Hydrologic budget of the lagoon of Bizerte (Northeastern Tunisia)
The water and solid fluxes (drained from the principal tributaries of the Bizerte Lagoon) were positively correlated and were influenced by the environmental conditions and by the upstream hydraulic installations. It is within this context that we present this study on the monthly variation of water, solid and dissolved nutrient fluxes associated with the principal tributaries of the Bizerte Lagoon during the October 2004 – September 2005 hydrologic year. The frequent and intensive use of chemical nitrogenous and phosphate fertilizer by farmers, on one hand, and the discharge of domestic sewage and industrial wastewater to the principal tributaries of this lagoon, on the other hand, actively contribute to the pollution of the lagoon waters. The Bizerte Lagoon is linked to the garaet Ichkeul by the Tinja wadi. In winter, waters flow from garaet Ichkeul towards the Bizerte Lagoon, and the water and solid fluxes are estimated to be 418 ± 29 Mm3 and (28 ± 5) x 103 (t), respectively. Thus, the Tinja wadi represents the main nutrient supply to the Bizerte Lagoon: 75 ± 15; 954 ± 76; 92 ± 11; and 70 ± 11 (t) for nitrite, nitrate, ammonium and phosphate, respectively. In contrast, during the dry period, this wadi allows marine waters (84 ± 2.5 Mm3) to penetrate in the garaet Ichkeul through the Bizerte Lagoon.