Changes in interstitial water salinity of a Mississippi tidal marsh     

Courtney T. Hackney  Armando A. de la Cruz 《Estuaries and Coasts》1978,1(3):185-188

The salinity of interstitial water (i.e., the salinity of the free soil water) was examined at 11 equidistant stations along a transect on a Mississippi tidal marsh dominated byJuncus roemerianus andSpartina cynosuroides. Changes in the nearby surface water (e.g., bay water) were reflected in the changes in interstitial water salinity. The salinity of interstitial water was usually higher, varying between 2.5 and 15.8‰ from February 1975 through January 1976, than the salinity of the nearby surface water which ranged from 0.0 to 11.5‰. Following a long period of high salinity in the bay and sound (exceeding 14‰), the salinity of the interstitial water increased to a maximum of 16.8‰ in October. The salinity increased as the distance of the sampling station from the source of the flood water increased. Mean interstitial wate salinity across the marsh studied was within 10‰ which did not seem to influence the marsh plant zonation occurring on the marsh.  相似文献   

The meteorologically abnormal year of 2006 and natural disasters in the Philippines     

Graciano P. Yumul Jr. Nathaniel A. Cruz Nathaniel T. Servando Carla B. Dimalanta 《《幕》》2008,31(4):378-383

In the early part of 2006 the Philippines was hit by a La Nina event which brought floods, flashfloods and landslides. The most significant event was the February 2006 landslide that covered the whole community of Guinsaugon, in Southern Leyte, resulting in 154 deaths with 973 people still missing. Another rare event was the simultaneous presence of two tropical cyclones inside the Philippine Area of Responsibility （PAR） in August-- Tropical Depression Bopha and Tropical Storm Saomai--that enhanced the southwest monsoon. With the strong winds and high waves associated with the southwest mon- soon, an oil tanker, the M/T Solar 1, sank, resulting in the worst oil spill the country has ever suffered. Lastly, with a weak El Nino phenomenon forming in the Pacific Ocean and affecting the Philippines, a destructive typhoon, Xangsane, made a multi-landfall before hitting Metropolitan Manila. This was followed by the landfall of three superty- phoons--Cimaron, Chebi and Durian--during the last quarter of the year, bringing tremendous destruction of life and property. The occurrence of these weather events are attributed to climate variability the effects of which were exacerbated by a range of factors that include inappropriate land use.  相似文献   

Pliocene extensional tectonics in the Eastern Central Patagonian Cordillera: geochronological constraints and new field evidence     

Yves Lagabrielle  Manuel Surez  Jacques Malavieille  Diego Morata  Felipe Espinoza  Ren C. Maury  Bruno Scalabrino  Luis Barbero  Rita de la Cruz  Eduardo Rossello  Herv Bellon 《地学学报》2007,19(6):413-424

Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera‐Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (∼2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause‐and‐effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.  相似文献   

Direct dating of the Sete Lagoas cap carbonate (Bambuí Group,Brazil) and implications for the Neoproterozoic glacial events     

Marly Babinski  Lucieth Cruz Vieira  Ricardo I. F. Trindade 《地学学报》2007,19(6):401-406

The end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the São Francisco craton. Six samples from aragonite‐pseudomorph crystal‐rich facies, showing pristine textures and constant ⁸⁷Sr/⁸⁶Sr ratios around 0.7075, yielded a Pb–Pb isochron age of 740 ± 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low‐to‐moderate palaeolatitude of 20–30° for carbonate (and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long‐standing ‘Sturtian’ interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma.  相似文献   

A GIS-based WFD oriented typology of shallow micro-tidal soft bottom using wave exposure and turbidity mapping     

Jacek Andrzej Urbański  Gabriela GruszaNatalia Chlebus  Lucyna Kryla 《Estuarine, Coastal and Shelf Science》2008

Our GIS based project aims at producing a classification scheme to develop a typology of the bottom of the Bay of Gdansk in the southern Baltic. The typology was based on the abiotic factors which are used to define water body types by the European Water Framework Directive (WFD). Significance analysis of particular factors has shown that within the discussed area wave exposure seems to play the most important role. All other factors are to a greater or lesser degree correlated with these two. Taking into consideration the shallows and the varied coastline of the investigated area it was decided to make use of the SWAN numerical wave model to determine the influence of wave impact upon the bottom. The model was used to produce raster maps of orbital velocity near the bottom for each wind scenario. With the help of the GIS analysis the maps were turned into layers: the mean velocity and the maximum velocity at the bottom. To produce the layer of yearly amount of solar radiation a GIS model was built which main parameters were the layer of depth and three layers of turbidity for three seasons. The layers of the maximum orbital velocity and of the solar radiation at the bottom were then used in a classificatory procedure consisted in an iterative sequence of the three following steps: cluster formation, dendrogram analysis and classification using the maximum likelihood method. Ecological importance of the classification has been obtained by means of the aggregation of a part of classes based upon the statistics calculated for them within the GIS system with the help of the zonal function out of the following parameters: salinity, depth, mean and maximum orbital velocity at the bottom, temperature differences between warm and cold seasons, solar radiation, and type of sediments. The method proposed here makes it possible to produce high resolution thematic maps of the bottom even with incomplete data cover of the investigated area.  相似文献   

On using a generalized linear model to downscale daily precipitation for the center of Portugal: an analysis of trends and extremes     

Mário Pulquério  Pedro Garrett  Filipe Duarte Santos  Maria João Cruz 《Theoretical and Applied Climatology》2015,120(1-2):147-158

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Geotechnical Characterization by In situ and Lab Tests to the Back-Analysis of a Supported Excavation in Metro do Porto   总被引：1，自引：1，他引：0  

António Viana da Fonseca  Sara Rios Silva  Nuno Cruz 《Geotechnical and Geological Engineering》2010,28(3):251-264

This paper summarizes the geotechnical characterization conducted for the design and subsequent analysis of a strutted excavation in “Metro do Porto”. This region is geologically dominated by heterogeneous weathered granite masses with deep residual soil profiles. Local saprolitic soils exhibit, by their nature, a particular behavior characterized by very sensitive and weak relic micro-structures, due to their specific genesis. This study has included the interpretation of a significant volume of in situ test results, triaxial tests over undisturbed samples and monitoring data, giving rise to specific correlations between testing and design parameters. Real time monitoring enabled a back-analysis by FEM of a well instrumented section of the strutted excavation, which was calibrated taking into account the derived correlations and the deformability behavior of this specific geotechnical ambient. This geomaterial, although revealing very high initial stiffness values (for very small strain ranges) has shown low stiffness values for “medium to high” strain levels, reflecting a singular strong non-linearity in the stress-strain behavior.  相似文献   

Procedure for the selection of runout model parameters from landslide back-analyses: application to the Metropolitan Area of San Salvador, El Salvador   总被引：1，自引：1，他引：0  

José Cepeda  José Alexander Chávez  Celina Cruz Martínez 《Landslides》2010,7(2):105-116

The existing procedures for the selection of runout model parameters from back-analyses do not allow integrating different types of runout criteria and generally lack a systematic approach. A new method based on receiver operating characteristic (ROC) analyses and aimed at overcoming these limitations is herein proposed. The method consists of estimating discrete classifiers for every runout simulation associated with a set of model parameters. The set of parameters that yields the best prediction is selected using ROC metrics and space. The procedure is illustrated with the back-analyses of a rainfall-triggered debris flow that killed 300–500 people in the Metropolitan Area of San Salvador in 1982. The selected model parameters are used to estimate forward predictions for scenarios that correspond to different return periods. The proposed procedure may be useful in the assessment of areas potentially affected by landslides. In turn, this information can be used in the production or updating of land use plans and zonations, similar to that currently being carried out by the Office for Urban Planning of the Metropolitan Area of San Salvador in El Salvador.  相似文献   

Distribution and characteristics of marine habitats in a subpolar bay based on hydroacoustics and bed shear stress estimates—Potter Cove,King George Island,Antarctica     

Anne-Cathrin Wölfl  Chai Heng Lim  H. Christian Hass  Sebastian Lindhorst  Gabriela Tosonotto  Karsten Alexander Lettmann  Gerhard Kuhn  Jörg-Olaf Wolff  Doris Abele 《Geo-Marine Letters》2014,34(5):435-446

Marine habitats worldwide are increasingly pressurized by climate change, especially along the Antarctic Peninsula. Well-studied areas in front of rapidly retreating tidewater glaciers like Potter Cove are representative for similar coastal environments and, therefore, shed light on habitat formation and development on not only a local but also regional scale. The objective of this study was to provide insights into habitat distribution in Potter Cove, King George Island, Antarctica, and to evaluate the associated environmental processes. Furthermore, an assessment concerning the future development of the habitats is provided. To describe the seafloor habitats in Potter Cove, an acoustic seabed discrimination system (RoxAnn) was used in combination with underwater video images and sediment samples. Due to the absence of wave and current measurements in the study area, bed shear stress estimates served to delineate zones prone to sediment erosion. On the basis of the investigations, two habitat classes were identified in Potter Cove, namely soft-sediment and stone habitats that, besides influences from sediment supply and coastal morphology, are controlled by sediment erosion. A future expansion of the stone habitat is predicted if recent environmental change trends continue. Possible implications for the Potter Cove environment, and other coastal ecosystems under similar pressure, include changes in biomass and species composition.  相似文献   

Groundwater geochemistry of the Chihuahua City region in the Rio Conchos Basin (northern Mexico) and implications for water resources management     

Jürgen Mahlknecht  Axel Horst  Gabriela Hernández-Limón  Ramon Aravena 《水文研究》2008,22(24):4736-4751

The Chihuahua City region, located in the semiarid-arid northern highlands of Mexico, has experienced intensive groundwater abstraction during the last 40 years to meet water demands in the region. A geochemical survey was carried out to investigate the evolution from baseline to modern conditions of a 130-km flow path including the El Sauz–Chihuahua–Aldama–San Diego de Alcalá regions. The research approach included the use of major chemical elements, chlorofluorocarbons and environmental isotope (¹⁸O, ²H, ¹³C and ¹⁴C) tracers. Stable isotopes indicate that groundwater evolves from the evaporation of local rainfall and surface water. Groundwater located at the lower end of the flow section is up to 6000 years old and older groundwater in the order of 9000 years BP was found in a deep well located in the upper part of the flow system, implying contribution from a neighbour basin. The background groundwater chemistry upstream of Chihuahua City results from feldspar weathering. Beyond Chihuahua City the chemical conditions are strongly modified owing to disposal of sewage from public and industrial water supplies into the Rio Chuviscar, subsequent allocation of this water to agricultural irrigation areas and direct infiltration under the river bed. As a consequence, anions like chloride and sulphate are mainly related to surface sources. Nitrate is controlled in part by sewage from public supply and industry and in part by agricultural practices. Arsenic and fluoride are related to weathering of rock formations of local mineralized ranges and subsequent enrichment of the basin-fill by magmatic processes. The results of this study have implications for groundwater management in an arid region that depends entirely on groundwater for domestic, industrial and agricultural water consumption. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献