Hydrogeochemical and biological assessment of spring and stream water quality for its suitability for drinking in Kanglung locality, Trashigang, Bhutan

Abstract

Springs are important water sources for domestic and agricultural uses in eastern Himalayas. This study describes the water quality scenario and major geochemical processes of the springs utilized for drinking in Kanglung locality, Bhutan. Water samples were collected at 2 end-user taps and 3 spring sources from October 2020 through April 2021 for laboratory analyses. Water samples analyzed met the WHO drinking water quality standard except for turbidity and thermotolerant coliform in some samples. The Water Quality Index values of the spring water ranged from 5.75 to 41.64, majority falling under excellent class demonstrating potability of springs tapped. The order of anion and cation chemistry were HCO3− >Cl− >SO42−, and Na+ >Ca2+>Mg2+>K+, respectively. The scatter diagrams and molar ratios of major ions indicated silicate and carbonate weathering controlling the spring water chemistry. The piper diagram indicated that springs are predominantly Ca-Mg-Cl and Na-Cl types. Gibbs diagrams inferred that spring chemistry is mainly controlled by rainwater followed by water-rock interaction. Statistical analyses indicated different sources of dissolved ions including carbonate and silicate weathering, atmospheric precipitation, dissolution of sulphate minerals, and oxidation of sulphides.