近期长江北支口门圆陀角附近潮滩地貌动态变化

圆陀角位于长江北支岸线与江苏海岸线的交会处,独特的互花米草潮滩、淤泥质光滩环境和复杂的河海沉积动力,决定了潮滩地貌对海洋环境变化的响应具有敏感性。由于大规模的围垦,圆陀角附近过去40年来海岸线向东推进了6km。根据2006年以来多次的野外调查和室内粒度与钻孔岩芯的¹³⁷Cs分析, 2006年以来圆陀角附近潮滩淤积明显加强,由¹³⁷Cs时标估算的互花米草滩多年平均沉积速率为2.3cm/a, 2006~2008年观测到的互花米草滩淤积速率>4cm/a,粉砂淤泥质光滩的淤积速率更高;圆陀角风景区内互花米草滩前缘陡坎在风暴潮影响下侵蚀后退,并因粉砂淤泥质光滩的快速淤长而消亡,圆陀角附近潮滩地貌动态是对人类围垦活动、风暴潮与潮汐海洋动力的综合响应,互花米草与光滩快速淤积是近期圆陀角附近潮滩地貌演化的主要特点。

Recent morphological changes of tidal flat at Yuantuojiao Point,estuary of the north branch of the Yangtze River

Yuantuojiao Point is located at intersecting point of the coastal lines of the north branch of the Yangtze River and the south Yellow Sea. The specific geographic location with the salt marsh environment (tidal flat) and the complexity of regional morphological dynamics that determined the tidal flat at Yuantuojiao Point had the sensitive response to the environmental changes. Because of the rapid sea reclamation, the coastline has shifted eastward over 6 km in the past 40 years. Based on the field investigation, grain size analysis of the surface sediments in the tidal flat and the ¹³⁷ Cs dating analysis of the short core samples, the tidal flat at Yuantuojiao Point has experienced the extensive siltation since 2006. The annual average sedimentation rate was about 2.3 cm/a from 1963 to 2006 according to the ¹³⁷ Cs dating analysis. From 2006 to 2008 the observed sedimentation rate was more than 4.0 cm/a in the salt marsh region and even high sedimentation rate occurred on the muddy tidal flat. The front cliff of the salt marsh retreated under the storm surge condition compounding with the increasing sedimentation in the muddy tidal flat, which resulted in the extinction of the cliff. The recent morphological changes of the tidal flat at Yuangtuojiao Point was the response to the sea reclamation, storm surge and the tide process. Both the salt marsh and the muddy tidal flat that experienced the accelerating sedimentation are the main characteristics of the morphological changes of the tidal flat at Yuantuojiao Point.