Albert Folch

Nitrate pollution of groundwater; all right. . ., but nothing else?

Contamination from agricultural sources and, in particular, nitrate pollution, is one of the main concerns in groundwater management. However, this type of pollution entails the entrance of other substances into the aquifer, as well as it may promote other processes. In this study, we deal with hydrochemical and isotopic analysis of groundwater samples from four distinct zones in Catalonia (NE Spain), which include 5 different aquifer types, to investigate the influence of fertilization on the overall hydrochemical composition of groundwater. Results indicate that intense fertilizer application, causing high nitrate pollution in aquifers, also homogenize the contents of the major dissolved ions (i.e.; Cl(-), SO4(2-), Ca(2+), Na(+), K(+), and Mg(2+)). Thus, when groundwater in igneous and sedimentary aquifers is compared, significant differences are observed under natural conditions for Cl(-), Na(+) and Ca(2+) (with p-values ranging from <0.001 to 0.038), and when high nitrate concentrations occur, these differences are reduced (most p-values ranged between 0.054 and 0.978). Moreover, positive linear relationships between nitrate and some ions are found indicating the magnitude of the fertilization impact on groundwater hydrochemistry (with R(2) values of 0.490, 0.609 and 0.470, for SO4(2-), Ca(2+) and Cl(-), respectively). Nevertheless, the increasing concentration of specific ions is not only attributed to agricultural pollution, but to their enhancing effect upon the biogeochemical processes that control water-rock interactions. Such results raise awareness that these processes should be evaluated in advance in order to assess an adequate groundwater resources management.

Analyzing Hydrological Sustainability Through Water Balance

The objective of the Water Framework Directive (2000/60/EC) is to assist in the development of management plans that will lead to the sustainable use of water resources in all EU member states. However, defining the degree of sustainability aimed at is not a straightforward task. It requires detailed knowledge of the hydrogeological characteristics of the basin in question, its environmental needs, the amount of human water demand, and the opportunity to construct a proper water balance that describes the behavior of the hydrological system and estimates available water resources. An analysis of the water balance in the Selva basin (Girona, NE Spain) points to the importance of regional groundwater fluxes in satisfying current exploitation rates, and shows that regional scale approaches are often necessary to evaluate water availability. In addition, we discuss the pressures on water resources, and analyze potential actions, based on the water balance results, directed towards achieving sustainable water management in the basin.

Development of a stream-aquifer numerical flow model to assess river water management under water scarcity in a Mediterranean basin.

Stream flow, as a part of a basin hydrological cycle, will be sensible to water scarcity as a result of climate change. Stream vulnerability should then be evaluated as a key component of the basin water budget. Numerical flow modeling has been applied to an alluvial formation in a small mountain basin to evaluate the stream-aquifer relationship under these future scenarios. The Arbúcies River basin (116 km(2)) is located in the Catalan Inner Basins (NE Spain) and its lower reach, which is related to an alluvial aquifer, usually becomes dry during the summer period. This study seeks to determine the origin of such discharge losses whether from natural stream leakage and/or induced capture due to groundwater withdrawal. Our goal is also investigating how discharge variations from the basin headwaters, representing potential effects of climate change, may affect stream flow, aquifer recharge, and finally environmental preservation and human supply. A numerical flow model of the alluvial aquifer, based on MODFLOW and especially in the STREAM routine, reproduced the flow system after the usual calibration. Results indicate that, in the average, stream flow provides more than 50% of the water inputs to the alluvial aquifer, being responsible for the amount of stored water resources and for satisfying groundwater exploitation for human needs. Detailed simulations using daily time-steps permit setting threshold values for the stream flow entering at the beginning of the studied area so surface discharge is maintained along the whole watercourse and ecological flow requirements are satisfied as well. The effects of predicted rainfall and temperature variations on the Arbúcies River alluvial aquifer water balance are also discussed from the outcomes of the simulations. Finally, model results indicate the relevance of headwater discharge management under future climate scenarios to preserve downstream hydrological processes. They also point out that small mountain basins could be self-sufficient units so long as the response of the main hydrological components to external forces that produce water scarcity, as climate change or human pressures, is appropriately considered in water resource planning.

Constraining the temporal variations of Ra isotopes and Rn in the groundwater end-member: Implications for derived SGD estimates

Submarine groundwater discharge (SGD) has been recognized as an important supplier of chemical compounds to the ocean that may influence coastal geochemical cycles. Radium isotopes (223Ra, 224Ra, 226Ra,228Ra) and radon (222Rn) have been widely applied as tracers of SGD. Their application requires the appropriate characterization of both the concentrations of tracers in the discharging groundwater and their distribution in the coastal water column. This study evaluates the temporal evolution of Ra isotopes and 222Rn concentrations in a dynamic subterranean estuary of a microtidal Mediterranean coastal aquifer that experiences large displacements of the fresh-saltwater interface as a necessary initial step in evaluating the influence of SGD in coastal waters. We show that changes in groundwater salinities due to the seaward displacement of the fresh-saltwater interface produced large variations in Ra activities in groundwater (by a factor of ~19, ~14, ~6, and ~11 for 223Ra, 224Ra, 226Ra and 228Ra, respectively), most importantly during rainfall events. In contrast, the 222Rn activities in groundwater oscillated only by a factor of 3 during these rainy periods. The large temporal variability in Ra activities hampers the characterization of the SGD end-member when using Ra isotopes as tracers, and thus presents a challenge for obtaining accurate SGD estimates. This study emphasizes the need to understand the hydrodynamics of coastal aquifers to appropriately constrain the Ra isotopes and 222Rn concentrations in groundwater and when applying both tracers in dynamic microtidal coastal systems.

The impact of poplar tree plantations for biomass production on the aquifer water budget and base flow in a Mediterranean basin.

Poplar plantations are used for biomass production in many countries. These plantations are often located in areas where the tree roots can reach the water table of shallow aquifers to reduce irrigation costs and increase evapotranspiration, mainly during the summer. This study aims to assess the effects of these plantations on an aquifer water budget and on the stream flow of a Mediterranean basin (Santa Coloma River, 321.3 km(2) NE Spain). A numerical flow model was constructed to simulate shallow aquifers and to simulate the stream-aquifer interaction for a period of 9 years. Once the model was calibrated, different land use scenarios, such as deciduous forests, dry farming and irrigated farming, were simulated for comparison. The mass balance shows that poplar extracts an average of 2.40 hm(3) from the aquifer, i.e., approximately 18% of the average recharge of the modelled area. This effect reduces the groundwater flow to the main stream and increases the infiltration from the stream to the aquifer. As a result, there is an average reduction in the main stream flow by 46% during the summer, when the lowest flow occurs and when the river is most sensitive. The results indicate that these impacts should be considered in basin management plans and in evaluating the benefits of this type of biomass production.

Fungal permeable reactive barrier to remediate groundwater in an artificial aquifer

Biobarriers, as permeable reactive barriers (PRBs), are a common technology that mainly uses bacteria to remediate groundwater in polluted aquifers. In this study, we propose to use Trametes versicolor, a white-rot fungus, as the reactive element because of its capacity to degrade a wide variety of highly recalcitrant and xenobiotic compounds. A laboratory-scale artificial aquifer was constructed to simulate groundwater flow under real conditions in shallow aquifers. Orange G dye was chosen as a contaminant to visually monitor the hydrodynamic behaviour of the system and any degradation of the dye by the fungus. Batch experiments at different pH values (6 and 7) and several temperatures (15 °C, 18 °C, 20 °C and 25 °C) were performed to select the appropriate residence time and glucose consumption rate required for continuous treatment. The maximum Orange G degradation was 97%. Continuous degradation over 85% was achieved for more than 8 days. Experimental results indicate for the first time that this fungus can potentially be used as a permeable reactive barrier in real aquifers.

Improving degradation of emerging organic compounds by applying chaotic advection in Managed Aquifer Recharge in randomly heterogeneous porous media

Improving degradation rates of emerging organic compounds (EOCs) in groundwater is still a challenge. Although their degradation is not fully understood, it has been observed that some substances are preferably degraded under specific redox conditions. The coupling of Managed Aquifer Recharge with soil aquifer remediation treatment, by placing a reactive layer containing organic matter at the bottom of the infiltration pond, is a promising technology to improve the rate of degradation of EOCs. Its success is based on assuming that recharged water and groundwater get well mixed, which is not always true. It has been demonstrated that mixing can be enhanced by inducing chaotic advection through extraction-injection-engineering. In this work, we analyze how chaotic advection might enhance the spreading of redox conditions with the final aim of improving degradation of a mix of benzotriazoles: benzotriazole, 5-methyl-benzotriazole, and 5-chloro-benzotriazole. The degradation of the first two compounds was fastest under aerobic conditions whereas the third compound was best degraded under denitrification conditions. We developed a reactive transport model that describes how a recharged water rich in organic matter mixes with groundwater, how this organic matter is oxidized by different electron acceptors, and how the benzotriazoles are degraded attending for the redox state. The model was tested in different scenarios of recharge, both in homogenous and in heterogenous media. It was found that chaotic flow increases the spreading of the plume of recharged water. Consequently, different redox conditions coexist at a given time, facilitating the degradation of EOCs.

Stratigraphic and structural controls on groundwater flow in an outcropping fossil fan delta: the case of Sant Llorenç del Munt range (NE Spain)

AbstractsHydrogeological models of mountain regions present the opportunity to understand the role of geological factors on groundwater resources. The effects of sedimentary facies and fracture distribution on groundwater flow and resource exploitation are studied in the ancient fan delta of Sant Llorenç de Munt (central Catalonia, Spain) by integrating geological field observations (using sequence stratigraphy methods) and hydrogeological data (pumping tests, hydrochemistry and environmental isotopes). A comprehensive analysis of data portrays the massif as a single unit, constituted by different compartments determined by specific layers and sets of fractures. Two distinct flow systems—local and regional—are identified based on pumping test analysis as well as hydrochemical and isotopic data. Drawdown curves derived from pumping tests indicate that the behavior of the saturated layers, whose main porosity is given by the fracture network, corresponds to a confined aquifer. Pumping tests also reflect a double porosity within the system and the occurrence of impervious boundaries that support a compartmentalized model for the whole aquifer system. Hydrochemical data and associated spatial evolution show the result of water–rock interaction along the flow lines. Concentration of magnesium, derived from dolomite dissolution, is a tracer of the flow-path along distinct stratigraphic units. Water stable isotopes indicate that evaporation (near a 5% loss) occurs in a thick unsaturated zone within the massif before infiltration reaches the water table. The hydrogeological analysis of this outcropping system provides a methodology for the conceptualization of groundwater flow in similar buried systems where logging and hydrogeological information are scarce.RésuméLes modèles hydrogéologiques en zones montagneuses présentent l’intérêt de comprendre le rôle de facteurs géologiques sur les ressources en eau souterraine. Les effets des faciès sédimentaires et de la distribution de la fracturation sur l’écoulement des eaux souterraines et l’exploitation de cette ressource sont étudiés dans l’ancien delta de Sant Llorenç del Munt (Catalogne centrale, Espagne) en intégrant des observations géologiques de terrain (utilisant les méthodes de stratigraphie séquentielle) et des données hydrogéologiques (essais de pompage, hydrochimie, et isotopes environnementaux). Une analyze globale des données représente le massif comme une entité unique, constituée de différents compartiments caractérisés par des couches spécifiques et des ensembles de fractures. Deux systèmes d’écoulement distincts—local et régional—sont identifiés à partir de l’analyze des essais de pompage ainsi que des données hydrochimiques et isotopiques. Les courbes de rabattement dérivées des essais de pompage indiquent que le comportement des couches saturées, dont l’essentiel de la porosité est. associé au réseau de fractures, correspond à un aquifère captif. Les essais de pompage sont le reflet d’une double porosité au sein du système et de l’existence de limites imperméables, ce qui est. en faveur d’un modèle compartimenté pour l’ensemble du système aquifère. Les données hydrochimiques et leur évolution spatiale associée montrent l’influence des interactions eau-roche le long des lignes d’écoulement. La concentration en magnésium, issue de la dissolution de la dolomite, est. un traceur des voies d’écoulements via des unités stratigraphiques distincts. Les isotopes stables de l’eau indiquent que l’évaporation (environ 5% de perte) se produit dans une zone non saturée épaisse, au sein du massif, avant que les infiltrations n’atteignent le toit de la nappe. L’analyze hydrogéologique de ce système fournit une méthodologie pour conceptualiser les écoulements d’eau souterraine dans des systèmes similaires sous couverture, pour lesquels les données de diagraphies et hydrogéologiques sont peu nombreuses.ResumenLas regiones montañosas ofrecen la oportunidad de comprender la influencia de los factores geológicos en los recursos hídricos subterráneos. El abanico deltaico de Sant Llorenç de Munt (Cataluña Central, España) de edad Terciaria permite estudiar los efectos de las facies sedimentarias y de la distribución de las fracturas en el flujo de agua subterránea mediante la integración de observaciones geológicas de campo (utilizando métodos de estratigrafía secuencial) y datos hidrogeológicos (ensayos de bombeo, hidroquímica e isótopos ambientales). Un análisis exhaustivo de los datos describe el macizo como una sola unidad, constituida por diferentes compartimentos determinados por niveles sedimentarios específicos y conjuntos de fracturas. Se identifican dos sistemas de flujo distintos, a escalas local y regional, basados en el análisis de los ensayos de bombeo y de los datos hidroquímicos e isotópicos. Las curvas de descenso derivadas de los ensayos de bombeo indican que el comportamiento de las capas saturadas, cuya porosidad principal es dada por la red de fracturas, corresponde a un acuífero confinado. Los ensayos de bombeo también reflejan una doble porosidad dentro del sistema y la ocurrencia de límites impermeables que apoyan un modelo compartimentado para todo el sistema acuífero. Los datos hidroquímicos y la evolución espacial asociada muestran el resultado de la interacción agua-roca a lo largo de las líneas de flujo. La concentración de magnesio, derivada de la disolución de dolomita, es un trazador de la trayectoria de flujo a lo largo de distintas unidades estratigráficas. Los isótopos estables del agua indican que se produce evaporación (con una pérdida cerca del 5%) en una potente zona no saturada dentro del macizo, antes de que la infiltración alcance la capa freática. El análisis hidrogeológico de esta unidad de relieve proporciona una metodología para la conceptualización del flujo de agua subterránea en sistemas similares no aflorantes, donde la información hidrogeológica derivada de pozos o prospección geofísica es escasa.摘要山区的水文地质模型提供了了解地质因素在地下水资源中的作用的机会。通过综合(使用序列地层方法得到的)地质野外观测结果及(抽水试验、水化学和环境同位素)水文地质数据研究了(西班牙加泰罗尼亚中部)Sant Llorenç de Munt古扇形三角洲沉积相和断裂分布对地下水流和资源开发的影响。数据的综合分析把断层块作为单个的单元描述,单元由特殊地层和系列断裂确定的不同分隔区域构成。根据抽水试验分析以及水化学和同位素数据确定了两个明显的水流系统----局部水流系统和和区域水流系统。源自抽水试验的水位下降曲线表明,饱和层的主要孔隙度由断裂网络造成,其行为符合承压含水层。抽水试验还反映了系统内的一个双重孔隙度以及出现不渗透边界,这个边界支持整个含水层系统的区分化的模型。水化学数据和相关的空间演化显示出了沿水流线的水岩相互作用结果。源自白云岩溶解的镁浓度是沿明显地层单元的水流通道示踪剂。水中稳定同位素表明,在渗入达到水位之前,蒸发(大约5%的损失)出现在断块内厚的非饱和带。本出露系统的水文地质分析为录井和水文地质信息匮乏的相似埋藏系统中的地下水流提供了研究方法。ResumoOs modelos hidrogeológicos de regiões montanhosas oferecem a oportunidade de entender o papel do fator geológico nos recursos hídricos subterrâneos. Os efeitos das fácies sedimentares e da distribuição de fraturas no escoamento e exploração de recursos são estudados no antigo delta em leque de Sant Llorenç de Munt (Catalunha Central, Espanha) através da integração de observações geológica de campo (usando métodos de estratigrafia de sequências) e de dados hidrogeológicos (teste de bombeamento, hidroquímica e isótopos ambientais). Uma análise abrangente dos dados retrata o maciço como uma única unidade, constituída por diferentes comportamentos determinados por camadas específicas e um conjunto de fraturas. Dois sistemas de fluxo distintos—local e regional—são identificados baseado no teste de bombeamento, bem como dados hidroquímicos e isotópicos. As curvas derivadas do teste de bombeamento indicam que o comportamento das camadas saturadas, cuja porosidade principal é dada pela rede de fraturas, corresponde a um aquífero confinado. O teste de bombeamento também reflete a dupla porosidade entre o sistema e a ocorrência de limites impermeáveis que sustentam um modelo compartimentado para todo o sistema aquífero. Os dados hidroquímicos associados a evolução espacial mostram o resultado da interação rocha-água ao longo das linhas de fluxo. Concentração de magnésio, derivada da dissolução de dolomita, é um traçador do caminho do fluxo ao longo das distintas unidades estratigráficas. Isótopos estáveis na água indicam que a evaporação (próxima a 5% de perda) ocorre e uma zona não saturada espessa dentro do maciço antes que a infiltração atinja o lençol freático. A análise hidrogeológica deste sistema de afloramento fornece uma metodologia para a conceituação do fluxo de água subterrânea em sistemas enterrados similares, onde registros e informações hidrogeológicas são escassas.

Hydrogeological and geophysical characterization of fractured aquifer of Òdena (Barcelona, Catalunya)

Summary The results of the geophysical survey reflects the presence of heterogeneity distribution of electrical resistivity values. This allowed to delimit the geometry of the three layers, as indicated by borehole logging. At the same time, it has been possible to highlight several zones with low electrical resistivity values in the central part of some profiles. These have been considered as fractured areas. In many cases, these areas of low resistivity fractures coincide with areas where the wells have registered low values of the electrical conductivity. This fact reveals the effect as preferential flow areas that have these fractures throughout the circulation system of the contaminant.