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91.
Environmental influences on the demersal fish assemblages in the Sepetiba Bay, Brazil 总被引:1,自引:0,他引:1
Francisco Gerson Araújo Márcia Cristina Costa de Azevedo Márico de Araújo Silva André Luiz Machado Pessanha Iracema David Gomes Antônio Gomes da Cruz-Filho 《Estuaries and Coasts》2002,25(3):441-450
The structure of the demersal fish assemblage in Sepetiba Bay, southeast Brazil (22°54′–23°04′S, 43°34′–44°10′W) was described and related to environmental variables. A 3-yr long trawl survey (from July 1993 to June 1996) was conducted using a stratified random sampling strategy at 158 stations. One hundred and seven species of fishes in 80 genera and 44 families were identified. Gerreidae and Ariidae made up 30.5% and 28.6%, and 19.8% and 28.1% of the total number and weight, respectively. Sciaenidae, Engraulididae, Sparidae, and Carangidae were other prominent families. Three assemblages existed in the bay: one inhabited shallow, less saline and less transparent water in the inner zone (depth <5 m, transparency <2 m, salinity <30 psu, and slightly higher temperature); another in the outer zone with the opposite situation (depth >10 m, transparency >3 m, salinity >30 psu, and slightly lower temperature); and a third assemblage in the middle zone likely to prefer average values or show no clear preferences. Most species decreased in abundance over the 3-yr period of study. No seasonal change was detected in the assemblage structure, but many species were rare, indicating high spatial and temporal patchiness. Canonical correlation analyses were used to describe and compare the fish assemblages in the three different habitats. The outer zone had the greatest number of species recorded, lowest abundance, highest diversity and evenness, and was comprised mainly byCynossion leiarchus, Prionotus punctatus, Anchoa tricolor, Haemulon steindachneri, Diplectrum radiale, Etropus crossotus, andSphoeroides greeleyi; the inner zone had the lowest number of species recorded but the greatest number of species per sample, highest abundance, lowest diversity and evenness, being comprised mainly byDiapterus rhombeus, Genidens genidens, Cathrops spixii, Chloroschombrus chrysurus, Sciadeichthyes luniscutis, Cetengraulis edentulus, andArchorsargus rhomboidalis; while the third group had the lowest number of species per sample, being comprised by species widely distributed asGerres aprion, G. genidens, Gerres gula, andMicropogonias furnieri. Depth, followed by transparency and salinity, were the primary factors influencing assemblage distribution. 相似文献
92.
Eutrophication and hypoxia in four streams discharging in Guanabara Bay, RJ, Brazil, a case study 总被引:1,自引:0,他引:1
Four streams in the city of São Gonçalo, were sampled to evaluate their potential as sources of nutrients to Guanabara Bay aiming to contribute with the government program to decrease the levels of pollution in this area. Imbuaçu, Guaxindiba, Marimbondo and Brandoas streams were sampled in 2007, 2008 and 2009. The streams revealed to be hipereutrophic with severe limitation of primary production by nitrogen, as shown by the N/P molar ratio. Phosphate levels were abnormally high varying between 4.35 and 130.82 μM, whereas nitrate and nitrite ranged from 0.06 to 54.05 μM and from 0.28 to 19.23 μM, respectively. The streams also presented severe hypoxia and anoxia, with oxygen values varying from non-detected to 3.72 ml l−1. Heavy loads of particulate suspended material were recorded in the studied streams, ranging between 6.00 and 400.00 mg l−1. The streams were considered inexorable sources of nutrients, enhancing the severe eutrophication process in Guanabara Bay. 相似文献
93.
Ana L. Santos Isabel Henriques Newton C. M. Gomes Adelaide Almeida António Correia Angela Cunha 《Aquatic Sciences - Research Across Boundaries》2011,73(1):63-77
The effects of ultraviolet-B (0.4 W m−2) radiation on the abundance, diversity and heterotrophic metabolism of bacterioneuston and bacterioplankton communities from
Ria de Aveiro (Portugal) were assessed and compared to those of freshwater communities from Lake Vela (Portugal) in microcosm
experiments. Exposure to 9 h of artificial ultraviolet radiation (UVR) led to 24–33% reduction in bacterial abundance and
up to a 70% decrease in bacterial diversity. Maximum extracellular enzyme activity and monomer incorporation rates were reduced
by 16–90% and 80–100%, respectively. Recovery of bacterial activity during post-UV dark incubations ranged from 10 to 100%
for extracellular enzyme activity and 40% for monomer incorporation rates. In general, the heterotrophic activity of bacterioneuston
was more inhibited by UVR than that of bacterioplankton. However, DGGE profiles revealed greater UVR-induced reductions in
the diversity of bacterioplankton compared to bacterioneuston. The similarity between bacterioneuston and bacterioplankton
communities in samples collected at early morning was lower than at noon (pre-exposed communities) and increased upon experimental
irradiation, possibly indicating selection for UV-resistant bacteria. The observation that UV exposure resulted in enhanced
reduction of bacterioneuston activity, but a lower reduction in bacterial diversity accompanied by enhanced dark recovery
potential compared to bacterioplankton, indicates re-directioning of bacterioneuston metabolism towards stress defence/recovery
strategies rather than the sustained heterotrophic metabolism. Our results indicate that UVR can significantly decrease the
abundance, diversity and activity of bacteria inhabiting the surface and sub-surface layers of freshwater and estuarine systems
with potentially important impacts on the biogeochemical cycles in these environments. 相似文献
94.
Maurício Dambros Melati Fernando Mainardi Fan Gustavo Barbosa Athayde Pedro Antônio Roehe Reginato Walter Collischonn Camila de Vasconcelos Muller Athayde 《水文研究》2021,35(10):e14388
The anomalous entrance of water into groundwater systems can affect storage throughout long periods and normally relies on infrequent and irregular pulses of groundwater recharge defined by the term episodic recharge. Recently there was a groundwater recharge of large magnitude with unknown circumstances in the Caiuá aquifer. This unique event was explored in detail here and allowed to better understand the occurrence of such events in humid subtropical climates in South America. For this study, groundwater monitoring daily data from the Integrated Groundwater Monitoring Network was used combined with a specific yield obtained from geophysical wireline logging to obtain groundwater recharge rates. To improve the investigation, we also used a baseflow separation method to obtain the groundwater contribution into local rivers. The groundwater storage variations were also assessed by remote sensing with the GRACE data. Results showed the importance of high soil moisture storage on the occurrence of large episodic recharge events. We estimated that the groundwater recharger volumes derived from 1 year that included the unique episodic recharge observed (total of 866 mm for April 2015–March 2016) were comparable with the sum of 7 years of groundwater recharge (total of 867 mm). Atypical rainfall in winter periods were responsible for the increase in soil moisture that explained that unique event. GRACE-based GWS showed concordance detecting the occurrence of the unique episodic recharge. However, the variation in terms of volumes obtained by GRACE does not represent the behaviour observed in the aquifer by the WTF method. The results also indicated that changes in aquifer storage caused by episodic recharge events directly affect low flows in rivers over long periods. The main knowledge gap addressed here relates to exploring a unique episodic recharge event quite rare to observe with its long-term impacts on hydroclimatic variability over a humid subtropical portion of the Caiuá aquifer. 相似文献
95.
The cyclic behaviour of reinforced concrete columns has been the subject of many experimental studies in recent years. However, most of these studies have focused on the unidirectional loading of columns with square cross‐sections under constant axial loading conditions. In the present study, four types of full‐scale quadrangular building columns were tested under different types of loading, including uniaxial and biaxial loading conditions. The first two specimens of each column type were independently cyclically tested in the strong and weak directions. Bidirectional tests using different loading paths were performed on the other column specimens. All columns were tested under constant axial loading conditions. In this paper, the experimental results are presented, and the global behaviour of tested columns is discussed, particularly focusing on the stiffness and strength degradation because of the increasing cyclic demand. Finally, the deformation‐based performance limits proposed in Part 3 of Eurocode 8 were calculated and compared with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
96.
Hydro‐morphodynamic evolution in a 90° movable bed discordant confluence with low discharge ratio 下载免费PDF全文
Sebastián Guillén‐Ludeña Mário J. Franca António H. Cardoso Anton J. Schleiss 《地球表面变化过程与地形》2015,40(14):1927-1938
Confluences with low discharge and momentum ratios, where narrow steep tributaries with high sediment load join a wide low‐gradient main channel that provides the main discharge, are often observed in high mountain regions such as in the upper‐Rhone river catchment in Switzerland. Few existing studies have examined the hydro‐morphodynamics of this type of river confluence while considering sediment discharge in both confluent channels. This paper presents the evolution of the bed morphology and hydrodynamics as observed in an experimental facility with a movable bed. For that purpose, one experiment was carried out in a laboratory confluence with low discharge and momentum ratios, where constant sediment rates were supplied to both flumes. During the experiment, bed topography and water surface elevations were systematically recorded. When the bed topography reached a steady state (so‐called equilibrium) and the outgoing sediment rate approximated the incoming rate, flow velocity was measured at 12 different points distributed throughout the confluence, and the grain size distribution of the bed surface was analyzed. Typical morphodynamic features of discordant confluences such as a bank‐attached bar and a flow deflection zone are identified in this study. Nevertheless, the presence of a marked scour hole in the discordant confluence and distinct flow regimes for the tributary and main channel, differ from results obtained in previous studies. Strong acceleration of the flow along the outer bank of the main channel is responsible for the scour hole. This erosion is facilitated by the sediment discharge into the confluence from the main channel which inhibits bed armoring in this region. The supercritical flow regime observed in the tributary is the hydrodynamic response to the imposed sediment rate in the tributary. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
97.
António Viana da Fonseca Rodrigo Caberlon Cruz Nilo Cesar Consoli 《Geotechnical and Geological Engineering》2009,27(6):681-686
Soil stabilization with cement is a good solution for the construction of subgrades for roadway and railway lines, especially
under the platforms and mostly in transition zones between embankments and rigid structures, where the mechanical properties
of supporting soils are very influential. These solutions are especially attractive in line works where other ground improvement
techniques are extensive and, therefore, very expensive. On the other hand, the economic and environmental costs of such works
should be optimized with good balances between excavation and embankment volumes. For this purpose, the improvement of locally
available soils can bring great advantages, avoiding a great amount in borrowing appropriate material, as well as the need
of disposing huge volumes in deposits. This paper focus on the characteristics of two soils, Osorio sand and Botucatu residual
sandstone, which can be converted to well acceptable materials for this purpose, if stabilized with cement. The study of soil
stabilization with cement relies on the quantification of the influence of percentage of cement and porosity adopted in the
admixing process for different state and stress conditions. This influence will be evaluated from the analysis of unconfined
compression strength (UCS or q
u
) test results. This experimental framework will enable a good definition of mechanical parameters used in design of foundations
and subgrades of railways platforms and for their execution quality control. 相似文献
98.
Hugo Rodrigues António Arêde Humberto Varum Aníbal Costa 《Bulletin of Earthquake Engineering》2013,11(5):1517-1540
An analysis of the damage observed in 24 reinforced concrete (RC) columns tested under uniaxial and biaxial horizontal loading is presented. The test results show that for biaxial loading conditions specific damage occurs for lower drift demands when compared with the corresponding uniaxial demand (a reduction of 50–75 % was found). The damage distribution observed in each column is also analysed. No significant differences are found in the plastic hinge length for uniaxial and biaxial loading. The drift demands associated with each damage state are compared with reference values proposed in international guidelines. Finally, and based on the philosophy of the Park and Ang uniaxial damage index, two new expressions are proposed for the evaluation of damage in RC elements under biaxial loading. The results of the application of these expressions to the experimental results are discussed. 相似文献
99.
Alessandra F. S. Ferreira Antônio F. B. A. Prado Othon C. Winter Denilson P. S. Santos 《Astrophysics and Space Science》2018,363(7):145
Analytical equations describing the velocity and energy variation of a spacecraft in a Powered Swing-By maneuver in an elliptic system are presented. The spacecraft motion is limited to the orbital plane of the primaries. In addition to gravity, the spacecraft suffers the effect of an impulsive maneuver applied when it passes by the periapsis of its orbit around the secondary body of the system. This impulsive maneuver is defined by its magnitude \(\delta V\) and the angle that defines the direction of the impulse with respect to the velocity of the spacecraft (\(\alpha\)). The maneuver occurs in a system of main bodies that are in elliptical orbits, where the velocity of the secondary body varies according to its position in the orbit following the rules of an elliptical orbit. The equations are dependent on this velocity. The study is done using the “patched-conics approximation”, which is a method of simplifying the calculations of the trajectory of a spacecraft traveling around more than one celestial body. Solutions for the velocity and energy variations as a function of the parameters that define the maneuver are presented. An analysis of the efficiency of the powered Swing-By maneuver is also made, comparing it with the pure gravity Swing-by maneuver with the addition of an impulse applied outside the sphere of influence of the secondary body. After a general study, the techniques developed here are applied to the systems Sun-Mercury and Sun-Mars, which are real and important systems with large eccentricity. This problem is highly nonlinear and the dynamics very complex, but very reach in applications. 相似文献
100.
Luz Filipa Mateus António Rosa Carlos Figueiras Jorge 《Natural Resources Research》2020,29(6):3613-3652
Natural Resources Research - Massive sulfide deposits of the Iberian Pyrite Belt (IPB) document the progression of ore-forming processes in the SW Iberian Variscides, throughout uppermost Devonian... 相似文献