Nutrient recharge effect of Yangtze River to tributary backwater area in Three Gorges Reservoir, China

Abstract

Interaction between the Yangtze River and its tributaries in the Three Gorges Reservoir has an important influence on tributary algal blooms. Taking the Xiaojiang River as a typical tributary, a binary mixing model used stable isotopes of hydrogen and oxygen to quantitatively analyze the water contribution and nutrient source structure of the tributary backwater area. Results showed that the isotope content (δD: −54.7‰, δ¹⁸O−7.8‰) in the Yangtze River was higher than that in the tributaries (δD:−74.2‰, δ¹⁸O−17.0‰) in the non-flood season and lower than that in the tributaries in the flood season. The Yangtze River contributed more than 50% water volume of the tributary backwater area in the non-flood season. The total nitrogen and total phosphorus concentrations in the backwater area were estimated based on water contribution ratio, and the results were in good agreement with the monitoring results. Load estimation showed that the nitrogen and phosphorus contribution ratio of the Yangtze River to the tributary backwater area was approximately 40%-80% in the non-flood season, and approximately 20%-40% in the flood season, on average. This study showed that the interaction between the Xiaojiang River and the Yangtze River is significant, and that Yangtze River recharge is an important source of nutrients in the Xiaojiang backwater area, which may play a driving role in Xiaojiang River algal blooms.