Origin of resources and trophic pathways in a large SW Atlantic estuary: An evaluation using stable isotopes     

Florencia Botto  Esteban Gaitán  Hermes Mianzan  Marcelo Acha  Diego Giberto  Agustín Schiariti  Oscar Iribarne 《Estuarine, Coastal and Shelf Science》2011

The Río de la Plata (34° 36′ S, 55° 58′ W; Argentina and Uruguay) estuary, one of the most important South American estuarine environments, is characterized by weak seasonal freshwater discharge, low tidal amplitude (<1 m), a wide and permanent connection to the sea, and a salt-wedge regime. Using stable isotope analysis, we explored the relative importance of the different sources of primary production in the food web. Our results show that phytoplankton and macrodetritus from terrestrial salt and freshwater marshes both contribute to the food web of the Río de la Plata estuary. On the basis of the sampled species, we identified four trophic levels. The clam Mactra isabelleana, the calanoid copepod Acartia tonsa, and the opossum shrimp Neomysis americana are the primary consumers. The rays Atlantoraja castelnaui and Squatina guggenheim and the shark Galeorhinus galeus are the top predators. The Río de la Plata food web shows an important input of nutrients derived from phytoplankton. Rays, sharks, and predatory gastropods reveal an important contribution of C4 plants (likely Spartina spp.). However, production derived from C3 plants is also important for some species. The fishes Brazilian menhaden, Brevoortia aurea; the stripped weakfish Cynoscion guatucupa; and the whitemouth croaker, Micropogonias furnieri, showed differences in their isotopic signatures as juveniles and adults, indicating different food sources, and they were therefore treated as different components of the food web. Our data suggest that detritus from salt and freshwater marshes is reaching the Río de la Plata estuary and can be an important allocthonous source of energy to this environment.  相似文献   

Sea,freshwater or saltpans? Foraging ecology of terns to assess mercury inputs in a wetland landscape: The Ebro Delta     

Javier Cotin  Manuel García-Tarrasón  Carolina Sanpera  Lluis Jover  Xavier Ruiz 《Estuarine, Coastal and Shelf Science》2011

The Ebro catchment, the largest river basin in Spain, includes various heavily industrialized areas. Among these is the Flix site, where a chemical plant has been operating since the beginning of the 20th century. This extended operational period, together with the construction of a dam next to the factory around 1960, resulted in the accumulation of large amounts of heavily polluted sediments in the adjacent riverbed, many of which are contaminated by mercury. Pollutants from Flix are carried downstream by the Ebro River to its delta. In order to assess the transfer of mercury to the complex river estuary ecosystem, we studied the ecology of the tern community living there as these birds segregate into a range of habitats. For this purpose, first we used stable isotope analysis (SIA) (δ³⁴S, δ¹³C, δ¹⁵N) of eggs to determine the trophic ecology and habitat partitioning of several tern species (Common, Sandwich, Little, Gull-Billed and Whiskered Tern) breeding sympatrically, in order to link their foraging ecology with habitat types. Next we measured mercury concentrations in eggs to monitor the input of this metal into the diverse habitats. With the exception of the Little Tern, the other terns used a restricted habitat range in the Ebro Delta, as shown by C and S isotopes; the Gull-Billed and Whiskered Tern foraged in freshwater habitats, while the Common and Sandwich Tern used marine habitats. This restricted feeding behavior of the Gull-Billed and Common Tern contrasts with previous reports in other breeding sites. The Little Tern, which showed a wide range of isotopic values, was found to be an opportunistic forager but fed mainly in saltpans, a feeding habitat not reported previously for this species in this area. We found that mercury concentrations are related to foraging habitat and diet, and are unexpectedly higher in species feeding on demersal prey in marine habitats and also higher in birds feeding in saltpans than in those feeding in freshwater habitats. The mercury concentrations found in the Little and Common Tern eggs sampled in “Punta de la Banya” may be sufficiently high to endanger breeding success.  相似文献   

An institutional analysis of the sustainability of fisheries: Insights from FishBanks simulation game     

Manuel Ruiz-Pérez  Fátima Franco-Múgica  Miguel A. Alberruche-Rico 《Ocean & Coastal Management》2011,54(8):585-592

FishBanks, a well-known fisheries management simulation game, was used to test the effect of institutional settings on the biological and economic performance of fisheries. The game was played by 48 groups of between 20 and 25 undergraduate Environmental Science students in two different time lengths (10 years versus 15 years) and institutional settings (open access versus regulated access through a resource management regime). Sessions run under an institutional regime for resource management performed better than those under open access in terms of fish population, aggregate asset value and income distribution amongst competing companies. Fleet size, a proxy for human pressure on the resource, had a more intense effect than the existence or not of an institutional setting. Results also indicate that once a critical threshold is reached in stock deterioration, institutions may be insufficient to revert change, suggesting ultimate environmental limits to the effectiveness of institutions.  相似文献   

Technical, economics and environmental analysis of semi-intensive shrimp (Litopenaeus vannamei) farming in Sonora, Sinaloa and Nayarit states, at the east coast of the Gulf of California, México     

Jesús T. Ponce-Palafox  Arturo Ruiz-LunaSergio Castillo-Vargasmachuca  Manuel García-UlloaJosé Luis Arredondo-Figueroa 《Ocean & Coastal Management》2011,54(7):507-513

In Mexico shrimp pond aquaculture is the main activity and contributes with 45.9% of the total fisheries volume and 74.3% of gross profit generated by the national products, being Sonora, Sinaloa and Nayarit in the east coast of the Gulf of California the states generating around 70% of region gross profit. The main species cultivated is the white shrimp Litopenaeus vannamei, and for this reason academic and government sector devoted much attention in this species, however, still researching on economic feasibility is scarce and needed. In this paper, the technical, economics, production and environment parameters of 80 semi-intensive commercial in these states are analyzed and discussed. The results showed the main external constraints affecting short and long run farm performance. The overall observations pointed out that there is an increase on yield and income when shrimp farms invest in higher quality inputs such as equipment and technology for more efficiency in using water, use of certified post-larvae and better design of farm facility. Nevertheless, further research is needed to adjust shrimp production strategies to specific farm requirement by investing in premium quality inputs. Furthermore, the most serious threat from shrimp aquaculture is the potential effect on water quality and the infrastructure associated, that having more serious effects on the environment, particularly in the coastal wetlands. The economic and the environment care must be driven to lead a more sustainable scenario.  相似文献   

Trophic ecology of Mustelus schmitti (Springer, 1939) in a nursery area of northern Patagonia     

Juan Manuel Molina  Andrea López Cazorla 《Journal of Sea Research》2011,65(4):381-389

Mustelus schmitti is an endangered endemic shark of the southwest Atlantic, and an important economical resource in Argentina, Brazil and Uruguay. The objective of this study was to describe the trophic ecology of M. schmitti in Anegada Bay, its feeding strategy and diet composition, along with the possible dietary shifts, due to season, sex, ontogeny and the different geographical features of the bay. Our results show that M. schmitti is a carnivorous opportunistic predator, feeding on a variety of benthic invertebrates. The diet presented seasonal and ontogenetic variations, while no differences in diet composition were observed between sexes or the different sampling sites. This species behave as a generalize feeder, with a wide trophic spectrum and a diverse diet.  相似文献   

Petrogenetic links between lepidolite-subtype aplite-pegmatite,aplite veins and associated granites at Segura (central Portugal)     

Isabel Margarida Horta Ribeiro Antunes  Ana Margarida Ribeiro Neiva  João Manuel Farinha Ramos  Paulo Bravo Silva  Maria Manuela Vinha Guerreiro Silva  Fernando Corfu 《Chemie der Erde / Geochemistry》2013

In the Segura area, Variscan S-type granites, aplite veins and lepidolite-subtype granitic aplite-pegmatite veins intruded the Cambrian schist-metagraywacke complex. The granites are syn D3. Aplite veins also intruded the granites. Two-mica granite and muscovite granite have similar ages of 311.0 ± 0.5 Ma and 312.9 ± 2.0 Ma but are not genetically related, as indicated by their geochemical characteristics and (⁸⁷Sr/⁸⁶Sr)₃₁₁ values. They correspond to distinct pulses of magma derived by partial melting of heterogeneous metapelitic rocks. Major and trace elements suggest fractionation trends for: (a) muscovite granite and aplite veins; (b) two-mica granite and lepidolite-subtype aplite-pegmatite veins, but with a gap in most of these trends. Least square analysis for major elements, and modeling of trace elements, indicate that the aplite veins were derived from the muscovite granite magma by fractional crystallization of quartz, plagioclase, K-feldspar and ilmenite. This is supported by the similar (⁸⁷Sr/⁸⁶Sr)₃₁₁ and δ¹⁸O values and the behavior of P₂O₅ in K-feldspar and albite. The decrease in (⁸⁷Sr/⁸⁶Sr)₃₁₁ and strong increase (1.6‰) in δ¹⁸O from two-mica granite to lepidolite-subtype aplite-pegmatite veins, and the behaviors of Ca, Mn and F of hydroxylapatite indicate that these veins are not related to the two-mica granite.  相似文献   

Multivariate discriminant analysis distinguishes metal- from non metal-related biomarker responses in the clam Chamaelea gallina     

Rodríguez-Ortega MJ  Rodríguez-Ariza A  Gómez-Ariza JL  Muñoz-Serrano A  López-Barea J 《Marine pollution bulletin》2009,58(1):64-327

Molecular biomarkers are among the most sensitive and earliest responses to pollutants. However, lack of detailed knowledge on variability of responses and their possible seasonal variation limit their use. In addition, the seasonality of biological processes modulates the response of organisms to pollutant stressors. Using multivariate statistics, we have studied the influence of environmental and biological factors on the response of a battery of molecular biomarkers in the clam Chamaelea gallina collected along the South-Spanish littoral. Multivariate discriminant analysis clearly distinguished biomarker response between clean and polluted areas, using heavy metals as indicator of pollution. Such differences disappeared when the dataset was normalised for metal content, thus indicating that pollution was the main significant cause of the changes observed between clean and polluted sites. In conclusion, this work shows that, when applying a complete biomarker panel, multivariate statistical tools can be used to discern pollutant- from non pollutant-related responses.  相似文献   

Estimation of load reduction factors for clay masonry walls     

Francesca da Porto  Manuel Grendene  Claudio Modena 《地震工程与结构动力学》2009,38(10):1155-1174

The in‐plane cyclic behaviour of three types of unreinforced clay masonry was characterized by means of laboratory tests on full‐scale specimens. The masonry walls were assembled with various bonding arrangements (head joints made with mortar pockets, dry head joints with mechanical interlocking, thin‐layer mortar bed joints), which are not yet inserted in seismic codes. Experimental behaviour was modelled with an analytical hysteretic model able to predict lateral load–displacement curves in case of shear failure of the unreinforced walls. According to the experimental results and those of the selected analytical model, parametric study to evaluate the reduction in lateral strength demand produced by non‐linear behaviour in masonry walls, i.e. the load reduction factor was carried out by non‐linear dynamic analyses. The calculated values of the load reduction factor were modest. The differences in values found for the three masonry types, although consistent with them, were not great. This may indicate that, in the ultimate limit state, the type of masonry cannot significantly affect the behaviour of an entire building. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Precursory seismicity of the 1994 eruption of Popocatépetl Volcano,Central Mexico   总被引：1，自引：1，他引：0  

Servando De la Cruz-Reyna  Izumi Yokoyama  Alicia Martínez-Bringas  Esteban Ramos 《Bulletin of Volcanology》2008,70(6):753-767

Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over 20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions, including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-and-destruction episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime, the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this paper we analyze five years of volcano-tectonic seismicity preceding the initial eruption of the current episode. The evolution of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes, limit that was reached by Popocatépetl before the eruption.  相似文献   

Geographies of the financial crisis   总被引：4，自引：0，他引：4  

Manuel Aalbers 《Area》2009,41(1):34-42

Real estate is, by definition, local as it is spatially fixed. Mortgage lending, however, has developed from a local to a national market and is increasingly a global market today. An understanding of the financial crisis is ultimately a spatialised understanding of the linkages between local and global. This article looks at the geographies of the mortgage crisis and credit crunch and asks the question: how are different places affected by the crisis? The article looks at different states, different cities, different neighbourhoods and different financial centres. Investors in many places had invested in residential mortgage backed securities and have seen their value drop. Housing bubbles, faltering economies and regulation together have shaped the geography of the financial crisis on the state and city level in the US. Subprime and predatory lending have affected low-income and minority communities more than others and we therefore not only see a concentration of foreclosures in certain cities, but also in certain neighbourhoods. On an international level, the long-term economical and political consequences of this are still mostly unknown, but it is clear that some financial centres in Asia (including the Middle East) will become more important now that globalisation is coming full circle. This article does not present new empirical research, but brings together work from different literatures that all in some way have a specific angle on the financial crisis. The aim of this article is to make the geographical dimensions of the financial crisis understandable to geographers that are not specialists in all – or even any – of these literatures, so that they can comprehend the spatialisation of this crisis.  相似文献