The water quality of the backwater areas in the Xiangxi River and Shennong River, which are typical tributaries of the Three Gorges Reservoir, was monitored in September 2018. The vertical distribution characteristics of dissolved oxygen, chlorophyll a, and other indicators in the two rivers were analyzed and compared, and the environmental factors affecting their vertical distribution were discussed. The results showed that the dissolved oxygen concentration 0-10 m and 0-12 m from the surface of the Xiangxi River and Shennong River, respectively, showed significant stratification and decreased with increasing water depth. The dissolved oxygen saturation of surface water was 139.20% and 107.78%, respectively, reaching a state of supersaturation (SDO>100%).The dissolved oxygen concentration in the middle and bottom water was more stable without stratification. The vertical distribution characteristics of chlorophyll a were consistent with those of dissolved oxygen in the Xiangxi River and Shennong River, and the chlorophyll a concentration in the surface water showed moderate eutrophication (5μg·L-1 < Chl-a < 20 μg·L-1). According to Pearson correlation analysis, the vertical distribution of dissolved oxygen in the Xiangxi River and Shennong River was significantly correlated with that of water temperature and phytoplankton. The stratification of water temperature and the life activities of phytoplankton were the key factors affecting the vertical distribution of dissolved oxygen. Chlorophyll a was positively correlated with water temperature and pH, and negatively correlated with turbidity, indicating that the vertical distribution of phytoplankton was mainly affected by the attenuation of light intensity along the water depth and the stratification of water temperature.
Keywords: Shennong River; Three Gorges Reservoir; Xiangxi River; chlorophyll a; dissolved oxygen; impoundment period; vertical distribution.