Hydrodynamical changes and their consequences on groundwater hydrochemistry induced by three decades of intense exploitation in a Mediterranean Karst system

Abstract

The Lez karst spring, located in the Mediterranean basin (southern France) supplies drinking water to the metropolitan area of Montpellier (France) since the nineteenth century. Since 1981, an intense pumping is being performed directly in the main conduit with a maximum exploitation flow rate of about 1,700 l/s. To improve the understanding of groundwater origins and circulation dynamic in this karst system, as well as the impact of three decades of intense water exploitation, groundwater samples have been collected during various hydrologic conditions since March 2006. A previous hydrochemical study on the Lez karst system had been carried out before the installation of the pumping plant. This dataset was compared to the present one to identify possible changes on groundwater hydrochemistry. The results of this analysis indicate the existence of historical changes in water hydrogeochemistry and evidence a decrease of the deep compartment participation to the Lez spring outflow. This change in spring water hydrogeochemistry may be attributed to the intense pumping of the karst system and, in the absence of noticeable climatic changes, expresses the direct consequences of anthropogenic forcing on the overall functioning of the aquifer. This study aims to analyze the differences, to understand the water chemistry changes and to better foresee the aquifer evolution for the future.