Major ions and trace elements of two selected rivers near Everest region, southern Himalayas, Nepal

During pre-monsoon of 2013, water samples were collected from 30 sites of two major rivers, viz. Dudh Koshi and Indrawati to assess the river water quality on the southern side of the Nepalese Himalayas. The physical parameters such as pH, EC, turbidity and water temperature were measured in the field and major ions (Na⁺, NH₄ ⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SO₄ ²⁻, and NO₃ ⁻) and element concentrations (Li, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Cs, Ba, Pb, U, Y, Zr, Nb and Cd) in the water samples were analyzed in the laboratory. The result indicated river waters were neutral to mostly alkaline with pH ranging from 6.57 to 8.81 and EC ranging from 10.5 to 321 μS/cm. The lower values of turbidity were recorded in the pristine tributaries of Dudh Koshi, whereas the main rivers had the higher values with a range of 0.51–515 NTU. Bicarbonate (HCO₃ ⁻) showed a significant correlation with Ca²⁺ and Mg²⁺, suggesting carbonate weathering as the dominant geochemical process in the region. Furthermore, the Gibbs plot also suggested the dominance of rock weathering. Very low concentration of trace elements was found in most of the samples which were within the WHO guidelines. In addition, the concentrations of toxic elements such as As and Pb were below the detectable limits in most of the samples. Furthermore, the analysis of PCA suggests that most of the elements originated from natural weathering; however, there were some evidences of anthropogenic effect on water quality which may not be critical issue at present but can be of concern in future.