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171.
Paulo C. Abreu Marli Bergesch Luis A. Proen?a Carlos A. E. Garcia Clarisse Odebrecht 《Estuaries and Coasts》2010,33(2):554-569
In the shallow microtidal Patos Lagoon estuary, southern Brazil (32° 07′ S–52° 06′ W), chlorophyll a (Chl a) variability was studied at different time scales during the last 25 years (hourly–daily sampling in 1984/1985; weekly sampling
in 1986 and from 1988 to 1990; monthly sampling from 1993 to 2008). Phytoplankton biomass variation seems to be most influenced
by hydrology, which is primarily driven by meteorological factors like wind, rainfall, and evaporation. However, it was observed
that the hydrological driving forces play different roles at different time scales. For instance, short-term Chl a variability is mainly controlled by winds, while long-term changes are related to the freshwater input by rainfall. Significant
correlation was found between the total amount of rain in the year and the mean annual value of Chl a, though this relationship was linear until 1,500 mm of rain per year. After this threshold, mean annual Chl a values dropped significantly, probably due to a washout of the produced biomass from the estuary. Similarly, low rainfall
levels and drought years lead to small phytoplankton biomass due to scarcity of nutrient, mainly silicate, or a possible inhibitory
effect generated by high ammonium concentration. In this sense, large-scale Chl a variability would be related to the El Ni?o-Southern Oscillation climatic anomaly, which influences the rainfall levels in
Southern Brazil, though sampling periodicity has also great influence on this relationship. No Chl a or nutrient enrichment was observed in the estuarine region along the last years, indicating that this estuary is not subject
to an eutrophication process. In contrast, signals of an ongoing oligotrophication are observed, possibly a remote effect
of the eutrophication in the Northern area of the lagoon where the phytoplankton nutrients uptake may act as a biological
filter mechanism. 相似文献
172.
Roberto Wagner Lourenço Paulo M. Barbosa Landim André Henrique Rosa José Arnaldo F. Roveda Antonio César Germano Martins Leonardo Fernandes Fraceto 《Environmental Earth Sciences》2010,60(3):495-504
Spatial analysis and fuzzy classification techniques were used to estimate the spatial distributions of heavy metals in soil.
The work was applied to soils in a coastal region that is characterized by intense urban occupation and large numbers of different
industries. Concentrations of heavy metals were determined using geostatistical techniques and classes of risk were defined
using fuzzy classification. The resulting prediction mappings identify the locations of high concentrations of Pb, Zn, Ni,
and Cu in topsoils of the study area. The maps show that areas of high pollution of Ni and Cu are located at the northeast,
where there is a predominance of industrial and agricultural activities; Pb and Zn also occur in high concentrations in the
northeast, but the maps also show significant concentrations of Pb and Zn in other areas, mainly in the central and southeastern
parts, where there are urban leisure activities and trade centers. Maps were also prepared showing levels of pollution risk.
These maps show that (1) Cu presents a large pollution risk in the north–northwest, midwest, and southeast sectors, (2) Pb
represents a moderate risk in most areas, (3) Zn generally exhibits low risk, and (4) Ni represents either low risk or no
risk in the studied area. This study shows that combining geostatistics with fuzzy theory can provide results that offer insight
into risk assessment for environmental pollution. 相似文献
173.
Darren M. O'Brien Paulo J.V. Garcia Jonathan Ferreira Sylvie Cabrit Luc Binette 《Astrophysics and Space Science》2004,292(1-4):609-617
The effects of phenomenological heating functions on the flow thermodynamics of cold T-Tauri disk winds are examined. Turbulent dissipation (mechanical) heating and a warm disk corona are invoked to heat the wind. The temperature and ionization evolution are solved for along the flow. The results allow the construction of synthetic observations; emission maps, forbidden line ratios, line fluxes and line profiles; and successfully reproduce a number of observed trends. Mechanical heating produces line ratios and fluxes that fit very well with observations. Invoking a warm disk corona successfully reproduces forbidden line profile low velocity components. 相似文献
174.
Marcos Paulo Santos Pereira Marcos Heil Costa Ana Cláudia Mendes Malhado 《Theoretical and Applied Climatology》2013,111(3-4):569-576
Spatially precise forecasts of the impacts of climate change on the distribution of major vegetation types are essential for the implementation of effective conservation and land use policy. However, existing studies frequently omit major sources of climate variability that can significantly increase the uncertainty of projections. In this study we demonstrate how different predictions for sea surface temperature (SST) for the first half of the twenty-first century increase the uncertainty associated with forecasts of the future distribution of major ecosystems in South America. This is demonstrated through a numerical experiment using a coupled climate–vegetation model (CCM3-IBIS) for IPCC emission scenario A2 that incorporates the SST data from ten different models. The study reveals an increasing uncertainty in the ability to forecast future vegetation patterns, such that by 2050 the simulation is unable to robustly forecast the vegetation cover in an area equivalent to 28 % in South America (5?×?106 km2). The future of the central and northeastern regions of Brazil is especially uncertain, with outcomes, ranging from savanna, and open shrubland to grassland. Recognizing and managing such uncertainty should be a priority for decision makers. 相似文献
175.
Violante-Carvalho Nelson Skvortsov Alexei Babanin Alexander Pereira Henrique Pinho Uggo Esperança Paulo T. T. 《Ocean Dynamics》2021,71(3):379-389
Ocean Dynamics - Dispersion of a passive tracer by water waves is of significant importance for many scientific and technological problems including bio-diversity of marine life, ecological impact... 相似文献
176.
Michel Michaelovitch de Mahiques Samara Cazzoli y Goya Maria Carolina da Silva Nogueira de Matos Rodrigo Augusto Udenal de Oliveira Bianca Sung Mi Kim Paulo Alves de Lima Ferreira Rubens Cesar Lopes Figueira Marcia Caruso Bícego 《国际泥沙研究》2021,36(2):317-327
The current study aims to do a comparative analysis of the results obtained with two End-Member(EM)grain-size modeling techniques(AnalySize and BasEMMA)and the Environmental Sensitive Grain-Size(ESGS)modeling for sediment samples collected in the mudbelts of the southern Brazilian shelf.The methods were compared using grain-size data from the south Brazilian shelf,and the results are discussed here.It is the first time that the concept of ESGS,in its present form,is utilized outside China.The results show that despite its relative ease of use,the ESGS is not fully comparable to the EM analyses,and only two grain-size ESGS classes were recognized as analogous to EMs.The comparison of the AnalySize and BasEMMA procedures also revealed significant differences between the techniques.A comparative analysis between the two EM techniques revealed advantages in the BasEMMA,especially in the better correlation of the end-members with the original grain size distribution.The analysis of the geographical distribution of the EM abundances allowed point sources of sandy populations to be recognized as well as the contribution of the Rio de la Plata as a source of silty sediments to be inferred. 相似文献
177.
Ana?C.?L.?SáEmail author José?M.?C.?Pereira Martin?E.?Charlton Bernardo?Mota Paulo?M.?Barbosa A.?Stewart Fotheringham 《Journal of Geographical Systems》2011,13(3):227-248
This study analyses the relationship between fire incidence and some environmental factors, exploring the spatial non-stationarity
of the phenomenon in sub-Saharan Africa. Geographically weighted regression (GWR) was used to study the above relationship.
Environment covariates comprise land cover, anthropogenic and climatic variables. GWR was compared to ordinary least squares,
and the hypothesis that GWR represents no improvement over the global model was tested. Local regression coefficients were
mapped, interpreted and related with fire incidence. GWR revealed local patterns in parameter estimates and also reduced the
spatial autocorrelation of model residuals. All the covariates were non-stationary and in terms of goodness of fit, the model
replicates the data very well (R
2 = 87%). Vegetation has the most significant relationship with fire incidence, with climate variables being more important
than anthropogenic variables in explaining variability of the response. Some coefficient estimates exhibit locally different
signs, which would have gone undetected by a global approach. This study provides an improved understanding of spatial fire–environment
relationships and shows that GWR is a valuable complement to global spatial analysis methods. When studying fire regimes,
effects of spatial non-stationarity need to be incorporated in vegetation-fire modules to have better estimates of burned
areas and to improve continental estimates of biomass burning and atmospheric emissions derived from vegetation fires. 相似文献
178.
The behaviour of an embankment built on a Portuguese soft soil is analysed considering the material and geometric non-linearity associated with a coupled soil–water formulation. The numerical predictions are compared with the field data in terms of settlements, horizontal displacements and excess pore water pressures. The repercussions of including the large displacements formulation are also studied. It is found that the analysis considering large displacements results in a decrease in settlements and an increase in the rate of excess pore pressure dissipation, both of which are related to the reduction of the thickness of a deformable layer. 相似文献
179.
Eduardo M. Bretas José V. Lemos Paulo B. Lourenço 《Rock Mechanics and Rock Engineering》2013,46(2):327-339
A numerical model for the hydromechanical analysis of masonry dams based on the discrete element method is presented. The dam and the rock foundation are represented as block assemblies, and a coupled flow-stress analysis is performed in an integrated manner for the entire system. Complex block shapes may be obtained by assembling elementary blocks into macroblocks, allowing the application of the model to situations ranging from equivalent continuum to fully discontinuum analysis. A contact formulation was developed based on an accurate edge–edge approach, incorporating mechanical and hydraulic behavior. The main numerical aspects are described, with an emphasis in the flow analysis explicit algorithm. An application to an existing masonry dam is presented, analyzing its present condition, with excessive seepage, and the proposed rehabilitation intervention. An evaluation of sliding failure mechanisms was also performed, showing the expected improvement in the safety of the structure. 相似文献
180.
Numerical study on the effect of submerged depth on the horizontal plate wave energy converter 总被引:2,自引:0,他引:2
Flávio Medeiros SEIBT ;Eduardo Costa COUTO ;Elizaldo Domingues dos SANTOS ;Liércio André ISOLDI ;Luiz Alberto Oliveira ROCHA 《中国海洋工程》2014,28(5):687-700
The growing search for clean and renewable energy sources has given rise to the studies of exploring sea wave energy. This paper is concerned with the numerical evaluation of the main operational principle of a submerged plate employed for the conversion of wave energy into electrical one. The numerical model used to solve the conservation equations of mass, momentum and transport of volume fraction is based on the finite volume method (FVM). In order to tackle with the flow of mixture of air-water and its interaction with the device, the multiphase model volume of fluid (VOF) is employed. The purpose of this study is the evaluation of a numerical model for improvement of the knowledge about the submerged plate wave energy converter, as well as the investigation of the effect of the distance from the plate to the bottom of the sea (HP) on the performance of the converter. The simulations for several distances of the plate from the seabed show that the optimal efficiency is 64%, which is obtained for HP=0.53 m (88% of the depth). This efficiency is 17% larger than that found in the worst case (HP=0.46 m, 77% of the depth). 相似文献