Multi-tracer assessment of seasonal water source changes in coastal water systems along the southeastern coast of Ivory Coast (West Africa)     

Isimemen Osemwegie  Christine Stumpp  Jean Biemi  Barbara Reichert 《水文科学杂志》2013,58(15-16):2124-2145

ABSTRACT

Proper management of coastal freshwater resources depends on an understanding of processes controlling their chemistry and seasonal flowpaths. A quantitative approach involving the coupling of major solutes and isotopes (δ¹⁸O, δ²H) of 180 samples in end-member mixing analysis (EMMA) was adopted to elucidate seasonal patterns of hydraulic exchanges amongst coastal waters along the Ebrié Lagoon catchment, Ivory Coast. The results show that the Ebrié Lagoon is a hydrologically dynamic system. In the dry season, evaporation and seawater inflow are the dominating processes, while in the wet season, river discharge is the main water source in the lagoon. Regional geology plays a significant role in aquifer recharge patterns. The Quaternary aquifer responds faster to precipitation, while the Mio-Pliocene aquifer is recharged indirectly via floodplain seepages. Salinization of over 90% of wells arises from hydrological exchanges with the Ebrié Lagoon. A diluted seawater effect was recorded in wells during the wet season owing to the relative increase in freshwater inflow.  相似文献   

A model for conductive faults with non-matching grids     

Xavier Tunc  Isabelle Faille  Thierry Gallou?t  Marie Christine Cacas  Pascal Havé 《Computational Geosciences》2012,16(2):277-296

In this paper, we are interested in modeling single-phase flow in a porous medium with known faults seen as interfaces. We mainly focus on how to handle non-matching grids problems arising from rock displacement along the fault. We describe a model that can be extended to multi-phase flow where faults are treated as interfaces. The model is validated in an academic framework and is then extended to 3D non K-orthogonal grids, and a realistic case is presented.  相似文献   

Evaluating alternative future sea-level rise scenarios     

Christine C. Shepard  Vera N. Agostini  Ben Gilmer  Tashya Allen  Jeff Stone  William Brooks  Michael W. Beck 《Natural Hazards》2012,63(2):1223-1224

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Do human activities affect the picoplankton structure of the Ahe atoll lagoon (Tuamotu Archipelago, French Polynesia)?     

Bouvy M  Dupuy C  Pagano M  Barani A  Charpy L 《Marine pollution bulletin》2012,65(10-12):516-524

The spatial variations of the picoplankton (photoautotrophic and heterotrophic microorganisms) in the Ahe atoll lagoon were studied in May and October 2008 to assess whether they were affected by human activities along the atoll. Spatial patterns were studied using 10 sampling stations chosen according to the location of the anthropogenic activities (pearl farming, harbor). Experiments were also carried out to determine whether bacterial growth, with or without predators, was limited by inorganic (N and P) substrates. The results showed that heterotrophic bacterioplankton abundance was superior to the photoautotrophic organisms, especially in May. Significant increases in bacterial abundance were observed in May after 24h incubation with +P and +N (but not in October). All samples complied with the quality levels for fecal indicator bacteria (FIB) defined by the European Union and there was no evidence that human sewage had any impact on picoplankton over the whole atoll.  相似文献   

Timescales of interface-coupled dissolution-precipitation reactions on carbonates     

Fran?ois Renard  Anja R?yne  Christine V.Putnis 《地学前缘(英文版)》2019,10(1):17-27

In the Earth's upper crust, where aqueous fluids can circulate freely, most mineral transformations are controlled by the coupling between the dissolution of a mineral that releases chemical species into the fluid and precipitation of new minerals that contain some of the released species in their crystal structure, the coupled process being driven by a reduction of the total free-energy of the system. Such coupled dissolution-precipitation processes occur at the fluid-mineral interface where the chemical gradients are highest and heterogeneous nucleation can be promoted, therefore controlling the growth kinetics of the new minerals. Time-lapse nanoscale imaging using Atomic Force Microscopy (AFM) can monitor the whole coupled process under in situ conditions and allow identifying the time scales involved and the controlling parameters. We have performed a series of experiments on carbonate minerals (calcite, siderite, dolomite and magnesite) where dissolution of the carbonate and precipitation of a new mineral was imaged and followed through time. In the presence of various species in the reacting fluid (e. g. antimony, selenium, arsenic, phosphate), the calcium released during calcite dissolution binds with these species to form new minerals that sequester these hazardous species in the form of a stable solid phase. For siderite, the coupling involves the release of Fe²⁺ ions that subsequently become oxidized and then precipitate in the form of Fe^III oxyhydroxides. For dolomite and magnesite, dissolution in the presence of pure water (undersaturated with any possible phase) results in the immediate precipitation of hydrated Mg-carbonate phases. In all these systems, dissolution and precipitation are coupled and occur directly in a boundary layer at the carbonate surface. Scaling arguments demonstrate that the thickness of this boundary layer is controlled by the rate of carbonate dissolution, the equilibrium concentration of the precipitates and the kinetics of diffusion of species in a boundary layer. From these parameters a characteristic time scale and a characteristic length scale of the boundary layer can be derived. This boundary layer grows with time and never reaches a steady state thickness as long as dissolution of the carbonate is faster than precipitation of the new mineral. At ambient temperature, the surface reactions of these dissolving carbonates occur on time-scales of the order of seconds to minutes, indicating the rapid surface rearrangement of carbonates in the presence of aqueous fluids. As a consequence, many carbonate-fluid reactions in low temperature environments are controlled by local thermodynamic equilibria rather than by the global equilibrium in the whole system.  相似文献   

Organic matter degradation in paper sludge amendments over gold mine tailings     

Christine Cousins  Glenn H. Penner  Bruce Liu  Peter Beckett  Graeme Spiers 《Applied Geochemistry》2009

The long-term stability of paper sludge amendments as covers for reclaimed mine waste storage facilities must be assessed by the mining industry. This study examines a 6 yr old sequence of paper sludge amendments applied over wastes from historic Au mines located in Northern Ontario, Canada. As paper sludge is mostly comprised of C-rich organic compounds, elemental quantification, ¹³C cross polarization/magic angle spinning nuclear magnetic resonance (¹³C CP/MAS NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were used to examine the minimal changes in the C content and speciation observed of the amendments over time. These results suggest that paper sludge covers are suitable for use in medium to long-term mining reclamation strategies.  相似文献   

Flowing fluid electrical conductivity logging of a deep borehole during and following drilling: estimation of transmissivity,water salinity and hydraulic head of conductive zones   总被引：1，自引：0，他引：1  

Christine Doughty  Chin-Fu Tsang  Jan-Erik Rosberg  Christopher Juhlin  Patrick F. Dobson  Jens T. Birkholzer 《Hydrogeology Journal》2017,25(2):501-517

Flowing fluid electrical conductivity (FFEC) logging is a hydrogeologic testing method that is usually conducted in an existing borehole. However, for the 2,500-m deep COSC-1 borehole, drilled at Åre, central Sweden, it was done within the drilling period during a scheduled 1-day break, thus having a negligible impact on the drilling schedule, yet providing important information on depths of hydraulically conductive zones and their transmissivities and salinities. This paper presents a reanalysis of this set of data together with a new FFEC logging data set obtained soon after drilling was completed, also over a period of 1 day, but with a different pumping rate and water-level drawdown. Their joint analysis not only results in better estimates of transmissivity and salinity in the conducting fractures intercepted by the borehole, but also yields the hydraulic head values of these fractures, an important piece of information for the understanding of hydraulic structure of the subsurface. Two additional FFEC logging tests were done about 1 year later, and are used to confirm and refine this analysis. Results show that from 250 to 2,000 m depths, there are seven distinct hydraulically conductive zones with different hydraulic heads and low transmissivity values. For the final test, conducted with a much smaller water-level drawdown, inflow ceased from some of the conductive zones, confirming that their hydraulic heads are below the hydraulic head measured in the wellbore under non-pumped conditions. The challenges accompanying 1-day FFEC logging are summarized, along with lessons learned in addressing them.  相似文献   

Shake table tests of stiff,unattached, asymmetric structures          下载免费PDF全文

Christine E. Wittich  Tara C. Hutchinson 《地震工程与结构动力学》2015,44(14):2425-2443

Stiff, unattached structures are highly vulnerable to damage and failure during an earthquake, as evidenced following numerous past events. This class of structures encompasses a wide range of objects and systems such as electrical transformers, radiation shields, office furniture, and marble statues. The vulnerability of these objects is exacerbated when it is highly asymmetric and unattached. Although a number of studies have focused on rigid blocks, few have concentrated on blocks with asymmetric geometries. In an effort to better understand the implications of asymmetries, an extensive shake table testing campaign including more than 150 tests was conducted. These tests incorporate a systematic variation of the mass eccentricities of stiff, unattached structures. The primary modes of rocking, sliding, and twisting as well as interactive modes were recorded for the duration of numerous earthquake motions. The magnitude and direction of response are experimentally correlated with the geometric variations in the various models. These tests indicate that even for symmetric structures with uniaxial shaking, multiple modes and three‐dimensional responses are probable. Furthermore, certain asymmetric geometries exhibited both increased rocking (and overturning) as well as increased sliding when compared with their symmetric counterparts. A final aspect of this study compared the free rocking response of symmetric and asymmetric structures to classical, two‐dimensional rocking analysis. While the theoretical values for the coefficient of restitution yielded a significant overestimation in the simulation (up to ≈90%), reduced coefficients greatly improved the performance of the model. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献