Evidence for palaeowaters in the coastal aquifers of France
L. Dever, Y. Travi, F. Barbecot, C. Marlin, E. Gibert, 2001. "Evidence for palaeowaters in the coastal aquifers of France", Palaeowaters in Coastal Europe: Evolution of Groundwater since the Late Pleistocene, W. M. Edmunds, C. J. Milne
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Over time, coastal aquifers, which constitute a great part of available freshwater resources from sedimentary basins in France, have been subjected to changes in hydraulic gradients and hydrodynamic properties, mainly due to discharge–recharge phases in response to sea-level variations and/or human influences. This work aims to understand the salinization process originating from the recharge–discharge conditions as recognized at three sites: the calcareous Dogger aquifers along the English Channel (Caen area); along the Atlantic coast (Marais Poitevin), and the Astian sandy aquifer (Cap d’Agde). In addition to conventional hydrogeological and hydrochemical techniques, the main tools used for investigation are those of isotope geochemistry.
For the three study sites, the evolution of isotopic signatures along a flow path, depending on the mineralogy of the aquifer matrix, is linked to water–rock interactions such as cation exchange and equilibrium with aluminosilicates. Residence times of these fresh groundwaters are from Modern (Atlantic site) up to the 14C detection limit (English Channel site). Groundwater of the Astian aquifer (Mediterranean) belongs to the Holocene, as determined by 14C analyses.
The saline waters identified in the three study sites have a marine origin and were modified either by interaction with organic-rich layers, by cation exchange, or by deep carbon input. The salinization process has been associated with marine overflow onto a plain and to an upward leakage of water rich in CO2. The marine intrusion registered in the English Channel and Atlantic aquifers is associated with the Flandrian transgression; for the Astian aquifer, the salinization is related to mixing with older water.
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Palaeowaters in Coastal Europe contains 17 contributions from an international array of authors. They discuss the history of groundwater evolution during the late Pleistocene in the coastal areas of Europe from the Baltic region to the Iberian peninsula and the Canary Islands. Geochemical and geophysical techniques for evaluating palaeowaters are reviewed. The focus of the book is on changes in the hydrogeological regime during the Quaternary and their impacts on groundwater movement and chemistry in European coastal aquifers.
The work summarized in the papers was carried out by a partnership of European scientists under the auspices of the PALAEAUX project, an EC initiative. Researchers from the fields of hydrogeology, geochemistry, isotope hydrology and Quaternary studies attempted to reconstruct the most probable movement of groundwater in the study area over the past 100 000 years and its response to climatic events of global significance during the last glacial cycle. The results of this work, summarized in this volume, allow a better understanding of the water resources found at and near the coastlines of northern and western Europe. During times of lowered sea level, it appears that groundwaters were replenished to depths greater than occur at the present day. These pristine freshwater reserves are an irreplaceable asset. Their location at coastlines where populations and water demands are high and often seasonal means that they need careful management to avoid over-exploitation or contamination. The inevitable conflicts that this resource management creates are discussed.
Palaeowaters in Coastal Europe: evolution of groundwater since the late Pleistocene will be of interest to Quarternary scientists, hydrogeologists, marine scientists engaged in coastal research and those involved in environmental science and the management of groundwater assests.