Vulnerabilidade da água subterrânea para nitratos numa região árida

ABSTRACT: One of the major challenges in assessing groundwater vulnerability is the factors number and weight assigned. Therefore, to improve groundwater vulnerability assessment, a model independent of weight assignment errors must be considered. Groundwater specific vulnerability index (SVI) was applied in the region of Gabès (Tunisia). Intrinsic vulnerability index (IVI) assessment was firstly determined by the arithmetic mean calculation of index overlay method (IOM), based on the Depth of aquifer (D), annual average Precipitation (P), Lithology of the vadose zone (L) and percent of Slope (DPLS). Then SVI was assessed by linking new factors (Land Use and NO3-) to IVI. A total of one hundred groundwater samples were analysed for NO3-, exceeding 50 mg L-1. The spatial distribution of IVI shows four vulnerability classes: low (15%), moderate (35%), high (23%) and very high (27%). About 95% of the area registered high SVI values. This situation reinforces water-saving irrigation actions for adequate groundwater management.