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Sanchez-Espana J.,Instituto Geologico Y Minero Of Espana Igme | Yusta I.,University of the Basque Country | Diez-Ercilla M.,Instituto Geologico Y Minero Of Espana Igme
Applied Geochemistry | Year: 2011

The solubility of schwertmannite and hydrobasaluminite and their control on the concentration of Fe(III) and Al in acid-sulfate aqueous systems has been re-examined through a series of titration experiments with waters from two acidic pit lakes (Cueva de la Mora and San Telmo) from the Iberian Pyrite Belt in SW Spain. The work also includes a microscopic study (SEM-EDS) of natural Fe(III) precipitates found in the water column of both lakes. The microscopic study of natural precipitates confirms that schwertmannite constitutes a major control of Fe3+ concentration in the lakes at pH~3.0, whereas jarosite may also be abundant at near-surface conditions and is typical of low pH (<2.5). Goethite is eventually found, although it basically results from ageing of less stable precursor phases. The titration study comprised chemical analysis of waters sampled at increments of 0.2 pH units in the pH range 2.6-10.0, along with chemical (ICP-AES, XRF) and mineralogical (XRD, SEM, EDS, TEM) analysis of the resulting precipitates at different pH values (3.5, 4.5, 4.8, 5.2). The experimental results indicate that the precipitation of a highly hydrated schwertmannite (with empirical formula Fe8O8(SO4)x(OH)y·nH2O, where x=1.4-1.5, y=5.0-5.2, and n=13-17) strongly buffers the solutions in the pH range of 3.0-3.5 and appears to control the aqueous concentration of Fe3+ up to pH~5. Precipitation of Al3+ also constitutes an important buffering system at pH 4.2-4.7 and is controlled by the formation of poorly crystalline hydrobasaluminite (with empirical formula Al4(SO4)(OH)10·15H2O), which is highly unstable in low relative humidity conditions and tends to dehydrate to basaluminite (Al4(SO4)1.2(OH)9.6·9-10H2O). Removal rates for Fe3+ and Al3+ by precipitation of these two minerals approached 96-98% at pH 3.5 and 5.2, respectively. The obtained compositional stoichiometries, along with computation of the activities of Fe3+, Al3+, SO42- and H+ in solution, allowed the calculation of ionic activity products (log IAP) and solubility product constants (logKsp) for the precipitating phases. The solubility product constants have been deduced by two independent approaches. The first one averages ionic activity products obtained for a given pH range, whereas the second one deduces logKsp values from linear regression lines in ion activity-pH plots. Both methods tend to converge and give logKsp=18.8±1.7 for schwertmannite, and logKsp=23.9±0.7 for hydrobasaluminite. In the pH range 5-9, the results are compatible with additional solubility controls from ferrihydrite and an amorphous to nano-crystalline Al(OH)3 phase on the aqueous concentrations of Fe and Al, respectively, although formation of these latter compounds could not be demonstrated. The present work confirms the results originally obtained for schwertmannite solubility and reports a reliable solubility product constant for freshly precipitated hydrobasaluminite. Integration of the resulting logKsp values in the MINTEQ.V4 database and the PHREEQCI geochemical modeling program provides a precise description of the geochemical behaviour of Fe and Al in these acidic pit lakes. © 2011 Elsevier Ltd.

Pardo-Iguzquiza E.,Instituto Geologico Y Minero Of Espana Igme | Rodriguez-Tovar F.J.,University of Granada
Geo-Marine Letters | Year: 2011

One important handicap when working with stratigraphic sequences is the discontinuous character of the sedimentary record, especially relevant in cyclostratigraphic analysis. Uneven palaeoclimatic/palaeoceanographic time series are common, their cyclostratigraphic analysis being comparatively difficult because most spectral methodologies are appropriate only when working with even sampling. As a means to solve this problem, a program for calculating the smoothed Lomb-Scargle periodogram and cross-periodogram, which additionally evaluates the statistical confidence of the estimated power spectrum through a Monte Carlo procedure (the permutation test), has been developed. The spectral analysis of a short uneven time series calls for assessment of the statistical significance of the spectral peaks, since a periodogram can always be calculated but the main challenge resides in identifying true spectral features. To demonstrate the effectiveness of this program, two case studies are presented: the one deals with synthetic data and the other with paleoceanographic/palaeoclimatic proxies. On a simulated time series of 500 data, two uneven time series (with 100 and 25 data) were generated by selecting data at random. Comparative analysis between the power spectra from the simulated series and from the two uneven time series demonstrates the usefulness of the smoothed Lomb-Scargle periodogram for uneven sequences, making it possible to distinguish between statistically significant and spurious spectral peaks. Fragmentary time series of Cd/Ca ratios and δ18O from core AII107-131 of SPECMAP were analysed as a real case study. The efficiency of the direct and cross Lomb-Scargle periodogram in recognizing Milankovitch and sub-Milankovitch signals related to palaeoclimatic/palaeoceanographic changes is demonstrated. As implemented, the Lomb-Scargle periodogram may be applied to any palaeoclimatic/palaeoceanographic proxies, including those usually recovered from contourites, and it holds special interest in the context of centennial- to millennial-scale climatic changes affecting contouritic currents. © 2011 Springer-Verlag.

Llopis-Albert C.,Instituto Geologico Y Minero Of Espana Igme | Palacios-Marques D.,Polytechnic University of Valencia | Merigo J.M.,University of Manchester
Journal of Hydrology | Year: 2014

In this paper a methodology for the stochastic management of groundwater quality problems is presented, which can be used to provide agricultural advisory services. A stochastic algorithm to solve the coupled flow and mass transport inverse problem is combined with a stochastic management approach to develop methods for integrating uncertainty; thus obtaining more reliable policies on groundwater nitrate pollution control from agriculture. The stochastic inverse model allows identifying non-Gaussian parameters and reducing uncertainty in heterogeneous aquifers by constraining stochastic simulations to data. The management model determines the spatial and temporal distribution of fertilizer application rates that maximizes net benefits in agriculture constrained by quality requirements in groundwater at various control sites. The quality constraints can be taken, for instance, by those given by water laws such as the EU Water Framework Directive (WFD). Furthermore, the methodology allows providing the trade-off between higher economic returns and reliability in meeting the environmental standards. Therefore, this new technology can help stakeholders in the decision-making process under an uncertainty environment. The methodology has been successfully applied to a 2D synthetic aquifer, where an uncertainty assessment has been carried out by means of Monte Carlo simulation techniques. © 2014 Elsevier B.V.

Olea R.A.,U.S. Geological Survey | Pardo-Iguzquiza E.,Instituto Geologico Y Minero Of Espana Igme
Mathematical Geosciences | Year: 2011

The semivariogram and its related function, the covariance, play a central role in classical geostatistics for modeling the average continuity of spatially correlated attributes. Whereas all methods are formulated in terms of the true semivariogram, in practice what can be used are estimated semivariograms and models based on samples. A generalized form of the bootstrap method to properly model spatially correlated data is used to advance knowledge about the reliability of empirical semivariograms and semivariogram models based on a single sample. Among several methods available to generate spatially correlated resamples, we selected a method based on the LU decomposition and used several examples to illustrate the approach. The first one is a synthetic, isotropic, exhaustive sample following a normal distribution, the second example is also a synthetic but following a non-Gaussian random field, and a third empirical sample consists of actual raingauge measurements. Results show wider confidence intervals than those found previously by others with inadequate application of the bootstrap. Also, even for the Gaussian example, distributions for estimated semivariogram values and model parameters are positively skewed. In this sense, bootstrap percentile confidence intervals, which are not centered around the empirical semivariogram and do not require distributional assumptions for its construction, provide an achieved coverage similar to the nominal coverage. The latter cannot be achieved by symmetrical confidence intervals based on the standard error, regardless if the standard error is estimated from a parametric equation or from bootstrap. © 2010 International Association for Mathematical Geosciences.

Pardo-Iguzquiza E.,Instituto Geologico Y Minero Of Espana Igme | Olea R.A.,U.S. Geological Survey
Computers and Geosciences | Year: 2012

In applied geostatistics, the semivariogram is commonly estimated from experimental data, producing an empirical semivariogram for a specified number of discrete lags. In a second stage, a model defined by a few parameters is fitted to the empirical semivariogram. As the experimental data are usually few and sparsely located, there is considerable uncertainty about the calculated semivariogram values (uncertainty of the empirical semivariogram) and about the parameters of any model fitted to them (uncertainty of the estimated model parameters). In this paper, the uncertainty in the modeling of the empirical semivariogram is numerically assessed by the generalized bootstrap, which is an extension of the classic bootstrap procedure modified for spatially correlated data. A computer program is described and provided for the assessment of those uncertainties. In particular, the program provides for the empirical semivariogram: the standard errors, the bootstrap percentile confidence intervals, the complete variance-covariance matrix, standard deviation correlation matrix. A public domain, natural dataset is used to illustrate the performance of the program. A promising result is that, for any distance, the median of the bootstrap distribution for the empirical semivariogram approximates more closely the underlying semivariogram than the estimate derived from the empirical sample. © 2011.

Llopis-Albert C.,Instituto Geologico Y Minero Of Espana Igme | Pulido-Velazquez D.,Instituto Geologico Y Minero Of Espana Igme
Hydrological Processes | Year: 2014

Analytical models have been exhaustively used to study simple seawater intrusion problems and the sustainable management of groundwater resources in coastal aquifers because of its simplicity, easy implementation, and low computational cost. Most of these models are based on the sharp-interface approximation and the Ghyben-Herzberg relation, and their governing equations are expressed in terms of a single potential theory to calculate critical pumping rates in a coastal pumping scenario. The Ghyben-Herzberg approach neglects mixing of fresh water and seawater and implicitly assumes that salt water remains static. Therefore, the results of the analytical solutions may be inaccurate and unacceptable for some real-complex case studies. This paper provides insight into the validity of sharp-interface models to deal with seawater intrusion in coastal aquifers, i.e. when they can be applied to obtain accurate enough results. For that purpose, this work compares sharp-interface solutions, based on the Ghyben-Herzberg approach, with numerical three-dimensional variable-density flow simulations for a set of heterogeneous groundwater flow and mass transport parameters, and different scenarios of spatially distributed recharge values and spatial wells placement. The numerical experiment has been carried out in a 3D unconfined synthetic aquifer using the finite difference numerical code SEAWAT for solving the coupled partial differential equations of flow and density-dependent transport. This paper finds under which situations the sharp-interface solution gives good predictions in terms of seawater penetration, transition zone width and critical pumping rates. Additionally, the simulation runs indicate to which parameters and scenarios the results are more sensitive. © 2013 John Wiley & Sons, Ltd.

Garcia-Garizabal I.,CSIC - Centro de Investigación y Tecnología Agroalimentaria | Causape J.,Instituto Geologico Y Minero Of Espana Igme
Journal of Hydrology | Year: 2010

Irrigated agriculture is working towards environmental sustainability but more study is needed regarding the agro-systems' response to alterations imposed on them. This work analyzed the repercussions that alternative irrigation management can cause on water use and on the quality of irrigation return flows. The case of Bardenas Canal Irrigation District no. V (ID-V) was studied, by analyzing the change of salinity and nitrate concentration in the drainage network through monthly samplings, before (2000) and after (2007) ID-V implanted alternative flood irrigation management. The results showed that the electric conductivity (25 °C) and nitrate concentration in the drainage ditches increased in 2007 (0.99 dS/m and 62 mg/l) with respect to 2000 (0.86 dS/m and 57 mg/l). Nevertheless, the decrease in irrigation drainage in 2007 (88% lower in 2007 when compared to that of 2000) was a result of the decrease in water requirement (594 mm in 2007 against 752 mm in 2000) and of the increase in irrigation efficiency (93% in 2007 and 67% in 2000), causing the Riguel River to present a lower flow (13% inferior when compared with 2000), lower salinity (1.08 dS/m in 2007 and 1.18 dS/m in 2000), and lower nitrate concentration (29 mg/l in 2007 and 33 mg/l in 2000) when exiting ID-V in 2007. In summary, simple alternatives in irrigation management achieved an increment of 26% in water use, decreasing by 20% and 24% the salt and nitrate masses exported, respectively, ameliorating the quality of the system receiving the irrigation return flows (Riguel River). © 2010 Elsevier B.V. All rights reserved.

Martin-Gonzalez F.,Rey Juan Carlos University | Heredia N.,Instituto Geologico Y Minero Of Espana Igme
Tectonophysics | Year: 2011

The tectonic and tectonostratigaphic evolution of foreland basins and related Tertiary depressions are the key to investigate deformation history and the uplifting of the continental lithosphere of the Alpine-Pyrenean Orogeny. The northern part of the Duero basin is the foreland basin of the Cantabrian Mountains, which are, in turn, the western part of the Pyrenean Orogen. We have studied the western sharp end of the Duero foreland basin, and its relation to the Tertiary deposits of the NW Iberian Peninsula and the topography evolution. In order to propose a coherent tectonic and tectonosedimentary model that could explain all Tertiary deposits, we have analysed the depositional environment, stratigraphic sequences, paleocurrents and established a correlation of the main outcrops. Besides, a detailed structural mapping of the Alpine structures that limit and affect the main Tertiary outcrops has been carried out. The Tertiary deposits of the NW Iberian Peninsula depressions are affected and fragmented by Alpine structures that limit their extensions and locations. The stratigraphic succession is similar in the NW Tertiary outcrops; they are mainly terrigenous and carbonated continental deposits formed by assemblage of alluvial fans developed at the mountains front, in arid or semiarid conditions. Three formations can be identified in the main depressions: Toral Fm, Santalla Fm and Médulas Fm. The NW Tertiary outcrops were the western deposits of the Duero foreland basin that surrounded the lateral termination of the Pyrenean Orogen. These deposits were fragmented and eroded by the subsequent uplift of the Galaico-Leoneses Mountains and the NE-SW strike-slip faults activity (broken foreland basin). Only the latest stages of some of these outcrops can be considered as intramontane basins as traditionally have been interpreted. The sedimentation started in the northeast (Oviedo-Infiesto) during the Eocene and migrated to the west (As Pontes) during the Late Oligocene-Early Miocene times. Meanwhile, southern areas were far away from the tectonic activity (El Bierzo, O Barco, Monforte, Sarria depressions). © 2010 Elsevier B.V.

Gonzalez-Menendez L.,Instituto Geologico Y Minero Of Espana Igme | Gallastegui G.,Instituto Geologico Y Minero Of Espana Igme | Cuesta A.,University of Oviedo | Heredia N.,Instituto Geologico Y Minero Of Espana Igme | Rubio-Ordonez A.,University of Oviedo
Gondwana Research | Year: 2013

Early Paleozoic mafic igneous rocks from the Central Andean basement are located in N-S belts interpreted as suture zones among different terranes. In the western Cuyania terrane (Andean Argentine Precordillera), Sierra del Tigre mafic rocks are part of one of these belts and consist of clinopyroxene+plagioclase basalts and gabbros of tholeiitic-transitional geochemistry. These rocks were emplaced as volcanic-subvolcanic bodies during the Mid/Late Ordovician/Silurian. Distinctive geochemical features include moderate to slightly elevated light rare earth element (LREE) concentrations; low to moderate large ion lithophile element (LILE)/high field strength element (HFSE) ratios; absence of negative Nb-Ta anomalies; low Rb concentrations; negative anomalies of K (strong) and positive Ba anomalies. This geochemistry differs from that of normal-type mid-oceanic ridge basalt (N-MORB) or oceanic island basalt (OIB) and excludes the existence of subduction components. REE patterns and LILE/HFSE ratios are similar to those of enriched MORB (E-MORB) and some continental flood basalts. Geochemical modeling suggests that the parental magmas of these basalts and gabbros derived from mantle sources with compositions similar to that of the primordial mantle in the garnet-spinel transition zone. Further magmatic evolution consisted of olivine crystal fractionation and olivine+clinopyroxene+plagioclase equilibrium crystallization under low pressure, H2O, and oxidation conditions. Continental crust contamination may have occurred, but only in low proportions. Post-magmatic hydrothermal alteration consisted of slight to moderate metasomatism that added Ba, removed K±Rb, and generated the observed secondary mineral assemblage (mainly chlorite, epidote, and carbonates). The most probable tectonic setting for the generation and emplacement of this mafic suite is an evolved rifted margin (tholeiitic-transitional nature, E-MORB) within a thin continental crust that was unrelated to subduction-type margins. This model suggests that a western terrane (Chilenia) rifted partially from Cuyania during the Late Ordovician. © 2012 International Association for Gondwana Research.

Santofimia E.,Instituto Geologico Y Minero Of Espana Igme | Lopez-Pamo E.,Instituto Geologico Y Minero Of Espana Igme
Journal of Hydrology | Year: 2013

The hydraulic system of the Concepción mine is made up of an open pit and an underground mine, which are currently flooded and hydraulically connected. The Concepción pit lake has shown permanent chemical stratification (meromictic lake), where two layers with different density and chemical composition can be differentiated: (i) a thick superficial layer of 11±2 m deep, with a low concentration of dissolved solids (mixolimnion) and (ii) a thin bottom layer from 11±2 m to 16. m deep (monimolimnion), exhibiting vertical changes in its physico-chemical parameters, with decreasing redox potential and increasing T, pH and dissolved solids content with depth. The distribution of the Concepción pit lake layers depends on recharge processes and the loss of water from the system. In winter, rainfall and runoff result in a rapid increase of lake levels. The lake regains its initial level whenever water is lost through an old mine adit, since galleries and shafts act as preferential pathways for inflowing and outflowing water. This network is connected to the bottom of the lake, resulting in the progressive downward movement of the chemocline. Furthermore, runoff generates a less dense superficial layer, which triggers the development of an ephemeral chemocline in the mixolimnion. In summer, the mixolimnion loses water by evaporation which is partially compensated by groundwater inflowing from the lake bottom, resulting in the upward movement of the permanent chemocline. During this period the water level in the system is below the outlet level, which therefore renders the outflow of water inactive. During this stage, the mixolimnion remains homogeneous and the shallow chemocline disappears. Taking into consideration the hydrochemical characteristics of this pit lake and the spatial distribution of the layers identified, a model that explains its seasonal limnological evolution is presented. © 2013 Elsevier B.V.

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