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排序方式: 共有205条查询结果,搜索用时 31 毫秒
41.
Chemistry of the Ferraria thermal water, S. Miguel Island, Azores: mixing and precipitation processes 总被引:1,自引:1,他引:0
Maria do Rosário Carvalho António Mateus Jo?o C. Nunes José M. Carvalho 《Environmental Earth Sciences》2011,64(2):539-547
The Ferraria thermal water emerges at the sea level in the Ferraria lava delta (western edge of S. Miguel Island, Azores)
with temperature of ca. 60°C and pH varying between 5.4 and 6.2. It is of sodium chloride type, resulting from ca. 50% seawater
mixing with an acid brackish, at ≈100°C, denoting the presence of significant CO2(g) and the progress of water–rock interactions in open system conditions. The thermal Na–Cl water is strongly enriched with
Sr and Mn and, comparatively, has low concentrations in Al, Fe and As. These elements are removed from the solution as critical
conditions for the formation of several neo-formed mineral phases are gradually attained. Thermodynamic equilibrium calculations
are consistent with this interpretation, showing that the thermal fluid can precipitate Fe3+-(hydr-)oxides, kaolinite and non-crystalline silica. Wells logging show fracture planes and pores fully/partly filled up
with polyphase botryoidal aggregates mostly composed of goethite + ferrihydrite and displaying variable adsorbed contents
of Si, P and As. These neo-formed phases result from the pristine fluid oxidation due to seawater mixing; its precipitation
is easily affected by pH and redox variations of the brackish, due to volcanic gases pressure alterations, and fluid pressure
or flow-velocity oscillation in the fractured aquifer. 相似文献
42.
Geochemistry of granites and metasediments of the urban area of Vila Real (northern Portugal) and correlative radon risk 总被引:2,自引:2,他引:0
M. E. P. Gomes L. J. P. F. Neves F. Coelho A. Carvalho M. Sousa A. J. S. C. Pereira 《Environmental Earth Sciences》2011,64(2):497-502
Radon concentration was evaluated in dwellings of the urban area of Vila Real (Northern Portugal). The area is mainly composed
of Hercynian granites and Cambrian metasediments, and CR-39 passive detectors (n = 112) were used for the purpose. The results obtained in winter conditions suggest that the most productive geological unit
is the Hercynian granite G1 (geometric mean of 364 Bq/m3), while Cambrian metasediments of the Douro Group show the lowest average indoor radon concentration (236 Bq/m3). The geological, geochemical and radiological data obtained suggest that the most effective control on the radon concentrations
of the area is related with the uranium content of the rocks; indeed, the highest contents were observed in granite G1 (21 ppm)
and the lowest in the metasediments (3 ppm). This is also confirmed by the results obtained for groundwater, where granites
present the highest concentrations of dissolved radon (up to 938 Bq/l), uranium (5–18 ppb) and gross α activities (0.47–0.92 Bq/l). No important radiometric anomalies were found in relation with geological structures such as
faults, veins and contacts, but a moderate increase of the uranium content can occur locally in such structures. Petrographic
observations and SEM studies show that uranium is mainly contained within the rock in heavy accessory minerals (apatite, zircon,
monazite, xenotime), which reduces radon emanation. Notwithstanding, due to the high U contents granites show a significant
potential to induce indoor radon concentrations in dwellings in excess of the recommended value of 400 Bq/m3. Overall, we can conclude that the region of Vila Real presents a moderate to high radon risk in dwellings and groundwater. 相似文献
43.
Sílvia Santos Joana F.M.F. Cardoso Célia Carvalho Pieternella C. Luttikhuizen Henk W. van der Veer 《Estuarine, Coastal and Shelf Science》2011
Monthly investment in soma and gonads in the bivalve Scrobicularia plana is described for three populations along its distributional range: Minho estuary, Portugal; Westerschelde estuary, The Netherlands and Buvika estuary, Norway. Seasonal cycles in body mass (BMI), somatic mass (SMI) and gonadal mass (GMI) indices were observed for all populations. In Portugal, BMI and SMI peaked in mid-autumn, while in The Netherlands both indices were at their highest in mid-spring. Norway showed a different pattern with two distinct peaks: one in mid-autumn and a second peak in spring. GMI reached maximum values in July in Portugal and Netherlands and in June in Norway. Overall, mean BMI and SMI were lower in Portugal while mean GMI was lower in Norway. The spawning period lasted the whole summer in Portugal, but was shorter (only two months) in The Netherlands and Norway. The reproductive investment in The Netherlands was significantly higher than in Portugal and Norway, with the lowest values being observed in Norway. Differences in annual cycles between populations were attributed to environmental factors, namely temperature and food availability. Temperature seems important in shaping the reproductive pattern with more northern populations showing shorter reproductive periods starting later in the year, and a lower reproductive output. In addition, winter water temperatures can explain the lower mean body and somatic mass values observed in Portugal. Food availability influenced the physiological performance of the species with peaks in somatic mass coinciding with phytoplankton blooms. This relation between physiological performance and environmental factors influences S. plana distribution, densities and even survival, with natural consequences on its commercial importance. 相似文献
44.
Giovanni Dolif Andre Engelbrecht Alessandro Jatobá Antônio José Dias da Silva José Orlando Gomes Marcos R. S. Borges Carlos A. Nobre Paulo Victor R. de Carvalho 《Natural Hazards》2013,65(3):1831-1847
Natural disasters, particularly those triggered by heavy rainfall, may cause major damage and death. However, if an accurate early warning is issued, the damage can be mitigated. In Latin America and Brazil, characteristics of socioeconomic development often lead to a disorderly growth of cities and, consequently, occupation and irregular construction in risk areas. Therefore, forecasts of heavy rainfall, as well as preventative and mitigatory actions based on meteorological data/alerts, are essential to saving lives and minimizing material loss. An event that would have benefited from such actions is that which occurred in the mountainous region of Rio de Janeiro in January 2011, when over 800 people lost their lives. This work describes the first research initiative on resilience engineering domain in systems to forecast heavy rains in Rio de Janeiro. The results indicate important sources of brittleness in the system that supports the work of meteorologists, mainly related to the technical and organizational framework, and suggests that the main source of resilience in dealing with critical situations is the tacit knowledge of experts. 相似文献
45.
Francisco C. F. Barros Francisco W. Sousa Rivelino M. Cavalcante Tecia V. Carvalho Francisco S. Dias Danilo C. Queiroz Luiz C. G. Vasconcellos Ronaldo F. Nascimento 《洁净——土壤、空气、水》2008,36(3):292-298
In this work, 8‐hydroxyquinoline is used as the active sites in cross‐linked chitosan beads with epichlorohydrin (CT‐8HQ). The CT‐8HQ material was shaped in bead form and used for heavy metal removal from aqueous solution. The study was carried out at pH 5.0 with both batch and column methods and the maximum adsorption capacity of metal ions by the CT‐8HQ was attained in 4 h in the batch experiment. The adsorption capacity order was: Cu2+ > Ni2+ > Zn2+ for both mono‐ and multi‐component systems with batch conditions. From breakthrough curves with column conditions, the adsorption capacity followed the order Cu2+ > Zn2+ > Ni2+ for both mono‐ and multi‐component systems. The CT‐8HQ beads maintained good metal adsorption capacity for all five cycles with absorbent restoration achieved with the use of 1.0 mol L–1 HCl solution, with 90% regeneration. 相似文献
46.
47.
Ilson Guimaraes Carvalho Suely S.P. Mestrinho Vanice M.S. Fontes Om P. Goel Francisco de A. Souza 《Journal of Geochemical Exploration》1991,40(1-3)
Lateritic covers developed during the Pleistocene in two distinct areas (Gentio do Ouro District and Sento Sé) of the State of Bahia, Brazil, have been investigated geochemically. Samples of the bedrock (gabbros, from the Gentio do Ouro District, and silicate facies iron formation and associated iron-rich banded carbonates, from the Sento Sé Area) and the lateritic products (latosols, cuirasses and pisolites) were analyzed for major and selected trace elements (Co, Cu, Cr, Ni, V, Pb, Ba, Au and ree). The purpose of the research was to study the geochemical evolution of the laterites and the relationship of weathering processes to secondary gold mineralization.Four types of element mobilities are recognized, defined by progressive depletion (type A) or enrichment (type C) in the sequence latosol-cuirasse-pisolite or by extreme enrichment (type B) or depletion (type D) in the cuirasse. Cr and V have similar behavior (type C), whatever the type of parent rock: however, when the original rocks are gabbros, Co, Cu and Ni demonstrate behavior A, B and A, respectively. Also Ti has the same type of mobility (type A), whatever the type of parent rock.The concentrations of some residual elements, e.g., Ti, V, Mn, Fe and Au, are inherited from the original rocks, that is, they exhibit higher values in the lateritic materials on parent rocks in which their contents are high.The enrichment of ree in the lateritic materials on iron-rich carbonates is attributed to relatively basic and reducing conditions at depth. This environment allowed the ions of these elements (Ce, Sm, Eu and Yb in the reduced ionic form) to stay in solution along with Fe2+. At shallow depht, under oxidizing conditions, the iron oxyhydroxides adsorbed the ree ions. This adsorption was more effective for La, Ce and Yb ions.The ree contents in the lateritic products from gabbros indicate a depletion of hree plus Eu, Nd and Sm are also depleted in cuirasses and Ce is depleted in pisolites. The loss of these ree and the slight concentration of lree in the red latosol of the Gentio do Ouro District are attributed to partial leaching of ree by a relatively acidic solution. The adsorption of ree by iron oxyhydroxides was less intense here than in the weathering of the iron-rich carbonates at Sento Sé Area. It was also more effective for La and Ce (ions). This type of weathering solution may be generated from oxidation of the accessory pyrite present in the gabbros of the Gentio do Ouro District. It may dissolve primary gold which then precipitates on encountering basic conditions at depth. 相似文献
48.
Distribution and feeding ecology of three juvenile mojarras in a hypersaline tropical estuary in Northeastern Brazil
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Although mojarra species usually demonstrate a wide distribution in tropical and subtropical estuaries, relatively little is known about the process influencing the spatial resource partitioning to nearshore habitats. Therefore, the aim of this study was check the existence of habitat and food partitioning among confamiliar species in a hypersaline estuary. The dietary compositions of three co‐occurring species of mojarras were determined, using samples collected with a beach seine from an inverse tropical estuary in Northeastern Brazil, during the rainy and the dry seasons of 2012. Eucinostomus argenteus and Ulaema lefroyi were abundant throughout the year, while Eugerres brasilianus was most abundant during the rainy season. Although these mojarras were found together in all areas of the estuary, there was evidence of habitat partitioning: E. argenteus and E. brasilianus were dominant in areas with submerged vegetation, while U. lefroyi was most abundant in areas with little habitat complexity and minimal shelter. All mojarras consumed, to different degrees, zooplankton, Bivalvia and Polychaeta. However, E. brasilanus also consumed a considerable amount of algae. Although the niches of the mojarra species appeared to significantly overlap, some resource partitioning patterns were apparent. While E. brasilanus was clearly different along the trophic niche, segregation of the other species was more important with respect to the spatial dimension. The different feeding strategies appear to minimize inter‐specific overlap and allow the co‐occurrence of these species in this hypersaline tropical estuary. 相似文献
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