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排序方式： 共有323条查询结果，搜索用时 437 毫秒
21.
Wagner José Barreto Ieda Scarminio Maria Cristina Solci Dílson Norio Ishikawa Melissa Tiemi Ogasawara Sônia Naomi Nomi Sônia Regina Giancoli Barreto 《洁净——土壤、空气、水》2007,35(3):239-245
Seventeen physical and chemical parameters were obtained from a hydroelectric reservoir located in a tropical region in the south of Brazil. Multivariate Principal Component Analysis (PCA) and Hierarchical Group Analysis (HGA) were used to identify the parameters discriminating the origin of water from the Tibagi and the Primeiro de Maio River, after it has passed the mixing region. The study was conducted during the dry and rainy seasons in July 2002 and February 2003 at three depths and three sampling sites located 0, 5, and 10 km away from the mixing region. The statistical methods showed to be appropriate for identifying the contribution of each tributary in the water mixing site of a complex water system. The most important discriminating parameter was the absorbance relation A(253 nm)/A(203 nm), followed by the concentrations of Fe(III), Mn(III), and Ni(II). An anthropogenic interference was found in the reservoir due to high Ni(II) and orthophosphate concentrations caused by a nearby town sewage discharge. The interference was more important during the dry periods due to the lower dispersion of the pollutants. Urgent initiatives should be taken from the state government to build treatment stations for the wastewater of the small cities around the Capivara hydroelectric reservoir to prevent the drinking water quality from deteriorating. 相似文献
22.
The oxidation rates of natural realgar and amorphous synthetic AsS by dissolved oxygen were evaluated using mixed flow reactors at pH 7.2 to 8.8 and dissolved oxygen contents of 5.9 to 16.5 ppm over a temperature range of 25 to 40°C. The ratios of As/S are stoichiometric for all amorphous AsS oxidation experiments except for two experiments conducted at pH ∼8.8. In these experiments, stoichiometric ratios of As/S were only observed in the early stages of AsS (am) oxidation whereas lower As/S ratios were observed during steady state. For realgar oxidation experiments, the As/S ratio is less than the stoichiometric ratio of realgar, ranging between 0.61 and 0.71. This nonstoichiometric release of As and S to solution indicates that realgar oxidation is more selective for S after the rates of oxidation become constant. All measured oxidation rates at 25°C can be described within experimental uncertainties as follows: Table 1
Rate Expression Activation Energy (kJ/mol) R(Realgar/As) = 10−9.63(±0.41)[DO]0.51(±0.08)[H+]−0.28(±0.05) 64.2 ± 9.8 R(Realgar/S) = 10−9.74(±0.35)[DO]0.54(±0.05)[H+]−0.31(±0.04) 62.2 ± 9.0 R(AsS(am)) = 10−13.65(±0.82)[DO]0.92(±0.08)[H+]−1.09(±0.10) 124 ± 18.8 - Full-size table
23.
A well-established and widely used correlative climate-vegetation model (Holdridge Life Zone model) was compared to three mechanistic simulation models (BIOME2, Dynamic Global Phytogeography Model (DOLY), and Mapped Atmosphere-Plant-Soil System (MAPSS)) for the conterminous United States under contemporary climate and a set of future climates prescribed by three Global Circulation Model experiments. Output from the mechanistic models were from the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) intercomparison. Holdridge modeling approaches, using a Simple implementation (vegetation distribution based on biotemperature and precipitation alone) or a Full implementation (vegetation distribution based on biotemperature, precipitation, altitudinal region, latitudinal belt, and transitional vegetation zones), represented current potential natural U.S. vegetation poor to fair, respectively. The more sophisticated mechanistic models were superior at reproducing potential vegetation under current climate compared to Holdridge, although there was significant variability among these models. The Holdridge implementations generally showed similar or greater climate sensitivity with respect to spatial redistribution of vegetation compared to the mechanistic models run both with and without doubled CO2 levels; however, the sensitivity of the Holdridge model depended on the implementation. Reduced sensitivity of the mechanistic models arises from direct (physiological) CO2 effects and other compensating feedbacks not captured by the Holdridge model. The greater degree of physical realism in the mechanistic models makes them the model class of choice for climate impact assessment. However, under circumstances of limited data availability, computation resources, and access to mechanistic models and model expertise, simple correlational models such as Holdridge may be the only method that can be applied. The paper makes some recommendations on the use of the Holdridge model for impact assessment if it is the only available model. 相似文献
24.
We report here, for the first time, on the new finding of extrusive calciocarbonatite (alvikite) rocks from the Pleistocene Mt. Vulture volcano (southern Italy). These volcanic rocks, which represent an outstanding occurrence in the wider scenario of the Italian potassic magmatism, form lavas, pyroclastic deposits, and feeder dikes exposed on the northern slope of the volcano. The petrography, mineralogy and whole-rock chemistry attest the genuine carbonatitic nature of these rocks, that are characterized by high to very high contents of Sr, Ba, U, LREE, Nb, P, F, Th, high Nb/Ta and LREE/HREE ratios, and low contents of Ti, Zr, K, Rb, Na and Cs. The O–C isotope compositions are close to the “primary igneous carbonatite” field and, thus, are compatible with an ultimate mantle origin for these rocks. The Sr–Nd–Pb–B isotope compositions, measured both in the alvikites and in the silicate volcanic rocks, indicate a close genetic relationship between the alvikites and the associated melilitite/nephelinite rocks. Furthermore, these latter products are geochemically distinct from the main foiditic-phonolitic association of Mt. Vulture. We propose a petrogenetic/geodynamic interpretation which has important implications for understanding the relationships between carbonatites and orogenic activity. In particular, we propose that the studied alvikites are generated through liquid unmixing at crustal levels, starting from nephelinitic or melilititic parent liquids. These latter were produced in a hybrid mantle resulting from the interaction through a vertical slab window, between a metasomatized mantle wedge, moving eastward from the Tyrrhenian/Campanian region, and the local Adriatic mantle. The occurrence of carbonatite rocks at Mt. Vulture, that lies on the leading edge of the Southern Apennines accretionary prism, is taken as an evidence for the carbonatation of the mantle sources of this volcano. We speculate that mantle carbonatation is related to the introduction of sedimentary carbon from the Adriatic lithosphere during Tertiary subduction. 相似文献
25.
Palaeomagnetic investigations and Rb–Sr dating were carried out on samples from two plutons from the Granite Harbour Intrusives of the Transantarctic Mountains inland of Terra Nova Bay. The Rb–Sr whole rock–biotite ages from Teall Nunatak (475±4, 483±4 Ma), a quartz-diorite pluton cropping out to the south of Priestley Glacier, are older than that from the Mount Keinath monzogranite (450±4 Ma), which is located to the north of the glacier. These results are consistent with the literature data, which suggest that during the last phases of the Ross Orogeny the cooling rate of the basement was significantly lower to the north than to the south of Priestley Glacier. The Teall Nunatak quartz-diorite is characterized by a stable magnetization, whose blocking-temperature spectrum ranges from 530 to 570 °C. At one site, the stable magnetization is screened by a large secondary component of opposite polarity, removed by thermal demagnetization below 300 °C. The characteristic directions after thermal demagnetization yielded a southern pole located at lat. 11°S, long. 21°E. The magnetization of Mount Keinath monzogranite consists of several components with overlapping stability spectra. A characteristic direction was isolated at one site only, obtained by demagnetizing the specimens in the temperature range from 380 to 460 °C.
Comparison with the other East Antarctica poles shows that those from Victoria Land are very well grouped and give a reliable early Ordovician palaeopole (lat. 5°S, long. 23°E, with K =196 and A95 =3.7°), whereas the poles from Wilkes, Enderby and Dronning Maud Land are dispersed. We tentatively advance the hypothesis that the dispersion reflects different magnetization ages due to the slow cooling of these regions during the last stages of the Ross Orogeny. 相似文献
Comparison with the other East Antarctica poles shows that those from Victoria Land are very well grouped and give a reliable early Ordovician palaeopole (lat. 5°S, long. 23°E, with K =196 and A
26.
Herbert Siegel Wolfgang Matthäus Regina Bruhn Monika Gerth Günther Nausch Thomas Neumann Christa Pohl 《Ocean Dynamics》1998,50(2-3):145-167
The exceptional Oder flood in summer 1997 was a unique event in order to investigate the impacts on and the consequences for the ecosystem of the Baltic Sea of about 6.5 km3 additional water loaded with nutrients and contaminants and discharged within only 5 weeks. About 15 institutions participated in this investigation in both the Szczecin Lagoon and the Pomeranian Bight. The Baltic Sea Research Institute Warnemünde studied the water and nutrient inflow, the spreading of the Oder discharge, and the impact of the discharge on the ecosystem. The main topic of the presented investigations is a detailed study of the spatial and temporal spreading of the extreme river discharge in the Pomeranian Bight and the southern Baltic Sea by satellite data, ship observations and continuous buoy measurements as well as numerical modelling. The meteorological conditions were characterized by mainly easterly winds which guided the outflowing riverine water along the German coast into the Arkona Sea. The spatial and temporal development of the distribution patterns of the Oder discharge was monitored by about 80 Sea Surface Temperature (SST) images of NOAA satellites. Shipborne measurements showed that the vertical extent of the Oder plume ranged between 5 and 7 metres. The concentrations of inorganic nutrients, except higher silicate, were comparable to typical winter/early spring values (seasonal maximum) in this region. The high dilution effect of the flood water reduced the concentration of contaminants and thus, prevented a direct negative impact of trace metals and chlorinated organic compounds on the marine environment. Coupled physical-biochemical modelling in combination with SST-images demonstrated the temporal development and satellite data in the visible spectral range delivered the maximum extent of discharged river water into the southern Arkona Sea where a further western transport was limited by the upwelling region off Hiddensee. Thus, all detected effects of the Oder flood were confined to the Pomeranian Bight and the southern Arkona Sea, without long-term consequences for the ecosystem. 相似文献
27.
28.
The energy balance over land and oceans: an assessment based on direct observations and CMIP5 climate models 总被引：2，自引：0，他引：2
29.
Raquel Souza Teixeira Philippe Cambier Regina Davison Dias José Paulo Peccinini Pinese Anne Jaulin-Soubelet 《Applied Geochemistry》2010
The contamination of soils by metals issuing from municipal solid waste (MSW) disposal in tropical environments has hardly been studied with regard to the particular problems associated with them, i.e., generally a high permeability of soils despite the abundance of clay, and the role of reactive Fe compounds. From a previous geotechnical and chemical survey, three latosol profiles differently affected by MSW leachates in the region of Londrina (Paraná, Brazil) were selected. The aims were to evaluate the extent of their contamination, to better understand the fate of potentially harmful metals in tropical soils and rank the determining factors. Samples between 0.5 and 7 m depth were analyzed for their physical, mineralogical and chemical properties, and their micro-morphology was described by optical and transmission electron microscopy. Two steps of a sequential extraction procedure helped to assess the mobility of elements and to better discriminate between metals originating from pedogenesis and issued from MSW. These combined approaches showed that exposed soil profiles have been impacted at various depths, down to 7 m, through increased metal content, especially enhanced mobility of Zn, Co, Mn, Cu and Fe, and through increased salinity and organic matter. The mobility of potentially harmful metals should decrease with pH, which significantly increased in some impacted horizons, but other factors can reverse this trend. 相似文献
30.
The morphology of the Alpine and adjacent landscapes is directly related to glacial erosion and associated sediment transport.
Here we report the effects of glacio-hydrologic erosion on bedrock topography in the Swiss Plateau. Specifically, we identify
the presence of subsurface valleys beneath the city of Bern and discuss their genesis. Stratigraphic investigations of more
than 4,000 borehole data within a 430 km2-large area reveal the presence of a network of >200 m-deep and 1,000 m-wide valleys. They are flat floored with steep sided
walls and are filled by Quaternary glacial deposits. The central valley beneath Bern is straight and oriented towards the
NNW, with valley flanks more than 20° steep. The valley bottom has an irregular undulating profile along the thalweg, with
differences between sills and hollows higher than 50–100 m over a reach of 4 km length. Approximately 500 m high bedrock highlands
flank the valley network. The highlands are dissected by up to 80 m-deep and 500 m-broad hanging valleys that currently drain
away from the axis of the main valley. We interpret the valleys beneath the city of Bern to be a tunnel valley network which
originated from subglacial erosion by melt water. The highland valleys served as proglacial meltwater paths and are hanging
with respect to the trunk system, indicating that these incipient highland systems as well as the main gorge beneath Bern
formed by glacial melt water under pressure. 相似文献