[Dynamic Replenishment Process of Nutrients in Tributary of Channel Reservoir]

The process of phytoplankton succession and change in primary productivity are directly determined by the seasonal variations in nutrients in tributary bays of channel reservoirs. This study aimed at analyzing the effects of the main nutrient sources on seasonal distribution of nutrients in Xiangxi Bay based on the field data collected in 2010 and 2011. The tracing inorganic ions were Cl^- and Na⁺ that showed significant differences (P<0.01) between the mainstream and the tributary. The nutrient contribution rates of different sources were calculated by the binary linear model. The results showed that the nutrient contribution rate of the mainstream was more than 75% during the dry season and the impoundment period. The intrusion of the mainstream was the main source of nutrients in Xiangxi Bay. The difference in the contribution rates between the mainstream and the upstream decreased during the pre-flood drawdown period and the flood season. The concentration of total phosphorus was higher in the upstream, while the concentration of total nitrogen was higher in the mainstream. The patterns of density currents were different and the nutrient contribution rates of different sources changed accordingly. Therefore, the nutrients of Xiangxi Bay changed regularly in different operation periods of the Three Gorges Reservoir.