长江口盐度的时空变化特征及其指示意义

Characteristics of temporal and spatial variation of salinity and their indicating significance in the Changjiang Estuary

2003年2,7月在长江口进行了枯、洪季大规模综合水文测验,布控范围西自江阴东至口外-20m,测验站点覆盖4条入海汊道.测验资料统计分析表明:(1)径流大小、汊道分流比、潮汐强弱和地形条件是控制盐度时空变化的主要要素;(2)在盐度空间分布上从大至小的顺序是:北支,南槽,北槽,北港口;(3)北支枯季发生盐水倒灌南支,而洪季可有一半以上区段为淡水所控;在其他3个入海汊道中,北港口门段是长江口盐淡水混合相对最弱的区段,盐度潮周期变幅最大,但洪枯变幅最小;南槽的盐淡水混合较强,盐度潮周期变幅较小,但洪枯变幅很大;北槽介于两者之间.(4)盐度时空变化反映洪季北支、南港和南槽分流比都有所增加.

Large scale hydrological observations in the Changjiang Estuary have been respectively carried out in February and July, 2003. The survey range extends from Jiangyin to -20 m iso-depth out of the mouth, and the measuring stations distribute in four outlets. Field observations show that: (1) temporal and spatial variation of salinity is mainly controlled runoff discharge, flow distribution ratio of the outlets, tidal range and geomorphologic situation; (2) the order from high to low for the distribution of salinity is the North Branch, South Passage, North Passage, and the North Channel; (3) the saltwater flows backwards from the North Branch to the South Branch during the dry season, but more than half section of the North Branch is still held by freshwater during the flood season; the mouth sector of the North Channel, where tidal variation of salinity is major and seasonal variation is minor, has stratified interface between saltwater and freshwater; the South Passage, where tidal variation of salinity is minor and seasonal variation is major, is characteristic of mid-strongly mixed type; and the situation of the North Passage is between situations of the North Channel and the South Passage; (4) the temporal and spatial variation of salinity reflects that flow distribution ratio to the North Branch, the North Channel and the South Passage increases to a certain extent in the flood season.