Iñaki Vadillo

Carbon dioxide concentration in air within the Nerja Cave (Malaga, Andalusia, Spain)

INTRODUCTION In caves adapted for tourism, the control of carbon dioxide levels is crucial for the cave’s conservation as well as for public health, so that an adequate air quality is maintained for the visitors. On one hand, the CO2 concentration in the air in karstic caves conditions the development of different speleogenetic processes within these caves given that it directly influences the precipitation/dissolution of carbonates (White, 1988, 1997; Dreybrodt, 2000; Dreybodt & Eisenlohr, 2000). On the other hand, the CO2 concentration determines the cave’s air quality, as elevated CO2 concentrations above 5000 ppmv are noxious to human health (Halbert, 1982). Numerous authors have studied CO2 from diverse standpoints. Pioneering studies have been made on the presence and dynamics of CO2 in caves with respect to the exterior environment, for example Renault (1968), Ek (1968, 1979, 1981), James (1977) and Troester & White (1984). Other authors

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).

Spatial distribution of paleoclimatic proxies in stalagmite slabs using laser-induced breakdown spectroscopy

The spatial distribution of paleoclimatic proxies in stalagmite slabs using laser-induced breakdown spectroscopy (LIBS) has been performed in this study. Stalagmites from different locations in the north of Spain were cut and analyzed along the main growth axis by LIBS. For comparative purposes, powders drilled from along the growth axis were also analyzed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Advantages of LIBS include fast analysis of long stalagmite sections at atmospheric pressure, lateral resolution in the μm range and no sample preparation beyond having optical access to the stalagmite section to be inspected. Mg/Ca and Sr/Ca intensity ratios are of major interest for paleoclimate applications. An excellent agreement between the Mg/Ca intensity ratios measured in LIBS and in ICP-AES was observed. Sr/Ca trends were well matched only in high Sr stalagmites. Also, this work reports the employment of detrital layers as paleoclimatic proxies in speleothems by LIBS. Large concentrations of Si and Al are indicative of flood events inside the cave.

Groundwater contamination in caves: four case studies in Spain

INTRODUCTION Soil and vadose zone of aquifers act as protective covers to groundwater (Mudry et al., 2003), so specific studies of subsurface water flow and solute transport that could be contaminants in both environments are necessary. These studies are essential for a better understanding of the attenuation factors affecting the contaminants before their arrival to the underground resource. The methodology applied to the study of porous aquifers is different from that applied to carbonate (karstic) aquifers (Stephens, 1����� Selker et al., 1���). The reason for this difference is

Isotopic (13C) Signature of CO2 Sources in the Vadose Zone of a Mediterranean Karst (Nerja Cave Site, Southern Spain)

This study is based on in situ measurements of the soil and the vadose zone (<60 m) in a Mediterranean karst experimental site near Nerja Cave (a show cave in dolomite marbles in South Spain). CO2 concentrations in depth were registered in boreholes drilled in experimental site. The CO2 content generally increases with depth. Measurements indicate average vadose air CO2 concentrations of nearly 40,000 ppm, with a maximum of nearly 60,000 ppm. In this context, the cave itself appears to be a vadose subsystem above the groundwater level, with significantly lower CO2 concentrations (a few thousands of ppm maximum) due to its ventilation. The δ13C–CO2 data of the vadose air point to an origin of the gas mainly related to microbiological processes associated to the consumption of dissolved organic matter in the groundwater surface. This gas can diffuse or flow laterally, upward or downward through karst conduits. Interactions between air masses of surface origin (relatively dry, with variable temperature and low CO2 content) and typical vadose attributes (relatively high CO2 content, near-saturated humidity and 21 °C temperature) produce clear ascendant or descendant air fluxes inside the boreholes, especially those that cross significant karst voids.

Nitrate contamination in a shallow urban aquifer in East Ukraine: evidence from hydrochemical, stable isotopes of nitrate and land use analysis

Abstract A combined hydrochemical and stable isotope approach was used to investigate the origin of nitrate in the shallow unconfined groundwater of Kharkiv city, Eastern Ukraine. The contamination was investigated in the context of land use within the catchment area. The observed enrichment of sulfate, chloride and nitrate suggests significant groundwater contamination in the shallow urban aquifer, which is widely used as drinking water source for the urban population. Characteristic nitrate/chloride ratios as well as stable isotope ratios (N and O) of nitrate in the most contaminated springs confirmed that septic waste from leaky sewer systems was the main source of nitrate contamination in the groundwater. Nitrate contamination is linked to the type of land use and sewage treatment regime in the catchment area. It is also modulated by the regional hydrogeology, which determines the susceptibility of a given aquifer toward groundwater pollution. A more quantitative assessment of nitrate sources based on the nitrate isotope analysis alone is rather difficult. However, our study confirms that the combination of hydrochemical tracers, robust land-use analysis and nitrate stable isotope measurements represents a valuable approach to identify the origin of the nitrate contamination.

Algae metabolism and organic carbon in sediments determining arsenic mobilisation in ground- and surface water. A field study in Doñana National Park, Spain.

A study has been performed to explore the origin, spatiotemporal behaviour and mobilisation mechanism of the elevated arsenic (As) concentrations found in ground water and drinking ponds of the Doñana National Park, Southern Spain. At a larger scale, 13 piezometers and surface water samples of about 50 artificial drinking ponds and freshwater lagoons throughout the National Park were collected and analysed for major ions, metals and trace elements. At a smaller scale, 5 locations were equipped with piezometers and groundwater was sampled up to 4 times for ambient parameters, major ions, metals, trace elements and iron (Fe) speciation. As was analysed for inorganic and organic speciation. Undisturbed sediment samples were analysed for physical parameters, mineralogy, geochemistry as well as As species. Sediment analyses yielded total As between 0.1 and 18 mg/kg and are not correlated with As concentration in water. Results of the surface- and groundwater sampling revealed elevated concentration of As up to 302 μg/L within a restricted area of the National Park. Results of groundwater sampling reveals strong correlation of As with Fe(2+) pointing to As mobilisation due to reductive dissolution of hydroferric oxides (HFO) in areas of locally elevated amounts of organic matter within the sediments. High As concentrations in surface water ponds are correlated with elevated alkalinity and pH attributed to algae metabolism, leading to As desorption from HFO. The algae metabolism is responsible for the presence of methylated arsenic species in surface water, in contrast to ground water in which only inorganic As species was found. Temporal variations in surface water and groundwater are also related to changes in pH and alkalinity as a result of enhanced algae metabolism in surface water or related to changes in the redox level in the case of groundwater.

A Field Analog of CO2-Closed Conditions in a Karstified Carbonate Aquifer (Nerja Cave Experimental Site, South Spain)

We present new data that illustrate the hydrochemical evolution of groundwater along a flow line in the Triassic marbles around the Nerja Cave, South Spain. Water dissolves calcite and dolomite, and then CaSO4. The environment is locally rich in CO2 (up to near 60,000 ppmv) and consequently the water increases significantly its content in Ca2+, Mg2+, HCO3 − and SO4 2− along the flow, with EC values between 500 and 900 μS/cm. The pH values are typically in the 7–8 range, and the equilibrium PCO2 of the water varies between 10−1.5 and 10−2.5 atm. In the considered flow line there is a relatively deep borehole (S2: 380 m; 280 m saturated) that shows pH values around 10 and equilibrium PCO2 of 10−6 atm, with EC values generally in the 150–200 μS/cm range. Most of its solutes derive from rainwater concentration, together with the dissolution of carbonate minerals in a system closed to CO2. For this reason we consider S2 to be a field analog of such conditions. The nearly stagnant water of this well also shows evidence of sulphate reduction. Unlike its solute contents, isotopically (δ2H and δ18O) the water of S2 does not show any modification with respect to the other points along the flow line.

Highlighting the importance of transitional ventilation regimes in the management of Mediterranean show caves (Nerja-Pintada system, southern Spain)

This study shows the utilization of the air CO2 exhaled by a very high number of visitors in the Nerja Cave as both a tracer and an additional tool to precisely evaluate the air circulation through the entire karst system, which includes non-touristic passages, originally free of anthropogenic CO2. The analysis of the temporal - spatial evolution of the CO2 content and other monitoring data measured from January 2015 to December 2016 in the Nerja-Pintada system, including air microbiological controls, has allowed us to define a new general ventilation model, of great interest for the conservation of the subterranean environment. During the annual cycle four different ventilation regimes and two ventilation modes (UAF-mode and DAF-mode) exist which determine the significance of the anthropogenic impact within the caves. During the winter regime, the strong ventilation regime and the airflow directions from the lowest to the highest entrance (UAF-mode) contribute to the rapid elimination of anthropogenic CO2, and this affects the whole karstic system. During the summer regime the DAF-mode ventilation (with airflows from the highest to the lowest entrances) is activated. Although the number of visitors is maximum and the natural ventilation of the karstic system is the lowest of the annual cycle, the anthropogenic impact only affects the Tourist Galleries. The transitional ventilation regimes -spring and autumn- are the most complex of the annual cycle, with changing air-flow directions (from UAF-mode to DAF-mode and vice versa) at diurnal and poly diurnal scale, which conditions the range of the anthropogenic impact in each sector of the karst system. The activation of the DAF-mode has been observed when the temperature difference between the external and air cave is higher than 5°C.

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.