Una revisión de los procesos geoquímicas de baja temperatura en la interacción agua-roca

Mineral alteration processess give raise to the physico-chemical characteristics of natural waters by means of water-rock interactions during the hydrogeological cycle. Rainwaters acquire their main components by exchange ions with the cation exchange complex of the insaturated zone. The superficial alteration of the primary rocks origines the secondary minerals and remain reflected in the solutes incorporation in the waters. The origin of groundwaters composition from igneous rocks would be predicted with chemical cuantitative models if thermodinamic constants of some alteration products would be known. The sulfide oxication and the sulphate reduction are two important redox hydrogeochemical processes involved in the changes of the redox potential and the bacteries are present as catalytic of the reactions. The dolomite formation and the de dolomitization are present in the limestones and several problems appear with the kinetic in the reaction of the dolomite formation.Los procesos de alteración mineral superficial dan lugar a la adquisición de las características físico-químicas de las aguas naturales mediante procesos de interacción con la fase sólida con la que se pone en contacto a través del ciclo hidrogeológico. Las aguas de lluvia comienzan a adquirir los principales componentes químicos al percolar a través de la zona insaturada por medio de intercambios iónicos con el complejo de intercambio catiónico de los suelos. La alteración hipergénica de las rocas primarias provoca la aparición de los minerales secundarios y se refleja en la incorporación de nuevos solutos a las aguas. El origen de la composición del agua subterránea de las rocas ígneas podría conocerse mediante modelos químicos cuantitativos relativamente sencillos si se conocieran determinadas incógnitas sobre las constantes termodinámicas de algunos productos de alteración mineral. La oxidación de sulfuros y la reducción de sulfatos son dos de los principales procesos hidrogeoquímicos redox que confieren a las aguas características relacionadas con aumentos y descensos de los potenciales de oxidación-reducción. En ambos procesos las bacterias actúan como catalizadores esenciales que regulan la cinética de las reacciones. La formación de dolomita y su proceso de ruptura es propio de formaciones carbonatadas y confieren a las aguas características químicas distintas debido a la presencia de estos nuevos solutos. Los procesos de dolomitización presentan problemas en relación con la cinética de las reacciones

Stable isotopes applied to the study of the concrete/bentonite interaction in the FEBEX in situ test

Stable isotope analysis was carried out on a set of samples from the concrete-bentonite interface from the FEBEX real-scale in-situ experiment. The concrete and bentonite that simulated the engineering barriers system of a deep geological repository have interacted for 13 years in saturated conditions up to dismantling. The monitoring of the experiment during the years of operation has made possible to know not only the baseline status but also the evolution of the system and the mass transfer processes. Thus, the FEBEX experiment has been a unique opportunity to study concrete degradation within a broader multi-proxy approach under real-scale repository conditions. Analysis of carbon and oxygen isotopes of carbonates in groundwater, concrete and clay have provided evidence of how dissolution and mass transfer processes occur in the Engineered Barrier System (EBS). Spatial distribution of δ13C values points to the existence of a dominant process of diffusion of carbon species from bentonite towards the concrete/bentonite interface. Variations in δ18O values suggest a non-homogeneous geochemical and hydraulic behavior of the EBS in the vicinity of both, the granite-concrete interface and the concrete-bentonite interface. These differences might be related to different degrees of exposure of each sample to bentonite porewater, groundwater and concrete/bentonite leachates. This seem to be in agreement with the existence of different chemical environments depending on the location of the samples in the experiment.The work was financially supported by the European Union's Horizon 2020 grant agreement n° 662147 (www.cebama.eu) and the Annex XLII of the ENRESA-CIEMAT framework agreement. The FEBEX project was financed by ENRESA and the EC Contracts FI4W-CT95-006 and FIKWCT-2000-00016. The FEBEX-DP Consortium (NAGRA, SKB, POSIVA, CIEMAT, KAERI) financed the dismantling operation and onsite determinations in 2015

Application of mineralogical, petrological and geochemical tools for evaluating the palaeohdrogeological evolution of the PADAMOT study sites

The role of Work Package (WP) 2 of the PADAMOT project – ‘Palaeohydrogeological Data Measurements’ - has been to study late-stage fracture mineral and water samples from groundwater systems in Spain, Sweden, United Kingdom and the Czech Republic, with the aim of understanding the recent palaeohydrogeological evolution of these groundwater systems. In particular, the project sought to develop and evaluate methods for obtaining information about past groundwater evolution during the Quaternary (about the last 2 million years) by examining how the late-stage mineralization might record mineralogical, petrographical and geochemical evidence of how the groundwater system may have responded to past geological and climatological changes. Fracture-flow groundwater systems at six European sites were studied: • Melechov Hill, in the Bohemian Massif of the Czech Republic: a shallow (0-100 m) dilute groundwater flow system within the near-surface weathering zone in fractured granitic rocks; • Cloud Hill, in the English Midlands: a (~100 m) shallow dilute groundwater flow system in fractured and dolomitized Carboniferous limestone; • Los Ratones, in southwest Spain: an intermediate depth (0-500 m) dilute groundwater flow system in fractured granitic rocks; • Laxemar, in southeast Sweden: a deep (0-1000 m) groundwater flow system in fractured granitic rocks. This is a complex groundwater system with potential recharge and flushing by glacial, marine, lacustrine and freshwater during the Quaternary; • Sellafield, northwest England: a deep (0-2000 m) groundwater flow system in fractured Ordovician low-grade metamorphosed volcaniclastic rocks and discontinuous Carboniferous Limestone, overlain by a Permo-Triassic sedimentary sequence with fracture and matrix porosity. This is a complex coastal groundwater system with deep hypersaline sedimentary basinal brines, and deep saline groundwaters in crystalline basement rocks, overlain by a shallow freshwater aquifer system. The site was glaciated several times during the Quaternary and may have been affected by recharge from glacial meltwater; • Dounreay, northeast Scotland: a deep (0-1400 m) groundwater flow system in fractured Precambrian crystalline basement overlain by fractured Devonian sedimentary rocks. This is within the coastal discharge area of a complex groundwater system, comprising deep saline groundwater hosted in crystalline basement, overlain by a fracture-controlled freshwater sedimentary aquifer system. Like Sellafield, this area experienced glaciation and may potentially record the impact of glacial meltwater recharge. In addition, a study has been made of two Quaternary sedimentary sequences in Andalusia in southeastern Spain to provide a basis of estimating the palaeoclimatic history of the region that could be used in any reconstruction of the palaeoclimatic history at the Los Ratones site: • The Cúllar-Baza lacustrine sequence records information about precipitation and palaeotemperature regimes, derived largely from the analysis of the stable isotope (δ18O and δ13C) signatures from biogenic calcite (ostracod shells). • The Padul Peat Bog sequence provided information on past vegetation cover and palaeogroundwater inputs based on the study of fossil pollen and biomarkers as proxies for past climate change. Following on from the earlier EC 4th Framework EQUIP project, the focus of the PADAMOT studies has been on calcite mineralization. Calcite has been identified as a late stage mineral, closely associated with hydraulically-conductive fractures in the present-day groundwater systems at the Äspö-Laxemar, Sellafield, Dounreay and Cloud Hill sites. At Los Ratones and Melechov sites late-stage mineralization is either absent or extremely scarce, and both the quantity and fine crystal size of any late-stage fracture mineralization relevant to Quaternary palaeohydrogeological investigations is difficult to work with. The results from the material investigated during the PADAMOT studies indicate that the fracture fillings at these sites are related to hydrothermal activity, and so do not have direct relevance as Quaternary indicators. Neoformed calcite has not been found at these two sites at the present depth of the investigations. Furthermore, the HCO3 - concentration in all the Los Ratones groundwaters is mainly controlled by complex carbonate dissolution. The carbonate mineral saturation indices do not indicate precipitation conditions, and this is consistent with the fact that neoformed calcite, ankerite or dolomite have not been observed petrographically

Long-term hydrological changes in northern Iberia (4.9–0.9 ky BP) from speleothem Mg/Ca ratios and cave monitoring (Ojo Guareña Karst Complex, Spain)

An absolute-dated stalagmite from Kaite Cave (Ojo Guareña Karst Complex, N Spain) provides a nearly continuous, high-resolution record of a proxy of regional precipitation patterns through the 4.9–0.9 ka BP interval. This record is based on the Mg/Ca ratio of the calcite and its variation through the stalagmite stratigraphy, which is interpreted to be primarily driven by changes in precipitation amount. The calibration of the proxy is supported by the present-day monitoring carried out in the cave for the last 10 years, which reveals a robust inverse relationship between the inter-annual/inter-decadal variability of rainfall and the Mg concentration of dripwaters and precipitating speleothems. The record of paleoprecipitation, based on 2400 Mg/Ca measurements, shows strong variability at inter-annual to inter-decadal scales, and more subtle but significant changes at secular to millennial scales. This long-term paleohydrological evolution outlines five successive intervals with consistent trends, which are bounded by abrupt shifts in the regional precipitation. These shifts took place at 4.65, 4.2, 2.6, and 1.3 ka BP. Significantly, the intervals of maximum precipitation of the whole record (around 4.9–4.65, 2.6–2.45, and 1.3–1.1 ka BP) can be related with episodes of minimum solar activity and correlated with cold climatic events elsewhere.Contribution to research projects 28 CGL2010-21499-BTE and CGL2013-43257-R of the Spanish R+D National Program 29 (MINECO) and research groups ‘‘Paleoclimatology and Global Change’’ and ‘‘Laser Induced 30 Breakdown Spectroscopy (LIBS)’’ from the UCM (Spain).Peer reviewe

Pore water chemistry of a Paleogene continental mudrock in Spain and a Jurassic marine mudrock in Switzerland: Sampling methods and geochemical interpretation

Este trabajo resume una serie de metodologías y aproximaciones desarrolladas en CIEMAT durante los últimos 10 años con el objetivo de obtener información del agua intersticial de dos formaciones arcillosas: la Opalinus Clay procedente de Suiza y una formación de edad Oligoceno Mioceno española. Ambas tienen características bastante diferentes tanto desde el punto de vista de la metodología aplicada para su estudio como del origen sedimentario en sí mismo de las dos formaciones. La arcilla Suiza se estudió a través de la participación en el experimento DI-B en el laboratorio subterráneo de Mont Terri, en Suiza, uno de cuyos objetivos fue el muestreo y análisis in situ del agua intersticial de la arcilla. Las muestras de agua se recogieron después de desarrollar equipos y metodologías para conseguir una alteración mínima de los parámetros críticos del agua de la arcilla: pH, Eh, pCO2, Fe(II) y alcalinidad. La modelización geoquímica se utilizó como herramienta para interpretar y entender los principales procesos geoquímicos que controlan la química del agua y el estado actual del sistema. En relación con la arcilla española, el artículo muestra el desarrollo de una metodología integrada para caracterizar el agua intersticial de la formación arcillosa a partir de muestras de testigos correspondientes a un sondeo, denominados S1. El estudio trata de integrar todos los datos disponibles sobre la composición del agua intersticial obtenida mediante la técnica de compresión bajo presión (squeezing) y mediante extractos acuosos, con la caracterización mineralógica y geoquímica de los testigos. La modelización geoquímica se utilizó con dos objetivos principales: para valorar la consistencia de los datos analíticos del agua intersticial y para determinar la importancia relativa de los principales procesos que gobiernan la química del agua intersticial. Específicamente, la modelización se utilizó para simular los procesos que controlan la evolución redox del sistema. Se consideró equilibrio para los minerales reactivos como la calcita, dolomita, yeso y ferrihidrita. Además, se trató la degradación de la materia orgánica y la disolución oxidativa de la pirita desde un punto de vista cinético

Increased mitochondrial DNA diversity in ancient Columbia River basin Chinook salmon Oncorhynchus tshawytscha

The Columbia River and its tributaries provide essential spawning and rearing habitat for many salmonid species, including Chinook salmon (Oncorhynchus tshawytscha). Chinook salmon were historically abundant throughout the basin and Native Americans in the region relied heavily on these fish for thousands of years. Following the arrival of Europeans in the 1800s, salmon in the basin experienced broad declines linked to overfishing, water diversion projects, habitat destruction, connectivity reduction, introgression with hatchery-origin fish, and hydropower development. Despite historical abundance, many native salmonids are now at risk of extinction. Research and management related to Chinook salmon is usually explored under what are termed “the four H’s”: habitat, harvest, hatcheries, and hydropower; here we explore a fifth H, history. Patterns of prehistoric and contemporary mitochondrial DNA variation from Chinook salmon were analyzed to characterize and compare population genetic diversity prior to recent alterations and, thus, elucidate a deeper history for this species. A total of 346 ancient and 366 contemporary samples were processed during this study. Species was determined for 130 of the ancient samples and control region haplotypes of 84 of these were sequenced. Diversity estimates from these 84 ancient Chinook salmon were compared to 379 contemporary samples. Our analysis provides the first direct measure of reduced genetic diversity for Chinook salmon from the ancient to the contemporary period, as measured both in direct loss of mitochondrial haplotypes and reductions in haplotype and nucleotide diversity. However, these losses do not appear equal across the basin, with higher losses of diversity in the mid-Columbia than in the Snake subbasin. The results are unexpected, as the two groups were predicted to share a common history as parts of the larger Columbia River Basin, and instead indicate that Chinook salmon in these subbasins may have divergent demographic histories.Ye

Técnicas de caracterización hidrogeoquímica de ambientes profundos

The characterisation of the hydrogeochemical parameters controlling the radionuclide migration towards the biosphere implicates the deve10pment of a methodology including instrumentation and equipment for working in deep boreholes, according with the data in which we are more interested. This methodology consists of a systematic and detailled study of the boreholes (studies on the cores, geophysical parameters, hydraulic tests ... ) that allows to select zones for water sampling and characterisation. The selected areas are adequately isolated with a double packer system and coupled instrumentation for pumping water (pumps or gas lift systems). The isolated zone is cleaned by pumping, and the tracer concentration, tritium measures or the control of the stabilization of physico-chemical parameters, are good indicators of the representativity of the sample. Water, gases, particles, colloids and microorganisms sampling is made in glove boxes and the analysis are made in a movillaboratory in situ for determining the more sensible parameters, avoiding the sample alterations with the transport.El estudio de los posibles emplazamientos de residuos radiactivos en un medio geológico cualquiera en profundidad, requiere la caracterización de los parámetros hidrogeológicos e hidrogeoquímicos que controlan la migración de los radionucleidos hacia la biosfera. Para llevar a cabo esa caracterización se ha desarrollado una metodología que incluye: (1) estudio sistemático y minucioso de sondeos profundos con el fin de seleccionar zonas favorables para el muestreo del agua y su caracterización; (2) sellado de las zonas seleccionadas mediante obturadores; (3) bombeo de agua de la zona aislada, mediante bombas o sistemas de elevación con gas, con el fin de eliminar la contaminación producida por el agua de perforación. El control de la limpieza se realiza mediante el seguimiento de trazadores y la estabilización de los parámetros físico-químicos del agua; (4) muestreo y análisis in situ de agua, gases, partículas, coloides y microorganismos, para 10 cual se ha diseñado una unidad móvil de caracterización hidrogeoquímica (UMCH) que permite determinar in situ los parámetros más sensibles, evitando así los problemas de alteración debidos al transporte de las muestras

Evaluation of Laser Induced Breakdown Spectroscopy (LIBS) for detection of trace element variation through stalagmites: potential for paleoclimate series reconstruction

Laser Induced Breakdown Spectroscopy (LIBS) is applied to evaluate the potential of this technique for characterizing trace element ratios (particularly Mg/Ca and Sr/Ca) in the speleothems (cave deposits of calcium carbonate such as stalagmites) that are commonly used to reconstruct time series of past climate change. These geological materials are characterized by a relatively simple internal stratigraphy that reflects their growth history and geochemical changes through that history can reflect variability in environmental parameters such as temperature and rainfall. In this paper, the characterization of methodological and experimental parameters such as sample preparation, microsample size and representativity, sensitivity, linearity, and replicability reveals the high potential of the technique and show clear advantages versus other commonly-used techniques.Peer Reviewe