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Etude hydrochimique du système aquifère de la basse vallée du Var Apport des éléments traces et des isotopes (Sr, Pb, δ18O, 226, 228Ra)

Abstract : The main goal of this study is to improve the knowledge of the Lower Var Valley aquifers, under both Mediterranean and Alpine influences. Majors, trace elements, and O, Sr and Pb isotopes have been analysed under various hydrological conditions in water of the Low Var Valley including the alluvial aquifer, the Var River, its tributaries and groundwaters from Jurassic limestones and Pliocene conglomerates, which are the substrate of alluvia. Concentrations of most majors and trace elements are often close to the natural background, which gives a baseline quality for waters. High sensitivity in trace element measurement may allow to early detect contamination in any water body. Agricultural and/or residential contaminations have been detected in limestone and above all in conglomerate groundwater. The Var River is the main source of water for the alluvial aquifer, especially in upstream part. Conglomerate groundwater inputs stand for about 20% of alluvial water recharge, which is lower than previously estimated. The use of both major and trace elements gives evidences of high heterogeneity in conglomerate groundwater and leads to estimate the proportions of inputs to the alluvial aquifer. Recharge of the alluvial aquifer by Jurassic limestones seems to be insignificant. Strong influence of Triassic evaporites in most samples gives limitation to the use of strontium isotopes as tracers of water origin. Pb isotopes gave complex results, which could suggest both a natural origin and an anthropogenic one that could be related to rainwater. Radium isotopes were used to estimate the flow velocity in the alluvial aquifer. Several techniques demonstrate the analytical feasibility of this approach and despite important exchanges with aquifer matrix, the use of isotopic ratios apparently minimizes the effect of complex processes.
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Submitted on : Monday, April 18, 2011 - 2:38:14 PM
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Cécile Potot. Etude hydrochimique du système aquifère de la basse vallée du Var Apport des éléments traces et des isotopes (Sr, Pb, δ18O, 226, 228Ra). Autre. Université Nice Sophia Antipolis, 2011. Français. ⟨tel-00586806⟩

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