Karst aquifers are productive groundwater systems around the world, supplying approximately 25% of the world's drinking water. However, they are highly vulnerable to contamination due to rapid groundwater transit in the transmission zone (KWI 2006). The epikarst, also known as the subcutaneous zone, is an interface between the soil overburden and the transmission zone. The epikarst is considered a critical zone as it can control hydrologic and geochemical characteristics of recharge to the underlying karst aquifer.  The overall goal of this thesis is to utilize time series hydrologic and geochemical data collected at James Cave, Virginia, to examine the influence of epikarst on the quantity, quality, and rates of recharge to aquifers in Appalachian karst. Results of this study indicate a strong seasonality of both the hydrology and geochemistry of recharge. The conceptual model of the epikarst developed in this study identifies three hydrologic seasons: recharge, recession, and baseflow. Seasonality of recharge geochemistry coincides with these three hydrologic seasons.  These results have implications for management of karst aquifers.  First, recharge to Appalachian karst aquifers is seasonal, reaching a maximum during the winter-early spring; the onset of recharge depends on antecedent climatic conditions.  Second, water that infiltrates into the epikarst will have seasonally variable residence times due to changes in hydrologic storage; these variations in attenuation affect geochemical reactions in the epikarst, which can influence recharge quality. Overall, these results point to the complex influence of epikarst on karst recharge, which necessitates collection of long-term and high resolution datasets. / Master of Science

Karst aquifers host significant water supplies but are easily contaminated because highly conductive inlets can rapidly transmit water to depth. The epikarst, which is the region of vegetation, soil, and weathered bedrock above karst aquifers, is a critical zone as it regulates the quantity and quality of recharge to the aquifer. As the epikarst exhibits complex heterogeneity, characterization at the field scale can be challenging. The objective of this thesis was to develop a model of epikarst hydrodynamics using longterm field measurements. To meet this objective, continuous hydrologic data of precipitation, speleothem drips, and an underground stream in James Cave in Pulaski County, VA, were collected to delineate seasonal recharge patterns, estimate effective recharge and catchment areas, characterize the number and permeability of flow paths, and evaluate storativity in the epikarst. Results demonstrate that after significant seasonal recharge, which occurs in the late winter and early spring, the epikarst can temporarily store a significant portion of recharge in low permeability flow paths. Effective recharge was estimated to be approximately 30% of total precipitation (2008-2009). Hydrograph recession analysis aided in delineation of flowpaths in the epikarst, including quickflow, moderate flow, and baseflow components. Hydrograph shape analysis suggests flow restrictions at two of the drip sites that may reveal spatial differences in storage capacity and retention time. Results of this work are intended to aid karst aquifer management by providing a multitechnique approach that can be used to assess seasonal patterns of recharge, quantify flowpath and storage characteristics, and delineate recharge zones. / Master of Science

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Depuis son invention en 1940 mais surtout consécutivement à sa fermeture au public en 1963, la conservation de la Grotte de Lascaux se base entre autres sur la compréhension de ses interactions avec le massif karstique environnant et notamment les processus siégeant dans l’épikarst et la zone de transmission superficielle. Ces travaux de thèse se sont donc attachés à comprendre la dynamique du CO2 dans le continuum sol-épikarst-cavité afin d’en évaluer les potentiels impacts sur la conservation des parois. Nous bénéficions à Lascaux d’une fenêtre d’observation sur les écoulements provenant de l’épikarst sus-jacent dans le SAS 1 de la cavité, mais aussi d’une instrumentation conséquente. Elle permet l’acquisition de nombreuses séries de données temporelles des paramètres microclimatiques ainsi que des teneurs en CO2 de l’air en différents points de la cavité ou encore du débit de l’émergence épikarstique depuis le début des années 2000.Une première partie de l’étude est consacrée à la caractérisation de la dynamique du CO2 dans le contexte d’un épikarst sous couverture pédologique. A cette fin, une parcelle expérimentale est instrumentée afin d’effectuer un suivi des paramètres hydroclimatiques et des teneurs en CO2 à différentes profondeurs. Des périodes de recharge (accumulation) et de vidange (émanations vers l’atmosphère) du CO2 de l’épikarst superficiel sont démontrées tout comme la constitution d’un stock de CO2 peu variable dans l’épikarst subsuperficiel. La compréhension de ces différents mécanismes aboutit à un schéma général de la dynamique du CO2 dans l’épikarst.Cette dynamique est étudiée dans la Grotte de Lascaux au cours d’une seconde partie à partir des séries temporelles des paramètres microclimatiques et des teneurs en CO2, mais aussi du signal isotopique en 13C. Il est alors démontré que les flux de CO2 entrant dans la cavité proviennent de trois origines distinctes : l’atmosphère (entrée), l’épikarst superficiel (Galerie Mondmilch et Salles Ensablées) et le massif (éboulis du Puits du Sorcier). Parallèlement, deux régimes aérologiques responsables de la répartition spatio-temporelle des teneurs en CO2 dans la cavité sont observés : stratification et thermoconvections. Ils sont les principaux responsables de la dynamique du CO2 dans la Grotte de Lascaux du fait des faibles échanges entre cette dernière et l’atmosphère comparativement à d’autres cavités karstiques de la région. Enfin, l’impact du dispositif du pompage de l’air sur l’aérologie et la dynamique du CO2 dans la Grotte de Lascaux est évalué. La comparaison de ces dynamiques avec et sans extraction de l’air de la cavité conduit à la création de schémas conceptuels de la dynamique du CO2 dans la Grotte Lascaux.L’étude des conditions d’écoulement dans l’épikarst de la Grotte de Lascaux, troisième partie de ces travaux, a été effectuée à partir d’un suivi en continu des débits, paramètres physico-chimiques et de la fluorescence naturelle de l’eau. L’analyse des séries temporelles de ces traceurs naturels conduit caractériser de façon détaillée les conditions d’écoulement et notamment l’importance de la teneur en eau de l’épikarst sur la taille zone d’alimentation et les types d’eau arrivant à l’exutoire. Parallèlement, l’impact de ces conditions d’écoulement sur les équilibres calco-carboniques des eaux arrivant dans la cavité est analysé.Enfin, les connaissances acquises sont appliquées pour déterminer l’impact potentiel en continu des eaux (condensation et exfiltration) présentes aux parois ornées de la cavité. A cette fin, une méthodologie d’estimation de la masse de calcite potentiellement précipitée par les eaux d’exfiltration et dissoute par les eaux de condensation basée sur des simulations hydrogéochimiques est développée. Son application à la paroi gauche de la Salle de la Taureaux en contextes de pompage et naturel conduit à l’évaluation de l’impact potentiel du pompage mais aussi de l’aérologie de la cavité sur la conservation des parois. / Since its invention in 1940 but especially as a result of its closure to the public in 1963, the preservation of the Cave of Lascaux bases itself among others on the understanding of its interactions with the surrounding karstic massif in particular the processes sitting in the épikarst and the zone of superficial transmission. That is why this thesis research attempted to understand the dynamics of the CO2 in the continuum soil-epikarst-cave to estimate the potential impacts on the preservation of walls. We benefit in Lascaux of an observation window on the flows resulting from the epikarst known emergence in the SAS 1 of the cavity, but also the consequent instrumentation. It allows the acquisition of numerous time series data of the microclimatic parameters, carbon dioxide partial pressures at different points of the cave and the discharge of the epikarstic emergence since the beginning of the century.A first part of the study is dedicated to the characterization of the dynamics of the CO2 in the context of an epikarst under soil cover. To this end, an experimental parcel is instrumented to follow the hydroclimatic parameters and the contents in PCO2 at various depths. Periods of recharge (accumulation) and draining (emanations towards the atmosphere) of the superficial epikarst CO2 are highlighted when the constitution of a low variable CO2 stock is observed in the subsuperficiel epikarst. The understanding of these various mechanisms ends in a conceptual scheme of the CO2 dynamics in the epikarst.In a second part, this dynamic is studied in the Cave of Lascaux from the temporal series of the microclimatic parameters and the contents in CO2, but also the δ13CCO2. It is then demonstrated that the flows of CO2 entering the cavity result from three different origins: the atmosphere (entrance), the superficial epikarst (Mondmilch Gallery and Silted-up Rooms) and the massif (screw of the Shaft of the Sorcerer). At the same time, two aerological regimes responsible for the spatiotemporal distribution of the PCO2 in the cavity are observed: stratification and thermoconvection. They are the main mechanisms responsible for the dynamics of the CO2 in the Cave of Lascaux because of the low exchanges with the atmosphere. Finally, the impact of the pumping of the air on the aerology and the dynamics of the CO2. The comparison of these dynamics with and without extraction of the air of the cavity leads to the creation of conceptual schemes of the dynamics of the CO2 in the Cave Lascaux.The study of the flowing conditions in the epikarst of the Cave of Lascaux, the third part of these works, was made from a continuous monitoring of the discharge, physico-chemical parameters and the natural fluorescence of the water. The analysis of the temporal series of these natural tracers leads to characterize in a detailed way the flowing conditions and the importance of the moisture content of the epikarst on the size of the recharge area and the types of water arriving at the emergence. In parallel, the impact of these conditions on the calco-carbonic balances of waters arriving in the cavity is analyzed.Finally, the acquired knowledge are applied to determine the potential continuous impact of the waters (condensation and exfiltration) present at the adorned walls of the cave. To this end, a methodology of estimation of the mass of calcite potentially precipitated by exfiltration and dissolved by condensation based on hydrogeochemical simulations is developed. Its application to the left wall of the Hall of the Bulls with and without pumping leads to the evaluation of the potential impact of this device but also the aerology of the cavity on the preservation of walls.

Il est communément admis que la recharge des aquifères carbonatés est contrôlée par la zone non saturée, siège d’une mise à l’équilibre des phases liquides, solides et gazeuses. L’épikarst, zone superficielle de ces aquifères, recueille les pluies efficaces et les transfère en profondeur via une double porosité de fissure et de fracture. Des épandages détritiques sablo-argileux fossilisent souvent les paléo-reliefs, changeant ainsi les caractéristiques des zones d’infiltration. Toutefois, les données sur ces dépôts superficiels sont rares, et leur impact sur les modalités de recharge en contexte karstique est aujourd’hui mal connu et peu décrit.La célèbre grotte préhistorique ornée de Lascaux offre une fenêtre d’observation à l’intérieur de l’épikarst et constitue ainsi un site privilégié pour le suivi des processus de transferts. La grotte fait partie d’un réseau karstique fossile partiellement comblé par du matériel détritique sablo-argileux. Les parties basses de la cavité montrent des fortes teneurs en CO2 dans l’air, supérieures à 8% (80 000 ppmv) lors de certaines périodes estivales. Cette thèse propose une étude des caractéristiques de l’infiltration en milieu karstique grâce au suivi des variations chimiques et isotopiques d’une émergence épikarstique au plafond de l’entrée de la grotte. Les principaux objectifs sont la compréhension de la dynamique des fluides en transit dans l’épikarst, la recherche de la source des fortes teneurs en CO2 ainsi que la détermination du rôle des épandages détritiques dans les modalités de recharge de l’aquifère karstique.Après avoir mener une étude approfondie de l’environnement géologique et géomorphologique du site, l’analyse hydroclimatique, combinée au suivi bimensuel de la chimie et des variations isotopiques des eaux épikarstiques, a permis d’investiguer le fonctionnement de la zone d’infiltration du karst d’un point de vue des transferts de masse.Les premières observations montrent que l’émergence épikarstique n’est pas pérenne avec un tarissement qui débute au début de l’été. Le système nécessite environ 250 mm de recharge automnale pour se réactiver. Le signal 18O à l’émergence est fortement amorti comparé au signal 18O dans les pluies ce qui démontre la création d’une réserve épikarstique qui conduit à l’homogénéisation chimique des eaux. Ainsi, les transferts de masse sont lents dans ce système caractérisé par un comportement de type fissuré et non karstique. Les données de 13C collectées à l’émergence permettent de retracer les conditions physico-chimiques qu’ont rencontrées les eaux au cours de leur transit. Elles montrent différentes origines possible de l’infiltration et révèlent des phénomènes de dégazage – précipitation lors des périodes de fortes pluies.De plus, les eaux épikarstiques sont fortement sursaturées vis-à-vis de la calcite et leur forte minéralisation résulte de la mise à l’équilibre avec une pCO2 importante (5% en moyenne). De telles valeurs ne correspondent pas à la production de CO2 du sol. L’autre origine supposée est les épandages détritiques sablo-argileux où des teneurs importantes en CO2 ont été mesurées (pCO2air de 4 à 8%). De plus, la présence d’eau dans ces niveaux suggère que le système est en partie alimenté par ces formations. Ainsi, le transit des eaux au travers de milieux aux conditions physico-chimiques très contrastés pourrait être à l’origine de la sursaturation des eaux qui entrent dans la cavité.Enfin, l’étude montre que les épandages détritiques tiennent deux rôles majeurs dans les processus d’infiltration des eaux : (i) ils participent à leur homogénéisation en les stockant proche du sol et (ii) ils fournissent un fort potentiel de karstification au système. / It is widely recognized that the recharge of deep carbonated aquifers is controlled by a non saturated zone in which liquids, solids and gases are exchanged to attain equilibrium. The epikarstic zone, which represents the bottom of these aquifers, collects the efficient rain waters and transfers them deeper through a dual fractured and fissured porosity. Sandy-clayey detritic coatings are often observed to fossilize the paleo-relief changing the features of the infiltration zones. However, field data on these superficial deposits are sparse and their impact on the recharge modalities in karstic context is not yet well known and described.The famous prehistoric painted cave of Lascaux (France) provides a window into the epikarstic system and offers a privileged environment for the monitoring of transfer processes. The Lascaux cave is part of a fossil karstic network partly filled with detritic material and it is known to have high CO2 concentrations, greater than 8% (80,000 ppmv) in some summer periods, when measured in the air of the lower parts of the cave. Here, we study the epikarstic seepage traits monitoring the chemical and isotopic variations in waters which seep from the entrance roof of the cave. The aims of this work are to understand the dynamics of the fluids in the epikarstic system, to find the source of the high CO2 concentrations measured into the cave and to understand how the detritic coatings impact on the recharge modalities. After carried out an in-depth geological and geomorphological study of the site, the use of hydroclimatic analysis combined with the semi-monthly hydrochemical and isotopic monitoring of the epikarstic waters allowed us to investigate the karstic infiltration zone functioning in term of matter transfer. First, we observed that the epikarstic emergence is non perennial and dries up at the beginning of summer. The system needs an approximately 250 mm recharge in autumn before seeing flows at the emergence. The 18O signal at the emergence is highly amortized compared to the rain 18O signal which reveals the creation of an epikarstic water table that chemically homogenises waters. Thus, the mass transfers are slow in this system characterized by a fissured and nonkarstic behaviour type. The 13C data obtained at the epikarstic emergence seem to characterize the physicochemical conditions of the environments in which waters circulate during their transit in the system. They confirm the possible various origins of waters and reveal degassing – precipitation phenomena during rising periods.Moreover, épikarstic waters are always supersaturated with respect to the calcite and the the high bicarbonates and calcium concentrations result from water equilibrate with an important pCO2 at saturated state (5% on average). Such values of pCO2 do not correspond to the soil CO2 production. The other supposed origin is the sandy clayey detritic formations where we measured important pCO2 (data range from 4 to 8% in the atmosphere of the coatings). Furthermore, the presence of water in the sandy levels of the coatings suggests that the system can be partly fed by these formations. The transit of water through two physicochemicaly highly contrasted environments would be at the origin of the general flows supersaturation state in the cave.Finally, the study shows that the detritic coatings are involved in two aspects of the epikarstic waters run-off conditions: (i) they homogenize them while retaining near to the soil and (ii) give to them a very high karstification potential.

L’infiltration correspond à l’ensemble des écoulements contribuant à la recharge des réserves des systèmes karstiques ou aux variations des débits à leurs exutoires. L’objectif de cette thèse est la caractérisation de l’infiltration et son utilisation dans l’étude des transferts pour la compréhension du fonctionnement des systèmes karstiques.Deux sites sont utilisés pour analyser cette infiltration : celui de la colline de Lascaux en Dordogne et celui du Nord du Vaucluse en Provence composé de plusieurs sources karstiques. Ces sites, en milieu carbonaté, se différencient tant par leur structuration – système épikarstique et aquifère karstique perché, pour le premier, et systèmes épikarstique, fissuré ou karstiques à zone noyée, pour le second – que par les conditions climatiques rencontrées au niveau de leurs impluviums respectifs.L’étude hydrodynamique des systèmes épikarstiques par les modèles réservoirs ne convient actuellement pas : la fonction de production ne permet pas la génération d’une infiltration satisfaisante. L’utilisation d’un modèle réservoir, initialement basé sur les équations de Coutagne, a permis de souligner la nécessité d’ajouter deux modules de calcul. Le premier concerne l’estimation d’une évapotranspiration effective, issue d’une loi exponentielle, considérant la hauteur d’eau dans le réservoir sol. Le deuxième module insiste sur l’utilité d’une fonction de stockage de l’épikarst pour caractériser au mieux les transferts vers l’aval du système.L’étude hydrochimique s’appuie majoritairement sur les équilibres calco-carboniques de l’eau et donc sur les transferts de masses de carbone inorganique. Ils permettent d’accéder à différentes grandeurs telles que la pression partielle de dioxyde de carbone – équilibrante (Pco2_eq) ou à saturation (Pco2_sat) – et à l’indice de saturation vis-à-vis de la calcite (ISc). La mise en relation de ces deux paramètres au sein d’un graphique {–log(Pco2) : ISc} a permis de distinguer différents types d’eaux issus des différents compartiments du karst. Il en a résulté un schéma de transfert des différents types d’eaux passant à l’exutoire tenant compte de l’état d’ennoiement du système. L’évolution pluriannuelle de l’infiltration a aussi été mise en avant par la variation de sa composition chimique pouvant être en relation avec des facteurs climatiques.A l’issue de ce travail, il apparaît que la connaissance des processus liés à l’infiltration est fondamentale pour la compréhension des écoulements en milieux karstiques dans un objectif de quantification de la recharge et de protection de la ressource. / Infiltration corresponds to flows contributing to the system recharge and its discharge variations. This thesis aims at characterize infiltration and its utilization in transfer analyses to understand karst system behavior.Two sites are used to study this infiltration: this of the Lascaux hill in Dordogne and one in the North of the Vaucluse county composed of several karst springs. These locations are different in their structure as well as climatic conditions on their respective intake areas. The first site consists on an epikarst and a perched karst aquifer systems, since the second is composed of an epikarst, a fissured and a developed saturated zone systems.Nowadays, hydrodynamic study of an epikarst system using reservoir models is not satisfying: the production function is not able to generate a sufficient infiltration. In this study, a reservoir model initially based on Coutagne’s equations had been used. Results highlighted the necessity to add two new calculation functions. The first is related to an evapotranspiration estimation using an exponential law considering the amount of water in the soil reservoir. The second underlines the necessity of taking into account the storage function of the epikarst to characterize in a better way flows in karst systems.Hydrochemical study was carried on from calcium-bicarbonate equilibriums and then by mass transfers. They permit to describe several parameters as the carbon dioxide partial pressure at atmospheric equilibrium (Pco2_eq) or at saturation (Pco2_sat) and the saturation index with respect to calcite (SIc). These parameters can be expressed through the {–log(Pco2); SIc} graph to identify different water types. A transfer schema had been proposed, considering the saturation state of the system. Multi-year evolution of the infiltration had been underlined by variations of the chemical composition of infiltration water. This evolution can be linked to climatic conditions.Finally it appears that the knowledge of infiltration processes is essential to understand karst flows to quantify karst recharge and protect the resource.

The groundwater in agricultural karst areas is susceptible to contamination from organic soil amendments and pesticides. During major storm events during 2011, dye traces were initiated using sulphorhodamine-B, fluorescein and eosine in a groundwater recharge area where manure was applied to the ground. Fecal coliform samples were collected from significant storm events from January-September 2011. Water samples and geochemical data were collected every four hours before, during, and between the storm events from a waterfall in Crumps cave flowing from the known recharge area to track the transport and residence time of the epikarst water and organic soil amendments during variable flow conditions. Two dataloggers at the same waterfall were set up to collect 10-minute data, which included pH, specific conductivity, temperature, and discharge. Total rainfall amount and other surface meteorological data were collected from a rain station located above the cave. Cave water samples were collected for the analysis of anions, cations, bacterial count, and the presence of dye. The dye traces show variability in the characteristics of epikarstic response and flowpaths. The changes in geochemistry indicate simultaneous storage and transport of meteoric water through epikarst pathways into the cave, with rapid transport of bacteria occurring through the conduits that bypass storage. Fecal coliform counts were elevated all through the study period indicating survivability in soils through the seasons. The results indicate that significant precipitation events affect the storage properties and rapidly impact the various pathways and timing of contaminant transport through the epikarst zone, eventually allowing these contaminants to be transported unfiltered in to the groundwater supply. This study shows that current best management practices in karst lands need to be revisited to incorporate areas that do not have surface runoff but where contaminants are transported by seepage into local aquifer.

Flow and mean residence time in epikarst and unsaturated zone was studied above the Ochoz cave in the Moravian Karst. I studied various flow components with different residence time in unsaturated zone and the influence of soil and epikarst on seepage composition and residence time by means of several methods (longterm monitoring of conductivity, flowrate of seepage and soil water, use of environmental tracers - 18 O, 3 H, CFC and SF6, flow into the soil and detailed sampling during intesive rain events). Seepage sites Kašna in the Rudické propadání cave system and Mapa Republiky in Býčí skála were reference localities in unsaturated zone. For comparison I modeled residence time in saturated zone: at Kaprálka outlet close to the Ochoz cave, at Stará řeka (Rudické propadání) and Konstantní přítok (Amatérská cave). Mean residence time in unsaturated zone above the Ochoz cave reaches 7 - 20 years, while it is only few months in the soil (1 - 8 months, depending on the depth). At Kašna seepage site, the reasidence time is similar to the Ochoz cave - about 18 - 20 years, at Mapa republiky seepage site, it reaches 150s year due to unusual geological settings. Mean residence time in order of 10 - 20 years corresponds to storativity values (0.6 % in average) calculated from parallel water level recession...

This study is focused on the flow through the uppermost part of the unsaturated zone in karstified areas. The information about distribution of transit times and chemical reactions taking place in the unsaturated zone is based on isotopic and chemical composition of cave dripwaters, precipitations and water caught by gravitation lysimeters. The water balance was calculated using measurements of intensity of dripwaters and amounts of water caught by lysimeters and rain gauges. The velocity of a hydraulic shockwave between monitored objects was also estimated according to the delay between significant precipitation event and dripwater intensity increase. The field study took place in the Němcova 1 cave in the northern part of Moravian Karst, near the village Suchdol. It was carried out during the hydrological year 2010/2011. The cave is about 13 m under the surface. The information about composition of overlaying rock above the cave was obtained using geoelectrical and electromagnetic measurements. Studied geological environment is built of 0.5 - 1.5 m of soil, 0.5 - 3.5 m of epikarst and a layer of massive limestone as thick as 10 m. About 70 to 90 % of dripwaters have residence time over 4 years. The distribution of transit time of younger water can be described using the exponencial model (well...

Water flow and geochemical processes within the unsaturated zone (UZ) in two distinct types of karst environment were investigated using natural tracers (chemistry, stable isotopes 13 C, 18 O, 2 H, and 3 H, 14 C, 87 Sr/86 Sr). The extent of horizontal flow component and the response of drip water chemistry to recharge events were examined in the Moravian Karst (Czech Republic), while the character of water flow and its chemistry were studied in salt diapirs in southeastern part of the Zagros mountains (Iran). Under the conditions of well-developed epikarst, the horizontal flow component, defined as Hmax/T (Hmax = horizontal migration component, T - thickness of VZ) typically reaches values of 0.1 - 0.6 (Moravian and Slovenian Karst). However, in areas where epikarst was stripped off by glacial or human activity, the proportion of horizontal flow component is far greater (Hmax/T 1.6 - 24). This parameter is vital for the design of water source protection zones above caves. Nitrate mean residence time in 120 m thick VZ of the Moravian karst exceeded 16 years. The VZ above the Ochoz Cave (Moravian Karst) represents a semi-open to open system with respect to soil CO2. Under a high drip rate (high flow), the event water only made 5% of the total. During the year, water degassing and so called prior...