南水北调中线工程对汉江中下游“水华”影响

Impact of middle route S-N water transfer project on “algae bloom” in middle & lower reach of Hanjiang river

汉江中下游近年出现“水华”的根本原因是汉江下游水体水质污染严重 ,氮、磷等污染物浓度过高。春季枯水期流量小于一定值时 ,汉江下游水体成为狭长的“湖泊” ,水流缓慢 ,当气温升高时 ,藻类大量繁殖形成“水华”。采用WQRRSQ生态模型模拟汉江水质 ,结果表明 ,南水北调中线工程投入运行后 ,调水 82亿m3,无“引江济汉”工程方案下 ,由于水库调度作用 ,春季流量增大 ,满足春季“水华”发生的水文条件的年度比调水前没有增加 ,调水基本没有影响汉江下游“水华”的年内持续时长。其他调水方案下 ,由于实施“引江济汉”工程 ,目前汉江中下游“水华”现象将基本得到控制。

The ultimate reason for the appearance of “algae bloom” in middle & lower reach of Hanjiang river is serious water pollution and excessive high concentration of nitrogen and phosphorus pollutants. In spring, when the low water flow is under a certain value, the river in lower reach, flowing slowly, turns into a “long & narrow lake”. When air temperature rises, algae propagate rapidly and the phenomenon of “algae bloom” appears. Numerical simulation result obtained by WQRPSQ model indicates that after the completion of middle route project of S N Water transfer, under the scheme of transferring 8.2 billion m\+3 of water and without water supplement for Hanjiang river from the Yangtze, as the reservoir regulation causes the increment of spring discharge, the years meeting the hydrological condition of “algae bloom” appearance will not increase. Water transfer imposes little influence on the duration of “algae bloom” appearing in lower reach of Hanjiang river. Under other water transfer schemes, due to the implementation of “diverting water from the Yangtze to Hanjiang river” project, the present “algae bloom” phenomenon will be controlled basically.