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Summary: Hydrochemical and stable isotopic (2H, 18O) data were used to characterize the groundwater flow and major chemical features within a complex fractured volcanic aquifer system, the Argnat basin, which is located in the Chaîne des Puys (French Massif Central). From 10 sampling points, the study of the transfer into the saturated zone from upstream to downstream, given the geological context and topography, allows to estimate the role of supply from high and low altitudes to the recharge processes. This work shows the existence of different types of supply between pahoehoe and a’a flows. Therefore, the morphology of volcanic flows impacts the chemical and isotopic signatures of groundwater, enhancing or reducing the influence of the unsaturated zone on the pathways of infiltrated water. Pahoehoe flows imply horizontal water flows of low discharge at the top of the lava whereas a’a flows seems to be much more heterogeneous and locally able to promote the existence of perched water bodies and further vertical circulations. Taking into account these two types of behaviour, a conceptual scheme of the functioning of this heterogeneous environment is proposed, which will help towards a sustainable management of volcanic aquifers in relation with the . [ABSTRACT FROM AUTHOR]

From March 1997 to March 1999, sequential rainwater samples were collected during 12 rainfalls at Avignon, Southern France, with the objective of investigating how the formation conditions affect the isotopic composition of the most frequent rain types occurring in the western Mediterranean region. Three major isotopic trends were identified: (i) a descending δ18O trend, produced when a cold front penetration causes the rise of warm and humid air masses, accompanied by adiabatic cooling and precipitation. The temperature variation is the predominant feature of frontal rainfalls; (ii) an L-shaped δ18O trend, which can be produced by convective rains, with an initial rapid decrease followed by a stationary value; (iii) a V-shaped trend, in which the final phase of precipitation obeys a different mechanism from the first phase. Frontal and convective rainfalls may produce this trend.Three heavy rainfalls were selected for applying a numerical Rayleigh condensation model to describe their isotopic trends. Some irregularities in the generally monotonously decreasing isotopic trend were attributed to inputs of new air masses, which were often recorded by chemical variations as well. The numerical model indicates that about 80, 60 and 45% of the vapour initially present was condensed. The lowest fraction corresponds to the most abundant rainfall, and it is due to the convective nature of the latter implying a continuous supply of condensable vapour. [Copyright &y& Elsevier]

Summary: The study was carried out in the northern part of the Aquitaine Basin extending in Southwest France. The basin has been intensively exploited for various purposes for many years. Although the geological context is well known, there are still some gaps in the knowledge about the hydrogeochemical regime, groundwater average residence time and the palaeohydrological conditions prevailing during the recharge period which would help to secure sustainable exploitation of the resources. Environmental isotopes (18O, 2H, 3H, 13C) together with radiocarbon were used to evaluate hydrochemical evolution, residence time and palaeorecharge conditions for Jurassic, Cretaceous and Eocene aquifers. Radiocarbon activity in the aquifers varies widely between 0 and 94pmc. After radiocarbon corrections the ages indicate both modern and old waters sometimes exceeding the limit for 14C dating. The Fontes and Garnier model is best adapted to the specificity of the carbonate system. The content in stable isotopes of water is varying between −7.7‰ and −4.9‰ for δ18O and −52.3‰ to −29.6‰ for δ2H. The wide ranges of stable isotopic values imply variable climatic conditions. A group of isotopically depleted samples was detected, indicating colder climatic conditions during the recharge. Radiocarbon ages calculation, together with isotopic signature, point out that the depletion in stable isotopic values fits the period between 20 and 15ka B.P. and therefore indicate the Last Glacial Maximum (LGM). According to the correction model, the transition from Pleistocene to Holocene would occur between 15 and 12ka B.P. Palaeohydrological data from the Northern Aquitaine Basin does not confirm a significant hiatus in the recharge history. The recharge conditions in South Europe seem to have occurred under discontinuous permafrost conditions as documented by many palaeoclimatological archives. This is in favour of an uninterrupted recharge of the confined aquifers of Northern Aquitaine Basin. Such information should be considered by modellers in their attempts to simulate the hydrogeological functioning of large confined aquifers on the very long time range. [Copyright &y& Elsevier]