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

Liqiang Yao,Congfeng Wang,Qingqing Su,Yachen Zhang,Lubo Liu

doi:10.13189/eee.2019.060201

Abstract

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 the Xiangxi River during the period from January to November 2010, total nitrogen is the limiting factor. The amount of water accumulated in the Xiangxi River was 1.108×1010 m3, 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.

Highlights

Rivers have sustained life and promoted the reproduction, survival, and ecological stability of terrestrial aquatic organisms
The exchange between water bodies weakens, a slow flow rate is beneficial for the deposition of matter
Impounding the Three Gorges Reservoir changed the hydrodynamic characteristics of the Xiangxi River substantially, with backflow becoming commonplace

Summary

Introduction

Rivers have sustained life and promoted the reproduction, survival, and ecological stability of terrestrial aquatic organisms. The rise of modern society and industrial development has created significant levels of non-point pollution from domestic sewage, farmland drainage, and other harmful substances that directly or indirectly enter our river systems, leading to deteriorating water quality and changes in the biota. As one of the world’s largest hydropower engineering structures, the Three Gorges Dam is the backbone of the flood control system in the middle and lower reaches of the Yangtze River, the most important river in China. It provides flood control and electricity generation, and a navigable waterway for the main channel of the Yangtze River. In 2003, the Three Gorges Reservoir was successfully impounded, [2] after which the water level in the reservoir area continued to increase and the water flow in the tributary rivers slowed, decreasing their self-purification ability and increasing the retention time of pollutants in the tributary bay

Methods

Results

Conclusion