Evolution spatio-temporelle des teneurs en nitrates dans les eaux souterraines du bassin versant de la Baya (Est Côte d'Ivoire)

This study proposes to follow the temporal evolution of nitrate contents of groundwater and to map their spatial distribution. For this purpose, physicochemical analyzes and statistical treatments were carried out on 10 boreholes and 12 wells. The nitrate distribution map is obtained using the IDW (Inverse Distance Weitling) interpolation method. Nitrate levels in the Baya watershed range from 0.5 mgL-1 to 196.2 mgL-1. Well water is richer in nitrate than drilling water with an average grade of 28.77 and 13.51 mg.L-1, respectively. Only 12% of nitrate levels are above the WHO guideline (50 mg.L-1) for drinking water. These are the waters of P3 (79.5 mg.L-1), P5 (110.8 mg.L-1) and P8 (56 mg.L-1) and F1 wells (47.1 mg. L-1) F10 (109.6 mg.L-1). In terms of time, unlike the drilling water, the nitrate concentrations of the wells of the rainy season are generally higher (33.96 mg.L-1) than that of the dry period (23.59 mg. L-1). Excessive nitrate levels are observed in the localities of Agnibilekro, Koun-fao, Tanda and the outlet of the main stream of Baya. This increase in nitrate levels is related to the geological nature of the soil and the anthropogenic pressure in the region.