Evidence of distinct contaminant transport patterns in rivers using tracer tests and a multiple domain retention model     

Andrea Bottacin-Busolin  Andrea Marion 《Advances in water resources》2011,34(6):737-746

Solute transport in rivers is controlled by surface hydrodynamics and by mass exchanges with distinct retention zones. Surface and hyporheic retention processes can be accounted for separately in solute transport models with multiple storage compartments. In the simplest two component model, short term storage can be associated to in-channel transient retention, e.g. produced by riparian vegetation or surface dead zones, and the long-term storage can be associated to hyporheic exchange. The STIR (Solute Transport In Rivers) multiple domain transport model is applied here to tracer test data from three very different Mediterranean streams with distinctive characteristics in terms of flow discharge, vegetation and substrate material. The model is used with an exponential residence time distribution (RTD) to represent surface storage processes and two distinct modeling closures are tested to simulate hyporheic retention: a second exponential RTD and a power-law distribution approximating a known solution for bedform-induced hyporheic exchange. Each stream shows distinct retention patterns characterized by different timescales of the storage time distribution. Both modeling closures lead to very good approximations of the observed breakthrough curves in the two rivers with permeable bed exposed to the flow, where hyporheic flows are expected to occur. In the one case where the occurrence of hyporheic flows is inhibited by bottom vegetation, only the two exponential RTD model is acceptable and the time scales of the two components are of the same magnitude. The significant finding of this work is the recognition of a strong signature of the river properties on tracer data and the evidence of the ability of multiple-component models to describe individual stream responses. This evidence may open a new perspective in river contamination studies, where rivers could possibly be classified based on their ability to trap and release pollutants.  相似文献   

The effects of UVR irradiance and spectral composition on yellow perch (<Emphasis Type="Italic">Perca flavescens</Emphasis>) larvae survival     

Véronique Boily  Andrea Bertolo  Pierre Magnan  Maria-Grazia Martinoli  Hélène-Marie Thérien 《Aquatic Sciences - Research Across Boundaries》2011,73(3):345-354

The purpose of this study was to determine experimentally the effects of the quality (UV-A/UV-B ratio) and quantity (irradiance) of natural ultraviolet radiation (UVR) on the survival of yellow perch (Perca flavescens) larvae and on the oxidative stress in their cytoplasm, estimated by the activity of the superoxide dismutase (SOD). We also estimated the potential accumulation of photodamage in DNA by using UV dosimeters. Freshly-hatched yellow perch and UV dosimeters were incubated in controlled conditions under a factorial combination of selective and non-selective filters offering different levels of UVR protection and exposed to natural solar light. Larval survival was inversely related to the UVR intensity gradient, and responded similarly to the presence of both UV-A and UV-B or UV-A only. In contrast, the responses of SOD activity and UV dosimeter were stronger in the presence of both UV-A and UV-B than UV-A only, leading to a partial mismatch with the results on survival. Our results, obtained under natural solar light, suggest that incident UV-A radiation, despite its lower energy per unit photon than UV-B, could be a serious threat for yellow perch larvae. They also show that UV dosimeters and SOD activity predict only some components of UVR risk for yellow perch larvae. The partial mismatch between UV dosimeters results and larval survival cautions against the use of UV dosimeters alone as a proxy for UVR risk in the field.  相似文献   

Long-term solar activity influences on South American rivers     

Pablo J.D. Mauas  Andrea P. Buccino  Eduardo Flamenco 《Journal of Atmospheric and Solar》2011,73(2-3):377-382

River streamflows are excellent climatic indicators since they integrate precipitation over large areas. Here we follow up on our previous study of the influence of solar activity on the flow of the Paraná River, in South America. We find that the unusual minimum of solar activity in recent years have a correlation on very low levels in the Paraná's flow, and we report historical evidence of low water levels during the Little Ice Age. We also study data for the streamflow of three other rivers (Colorado, San Juan and Atuel), and snow levels in the Andes. We obtained that, after eliminating the secular trends and smoothing out the solar cycle, there is a strong positive correlation between the residuals of both the Sunspot Number and the streamflows, as we obtained for the Paraná. Both results put together imply that higher solar activity corresponds to larger precipitation, both in summer and in wintertime, not only in the large basin of the Paraná, but also in the Andean region north of the limit with Patagonia.  相似文献   

A decision support system for post-earthquake reliability assessment of structures subjected to aftershocks: an application to L��Aquila earthquake, 2009     

Fatemeh Jalayer  Domenico Asprone  Andrea Prota  Gaetano Manfredi 《Bulletin of Earthquake Engineering》2011,9(4):997-1014

The post-earthquake assessment of existing structures can be further complicated by the progressive damage induced by the occurrence of a sequence of aftershocks. This work presents a simple methodology for the calculation of the probability of exceeding a certain limit state in a given interval of time. The time-decaying mean daily rate of occurrence of significant aftershock events is modeled by employing a site-specific aftershock model for the L??Aquila 2009 aftershock sequence (central Italy). The number of aftershock events occurring in a given interval of time elapsed after the main event is modeled using a non-homogenous Poisson model. An equivalent single-degree of freedom structure with cyclic stiffness degradation is used in order to evaluate the progressive damage caused by a sequence of aftershock events. Given the time history of the main-shock and the residual damage caused by it, the probability of exceeding a set of discrete limit states in a given interval of time is calculated. Of particular importance is the time-variant probability of exceeding the limit state in a 24-h (a day) interval of time which can be used as a proxy for the life-safety considerations regarding the re-occupancy of the structure and to complement the results of visual inspections for prioritizing the emergency operations. The method presented herein can also be used in an adaptive manner, progressively conditioned on the time-histories of aftershock events following the main-shock and on the corresponding residual damage caused by them.  相似文献   

Autonomous underwater vehicle teams for adaptive ocean sampling: a data-driven approach   总被引：1，自引：1，他引：0  

Andrea?MunafòEmail author  Enrico?Simetti  Alessio?Turetta  Andrea?Caiti  Giuseppe?Casalino 《Ocean Dynamics》2011,61(11):1981-1994

The current technological developments in autonomous underwater vehicles (AUVs) and underwater communication have nowadays allowed to push the original idea of autonomous ocean sampling network even further, with the possibility of using each agent of the network not only as an operative component driven by external commands (model-driven) but as a reactive element able to act in response to changing conditions as measured during the exploration (data-driven). With this paper, we propose a novel data-driven algorithm for AUVs team for adaptive sampling of oceanic regions, where each agent shares its knowledge of the environment with its teammates and autonomously takes decision in order to reconstruct the desired oceanic field. In particular, sampling point selection is made in order to minimize the uncertainty in the estimated field while keeping communication contact with the rest of the team and avoiding to repeatedly sampling sub-regions already explored. The proposed approach is based on the use of the emergent behaviour technique and on the use of artificial potential functions (interest functions) to achieve the desired goal at the end of the mission. In this way, there is no explicit minimization of a cost functional at each decision step. The oceanic field is reconstructed by the application of radial basis functions interpolation of irregularly spaced data. A simulative example for the estimation of a salinity field with sea data obtained using the Mediterranean Sea Forecasting System is shown in the paper, in order to investigate the effect of the different uncertainty sources, including sea currents, on the behaviour of the exploration team and ultimately on the reconstruction of the salinity field.  相似文献   

Sb–Hg ore deposit distribution controlled by brittle structures: The case of the Selvena mining district (Monte Amiata, Tuscany, Italy)     

Andrea Brogi  Lorenzo Fabbrini  Domenico Liotta 《Ore Geology Reviews》2011,41(1):35-48

This paper deals with the tectonic control on the hydrothermal system that gave rise to Sb–Hg ore deposits in the Monte Amiata area that was one of the most relevant mining district for the exploitation of mercury in Italy. The study area (Selvena mining district) is located in southern Tuscany (inner Northern Apennines) one of the most important mineralized area in the western Mediterranean region. Southern Tuscany was severely affected by Middle–Late Miocene low-angle normal faults, later dissected by Pliocene–Pleistocene faults, coeval magmatism (Late Miocene–Pleistocene) and hydrothermal activity (Pliocene–Present). The Selvena mining district is located south of Middle Pleistocene Monte Amiata volcanic complex. Our structural and kinematic study is based on the integration among fieldwork, borehole and mine data. The results highlight two Pleistocene–Holocene left-lateral transtensional shear zones linked by normal faults, defining a coeval pull-apart structure. Here, the Sb–Hg mineralization, transported by meteoric hydrothermal fluids mainly, is particularly diffuse and concentrated in the cataclasites and in damage zones of the normal faults. Furthermore, a widespread mineralization also occurs in the cataclasites of Miocene low-angle normal faults. Mine evidence suggests that ore-bearing fluids percolated through structural conduits located along the fault planes and resulting parallel to the intermediate stress axis. Geological structures and ore deposit distribution are related to a single hydrothermal circuit, with meteoric water channelled to depth through conduits parallel to the intermediate stress axis of the transcurrent shear zones; then, hydrothermal fluids mainly ascended through the almost vertical deformation zones located at the intersection between normal and strike-slip faults. Thus, hydrothermal fluids permeated also the Middle–Late Miocene cataclasites. This study shed light on the relationships between geological structures and mineralization in southern Tuscany and underlines the importance to investigate mine areas to understand hydrothermal fluids path.  相似文献   

Cretaceous-Eocene compression in the central Southern Alps (N Italy) inferred from Ar/Ar dating of pseudotachylytes along regional thrust faults     

Stefano Zanchetta  Paolo D’Adda  Andrea Zanchi  Valentina Barberini  Igor M. Villa 《Journal of Geodynamics》2011

The integration of structural analyses with ⁴⁰Ar/³⁹Ar dating of fault-related pseudotachylytes provides time constraints for the reconstruction of the Alpine evolution of the central portion of the South Alpine orogenic wedge. In the northern sector of the belt a Variscan basement is stacked southward on the Permian to Mesozoic cover along regional faults (Orobic and Porcile thrusts). Fault zones, slightly postdating a first folding event of Alpine age, experienced a complex evolution through the ductile and brittle deformation regime, showing greenschist facies mylonites overprinted by a penetrative cataclastic deformation. Generation of fault-related pseudotachylyte veins marks the onset of brittle conditions, lasting up to the youngest episodes of fault activity. ⁴⁰Ar/³⁹Ar dating of the pseudotachylyte matrix of 9 samples give two separated age clusters: Late Cretaceous (80–68 Ma) and latest Palaeocene to Middle Eocene (55–43 Ma). These new data provide evidence that the pre-Adamello evolution of the central Southern Alps was characterised by the superposition of different tectonic events accompanying the exhumation of the deepest part of the belt through the brittle–ductile transition. The oldest pseudotachylyte ages demonstrate that south-verging regional thrusting in the central Southern Alps was already active during the Late Cretaceous, concurrently with the development of a synorogenic foredeep basin where the Upper Cretaceous Lombardian Flysch was deposited.  相似文献   

Rock magnetic,petrographic and dielectric characterization of prehistoric Amerindian potsherds from Venezuela     

Myriam Andrea Rada Torres  Vincenzo Costanzo-Álvarez  Milagrosa Aldana  Nery Suárez  Corina Campos  Maria Magdalena Mackowiak-Antczak  María Carmela Brandt 《Studia Geophysica et Geodaetica》2011,55(4):717-736

Rock magnetic, petrographic and dielectric analyses were carried out, in a number of archeological ceramic potsherds, in order to characterize the different manufacturing techniques used by Prehistoric Venezuelan Amerindian potters. Samples were excavated in 7 Venezuelan islands and ascribed to distinct cultural groups on purely stylistic grounds (i.e. Valencioide, Ocumaroide, Dabajuroide and Unknown). Mean coercivity values were determined through a direct signal analyses (DSA) applied to isothermal remanent magnetization (IRM) acquisition curves. Logarithmic plots of these mean coercivities are the best quantitative means to classify diverse ceramics. The mean coercivity values seem to group the samples according to the manufacturing development. These values also seem to discriminate the samples provenance, indeed, this plot displays a good grouping of data for samples presumably manufactured by the same culture but excavated at different locations. Thermomagnetic cycles supply helpful information about original ceramic firing conditions. The irreversibility parameter (IP) for thermomagnetic curves (heating and cooling), serves as an indicator of the amount of organic matter burnt during original pottery firing. The IP for a number of pottery samples from Venezuelan islands and mainland, with ages ranging between 300 BC to 1500 AD, might suggest a possible increasing trend in time towards the complete reversibility line of IP = 0. Most samples, independently of age and cultural group, have IP values that suggest that most open fires, used by primitive Venezuelan Amerindian potters, had enough ventilation and oxidizing atmospheres. A scatter plot of maximum current depolarization temperatures versus natural remanent magnetization (NRM) suggests a complex non-linear relationship between these two parameters most likely due to the fact that both, dielectric and rock magnetic data, are linked to pore-related features.  相似文献   

Far-zone gravity field contributions corrected for the effect of topography by means of molodensky’s truncation coefficients   总被引：1，自引：0，他引：1  

Robert Tenzer  Pavel Novák  Peter Vajda  Artu Ellmann  Ahmed Abdalla 《Studia Geophysica et Geodaetica》2011,55(1):55-71

A spectral representation of the topographic corrections to gravity field quantities is formulated in terms of spherical height functions. When computing the far-zone contributions to the topographic corrections, various types of the truncation coefficients are applied to a spectral representation of Newton’s integral. In this study we utilise Molodensky’s truncation coefficients in deriving the expressions for the far-zone contributions to topographic corrections. The expressions for computing the far-zone gravity field contributions corrected for the effect of topography are then obtained by combining the expressions for the far-zone contributions to the gravity field quantities and to the respective topographic corrections, both expressed in terms of Molodensky’s truncation coefficients. The numerical examples of the far-zone contributions to the topographic corrections and to the topography-corrected gravity field quantities are given over the study area situated in the Canadian Rocky Mountains with adjacent planes. Coefficients of the global elevation and geopotential models are used as the input data.  相似文献   

Modelling time varying scouring at bed sills     

Matteo Tregnaghi  Andrea Marion  Andrea Bottacin‐Busolin  Simon J. Tait 《地球表面变化过程与地形》2011,36(13):1761-1769

In this paper a modelling approach is presented to predict local scour under time varying flow conditions. The approach is validated using experimental data of unsteady scour at bed sills. The model is based on a number of hypotheses concerning the characteristics of the flow hydrograph, the temporal evolution of the scour and the geometry of the scour hole. A key assumption is that, at any time, the scour depth evolves at the same rate as in an equivalent steady flow. The assumption is supported by existing evidence of geometrical affinity and similarity of scour holes formed under different steady hydraulic conditions. Experimental data are presented that show the scour hole development downstream of bed sills due to flood hydrographs follow a predictable pattern. Numerical simulations are performed with the same input parameters used in the experimental tests but with no post‐simulation calibration. Comparison between the experimental and model results indicates good correspondence, especially in the rising limb of the flow hydrograph. This suggests that the underlying assumptions used in the modelling approach are appropriate. In principle, the approach is general and can be applied to a wide range of environments (e.g. bed sills, step‐pool systems) in which scouring at rapid bed elevation changes caused by time varying flows occurs, provided appropriate scaling information is available, and the scour response to steady flow conditions can be estimated. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献