Silvino Castaño

Model of hydrological behaviour of the anthropized semiarid wetland of Las Tablas de Daimiel National Park (Spain) based on surface water–groundwater interactions

Las Tablas de Daimiel National Park (TDNP) in Spain is one of the most important semiarid wetlands of the Mediterranean area. The inversion of the regional groundwater flow, primarily due to overexploitation and inadequate aquifer management, has led to degradation. The system has turned from a groundwater discharge zone into a recharge zone, and has remained mostly dry since the 1980s. High heterogeneity and complexity, enhanced by anthropogenic management action, hampers prediction of the surface–groundwater system response to flooding events. This study analyses these interactions and provides empirical evidence to define a conceptual model of flooding-infiltration-groundwater dynamics through the application of a few simple analysis tools to basic hydrological data. Relevant surface water–groundwater interactions are mainly localized in the left (west) margin of TDNP, as confirmed by the fast responses to flooding observed in the hydrochemic, hydrodynamic and isotopic data. During drying periods, small artificial and/or low-flow natural floods are followed by infiltration of evaporated poor-quality ponding water into saline low-permeability layers. The results allow an improved understanding of the hydrological behaviour essential to support efficient management practices. The relative simplicity of the methodology allows for its application in other similar complex groundwater-linked wetlands where detailed knowledge of local geology is still absent.RésuméLas Tablas de Daimiel National Park (TDNP) en Espagne est l’une des plus importantes zones humides semi-arides de la région méditerranéenne. L’inversion de l’écoulement régional des eaux souterraines, principalement en raison d’une surexploitation et d’une gestion inadaptée, a conduit à sa dégradation. Le système a évolué d’une zone de décharge à une zone de recharge et est resté la plupart du temps sec depuis les années 80. Sa grande hétérogénéité et sa complexité, renforcées par les actions de gestion, entravent la modélisation de la réponse du système eaux de surface–eaux souterraines face aux inondations. Cette étude analyse ces interactions et fournit des critères empiriques afin de définir un modèle conceptuel dynamique inondation-infiltration-eaux souterraines utilisant quelques outils d’analyse simples à base de données hydrologiques. Les interactions eaux de surface–eaux souterraines pertinentes sont principalement localisées dans la partie gauche (ouest) de la TDNP, tel que le confirment les réponses rapides aux inondations observées grâce aux données hydrochimiques, hydrodynamiques et isotopiques. Pendant les périodes sèches, les crues de faibles débits artificielles et/ou naturelles sont suivies par une infiltration d’eau évaporée de mauvaise qualité dans les couches salées de faible perméabilité. Les résultats permettent une meilleure compréhension du comportement hydrologique, essentielle pour assurer une gestion efficace. La relative simplicité de la méthode permet son application dans d’autres complexes eaux souterraines-zones humides similaires où une connaissance détaillée de la géologie locale est encore absente.ResumenEl Parque Nacional de Las Tablas de Daimiel (TDNP) en España es uno de los más importantes humedales semiáridos del área Mediterránea. La inversión del flujo regional de agua subterránea, principalmente debido a la sobreexplotación y a un manejo inadecuado del acuífero, ha llevado a la degradación. El sistema se convertido de ser una zona de descarga de agua subterránea a una zona de recarga, y ha permanecido mayormente seco desde los 80. La alta heterogeneidad y complejidad, enriquecida por las acciones de manejo antropogénico, dificulta la predicción de la respuesta del sistema de aguas superficiales–aguas subterráneas a eventos de inundación. Este estudio analiza estas interacciones y provee evidencias empíricas para definir un modelo conceptual de la dinámica agua subterránea–infiltración–inundación a través de la aplicación de unas pocas herramientas simples de análisis para datos hidrológicos básicos. Las interacciones agua superficial–agua subterránea relevantes están principalmente localizadas en la margen izquierda (oeste) del TDNP, según fue confirmado por las rápidas respuestas a las inundaciones observadas en los datos hidroquímicos, hidrodinámicos e isótopos. Durante los períodos secos, las pequeñas inundaciones artificiales y/o las inundaciones naturales de bajo flujo son seguidas por infiltración en bajos de agua de pobre calidad evaporadas en capas salinas de baja permeabilidad. Los resultados permiten una mejor comprensión del comportamiento hidrológico esencial para sustentar prácticas eficientes de manejo. La relativa simplicidad de la metodología permite su aplicación en otros humedales complejos similares vinculados por el agua subterránea, donde el conocimiento detallado de la geología local está aún ausente.摘要西班牙Las Tablas de Daimiel国家公园(TDNP)是地中海地区最重要的半干旱湿地之一。由于过度开采和不恰当的含水层管理,区域地下水流的转化已经导致了地下水的退化。区域地下水系统已由排泄区变为了补给区,而且自20世纪80年代以来,此地区的地下水一直保持着几乎干涸的水平。水文地质条件高度的非均质性和复杂性,加之人工管理措施的干扰,阻碍着对地表水-地下水系统对洪水事件的相应的预测。本次研究分析了这些相互作用,通过应用一些简单的分析工具对基础的水文数据进行处理,为定义洪水-入渗-地下水动态的概念模型提供了经验性的证据。正如在水化学、水文动态和同位素数据中观察到的对洪水的快速响应所证实的,相关的地表水-地下水相互作用主要发生在TDNP的左侧(西部)边缘。在旱季,在小规模的人工的或低流量的自然洪水之后,蒸发的劣质池塘水渗入低渗透性的咸水层。本次研究的结果,增强了对支持有效率的管理实践至关重要的水文行为的理解。考虑到当缺乏详细的区域地质资料时,在其它与之相似的复杂的与地下水有联系的湿地应用此种方法相对简单。ResumoO Parque Nacional de Las Tablas de Daimiel (PNTD) em Espanha é uma das zonas húmidas semiáridas mais importantes da área mediterrânica. A inversão do escoamento regional de águas subterrâneas, principalmente devido a sobre-exploração e a gestão inadequada do aquífero, conduziu à sua degradação. O sistema tornou-se de uma zona de descarga de águas subterrâneas numa zona de recarga e permaneceu maioritariamente seco desde os anos 1980. Heterogeneidade e complexidade altas, realçadas por ação de gestão antropogénica, dificultam a previsão da resposta do sistema águas superficiais-águas subterrâneas aos eventos de cheia. Este estudo analisa estas interações e dá evidências empíricas para definir um modelo conceptual da dinâmica de cheia-infiltração de águas subterrâneas através da aplicação de algumas ferramentas de análise simples a dados hidrológicos básicos. As interações águas superficiais-águas subterrâneas relevantes localizam-se principalmente na margem esquerda (ocidental) do PNTD, como confirmado pelas respostas rápidas às cheias observadas nos dados hidroquímicos, hidrodinâmicos e isotópicos. Durante períodos de seca, algumas cheias artificiais e/ou naturais de baixo fluxo são seguidas por infiltração de água de encharcamento evaporada de pobre qualidade para camadas de baixa permeabilidade, salinas. Os resultados permitem uma compreensão melhorada do comportamento hidrológico, essencial para apoiar práticas de gestão eficientes. A simplicidade relativa da metodologia permite a sua aplicação a outras zonas húmidas complexas similares ligadas a águas subterrâneas onde o conhecimento detalhado da geologia local ainda esteja ausente.

Long-term effects of aquifer overdraft and recovery on groundwater quality in a Ramsar wetland: Las Tablas de Daimiel National Park, Spain

Las Tablas de Daimiel National Park is one of Spains most representative groundwater‐dependent ecosystems. Under natural conditions, water inflows combined brackish surface water from River Giguela with freshwater inputs from River Guadiana and the underlying aquifer. Since the mid‐1970s, aquifer overexploitation caused the desiccation of the wetlands and neighbouring springs. The National Park remained in precarious hydrological conditions for three decades, with the only exception of rapid floods due to extreme rainfall events and sporadic water transfers from other basins. In the late 2000s, a decrease in groundwater abstraction and an extraordinarily wet period reversed the trend. The aquifer experienced an unexpected recovery of groundwater levels (over 20 m in some areas), thus restoring groundwater discharge to springs and wetlands. The complex historical evolution of the water balance in this site has resulted in substantial changes in surface and groundwater quality. This becomes evident when comparing the pre‐1980 groundwater quality and the hydrochemical status in the wetland in two different periods, under “dry” and “wet” conditions. Although the system is close to full recovery from the groundwater‐level viewpoint, bouncing back in the major hydrochemical constituents has not yet been obtained. These still appear to evolve in response to the previous overexploitation state. Moreover, in some sectors, there are groundwater‐dependent ecosystems that remain different to those found in preoverexploitation times. The experience of Las Tablas de Damiel provides an observatory of long‐term changes in wetland water quality, demonstrating that the effects of aquifer overexploitation on aquatic ecosystems are more than a mere alteration of the water balance and that groundwater quality is the key to aquifer and aquatic ecosystem sustainability.

Identification of Spatial Models of \(\updelta ^{18}\)O in Precipitation of the Wet Season Over Spain Using Genetic Algorithms

The isotopic content in precipitation is a function of climatological conditions at the site of occurrence and at the source of the water vapour. In hydrogeology, the spatial trend of \(\updelta ^{18}\mathrm{{O}}\) in precipitation allows to identify the areas of recharge and transit time. The explicative variables of the spatial trend of \(\updelta ^{18}\mathrm{{O}}\) in precipitation are geographical and climatological. A regression model to describe the spatial trend of \(\updelta ^{18}\mathrm{{O}}\) in precipitation can include these variables in a variety of terms: linear, quadratic, cubic, reciprocal or logarithm. The number of possible models is so large that it is impossible to apply traditional methods in order to select the best combination of variables. However, it is possible to apply soft-computing techniques (genetic algorithms) for stochastic optimization in regression problems with a large number of variables. A modified fitting function is used in order to account for the parsimony principle and the goodness of fitness. The optimal models identified will allow a mapping of the spatial trend of \(\updelta ^{18}\mathrm{{O}}\) in precipitation of the wet season and it will help to characterize the water resources.

Assessment of Pollution Risk in the Western La Mancha Carbonated Aquifer Due to Anthropogenic Degradation of the Tablas de Daimiel National Park (Spain)

The inversion of the hydraulic gradient, primarily due to overexploitation and inadequate hydraulic management of the Western La Mancha carbonated aquifer, has led to the desiccation of the Tablas de Daimiel National Park (TDNP). As a consequence, a permanent unsaturated zone (UZ) has appeared beneath the former wetland area, making the carbonated aquifer extremely vulnerable to contamination. Besides, the strong human induced disturbance of the UZ (i.e. smouldering peat fires) is releasing nutrients that used to be retained in the soil matrix under natural conditions. The present research demonstrates how this degradation process might result in aquifer contamination.