Hydrochemical Characteristics and Groundwater Quality Assessment in the Wudaoxian Area of Lanzhou New Area, China

In arid and semi-arid regions, groundwater is the main domestic and agricultural irrigation water source, supporting regional water security and agricultural development. Under persistent human interference, groundwater pollution has worsened in the Wudaoxian area of Lanzhou New Area. In this study, 44 groundwater samples (13 unconfinedand 31 confined groundwater samples) were analyzed. Multiple approaches including Piper trilinear diagrams, Gibbs plots, ion ratio analysis, correlation analysis and factor analysis were adopted to reveal groundwater hydrogeochemical characteristics and formation mechanisms, and distinguish the influences of natural processes and anthropogenic activities. The Water Quality Index (WQI), United States Salinity Laboratory (USSL) diagram and Wilcox diagram were further used to evaluate groundwater suitability for drinking and irrigation. Hydrogeochemical results show that local groundwater is weakly alkaline, and unconfined and confined groundwater share similar Na-Cl-dominated hydrochemical types. Rock weathering, evaporation-concentration and ion exchange jointly control groundwater chemistry, whereas agricultural fertilization and pesticide application cause aquifer N pollution. WQI results suggest 81.82% of groundwater is fit for drinking. Nevertheless, irrigation assessment via SAR and %Na indicates that 92.31% of unconfined groundwater and 64.51% of confined groundwater are unsuitable for irrigation, with 6.45% marginally usable only for salt-tolerant crops. We recommend popularizing water-saving irrigation to curb water quality degradation. This study provides references for rational groundwater utilization and targeted protection.