Hydrogeological functioning of a karst aquifer deduced from hydrochemical components and natural organic tracers present in spring waters. The case of Yedra Spring (Southern Spain)

The major chemical parameters, TOC and natural fluorescence of Yedra spring, Malaga province, southern Spain were moni­tored from April 2008 to March2009. The electrical conductiv­ity and the concentrations of most major ions decreased follow­ing recharge periods. The TOC and NO3–, representing tracers from the soil that infiltrate throughthe unsaturated zone, were found to vary inversely withthe Mg2+ content, whichis a natu­ral indicator of groundwater residence time. Furthermore, a strong, direct relation was found between TOC and the natu­ral fluorescence associated withhumic and fulvic acids. Bothparameters respond similarly to rainfall events, exhibiting sig­nificant increases during recharge followed by reductions dur­ing recession. This relation means that TOC mainly originates from organic acids. The results document rapid infiltration pro­cesses witha lag of less than one day following rainfall, whichis typical of a karst aquifer withconduit flow, rapid drainage and limited natural regulation. The combined use of conventional hydrochemical parameters and natural organic tracers facili­tates aquifer characterization and validates the vulnerability to contamination

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

Preliminary Assessment Of Sediment Transport And Associated Bacteriological Contamination In A Mountainous Rural Karst Area (Sierra De Ubrique, S Spain)

In rural karst areas, where agricultural and cattle activities are developed and quite often urban waste waters are not properly treated, the high probability of groundwater pollution occurrence together with the high vulnerability of carbonate aquifers poses a potential risk for human health. Sierra de Ubrique is a karstified carbonate aquifer system developed in Jurassic limestones and dolostones located in one of the wettest regions in Spain. This karst aquifer is recharged by rainfall infiltration through karst features, but also from concentrated runoff trough Villaluenga shaft. Groundwater discharge, which is mainly produced through three karst, is also used for drinking water supply of Ubrique town. During flooding conditions, high turbidity events at the two permanent springs are simultaneous to maximum discharge, hindering the exploitation of groundwater for human consumption. This work aims to identify and characterize the main contamination sources and to understand the role of sediment transport in the occurrence of polluted groundwater episodes. For that purpose, a complete climate and groundwater monitoring network has been installed including a weather station and field devices for continuous record of physical‐chemical parameters. Additionally, numerous surface and groundwater sampling campaigns were performed to take samples for chemical and bacteriological determinations. The obtained results allowed the identification of different contamination types of anthropogenic origin as (1) organic (poorly treated waste waters, fecal remains from cattle activity and food factories) and (2) inorganic. The response times in output signals of the two main springs, maximum thresholds of pollutants and statistical correlations among specific chemical/bacteriological‐like parameters lead to explain the main contaminant transport mechanisms, which greatly differ in the examined karst connections.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Coupling major ions and trace elements to turbidity dynamics for allogenic contribution assessment in a binary karst system (Sierra de Ubrique, S Spain).

This investigation deals with the application of a multi-technique approach combining data from turbidity, major ions, and trace elements to characterize the implications of allogenic recharge in a binary karst system and assess the relative hydrochemical contribution to karst springs captured for drinking use. Hydrodynamic and hydrochemical responses of the outlets to storm events were continuously monitored during four selected flooding events, and water samples were collected at the main sinking stream in the recharge area and discharge points (Cornicabra and Algarrobal springs) for chemical analysis. The obtained hydrogeochemical dataset was analyzed through mean of time-series and statistical analysis and allowed to describe the fate and origin of trace elements. Despite that most of analyzed components present a natural origin, the existence of a Wastewater Treatment Plant in the recharge area was determined to be the main source of P (phosphorus) concentrations measured in the karst springs. Sediment (particulate) transport constitutes the most important factor in the mobilization of Al, Mn, Ni, and Ba in both surface and groundwater, whilst Li, Sr, and P are mainly controlled by solute migration. The hydrochemical signature of allogenic water component was constrained by identifying characteristic correlations between Ba and Ca/Sr ratio in water samples. The combination of specific hydrogeological processes as ion solution and sorption processes onto solids between solutes and particles as well as water mixing processes (allogenic vs diffuse) result more evident in Algarrobal spring, which receives a higher contribution of allogenic component due to a greater feeding catchment.Funding for open access charge: Universidad de Málaga / CBU

Hydrogeological parameters assessment by tidal influence analysis in the coastal aquifers of Bajo Guadalhorce (Malaga province, southern Spain)

By the use of continuous data recording on two points of the Bajo Guadalhorce coastal sector (Malaga province, southern Spain), located at 626 m and 985 m inland, it has been possible to verify a clear influence of tidal oscillations on the water table of the unconfined and the confined aquifers. Various methods to estimate aquifer transmissivity have been applied. The results depends on the method and, more important, on the storage coefficient (S) values. After the calculations it is possible to confirm that the time lag and tidal efficiency factor methods give coherent results with previous data, although with the time lag method the transmissivity values are an order of magnitude higherEl registro continuo de las variaciones piezométricas en dos puntos del sector costero del Bajo Guadalhorce (Málaga), ubicados a 626 m y 985 m de la línea de costa, ha permitido constatar la influencia de las oscilaciones mareales en los niveles piezométricos de los acuíferos libre y confinado. Se han podido aplicar varias metodologías para estimar la transmisividad de ambos. Los resultados dependen del método utilizado y, en mayor medida, de los valores de coeficiente de almacenamiento (S). Tras los cálculos se puede afirmar que las metodologías de retraso de mareas y eficiencia de mareas presentan resultados coherentes con los datos previos, aunque con el método de retraso de mareas se obtienen valores de transmisividad de hasta un orden de magnitud mayore

Combining different tracers (CFC-12, 3H, 3He, 4He) to understand the hydrogeological functioning of a semiconfined aquifer.

The hydrochemical results obtained in a semiconfined aquifer called Niebla-Posadas aquifer (S of Spain) show an increase in mineralisation and δ13C in the flow direction, suggesting increasing residence time in the aquifer. However, different agricultural contaminants associated with recently infiltrated waters appear in the confined section. The combination of different groundwater-age tracers (CFC-12, 3H, 3He, 4He) provides valuable information to understand the hydrogeological processes and water quality intending to achieve proper water supply management. The preliminary result of tracers suggests that samples may be a mixture of a majority of tritium-free old groundwater and a minor fraction of recently infiltrated water.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Control of Environmental Parameters for Management and Conservation of Nerja Cave (Malaga, Spain)

V povprečju obišče jamo Nerja ve~ kot 500.000 ljudi letno. Od leta 1993 je v jami instalirana mreža monitoringa, ki vsako uro meri številne parametre, da bi ugotovili vplive obiskovalcev na podzemno okolje. Od 1991 izvršujejo hidrokemične meritve vode v curkih v jami in pri naravnih iztokih iz karbonatnega vodonosnika. Zvezna merjenja fizikalno kemijskih parametrov prenikajoče vode, dnevni odtok, kakor tudi temperatura in relativna vlažnost zraka, koncentracija CO2 in temperatura skale kažejo človekov vpliv. Glavne spremembe okoljskih parametrov so naslednje: 1. zračna temperatura zraste za 0,2 °C na vsakih 1000 obiskovalcev na dan; 2. relativni porast relativne zračne vlage med 2 in 3 %, ki v poletnih dneh doseže nasičenost; 3. koncentracija CO2 v zraku narase do vrednosti med 500 in 700 ppm v obdobju manjšega obiska in za desetkratno izhodiščno vrednost ob času velikega obiska (2.800 ppm); 4. temperatura skale narase med 0,02 °C do 0,15 °C na dan in 5. PCO2 prenikajo~e vode izkazuje spremembe, naraščajoče med velikim obiskom in padajoči indeks nasičenosti karbonatnih mineralov. The Nerja Cave receives on average more than 500,000 visitors per year. In order to know the possible impact in the underground environment by human visits, a monitoring network was installed since 1993, to control hourly several parameters. Also, since 1991 a hydrochemical control has been carried out in the drip water points of the cave and in the natural discharge points of the carbonate aquifer. This continuous record of physical-chemical parameters of drip water, its daily outflow, as well as temperature and relative humidity in the air, CO2 concentration and rock temperature shows the human influence. The main changes in environmental parameters are the following: 1. cave air temperature rises 0.2 °C by 1000 visitors/day; 2. a daily increase between 2 and 3 % in relative air humidity, reaching saturation on summer days; 3. CO2 concentration in air increases up to values between 500 and 700 ppm during low visitability periods and 10 times the background value during high visitability periods (2.800 ppm); 4. temperature of the rock rises between 0.02 °C and 0.15 °C/day, and (5) PCO2 of drip water also presents variations, increasing during the big influx of visits and decreasing the saturation index of carbonated minerals

Comparative study of the hydrodynamic response of several carbonate aquifers systems in southern Spain using correlation and spectral analysis

La utilización del análisis correlatorio y espectral para comparar la respuesta hidrodinámica de siete sistemas acuíferos carbonáticos distribuidos por la geografía andaluz, para un mismo intervalo de tiempo (1999/2000- 2002/2003) ha permitido caracterizar y comparar los diversos tipos de funcionamiento hidrogeológico que presentan acuíferos carbonáticos representativos de la Cordillera Bética, así como evaluar el grado de aplicabilidad de esta metodología para el estudio de los acuíferos carbonáticos. Los resultados obtenidos muestran que esta metodología permite diferenciar el mayor o menor poder regulador de estos acuíferos, sobre todo mediante el uso del parámetro tiempo de regulación, así como la necesidad de ampliar la clasificación hidrodinámica de los acuíferos kársticos propuesta por Mangin (1984), con nuevos tipos de comportamiento, entre otros el de mayor inercia (poder regulador hiperanual)The application of correlation and spectral analysis to compare the hydrodynamic response of seven carbonate aquifer systems distributed over Andalusia, in which have been monitored during the same time period (1999/2000-2002/2003) has permitted to characterize and to compare the different types of hydrogeological behavior of carbonate aquifers in the Betic Cordillera, as well as to evaluate the degree of applicability of this methodology to study carbonate aquifers. The results show that this methodology allows to differentiate variable regulation capacity of these aquifers, especially by using time regulation parameter and the need to extend the hydrodynamic classification of karstic aquifers proposed by Mangin (1984) with new types of behavior, including the most inertia (hyperannual regulation capacity