Abstract
In Nigerien Liptako, the quality of water to meet the needs of populations and ecosystems is jeopardized by the development of artisanal gold mining and the increased use of pesticides. It is urgent to improve scientific and local knowledge in order to preserve the health of populations and ecosystems. But to what extent can a good knowledge of the quality of the water resources of the Nigerien Liptako improve the health of the populations? The objectives of this thesis are 1/ to improve knowledge on the quality of water in the Niger Liptako, 2/ to determine the possible origins of these contaminations, and 3/ to develop and implement, in collaboration with the different actors of the territory, a knowledge transfer tool in order to promote the emergence of new practices.To achieve these objectives, a multidisciplinary methodology, at the interface between geology, metrology and sociology, was set up, articulating hard science and participatory research. 43 wells and boreholes were sampled during high and low water periods and analyzed by ICP/MS and ion chromatography. The surrounding rocks were analyzed by SEM-EDS and ICP/MS. In the agricultural areas, 6 sites were sampled along the Niger River and its tributary the Mekrou River, during both seasons, using POCIS and grab sampling. The collected samples were analyzed by HPLC/MS. At the agricultural sites, information on agricultural practices and pesticides used was collected from the producers. The co-construction of the research-field knowledge transfer system was based on the principles of companion modeling.The results of the groundwater analysis revealed arsenic and barium concentrations significantly higher than the WHO guideline values. Concentrations exceeding the quality limits in both geological environments were for manganese, nickel and boron. Descriptive statistics methods allowed to distinguish a main facies of calcic and magnesian bicarbonate type. SEM-EDS results showed the presence of sulfide minerals and manganese oxides. The origin of the arsenic in the groundwater appears to be associated with the alteration of the sulfide minerals and the slightly alkaline and oxidizing conditions favoring the desorption of arsenate from the surface of the iron and manganese oxides. Barium and manganese concentrations in groundwater are associated with their natural occurrence in rocks. Consumption of groundwater rich in arsenic and certain trace metals poses serious risks to human health in gold mining areas.Pesticide analyses of the water have made it possible to detect, locally, compounds with concentrations well above the guide values of the WHO and the EU directive: for diuron, atrazine and acetochlor. Poor pesticide application practices lead to water contamination: 70% of the pesticides used are not registered by the CILSS. The main source of pesticides in river water is related to their intensive use in urban agriculture, near Niamey, and for cotton production, for the Mekrou. These high concentrations of diuron, atrazine, and acetochlor raise questions about the health of market gardeners.On the issue of metal pollution, the co-construction of a knowledge transfer mechanism between research and the field initiated a participatory and collaborative research dynamic involving institutional stakeholders, NGOs and gold miners. The observation of this co-construction encourages the dissemination of this knowledge transfer mechanism to other gold panning sites.