排序方式： 共有21条查询结果，搜索用时 140 毫秒
11.
12.
Luiz Carlos Cotovicz Junior Eunice da Costa Machado Nilva Brandini Rafaela Cristine Zem Bastiaan Adriaan Knoppers 《Environmental Earth Sciences》2014,72(2):373-386
This study addresses the distribution of total phosphorus (TP) and its inorganic (IP) and organic (OP) fractions, grain-size and organic matter of surface and recent sediments, coupled to the behavior of total and dissolved inorganic phosphorus (TP and DIP) of the water column, of the semi-pristine Guaratuba Bay estuary, SE Brazil. Surface sediment samples were taken at 43 sites spread along the estuarine gradient and recent sediments from 3 short (35 cm long) cores from the upper, central and lower portions of the estuary, respectively. Highest TP and IP concentrations of surface sediments were detected within the upper sector and the transition zone between the upper and central sectors, all characterized by fine sediments, low salinities and water depths. In contrast, the lower sector and its narrow and deep tidal channel, subject to more intense tidal forcing, exhibited a higher fraction of sandy sediments with lower TP, IP and OP contents. In spite of the spatial variability in sediment grain size, IP corresponded to the major fraction of TP in all estuarine sectors and both TP and IP correlated significantly with the fine sedimentary (silt + clay) grain-size fraction. The fine surface sediments acted as a trap for IP at the fresh water–low salinity interface, which also corresponded to the region of a DIP sink in surface waters. In general, the short sediment cores showed that TP and IP contents increased from 15 cm depths to the top layer. Published sedimentation rates from additional cores taken at the sites of the short cores of this study, implied that depositional alterations of TP and IP increased during the early 1970s, which corresponded to the onset of anthropogenic disturbances from crop plantations in the lowland plains of the river end-member and urbanization at the estuary’s mouth and along the adjacent coast. 相似文献
13.
A multidisciplinary approach was used to analyse the role of pioneer trees (Populus nigra) on bar formation in the modern fluvial system of the River Loire (France). Data were collected on seven plots located on a secondary channel, chosen for their vegetation cover and their sedimentary context. Physical features of vegetation, topographical evolution, sediment grain size and flow velocity were investigated during and after floods between 2001 and 2003. Woody vegetation responds morphologically to fast‐flowing waters and sediment deposition. These adaptations influence the role played by trees on local sedimentary processes. Some morphological types of trees exert a strong influence during flood events by deflecting, reducing or increasing the flow energy. As a consequence, the evolution of bedforms, distribution of sediment grain size and slopes are controlled by the flood type, the morphological context (i.e. high‐ or low‐energy zones), the morphology of the vegetated bar and the characteristics of vegetation. Conceptual models are proposed to account for local processes and evolution of tree groves. The first model, which describes the behaviour of groves during a single flood, underlines the sediment deposition downstream of the trees and the trapping of bedload sediments. During the falling stage of the flood, the reorientation of current streams, constrained by both local bed topography and woody vegetation, induces transverse sediment fluxes. For these water levels, the control exerted by trees on small‐scale sedimentary processes becomes significant. The second model shows the evolution of vegetation bands over several flood events. In particular, it describes the influence of vegetation on the fixing and reworking of bedload sediments during the falling limb of the hydrograph. The coalescence of vegetation‐induced bedforms and the resulting morphological changes increase the deflection power of the vegetated bar, inducing the deposition of finer sediments. 相似文献
14.
The microped size distribution of erodible soils is one of the main factors controlling the emissions of mineral aerosol. To date, the microped size distributions of desert soils in natural field conditions are not well known and thus the existing dust source models cannot be applied to natural sites. Based on dry sieving and elemental analysis of 26 soil samples collected in arid and semiarid regions, it is shown that the microped size distributions of these desert soil samples involve a combination of four major mass size populations. These four size populations correspond to salty soils, fine quartz sand, coarse dune sand and aluminosilicate silt. We show that the microped size distributions of the various desert soils, according to their mineralogical characteristics, can be calculated by a mixture involving two or three of these four populations. The main field of application for this scheme is the characterization of the erodible soil size distributions for modelling the atmospheric dust cycle. 相似文献
15.
16.
Dbora Ferreira Barbosa Thelma Lúcia Pereira Dias Srgio de Faria Lopes Rafaela Cristina de Souza Duarte Fernanda Maria Duarte do Amaral 《Marine Ecology》2019,40(5)
This study investigated the community structure and functional traits of the mollusk fauna associated with macroalgae with different thallus morphologies in a reef environment in Northeastern Brazil. A total of 15 individuals of each species of macroalgae adhered to natural substrate and 15 individuals of Padina gymnospora detached from the substrate were collected. The structural complexity of algal habitats was measured and the associated malacofauna screened and identified. All three macroalgae differed significantly in the complexity of their habitat, with Sargassum polyceratium being the most complex. A total of 823 specimens of mollusks belonging to 22 species and 11 families were recorded, of which Columbellidae was the most represented with six species. The functional trait “size” revealed that micromollusks smaller than 10 millimeters were predominant in the community; however, individuals of larger sizes (up to 24.54 millimeters) belonging to young stages of other species were also present. Eight functional trophic groups were identified, of which “carnivorous” stood out with seven species. Six functional groups of microhabitats were identified, with intra‐specific variation in habitats, while habitat expansion was documented for species not yet recorded in association with macroalgae. The structure of the molluskan community differed among the three algae species with the greatest richness, abundance, and diversity of mollusks and functional traits occurring with S. polyceratium. Community structure differed between algae adhered to natural substrate and detached algae, with the latter having lower mollusk richness and diversity, but with greater abundance of some species that remained on algal fronds after release from the reef environment. This study reinforces the importance of algal habitat for marine invertebrate fauna, especially for micromollusks that spend their entire life cycle, or part of it, in association with macroalgae. 相似文献
17.
JACQUES CALLEDE EURIDES DE OLIVEIRA VALDEMAR S. GUIMARÃES MAURO S. RODRIGUES 《水文科学杂志》2013,58(6):903-913
Abstract The difficulties of exploiting the huge Brazilian hydrometeorological network led hydrologists of the Departamento Nacional de Águas e Energie Elétrica (DNAEE—Brazilian Department of Water and Electric Power) to use real time satellite telecommunications to improve network management. Data-gathering satellites, which are perfectly adapted to this network, were first used in 1975 and have interested DNAEE since 1980. Collaboration with ORSTOM permitted an initial evaluation of the technique in 1982. In 1984 DNAEE, together with ORSTOM, was able to set up a 20-station network in the Amazon. The results have been so encouraging that a scheme for 200 stations equipped with telecommunications facilities which use the Brazilian Satélite de Colecta de Dados number 1 (SCD1) satellite is in the final stages. This network will cover the entire country. 相似文献
18.
Barry W. Brook Kingsley Edney Rafaela Hillerbrand Rasmus Karlsson 《Climate Policy》2016,16(6):803-813
We propose that an international ‘Low-Emissions Technology Commitment’ should be incorporated into the United Nations Framework Convention on Climate Change (UNFCCC) negotiation process in order to promote innovation that will enable deep decarbonization. The goal is to accelerate research, development, and demonstration of safe, scalable, and affordable low-emissions energy technologies. Such a commitment should be based on three elements. First, it should operate within existing UNFCCC negotiations so as to encourage developed states to offer directed funding for energy research as part of their national contributions. Second, pledges should be binding, verifiable, and coordinated within an international energy-research plan. Third, expert scientific networks and participating governments should collaborate to design a coordinated global research and technology-demonstration strategy and oversee national research efforts. To this end an Intergovernmental Panel on Low-Emissions Technology Research might be established. This proposal offers some insurance against the risk that the political impasse in international negotiations cannot be overcome. The higher costs associated with low-emissions alternatives to fossil fuels currently creates significant economic and political resistance to their widespread adoption. To breach this impasse, a mechanism supporting accelerated energy research is needed that seeks to reduce future abatement costs, share experience and ‘learning-by-doing’ in first-of-a-kind demonstrations, and thus facilitate future widespread deployments. These actions will also assist in addressing inequalities in energy access.Policy relevanceOver the past decade, global fossil-fuel use and associated carbon emissions have risen steadily, despite the majority of nations agreeing, in principle, to work to limit global warming to less than 2?°C above pre-industrial conditions (IPCC, 2014). Accelerated research, development, and demonstration of low-emissions technologies will be required for successful and economically efficient decarbonization of the global economy, but how can the current deadlock be broken? The UNFCCC does not contain adequate mechanisms to promote increased investment in research, so climate-governance institutions are not capturing the gains that could be achieved through a globally coordinated approach. Here, we outline reform proposals that would enhance both the economic effectiveness of global abatement efforts and the political feasibility of accelerated innovation. 相似文献
19.
The pterodactyloid genus Germanodactylus is relatively poorly known. Two species have been described, although it has been recently suggested (Wang et al., 2008) that they might pertain to different genera. 相似文献
20.
Eocene igneous rocks from the Abrolhos Islands and surroundingsedimentary platform, offshore Brazil, 18?S, are largely Ti-richbasalt and diabase (4–6 wt.% TiO2), and cumulate rockssuch as wehrlite. Despite high Ti, incompatible-element abundancesare relatively low (e.g., K2O {small tilde} 1 wt.%; P2O5 0.5%; Zr 225 ppm; Rb 23 ppm; Ba 275 ppm); LREE enrichment yieldsLa/YbN {small tilde}8. Compared to other mafic rocks of theSouth Atlantic region, such as Mesozoic high-Ti dikes ({smalltilde}5 wt.% TiO2) and basalts (3–4 wt.% TiO2) of theSerra Geral (Paran?, southern Brazil) province, and high-Tibasalts ({small tilde}4 wt% TiO2) of some South Atlantic features(Walvis, southwest Indian ridge), Abrolhos basalts differ bylower incompatible-element concentrations and/or by isotopiccompositions that emphasize depleted characteristics (Sr–12;Nd 3) relative to bulk earth. Abrolhos isotopic compositionsdo, however, match those of some S. Atlantic islands (e.g.,Pb like those of nearby Trindade), and conform generally toDupal anomaly contours. Abrolhos high-Ti basalts can be modeled as liquids from about90% crystallization of parent picritic liquid emplaced nearthe base of the Brazilian crustal margin; no mantle geochemicalanomaly or special metasomatism are needed to account for theTi contents. Isotopic and trace-clement compositions (e.g.,Zr, Nb, Y) of the Abrolhos province suggest parentage in a mantlerepresenting a plume of bulk earth or ‘enriched’composition that interacted with overlying depleted mantle. 相似文献