Post-LGM sedimentation on the outer shelf-upper slope of the northernmost part of the São Paulo Bight, southeastern Brazil     

Michel Michaelovitch de Mahiques  Ilson Carlos Almeida da SilveiraSilvia Helena de Mello e Sousa  Marcelo Rodrigues 《Marine Geology》2002,181(4):387-400

Sedimentary and isotope data as well as ¹⁴C AMS dating on 15 box cores were used to identify the main post-Last Glacial Maximum (LGM) processes in the outer shelf and upper slope of the northernmost part of the São Paulo Bight, southeastern Brazil. Results show slight but significant variations in calcium carbonate, total sulphur and nitrogen contents as well as carbon and oxygen isotope ratios. Sedimentation rates, varying from 5 to 184 mm kyr⁻¹ are controlled by the shelf and upper slope morphology, the Brazil Current meander dynamics, and the Coastal Water offshore motion.  相似文献   

The consequences of different scenarios in the management of the gillnet and purse-seine fisheries targeting Pomatomus saltatrix and Cynoscion guatucupa in southern Brazil: a bio-economic approach     

Lucena  Flavia; O'Brien  Carl M. 《ICES Journal of Marine Science》2005,62(2):201-213

  相似文献   

Another diet of worms: the applicability of polychaete feeding guilds as a useful conceptual framework and biological variable   总被引：1，自引：0，他引：1  

Paulo Roberto Pagliosa 《Marine Ecology》2005,26(3-4):246-254

  相似文献   

Tracing terrigenous dissolved organic matter and its photochemical decay in the ocean by using liquid chromatography/mass spectrometry     

Thorsten Dittmar  Kenia Whitehead  Elizabeth C. Minor  Boris P. Koch 《Marine Chemistry》2007

Reversed-phase liquid chromatography/mass spectrometry (LC/MS) is introduced as a new molecular fingerprinting technique for tracing terrigenous dissolved organic matter (DOM) and its photochemical decay in the ocean. DOM along a transect from the mangrove-fringed coast in Northern Brazil to the shelf edge was compared with mangrove-derived porewater DOM exposed to natural sunlight for 2–10 days in a photodegradation experiment. DOM was isolated from all samples via solid-phase extraction (C18) for LC/MS analysis. DOM in the estuary and ocean showed a bimodal mass distribution with two distinct maxima in the lower m/z range from 400 to 1000 Da (intensity-weighted average of 895 Da). Terrigenous porewater DOM from the mangroves was characterized by a broad molecular mass distribution over the detected range from 150 to 2000 Da (intensity-weighted average of 1130 Da). Polar compounds, i.e., those that eluted early in the reversed-phase chromatography, absorbed more UV light and had on average smaller molecular masses than the more apolar compounds.  相似文献   

Zooplankton responses to sandbar opening in a tropical eutrophic coastal lagoon   总被引：3，自引：0，他引：3  

Jayme M. Santangelo  Adriana de M. Rocha  Reinaldo L. Bozelli  Luciana S. Carneiro  Francisco de A. Esteves   《Estuarine, Coastal and Shelf Science》2007,71(3-4):657-668

The effects of a disturbance by sandbar opening on the zooplankton community were evaluated through a long-term study in an eutrophic and oligohaline system, Imboassica Lagoon, Rio de Janeiro, Brazil. Zooplankton samples and limnological data were collected monthly from March 2000 to February 2003. Before the sandbar was opened in February 2001, the lagoon showed eutrophic conditions, with high mean nutrient concentrations and low salinity (total nitrogen – TN = 190.28 μM, chlorophyll a content – Chl. a = 104.60 μg/L and salinity = 0.87′). During this period, the zooplankton species present, such as the rotifers Brachionus calyciflorus and Brachionus havanaensis, were typical of freshwater to oligohaline and eutrophic environments. After the sandbar opening, the lagoon changed to a lower trophic status and increased salinity (TN = 55.11 μM, Chl. a = 27.56 μg/L and salinity = 19.64′). As a result, the zooplankton community came to consist largely of the rotifer Brachionus plicatilis, marine copepods and meroplanktonic larvae, mainly Gastropoda. Salinity was the main force structuring the zooplankton community after the sandbar opening. Two years after this episode, the prior zooplankton community had not reestablished itself, indicating a low resilience to this disturbance. The conditions developed prior to a sandbar opening can be crucial to the community responses in the face of this disturbance and for the capacity of the original zooplankton community to re-establish itself.  相似文献   

Impacts anthropiques sur les termes du bilan hydrologique d’un aquifère alluvial dans le Nordeste semi-aride,Brésil / Human impacts on components of hydrological balance in an alluvial aquifer in the semiarid Northeast,Brazil     

《水文科学杂志》2013,58(1)

Abstract

Abstract The exploitation of an alluvial aquifer (2 × 10⁶ m³) has been developed since 1998 in the Valley of Forquilha (Quixeramobim, State of Ceará). For this purpose, 165 wells were drilled along the 23 km of the valley that supplies 500 families and their farms. Monthly monitoring of piezometric and electrical conductivity (2000–2003) show seasonal variations in the water volume (35%) and in the mean value of the conductivity (800–1200 µS cm^-1). A conceptual hydrogeological model was developed. Analysis of the data and simulations highlight that the recharge of the aquifer is mainly due to infiltration from the river in the rainy season, which is of the order of 1% of the rain over the catchment area (195 km²). The abstractions increase the recharge between 30 and 60%. The model makes it possible to propose scenarios of sustainable exploitation of the water resource in the catchment. For the period between 1970 and 1988, other simulations show that it would have been possible to maintain irrigated cultures on 75 ha for 80% of the time. During the remaining 20%, the water level is too low, and farmers would have to reduce the irrigated area.  相似文献   

Analysis of channel transmission losses in a dryland river reach in north‐eastern Brazil using streamflow series,groundwater level series and multi‐temporal satellite data     

Alexandre Cunha Costa  Saskia Foerster  José Carlos de Araújo  Axel Bronstert 《水文研究》2013,27(7):1046-1060

Scarcity of hydrological data, especially streamflow discharge and groundwater level series, restricts the understanding of channel transmission losses (TL) in drylands. Furthermore, the lack of information on spatial river dynamics encompasses high uncertainty on TL analysis in large rivers. The objective of this study was to combine the information from streamflow and groundwater level series with multi‐temporal satellite data to derive a hydrological concept of TL for a reach of the Middle Jaguaribe River (MJR) in semi‐arid north‐eastern Brazil. Based on this analysis, we proposed strategies for its modelling and simulation. TL take place in an alluvium, where river and groundwater can be considered to be hydraulically connected. Most losses certainly infiltrated only through streambed and levees and not through the flood plains, as could be shown by satellite image analysis. TL events whose input river flows were smaller than a threshold did not reach the outlet of the MJR. TL events whose input flows were higher than this threshold reached the outlet losing on average 30% of their input. During the dry seasons (DS) and at the beginning of rainy seasons (DS/BRS), no river flow is expected for pre‐events, and events have vertical infiltration into the alluvium. At the middle and the end of the rainy seasons (MRS/ERS), river flow sustained by base flow occurs before/after events, and lateral infiltration into the alluvium plays a major role. Thus, the MJR shifts from being a losing river at DS/BRS to become a losing/gaining (mostly losing) river at MRS/ERS. A model of this system has to include the coupling of river and groundwater flow processes linked by a leakage approach. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Distribution and feeding patterns of juvenile parrotfish on algal‐dominated coral reefs          下载免费PDF全文

João L.L. Feitosa  Beatrice P. Ferreira 《Marine Ecology》2015,36(3):462-474

By the consumption of algae, parrotfishes open space for young coral settlement and growth, thus playing a central role on the maintenance of coral reefs. However, juvenile parrotfish ecology is often overlooked due to the difficulty discerning species during this phase. Herein, we present the first attempt to investigate changes in habitat use and diet that happen to juveniles of the Redeye parrotfish Sparisoma axillare, focusing on four zones within an algal‐dominated reef: the macroalgal beds, back reef, reef flat, and fore reef. Smaller S. axillare juveniles (<5 cm) preferred to inhabit the macroalgal beds and the reef flat, whereas juveniles larger than 5 cm were more abundant in the back and fore reefs due to distinct post‐settlement habitat conditions. Aggressive interactions with the territorial damselfish Stegastes fuscus were the primary driving factor of juvenile distribution and feeding rates. Attack rates increased with juvenile size and the lowest bite rates were observed in zones with higher densities of territorial damselfish. In previous studies, the persistence of parrotfish recruits in habitats dominated by damselfish was reduced, but newly settled parrotfish occurred more densely within the damselfish domain by behaving as a cryptic reef fish. As these juveniles grew, their bite rates increased, a change associated with a shift from cryptic to roving behavior. Feeding preferences were determined by substrate cover, where juveniles fed on available food sources in each habitat. Juveniles relied on jointed calcareous algae in habitats dominated by these algae, a pattern not observed for thick leathery algae. Filamentous algae were the preferred food for smaller fish; for individuals greater than 10 cm, a higher ingestion of sand was observed. Most studies evaluating the functional role of parrotfish do not consider species feeding preferences. However, the potential for a species to turn an impacted reef back to a coral‐dominated phase is influenced by their food selection, which is dependent on the algal species composition.  相似文献   

TWO HUNDRED HECTARES OF GOOD BUSINESS: BRAZILIAN AGRICULTURE IN A THEMED SPACE*     

CHRISTIAN BRANNSTROM  PAULO R. B. BRANDÃO 《Geographical review》2012,102(4):465-485

Geographers have recognized that trade fairs and other temporary spaces function as centers of knowledge, but we have a weak understanding of how fairs are themed spaces, similar to parades, festivals, and built environments, that produce cultural and political meanings. In this article we analyze the morphology, iconography, and performance of a large agricultural fair in Brazil, the Bahia Farm Show, which produces a regional identity of highly productive, leading‐edge, and globally competitive agriculture in a former economic backwater. We discuss the production of themes in terms of power relations, cultural processes, relations with nature, and sociotechnological norms for agriculture. Omissions from the Farm Show indicate tension and accommodation between elites at different geographical scales. Brazil's high‐input, high‐output agriculture relies in part on the meanings that events such as agricultural fairs sustain and reproduce.  相似文献   

A less disastrous disaster: Managing response to climate-driven hazards in the Cayman Islands and NE Brazil     

Emma L. Tompkins  Maria Carmen Lemos  Emily Boyd 《Global Environmental Change》2008,18(4):736

This paper explores the relationship between disaster risk reduction and long-term adaptive capacity building in two climate vulnerable areas—the Cayman Islands in the Caribbean and Ceará, in NE Brazil. Drawing on past applications of the disaster risk reduction framework, we identify four critical factors that have led to reductions in risk: flexible, learning-based, responsive governance; committed, reform-minded and politically active actors; disaster risk reduction integrated into other social and economic policy processes; and a long-term commitment to managing risk. We find that while the presence of these factors has reduced overall risk in both regions, in Ceará, disaster response as it is currently practiced, has fallen short of addressing the fundamental causes of vulnerability that leave those prone to hazards able to cope in the short term, yet enmeshed in poverty and at risk from the longer-term changes associated with climate change. Although calls for integration of disaster risk management with poverty eradication are not new, there has been insufficient attention paid in the literature on how to foster such integration. Based on the two case studies, we argue that the adoption of good governance mechanisms (such as stakeholder participation, access to knowledge, accountability and transparency) in disaster risk reduction policy may create the policy environment that is conducive to the kind of structural reform needed to build long-term adaptive capacity to climate-driven impacts. We conclude that without a synergistic two-tiered approach that includes both disaster risk reduction and structural reform, disaster risk reduction, in the face of climate changes, will prove to be an expensive and ineffective palliative treatment of changing risks.  相似文献