Climate Change Impact on the Mineralization of Karst Groundwater in a Mediterranean Context

The aim of the current study is to investigate the geochemical evolution of groundwater mineralisation and the inter-connexion between shallow karst aquifer and deep aquifer groundwater. The studied aquifer system is considered as the principal outlet of the south-eastern end of the northern Pyrenean overthrust, with a volumetric flow reaching 2000 m 3 /h. Water at the emergence is characterized by high mineralisation and temperature relative to groundwater at the regional scale. An eight years survey was carried out at the outlet based on a geochemical and isotopic approach. Surprisingly spring water mineralisation increases with increasing precipitations. 87 Sr/ 86 Sr ratios of sampled water range from 0.7085 to 0.7090. This ratio contrasts with that of the aquifer matrix constituted by Mesozoic marine carbonates and underlying evaporites. Furthermore, these ratios are significantly higher than in groundwater impacted by current or ancient seawater at the regional scale. These high 87 Sr/ 86 Sr ratios may reflect the dissolution of 87 Sr rich minerals such as the Triassic salty clay deposits present at depth. The good correlation between 87 Sr/ 86 Sr and TDS confirm the hypothesis of a contribution of deep saline and 87 Sr rich water. The temporal variations in mineralization and Sr isotopic signature may be explained by high recharge inducing a higher hydraulic pressure on the deep aquifer and an increased contribution of deep saline groundwater to the spring water. The data acquired on this aquifer system allow predicting the evolution of mineralization with climate trends where decreasing recharge would induce a decreasing salinity at the spring outlet.