Chemical and isotopic study of groundwater of Sidi-Merzoug Sbiba plain (Center of Tunisia)

The creation of the new irrigated perimeters of apple tree fields in the Sbiba region induced increase to groundwaters. This situation generated an over exploitation of sidi Merzoug-Sbiba aquifer system materialized by a significant water level subsidence. The study area located at the north-west of Tunisia. This plain is characterized by an arid climate. The Sidi Merzoug Sbiba basin contains a number of underground reservoirs found in the sand layers of quaternary and miocene, caiman and eocene limestones layers. The hydrogeological studies have shown that these aquifers are communicated vertically and laterally. The hydrochemical study show similarity between the different chemical families of these waters in these aquifers, which allows to assume the existence of a wide interaction between these aquifers. Stables isotopes of these waters show that several samples of these aquifers present a same heavy tenors. These finding might be explained by the similarity in way of recharge of different aquifers, or by the existence of important communications between these aquifers, according to the hydrogeological characteristics the complex aquifers of this basin can be considered as a permanent hydrodynamic continuos system. Environmental isotopes (18O, 2H, and 14C) have used to clarify characteristics of theses aquifers and their subsurface continuity continuity. Deuterium content ranged from -37.12% to -40.98% vs Smo, oxygen -18 contents ranged between -5.64% to -6.56% vs SMOW. Water ages range between 1836 and 9273 years B.P. High activities of 14C observed in south-west of basin, demonstrated a recent recharge in this area (recharged from wadi El Breck and Sbibla). (Author)