Evolution des parmètres physico-chimiques des eaux du lac Ichkeul après la réalisation des aménagements hydrauliques (Tunisie) Physico-chemical properties evolution of Lake Ichkeul water after hydraulic adjustment

The National Park of the Ichkeul is situated in the North extreme of Tunisia. The Ichkeul lake communicates with the Mediterranean by the lagoon of Bizerte and the contact between the two lakes is made by a fairway of 5 Km along the Oued Tinja. This lake is known for the seasonal variability of its level of water and its saltiness. Indeed, in wintry period it is nourished in soft water by six main Oueds: Douimiss, Sejnane, Melah, Ghezala Joumine and Tine this leads to an increase of the water level and a reduction of the saltiness. In summery period, following the strong evaporation and the absence of contribution of soft water to the Oueds, the level of the water in the lake decreases, and there is an entry of ssalty water of the lagoon of Bizerte then by the Tinja Oued. Actually, this ecosystem has known some disruptions that provoked an ecological hydrologic and chemical unbalance, following the construction of dams on the main rivers (Joumine in 1983, Ghezala in 1984 and Sejnanes in 1994). To reduce these impacts and to protect a certain balance at this ecosystem, a work of regularization has been constructed to the outlet of the Ichkeul lake in the Tinja Oued named " Sluice of Tinja " to control the entry and the exit of the waters of the Ichkeul lake. This Sluice could have dragged a certain correction for the ecosystem but its working provoked the apparition of the eutrophisation phenomenon in the lake and along the Tinja Oued in the period of closing, as well as the accumulation of sediments upstream of the Sluice.