Hydrochemical and isotopic characterisation of the Bathonian and Bajocian coastal aquifer of the Caen area (northern France)

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• 作者：Barbecot ; Florent ; Marlin ; Christelle ; Gibert ; Elisabeth ; Dever ; Laurent
• 关键词：Geochemistry ; Coastal aquifer ; Radiocarbon ; Holocene
• 刊名：Applied Geochemistry
• 出版年：2000
• 出版时间：July 1, 2000
• 年：2000
• 卷：15
• 期：6
• 页码：791-805
• 全文大小：819 K

文摘

This paper describes the geochemical evolution of groundwater in the Bathonian and Bajocian aquifer along its flowpath. Since this aquifer represents one of the main sources of fresh water supply in the Caen area and has been subjected to a Holocene marine intrusion, its management requires a sound knowledge of (1) the primary conditions and (2) the potential influence of either natural or anthropogenic pressures. Groundwater vertical sampling validity is discussed with the contribution of high resolution temperature logging. The main processes of geochemical evolution along a groundwater flow line and the sea-water intrusion characteristics are discussed using ionic concentrations (Br⁻, F⁻ and major elements) and isotopes (water δ²H and δ¹⁸O, TDIC δ¹³C and A¹⁴C, sulphate δ¹⁸O and δ³⁴S). As the ¹³C content of TDIC is used as a tracer of water-rock interaction, it shows evidence of specific chemical and isotopic evolutions of groundwater within the aquifer, both related to water-rock interaction and mineral equilibria in groundwater. All the above-mentioned tracers evolve downflow: cation concentrations are modified by exchange with clay minerals allowing a high F⁻ concentration in groundwater, whereas Br⁻ and SO²⁻₄ concentrations appear to be redox condition dependant. Superimposed on these geochemical patterns, δ¹⁸O and δ²H compositions indicate that aquifer recharge has varied significantly through time. The chemical evolution of groundwater is locally affected by a salty water intrusion that is characterised by mixing between Flandrian fresh water and sea-water which has interacted with peat as evidenced by a high Br⁻/Cl⁻ ratio and SO²⁻₄ reduction.