Hydrogeochemical evaluation and characterization of water quality in the Phewa Lake, Pokhara, Nepal

The study was carried out in the Phewa Lake of Pokhara Metropolitan City, Gandaki Province, Nepal, for geochemical assessment and characterization of the lake water quality. A total of 28 water samples were collected in each season from the different zones of the lake in March 2022 (pre-monsoon) and November 2022 (post-monsoon). The lake exhibited elevated levels of PO₄³⁻, NO₃⁻, and NH₃, indicating that anthropogenic activities are interfering the lake water. The significant differences in many monitored physicochemical parameters between the pre- and post-monsoon visualize dilution effect in the lake during post-monsoon. Piper diagram illustrates that the majority of water samples in the lake are of Ca–HCO₃ type. Additionally, Piper diagram, Gibbs diagram, and Mixing plot illustrate that carbonate weathering is dominant in both seasons. Principal component analysis (PCA) reveals significant correlations among NO₃⁻, SO₄²⁻, Na⁺, and Cl⁻, demonstrating that pollution in the lake water is attributed to agricultural activities and domestic effluents. In the majority of samples, water quality index (WQI) depicts that the lake water quality is very poor to poor in the pre-monsoon and poor to good in the post-monsoon. Sodium absorption ratio (SAR), % Na (percent sodium), electrical conductivity (EC), cation ratio of soil structural stability (CROSS), and United States Salinity Laboratory (USSL) diagram illustrate that the lake water is suitable for irrigation.