Organochlorine compounds in sharks from the Brazilian coast     

Claudio Eduardo de Azevedo e Silva  Adriana de Cássia Lima Dias  José Lailson-Brito  Jean Remy Daveé Guimarães 《Marine pollution bulletin》2009,58(2):294-298

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Anthropogenic debris on beaches in the SE Pacific (Chile): Results from a national survey supported by volunteers     

Macarena Bravo  Mª de los ngeles Gallardo  Guillermo Luna-Jorquera  Paloma Núez  Nelson Vsquez  Martin Thiel 《Marine pollution bulletin》2009,58(11):1718-1726

Anthropogenic marine debris (AMD) is an ubiquitous problem, which has motivated public participation in activities such as beach surveys and clean-up campaigns. While it is known that beaches in the SE Pacific are also affected by this problem, the quantities and types of AMD remain largely unknown. In the context of an outreach project, volunteers (1500 high-school students) participated in a nation-wide survey of AMD on 43 beaches distributed randomly along the entire Chilean coast (18°S to 53°S). The mean density of AMD was 1.8 items m⁻² and the major types were plastics, cigarette butts and glass. Densities in central Chile were lower than in northern and southern Chile, which could be due to different attitudes of beach users or to intense beach cleaning in central regions. We suggest that public participation in surveys and cleaning activities will raise awareness and thereby contribute to an improvement of the situation.  相似文献   

Contrasting regional discharge evolutions in the Amazon basin (1974–2004)   总被引：1，自引：0，他引：1  

Jhan Carlo Espinoza Villar  Jean Loup Guyot  Josyane Ronchail  Grard Cochonneau  Naziano Filizola  Pascal Fraizy  David Labat  Eurides de Oliveira  Juan Julio Ordoez  Philippe Vauchel 《Journal of Hydrology》2009,375(3-4):297-311

Former hydrological studies in the Amazon Basin generally describe annual discharge variability on the main stem. However, the downstream Amazon River only represents the mean state of the Amazonian hydrological system. This study therefore uses a new data set including daily discharge in 18 sub-basins to analyze the variability of regional extremes in the Amazon basin, after recalling the diversity of the hydrological annual cycles within the Amazon basin. Several statistical tests are applied in order to detect trends and breaks in the time series. We show that during the 1974–2004 period, the stability of the mean discharge on the main stem in Óbidos is explained by opposite regional features that principally involve Andean rivers: a decrease in the low stage runoff, particularly important in the southern regions, and an increase in the high stage runoff in the northwestern region. Both features are observed from the beginning of the nineties. These features are also observed in smaller meridian sub-basins in Peru and Bolivia. Moreover we show that the changes in discharge extremes are related to the regional pluriannual rainfall variability and the associated atmospheric circulation as well as to tropical large-scale climatic indicators.  相似文献   

Using semivariogram parameter uncertainty in hydrogeological applications   总被引：1，自引：0，他引：1  

Pardo-Igúzquiza E  Chica-Olmo M  Garcia-Soldado MJ  Luque-Espinar JA 《Ground water》2009,47(1):25-34

Geostatistical estimation (kriging) and geostatistical simulation are routinely used in ground water hydrology for optimal spatial interpolation and Monte Carlo risk assessment, respectively. Both techniques are based on a model of spatial variability (semivariogram or covariance) that generally is not known but must be inferred from the experimental data. Where the number of experimental data is small (say, several tens), as is not unusual in ground water hydrology, the model fitted to the empirical semivariogram entails considerable uncertainty. If all the practical results are based on this unique fitted model, the final results will be biased. We propose that, instead of using a unique semivariogram model, the full range of models that are inside a given confidence region should be used, and the weight that each semivariogram model has on the final result should depend on its plausibility. The first task, then, is to evaluate the uncertainty of the model, which can be efficiently done by using maximum likelihood inference. The second task is to use the range of plausible models in applications and to show the effect observed on the final results. This procedure is put forth here with kriging and simulation applications, where the uncertainty in semivariogram parameters is propagated into the final results (e.g., the prediction of ground water head). A case study using log-transmissivity data from the Vega de Granada aquifer, in southern Spain, is given to illustrate the methodology.  相似文献   

A Burst with Double Radio Spectrum Observed up to 212 GHz     

C. G. Giménez de Castro  G. D. Cristiani  P. J. A. Simões  C. H. Mandrini  E. Correia  P. Kaufmann 《Solar physics》2013,284(2):541-558

We study a solar flare that occurred on 10 September 2002, in active region NOAA 10105, starting around 14:52 UT and lasting approximately 5 minutes in the radio range. The event was classified as M2.9 in X-rays and 1N in Hα. Solar Submillimeter Telescope observations, in addition to microwave data, give a good spectral coverage between 1.415 and 212 GHz. We combine these data with ultraviolet images, hard and soft X-ray observations, and full-disk magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic Imager data are used to identify the locations of X-ray sources at different energies, and to determine the X-ray spectrum, while ultraviolet images allow us to characterize the coronal flaring region. The magnetic field evolution of the active region is analyzed using Michelson Doppler Imager magnetograms. The burst is detected at all available radio frequencies. X-ray images (between 12 keV and 300 keV) reveal two compact sources. In the 212 GHz data, which are used to estimate the radio-source position, a single compact source is seen, displaced by 25″ from one of the hard X-ray footpoints. We model the radio spectra using two homogeneous sources, and we combine this analysis with that of hard X-rays to understand the dynamics of the accelerated particles. Relativistic particles, observed at radio wavelengths above 50 GHz, have an electron index evolving with the typical soft–hard–soft behavior.  相似文献   

Terrestrial photogrammetric techniques applied to the control of a parabolic dune in the Liencres dune system,Cantabria (Spain)     

Carlos Arteaga  José Juan de Sanjosé  Enrique Serrano 《地球表面变化过程与地形》2008,33(14):2201-2210

The spatial–temporal variations of a dune system can be determined by using diverse ‘geomatic’ methodologies: geodesy, global positioning system (GPS) and photogrammetry. In the case of the Liencres dune system, a study will be carried out using the ‘close‐range’ photogrammetry technique and the topography technique (total station and GPS). In order to determine the dynamic of the dune system it is necessary to repeat the process of study after a specific interval of time. For this reason, three dimensional data should be available in two different time periods, between which the displacement of the object of analysis (the front portion of the dune) will be significant enough to evaluate its magnitude. This work analyses the viability of photogrammetry for the determination of the spatial–temporal changes of a coastal parabolic dune. Two factors have been analysed: first, the comparison of the photogrammetric results with the results obtained from topographic methods (total station and GPS), and second, the quantification of the displacement of the dune system. The analysis of the correspondence between the movement of different parts of the dune and the influence of the intensity and direction of the prevailing wind in the area is also desired. The dune advanced 12·15 ± 0·06 m (an average of 8·5 m/yr), and the partial implications for the dynamic of human modified processes on the natural park have been established. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Underground Temperature Measurements as a Tool for Volcanic Activity Monitoring in the Island of Tenerife, Canary Islands     

A. Eff-Darwich  J. Coello  R. Viñas  V. Soler  M. C. Martin-Luis  I. Farrujia  M. L. Quesada  J. de la Nuez 《Pure and Applied Geophysics》2008,165(1):135-145

The spatial distribution of groundwater temperatures in the volcanic island of Tenerife, Canary Islands, has been inferred through measurements of water temperatures collected in the vast network of wells and subhorizontal tunnels, locally called “galleries,” which constitutes the main water supply of the island. The spatial coverage of the network of galleries allows us to reach from depth almost any geological feature of the island. The complex spatial distribution of temperatures in the interior of Tenerife is the result of the complex geological evolution of the island. Groundwater temperatures are greatly affected by groundwater flow and are considerably warmer in those galleries located in areas where water circulation is reduced due to the low permeability of materials and/or to the low infiltration rate of cooling meteoric water. In this sense, groundwater temperature should be characterized in quiescent conditions (background level), in order to facilitate monitoring changes in heat flow, such as those induced by ascending gases expected with an increase in volcanic activity.  相似文献   

An overview of physical and ecological processes in the Rio de la Plata Estuary     

E. Marcelo Acha  Hermes Mianzan  Raúl Guerrero  José Carreto  Diego Giberto  Norma Montoya  Mario Carignan 《Continental Shelf Research》2008

The Rio de la Plata is a large-scale estuary located at 35°S on the Atlantic coast of South America. This system is one of the most important estuarine environments in the continent, being a highly productive area that sustains valuable artisanal and coastal fisheries in Uruguay and Argentina. The main goals of this paper are to summarize recent knowledge on this estuary, integrating physical, chemical and biological studies, and to explore the sources and ecological meaning of estuarine variability associated to the stratification/mixing alternateness in the estuary. We summarized unpublished data and information from several bibliographic sources. From study cases representing different stratification conditions, we draw a holistic view of physical patterns and ecological processes of the stratification/mixing alternateness. This estuary is characterized by strong vertical salinity stratification most of the time (the salt-wedge condition). The head of the estuary is characterized by a well-developed turbidity front. High turbidity constrains their photosynthesis. Immediately offshore the turbidity front, water becomes less turbid and phytoplankton peaks. As a consequence, trophic web in the estuary could be based on two sources of organic matter: phytoplankton and plant detritus. Dense plankton aggregations occur below the halocline and at the tip of the salt wedge. The mysid Neomysis americana, a key prey for juvenile fishes, occurs all along the turbidity front. A similar spatial pattern is shown by one of the most abundant benthic species, the clam Mactra isabelleana. These species could be taken advantage of the particulate organic matter and/or phytoplankton concentrated near the front. Nekton is represented by a rich fish community, with several fishes breeding inside the estuary. The most important species in terms of biomass is Micropogonias furnieri, the main target for the coastal fisheries of Argentina and Uruguay. Two processes have been identified as producing partially stratified conditions: persistent moderate winds (synoptic scale), or low freshwater runoff (interannual scale). Less frequently, total mixing of the salt wedge occurs after several hours of strong winds. The co-dominance of diatoms (which proliferate in highly turbulent environments) and red tides dinoflagellates and other bloom taxa (better adapted to stratified conditions), would indicate great variability in the turbulence strength, probably manifested as pulses. Microplankton and ichthyoplankton assemblages defined for the stratified condition are still recognized during the partially mixed condition, but in this case they occupy the entire water column: vertical structure of the plankton featuring the stratified condition become lost. Bottom fish assemblages, on the contrary, shows persistence under the different stratification conditions, though the dominant species of the groups show some variations. Summarizing, the Río de la Plata Estuary is a highly variable environment, strongly stratified most of the time but that can be mixed in some few hours by strong wind events that occur in an unpredictable manner, generating stratification/partially mixed (less frequently totally mixed) pulses all along the year. At larger temporal scales, the system is under the effects of river discharge variations associated to the ENSO cycle, but their ecological consequences are not fully studied.  相似文献   

Algal pigment patterns and phytoplankton assemblages in different water masses of the Río de la Plata maritime front     

José I. Carreto  Nora MontoyaRut Akselman  Mario O. CarignanRicardo I. Silva  Daniel A. Cucchi Colleoni 《Continental Shelf Research》2008

The composition of phytoplankton assemblages were studied in three sections across the continental shelf between the Río de la Plata and the oceanic waters of the Subtropical Convergence, during late spring. Algal communities were examined using microscopy and HPLC-derived pigment concentrations. The CHEMTAX program was used to estimate the chlorophyll a (chl a) biomass of different algal classes. Trends in pigment ratios due to phytoplankton photo-adaptation and photo-acclimation were also examined. In order to accommodate the natural diversity of phytoplankton assemblages the original data have been split to represent five ecosystems. In addition, the pigment data for the Brazil Current ecosystem has been split by sample depth.  相似文献   

Impact of natural (waves and currents) and anthropogenic (trawl) resuspension on the export of particulate matter to the open ocean: Application to the Gulf of Lion (NW Mediterranean)     

B. Ferré  X. Durrieu de Madron  C. Estournel  C. Ulses  G. Le Corre 《Continental Shelf Research》2008

Modern sediment deposits on continental margins form a vast reservoir of particulate matter that is regularly affected by resuspension processes. Resuspension by bottom trawling on shelves with strong fishing activity can modify the scale of natural disturbance by waves and currents. Recent field data show that the impact of bottom trawls on fine sediment resuspension per unit surface is comparable with that of the largest storms.  相似文献