Hidrobio-geología del complejo sistema del diapiro de Añana (Araba)

Résumé

The hydrogeological system around the Añana salt diapir (protected biotope, 19 km2) is enormously complex and compart- mentalized, showing an important regulation of its slow flows in all observation points (springs and piezometers). Each part of the system has its own conditioning factors, which is reflected in the presence of salty water, used for of the production of salt, and the saline ones. As the hydrochemical information is more revealing than the piezometric information, a tentative model of End Members has been established, according to which the different waters that appear in the Salt Valley would be the result of mixing, in different proportions and depths, of at least 2 types of extreme waters: those more superficial of the eastern sector of the diapir (clearly sulphated, EC 7-25 mS/cm) and the deeper ones that condition the salty springs (clearly chlorinated, EC 170-220 mS/cm and T 15-18C, indicating thermalism). According to recent isotopic information, the salty waters show a relationship with those of the Arreo Lake sector (to the south of the diapir), and the saline waters with those of the eastern sector. Data from Tritium indicate slow flows. The sulphates in all of them come from Triassic gypsum and the isotopic content in Sr would be indicating a relationship with Tertiary rocks, crossed by the diapir structure, for all waters. The results of microbiological analysis, after the sequencing of 16S rRNA genes, reinforce this model and show a complex hypersaline ecosystem. In salty springs, archaea are detected in large numbers, and also extremophilic halophilic bacteria, although with limited prokaryotic diversity. However, in the saline waters, an absolute predominance of bacteria with a high prokaryote biodiversity has been detected.