Evaluation of the vulnerability of groundwater to nitrogen pollution in the commune of Mananara Avaratra by the SINTACS method

Abstract

The urban commune of Mananara Avaratra, located on the east coast of Madagascar in the Analanjirofo region, is characterized by alluvial soils, mainly sandy and ferruginous, and a tropical climate. Groundwater is considered as the main source of drinking water for the local population although the presence of pollution by nitrogen compounds has been a serious environmental problem for more than a decade This study aimed at developing a groundwater vulnerability model for nitrate and ammonium as a protective measure. Based on the intrinsic vulnerability determined by the SINTACS model, the influence of anthropogenic parameters related to nitrogen sources and groundwater use on contamination was verified using GIS. Chemical analyses showed high concentrations of nitrate (136.987 mg.l-1) and ammonium (1.120 mg.l-1) in the samples. The high nitrate and ammonium concentrations were found in the northern subwatershed, probably due to the area impacted by urbanization by urbanization, where the groundwater vulnerability index is high (high index is 197 - 210 and for the very high ones 215 - 223). On the other hand, the concentrations in the southern subwatershed are lower, and the index is moderate (137 - 178). In order to prevent the contamination of groundwater by nitrogen, it is necessary to develop management policies on surface land use and groundwater, as well as to continuously monitor the latter.