Salinization in coastal aquifers of arid zones: an example from Santo Domingo,Baja California Sur,Mexico

Groundwater quality in the Santo Domingo Irrigation District area in Baja California Sur, Mexico, indicates the presence of various salinization processes, (1) the geological matter of marine origin comprising the aquifer material suffers diagenetic effects due to its interaction with groundwater of low salinity, (2) the effects of intensive agriculture practices produce effluents that infiltrate to the saturated zone, and (3) the extraction of groundwater causes modifications in the natural flow system induces lateral flow of seawater from the coast line. However, groundwater management has been carried out with the belief that the latter is the main source of salinization. This has resulted in a policy of installing wells increasingly far from the coast, which is not solving the problem. Irrigation-return and seawater that remains in the geological units have been identified as major sources of salinization. Controls should be imposed when installing wells in contact with clayey units that form the base of the aquifer. Extracted groundwater consists of a mixture of (1) groundwater of relatively low salinity that circulates in the aquifer and (2) an extreme member with salinity different to seawater contained mainly in formations that have low permeability, which limits the aquifer underneath. The geochemistry of carbonates and cation-exchange reactions (both direct and reverse) control the concentration of Ca, Mg, Na, and HCO₃, as well as pH values. The concentrations of dissolved trace elements (F, Li, Ba, Sr) suggest that the extreme saline member is different from the average seawater composition. A distinction between the salinization caused by farming practices and that blamed on seawater is defined by the use of NO₃.     

Intrinsic random function of order<Emphasis Type="Italic"> k</Emphasis> kriging of electrical resistivity data for estimating the extent of saltwater intrusion in a coastal aquifer system

A saltwater intrusion study using electrical resistivity distribution was conducted in a coastal aquifer system in the southeastern part of Busan, Korea. This aquifer system is divided into four layers according to the hydrogeologic characteristics, and the horizontal extent of intruded saltwater is determined at each layer through the geostatistical interpretation of electrical resistivity data. Intrinsic random function of order k (IRF-k) kriging is performed with covariance models to produce the plane of spatial mean resistivities. The kriged estimates are evaluated by cross validation, and they showed a good agreement with the true values. The statistics of cross validation represented low errors for the estimates. In the resistivity contour maps more than 5 m below the surface, a dominant direction of saltwater intrusion was observed beginning from the east side. These results led the authors to conclude that the application of geostatistical technique to electrical resistivity data is useful for assessing saltwater intrusion in a coastal aquifer system.     

Development of a sharp interface model that simulates coastal aquifer flow with the coupled use of GIS

A simulation program, which works seamlessly with GIS and simulates flows in coastal aquifers, is presented in the present paper. The model is based on the Galerkin finite element discretization scheme and it simulates both steady and transient freshwater and saltwater flow, assuming that the two fluids are separated by a sharp interface. The model has been verified in simple cases where analytical solutions exist. The simulation program works as a tool of the GIS program, which is the main database that stores and manages all the necessary data. The combined use of the simulation and the GIS program forms an integrated management tool offering a simpler way of simulating and studying saline intrusion in coastal aquifers. Application of the model to the Yermasogia aquifer illustrates the coupled use of modeling and GIS techniques for the examination of regional coastal aquifer systems.

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Resumen Se ha desarrollado un modelo casi tridimensional de elementos finitos para simular el flujo de agua dulce y salada, tanto en régimen estacionario como en transitorio, en sistemas acuíferos costeros, bajo la hipótesis de separación por medio de una interfaz abrupta. Las ecuaciones del modelo han sido discretizadas mediante un esquema de Galerkin de discretización en elementos finitos. El modelo ha sido verificado en casos sencillos para los que existe solución analítica. Todos los datos necesarios se introducen y gestionan con un Sistema de Información Geográfica [SIG] por ordenador. El programa de simulación forma parte del programa de SIG, constituyendo una herramienta integrada de gestión para estudiar la intrusión salina en acuíferos costeros. La aplicación del modelo al acuífero de Yermasogia ilustra el uso acoplado de las técnicas de modelación y de SIG con el fin de examinar sistemas acuíferos costeros a escala regional.

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Résumé Pour étudier un système aquifère côtier, nous avons développé un modèle aux éléments finis en quasi 3-D qui simule les écoulements deau douce et deau salée en régime aussi bien permanent que transitoire. Les équations qui les régissent sont discrétisées par un schéma de discrétisation de Garlekin aux éléments finis. Le modèle a été vérifié dans des cas simples où il existe des solutions analytiques. Toutes les données nécessaires sont introduites et gérées grâce à un logiciel de gestion de SIG. Le programme de simulation est utilisé comme un outil du logiciel de SIG, constituant ainsi un outil de gestion intégrée dont le but est de simuler et détudier lintrusion saline dans les aquifères côtiers. Lapplication du modèle à laquifère de Yermasogia illustre lutilisation couplée de la modélisation et des techniques de SIG pour létude des systèmes aquifères côtiers régionaux.

     

The origin of increased salinity in the Cambrian-Vendian aquifer system on the Kopli Peninsula,northern Estonia

Monitoring of the confined Cambrian-Vendian aquifer system utilised for industrial water supply at Kopli Peninsula in Tallinn over 24 years reveals remarkable changes in chemical composition of groundwater. A relatively fast 1.5 to 3.0-fold increase in TDS and in concentrations of major ions in abstracted groundwater is the consequence of heavy pumping. The main sources of dissolved load in Cambrian-Vendian groundwater are the leaching of host rock and the other geochemical processes that occur in the saturated zone. Underlying crystalline basement, which comprises saline groundwater in its upper weathered and fissured portion, and which is hydraulically connected with the overlying Cambrian-Vendian aquifer system, is the second important source of ions. The fractured basement and its clayey weathering crust host the Ca-Cl type groundwater, which is characterised by high TDS values (2–20 g/L). Intensive water abstraction accelerates the exchange of groundwaters and increases the area of influence of pumping. Chemical and isotopic studies of groundwater indicate an increasing contribution of old brackish water from the crystalline basement and rule out the potential implication of an intrusion of seawater into aquifer.

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Resumen El origen del incremento en salinidad en un sistema de acuíferos Cámbrico-Vendiano en la Península Kopli, norte de EstonieMonitoreo a largo plazo de un sistema de acuíferos confinados, de edad Cámbrico-Vendiano, que se utiliza como fuente de abastecimiento industrial en la Península Kopli, al norte de Estonie, revela cambios notables en la composición química del agua subterránea. Un incremento de 1.5 a 3 veces en TDS y en concentraciones de iones mayores en agua subterránea explotada ha sido ocasionado por bombeo fuerte. Las fuentes principales de carga disuelta en el agua subterránea Cámbrico-Vendiano son la lixiviación de la roca encajonante y los procesos geoquímicos que ocurren en la zona saturada. Basamento cristalino subyacente, que aloja agua subterránea salada en la parte superior intemperizada y fisurada, y está conectado hidráulicamente con el sistema acuífero Cámbrico-Vendiano sobreyacente, es la segunda fuente importante de iones. El basamento fracturado y su corteza de intemperismo arcillosa alojan agua subterránea de tipo Ca-Cl la cual se caracteriza por valores altos de TDS (2–20 g/l). Debido a extracción intensiva se ha acelerado el intercambio de agua subterránea y se ha incrementado el área de influencia del bombeo. Los estudios químicos e isotópicos de agua subterránea indican una contribución creciente por filtración derivada del basamento cristalino. Es evidente una intrusión de agua salada hacia el sistema de acuíferos con implicaciones subsecuentes para la calidad del agua.

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Résumé Lorigine de la salinité croissante dans le système aquifère du Cambrien-Vendien dans la péninsule de Kopli, nord de lEstonieLe suivi à long terme du système aquifère captif du Cambrien-Vendien utilisé pour lapprovisionnement deaux industrielles dans la Péninsule de Kopli, nord de lEstonie, révèle de remarquables changements dans la composition chimique des eaux souterraines. Une augmentation de facteur 1.5 à 3 de la TDS et des concentrations en ions majeurs dans leau souterraine est la conséquence de pompages intensifs. Les sources principales des charges dissoutes dans les eaux de laquifère du Cambrien-Vendien sont le lessivage des roches et dautres phénomènes géochimiques ayant lieu dans la zone saturée. Le soubassement rocheux cristallin, qui renferme des eaux souterraines salines dans sa partie supérieure altérée et fissurée, et est hydrauliquement connecté avec laquifère supérieur du Cambrien-Vendien, est la deuxième importante source dions. Le soubassement fracturé et le matériel argileux de laltération, renferme leau souterraine de type Ca-Cl, caractérisée par un haut TDS (2–20 g/l). A cause de la mobilisation intensive de leau les échanges deau souterraine est sont accélérés et la zone dinfluence des pompages augmentent. Les études chimiques et isotopiques indiquent une contribution croissante du drainage des eaux du soubassement cristallin. Lintrusion deaux salées de la mer dans le système aquifère nest pas un phénomène évident.

     

SHRIMP U–Pb dating of the Antucoya porphyry copper deposit: new evidence for an Early Cretaceous porphyry-related metallogenic epoch in the Coastal Cordillera of northern Chile

The Antucoya porphyry copper deposit (300 Mt at 0.45% total Cu) is one of the largest deposits of a poorly known Early Cretaceous porphyry belt in the Coastal Cordillera of northern Chile. It is related to a succession of granodioritic and tonalitic porphyritic stocks and dikes that were emplaced within Jurassic andesitic rocks of the La Negra Formation immediately west of the N–S trending sinistral strike-slip Atacama Fault Zone. New zircon SHRIMP U–Pb data indicate that the porphyries of Antucoya crystallized within the time span from 142.7 ± 1.6 to 140.6 ± 1.5 Ma (±2 σ), and late, unmineralized, NW–SE trending dacite dikes with potassic alteration and internal deformation crystallized at 141.9 ± 1.4 Ma. The Antucoya porphyry copper system appears to be formed after a change of stress conditions along the magmatic arc from extensional in the Late Jurassic to transpressive during the Early Cretaceous and provides support for an Early Cretaceous metallogenic episode of porphyry-type mineralization along the Coastal Cordillera of northern Chile.     

Evaluation and numerical modeling of seawater intrusion in the Gaza aquifer (Palestine)

A numerical assessment of seawater intrusion in Gaza, Palestine, has been achieved applying a 3-D variable density groundwater flow model. A two-stage finite difference simulation algorithm was used in steady state and transient models. SEAWAT computer code was used for simulating the spatial and temporal evolution of hydraulic heads and solute concentrations of groundwater. A regular finite difference grid with a 400 m² cell in the horizontal plane, in addition to a 12-layer model were chosen. The model has been calibrated under steady state and transient conditions. Simulation results indicate that the proposed schemes successfully simulate the intrusion mechanism. Two pumpage schemes were designed to use the calibrated model for prediction of future changes in water levels and solute concentrations in the groundwater for a planning period of 17 years. The results show that seawater intrusion would worsen in the aquifer if the current rates of groundwater pumpage continue. The alternative, to eliminate pumpage in the intruded area, to moderate pumpage rates from water supply wells far from the seashore and to increase the aquifer replenishment by encouraging the implementation of suitable solutions like artificial recharge, may limit significantly seawater intrusion and reduce the current rate of decline of the water levels.     

The Mantos Blancos copper deposit: an upper Jurassic breccia-style hydrothermal system in the Coastal Range of Northern Chile

The Upper Jurassic Mantos Blancos copper deposit (500 Mt at 1.0% Cu), located in the Coastal Range of northern Chile, displays two superimposed hydrothermal events. An older phyllic alteration probably related to felsic magmatic–hydrothermal brecciation at ∼155 Ma, and younger (141–142 Ma) potassic, propylitic, and sodic alterations, coeval with dioritic and granodioritic stocks and sills, and dioritic dikes. Main ore formation is genetically related to the second hydrothermal event, and consists of hydrothermal breccias, disseminations and stockwork-style mineralization, associated with sodic alteration. Hypogene sulfide assemblages show distinctive vertical and lateral zoning, centered on magmatic and hydrothermal breccia bodies, which constitute the feeders to mineralization. A barren pyrite root zone is overlain by pyrite-chalcopyrite, and followed upwards and laterally by chalcopyrite-digenite or chalcopyrite-bornite. The assemblage digenite–supergene chalcocite characterizes the central portions of high-grade mineralization in the breccia bodies. Fluid inclusions show evidence of boiling during the potassic and sodic alteration events, which occurred at temperatures around 450–460°C and 350–410°C, and salinities between 3–53 and 13–45 wt% NaCl eq., respectively. The hydrothermal events occurred during episodic decompression due to fluid overpressuring, hydrofracturing, and sharp changes from lithostatic to hydrostatic conditions. Sulfur isotope results of hypogene sulfide minerals fall in a narrow range around 0 per mil, suggesting a dominance of magmatic sulfur. Carbon and oxygen isotopic data of calcites from propylitic alteration suggest a mantle-derived carbon and oxygen isotope fractionation due to low-temperature alteration.     

Low-frequency current variability observed at the shelfbreak in the northeastern Gulf of Mexico: May–October, 2004

High-resolution current measurements were made in the Northeastern Gulf of Mexico by the Naval Research Laboratory (NRL) as part of its Slope to Shelf Energetics and Exchange Dynamics (SEED) project. The major goal of SEED is to understand the mechanisms that transfer properties across the shelf slope. Fourteen acoustic Doppler current profilers (ADCPs) were deployed just west of the DeSoto Canyon on the shelf and down the slope from May to November, 2004 to measure nearly full water column current profiles. Currents were found more variable on the shelf than on the slope but in the mean strongly tended to follow bathymetry, particularly on the slope. During the SEED time period currents were driven by both local and remote winds, by cyclonic eddies associated with the Loop Current extension and Loop Current rings, by smaller eddies associated with the cyclonic eddies, by frontal meanders or streamers associated with the eddies, and by tropical storms. Currents were highly barotropic, accounting for more than 80% of the eddy kinetic energy (EKE). Current magnitudes generally increased from west to east, towards the DeSoto Canyon. Tropical storms had a relatively minor short-term effect upon mass transports. Cross-shelf transports were much smaller than the along-shelf transports. Onshore transports were stronger on the western side of the array while offshore transports were stronger on the eastern side of the array near the DeSoto Canyon. Offshore transports generally occurred during eastward flow periods, onshore transports during westward flow periods, and both during eddy periods. Mesoscale eddies also provided contributions to cross-shelf exchange. Large scale circulation features could be determined from the first two empirical-orthogonal function (EOF) modes which accounted for 83% of the variance and were strongly related to the integrated wind stress.     

Groundwater resources management under environmental constraints in Shiroishi of Saga plain, Japan

A sinking of the land surface due to the pumping of groundwater has long been recognized as an environmental issue in the Shiroishi plain of Saga, Japan. Land subsidence can have several negative economic and social implications such as changes in groundwater and surface water flow patterns, restrictions on pumping in land subsidence prone areas, localized flooding, failure of well casings as well as shearing of structures. To minimize such an environmental effect, groundwater management should be considered in this area. In this study, a new integrated numerical model that integrates a three-dimensional numerical groundwater flow model coupled with a one-dimensional soil consolidation model and a groundwater optimization model was developed to simulate groundwater movement, to predict ground settlement and to search for optimal safe yield of groundwater without violating physical, environmental and socio-economic constraints. It is found that groundwater levels in the aquifers greatly vary from season to season in response to the varying climatic and pumping conditions. Consequently, land subsidence has occurred rapidly throughout the area with the Shiroishi plain being the most prone. The predicted optimal safe yield of the pumping amount is about 5 million m³. The study also suggests that pumping with this optimal amount will minimize the rate of land subsidence over the entire area. An erratum to this article can be found at     

Combined wavelet and principal component analysis (WEof) of a scale-oriented model of coastal ocean gravity waves

Coastal ocean numerical modeling is basically the representation of the dynamics of the coastal ocean in a chosen range of length scales and over an associated frequency band, including the modeling of both coherent processes and associated transient processes. The ocean dynamical features can be individually identified by combining wavelet analysis for time and frequency localization and principal component analysis to “decorrelate” physically consistent structures. In the present paper, the so-called WEof analysis is applied for the extraction of external gravity waves and internal gravity wave lower modes in a simple case of a flat bottom, constant Brunt-Väisälä ocean. It is shown that, with some well known restrictive assumptions, WEof analysis is an efficient candidate for the recognition of frequency localized dynamical processes.