Strontium isotope geochemistry of alluvial groundwater: a tracer for groundwater resources characterisation

International audienceThis study presents strontium isotope and major ion data of shallow groundwater and river water from the Ile du Chambon catchment, located on the Allier river in the Massif Central (France). There are large variations in the major-element contents in the surface- and groundwater. Plotting of Na vs. Cl contents and Ca, Mg, NO3, K, SO4, HCO3, Sr concentrations reflect water–rock interaction (carbonate dissolution for Ca, Mg, HCO3 and Sr because the bedrock contains marly limestones), agricultural input (farming and fertilising) and sewage effluents (for NO3, K, SO4), although some water samples are unpolluted. Sr contents and isotope ratios (87Sr/86Sr vary from 0.70892 to 0.71180 along the hydrological cycle) in the groundwater agree with previous work on groundwater in alluvial aquifers in the Loire catchment. The data plot along three directions in a 87Sr/86Sr v. 1/Sr diagram as a result of mixing, involving at least three geochemical signatures–Allier river water, and two distinct signatures that might be related to different water-rock interactions in the catchment. Mixing proportions are calculated and discussed. The alluvial aquifer of the Ile du Chambon catchment is considered, within the Sr isotope systematic, in a larger scheme that includes several alluvial aquifers of the Loire Allier catchment. Keywords: : Loire river, major and trace elements, Sr isotopic ratio, alluvial aquifer, hydrolog

Boron Isotope Characterization to Design a Frame of Hydrogeological Functioning of a Wetland System (Massif Central, France)

AbstractMulti-isotopic approaches (Li, Sr, O, H), combined with hydrological tools, have been already appliedfor tracing the water and dissolved-element fluxes in a peatland in Central France. Here, we applied B isotopes. The δ11B ratios increase from river draining basalts (∼ 0‰) up to springs bordering the peatland (>+25‰). Peatland groundwaters have intermediate δ11B: 7.8 to 19.4‰. This range is accompanied by an increase in the Ca contents between the river draining basalts and water in the peatland. In aδ11B vs.Ca/B diagram, the role of water rock interaction and present day fertilizer inputs is evidenced, as for Sr isotopes

Micropollutants and boron isotopes as tracers of the presence of domestic wastewater effluents in surface and groundwaters

International audienc

La "Zone minéralisée de l'Entre-deux-Mers" : Caractérisation hydrogéologique, géochimique et isotopique - CARISMEAU 2.

Au nord du Bassin Adour-Garonne, la ressource en eau principalement exploitée pour l'alimentation en eau potable est l'aquifère Eocène (masse d'eau 5071). Le projet de recherche CARISMEAU 2, initié début 2009 s'inscrit étroitement dans le cadre de la Directive Cadre sur l'Eau. Il vise à mieux comprendre les hétérogénéités et les interconnections au sein de la masse d'eau 5071. En effet, cet aquifère présente des teneurs anomaliques en sulfates et fluor qui induisent des difficultés d'exploitation de la ressource. L'origine de ces minéralisations excessives, réparties de façon hétérogène, n'est pas encore connue. Le projet CARISMEAU 2, auquel est associée la thèse " Zone minéralisée de l'Entre-deux-Mers ", met en application une approche couplée hydrogéologique, géochimique et isotopique. Les objectifs sont de mieux connaître l'origine de la salinité et de définir les circulations de ces eaux minéralisées dans l'aquifère Eocène, lui-même compris au sein du système aquifère multicouche du Bassin aquitain. Afin de mieux caractériser cette masse d'eau, une cinquantaine de points ont été suivis fin 2009. Des méthodes de géochimie et de géochimie isotopique classiques sont utilisées, mais aussi des méthodes isotopiques innovantes et/ou expérimentales. Les premiers résultats des analyses géochimiques et multi-isotopiques sont présentés dans l'objectif de mieux comprendre l'origine de ces éléments, leur comportement et leur migration dans les aquifères

Faire face à la salinisation et à la contamination des aquifères côtiers dans le contexte des changements environnementaux planétaires et sociétaux : Approches géochimique et isotopique appliquées aux ressources en eau de Recife (Brésil)

National audienceEn raison d'une pression démographique croissante, la région métropolitaine de Recife a subi d'importants changements d'utilisation des terres et de l'eau au cours des dernières décennies. Ces évolutions ont notamment généré une baisse spectaculaire des niveaux piézométriques, la salinisation et la contamination des eaux souterraines. Cette dégradation des ressources naturelles est liée à l'augmentation de la demande en eau, ponctuellement amplifiée par des périodes de sécheresse qui ont conduit à la construction de milliers de puits privés. La région de Recife apparaît ainsi comme un "point chaud" typique illustrant les problèmes des pays émergents tels que l'urbanisation, la répartition inégale de la richesse, la faiblesse des structures décisionnelles, les rapides développements industriel et touristique, induisant des pressions fortes sur les ressources en eau (quantité et qualité) dans le contexte des changements globaux sociétaux et environnementaux. Le projet COQUEIRAL a pour objectif d'étudier l'impact des activités humaines sur les aquifères côtiers surexploités en (1) analysant les pressions sur les ressources en eau souterraine et leurs raisons sociales et structurelles,(2) identifiant les sources et les mécanismes de la dégradation des ressources en eau souterraine en termes de qualité et de quantité, en se concentrant sur les processus physiques et chimiques en tant que vecteurs de la réaction du système aux pressions extérieures et (3) évaluant les impacts des changements globaux sur les ressources en eau à l'échelle régionale

Applications of stable water and carbon isotopes in watershed research: Weathering, carbon cycling, and water balances

Research on rivers has traditionally involved concentration and flux measurements to better understand weathering, transport and cycling of materials from land to ocean. As a relatively new tool, stable isotope measurements complement this type of research by providing an extra label to characterize origin of the transportedmaterial, its transfer mechanisms, and natural versus anthropogenic influences. These new stable isotope techniques are scalable across a wide range of geographic and temporal scales. This review focuses on three aspects of hydrological and geochemical river research that are of prime importance to the policy issues of climate change and include utilization of stable water and carbon isotopes: (i) silicate and carbonate weathering in river basins, (ii) the riverine carbon and oxygen cycles, and (iii) water balances at the catchment scale. Most studies at watershed scales currently focus on water and carbon balances but future applications hold promise to integrate sediment fluxes and turnover, ground and surface water interactions, as well as the understanding of contaminant sources and their effects in river systems

Groundwater salinization in a coastal multilayer aquifer: Preliminary results on origins and mechanisms. Example of Recife (Brazil)

International audienceThe Recife Metropolitan Region (PE, Brazil) appears as a typical "hot spot" illustrating the problems of southern countries such as urbanization or rapid industrial and touristic development. All these factors induce high pressures on water resources both on quantity and quality in the context of global social and environmental changes. This paper focuses on the groundwater geochemistry in a costal multilayer aquifer aiming at investigating the sources and processes of salinization. The preliminary results of 62 groundwater samples from the five main aquifers are reported

Tracing the origins and processes of groundwater salinization in coastal aquifers with a multi-isotopes approach. Example of Recife, Northeast of Brazil

International audienceThe Recife Metropolitan Region (PE, Brazil) is a typical "hot spot" illustrating the problems of southern countries on water issues inducing high pressures on water resources both on quantity and quality in the context of global social and environmental changes. By focusing on the groundwater geochemistry in a costal multilayer aquifer, this work aims at investigating the sources and processes of salinization. Two different Precambrian blocks separated by a large lineament area constitute the site basement. The sedimentary fillings of the two basins present different origins that were distinguished by the Sr isotope composition. The northern deep Beberibe aquifer displays very high 87Sr/86Sr with a large range of values (0.7102-0.7233) illustrating the main continental origin of sediments whereas the southern deep Cabo aquifer showed lower values (0.7097-0.7141) indicating the contribution of the marine sedimentation. Although sulfate isotopes, Electrical Conductivity and Cl contents indicate a mixing with seawater for some samples of the deep Cabo and Beberibe aquifers, all 87Sr/86Sr values are above the present-day seawater composition. This can be related to the complex local history of transgression/regression phases that induced alternatively salinisation and freshening with gains and losses of cations and Sr, together with water-rock interactions. δ18O-δ2H clearly evidence the local present day recharge in the surficial aquifer, some samples being affected by in situ evaporation processes and/or recharge with evaporated water from dams used for water supply. The deep aquifers display a high range of B (20-600µg/L) and δ11B (6.7-68.5‰) with some of the highest values known to date. Multiple sources and processes affect the B behavior, among which mixing with saline water, B sorption on clays/organic matter and mixing with wastewater. The surficial aquifers are locally salinized possibly due to present seawater intrusion, and highly contaminated with wastewater

Geochemical, multi-isotopic and hydrogeological characterization of mineralized groundwaters, Entre-deux-Mers area, Gironde (SW France).

Groundwater quality sustainability In the south-west of France, the Eocene aquifer is one of the main resources for irrigation, thermo-mineral water, and mainly for drinking water in the Bordeaux region. This aquifer is characterized by the presence of a large mineralized area, centered on the Entre-deux-Mers region, between the Garonne and the Dordogne rivers, where the groundwaters show strong mineralization and anomalous levels of critical elements, such as sulphates and fluoride, leading to difficulties of resource exploitation for drinking water supply. Ongoing analyses of major elements confirm the salinity variation in the system and the multi-isotopes results will be presented at the conference, in order to decipher the origin of this salinity

Potential leakage between aquifers in a deeply anthropized coastal sedimentary basin (Recife, Brazil): Strontium isotope constraints

Code ADS 2013EGUGA..15.7691PInternational audienceDue to an increasing demographic pressure, the Metropolitan Region of Recife (RMR) went through remarkable changes of water and land uses over the last decades. These evolutions gave rise to numerous environmental consequences, such as a dramatic decline of the piezometric levels, groundwater salinization and contamination. This degradation of natural resources is linked to the increase of water demand, punctually amplified by drought periods which induced the construction of thousands of private wells. The preliminary results of 62 groundwater samples from the five main aquifers are reported. This part of the study focuses on the major elements together with Sr isotopes to (1) characterize the signature of the different aquifer compartments of the 5 main aquifers, and (2)assess the potential connections between aquifers, e.g. vertical exchanges between the aquifers that can be modified or amplified by overexploitation or triggered through failed or improperly constructed wells