Vertical structure of larval fish assemblages during diel cycles in summer and winter in the southern part of Bahía de La Paz, México     

Gerardo Aceves-Medina  Ricardo Saldierna-Martínez  Alejandro Hinojosa-Medina  Sylvia P.A. Jimnez-Rosenberg  Martín E. Hernndez-Rivas  Raúl Morales-vila 《Estuarine, Coastal and Shelf Science》2008,76(4):889-901

The effect of environmental variables on the vertical structure of larval fish assemblages in a tropical coastal lagoon was analyzed. Ichthyoplankton samples were collected from the near-bottom and surface strata near the mouth of a subtropical lagoon during contrasting seasonal conditions of temperature, photoperiod, light intensity, and tidal heights. During summer, larval fish assemblages had high species richness (R) and were dominated by tropical species. During winter, assemblages had lower R values and were dominated by subtropical and temperate species. Vertical distribution patterns of the taxa were determined by the interaction of environmental variables and behavior of each species to maintain their position in a stratum in the water column, or to achieve vertical migrations induced by environmental stimuli that, in this case, were thermal gradient, column water stratification, and intensity of light. Depth position and vertical migration of fish larvae, coupled with the flood and ebb tide conditions, played an important role in their retention and displacement toward the lagoon. Fish larvae with distribution restricted to the inner part of the inlet, such as Achirus mazatlanus, Etropus sp., and several gobies, were more abundant in the near-bottom stratum during the ebb tide, allowing them to avoid exportation, whereas those that could spawn outside, but depended on the inlet as a nursery area, were more abundant near the surface during flood tide, such as Abudefduf troschelii and Stegastes rectifraenum.  相似文献   

Urban hydrologic trend analysis based on rainfall and runoff data analysis and conceptual model calibration          下载免费PDF全文

Siao Sun  Sylvie Barraud  Flora Branger  Isabelle Braud  Hélène Castebrunet 《水文研究》2017,31(6):1349-1359

Urban stormwater is a major cause of urban flooding and natural water pollution. It is therefore important to assess any hydrologic trends in urban catchments for stormwater management and planning. This study addresses urban hydrological trend analysis by examining trends in variables that characterize hydrological processes. The original and modified Mann‐Kendall methods are applied to trend detection in two French catchments, that is, Chassieu and La Lechere, based on approximately 1 decade of data from local monitoring programs. In both catchments, no trend is found in the major hydrological process driver (i.e., rainfall variables), whereas increasing trends are detected in runoff flow rates. As a consequence, the runoff coefficients tend to increase during the study period, probably due to growing imperviousness with the local urbanization process. In addition, conceptual urban rainfall‐runoff model parameters, which are identified via model calibration with an event based approach, are examined. Trend detection results indicate that there is no trend in the time of concentration in Chassieu, whereas a decreasing trend is present in La Lechere, which, however, needs to be validated with additional data. Sensitivity analysis indicates that the original Mann‐Kendall method is not sensitive to a few noisy values in the data series.  相似文献   

Low‐P melting of metapelitic rocks and the role of H2O: Insights from phase equilibria modelling          下载免费PDF全文

Alfonso M. Sola  Pavlina Hasalová  Roberto F. Weinberg  Néstor O. Suzaño  Raúl A. Becchio  Fernando D. Hongn  Nilson Botelho 《Journal of Metamorphic Geology》2017,35(9):1131-1159

Water‐fluxed melting has long been thought to have a minor influence on the thermal and chemical structure of the crust. We report here on amphibolite facies metasedimentary rocks from the 490–450 Ma Famatinian Orogen, in northwest Argentina, that have undergone water‐fluxed incongruent biotite melting at relatively low temperature, which have produced and lost a significant volume of melt. The protoliths consist of the turbiditic Puncoviscana Formation (Neoproterozoic to Early Cambrian). The field area exhibits a condensed metamorphic field gradient, from greenschist to amphibolite facies suprasolidus conditions, recording a low pressure almost isobaric path, reaching peak conditions estimated at 700°C at 4 kbar. Thermodynamic modelling in the MnNCKFMASHTO system is applied to investigate melting at such low pressure as a function of water content. Calculations using a typical turbidite composition show how small amounts of added free H₂O may increase significantly the melt fraction with little or no change in either the melt or residual phase compositions. They indicate negligible difference in normative An–Ab–Or proportions and ferromagnesian contents between melts derived by dehydration and water‐fluxed melts. The same is true for the content of H₂O dissolved in melts, which remains constant and the melt produced is granitic whether or not aqueous fluids are present. Thus, neither the residue nor the melt composition are indicators of the presence of aqueous fluids during anatexis. Recognizing the impact of small additions of H₂O to an anatectic terrane may therefore be difficult. The most significant change related to water‐fluxing is the relative proportions of minerals and melt fraction, rather than the actual mineral assemblage. The modal proportion of feldspar decreased while those of cordierite and biotite increased in the residual assemblages, as <5 mol.% of free H₂O was added. The impact of this addition is to more than double the proportion of water‐undersaturated melt to 25–30 mol.%. We have also developed a simple way to estimate how much melt a residual rock has lost, if the compositional trends of the protoliths are known. In summary, we find that even though the addition of small amounts of free H₂O impacts significantly on rock fertility, there is little obvious record in the field. The combined application of careful petrological investigation and thermodynamic modelling is the key to identify the influence of aqueous fluids, and exploit systems that became open not only to fluid influx but also to the extraction of melt.  相似文献   

New chronology and extended palaeoenvironmental data to the 1975 loess profile of Madaras brickyard,South Hungary     

Pál Sümegi  Sándor Gulyás  Dávid Molnár  Gábor Bozsó  István Fekete  László Makó  Péter Cseh  Mihály Molnár  Balázs P. Sümegi  Peter Almond  Christian Zeeden  Tünde Törőcsik  Janina J. Nett  András Markó  Frank Lehmkuhl 《第四纪科学杂志》2021,36(8):1364-1381

The 10 m thick Madaras loess–palaeosol profile is one of the Hungarian outcrops that yielded Upper Palaeolithic artefacts in 1966. To clarify the nature of the deposits and establish a reliable litho- and chronostratigraphy, a profile was opened and sampled at 25 cm intervals on the northern side of the brickyard in 1975. Analyses focused on grain size, carbonate content and the mollusc fauna. The chronology was based on the mollusc composition and a single date from the archaeological layer at the depth of ca 7 m below the surface. The 1975 profile was destroyed by mining but the reposited samples allowed an extended analysis of this important Marine Isotope Stage 2 record to which archaeological features were directly assigned. A new absolute chronology was built based on 11 ¹⁴C dates. Environmental magnetic, geochemical and palaeoecological investigations allowed a refined view of site evolution with reliable chronology for the Last Glacial Maximum. Our results corroborated those of previous investigations done on other coeval loess–palaeosol sequences of the Southern Carpathian Basin. This also allowed for a temporal correlation to another local record with the published high-resolution chronology of the same brickyard and enabled modelling of local-scale heterogeneity of the environment in the long run.  相似文献   

Multi-objective fitting of concentration-discharge relationships     

José Manuel Tunqui Neira  Vazken Andréassian  Gaëlle Tallec  Jean-Marie Mouchel 《水文研究》2021,35(11):e14428

Concentration–discharge ($C–Q$) relationships are widely used to assess the link between hydrological and biogeochemical processes at the catchment scale. $C–Q$ relationships are mainly calibrated using mono-objective methods to represent, either concentrations or discharge-weighted concentrations (i.e., load). Based on its wide use in hydrological modelling, we test a multi-objective calibration for the $C–Q$ relationship parameters, using both concentration and load, and compare it to a mono-objective calibration applied on either concentrations or load. This work is carried out on a high-frequency dataset (ORACLE-Orgeval Observatory, France). Our findings show that the multi-objective calibration yield a better representation of $C–Q$ relationships parameters during the high and low-flow events. The multi-objective calibration can be used for all forms of $C–Q$ relationships and avoids issues of under-representation of dilution processes characterized by high-discharge, low-concentration periods.  相似文献   

Coastal aquifer response to extreme storm events in Emilia‐Romagna,Italy          下载免费PDF全文

Beatrice M.S. Giambastiani  Nicolò Colombani  Nicolas Greggio  Marco Antonellini  Micòl Mastrocicco 《水文研究》2017,31(8):1613-1621

With global warming and sea level rise, many coastal systems will experience increased levels of inundation and storm flooding, especially along sandy lowland coastal areas, such as the Northern Adriatic coast (Italy). Understanding how extreme events may directly affect groundwater hydrology in shallow unconfined coastal aquifers is important to assess coastal vulnerability and quantify freshwater resources. This study investigates shallow coastal aquifer response to storm events. The transitory and permanent effects of storm waves are evaluated through the real time monitoring of groundwater and soil parameters, in order to characterize both the saturated and unsaturated portions of the coastal aquifer of Ravenna and Ferrara (southern Po Delta, Italy). Results highlight a general increase in hydraulic head and soil moisture, along with a decrease in groundwater salinity and pore water salinity due to rainfall infiltration during the 2 days storm event. The only exceptions are represented by the observation wells in proximity to the coastline (within 100 m), which recorded a temporary increase in soil and water salinity caused by the exceptional high waves, which persist on top of the dune crest during the storm event. This generates a saline plume that infiltrates through the vadose zone down to the saturated portion of the aquifer causing a temporary disappearance of the freshwater lens generally present, although limited in size, below the coastal dunes. Despite the high hydraulic conductivity, the aquifer system does not quickly recover the pre‐storm equilibrium and the storm effects are evident in groundwater and soil parameters after 10 days past the storm overwash recess.  相似文献   

地理信息系统中时空多维数据可视化技术研究   总被引：23，自引：0，他引：23  

李红旮  崔伟宏 《遥感学报》1999,3(2):157-163

将科学可视化技术应用于地理信息系统之中,增强地理信息系统对时空多维数据的显示,处理胆当前的研究热点之一。通过对现有地理数据组织,显示简便概述的基础上,提出一种基于体素的时空多维数据组织方式。并通过二维,三维显示及动画形式的研究,从技术上对科学可视化与地理信息系统的结合进行初步的探索。  相似文献   

Detailed Study of Three Contiguous Segments of the Mid-Atlantic Ridge,South of the Azores (37° N to 38°30′ N), Using Acoustic Imaging Coupled with Submersible Observations     

Ondréas  Hélène  Fouquet  Yves  Voisset  Michel  Radford-Knoery  Joël 《Marine Geophysical Researches》1997,19(3):231-255

Using a new tool of seafloor characterisation (sonar images from FARA-SIGMA cruise; Needham et al., 1992), coupled with submersible observations (DIVA1 cruise) we compare, at different scales of observation, three contiguous segments of the Mid-Atlantic Ridge, South of the Azores Triple Junction, between 37° N and 38°30 N.The two northernmost segments (38°20 N and Menez-Gwen) show unusual morphological features for the MAR; the rift valley is absent and the present-day magmatism is focused on shallow axial volcanoes. On the third segment (Lucky Strike), the morphology is the one usually found on the MAR. On the Menez-Gwen and 38°20 N segments, volcanic constructional activity can obliterate, during periods of high magmatic supply, the morphology inherited from tectonic activity. The dive results constrain the recent evolution of each segment and show that a temporal variability in volcanic dynamics exists. On the three segments, outcrops of eruptive lavas alternate with large areas of explosive volcanic ejecta. This cycle in volcanic activity is influenced by changes in water depth, both spatially (i.e. between segments) and temporally (i.e. for the same segment through time).Each segment has known a specific history in its accretionary processes with a succession of tectonic and volcanic predominance and changes in its volcanic phases between volcanic ejecta and effusive dynamics.The hydrothermal activity is focused at the central part of each segment and is controlled by the presence of fresh lava and major tectonic features.  相似文献   

Rotation of a rigid satellite with a fluid component: a new light onto Titan’s obliquity     

Gwenaël Boué  Nicolas Rambaux  Andy Richard 《Celestial Mechanics and Dynamical Astronomy》2017,129(4):449-485

We revisit the rotation dynamics of a rigid satellite with either a liquid core or a global subsurface ocean. In both problems, the flow of the fluid component is assumed inviscid. The study of a hollow satellite with a liquid core is based on the Poincaré–Hough model which provides exact equations of motion. We introduce an approximation when the ellipticity of the cavity is low. This simplification allows to model both types of satellite in the same manner. The analysis of their rotation is done in a non-canonical Hamiltonian formalism closely related to Poincaré’s “forme nouvelle des équations de la mécanique”. In the case of a satellite with a global ocean, we obtain a seven-degree-of-freedom system. Six of them account for the motion of the two rigid components, and the last one is associated with the fluid layer. We apply our model to Titan for which the origin of the obliquity is still a debated question. We show that the observed value is compatible with Titan slightly departing from the hydrostatic equilibrium and being in a Cassini equilibrium state.  相似文献   

The Artificial Earth Satellite Motion in an Oblate,Rotating Atmosphere with Symmetrical Diurnal Effect     

L. Burs Deva  Liceul Minier  .Pl 《Astronomische Nachrichten》1982,303(4):269-275

The equations describing the disturbed motion of an artificial Earth satellite in the atmosphere are integrated by using a new variable instead of the true anomaly. The atmospheric flattening and rotation, the linear variation of the density scale height with the altitude, the symmetrical diurnal effect and the variation of its amplitude with the heigth are taken into account. Approximate formulae for the perturbations in all the orbital elements over a revolution of the satellite are given.  相似文献