Abstract: Through the determination of the concentrations of polycyclic aromatichydrocarbons (PAHs) in Xihe River in different seasons, this paper analyzed the
temporal variation of PAHs, their sources, and possible ecological risk. In the water body of Xihe River, the concentrations of 16 PAHs ranged in 0.214-0.857μg·L^-1 (averaged 0.562 μg·L^-1) in June (summer), 0.195-0.633 μg·L^-1 (averaged 0.380 μg·L^-1) in September (autumn), and 0.122-0.486 μg·L^-1 (averaged 0.236 μg·L^-1) in November (winter), with that of benzo［a］pyren much higher than the guidance value provided by the environmental quality standards for surface water (GB 3838-2002). In June and September, the PAHs in Xihe River mostly came from oil, oil burning residue, and oil refined process. The preliminary assessment with quotient method showed that the benzo［a］pyren in the river had great ecological risk, which should be paid more attention.

Key words: N₂O emission, Cropping system, Paddy soil, Water regime