如东县紫菜养殖对潮滩地貌的冲淤影响

摘要

在放射性核素210Pb测年分析的基础上,综合运用沉积物粒度、沉降板测量及遥感影像解译等方法,对如东县紫菜养殖前后潮滩沉积环境尤其是潮滩地貌的冲淤变化进行了初步探讨.研究结果表明:在以年计算的长时间尺度上,紫菜养殖对潮滩地貌的冲淤不会产生明显影响,紫菜养殖区沉积物的沉积速率符合自然状况下沉积物的沉积速率,这一变化规律与紫菜养殖区沉积物粒径变化规律相一致.但在紫菜养殖期间,由于网帘、竹竿的架设及紫菜对水动力的阻滞作用,会大大加速该区域潮滩的沉积,此期间紫菜养殖区呈淤积状态;而一旦进入非紫菜养殖期间,潮滩在水动力作用的冲刷下又将恢复到原来的自然状态,滩面保持冲淤平衡,这一变化规律与沉降板泥沙厚度测量及遥感影像分析结果互为印证.因此,潮滩紫菜养殖本身并不会对养殖区潮滩地貌的冲淤变化产生明显的影响,但养殖紫菜期间所引起的频繁人类活动,在一定程度上会加速该区域低潮滩的侵蚀.%The tidal flats along the Jiangsu coastline, China, are unique in the world, in terms of their huge geometric scale, abundant sediment supply associated with the large rivers, silt-dominated sediments and the geomorphologic assemblage of coastal tidal flats and an offshore radiant sand ridge field. Tidal flats of Rudong county located in the eastern part of Jiangsu province along the South Yellow Sea, which characterized by semidiurnal tides and strong tidal flow. Owing to the active tidal processes and the abundant sediment supply, the tidal flats here are well-developed and width from several kilometers to tens kilometers.rnWith the development of economy the tidal flats of Rudong county are mostly developed by human activities such as reclamation at the high-tidal flat and seaweed farming at the low-tidal flat. In the last decade porpyra cultivation grows rapidly in the tidal flat of Rudong county and has became the mainstay of the local economy.rnIt is a hot issue in the local society that whether and how the porphyra cultivation will impact the sedimentary and morphological evolution of tidal flat when the culture scale become larger more and more in the future. Common understanding of the consequence of the cultivation is dominated by simplification and empiricism which underlie many environment development policies.rnIn this paper four sediment cores(92 ~ 151 cm) were collected perpendicularly to the coast line in tidal flat of the eastern Yangkou Harbor,Rudong County. 210Pb dating and grain size analyze have been processed aiming to get the annual sedimentary velocity of this area. Besides, the daily sedimentary velocity has been estimated through placing settlement plates. Furthermore, remote sensing imageries at January and August, in accordance with the period of porphyra culture, are processed to show morphological evolution of tidal flat of this area, respectively on the year of 2002, 2003 and 2005. Results show that the cultivation of porphyra in this area increases the rate of sedimentation and expands the siltation area slightly. However,once the cultivation of porphyra is stopped,the extra accumulated part will be eroded in a short period of time. In the present work, it was proved that the cultivation of porphyra has actually very limited influence on the sedimentation of tidal flat and the morphological evolution of tidal marshes in the long run equilibrium. Meanwhile the human activities during the cultivation of porphyra accelerate the erosion rate of tidal flat in certain degree, which should be paid attention to by the local government and make further research.