TENEURS EN NITRATES DANS LES AQUIFERES DISCONTINUS DU SOCLE DU DAMAGARAM MOUNIO (EST DU NIGER)

The basement of Damagaram Mounio, study area, outcrops in the eastern part of the Zinder region. It is a very populated area and where the problem of water resources is acute. In addition to the low availability of this water resource, its quality remains questionable in several areas. Thus, the contents of certain chemical parameters, including nitrates in particular, greatly exceed the drinking water standards for human consumption, hence the present study, which has as its main objective, the determination of the percentages of boreholes whose the waters have nitrate levels above the WHOstandard. The methodological approach based on the sampling of hydraulic structures capturing the aquifers of the basement, the analysis of the physicochemical and isotopic parameters of the waters of several boreholes, the determination of the characteristics of the nitrates, made it possible to lead to several interesting results.Thus, the nitrate contents of the waters of the Damagaram Mounio basement aquifers vary from 0.22 to 313.3 mg/L, with an average of 72.23 mg/L, and a standard deviation of 62.23. This study made it possible to show that 32% of the modern structures sampled have nitrate levels above the admissible limit value for drinking water, set at 50 mg/L, according to the standards of the World Health Organization (WHO) these waters are unfit for human consumption. The spatial distribution of nitrate levels in groundwater in the area showed that these are more accentuated between the towns of Damagaram Takaya and Birni Kazoe, which are characterized by values ​​above 100 mg/l. The relation between nitrate contents and water electrical conductivity values ​​showed that the mineralization of groundwater in the area is controlled by nitrate ions. Furthermore, the isotopic levels of Nitrogen 15 (15N), obtained in the waters of the area, vary from 0 to 7.2, thus showing that these nitrates could come from the nature of the soil (quagmire around water points) and chemical fertilizers (ureas and fertilizers used in the study area).