基于数字化海图与多时相卫星遥感的 长江口九段沙形成演化研究*

九段沙位于长江河口南北槽之间,为新形成的河口沙洲,其形成距今只有50年的历史。利用对大通水文站1950~2003年的水沙资料的分析,结合对数字化海图和多时相卫星遥感影像的解译及野外现场考察,对九段沙形成过程和演化过程中的面积、体积、高程和地貌特征等进行了综合研究,研究结果表明九段沙自形成以来面积、体积总体上是处于增大过程中,高程也在增高,成陆化作用明显。但由于来水来沙的不同和河口动力作用,这种增长不是线形的,有时因受到冲刷而面积减小,高程降低。利用采自九段沙上沙的短柱状样分析发现潮间带和潮上带的沉积速率不同,植物群落对九段沙的形成演化具有一定的影响,但总体上九段沙正处于从河口沙洲向河口沙岛的演化过程之中。九段沙的植被保持着自然演替的原生状态,植物群落结构简单,生物多样性尚较低,以芦苇群落为代表的高等湿地植被主要分布在九段沙潮间带上部和潮上带,九段沙属于发展过程中的河口湿地。

FORMATION AND EVOLUTION OF THE JIUDUANSHA SHOAL AT THE CHANGJIANG ESTUARY BASED ON THE DIGITIZED SEA CHART AND MULTI-TEMPORAL SATELLITE IMAGES

Jiuduansha Shoal is originated in 1954 due to a flood which caused the Tongsha Tidal Flat tentatively isolated, initiating this new estuarine island in the Changjiang Estuary. During the past half century, in general sense the size, volume, and elevation of the Jiuduansha Shoal have been increased, although in some years, because of insufficient sediment offering or strong dynamics from flow and wave and tidal currents, the size and elevation might be decreased. Based on the data of water and sediment discharge during 1950 - 2003 from the Datong Hydraulic Station, the field survey in 2003, as well as the digitized sea chart and satellite images, it has shown that the Jiuduansha Shoal is in the process changing from an estuarine shoal to an estuarine island. The analysis of short column section collected in inter-tidal between these two zones, with that zone and supratidal zone has shown in the former 0. 74cm/a, and the that the sedimentation rate is different latter 3.34cm/a. The vegetation on Jiuduansha Shoal is in its natural state, with simple composition and low diversity. Phragmites occupying the upper inter-tidal zone and supra-tidal zone. Along with the development of the shoal, th is in the course of changing from a wetland one to a terrestrial one. dominates, e vegetation