Nitrate contamination of groundwater in Ambohidrapeto–Antananarivo-Madagascar using hydrochemistry and multivariate analysis

Abstract

Abstract Nitrate contamination of groundwater was assessed in the crowded area of Ambohidrapeto, Antananarivo city-Madagascar using hydrochemistry and multivariate analysis. Seventeen dug well waters and three spring waters were collected and measured in the field for physical parameters and in the laboratory for major ions. The results showed that all water samples have nitrate concentration above the standard value of 50 mg/L-NO3 set by the World Health Organization, with a minimum value of 79.3 mg/L-NO3 and a maximum value of 394.5 mg/L-NO3. Anthropogenic activities, from the surrounding pit latrines are the main sources of the groundwater nitrate contamination and are dominant over natural processes, which contribute to a lower degree to the groundwater mineralization. Ionic ratios indicated the occurrence of mineral dissolution and silicate weathering as the natural sources of magnesium and sodium, respectively. Furthermore, the correlation between calcium and sodium as well as the Piper diagram revealed the occurrence of ion exchange, resulting in sodium being the dominant cation over calcium. Forty percent (40%) of the water samples have the hydrochemical facies Na–Mg–Cl, followed by Na–Mg–Ca–Cl facies for 25% and Na–Mg–Cl–HCO3 facies for 20%. By applying principal component analysis, the influence of anthropogenic activities is confirmed. The first principal component extracted, which explained 52.88% of the total variance showed strong positive loadings on TDS, NO3 −, Cl−, Mg2+, Na+, K+ and Ca2+, indicating that these ions contribute as anthropogenic sources, although Mg2+, Na+, K+ and Ca2+ contribute to a lesser extent than NO3 −, and Cl−.

Keywords

• Nitrate
• Groundwater
• Pit latrines
• Hydrochemistry
• Principal component analysis
• Ambohidrapeto-Madagascar