Karst flow system information from shape analysis and numerical modeling of tracer concentration curves

Dye tracing constitute a very valuable tool for investigating the origin of groundwater and delineating flowpaths in karst media, providing direct and quantitative information about the hydraulic properties and solute transport dynamic within a conduit (and/or fracture) dominated system. In this sense, data obtained from 8 single- and multi-injection tracer experiments performed during last years in different carbonate aquifers located in Malaga province (southern Spain) have been re-examined following the numerical solutions provided by a dual process-based approach: advection–dispersion model (ADM) and two-region non-equilibrium model (2RNE). Tracer tests were conducted under different hydrological conditions (high-intermediate-low flow) affecting the aquifers, and the fluorescent substances were injected into sinkholes (5), losing streams (4), karrenfields (1) and dolines (1), while springs commonly served as detection points (manual sampling and eventually field fluorimeters). Flow and transport parameters estimates obtained from the simulation of 13 tracer breakthrough curves (BTCs) provided mixed information on a wide range of hydrogeological behaviors: from well-developed conduit flow paths to flow and storage modalities in a fissured-like systems. The statistical treatment of the analytical and numerical results, jointly to the field observations, has been especially useful for the characterization of the predominant solute transport processes in the studied experimental sites, given the significant deviations that have been eventually found between the shape of the measured and modeled curves (marked skewness, single/multi-pulse geometry, long-tailing effect, etc). These findings will allow for a better understanding of the structure and dynamic of the karst systems investigated and will may help to protect and preserve karst water resources in the region.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

TOC and NO3-, two natural tracers of infiltration with different hydrochemical behaviour in karst aquifers

International audienceAnalysis of TOC and NO3- contents in the water at four 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 the consequence of the distinct 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 oxidising conditions prevailing within the karst medium, which impede its denitrification and favour its preservation within the saturated zone. 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 hydrogeochemical evolution provide 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

Studying hydrogeochemical processes to understand hydrodiversity and the related natural and cultural heritage. The case of Los Hoyos area (South Spain)

The protection of geodiversity has been gaining interest during the last decades. However, the study of hydrodiversity has been much less developed than other aspects of the geological heritage (lithology, mineralogy, geomorphology, palaeontology). The objective of this work is to help with an inclusive definition of hydrodiversity by assessing its importance as part of geodiversity and how it can condition the natural and cultural heritage of a region. To that end, we have selected as a study area an evaporitic karst enclave of great geomorphological and environmental value located in southern Spain, named Los Hoyos, where diverse water features are found. Based on the hydrochemical and isotopic analysis of the water points, five main processes explain the hydrodiversity of the area: (1) the availability of minerals in the environment, (2) the residence time of groundwater, (3) the evaporation of water in the wetlands, (4) the common-ion effect (5) and the high ionic strength of groundwater. All these processes, directly related to the geology and geomorphology of the area (geodiversity), have given rise to diverse ecosystems (including protected wetlands), which enhance local biodiversity and geological forms (travertines), and are connected to the area's cultural heritage (salt extraction from the Paleolithic). This hydrodiversity is partially or totally responsible for a series of services to society related to its intrinsic, cultural, aesthetic, economic, functional, and scientific values. The case here presented exemplifies the importance of hydrodiversity in the natural and cultural heritage and highlights the need of advancing on the definition, promotion and protection of the hydrological heritage.This work was supported by the Autonomous Government of Andalusia (Junta de Andalucía) [grant numbers P11-RNM-8087, P10-RNM-6895R and P20-01118] and the LifeWatch ERIC call of the European Regional Development Fund [grant number LIFEWATCH-2019-04-AMA-01]. Funding for open access charge: Universidad de Málaga / CBUA

Preliminary hydrogeological characterization of an evaporite karst area (province of Cordoba, South Spain)

The northern sector of the Subbetic Domain in the Betic Cordillera is formed by an olistostrome unit known as the Chaotic Subbetic Complex (CSC). This megabreccia is basically made of Triassic (Keuper) clays and evaporites (gypsum, anhidrite and halite) as well as blocks of other lithologies (limestones, dolostones, sandstones, etc). Despite that low permeability has been traditionally assumed for these materials, water flow and storage through them is likely derived of their aquitard behavior, but also because of the highly permeable conduits generated by dissolution/karstification processes within the evaporite rocks. The geological complexity of the CSC materials determines their hydrogeological heterogeneity, with groundwater flow systems of different length and various scales from recharge areas to discharge zones. Three springs draining the CSC outcrops have been identified around an evaporitic karst plateau located between the Anzur River (to the North) and the Genil River (to the South), in the province of Cordoba (Spain). Data logger devices have been installed in two of them, located at the Anzur River (left margin), providing an hourly record of discharge, electrical conductivity and water temperature. Water samples have been collected fortnightly for subsequent chemical analysis. After two years of record, the results obtained show that the response of the springs to rainfall events is completely different between them. One has a clearly karstic behavior, with a rapid response to recharge whereas the other one is more inertial, and variations in its waters occur in a yearly scale. This is an evidence of the aforementioned hydrogeological heterogeneity of the CSC.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Dating the groundwater drained by the Meliones spring (Málaga province) for integration into a regional hydrogeological conceptual model

El manantial de Meliones (provincia de Málaga) es una polisurgencia hipersalina asociada a la formación arcilloso- evaporítica del Trías de Antequera. Su drenaje natural deteriora la calidad química del agua embalsada en la presa del Guadalhorce, una de las fuentes de abastecimiento a la ciudad de Málaga. Algunos organismos públicos ejecutaron medidas correctoras con un enfoque muy local, centradas en la alteración de los procesos de infiltración rápida en el entorno inmediato al manantial, que no han solucionado el problema. Sin embargo, existen evidencias de que el Trías de Antequera es un sistema hidrogeológico complejo, en el que flujos rápidos localizados en los enclaves kársticos evaporíticos coexistirían con otros de tipo difuso. En este trabajo se ha datado el agua del manantial de Meliones con 3H, CFC-12 y 4He. Además, se han creado modelos de parámetros agregados que definen la distribución de edad de la muestra. Los resultados evidencian que la mayor parte del agua hipersalina drenada por la surgencia fue infiltrada hace más de un siglo. Esto confirma la existencia de un sistema regional con flujos jerarquizados donde flujos regionales lentos y de gran recorrido confluyen con otros rápidos y más cortos.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Estudio preliminar de la hidrodiversidad de humedales andaluces de origen kárstico-evaporítico

Los resultados preliminares obtenidos muestran una gran variedad de facies hidroquímicas (Fig. 3 y 4) y un amplio rango de mineralización de las aguas (Fig. 3 y Tab. 1). Los valores isotópicos de δ18O y δD de las muestras (Fig. 5) indican un enriquecimiento isotópico y presentan un claro desvío con respecto a las líneas meteóricas local y global. Ello demuestra la influencia de la evaporación sobre el agua de los humedales estudiados, más patente en el caso de lagunas estacionales con periodo de inundación prolongado que en aquellas con un hidroperiodo más efímero. Las aguas de las lagunas permanentes, pese a estar expuestas de forma continua a la evaporación, se sitúan en la figura 5 en una posición intermedia, lo que podría deberse a la mezcla de aguas evaporadas con otras de aporte subterráneo. Los humedales de génesis kárstico-evaporítica, pese a tener un origen similar, presentan una gran diversidad geomorfológica, hidrológica e hidrogeológica como consecuencia de condiciones topográficas y geológicas particulares así como de su ubicación dentro de sistemas de flujo subterráneo locales, intermedios o regionales. Dichas particularidades han de ser tomadas en consideración a la hora de gestionar estas áreas naturales y plantear medidas de conservación y restauración, por lo que es necesario profundizar en el conocimiento hidrogeológico de los CCS y de la relación de las aguas subterráneas con los humedales formados en este contexto.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Grupo Español de la Asociación Internacional de Hidrogeólogo

Monitoring groundwater in the discharge area of a complex karst aquifer to assess the role of the saturated and unsaturated zones

International audienceThe hydrochemical response at springs in the drainage area of the Sierra del Rey--Los Tajos carbonate aquifer (province of Ma'laga, southern Spain) was monitored in order to determine the hydrogeological functioning of this aquifer. Analysis of the most important chemical parameters, using methodologies such as the temporal evolution of chemical components, principal component analysis and discriminant factorial analysis revealed that the high level of hydrochemical heterogeneity to be found in this discharge zone, in addition to particular spatial and temporal factors, is responsible for the mineralisation of the spring water. Sampling in karst systems where discharge occurs by several springs should take into account the hydrochemical variability of them; otherwise conclusions about the hydrological functioning of aquifers deduced from mixture of spring waters can be inaccurate

Characterisation of Dissolved Organic Matter in Karst Spring Waters Using Intrinsic Fluorescence: Relationship With Infiltration Processes

From analysis of spectrophotometric properties of dissolved organic matter (OM) and the hydrochemical responses of some karst springs under different hydrologic conditions, an assessment of the origin and transfer pathway of OM present in karst spring waters, from soil and epikarst toward the spring, has been conducted for three karst aquifers in southern Spain: Alta Cadena, Sierra de Enmedio and Los Tajos. Intrinsic fluorescence (excitation–emission matrices or EEMs), together with major water chemistry (electrical conductivity, temperature, alkalinity, Cl−, Mg+ 2) and PCO2 along with natural hydrochemical tracers (TOC and NO3−), have been monitored in 19 springs which drain the three karst aquifers examined in this study. The spring water EEM spectra indicate that fulvic acid-like substances, produced in the soil as a consequence of the decomposition of OM, are the dominant fluorophores, although some of the OM appears to originate from in situ microbiological activity but could be indicative of contamination present in recharge waters from livestock. During each recharge event, TOC and NO3− concentrations increased and variations in fluorescence intensities of peaks attributed to fulvic acid-like compounds were observed. In areas with minimal soil development, spatial and temporal variations in the fluorescence intensity of fulvic acid-like substances and other fluorophores derived from microbiological activity, together with other hydrochemical parameters, provide insights into the hydrogeological functioning of karst aquifers and the infiltration velocity of water from soil and facilitate assessment of contamination vulnerability in these aquifers