P. M. Carreira

Conceptualizing a mountain hydrogeologic system by using an integrated groundwater assessment (Serra da Estrela, Central Portugal): a review

Mountains are often considered as the world’s water towers. This paper presents a critical review on the research concerning the integrated assessment of groundwater resources of the mountain hydrogeologic system of Serra da Estrela Natural Park (central Portugal). The study area is the Zêzere river basin upstream of Manteigas village located at the Serra da Estrela Mountain in Central Portugal. It provides the source of strategic water resources for the Portuguese mainland, including normal groundwaters, thermomineral waters and surface waters. An integrated approach has been used to formulate a conceptual model for this complex mountain hydrogeological system by integrating the geological, morphotectonic, hydroclimatic, unsaturated soil zone, hydrogeological, hydrogeophysical, hydrogeochemical and isotopic data. This model has been useful to: i) evaluate the water resources; ii) provide the basis for a sustainable management of water resources, iii) design measures for groundwater exploitation and contamination control; and iv) set up land-use policies.

Assessment of recharge and flowpaths in a limestone thermomineral aquifer system using environmental isotope tracers (Central Portugal)

We conducted chemical and isotopic analyses to develop and test a hydrogeological model of thermomineral water circulation in a limestone aquifer system at Caldas da Rainha (Central Portugal), contributing to future borehole-drilling and development strategies, with the aim of extracting waters with the best possible flow and/or temperature. The thermomineral waters (T ≈ 33 °C) discharge from springs and boreholes located close to a locally N–S-oriented oblique fault (60°E) that places loamy and detritic Upper Jurassic rocks and Hettangian-Rhaetian marls (and evaporitic deposits) in contact. 14C determinations indicate a pmC content between 29.33±0.14 and 44.39±0.20 pmC. The presence of HCO , Ca2+ (and Mg2+) are ascribed to water–limestone interactions, while Na+, Cl− and SO concentrations are mainly associated with the dissolution of halite and gypsum lenses found along the regional syncline structure. The δ18O values of Caldas da Rainha thermomineral water were slightly lower than those of shallow groundwater from the Upper Jurassic rocks, suggesting the existence of two distinct aquifer systems. The different isotopic composition of water also indicates that the main recharge of the thermomineral waters likely occurs in the Middle and Lower Jurassic limestone formations of the Candeeiros Mountains. The presence of 3H (from 1.1 to 2.8 TU) in some thermomineral borehole waters (showing rather similar geochemical signatures) suggests mixing of small amounts of shallow groundwater with thermomineral waters, as a result of leaking borehole casing construction or a recharge when the 3H content in the atmosphere was higher than that at present. Caldas da Rainha thermomineral waters having δ34Ssulphate and δ18Osulphate values between+14.9 and+19.1 ‰ and+11.1 and+16.2 ‰, respectively, indicate that the sulphate is the result of water–rock interaction with evaporitic formations. The obtained chemical and isotopic data have informed the further development of a hydrogeological model that will be used by decision-makers, in order to contribute to the socio-economic development of the spa region.

Nitrogen isotopes determination in natural gas: analytical method and first results on magmatic, hydrothermal and soil gas samples †

A continuous-flow GC/IRMS technique has been developed to analyse δ15N values for molecular nitrogen in gas samples. This method provides reliable results with accuracy better than 0.15 ‰ and reproducibility (1σ) within±0.1 ‰ for volumes of N2 between 1.35 (about 56 nmol) and 48.9 μL (about 2 μmol). The method was tested on magmatic and hydrothermal gases as well as on natural gas samples collected from various sites. Since the analysis of nitrogen isotope composition may be prone to atmospheric contamination mainly in samples with low N2 concentration, we set the instrument to determine also N2 and 36Ar contents in a single run. In fact, based on the simultaneously determined N2/36Ar ratios and assuming that 36Ar content in crustal and mantle-derived fluids is negligible with respect to 36Ar concentration in the atmosphere, for each sample, the degree of atmospheric contamination can be accurately evaluated. Therefore, the measured δ15N values can be properly corrected for air contamination.

Role of high mountain areas in catchment hydromineral resources - Northern/Central Portugal: environmental issues.

This study summarizes the results of geological, geomorphological, tectonic, geochemical, geophysical, hydrogeological and isotopic techniques in hydromineral resources assessment (issue temperature between 27oC and 45oC). Two case studies are presented: i) Serra da Estrela mountain region, the highest mountain in Portuguese mainland and ii) Serra do Marao mountain region. A special emphasis is dedicated to the recharge and discharge processes and the role of snowmelt as a source of hydromineral resources. Since local Spas are particularly dependent on water quality, the existence of mixing between hydromineral waters and local shallow groundwaters is also considered.

Pollution assessment in the Trancão river basin (Portugal) by PIXE, EDXRF and isotopic analysis

Abstract This paper reports on the inorganic contamination assessment of a river basin and local water resources in order to establish quality standards. PIXE was applied to the elemental determination of the freeze-dried water dry residue and EDXRF was used for the evaluation of elemental content of sediments. To infer the water provenance the electrical conductivity was measured as well as the isotopic composition of surface waters using the 18 O/ 16 O ratio. The combined isotopic and elemental composition information enables to establish dominant contamination contributions from the several tributaries. Moreover, the variability observed for certain parameters, associates them with specific basin regions as for instance, dry residue mass, conductivity and Br, or S, Cl and As or Cr, Ni, Zn and Pb which permit to establish both pollution characterisation and their origin (agriculture, industrial, etc.). At certain locations, enhanced concentrations of elements as Cr, Cu, Zn and Pb are observed both in sediments and in the surface water. The elemental particular associations also permit to characterise pollution sources.

Revision of the hydrogeological conceptual models of two Portuguese thermomineral water systems: similarities and differences

This paper aims to highlight the role that the assessment of hydrogeological conceptual models of the thermomineral water systems of a given region plays in the sustainable management and protection of its resources (e.g., possible drilling plans to capture thermomineral waters with higher flow rate and/or temperature) and development (use of thermomineral waters in the various forms). Therefore, a multi and interdisciplinary approach from a variety of scientific fields of the domain of geoscience such as geology, geochemistry, hydrogeology, and isotope hydrology was applied. Despite the contrasting features of the two thermomineral systems studied, namely, different geochemical signatures ascribed to distinct geological environments (e.g., the Caldas do Moledo system HCO3-Na with 8 < pH < 9, and the Cabeço de Vide system Na-Cl/Ca-OH with pH ≈ 11.5), the respective hydrogeological conceptual models show clear similarities. Regional/local higher altitude areas associated with highly fractured rocks play an important role in conducting the infiltrated meteoric waters towards the discharge zones near the Thermal Spas. The discharge zones are mainly related to the intersection of the main local/regional fault lineaments and conjugate structures, responsible for promoting the ascent of the thermomineral waters. The use of thermomineral waters in spas, bottling industries, or low-temperature geothermal facilities often promote social and economic development at local and/or regional scale. In many cases, it is even a major, if not the main, source of local/regional development. Thus, the importance of such multidisciplinary studies for the sustainable management of these important types of georesources is obvious.

Correction: Tracing salinization processes in coastal aquifers using an isotopic and geochemical approach: comparative studies in western Morocco and southwest Portugal

Environmental stable and radioactive isotopes (δ2H, δ13C, δ18O; 3H and 14C), together with physical and geochemical data, were used in the determination of the origins of groundwater salinization and geochemical evolution processes in coastal regions. Two case studies on the Atlantic Coast are discussed, one located in the Essaouira sedimentary basin, western Morocco, and the second, in the Lower Tagus–Sado sedimentary basin, southwest Portugal. In both regions, groundwater degradation occurs by salinization increase to different concentrations and in relation to different origins. The main quality issues for the groundwater resources are related to seawater intrusion, dissolution of diapiric structures intruding the aquifer layers, brine dissolution at depth, and/or evaporation of irrigation water. Anthropogenic pollution ascribed to agricultural activities is another source for groundwater degradation, affecting mainly the shallow aquifers. The apparent 14C age of the analysed samples ranges from 2.9 ± 0.3 up to 45.6 ± 0.6 pmC in the Miocene groundwater samples from the basin in Portugal; at the Essaouira basin in Morocco, the 14C content varies from 60 to 86 pmC. In most of the water samples, the 3H concentration is below the detection limit. In both basins, the isotopic results together with the geochemical data provided an effective label for tracing the mineralization origin and groundwater degradation processes. Further, the isotopic signatures were used in the identification of a paleoclimate (colder period), recorded in the stable isotopic composition and corroborated with the 14C data.RésuméDes isotopes stables et radioactifs de l’environnement (δ2H, δ13C, δ18O; 3H et 14C), ainsi que des données physiques et géochimiques, ont été utilisés pour déterminer l’origine de la salinisation et les processus d’évolution géochimique des régions côtières. Deux cas d’études sur la côte atlantique sont discutés, l’un localisé dans le bassin sédimentaire d’Essaouirra à l’ouest du Maroc et le second dans le bassin sédimentaire du bas Tagus-Sado au sud du Portugal. Dans ces deux régions, la dégradation des eaux souterraines se produit par une augmentation de la salinisation selon différentes concentrations et origines. Les principales questions de qualité pour les ressources en eaux souterraines sont liées à l’intrusion de l’eau de mer, à la dissolution de diapirs qui sont intrusifs dans les couches aquifères, à la dissolution de saumures en profondeur et/ou à l’évaporation de l’eau d’irrigation. La pollution anthropique attribuée aux activités agricoles est une autre source de dégradation des eaux souterraines, affectant principalement les aquifères peu profonds. Les âges apparents 14C des échantillons analysés donnent une gamme de valeurs comprise entre 2.9 ± 0.3 et 45.6 ± 0.6 pmC pour les eaux échantillonnées de l’aquifère du Miocène du bassin du Portugal; dans le bassin d’Essaouira au Maroc, les teneurs en 14C varient de 60 à 86 pmC. Dans la plupart des échantillons d’eau, les concentrations en 3H sont inférieures aux limites de détection. In both basins, the isotopic results together with the geochemical data provided an effective label for tracing the mineralization origin and groundwater degradation processes. Dans les deux bassins, les résultats isotopiques ainsi que les données géochimiques fournissent des informations essentielles pour tracer l’origine de la minéralisation et les processus de dégradation des eaux souterraines. De plus, les signatures isotopiques ont été utilisées pour l’identification d’un paléoclimat (période plus froide), attesté par la composition des isotopes stables et confirmé par les données de 14C.ResumenLos isótopos radiactivos ambientales y estables y (δ2H, δ13C, δ18O; 3H y 14C), junto con los datos físicos y geoquímicos, se utilizaron en la determinación de los orígenes de la salinización del agua subterránea y los procesos de evolución geoquímica en regiones costeras. Se discuten dos casos de estudio en la costa atlántica, uno ubicado en la cuenca sedimentaria de Essaouira, en el oeste de Marruecos, y el segundo, en la cuenca sedimentaria del Bajo Tajo-Sado, al suroeste de Portugal. En ambas regiones, la degradación del agua subterránea se produce por aumento de salinización a diferentes concentraciones y en relación con diferentes orígenes. Los principales problemas de calidad para los recursos de aguas subterráneas están relacionados con la intrusión de agua de mar, la disolución de las estructuras diapíricas que invaden las capas del acuífero, la disolución de la salmuera en la profundidad y/o la evaporación del agua de riego. La contaminación antropogénica atribuida a las actividades agrícolas es otra fuente de degradación del agua subterránea, que afecta principalmente a los acuíferos poco profundos. La edad aparente 14C de las muestras analizadas oscila entre 2.9 ± 0.3 hasta 45.6 ± 0.6 pmC en las muestras de agua subterránea del Mioceno de la cuenca en Portugal; en la cuenca de Essaouira en Marruecos, el contenido de 14C varía de 60 a 86 pmC. En la mayoría de las muestras de agua, la concentración de 3H está por debajo del límite de detección. En ambas cuencas, los resultados isotópicos junto con los datos geoquímicos proporcionaron una etiqueta eficaz para rastrear el origen de la mineralización y los procesos de degradación del agua subterránea. Además, las firmas isotópicas se usaron en la identificación de un paleoclima (período más frío), registrado en la composición de isótopos estables y corroborado con los datos 14C.摘要利用环境稳定同位素和放射同位素(δ2H, δ13C, δ18O; 3H和 14C))以及物理和地球化学数据确定沿海地区地下水盐化的成因和地球化学演化过程。论述了大西洋西海岸两个研究案例,一个位于摩洛哥西部的索维拉沉积盆地,另一个位于葡萄牙西南部塔霍河-撒多沉积盆地。在这两个地区,由于含盐浓度不同程度增加致使地下水退化,造成地下水退化的成因也不尽相同。地下水资源的主要质量问题与海水入侵、挤入构造的溶解进入到含水层地层、深部的卤水溶解以及/或灌溉水的蒸发等有关。归咎于农业活动造成的人为因素污染是地下水退化的另一个原因,主要影响浅层含水层。分析的样品明显的14C年龄范围为:葡萄牙盆地的中新世地下水样为2.9 ± 0.3 到 45.6 ± 0.6 pmC;而在摩洛哥索维拉盆地,14C含量从60到80 pmC不等。大部分水样中,3H浓度低于检出限。在两个盆地,同位素结果以及地球球化学数据为示踪矿化作用和地下水退化提供了有效的标签。而且,同位素印记用于识别稳定同位素成分中记录的古气候(较冷期),同位素印记并与14C数据进行了对比。ResumoIsótopos ambientais estáveis e radioativos (δ2H, δ13C, δ18O; 3H e 14C), juntamente com dados físico-químicos, foram usados na determinação da origem dos processos de salinização da água subterrânea e evolução geoquímica em regiões costeiras. Dois casos de estudo são discutidos, um localizado na bacia sedimentar de Essaouira, Marrocos ocidental, e o segundo, na bacia sedimentar do Baixo Tejo-Sado, no sudoeste de Portugal. Em ambas as regiões, a degradação da água subterrânea ocorre pelo aumento da salinização, com diferentes concentrações e com diferentes origens. Os principais problemas de qualidade dos recursos hídricos subterrâneos estão relacionados com intrusão marinha, dissolução de estruturas diapíricas intrusivas às camadas do aquífero, dissolução de salmoura em profundidade e/ou, evaporação de água de irrigação. Poluição antrópica atribuída às atividades agrícolas é outra fonte de degradação da água subterrânea, afetando principalmente os aquíferos mais superficiais. As idades aparentes em 14C das amostras de água subterrânea do Miocénico da bacia em Portugal, varia entre 2.9 ± 0.3 a 45.6 ± 0.6 pmC; na bacia de Essaouira, Marrocos, o conteúdo de 14C varia entre 60 a 86 pmC. Na maioria das amostras de água, a concentração de 3H está abaixo do limite de deteção. Em ambas as bacias, os resultados isotópicos, juntamente com os dados geoquímicos, forneceram indicação eficaz para delinear a origem da mineralização e os processos de degradação da água subterrânea. Além disso, as assinaturas isotópicas foram utilizadas na identificação de paleoclima (período mais frio), registrado na composição isotópica estável e corroborada com os teores em 14C.

Groundwater Responses to Climate Change in a Coastal Semi-arid Area from Morocco; Case of Essaouira Basin

During the last decades, a decrease in precipitation and an increase in air temperature are observed from arid and semi-arid areas. Therefore, changes in the water resource balance are expected. In this context, this study aimed to identify the climate change effects on groundwater from the Essaouira basin (southwestern Morocco). The average precipitation is about 300 mm/year and the temperatures oscillate around 20 °C. The climate study showed that the precipitation and the air temperatures show a general downward trend (~12%) and an upward trend (~1.5 °C), respectively. The decrease in recharge and recurrent drought episodes caused a continuous decrease in groundwater level. The hydrogeochemical approach indicates that (i) the groundwater facies was mainly of the Na–Cl type from 1990 to 2009, and Mg–Ca–Cl for 2015, (ii) a degradation of groundwater quality with an increase in salinity (80–3500 mg/L) that resulted from the dissolution of evaporate minerals and seawater intrusion. The concentration of 18O, 2H are determined, the local meteoric water line (LMWL) close to the global meteoric water line (GMWL) characterizing ocean precipitations is determined. The ground waters of Essaouira basin are very sensitive to any variation in the natural recharge, this makes them very vulnerable faced with the climate change. The results of this study should be taken in consideration for the future water management in this region.

Isotopic and geochemical methods for studying water–rock interaction and recharge mode: application to the Cenomanian–Turonian and Plio-Quaternary aquifers of Essaouira Basin, Morocco

Study of the Cenomanian–Turonian and Plio–Quaternary aquifers of Essaouira basin (Western Morocco), based on the interpretation of geochemical (major elements) and isotopic (18O, 2H, 13C and 14C) data, has aided the understanding of the hydrodynamics of these aquifers, which is greatly affected by tectonics. Hydrochemical characteristics based on the bivariate diagrams of major ions (Cl–, SO42–, NO3–, HCO3–, Na+, Mg2+, K+ and Ca2+) and electrical conductivity and mineral saturation indices indicate that the origins of groundwater mineralisation are the result of: (1) evaporite dissolution; (2) cation exchange reactions; (3) and evaporation processes. Radiogenic isotopes (3H and 14C) have highlighted the presence of significant recent recharge in the eastern part of the basin, with groundwater moving according to the general flow path (south-east to north-west). Stable isotope data from the Essaouira basin plot along the Global Meteoric Water Line and below the Local Meteoric Water Line. This suggests that groundwater has been recharged under several different climate regimes.

Geochemical and isotopic approach to decrypt the groundwater salinization origin of coastal aquifers from semi-arid areas (Essaouira basin, Western Morocco)

In arid and semi-arid areas, the groundwater is the main source of water supply and agricultural activity. Overexploitation of coastal aquifers and pollution vulnerability are among the main problems related to groundwater resources assessment and management in these zones. In fact, in the last decades, these resources have been threatened by a degradation of their quality and quantity that furthers natural and anthropic effects, such as climate change, seawater intrusion and overexploitation. However, the protection and management of these resources requires knowledge of the origin of their mineralization. In this study, the Essaouira basin is selected as a typical example. Stable isotopes (18O and 2H) together with geochemical data were used to identify the groundwater salinization origin in the coastal aquifers of the Essaouira basin. The results of both the approaches show that the groundwater mineralization is due to: (1) the dissolution of salt minerals, (2) the ion exchange phenomena, (3) seawater intrusion (1–7%), and (4) sulphate reduction. Also, the recharge is supported by fast infiltration of oceanic precipitation without significant evaporation.