The Newmarket Till is a regional aquitard in southern Ontario that overlies the Illinoian to Middle Wisconsinan Lower Sediments and is overlain by the Oak Ridges Moraine (ORM). Geological investigations have mapped the distribution of the till and it is understood that erosional channels, subsequently infilled with fluvial material, breach the till and may create enhanced hydraulic connection between overlying and underlying aquifers. However, little is known about the protective capability of the Newmarket Till where it is intact. This study used natural tracers to assess the extent of transport in the aquitard-aquifer system. Stable isotopes of water (δ18O and δ2H) showed a depletion trend versus depth. In the Newmarket Till most of the samples had isotope ratios similar to meteoric water data from the nearest location (Egbert, ON). The depleted values of δ18O in the Thorncliffe Formation suggest a remnant signature of early-Holocene precipitation (-16‰ at the depth of 60 m). Elevated levels of NO3- and Cl- were detected near the surface and because of the low permeability aquitard (Newmarket Till), they could not migrate to depth. Total extractable ammonium concentrations are ranging from 4.09 ppm from near the surface to 60 ppm in the lowest part of the Newmarket and then gradually increase to 514 ppm in the bottom of the Thorncliffe Formation. The combination of high NH4+ values and organic carbon content in the Thorncliffe Formation suggests a natural source from mineralization of organic N. The fractionation which happened between δ15Nsediment and δ15N-NH4 may have three explanations: (1) lighter isotopes diffuse faster than heavier ones, so the higher rate of diffusion can cause fractionation; (2) heavier isotopes partition to exchange sites, causing fractionation along the transport pathway; (3) dissociation of NH4+ to NH3 under anaerobic condition. Positive values for δ13C in groundwater in the Thorncliffe Formation are likely due to i) a contribution of carbonate mineral dissolution, and ii) methanogenesis - the Archea favor the lighter isotope of C (12C). Methanogenesis, therefore, enriches the δ13C-DIC was enriched; however, the δ13C in dissolved organic carbon (DOC) is depleted. These geochemical characteristics demonstrate a long residence time for the porewater in the system and indicate that the Newmarket till inhibits recharge of recent precipitation, thereby providing protection to the underlying aquifers from surface-derived contaminants.

La première étude du fonctionnement de la zone non saturée (ZNS) des aquifères karstiques, par accès direct, a été réalisée dans la galerie souterraine du LSBB, sur le bassin expérimental de la Fontaine de Vaucluse. Cette galerie recoupe arbitrairement le réseau karstique et les écoulements de la ZNS. Ceux-ci sont répartis tout au long de la galerie sous différentes épaisseurs de roche calcaire (de 30 à 514 m). 45 points d’écoulements ont été prélevés au moins une fois. Les suivis hydrodynamiques et hydrochimiques sur 8 ans montrent : (i) l’organisation des écoulements en fonction de la profondeur et de la densité de fracturation, (ii) les modalités de réponses hydrodynamiques et hydrochimiques des écoulements en fonction des précipitations et de l’état initial du système, (iii) la nécessité de prendre en compte la non-linéarité des réponses impulsionnelles dans la modélisation.Trois composantes d’écoulement sont caractérisées : (i) une composante lente, pérenne et caractérisée par des longs temps de séjour, (ii) une composante rapide, active seulement en période de très forte recharge, marquée par les traceurs d’infiltration et caractérisée par de faibles temps de séjour, (iii) une composante intermédiaire, associée à des comportements hystérétiques, également marquée par les traceurs d’infiltration et caractérisée par des temps de séjour intermédiaires. Ces observations directes justifient la prise en compte du phénomène d’hystérèse dans la modélisation de la ZNS. Confirmant des modèles conceptuels existants, ce travail contribue au développement d’un modèle de fonctionnement de l’aquifère karstique, qui devra à terme être transposable aux autres systèmes méditerranéens. / The first study of karst aquifers unsaturated zone (UZ) functioning, by direct access, was conducted on the experimental area of the Fontaine de Vaucluse, including the underground gallery of the LSBB. This gallery intersects arbitrarily, within the UZ, the karst network and flow paths. Observed flows are distributed throughout the gallery corresponding to different limestone thicknesses (30 to 514m). 45 flow points were observed and followed at least once. The hydrodynamic and hydrochemical monitoring over 8 years show that: (i) the flows spatial and temporal organisation is a function of depth and the fracturing density, (ii) the hydrodynamic and hydrochemical flows signatures are based on rainfall amount also as the initial state of the system (iii) in order to precise the conceptual model of karst aquifers is necessary to consider the nonlinearity of the hydrodynamic system’s responses.Three flow components are deduced: (i) a slow component, permanent, which is active regardless of hydrological conditions, and is characterized by significant residence time, (ii) a fast component, active only during strong recharge periods as marked by infiltration tracers. This component is characterized by low residence time and (iii) an intermediate component, highlighted by hysteretic behavior, as marked also by the infiltration tracers and is characterized by intermediate residence times. Considering the hysteresis phenomenon in UZ modeling by these direct observations confirms earlier conceptual models. The ultimate goal is to contribute to the development of a karst aquifer model, which could be transposed to other Mediterranean karst systems.

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...