Abstract: We examined the spatial variations and influencing factors of hydrochemical characteristics in the Chishui River, by measuring physical and chemical indicators (water temperature, pH, DO, conductivity, turbidity), key hydrochemical parameters (carbon, nitrogen, phosphorus, sulfur), and potential ecological risk indicators such as heavy metals, antibiotics and polycyclic aromatic hydrocarbons (PAHs). The results showed that the overall level of water quality in the Chishui River Basin was good. The concentrations of the detected eight heavy metals ranged from 0 to 1120 μg·L^-1. The concentrations of the detected five antibiotics ranged from 0 to 50 ng·L^-1. The total concentration of 16 PAHs was 11.6-390.7 ng·L^-1. The key hydrochemical parameters, antibiotics and PAHs decreased from upstream to downstream, while heavy metals showed an opposite pattern. Carbon and nitrogen concentrations in the basin were mainly influenced by industrial and domestic wastewater discharges, while total phosphorus and sulfate concentrations were primarily affected by nonpoint source pollution and mining activities. Heavy metals, such as arsenic (As), manganese (Mn), and iron (Fe), were mainly influenced by agricultural activities and domestic sewage. Zinc (Zn) and lead (Pb) were primarily associated with traffic pollution. Nickel (Ni) was mainly affected by mining activities, chromium (Cr) largely originated from the erosion of naturally high background soils. Copper (Cu) was influenced by multiple factors including mining and agricultural activities. Antibiotics were mainly derived from medical and livestock farming wastewater, while PAHs were primarily attributed to petroleum volatilization, combustion of coal and biomass (such as wood), and traffic-related pollution. Our findings provide data support for the protection of water ecological environment and the analysis of habitat functions for endangered fish species in typical river basins of the upper Yangtze River.

Key words: Chishui River, hydrochemical factor, heavy metal, antibiotic, polycyclic aromatic hydrocarbons (PAHs)