Hydrochemical characteristics and formation mechanism of groundwater in Lhasa area, China

Tibet is an important ecological barrier in China. Studies on the chemical characteristics and formation mechanism of groundwater in the Lhasa area play an important role in revealing the mechanism of current epigenetic changes on the Qinghai-Tibet Plateau, and they are of great significance in building ecological security in the nation. In this paper, we analyzed the chemical characteristics of groundwater and the mechanism of water-rock interaction by means of groundwater survey and water sample collection and analysis in the Lhasa area, combined with Gibbs model simulation and hydrochemical analysis. The results showed that the groundwater conductivity ranged from 38.80 to 1 193.00 μS/cm, averaging at 123.99 μS/cm; the TDS ranged from 44.05 to 1 050.55 mg/L, or 150.75 mg/L on average; the pH level of groundwater was greater than 7, weakly alkaline; and groundwater is HCO3-Ca and Cl-Na types, with the latter attributed to underground spring water. The groundwater formation process is mainly associated with the dissolution of carbonate and silicate rocks, cation exchange, and so on, and affected by human factors to a certain extent. The Na+, K+ and Cl- in groundwater are mainly from the weathering of salt minerals; the excess Na+, K+ are from the dissolution of silicate minerals, such as sodium and potassium feldspars; and HCO3-, Ca2+, Mg2+ and SO42- come mainly from the dissolution of calcite, dolomite, gypsum and other calcium-magnesium minerals. © 2021, Editorial Office of Earth Science Frontiers. All right reserved.