Geochemistry of Stream Waters of the Lo River Catchment, Ha Giang Province (Northern Vietnam)

A set of 41 stream water samples of the Lo River catchment, Ha Giang province, collected in dry season was analyzed for pH, major cation and anion, trace element concentrations. The stream waters exhibits a midly acidic to alkaline, meanwhile, the Total Dissolved Solids (TDS) values have a wide range of 17.4–284.9 mg L^–1. Among major cations and anions, the stream water within the Lo River catchment is characterized by the predominant presence of Ca²⁺ and \({\text{HCO}}_{3}^{ - }\). This compositional pattern gives rise to the emergence of the Ca–Mg–HCO₃ water type as the most dominant species, followed by Na–Cl, Ca–Mg–Cl–SO₄ and Na–HCO₃–Cl types. However, the distribution of these water types corresponds closely with the geological conditions, with Na–Cl type prevailing in the watershed of granite complex, while watersheds characterized by lithologies such as Quaternary sediments, limestone, marble, shale, schist, and sandstone primarily exhibit the Ca–Mg–HCO₃ water type. The dominant reaction in the water system is the dissolution of carbonate minerals, like calcite and dolomite, followed by the contribution of modest rainfall during the dry season, and small-scale processes of mixing and cation exchange. Comparison of major ions and trace element with technical standard reveal the stream waters are generally deemed suitable for the routine activities of the local population in Ha Giang province. However, stream water of a few specific sites may require treatment before these waters can be safely utilized.