J. A. Barberá

Combined use of natural and artificial tracers to determine the hydrogeological functioning of a karst aquifer: the Villanueva del Rosario system (Andalusia, southern Spain)

Analysis of natural responses of karst springs provides information on the behavior of the aquifers they drain. Detailed monitoring and qualitative and quantitative analyses of natural responses, and environmental—total organic carbon (TOC), NO3−, Cl− and intrinsic fluorescence—and artificial (fluorescent dye) tracers, in the water drained by Villanueva del Rosario spring (southern Spain), suggest the existence of a conduit flow system with rapid flows and very short transit times of water through the aquifer. This is in agreement with uranine and eosin breakthrough curves and with simple numerical models done using these data. However, due to the low capacity for natural regulation, not all the recharge effects are simultaneously transmitted to the spring water; given a single input, the system modulates and transfers hydrodynamic variations faster than variations of chemical composition and of water temperature. Additionally, time lags between maximum concentrations of natural and artificial tracers show that the global system response (including diffuse infiltration) is faster and more sensitive than that produced from infiltration concentrated at a single point on the surface (sinkholes).RésuméL’analyse des réponses naturelles des sources karstiques fournissent une information sur le comportement des aquifères qu’elles drainent. Un suivi détaillé et des analyses qualitatives et quantitatives des réponses naturelles, et des traceurs environnementaux—carbone organique total (COT), NO3−, Cl− et fluorescence intrinsèque—et artificiels (colorants fluorescents), dans l’eau drainée par la source de Villanueva del Rosario (Sud de l’Espagne), suggère l’existence d’un système d’écoulement dominé par des conduits avec des écoulements rapides et des temps de transit très courts de l’eau au sein de l’aquifère. Ceci est en accord avec les courbes de restitution de l’uranine et de l’éosine et avec des modèles numériques simples utilisant ces données. Cependant, à cause de la faible capacité de régulation naturelle, tous les effets de la recharge ne sont pas transmis simultanément à la source, considérant une contribution unique, le système module et transfère les variations hydrodynamiques plus vite que les variations de la composition chimique et de la température de l’eau. De plus, les décalages dans le temps entre les concentrations maximums des traceurs naturels et artificiels montrent que la réponse globale du système (y compris l’infiltration diffuse) est plus rapide et beaucoup plus sensible que celle produite par l’infiltration concentrée au niveau d’un point singulier d’introduction en surface (pertes).ResumenEl análisis de las respuestas naturales de manantiales kársticos informa sobre del comportamiento de los acuíferos que drenan. El muestreo detallado y los análisis cualitativos y cuantitativos de las respuestas naturales, y los trazadores ambientales—carbono orgánico total (TOC), NO3−, Cl− y fluorescencia natural—y artificiales (colorantes fluorescentes), en el agua drenada por el manantial de Villanueva del Rosario (sur de España), sugiere la existencia de un sistema de conductos con flujos rápidos y tiempos de tránsito del agua muy cortos a través del acuífero. Esto está de acuerdo con las curvas de concentración de la uranina y la eosina y con los modelos numéricos simples realizados usando estos datos. Sin embargo, debido a la baja capacidad de regulación natural, no todos los efectos de la recarga son transmitidos simultáneamente al agua del manantial; ante una entrada, el sistema modula y transfiere las variaciones hidrodinámicas más rápidamente que las variaciones en la composición química y en la temperatura del agua. Adicionalmente, los retardos temporales entre las concentraciones máximas de trazadores naturales y artificiales muestran que la respuesta global del sistema (incluyendo la infiltración difusa) es más rápida y más sensible que aquella producida a partir de la infiltración concentrada en un solo punto en la superficie (sumidero kárstico).摘要岩溶泉自然反应分析提供了其含水层的行为信息。(西班牙南部)Villanueva del Rosario泉自然反应的详细监测及定量和定性分析、水中的环境(总有机碳(TOC)、 NO3−、 Cl− 及内荧光)及人工(荧光染料)示踪剂显示存在着通过含水层的快速流动管道水流系统及很短的过渡时间。这与荧光素钠和曙红突破曲线一致,也与用这些数据做的简单数值模型一致。然而,由于自然调节能力很低,并不是所有的补给影响同时传到泉水;考虑到单一的输入项,系统调整和传输水文动力变化的速度比化学组分和水温变化要快。另外,天然和人工示踪剂最大含量之间的时滞显示,全球系统反应(包括弥散渗入)比集中在地表一个点(落水洞)产生的渗入更快、更敏感。ResumoA análise das respostas naturais de nascentes cársicas fornece informações sobre o comportamento dos aquíferos que drenam. A monitorização detalhada realizada, bem como os resultados de análises qualitativas e quantitativas das respostas naturais e ambientais—carbono orgânico total (COT), NO3−, Cl− rescência intrínseca—e com traçadores artificiais (corante fluorescente) na água drenada pela nascente de Villanueva del Rosario (sul de Espanha), sugerem a existência de um sistema de escoamento da água no aquífero efetuado por condutas com fluxos rápidos e tempos de percurso muito baixos. Esta análise está de acordo com os dados obtidos com curvas de traçadores de uranina e de eosina, e com modelos numéricos simples feitos usando esses dados. No entanto, devido à baixa capacidade de regulação natural, nem todos os processos de recarga são transmitidos simultaneamente à água de nascente; considerando uma única entrada, o sistema modela e transfere variações hidrodinâmicas mais rapidamente do que as variações da composição química e da temperatura da água. Além disso, os lapsos de tempo entre as concentrações máximas de marcadores naturais e artificiais mostram que a resposta do sistema global (incluindo infiltração difusa) é mais rápida e mais sensível do que a produzida a partir de infiltração concentrada num único ponto na superfície (algar).

Hydrochemical dynamics of TOC and NO 3 − contents as natural tracers of infiltration in karst aquifers

Analysis of Total Organic Carbon (TOC) and NO3− contents in the water at six springs in the province of Malaga (Southern Spain), sampled under different hydrologic conditions, revealed two different hydrochemical behaviour patterns for these natural tracers of infiltration. TOC content increased during every recharge period, following the rapid arrival of water infiltrating through the soil. On the other hand, NO3− content only rose during the first flood episodes (normally in autumn), and fell during the winter and spring ones. This difference is consequence of the distinctive biogeochemical kinetics of nitrogen with respect to organic carbon, both in the soil and within the aquifer. Unlike the mineralisation undergone by TOC from the surface to the spring, the NO3− ion remains in the aquifer almost unaffected, due to the oxidizing conditions prevailing within the karst medium, which do not allow its denitrification and favour its preservation within the saturated zone. In non-polluted aquifers, TOC and NO3− have a common origin in the soil and can be used to determine infiltration processes and the hydrogeological functioning of karst aquifers. Their different hydrochemical evolution provides information about mineralization and degradation processes of organic matter within karst aquifers, which can be used to validate the vulnerability to contamination in this type of medium.

Factors controlling groundwater salinization and hydrogeochemical processes in coastal aquifers from southern Spain

In detrital coastal aquifers, seawater and surface water may interact with groundwater in multiple ways. Understanding the interference of water fluxes in this type of environment is essential to effectively manage the groundwater resources in water-stressed regions, such as the Mediterranean coastal fringe. In this research, the characterization of the main hydrogeochemical processes and the interaction between surface water and groundwater in the Marbella-Estepona coastal aquifers (southern Spain) have been carried out by means of the combined use of different hydrogeochemical indicators along with isotope data. The results show that the diversity of source lithologies (peridotite, carbonate and/or metapelitic) substantially conditions the groundwater geochemistry. The analysis of ionic deltas made it possible a preliminary screening of the geochemical reactions that occur in the Marbella-Estepona aquifers, while the Discriminant Analysis allowed for a consistent classification of sampled groundwater types. The dissolution of calcite and dolomite determines the chemical composition of the groundwater from the eastern sector that are more conditioned by the rainwater infiltration. The dissolution of magnesium-bearing minerals (predominantly forming peridotite rocks) is observed in groundwater samples from the western and central sectors, whose chemical composition showed a greater influence of surface water. The spatial analysis of rCl-/Br- in groundwater has permitted to corroborate that saline intrusion is negligible, hardly affecting to its original water quality. The irregularly distributed recharge by precipitation (seasonal effect) and the atmospheric circulation of cloud fronts (coastal/continental effect) explains why most of groundwater sampled is isotopically impoverished with respect to the rainfall signature. The isotope approach also suggests the hydraulic relationship between surface water and groundwater in the study site. A deeper knowledge of spatial hydrogeochemical variations in coastal groundwater and the influence of water sources over them are crucial for a sustainable groundwater management and global change adaptation in equivalent Mediterranean water-stressed regions.

Hydrogeochemical tools applied to the study of carbonate aquifers: examples from some karst systems of Southern Spain

Karst aquifers present hydrogeological characteristics that distinguish them from others such as fractured and granular aquifers. In particular, they are characterized by highly heterogeneous functioning (large temporal and spatial variability), which makes difficult the application of traditional research methods to karst hydrogeology. For this reason, during the last decades, hydrogeochemical tools have been developed for carbonate aquifers characterization by means of spatial and temporal hydrochemical variability, mixing processes (recharge vs. stored water in the system), groundwater origin (saturated/unsaturated zones, epikarst, etc.), karstification degree and, in general, the hydrogeological functioning of karst aquifers. In the present work, some of the most used techniques to study this type of media are applied to pilot sites from South Spain, in order to show hydrogeochemical processes related to karst aquifers functioning: groundwater origin, distribution of its chemical composition, aquifer behavior, water residence time, substratum influence and geochemical modelling. The results display that the combination of different hydrogeochemical tools provides a comprehensive understanding of the functioning of karst systems, which is useful for groundwater management and protection as well as for environmental applications (groundwater ecodependent systems, wetlands, coastal aquifers, etc).

Using non-conservative tracers to characterise karstification processes in the Merinos-Colorado-Carrasco carbonate aquifer system (southern Spain)

The systematic sampling of the chemical composition of the groundwater from five karst springs (including an overflow spring) and one outflowing borehole have permitted to determine distinctive chemical changes in the waters that reflect the geochemical processes occurring in a carbonate aquifer system from southern Spain. The analysis of the dissolution parameters revealed that geochemical evolution of the karst waters basically depends on the availability of the minerals forming aquifer rocks and the residence time within the aquifers. In the three proposed scenarios in the aquifers, which include the preferential flow routines, the more important geochemical processes taking place during the groundwater flow from the recharge to the discharge zones are: CO2 dissolution and exsolution (outgassing), calcite net dissolution, calcite and dolomite sequential dissolution, gypsum/anhydrite and halite dissolution, de-dolomitization and calcite precipitation. A detailed analysis of the hydrochemical data set, saturation indices of the minerals and partial pressure of CO2 in the waters joined to the application of geochemical modelling methods allowed the elaboration of a hydrogeochemical model of the studied aquifers. The developed approach contributes to a better understanding of the karstification processes and the hydrogeological functioning of carbonate aquifers, the latter being a crucial aspect for the suitable management of the water resources.

Regional-scale analysis of karst underground flow deduced from tracing experiments: examples from carbonate aquifers in Malaga province, southern Spain

Tracer concentration data from field experiments conducted in several carbonate aquifers (Malaga province, southern Spain) were analyzed following a dual approach based on the graphical evaluation method (GEM) and solute transport modeling to decipher flow mechanisms in karst systems at regional scale. The results show that conduit system geometry and flow conditions are the principal factors influencing tracer migration through the examined karst flow routes. Solute transport is mainly controlled by longitudinal advection and dispersion throughout the conduit length, but also by flow partitioning between mobile and immobile fluid phases, while the matrix diffusion process appears to be less relevant. The simulation of tracer breakthrough curves (BTCs) suggests that diffuse and concentrated flow through the unsaturated zone can have equivalent transport properties under extreme recharge, with high flow velocities and efficient mixing due to the high hydraulic gradients generated. Tracer mobilization within the saturated zone under low flow conditions mainly depends on the hydrodynamics (rather than on the karst conduit development), which promote a lower longitudinal advection and retardation in the tracer migration, resulting in a marked tailing effect of BTCs. The analytical advection-dispersion equation better approximates the effective flow velocity and longitudinal dispersion estimations provided by the GEM, while the non-equilibrium transport model achieves a better adjustment of most asymmetric and long-tailed BTCs. The assessment of karst underground flow properties from tracing tests at regional scale can aid design of groundwater management and protection strategies, particularly in large hydrogeological systems (i.e. transboundary carbonate aquifers) and/or in poorly investigated ones.RésuméLes données de concentration de traceurs provenant d’expériences de terrain menées dans plusieurs aquifères carbonatés (province de Malaga, sud de l’Espagne) ont été analysées en suivant une approche duale basée sur la méthode d’évaluation graphique (MEG) et la modélisation du transport de soluté pour déchiffrer les mécanismes d’écoulement dans les systèmes karstiques à l’échelle régionale. Les résultats montrent que la géométrie du système de conduits et les conditions d’écoulement sont les principaux facteurs qui influencent la migration du traceur par les voies d’écoulement karstiques examinées. Le transport de soluté est. principalement contrôlé par l’advection longitudinale et la dispersion sur toute la longueur du conduit, mais aussi par le partage d’écoulement entre les phases fluides mobiles et immobiles, alors que le processus de diffusion matricielle semble moins pertinent. La simulation des courbes de percée du traceur (CPT) suggère que l’écoulement diffus et concentré à travers la zone non saturée peut avoir des propriétés de transport équivalentes pour une recharge extrême, avec des vitesses d’écoulement élevées et un mélange efficace en raison des gradients hydrauliques élevés générés. La mobilisation des traceurs dans la zone saturée dans des conditions d’écoulement faible dépend principalement de l’hydrodynamique (plutôt que du développement du conduit karstique), ce qui favorise une advection longitudinale inférieure et un retard dans la migration du traceur, entrainant un effet de traine marqué des CPT. L’équation analytique de l’advection-dispersion permet une meilleure approximation de la vitesse d’écoulement effective et des estimations de dispersion longitudinale fournies par le MEG, alors que le modèle de transport sans équilibre réalise un meilleur ajustement de la plupart des CPT asymétriques et à longue traine. L’évaluation des propriétés de l’écoulement souterrain karstique à partir des essais de traçage à l’échelle régionale peut aider à concevoir des stratégies de gestion et de protection des eaux souterraines, en particulier dans les grands systèmes hydrogéologiques (c-à-d. les aquifères carbonatés transfrontaliers) et/ou dans des systèmes peu étudiés.ResumenSe analizaron los datos de concentración de trazadores artificiales procedentes de varios ensayos realizados en algunos acuíferos carbonáticos de la provincia de Málaga (sur de España), mediante una aproximación dual basada en el método de evaluación gráfica (GEM) y transporte de solutos, para descifrar los mecanismos de flujo en sistemas kársticos a escala regional. Los resultados muestran que la geometría de los sistemas de conductos y las condiciones de flujo son los principales factores que influyen en la movilización del trazador a través de las líneas de flujo kárstico estudiadas. El transporte de solutos está controlado principalmente por procesos de advección y dispersión longitudinal a lo largo de los conductos, pero también por la partición del flujo entre fases móviles e inmóviles, mientras que el proceso de difusión desde la matriz de la roca parece ser menos relevante. La simulación de las curvas de paso de trazadores (BTCs) sugiere que el flujo difuso y concentrado a través de la zona no saturada puede tener propiedades equivalentes de transporte en condiciones extremas de recarga, con altas velocidades de flujo y una mezcla eficiente de flujos de agua como consecuencia de los elevados gradientes hidráulicos que se generan. La movilización del trazador dentro la zona saturada en condiciones de aguas bajas depende principalmente de las características hidrodinámicas (en lugar del desarrollo de los conductos kársticos), que promueven una menor advección longitudinal y un mayor retraso en el movimiento del trazador, lo que se traduce en BTCs con colas pronunciadas. La ecuación analítica de advección-dispersión se aproxima mejor a las estimaciones de la velocidad efectiva de flujo y de la dispersión longitudinal proporcionadas por el GEM, mientras que el modelo de transporte de no-equilibrio consigue un mejor ajuste de la mayoría de las BTCs asimétricas y con colas pronunciadas. La evaluación de las propiedades de los flujos subterráneos kársticos a partir de pruebas de trazadores a escala regional puede ayudar al diseño de estrategias de gestión y protección de las aguas subterráneas, particularmente en grandes sistemas hidrogeológicos (por ejemplo, en acuíferos carbonáticos transfronterizos) y/o poco investigados.摘要遵循基于图形评估方法和溶质运移模拟的双重方法分析了(西班牙南部Malaga省)几个碳酸盐含水层野外实验获取的示踪剂浓度数据,以在区域尺度上解译岩溶系统是水流机理。结果显示,通道系统的几何结构和水流条件是影响示踪剂通过岩溶水流路径迁移的主要因素。溶质运移主要受到整个通道长度内纵向平流和离散的控制,但是也受到移动和固定相之间水流分区的控制,而基质弥散过程似乎关联性较小。示踪剂突破曲线模拟表明,由于产生的很高的水力梯度,在伴有很高流速和有效混合的极端补给条件下,通过非饱和带的离散和集中水流可能有相等的传输特性。低水流条件下饱和带内的示踪剂活动化主要取决于水动力学(而不是取决于岩溶通道的发育),水动力学促进示踪剂迁移中较低的纵向平流和延迟,导致示踪剂突破曲线有明显的拖尾现象。解析平流-离散方程可以更好地估计图像评估方法得到的有效水流速度和纵向离散估算结果,而非平衡运移模型能够更好地调整大多数不对称和长尾示踪剂突破曲线。通过区域尺度示踪实验得到的岩溶地下水流特性评价结果可支持谋划地下水管理和保护战略,特别是在大的水文地质系统中(如跨边界碳酸盐含水层)及/或欠调查的水文地质系统中尤其如此。ResumoDados de concentração de traçadores de experimentos conduzidos em diversos aquíferos carbonáticos (província de Málaga, sul da Espanha) foram analisados seguindo uma abordagem dual baseada no método de avaliação gráfica (MAG) e modelagem de transporte de soluto para decifrar os mecanismos de fluxo em sistemas cársticos em escala regional. Os resultados mostram que a geometria do sistema de conduto e as condições de fluxo são os principais fatores que influenciam a migração do traçador através das rotas de fluxo cárstico examinadas. O transporte de soluto é controlado principalmente por advecção longitudinal e dispersão ao longo do comprimento do conduto, mas também por particionamento do fluxo entre as fases de fluido móvel e imobilizado, enquanto o processo de difusão da matriz parece ser menos relevante. A simulação das curvas de identificação (CI) do traçador sugere que o fluxo difuso e concentrado através da zona não saturada pode ter propriedades de transporte equivalentes sob recarga extrema, com altas velocidades de fluxo e mistura eficiente devido aos altos gradientes hidráulicos gerados. A mobilização do traçador dentro da zona saturada em condições de baixo fluxo depende principalmente da hidrodinâmica (e não do desenvolvimento do canal cárstico), que promove uma advecção e atraso longitudinal mais baixos na migração do traçador, resultando em um efeito de cauda marcado nas CI. A equação analítica de advecção e dispersão se aproxima melhor das estimativas de velocidade de fluxo efetivas e de dispersão longitudinal fornecidas pelo MAG, enquanto o modelo de transporte sem equilíbrio alcança um melhor ajuste da maioria das CI assimétricas e de cauda longa. A avaliação das propriedades de fluxo subterrâneo cárstico a partir de testes de traçadores em escala regional pode auxiliar na elaboração de estratégias de gestão e proteção de águas subterrâneas, particularmente em sistemas hidrogeológicos grandes (isto é, aquíferos carbonáticos transfronteiriços) e/ou em meios pouco investigados.

Groundwater dynamics in a hydrologically-modified alpine watershed from an ancient managed recharge system (Sierra Nevada National Park, Southern Spain): Insights from hydrogeochemical and isotopic information

In many of the alpine watersheds of Sierra Nevada (Southern Spain) exists an ancient network of dug canals that collect, transport and facilitate the recharge the snowmelt in the underlying aquifer during the spring season. This practice, known as careos, in the lower part of the watersheds supply drinking water as spring discharge during the dry season. To study how this managed recharge technique modifies the natural response of these basins this work focuses on characterizing the hydrological behavior of one of the sites, the Berchules watershed. The mechanisms for mineralization of groundwater are based on geochemical processes such as evapo-concentration in the soil layer and silicate mineral weathering due to dissolved CO2 originated from both soil biogenic processes and the atmosphere. Groundwater presents a main hydrogeochemical calcium‑magnesium-bicarbonate type facies, which is associated to groundwater flowing through the upper weathered silicates and quickly drained through springs located in the uplands and in the intermediate altitude catchment zone. Additionally, in the lower part of the basin some springs discharge mineralized groundwater with a sodium-calcium-bicarbonate composition associated to regional groundwater flow. In natural conditions, this hydrogeological system behaves as a sloping aquifer, occurring recharge between 1400 and 2500 m a.s.l. The springs discharge groundwater with an isotopic content and temperature in coherence with the local rainfall isotopic and thermal atmospheric altitudinal lines. Nevertheless, once the careo recharge begins the affected springs reveal the fingerprint of the concentrated recharge system by blurring the fingerprint of both the isotopic and thermal altitudinal dependence in the springs discharge. This validates the previous conceptual model and supports average recharge values of 141 ± 140 mm/yr and total average water resources of 181 ± 111 mm/yr which include a 40% increase in the study period due to the effect of the acequias de careo.

Karst development of an evaporitic system and its hydrogeological implications inferred from GIS-based analysis and tracing techniques

The geomorphological characteristics and hydrogeological functioning of a geologically heterogeneous evaporitic karst plateau in Southern Spain were studied. Land surfaceinformation (LiDAR data) was used to analyze the shape and distribution of closed depressions. An artificial tracer test and monitoring of the natural responses of the main spring have allowed to infer the karstic development of the studied system. Three dyes were injected in selected swallow holes to trace the main groundwater flowpaths and to estimate the dimension of the conduit network. Discharge, electrical conductivity and temperatura were monitored in the groundwater that drains the evaporitic plateau during an individual and intense recharge pulse. Tracing techniques were adapted to high salinity environments by using specific calibration standards (NaCl + dye). The hydrological connection detected between two of the swallow holes and the outlet, and the deduced orientation pattern for closed areas, would suggest that the karst evolution (internal and external) is related to fault orientation. The rapid tracer detection (16-20 h) and high estimated maximum flow velocities (125-192 m/h), together with the fast impulsional response of the controlled physicalchemical parameters in spring waters (~15-16 h) demonstrate the existence of quick flows under recharge conditions with well-defined system drainage, indicating a high degree of internal karstification (estimated master conduit diameter ~1.5 m). However, flooding of the depressions feeding swallow holes and analysis of the spring response times from natural and artificial tracers point to a restriction of the system´s drainage, most likely due to the constrained morphology of the karst conduits. This results in sustained recharge periods and delayed spring responses of some parameters, highlighting the relevant role of concentrated recharge in the hydrogeological behavior of the studied evaporitic karst.