Early succession of micro‐periphyton communities in kelp bed and barren ground ecological systems          下载免费PDF全文

Roberto A. Uribe  Marco Ortiz  Aldo S. Pacheco  Rubén Araya 《Marine Ecology》2015,36(4):1415-1427

In shallow sublittoral rocky habitats of the Southeast Pacific, two conspicuous ecological systems exist; kelp beds dominated by large Laminariales algae, and barren grounds dominated by crustose coralline algae and sea urchins. The aim of this study was to examine the successional development of micro‐periphyton communities in both ecological systems using a colonization experiment conducted in Northern Chile. In both ecological systems, we installed replicated ceramic plates at 10 m depth and samples were taken after 1, 2, 4, 6, 8 and 14 days of exposure. Bacteria, diatoms, protozoans and small eukaryotes were identified, quantified and analysed. The succession of micro‐periphyton communities in both ecological systems followed a common pattern consisting of a net accumulation of functional groups and taxa over time; however, the total density of all groups was significantly higher in the kelp beds. In addition, the community structure of the developing micro‐periphytons was different and specific for each ecological system. Although previous studies have suggested that kelp beds and barren grounds are capable of switching from one state to the other without substantial changes in biodiversity, our results show that each of these ecological systems promotes its own successional development, suggesting that they are unique, self‐organized entities. This study is the first step towards an understanding of these ecological systems operating independently at this scale of organization.  相似文献   

Analysis of the nonlinear storage–discharge relation for hillslopes through 2D numerical modelling     

Melkamu Ali  Aldo Fiori  Giorgio Bellotti 《水文研究》2013,27(18):2683-2690

Storage–discharge curves are widely used in several hydrological applications concerning flow and solute transport in small catchments. This article analyzes the relation Q(S) (where Q is the discharge and S is the saturated storage in the hillslope), as a function of some simple structural parameters. The relation Q(S) is evaluated through two‐dimensional numerical simulations and makes use of dimensionless quantities. The method lies in between simple analytical approaches, like those based on the Boussinesq formulation, and more complex distributed models. After the numerical solution of the dimensionless Richards equation, simple analytical relations for Q(S) are determined in dimensionless form, as a function of a few relevant physical parameters. It was found that the storage–discharge curve can be well approximated by a power law function Q/(LK_s) = a(S/(L²(? ? θ_r)))^b, where L is the length of the hillslope, K_s the saturated conductivity, ? ? θ_r the effective porosity, and a, b two coefficients which mainly depend on the slope. The results confirm the validity of the widely used power law assumption for Q(S). Similar relations can be obtained by performing a standard recession curve analysis. Although simplified, the results obtained in the present work may serve as a preliminary tool for assessing the storage–discharge relation in hillslopes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3D adaptive tomography using Delaunay triangles and Voronoi polygons     

Gualtiero Böhm  Paolo Galuppo  Aldo Vesnaver 《Geophysical Prospecting》2000,48(4):723-744

The solutions of traveltime inversion problems are often not unique because of the poor match between the raypath distribution and the tomographic grid. However, by adapting the local resolution iteratively, by means of a singular value analysis of the tomographic matrix, we can reduce or eliminate the null space influence on our earth image: in this way, we get a much more reliable estimate of the velocity field of seismic waves. We describe an algorithm for an automatic regridding, able to fit the local resolution to the available raypaths, which is based on Delaunay triangulation and Voronoi tessellation. It increases the local pixel density where the null space energy is low or the velocity gradient is large, and reduces it elsewhere. Consequently, the tomographic image can reveal the boundaries of complex objects, but is not affected by the ambiguities that occur when the grid resolution is not adequately supported by the available raypaths.  相似文献   

Oxygen isotope variations in phosphate of biogenic apatites,II. Phosphorite rocks     

Aldo Shemesh  Yehoshua Kolodny  Boaz Luz 《Earth and Planetary Science Letters》1983,64(3):405-416

Phosphorites from sedimentary sequences ranging in age from Archaean to Recent were analysed for δ¹⁸O in both the PO₄ (δ¹⁸O_p) and CO₃ (δ¹⁸O_c) in the apatite lattice. The oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts. The use of the Longinelli and Nuti [8] temperature equation yields temperatures for Recent phosphorites that are in good agreement with those measured in the field. The δ¹⁸O_p values of ancient phosphorites decrease with increasing age. These changes with time are not likely to be due to post-depositional exchange. Changes in δ¹⁸O values of seawater and variations of temperature with time can account for the δ¹⁸O_p time trend, but the latter explanation is preferred. In Ancient phosphorites δ¹⁸O_c in structurally bound carbonate in apatite is not a reliable geochemical indicator.  相似文献   

Magma contamination by direct wall rock interaction: constraints from xenoliths from the walls of a carbonate-hosted magma chamber (Vesuvius 1944 eruption)     

Aldo Del Moro  Paolo Fulignati  Paola Marianelli  Alessandro Sbrana   《Journal of Volcanology and Geothermal Research》2001,112(1-4)

During the 1944 eruption of Vesuvius different types of xenoliths were ejected. They represent fragments of the walls of a low volume (<0.5 km³) shallow (3–4 km depth) magma chamber. The study of these xenoliths enables us to estimate the amount of contamination occurring at the boundary of a high-T alkaline magma chamber hosted in carbonate rocks. The process of contamination of the magma by carbonates can be modelled, using isotopic and chemical data, as a mixing between magma and marbles. Mass exchanges occur at the boundary between the crystallizing magma and marble wall rocks, where endoskarn forms. The contamination of the solidification front of the chamber is very limited. The solidification front and the skarn shell effectively isolate the interior of the magma chamber from new inputs of contaminants from the carbonate wall rocks. Therefore, the main volume of magma, hosted in the magma chamber, did not undergo any significant mass exchange with the wall rocks.  相似文献   

Precise, absolute earthquake location under Somma–Vesuvius volcano using a new three-dimensional velocity model     

Anthony Lomax  Aldo Zollo  Paolo Capuano  Jean Virieux 《Geophysical Journal International》2001,146(2):313-331

  相似文献   

Environmental history since 11,000 C yr B.P. of the northeastern Pampas, Argentina, from alluvial sequences of the Luján River     

Aldo R. Prieto  Adriana M. Blasi  Celina Fernández 《Quaternary Research》2004,62(2):146-161

Sedimentological, malacological, and pollen analyses from ¹⁴C-dated alluvial sections from the Luján River provide a detailed record of environmental changes during the Holocene in the northeastern Pampas of Argentina. From 11,200 to 9000 ¹⁴C yr B.P., both sedimentary and biological components suggest that the depositional environment was eutrophic, alkaline, and freshwater to brackish shallow water bodies without significant water circulation. During this time, bioclastic sedimentation was dominant and the shallow water bodies reached maximum development as the climate became more humid, suggesting an increase in precipitation. Short-term fluctuations in climate during the last stage of this interval may have been sufficient to initiate changes in the water bodies, as reduction of the volume alternated with periods of flooding. The beginning of the evolution of shallow swamps in the wide floodplain or huge wetlands was contemporaneous with a sea level lower than the present one. From 9000 and 7000 ¹⁴C yr B.P., mesotrophic, alkaline, brackish, probably anoxic swamps existed. Between 7000 and 3000 ¹⁴C yr B.P., anoxic calcareous swamps were formed, with subaerial exposure and development of the Puesto Berrondo Soil (3500-2900 ¹⁴C yr B.P.). A trend to a reduction of water bodies is recorded from 9000 to ca. 3000 ¹⁴C yr B.P., with a significant reduction after ca. 7000 ¹⁴C yr B.P. A shift to subhumid-dry climate after 7000 ¹⁴C yr B.P. appears to be the main cause. During this time, an additional external forcing toward higher groundwater levels was caused by Holocene marine transgression causing changes in the water bodies levels. The climate became drier during the late Holocene (ca. 3000 yr B.P.), when clastic sedimentation increased, under subhumid-dry conditions. Flood events increased in frequency during this time. From ca. A.D. 1790 to present, the pollen record reflects widespread disturbance of the vegetation during the European settlement.  相似文献   

Late and post-glacial history of meromictic Längsee (Austria), in respect to climate change and anthropogenic impact     

Roland Schmidt  Sybille Wunsam  Ursula Brosch  Jan Fott  Andrea Lami  Heinz Löffler  Aldo Marchetto  Harald W. Müller  Miroslava Pražáková  Bernd Schwaighofer 《Aquatic Sciences - Research Across Boundaries》1998,60(1):56-88

  相似文献   

Chemistry and critical loads of Alpine lakes in Canton Ticino (Southern Central Alps)     

Angela Boggero  Alberto Barbieri  Jacolien de Jong  Aldo Marchetto  Rosario Mosello 《Aquatic Sciences - Research Across Boundaries》1998,60(4):300-315

  相似文献   

High frequency strong ground motion modelling in the Catania area associated with the Ibleo-Maltese fault system     

Aldo Zollo  Antonio Emolo  André Herrero  Luigi Improta 《Journal of Seismology》1999,3(3):279-288

A hybrid statistical-deterministic approach has been applied to estimate strong ground motion parameters (PGA, spectral ordinates) in South-Eastern Sicily for a M = 7 earthquake. A number of 100 different rupture processes have been simulated along a composite fault system representing two segments of the Ibleo-Maltese fault scarp. Map at regional scale of mean PGA in the 0.5–20 Hz frequency band shows highest values (0.4–0.5 g) nearby and North of Catania, due to a dominant directivity effect. The COV parameter, which expresses the variability of PGA values as a function of source complexity, is higher in the region nearby and South of the town of Augusta, where, depending on the rupture history, rather large PGA values can be observed (>0.4 g). PGA attenuation curves suggest that an azimuthal variation could be related to the source extent and directivity. The response and pseudo acceleration spectra are computed for different sites in the town of Catania including an approximate 1D site response. Ground motion amplification effects at high frequency (5–20 Hz) are produced by thin shallow layer of soft clay, loose pyroclastites and fill. We observe small amplification effects, in the frequency ranges 2–3 Hz and 5–10 Hz, in sites where recent alluvia reach a thickness of some tens of meters. Otherwise, sites located on outcrops of massive lavas show moderate attenuation.  相似文献