Are changes in the structure of nematode assemblages reliable indicators of moderate petroleum contamination?     

Daniel Silva Leite  Leonardo Sandrini-Neto  Manuela Zeglin Camargo  Micheli Cristina Thomas  Paulo C. Lana 《Marine pollution bulletin》2014

This study assesses through a multiple before-after-control-impact (MBACI) design the effects of diesel oil on the structure of nematode assemblages in unvegetated tidal flats of a subtropical estuary. Oil-exposed treatments were contrasted with controls for a duration of four successive days before and after an experimental spill in three distinct areas of the Paranaguá Estuarine Complex (Southern Brazil). No significant differences were observed in nematode total density, number of taxa and the overall assemblage structure between the control and impact treatments from before to after the experimental spill. This reinforces the idea that, despite being good indicators of environmental stress, free-living marine nematodes are able to tolerate low concentrations of hydrocarbons and to survive in moderately contaminated areas. We also show that robust experimental designs are useful to avoid confounding expected natural variability with the effects of a mild impact.  相似文献   

The role of site effects in the comparison between code provisions and the near field strong motion of the Emilia 2012 earthquakes   总被引：1，自引：1，他引：0  

Maria Rosaria Gallipoli  Leonardo Chiauzzi  Tony Alfredo Stabile  Marco Mucciarelli  Angelo Masi  Carmine Lizza  Luigi Vignola 《Bulletin of Earthquake Engineering》2014,12(5):2211-2230

A damaging seismic sequence hit a wide area mainly located in the Emilia-Romagna region (Northern Italy) during 2012 with several events of local magnitude \(\hbox {M}_\mathrm{l} \ge 5\) , among which the \(\hbox {M}_\mathrm{l}\) 5.9 May 20 and the \(\hbox {M}_\mathrm{l}\) 5.8 May 29 were the main events. Thanks to the presence of a permanent accelerometric station very close to the epicentre and to the temporary installations performed in the aftermath of the first shock, a large number of strong motion recordings are available, on the basis of which, we compared the recorded signals with the values provided by the current Italian seismic regulations, and we observed several differences with respect to horizontal components when the simplified approach for site conditions (based on Vs30 classes) is used. On the contrary, when using the more accurate approach based on the local seismic response, we generally obtain a much better agreement, at least in the frequency range corresponding to a quarter wavelength comparable with the depth of the available subsoil data. Some unresolved questions still remain, such as the low frequency behaviour ( \(<\) 1 Hz) that could be due either to complex propagation at depth larger than the one presently investigated or to near source effects, and the behaviour of vertical spectra whose recorded/code difference is too large to be explained with the information currently available.  相似文献   

S-Wave Velocities of the Lithosphere–Asthenosphere System in the Caribbean Region     

O’Leary F. González  José Leonardo Alvarez  Bladimir Moreno  Giuliano F. Panza 《Pure and Applied Geophysics》2012,169(1-2):101-122

An overview of the S-wave velocity (V _s) structural model of the Caribbean with a resolution of 2°?×?2° is presented. New tomographic maps of Rayleigh wave group velocity dispersion at periods ranging from 10 to 40?s were obtained as a result of the frequency time analysis of seismic signals of more than 400 ray-paths in the region. For each cell of 2°?×?2°, group velocity dispersion curves were determined and extended to 150?s by adding data from a larger scale tomographic study (Vdovin et al., Geophys. J. Int 136:324–340, 1999). Using, as independent a priori information, the available geological and geophysical data of the region, each dispersion curve has been inverted by the “hedgehog” non-linear procedure (Valyus, Determining seismic profiles from a set of observations (in Russian), Vychislitielnaya Seismologiya 4, 3–14. English translation: Computational Seismology (V.I. Keylis-Borok, ed.) 4:114–118, 1968), in order to compute a set of V _s versus depth models up to 300?km of depth. Because of the non-uniqueness of the solutions for each cell, a local smoothness optimization has been applied to the whole region in order to choose a three-dimensional model of V _s, satisfying this way the Occam's razor concept. Several known and some new main features of the Caribbean lithosphere and asthenosphere are shown on these models such as: the west directed subduction zone of the eastern Caribbean region with a clear mantle wedge between the Caribbean lithosphere and the subducted slab; the complex and asymmetric behavior of the crustal and lithospheric thickness in the Cayman ridge; the predominant oceanic crust in the region; the presence of continental type crust in Central America, and the South and North America plates; as well as the fact that the bottom of the upper asthenosphere gets shallower going from west to east.  相似文献   

Methane levels in shallow subtropical lake sediments: Dependence on the trophic status of the lake and allochthonous input     

Leonardo M. Furlanetto  Claudio C. MarinhoCleber Palma-Silva  Edélti F. AlbertoniMarcos Paulo Figueiredo-Barros  Francisco de Assis Esteves 《Limnologica》2012,42(2):151-155

The vertical sediment profiles (10 cm) of the margins of three shallow subtropical lakes (Rio Grande, Brazil) with different trophic states and surrounding areas were evaluated to identify the effects of the allochthonous input on the methane concentration in the sediment. Sediment cores were collected to quantify the organic matter content (OM) and total carbon (TC), total nitrogen (TN), total phosphorous (TP) and methane (CH₄) concentrations.The three lakes were distinguished according to the trophic status and classified as oligotrophic, dystrophic and eutrophic. The natural characteristics of the dystrophic and eutrophic lakes have been changed due to the allochthonous input of leaves and twigs (Eucalyptus sp.) and the excreta of birds, respectively. In the eutrophic lake, the allochthonous input contributed to high autochthonous production. The highest values of OM, TC, TN and TP were found in the superficial sediments of the dystrophic and eutrophic lakes. The accumulation of allochthonous organic matter in the littoral zone promoted changes in the vertical sediment profiles and contributed to increases in the CH₄ concentrations in the sediment.  相似文献   

On the determination of marine magnetotelluric receiver orientation using land magnetic observatory data          下载免费PDF全文

Leonardo G. Miquelutti  Emin U. Ulugergerli  Deivid Nascimento  Sergio L. Fontes 《Geophysical Prospecting》2016,64(5):1350-1367

Marine magnetotelluric measurements using “free‐fall’’ instruments without effective compasses suffer from the problem of unknown orientation of the receivers at the seafloor. While past works indicate that marine magnetotelluric orientation of the instruments can be estimated by reference to land deployments of known orientation using the transfer tensor method, there is limited published information on how this is implemented in practice. We document this method and propose a set of new time‐ and frequency‐domain approaches to solve this orientation problem of the seafloor receivers. We test these methodologies in onshore and offshore magnetotelluric data whose orientations are well known and apply these techniques to marine magnetotelluric data with unknown orientation. For the controlled tests, both time‐ and frequency‐domain approaches produce overall comparable results. To investigate the effects of the subsurface structure distribution on the orientation process, a dimensionality analysis of a controlled dataset is carried out. In subsequent analysis using the available disoriented marine magnetotelluric data from offshore Brazil and from the Vassouras magnetic observatory on the mainland for remote referencing, frequency‐domain methods yield approximate orientation angles among themselves with low standard deviation each. Time‐domain results are consistent for most cases but differ from frequency‐domain results for some situations.  相似文献   

Urbanization impacts upon catchment hydrology and gully development using mutli‐temporal digital elevation data analysis     

Osmar Carvalho Junior  Renato Guimaraes  Leonardo Freitas  Daniel Gomes‐Loebmann  Roberto Arnaldo Gomes  Eder Martins  David R. Montgomery 《地球表面变化过程与地形》2010,35(5):611-617

Urbanization can change catchment hydrology, accelerating gully erosion and causing serious damage to urban structures like roads, bridges and buildings. Increased impervious surfaces lead to large, rapid increases in surface runoff in urban catchments during storm events, as well as changes in the upslope contributing area due to rerouting of urban runoff that can exacerbate erosion. Accounting for changes in surface drainage patterns Gama City, Brazil, is used to predict areas prone to accelerate gullying and develop a method of assessing the potential for gully erosion produced by urbanization. The method is based on the analysis and comparison of detailed digital elevation models (DEMs) of the natural condition before urbanization and the topography after urbanization. The study site is located in an area where changes in drainage patterns associated with rapid urbanization in the last 30 years have resulted in severe gullying. Our analysis identifies areas potentially susceptible to gullying and highlights the erosional influence of increased flow concentration caused by urban occupation, a finding that has implications and applications for strategies to prevent gully development in cities or areas undergoing urban expansion. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Spatial Overlap and Coexistence in a Mussel-Associated Polychaete Assemblage on a South American Rocky Shore     

Mutsunori Tokeshi  & Leonardo Romero 《Marine Ecology》2000,21(3-4):247-261

Abstract. Mussel beds in the intertidal of subtropical South America are known to harbour a large number of invertebrates, particularly polychaetes. This paper presents a quantitative analysis of the patterns of spatial overlap and coexistence in an assemblage of polychaetes associated with mussel beds in a rocky intertidal habitat on the Pacific coast of Peru. Mussel beds are made up of two zones in the intertidal: the lower, more extensive zone formed by Semimytilus algosus and the upper zone formed by Perumytilus purpuratus . Null models were employed to assess the magnitude of spatial overlap between pairs of taxa encompassing a total of seven taxonomic groups. Two taxa belonging to the same functional group tended to be spatially segregated in the Semimytilus bed: Pseudonereis vs. Halosydna (large free-ranging predators) and Scoloplos vs. Mediomastus (deposit feeders), with further segregating tendencies between Pseudonereis and Mediomastus , and between Halosydna and Scoloplos . Small-sized, free-ranging ' Typosyllis ' and the bottom-dwelling scavenging predator Lumbrineris were also spatially associated. Thus, this polychaete assemblage appears to be loosely organised around groupings of taxa which are somewhat different in ecological traits and form mosaic patterns of distribution with reduced overlap within the Semimytilus bed. These relationships were weak to non-existent in the upper, drier Perumytilus habitat where polychaete density was low.  相似文献   

Decomposition algorithms for system reliability estimation with applications to interdependent lifeline networks          下载免费PDF全文

Roger Paredes  Leonardo Dueñas‐Osorio  Isaac Hernandez‐Fajardo 《地震工程与结构动力学》2018,47(13):2581-2600

Reliability and risk assessment of lifeline systems call for efficient methods that integrate hazard and interdependencies. Such methods are computationally challenged when the probabilistic response of systems is tied to multiple events, as performance quantification requires a large catalog of ground motions. Available methods to address this issue use catalog reductions and importance sampling. However, besides comparisons against baseline Monte Carlo trials in select cases, there is no guarantee that such methods will perform or scale well in practice. This paper proposes a new efficient method for reliability assessment of interdependent lifeline systems, termed RAILS, that considers systemic performance and is particularly effective when dealing with large catalogs of events. RAILS uses the state‐space partition method to estimate systemic reliability with theoretical bounds and, for the first time, supports cyclic interdependencies among lifeline systems. Recycling computations across an entire seismic catalog with RAILS considerably reduces the number of system performance evaluations in seismic performance studies. Also, when performance estimate bounds are not tight, we adopt an importance and stratified sampling method that in our computational experiments is various orders of magnitude more efficient than crude Monte Carlo. We assess the efficiency of RAILS using synthetic networks and illustrate its application to quantify the seismic risk of realistic yet streamlined systems hypothetically located in the San Francisco Bay Region.  相似文献   

Inter-annual changes in fish communities of a tropical bay in southeastern Brazil: What can be inferred from anthropogenic activities?     

Francisco Gerson Araújo  Samara Macedo Pinto  Leonardo Mitrano Neves  Márcia Cristina Costa de Azevedo 《Marine pollution bulletin》2017,114(1):102-113

We assessed inter-annual changes in fish assemblages of a tropical bay which experienced a heavily industrialized process in the last decades. A highly significant difference in community structure among the bay zones, and a decrease in fish richness and abundance over time were found. Changes in fish richness and abundance between the two first (1987–1988 and 1993–1995) and the two latter time periods (1998–2001 and 2012–2013) were sharpest in the inner bay zone, the most impacted bay area, and in the middle zone, whereas the outer zone remained comparatively stable over time. These changes coincided with increased metal pollution (mainly, Zn and Cd) in the bay and with the enlargement of the Sepetiba Port. Spatial changes in the fish community structure among the bay zones were related to differences in salinity, transparency and depth with this latter variable acting as a buffer stabilizing temporal community changes.  相似文献   

Magnetic susceptibility mapping of the Cambrian El Hongo pluton,Eastern Sierras Pampeanas,Argentina     

Silvana Geuna  Leonardo Escosteguy  Belena Díaz Appella  Fernando D’Eramo  Lucio Pinotti 《Studia Geophysica et Geodaetica》2017,61(2):219-232

A map of bulk magnetic susceptibility was obtained on El Hongo trondhjemite, a small Cambrian pluton intruding the metamorphic basement in Eastern Sierras Pampeanas, Argentina, based on systematic magnetic susceptibility measurement at 450 sites using a SM30 susceptibility meter. Samples were collected on 58 sites and their bulk magnetic susceptibility was measured in laboratory with a Bartington MS2 system. Point-to-point comparison showed differences, that were attributed to the effect of roughness of the surveyed surfaces, and to the development of a weathered cap. However, the difference was systematic and in accordance with expected values predicted by manufacturer tables, whereby, once corrected with the appropriate factor, the obtained values with SM30 susceptibility meter were regarded as representative of fresh rocks. The resulting map was interpreted in terms of variation in abundance of magnetite, which is present in the rocks as a magmatic mineral, altered to hematite (martitized) in varying degrees. The map revealed that El Hongo trondhjemite is a weakly magnetic pluton, with a typical bulk susceptibility of about 500 × 10^?6 SI, which would correspond to an abundance of magnetite below 0.2 vol%, but with conspicuous variations. Lows in the outer sector and in the vicinity of metamorphic xenoliths were interpreted as due to destruction of magnetic minerals linked to reactions between magma and host rock. A distinct concentric pattern in the western area could indicate the presence of a separate intrusion. Finally, alternate highs and lows in susceptibility follow the undulations in regional schistosity, which in turn would have controlled the emplacement of the pluton. Thus we provide a good example of the utility of magnetic susceptibility mapping in granitoid terrains, as an expeditious way for preliminary mapping that could guide further and more detailed research.  相似文献