汉江中下游生态环境变化特征及其影响因素

Characteristics and Influencing Factors of Ecological Environment Changes in the Middle and Lower Reaches of the Han River

摘要: 水利工程对于汉江中下游水文情势有着广泛的影响，在南水北调工程实施后，汉江中下游的水生态环境面临着极大的挑战。在独特的区位背景和复杂水文情势的双重影响下，汉江中下游流量、水位、流速、水质、鱼类资源、产卵场、水华特性时空都会发生不同程度的变化。基础现状的调查及趋势分析，对于研究汉江中下游生态变化的影响意义重大。汉江中下游的流量和水位在丹江口水库蓄水后均出现不同程度的下降，由于水体自净能力、汉江来水水质较好及周边城市采取的大力截污控污措施，汉江中下游水质基本保持稳定。由于汉江中下游存在众多水利调控工程、过度捕捞、流速下降等因素的多重影响，汉江中下游分隔的江段鱼类种群及产卵量逐年下降。由于汉江中下游梯级日益增加，下游流量及流速都产生了较大影响，水华暴发频率也逐年增加，水华暴发时期主要集中在春季枯水期(1~3月)。汉江水华波及钟祥以下约400 km的所有下游江段，有从汉江干流向汉江支流蔓延的趋势。汉江全年浮游藻类主要由硅藻、绿藻、蓝藻和隐藻构成，硅藻在全年都是绝对优势种。从时间特性来看，水华暴发年份大部分为汉江枯水年，水文特征成为水华年份差异的主控因子。

Abstract: Hydraulic engineering has a wide-ranging impact on the hydrological situation in the middle and lower reaches of the Han River. After the implementation of the South-to-North Water Diversion Project, the aquatic ecological environment in the middle and lower reaches of the Han River faces great challenges. Under the dual influences of unique geographical background and complex hydrological situation, the flow, water level, flow velocity, water quality, fish resources, spawning grounds, and water bloom characteristics in the middle and lower reaches of the Han River will undergo varying degrees of change in space and time. The investigation of the current situation and trend analysis are of great significance for studying the impact of ecological changes in the middle and lower reaches of the Han River. After the impounding of the Danjiangkou Reservoir, the flow and water level in the middle and lower reaches of the Han River have experienced varying degrees of decline. However, due to the self-purification capacity of the water body, the good quality of water from the Han River, and the vigorous measures taken by surrounding cities to intercept and control pollution, the water quality in the middle and lower reaches of the Han River has remained basically stable. Due to the multiple impacts of numerous water conservancy regulation projects, overfishing, and decreased flow velocity in the middle and lower reaches of the Han River, the fish population and spawning volume in the separated river sections have been declining year by year. Due to the increasing number of cascade dams in the middle and lower reaches of the Han River, the downstream flow and velocity have been greatly affected, and the frequency of water bloom outbreaks has also increased year by year. The outbreak period of water blooms is mainly concentrated in the dry season of spring (January to March). The water blooms in the Han River affect all downstream river sections about 400 kilometers below Zhongxiang, with a trend of spreading from the main stream to tributaries. The planktonic algae in the Han River throughout the year are mainly composed of diatoms, green algae, cyanobacteria, and cryptophytes, with diatoms being the absolute dominant species throughout the year. From the perspective of temporal characteristics, most of the years with water bloom outbreaks are dry years in the Han River, and hydrological characteristics become the main controlling factor for the differences in water bloom years.