall, accumulated rainfall and the snowfall level, traditionally considered as the relevant factors,
are analysed for a 25-year period. The results show a strong relevance of the rainfall on the day of the flow event over the
other factors. However, the relatively low probabilities returned for some real flow events suggest that the model does not
capture all the significant variables and the problem is more complex than as it has been traditionally assumed, and further
investigations are needed to develop predictive models of flow triggering. 相似文献
755.
Thomas B. Boving Mark H. Stolt Janelle Augenstern Brian Brosnan 《Environmental Geology》2008,55(3):571-582
The control of polluted surface runoff and the assessment of possible impacts on groundwater is a concern at the local and
regional scale. On this background, a study investigates possible impacts of organic and inorganic pollutants (including bacteria)
originating from a permeable asphalt parking lot on the water quality immediately beneath it. The functioning of the permeable
pavement, including clogging and restricted vertical percolation, was also evaluated. Four nested sample ports (shallow and
deep) were installed below low- and high-traffic areas, including one port outside the parking lot. At least initially there
was a good hydraulic connection between the parking surface and the shallow sample ports. The presence of a geotextile layer
at the base of the parking lot structure, however, was identified in lab tests as one factor restricting vertical percolation
to the deeper ports. Clogging of the permeable surface was most pronounced in heavy traffic areas and below snow pile storage
areas. Corroborated by high electric conductivity and chloride measurements, sand brought in by cars during winter was the
principal cause for clogging. No bacteria or BOD were found in percolating water. Polycyclic aromatic hydrocarbons (PAH) were
present at concentrations near minimum detection limit. Nutrients (nitrate and phosphate) were being leached into the ground
via the permeable parking lot surface at annual flux rates of 0.45–0.84 g/m2/year. A multi-species tracer test demonstrated a retention capacity of the permeable parking lot structure of >90% for metals
and 27% for nutrients, respectively. 相似文献
756.
Recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system,southwest of North China Plain 总被引:4,自引:0,他引:4
Fadong Li Guoying Pan Changyuan Tang Qiuying Zhang Jingjie Yu 《Environmental Geology》2008,55(5):1109-1122
Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population,
quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess
these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical
evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis
and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed
of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater
was recharged by precipitation and was characterized by Ca–HCO3 type water with depleted δ18O and δD (mean value of −8.8‰ δ18O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex
(Ca–Na–Mg–HCO3–Cl–SO4 type), and heavier δ18O and δD were observed (around −8‰ δ18O). Before the surface water with mean δ18O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion
exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred
water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study
area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ18O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal
end of the fan. The groundwater underwent chemical evolution from Ca–HCO3, Na–HCO3, to Na–SO4. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical
evolution, and groundwater flow paths in the complex alluvial fan aquifer system. 相似文献
757.
David M. Hirsch 《Contributions to Mineralogy and Petrology》2008,155(4):401-415
Garnet-bearing schists from the Waterville Formation of south-central Maine provide an opportunity to examine the factors
governing porphyroblast size over a range of metamorphic grade. Three-dimensional sizes and locations for all garnet porphyroblasts
were determined for three samples along the metamorphic field gradient spanning lowest garnet through sillimanite grade, using
high-resolution X-ray computed tomography. Comparison of crystal size distributions to previous data sets obtained by stereological
methods for the same samples reveals significant differences in mode, mean, and shape of the distributions. Quantitative textural
analysis shows that the garnets in each rock crystallized in a diffusion-controlled nucleation and growth regime. In contrast
to the typical observation of a correlation between porphyroblast size and position along a metamorphic field gradient, porphyroblast
size of the lowest-grade specimen is intermediate between the high- and middle-grade specimens’ sizes. Mean porphyroblast
size does not correlate with peak temperatures from garnet-biotite Fe-Mg exchange thermometry, nor is post-crystallization
annealing (Ostwald Ripening) required to produce the observed textures, as was previously proposed for these rocks. Robust
pseudosection calculations fail to reproduce the observed garnet core compositions for two specimens, suggesting that these
calc-pelites experienced metasomatism. For each of these two specimens, Monte Carlo calculations suggest potential pre-metasomatism
bulk compositions that replicate garnet core compositions. Pseudosection analyses allow the estimation of the critical temperatures
for garnet growth: ∼481, ∼477, and ∼485°C for the lowest-garnet-zone, middle-garnet-zone, and sillimanite-zone specimens,
respectively. Porphyroblast size appears to be determined in this case by a combination of the heating rate during garnet
crystallization, the critical temperature for the garnet-forming reaction and the kinetics of nucleation. Numerical simulations
of thermally accelerated, diffusion-controlled nucleation, and growth for the three samples closely match measured crystal
size distributions. These observations and simulations suggest that previous hypotheses linking the garnet size primarily
to the temperature at the onset of porphyroblast nucleation can only partially explain the observed textures. Also important
in determining porphyroblast size are the heating rate and the distribution of favorable nucleation sites. 相似文献
758.
Using ALSM to map sinkholes in the urbanized covered karst of Pinellas County,Florida—1, methodological considerations 总被引:1,自引:0,他引:1
Larry D. Seale Lee J. Florea H. L. Vacher Robert Brinkmann 《Environmental Geology》2008,54(5):995-1005
Comparison of a database of interpreted sinkholes made using airborne laser swath mapping (ALSM) with databases of sinkholes
made from interpretation of aerial photographs reveals substantial disagreement. The discrepancies involve the location, number,
areas, and circularity of interpreted sinkholes. Methodological factors that contribute to the discrepancies include blockage
of ALSM laser returns in thick vegetation, multi-path reflections, and misrepresentation of the true extent of sinkholes.
Comparison of two ALSM-derived databases made (1) independently from versus (2) in combination with earlier air photo analysis
in undeveloped regions had the following result: one-fourth of the sinkholes interpreted by using the composite method were
missed by the independent analysis, and one-third of the sinkholes that were interpreted from the independent analysis were
not interpreted as sinkholes using the composite method. Subjective interpretation leads to a high level of uncertainty such
that the results of the remote sensing studies are suspect, if not invalid. 相似文献
759.
Soil contamination from urban and industrial activity: example of the mining district of Linares (southern Spain) 总被引:1,自引:0,他引:1
J. Martínez J. F. Llamas E. de Miguel J. Rey M. C. Hidalgo 《Environmental Geology》2008,54(4):669-677
The Linares region (southern Spain) has been subjected to two important sources of pollution: the intensive mining works and
the urban-industrial activity. To obtain a geochemical characterisation of the soil, 31 trace elements were analysed and 669
soil samples were collected. By means of clustering analysis, we identified groups of elements and grid squares in which relations
could be established concerning soil lithology, urban and industrial activities and the degree of pollution impact; in addition,
we were able to characterise the geochemical background of the study area. The multivariate study led us to identify four
factors. Particularly important was factor 2, which represented the elements associated with mineral paragenesis (Cu, Pb,
As, Co, Mn, Zn, Sn, Ba). This factor also contains elements related with an urban-industrial activity, such as Pb, Cu, Zn,
As and Ba. Furthermore, we identified factor 4, associating Ni, V and Cr, and which is related to the use of fuels. 相似文献
760.
The state of land subsidence and prediction approaches due to groundwater withdrawal in China 总被引:7,自引:6,他引:7
This article gives a general introduction to land subsidence with the prediction approaches due to withdrawal of groundwater
in three subsided/subsiding regions in China: the deltaic plain of Yangtse River (YRDP), North China Plain (NCP), and Fenwei
Plain (FP). On YRDP, Shanghai is the typical subsided/subsiding city; on NCP Tianjin is the typical subsided/subsiding city,
and on FP Taiyuan is the typical subsided/subsiding city. The subsided area with subsidence over 200 mm on YRDP is about 10,000 km2 and the maximum subsided value reached 2.9 m at Shanghai; on NCP the subsided area reached 60,000 km2 with the maximum subsidence of 3.9 m at Tianjing; on FP the subsided area is relatively smaller than that on the other two
plains and is about 1,135 km2 with maximum subsidence of 3.7 m at Taiyuan city. In order to protect the civil and industrial facilities, it is necessary
to predict the future development of land subsidence based on present state. Many researchers proposed several approaches
to predict the land subsidence due to groundwater withdrawal according to different geological conditions and groundwater
withdrawal practice. This article classifies these approaches into five categories: (i) statistical methods; (ii) 1D numerical
method; (iii) quasi-3D seepage model; (iv) 3D seepage model; (v) fully coupled 3D model. In China, the former four categories
are presently employed in the prediction practice and their merits and demerits are discussed. According to the prediction
practice, 3D seepage model is the best method presently. 相似文献