Contribution of isotopic indicators to groundwater assessment and management in Grombalia plain (Northeastern Tunisia)

Grombalia Plain, situated in the Northeast of Tunisia, contains a very important multilayered aquifer. However, the exploitation rate of shallow groundwater resources reaches 170% in order to answer the increasing needs for socio-economic development and specially the agricultural sector. Irregular climate conditions combined with increasing human constraints have lead, as main consequences, to the lowering of the water level and to the salinisation of groundwater along the coast, enhancing the risk of marine intrusion. Multidisciplinary studies have been conducted on this aquifer for the assessment of groundwater resources. Hydrochemical results indicate that shallow and deep groundwaters show similar type of water fades, highlighting vertical hydraulic communication between these different levels. Isotopic tracers (18O, 2H, 3H, 14C) confirm the existence of groundwater mixing between different depths and levels. On the other hand, shallow groundwater presents high 14C activity, indicating a direct infiltration of rainfall. (author)