Chemical Composition of Rainwater at Selected Sites on Upolu Island, Samoa

Abstract

The study involved analysis of rainwater samples at four sites on Upolu Island, Samoa from November 2019 to April 2020. A total of 48 rainwater samples were analysed in order to determine the major cations (Na+, Mg2+, Ca2+, K+) and anions (Cl−, , ) in wet precipitation from the four sites. The average pH of the rainwater was 6.89, perhaps due to neutralization. Only 50% of the rain samples had a pH above 5.6. This shows strong inputs of alkaline species to rainwater samples in some sites. The average pH of samples higher than 5.6 is due to high loadings of sodium ions. The rainwater samples are dominated by Na+, Ca2+, Mg2+, Cl− and . The principal cations and anions, in decreasing order, are Na+ > Mg2+ > Ca2+ > K+ and Cl− > > . The correlation study and the comparison of major ion composition with other sites revealed that rainwater ion composition is strongly influenced by marine sources rather than anthropogenic and terrestrial sources.