Long-Term Effects of Tidal Exclusion on Salt Marsh Plain Species at Estero de Punta Banda,Baja California     

Silvia E. Ibarra-Obando  Miriam Poumian-Tapia  Hem Nalini Morzaria-Luna 《Estuaries and Coasts》2010,33(3):753-768

Disturbance is an important factor influencing plant species composition and diversity. We addressed changes in plant composition and soil characteristics in Estero de Punta Banda, Baja California, Mexico following 22 years of disturbance by tidal exclusion. Currently, sediments in the non-tidal site are dry, 26 ± 1% moisture, and hypersaline, 143 ± 12; while those at the tidal marsh are wet, 36.2 ± 1% moisture, with 40.3 ± 2.6 salinity. The non-tidal site has lost seven species including annuals, short- and long-lived perennials, ephemerals, and parasites. Current dominants are the perennials Batis maritima and Sarcocornia pacifica. Average species richness at the non-tidal site is 4.4 ± 0.32 vs.10 ± 0.18 species per square meter at the tidal site. Average species diversity index is lower at the diked area. The general biodiversity loss that results from tidal exclusion in arid estuaries, contrasts with the species-rich communities that develop in diked humid-climate estuaries.  相似文献   

Stochastic micromechanical model of the deterioration of asphalt mixtures subject to moisture diffusion processes     

Silvia Caro  Eyad Masad  Mauricio Sánchez‐Silva  Dallas Little 《国际地质力学数值与分析法杂志》2011,35(10):1079-1097

The deleterious effect of moisture in the microstructure of asphalt mixtures, usually referred to as moisture damage, has been recognized as a main cause of early deterioration of asphalt pavements. The initiation and evolution of moisture‐related deterioration is strongly influenced by the internal air void structure of asphalt mixtures. Despite its importance, the majority of works conducted on the micromechanical modeling of asphalt mixtures overlook the role of the air void structure, mainly because of its high complexity and variability. This paper explores the influence of air void variability on the performance of asphalt mixtures subjected to moisture diffusion processes. A stochastic modeling technique based on random field theory was used to generate internal distributions of physical and mechanical properties of the asphalt matrix of the mixture that depend on probable air voids distributions. The analysis was conducted by means of a coupled numerical micromechanical model of moisture damage. The results showed that the variability and distribution of air voids are decisive in determining the moisture‐dependent performance of asphalt mixtures. Furthermore, it was also shown that a stochastic characterization of the diverse air void configurations is a feasible and useful approach to better represent and understand mechanically related deterioration processes in asphalt mixtures. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Glaciovolcanic landsystems and large-scale glaciotectonic deformation along the Brekknafjöll–Jarlhettur,Iceland     

Matthew R. Bennett  David Huddart  Silvia Gonzalez 《Quaternary Science Reviews》2009,28(7-8):647-676

This paper documents the glaciovolcanic landsystem of the Brekknafjöll–Jarlhettur ridge in Central Iceland. Glaciolacustrine diamict is found beneath, and in association with, a complex assemblage of pillow lava, lava breccias and hyaloclastites. Three depositional environments are identified: glaciolacustrine fan, pillow lava dome, and hyaloclastite fan. These subaqueous environments occurred both simultaneously and at different times along the volcanic fissures which underlie the ridge and have given rise to a complex facies architecture. This facies architecture provides evidence that the ridge evolved in a time transgressive fashion during several episodes of volcanism, some of which may have been punctuated by periods of ice erosion. Associated with the ridge are large-diapiric folds in diamict and gravel which form by the loading and lateral displacement of saturated diamict beneath the developing volcanic pile. A depositional model is presented which emphasises the glaciolacustrine component and the time transgressive nature of the glaciovolcanic landsystem. Much of the eruption occurred in subglacial to englacial lakes or vaults, which were probably linked by water and sediment exchange. The initial subglacial vaults appear to have extended beyond the fissure limits and were infilled by glaciolacustrine diamicts, subaqueous outwash and the eruption of pillow lava. This was followed by the eruption of hyaloclastite sand and breccia forming an elongated fan.  相似文献   

Organic matter in sediments of canyons and open slopes of the Portuguese,Catalan, Southern Adriatic and Cretan Sea margins     

Antonio Pusceddu  Silvia Bianchelli  Miquel Canals  Anna Sanchez-Vidal  Xavier Durrieu De Madron  Serge Heussner  Vasilios Lykousis  Henko de Stigter  Fabio Trincardi  Roberto Danovaro 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(3):441-457

We describe the quantitative and compositional (phytopigment, protein, carbohydrate and lipid) patterns of sedimentary organic matter along bathymetric gradients in seven submarine canyons and adjacent open slopes located at four European regions: one along the NE Atlantic and three along the Mediterranean continental margins. The investigated areas are distributed along a putative longitudinal gradient of decreasing primary production from the Portuguese (northeastern Atlantic Ocean), to the Catalan (western Mediterranean Sea), Southern Adriatic (central Mediterranean Sea) and Southern Cretan (eastern Mediterranean Sea) margins. Sediment concentrations of organic matter differed significantly between the Portuguese margin and the Mediterranean regions and also from one study area to the other within the Mediterranean Sea. Differences in quantity and composition of sediment organic matter between canyons and open slopes were limited and significant only in the eutrophic Portuguese margin, where the differences were as large as those observed between regions (i.e. at the mesoscale). These results suggest that the overall trophic status of deep margin sediments is controlled mostly by the primary productivity of the overlying waters rather than by the local topography. Moreover, we also report that the quantity and nutritional quality of sediment organic matter in canyons and adjacent open slopes do not show any consistent depth-related pattern. Only the Nazaré and Cascais canyons in the Portuguese margin, at depths deeper than 500 m, displayed a significant accumulation of labile organic matter. The results of our study underline the need of further investigations of deep margins through sampling strategies accounting for adequate temporal and spatial scales of variability.  相似文献   

Distribution patterns of living benthic foraminifera from Cap Breton canyon,Bay of Biscay: Faunal response to sediment instability     

Silvia Hess  Frans J. Jorissen 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1555-1578

Analysis of living (Rose Bengal-stained) benthic foraminifera in 13 multicorer samples taken along the Cap Breton canyon (Bay of Biscay) revealed that the combination of organic-rich material and sediment instability provides very specific benthic ecosystem conditions. The active canyon hosts different foraminiferal assemblages that appear to be determined by different types and frequencies of environmental disturbance at the sites. Most of them are strongly dominated by shallow-infaunal living taxa that combine a tolerance for low-quality organic matter with a high reproductive potential. Foraminiferal assemblages characterized by high densities, very superficially living taxa and strong dominance of bolivinids and buliminids, follow a poor pioneer fauna dominated by Technitella melo. These assemblages are observed in the narrow canyon axis, where frequent sediment resuspension occurs and affects habitat stability. Assemblages studied from sites outside the canyon axis are still dominated by shallow-infaunal species but show lower foraminiferal densities and higher diversities. Deep-infaunal taxa are only present in some inner meanders and more distal stations. These assemblages are typical for ecological niches that are relatively stable and unaffected by re-sedimentation processes. They have attained a more advanced stage of ecosystem stability. They are influenced by neither lateral sediment nor enriched organic matter input.  相似文献   

A simple but effective cellular automaton for earthquakes   总被引：1，自引：0，他引：1  

Silvia Castellaro  Francesco Mulargia 《Geophysical Journal International》2001,144(3):609-624

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Composition and transport of settling particles in Lake Zurich: relative importance of vertical and lateral pathways     

Erich Wieland  Peter Lienemann  Silvia Bollhalder  Alfred Lück  Peter H. Santschi 《Aquatic Sciences - Research Across Boundaries》2001,63(2):123-149

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Radon anomalies and volcanic eruptions   总被引：1，自引：0，他引：1  

Paolo Gasparini  Marta Silvia Maria Mantovani   《Journal of Volcanology and Geothermal Research》1978,3(3-4)

A well-documented case of ²²²Rn anomaly preceding the eruptive activity of Karymsky volcano (Kamchatka) was recently reported in the literature. Stimulated by this example, we have attempted to utilize the available data on radon emanation from rocks, its solubility, and its circulation in waters to discuss how a ²²²Rn anomaly can be produced by magma approaching the surface. It is shown that the most likely process of radon release is the flushing of gases through pore fluids. Heating of extensive fracture surfaces by high-temperature gases may also be important. In order to survive in detectable amounts after moving distances greater than a few meters, radon must be transported by fast-moving fluids, such as those rising toward the surface through a fracture or in the ascending limbs of fluids convecting in very porous rocks under high temperature gradients. The pattern observed at Karymsky volcano is interpreted on the basis of these relations.  相似文献   

Eruptive dynamics and caldera collapse during the Onano eruption, Vulsini, Italy     

Danilo M. Palladino  Silvia Simei 《Bulletin of Volcanology》2005,67(5):423-440

The Onano explosive eruption of the Latera Volcanic Complex (Vulsini Volcanoes, Quaternary potassic Roman Comagmatic Region, Italy) provides an interesting example of multiple changes of eruptive style that were concomitant with a late phase of collapse of the polygenetic Latera Caldera. This paper reports a reconstruction of the event based on field analysis, laboratory studies of grain size and density of juvenile clasts, and re-interpretation of available subsurface geology data. The Onano eruption took place in a structurally weak area, corresponding to a carbonate substrate high bordered by the pre-existing Latera caldera and Bolsena volcano-tectonic depression, which controlled the ascent and eruption of a shoshonitic-phonotephritic magma through intersecting rim fault systems. Temporal changes of magma vesiculation, fragmentation and discharge rate, and consequent eruptive dynamics, were strongly controlled by pressure evolution in the magma chamber and changing vent geometry. Initially, pumice-rich pyroclastic flows were emplaced, followed by spatter- and lithic-rich flows and fallout from energetic fire-fountaining. The decline of magma pressure due to the partial evacuation of the magma chamber induced trapdoor collapse of the chamber roof, which involved part of the pre-existing caldera and external volcano slopes and eventually led to the present-day caldera. The widening of the vent system and the emplacement of the main pyroclastic flow and associated co-ignimbrite lag breccia marked the eruption climax. A sudden drop of the confining pressure, which is attributed to a pseudo-rigid behaviour of the magma chamber wall rocks during a phase of rapid magma drainage, led to extensive magma vesiculation and fragmentation. The disruption of the magma chamber roof and waning magma pressure in the late eruption stage favoured the explosive interaction of residual magma with groundwater from the confined carbonate aquifer. Pulsating hydrostatic and magma pressures produced alternating hydromagmatic pyroclastic surges, strombolian fallout and spatter flows.  相似文献   

Un réseau fluviatile d'âge Burdigalien terminal dans le Sud-Est de la France : remplissage,extension, âge,implications     

David Besson  Olivier Parize  Jean-Loup Rubino  Jean-Pierre Aguilar  Marie-Pierre Aubry  Bernard Beaudoin  William A. Berggren  Georges Clauzon  Philippe Crumeyrolle  Yann Dexcoté  Nicolas Fiet  Silvia Iaccarino  Gonzalo Jiménez-Moreno  Cécile Laporte-Galaa  Jacques Michaux  Katharina von Salis  Jean-Pierre Suc  Jean-Yves Reynaud  Roland Wernli 《Comptes Rendus Geoscience》2005,337(12):1045-1054

An integrated study combining facies analysis, multiple group biostratigraphy, identification of depositional sequences and mapping has been conducted on the Miocene Molasse Basin of the external Alps (southeastern France). The filling of the basin is described as resulting from a succession of fluvial incisions subsequently filled during marine transgressions. The major incision is dated as Latest Burdigalian and the major transgression as Langhian. This revised interpretation of the Miocene physiographic evolution of the Molasse Basin implies a re-examination of previous stratigraphic correlations within the basin. To cite this article: D. Besson et al., C. R. Geoscience 337 (2005).  相似文献