Changes in sediment and organic carbon accumulation in a highly-disturbed ecosystem: The Sacramento-San Joaquin River Delta (California, USA)     

Elizabeth A. Canuel  Elizabeth J. Lerberg  Rebecca M. Dickhut  Steven A. Kuehl  Thomas S. Bianchi  Stuart G. Wakeham 《Marine pollution bulletin》2009,59(4-7):154

We used the Sacramento-San Joaquin River Delta CA (Delta, hereafter) as a model system for understanding how human activities influence the delivery of sediment and total organic carbon (TOC) over the past 50–60 years. Sediment cores were collected from sites within the Delta representing the Sacramento River (SAC), the San Joaquin River (SJR), and Franks Tract (FT), a flooded agricultural tract. A variety of anthropogenic tracers including ¹³⁷Cs, total DDE (∑DDE) and brominated diphenyl ether (BDE) congeners were used to quantify sediment accumulation rates. This information was combined with total organic carbon (TOC) profiles to quantify rates of TOC accumulation. Across the three sites, sediment and TOC accumulation rates were four to eight-fold higher prior to 1972. Changes in sediment and TOC accumulation were coincident with completion of several large reservoirs and increased agriculture and urbanization in the Delta watershed. Radiocarbon content of TOC indicated that much of the carbon delivered to the Delta is “pre-aged” reflecting processing in the Delta watershed or during transport to the sites rather than an input of predominantly contemporary carbon (e.g., 900–1400 years BP in surface sediments and 2200 yrs BP and 3610 yrs BP at the base of the SJR and FT cores, respectively). Together, these data suggest that human activities have altered the amount and age of TOC accumulating in the Delta since the 1940s.  相似文献   

Inverse analysis of stochastic moment equations for transient flow in randomly heterogeneous media     

Monica Riva  Alberto Guadagnini  Shlomo P. Neuman  Emanuela Bianchi Janetti  Bwalya Malama 《Advances in water resources》2009

We present a nonlinear stochastic inverse algorithm that allows conditioning estimates of transient hydraulic heads, fluxes and their associated uncertainty on information about hydraulic conductivity (K) and hydraulic head (h  ) data collected in a randomly heterogeneous confined aquifer. Our algorithm is based on Laplace-transformed recursive finite-element approximations of exact nonlocal first and second conditional stochastic moment equations of transient flow. It makes it possible to estimate jointly spatial variations in natural log-conductivity (Y=lnK)$(Y=\ln K)$, the parameters of its underlying variogram, and the variance–covariance of these estimates. Log-conductivity is parameterized geostatistically based on measured values at discrete locations and unknown values at discrete “pilot points”. Whereas prior values of Y at pilot point are obtained by generalized kriging, posterior estimates at pilot points are obtained through a maximum likelihood fit of computed and measured transient heads. These posterior estimates are then projected onto the computational grid by kriging. Optionally, the maximum likelihood function may include a regularization term reflecting prior information about Y. The relative weight assigned to this term is evaluated separately from other model parameters to avoid bias and instability. We illustrate and explore our algorithm by means of a synthetic example involving a pumping well. We find that whereas Y and h can be reproduced quite well with parameters estimated on the basis of zero-order mean flow equations, all model quality criteria identify the second-order results as being superior to zero-order results. Identifying the weight of the regularization term and variogram parameters can be done with much lesser ambiguity based on second- than on zero-order results. A second-order model is required to compute predictive error variances of hydraulic head (and flux) a posteriori. Conditioning the inversion jointly on conductivity and hydraulic head data results in lesser predictive uncertainty than conditioning on conductivity or head data alone.  相似文献   

Seismic reliability of V‐braced frames: Influence of design methodologies     

Alessandra Longo  Rosario Montuori  Vincenzo Piluso 《地震工程与结构动力学》2009,38(14):1587-1608

According to the most modern trend, performance‐based seismic design is aimed at the evaluation of the seismic structural reliability defined as the mean annual frequency (MAF) of exceeding a threshold level of damage, i.e. a limit state. The methodology for the evaluation of the MAF of exceeding a limit state is herein applied with reference to concentrically ‘V’‐braced steel frames designed according to different criteria. In particular, two design approaches are examined. The first approach corresponds to the provisions suggested by Eurocode 8 (prEN 1998—Eurocode 8: design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings), while the second approach is based on a rigorous application of capacity design criteria aiming at the control of the failure mode (J. Earthquake Eng. 2008; 12 :1246–1266; J. Earthquake Eng. 2008; 12 :728–759). The aim of the presented work is to focus on the seismic reliability obtained through these design methodologies. The probabilistic performance evaluation is based on an appropriate combination of probabilistic seismic hazard analysis, probabilistic seismic demand analysis (PSDA) and probabilistic seismic capacity analysis. Regarding PSDA, nonlinear dynamic analyses have been carried out in order to obtain the parameters describing the probability distribution laws of demand, conditioned to given values of the earthquake intensity measure. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

SGeMS: A Free and Versatile Tool for Three-Dimensional Geostatistical Applications     

Marco Bianchi  Chunmiao Zheng 《Ground water》2009,47(1):8-12

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A seismic investigation into the geometry and controls upon alluvial architecture in the Walloon Subgroup,Surat Basin,Queensland     

D. Shields  V. Bianchi  J. Esterle 《Australian Journal of Earth Sciences》2017,64(4):455-469

The sedimentology of the Walloon Subgroup (WSG) has been extensively studied; however, gaps exist in our understanding of the succession's alluvial architecture and the mechanisms controlling its complex internal organisation. Successful coal-seam gas development in the Surat Basin requires the construction of predictive facies models, which in turn necessitates a fulsome understanding of the geometry and controls on the spatial and temporal distribution of alluvial sub-environments. To improve our models of WSG facies, this study employs an open-source high-resolution 3D seismic dataset available on the western limb of the Surat Basin. Integration of core, wireline and seismic data has resolved the geometries of four discrete alluvial architectural elements, representing simple channel, channel belt, crevasse splay complexes and peat-mire sub-environments. Channel belts were found to be 1600–2000 m wide, simple channels 400–800 m in width and crevasse splays averaging 3.5 × 5.5 km. Coal bodies mapped from seismic attribute extractions were found to be 4.2 km² on average. The high-resolution dataset has also yielded insight into the geological controls governing the spatial and temporal distribution of these sub-environments, explaining, in part the mechanisms responsible for the complex internal distribution of facies within the WSG. In places within the study area, the WSG's sedimentary organisation appears to be initiated by the rejuvenation of deep-seated tectonic features, the expression of which is propagated upward via the mechanics of compensational stacking.  相似文献   

A New Seismic Data Set on the Depth of the Moho in the Alps     

Irene Bianchi  Michael Behm  Eva Maria Rumpfhuber  Götz Bokelmann 《Pure and Applied Geophysics》2015,172(2):295-308

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Radionuclide Transport Behavior in a Generic Geological Radioactive Waste Repository          下载免费PDF全文

Marco Bianchi  Hui‐Hai Liu  Jens T. Birkholzer 《Ground water》2015,53(3):440-451

We performed numerical simulations of groundwater flow and radionuclide transport to study the influence of several factors, including the ambient hydraulic gradient, groundwater pressure anomalies, and the properties of the excavation damaged zone (EDZ), on the prevailing transport mechanism (i.e., advection or molecular diffusion) in a generic nuclear waste repository within a clay‐rich geological formation. By comparing simulation results, we show that the EDZ plays a major role as a preferential flowpath for radionuclide transport. When the EDZ is not taken into account, transport is dominated by molecular diffusion in almost the totality of the simulated domain, and transport velocity is about 40% slower. Modeling results also show that a reduction in hydraulic gradient leads to a greater predominance of diffusive transport, slowing down radionuclide transport by about 30% with respect to a scenario assuming a unit gradient. In addition, inward flow caused by negative pressure anomalies in the clay‐rich formation further reduces transport velocity, enhancing the ability of the geological barrier to contain the radioactive waste. On the other hand, local high gradients associated with positive pressure anomalies can speed up radionuclide transport with respect to steady‐state flow systems having the same regional hydraulic gradients. Transport behavior was also found to be sensitive to both geometrical and hydrogeological parameters of the EDZ. Results from this work can provide useful knowledge toward correctly assessing the post‐closure safety of a geological disposal system.  相似文献   

Effects of vegetation on flow and sediment transport: comparative analyses and validation of predicting models   总被引：1，自引：0，他引：1       下载免费PDF全文

Andrés Vargas‐Luna  Alessandra Crosato  Wim S.J. Uijttewaal 《地球表面变化过程与地形》2015,40(2):157-176

The presence of vegetation modifies flow and sediment transport in alluvial channels and hence the morphological evolution of river systems. Plants increase the local roughness, modify flow patterns and provide additional drag, decreasing the bed‐shear stress and enhancing local sediment deposition. For this, it is important to take into account the presence of vegetation in morphodynamic modelling. Models describing the effects of vegetation on water flow and sediment transport already exist, but comparative analyses and validations on extensive datasets are still lacking. In order to provide practical information for modelling purposes, we analysed the performance of a large number of models on flow resistance, vegetation drag, vertical velocity profiles and bed‐shear stresses in vegetated channels. Their assessments and applicability ranges are derived by comparing their predictions with measured values from a large dataset for different types of submerged and emergent vegetation gathered from the literature. The work includes assessing the performance of the sediment transport capacity formulae of Engelund and Hansen and van Rijn in the case of vegetated beds, as well as the value of the drag coefficient to be used for different types of vegetation and hydraulic conditions. The results provide a unique comparative overview of existing models for the assessment of the effects of vegetation on morphodynamics, highlighting their performances and applicability ranges. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Linear time history analysis for the out-of-plane seismic demand of infill walls in RC framed buildings     

Alessandra De Angelis  Marisa Pecce  Fernando Rossi 《Bulletin of Earthquake Engineering》2015,13(11):3325-3352

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BACI design reveals the decline of the seagrass Posidonia oceanica induced by anchoring     

Montefalcone M  Chiantore M  Lanzone A  Morri C  Albertelli G  Nike Bianchi C 《Marine pollution bulletin》2008,56(9):1637-1645

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