Temporal and Spatial Variation Characteristics of Water Chemistry and Evaluation of Irrigation Suitability in the Qingling River Basin in the Upper Reaches of the Yangtze River
The Qingling River, a representative silicate rock catchment in the upper Yangtze Basin, is vital for agricultural productivity in central Yunnan. To investigate its hydrochemical characteristics, river water samples were systematically collected during both dry and wet seasons. Employing hydrochemical diagrams, statistical analysis, and absolute principal component score-multiple linear regression (APCS-MLR) modeling, we identified influencing factors and their contributions to water chemistry and evaluated irrigation suitability. Results showed that pH ranged from 7.36 to 9.18 in dry season and 7.12 to 8.92 in wet season, with total dissolved solids (TDS) varying between 119–2684 mg·L−1 and 125–2342 mg·L−1, respectively. Dominant cations were Ca2+ and Na+, while anions were primarily SO4^2− and HCO3^− in both seasons; notably, SO4^2− concentrations significantly exceeded the Yangtze River Basin’s average. Hydrochemical types varied seasonally: HCO3·SO4-Ca·Mg and HCO3·SO4-Ca dominated in dry season, whereas HCO3·SO4-Ca·Na, HCO3·SO4-Ca·Mg, and HCO3-Ca prevailed in wet season. The river water was affected by five factors: sulfuric acid-dominated water-rock interactions, carbonic acid-dominated water-rock interactions, domestic sewage discharge, agricultural non-point source pollution, and unknown sources. Contribution rates were 47.90%, 24.80%, 16.98%, 2.40%, and 7.92% in dry season, and 28.23%, 28.94%, 27.48%, 2.02%, and 13.34% in wet season, respectively. Water-rock interactions emerged as the primary control on hydrochemistry. While most samples were suitable for irrigation, a few exhibited high salinity, warranting cautious use. This study provides scientific support for irrigation water resource management and safe utilization in the Qingling River Basin.