Hydrochemical Characteristics and Pollution Source Apportionment of a River Affected by Large-Scale Coal Mining in the Dry Season: A Case Study of the Qingyang–Binzhou Section of the Jinghe River, Northwest China

Understanding how the development of large-scale coal mining bases affects river hydrochemistry is a key scientific issue in the field of water environment research. In this study, the Qingyang–Binzhou section of the Jinghe River Basin was selected as the study area, and a total of 29 water samples were collected in April 2025 from the upper to lower reaches of the coal mining base. Hydrochemical analysis, ion ratio methods, and the positive matrix factorization (PMF) model were comprehensively applied to systematically characterize the hydrochemical features and identify the pollution sources in the river under the influence of large-scale coal mining activities. The results showed that the mean concentrations of Na+, SO42−, Cl−, and total dissolved solids (TDS) in the mainstream were as high as 414 mg/L, 728 mg/L, 226 mg/L, and 1636 mg/L, respectively, reflecting a significant impact of coal mining activities on river hydrochemistry. Four spatial variation patterns were observed along the river: the first pattern was characterized by “stable in the upper reaches, sharp increase in the middle reaches, and fluctuating increase in the lower reaches,” represented by Na+ and SO42−; the second pattern showed “stable in the upper reaches, slight decrease in the middle reaches, and fluctuating decrease in the lower reaches,” represented by pH; the third pattern exhibited “fluctuating in the upper reaches, sharp decrease in the middle reaches, and extremely low levels in the lower reaches,” represented by NO3−; and the fourth pattern was dominated by irregular variations controlled by nitrogen transformation processes, represented by NH4+ and NO2−. Gibbs plots and ion ratio diagrams indicated that the hydrochemistry of sites unaffected by coal mine drainage was primarily controlled by rock weathering, whereas contaminated samples shifted toward the evaporation-concentration zone and extended beyond its typical range, reflecting an “anthropogenic salinization effect” induced by the input of mine water superimposed on the arid to semi-arid climatic background. The PMF model identified three main pollution sources: coal mining and mine water discharge (48.3%), domestic sewage (30.2%), and carbonate weathering (21.5%). This study reveals the significant modification mechanism of river hydrochemistry by large-scale coal mining base development, providing a scientific basis for targeted water pollution control in the Jinghe River Basin and for water environment management in similar mining areas.