特大咸潮对珠江入海河段环境要素的影响

Influences of saline water intrusion on environmental elements in outlet section of Zhujiang River

2004年底至2005年初珠江三角洲流域发生了40a以来的特大咸潮,对珠江入海河段的环境要素产生较为明显的影响。在广州市区河段至伶仃洋的珠江主航道上共设置17个站进行取样分析。结果表明,咸潮上溯使入海河段的盐度大幅提升,而且入侵到广州市区河段。广州下游河段的硝化过程被很大程度地抑制,硝酸盐、亚硝酸盐和铵盐含量仅表现为随入海方向逐步稀释,与历史资料相比差异明显。从营养盐含量来看,与2004年的数据对比显示无机氮和硅酸盐有较大程度的下降,磷酸盐含量则有一定程度的上升。N/P值显著下降,虎门以下河口站点下降了近30倍,变化趋势也由沿入海方向递增转为递减;N/Si值则升高为原来2—4倍,市区河段更高。水体中营养盐结构变化显著。溶解氧含量增加,表观耗氧量降低,其平衡点上移了18km;受输入减少及咸潮稀释等作用的影响,广州下游入海河段的COD含量有一定程度的下降,但严重污染的广州市区河段水体中的COD含量仍保持在很高的水平,存在明显的贫氧现象。

The intense saline water intrusion taking place in the outlet section of the Zhujiang River in the end of 2004 and beginning of 2005 has been the most serious one since the late 40 years, and has brought some visible influences on the environment elements in the outlet section of the Zhujiang River. Seventeen sampling sites were set up along the Zhujiang River from the Guangzhou urban section to the Lingding Sea. The results showed that the saline water intrusion considerably upgraded the salinity in the outlet section of the Zhujiang River and the intrusion distance of saline water was about 50km farther than the average in the last year, and even had an influence on the Guangzhou urban section of the Zhujiang River. The nitrification process was considerably bated in the section from Xinzhou to the estuary, and the concentrations of nitrate, nitrite and ammonium showed decreasing trends towards the sea, which was obviously different from its usual conditions. Compared with the data in April of 2004, the concentrations of dissolved inorganic nitrogen and silicate decreased, while that of phosphate increased obviously. The nutrient structure was changed, with decrease of N/P ratio and increase of N/Si ratio. The saline water intrusion also influenced the contents of DO and AOU, their balance site moved about 18km upward, the exceedingly low content of oxygen still presented in the Guangzhou urban section. The concentration of COD was reduced due to the dilution of saline water intrusion as well as the decrease of input from land, especially in the Guangzhou downriver section of the Zhujiang River; but it still kept at a high level in the Guangzhou urban section because of serious pollution.