Assessment of Nitrate Occurrence in the Shallow Groundwater of Merimandroso Area, Analamanga Region, Madagascar Using Multivariate Analysis

摘要

Knowing the groundwater quality is important for the drinking water supply in the highland area of Madagascar, including Merimandroso Commune insofar that groundwater is the main source of drinking water for a large number of Malagasy people. In this way, this study assessed the shallow groundwater quality with special focus on nitrate occurrence using multivariate statistical techniques such as cluster analysis (CA) and principal component analysis (PCA). That was to determine the similarities among the water samples in terms of hydrochemical features and to identify the different mechanisms involved in the shallow groundwater hydrochemistry. The study was conducted on twenty-one water samples collected from dug wells. Cluster analysis grouped the water-sampling points into two main clusters: a highly nitrate polluted group (concentration greater than 50 mg/l) and a non-nitrate polluted group. The results showed a spatial variation of the groundwater chemistry processes, while no such variability was found temporally for water samples collected at different periods. Principal component analysis extracted three principal components accounted for over 82% of the total variance. It attributed the hydrochemical features of the water samples of high nitrate content to the nitrate pollution mechanisms along with the weathering of feldspar and ferromagnesian minerals. For some of the latter water samples, the water chemistry is likely affected by igneous rock weathering. This study confirmed both the usefulness and powerfulness of multivariate statistical techniques in water quality assessment, since they helped get a proper understanding of processes controlling the shallow groundwater chemistry.