Water Quality and Hydrogeochemical Mechanisms of River Water in the Strong Runoff Piedmont Region: Insight From Hydrochemical and Isotopic Evidence

Water quality and hydrogeochemical mechanisms of river water in recharge areas are of great significance for environmental safety and ecological stability. Here, water quality and associated mechanisms in river water of the Qingshui River were assessed using hydrochemical and isotopic data (δ²H_H2O and δ¹⁸O_H2O), combined with the Entropy-weighted Water Quality Index (E-WQI) and positive matrix factorization (PMF) model. The results showed that water quality of the agricultural reach is dominated by an "excellent level," while ~ 43% of samples from the urban reach showed a "good level." Water quality is mainly driven by mineral dissolution (36.8% and 57.0% for the agricultural and urban reaches) and agricultural inputs (37.7% and 21.7% for the agricultural and urban reaches), while positive cation exchange contributes less to hydrochemical components. Furthermore, the construction of artificial channels enhances the effect of evaporation on hydrochemistry and alters the water-rock interaction processes. Those results provide new insights into evaluating hydrogeochemical mechanisms in the river system of piedmont regions.