The Fate and Transport of Nutrient and Algal Contaminants in Xiangxi Bay of the Three Gorges Reservoir

摘要

Water quality in the Three Gorges Reservoir and all its tributaries is of critical significance for the ecological and economic development of the middle and lower Yangtze River watershed. The construction of the reservoir impoundment has caused higher water surface elevation, slower current velocity, and even backflow in its main tributaries, including the Xiangxi River. More nutrient species related to nitrogen and phosphorous are being conveyed to the water body and retained in the river's bay region much longer than previously, leading to more frequent eutrophic events such as algal blooms, and significantly threatening the downstream water quality. This study focuses on the nutrient species levels, statistically analyzing the available data to determine the effect of backflow and estimate the variation in algal levels, developing mass balances for the water budget and important contaminants, and calculating the ratio of total nitrogen to total phosphorus. Based on the data from the eutrophication processes happened in Xiangxi River during the period January to November 2010, total nitrogen is the limiting factor. The amount of water accumulating in the Xiangxi River was 1.108×10~(10) m~(3), and the water level rose by 5.78 m from January to November 2010. Most of the phosphorus and ammonia in the river came from non-point source pollution. The results will be used to help verify and calibrate variations in the water flow rate and the associated point source and non-point source pollution. Since the Xiangxi River is a representative tributary of the Three Gorges Reservoir, the research method developed and conclusions drawn will provide a valuable reference for eutrophication investigations of other tributaries.