This study aims to understand the extension of groundwater pollution downstream of a landfill, Andralanitra-Antananarivo-Madagascar. Twenty-one samples, composed of dug well waters, spring waters, river, and lake, were measured in stable isotopes (δ 2 H, δ 18 O) and tritium. Results showed that only two dug well waters, collected at the immediate vicinity of the landfill, have high tritium activities (22.82 TU and 10.43 TU), probably of artificial origin. Both upstream and further downstream of the landfill, tritium activities represent natural source, with values varying from 0.17 TU to 1.46 TU upstream and from 0.88 TU to 1.88 TU further downstream. Stable isotope data suggest that recharge occurs through infiltration of slightly evaporated rainfall. Using the radioactive decay equation, the calculated tracer ages related to two recent ground water samples collected down gradient of the landfill lay between [8-15] years and [4-7] years, taking into account the uncertainty of tritium measurements. For the calculation, a value of 2.36 TU was taken as A o . The latter was estimated based on similarity between stable isotope compositions of nearby spring and dug well waters as well as tritium activities of the local precipitation. Calculation of the tritium activities from the contaminated water point having 22.82 TU to further downstream using the calculated tracer ages showed values of one order of magnitude higher than the measured values. The absence of hydrological connection from the contaminated water point to further downstream the landfill would explain the lower tritium activities measured. Groundwater pollution seems to be limited to the closest proximity of the landfill.

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−.

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The upper catchment of Ikopa has great potential for surface or sub-surface water resources. The Ikopa River plays an important role in the water supply of the plain of Antananarivo. Knowing that surface water is abundant but exposed to the high risk of pollution, and groundwater remains less exploited because of the insufficiency of the study concerning the recharge and the sources of their mineralization. The objective of this research is to use the isotope method to characterize groundwater to determine their origin and recharge process. The results of chemical analysis show three different facies type of groundwater which dominated by the sodium, nitrate and chloride ions. The isotopic compositions of the waters sampled vary respectively from -7.25‰ to 5-.09‰ for δ18O and from -46.9‰ to -24.7‰ for  δ2H. water form the lakes are more enriched compared to those rivers and groundwater. The diagram δ18O- δ2H shows that groundwater is recharged from local rainwater but undergoes low evaporation before infiltration. However, the results obtained from the parameters measured in situ show that a lateral recharge of groundwater from the streams feeds the neighboring aquifers. Lakes are fed by run-off during the rainy season.

In the “Global Network of Isotopes in Precipitation” database, Antananarivo has two distinct datasets from two stations. Thirty-four years separate the two datasets. This study aims on the one hand to depict the variations of the water stable isotopes composition of precipitations from the two stations and understand their origins, mainly in relation to meteorological factors. On the other hand, the Antananarivo data are compared with regional and international data to identify other sources of isotope composition variability in precipitation. Isotope records showed that after thirty-four-year gap, summer and winter (the two main seasons) precipitations are more enriched in heavy isotopes. The precipitation amount fluctuation would mostly contribute to this temporal variation. Opposite to summer and winter precipitations, inter-season rainfalls have similar isotope values after thirty-four years. The two stations are geographically close and the spatial aspect is therefore negligible since there are no latitude nor altitude effects on the isotope composition of precipitations. Regarding the second order parameter d-excess, the monthly mean values from both stations are higher than 100/00 and could indicate moisture recycling. The comparison with regional/international data showed that the isotope variability in precipitation is primarily due to precipitation amount effect, different moisture source, the stations distance from it and the change of meteorological factors along the moisture trajectory.