基于多年遥感数据分析长江河口海岸带湿地变化及其驱动因子

Remote sensing time-series analysis of wetland variations and driving factors in estuarine and coastal regions of Yangtze River

研究河口海岸带湿地长时间演变对湿地保护管理和海岸带资源评估具有重要意义.本文获取长江口1979—2015年10景Landsat-MSS/TM/OLI影像和2015年13景GF1-PMS高空间分辨率数据,对比两个典型实验区分类算法,选用最优的决策树算法应用到长江口Landsat影像中,得到沿岸湿地要素近40年的面积变化情况.研究表明,2015年长江河口海岸带湿地总面积为4725 km2,自然湿地占63.5%,人工湿地占21.2%,湿地总面积相比1979年增加了662 km2,自然湿地面积减少了163 km2,而人工湿地面积增加了766 km2.长江口自然湿地面积在1979—2000年减少幅度较大,2000年后由于保护管理加强而减少幅度变小;人工湿地和建筑面积增加较为明显,主要是由于大型水库的修建和人工鱼塘开发及港口建设.湿地总的变化趋势为河口区不断淤积,自然湿地转变为人工湿地,人工湿地转变为建筑用地等非湿地;其中,滩涂面积减少283 km2,水库、养殖鱼塘和水稻田面积分别增加了92、355和319 km2,主要发生在崇明东滩和启东沿岸;非湿地中建筑用地面积增加154 km2,灌木草场面积减少147 km2,主要发生在上海和启东沿岸.同时比较分析长江口3个区域湿地驱动因子发现,北岸启东沿岸和南岸南汇东滩湿地因经济快速发展和港口水利工程修建,以及过度开垦滩涂等自然湿地使人工湿地增加明显;而长江上游径流量、区域降水和海平面上涨等自然因素控制着中支河道区(如崇明东滩)自然湿地的变化.

Studying time-series wetland changes is important for protecting and managing wetland and evaluating coastal resources. In this paper,10 Landsat images in 1979,1988,2000,2009 and 2015 as well as 13 images from GF-1 PMS in 2015 were used to study wetland in estuarine and coastal regions of the Yangtze River.We compared five remote sensing image classification methods,and we used the decision tree method which gives the best classification accuaracy.The classification results show that in Yangtze River estuarine and coastal regions,wetland area is 4725 km^2,in which the natural wetland area accounts for 63.5%（ 3000 km^2）,the human-made wetland area accounts for 21.2%（ 1002 km^2） in 2015.From 1979 to 2015,the total wetland area has increased 662 km^2-the growth of human-made wetlands positively contributed to 766 km^2 due to the development and constructions of large reservoirs,aquaculture ponds,and ports. The natural wetlands area shrunk to 920 km^2 at 2000. After that,the natural wetland coverage keeps relatively stable because of the enhancement of wetland protection and management. The general variation trend is the gradually deposition in estuarine zones and transformations from natural wetland to constructed wetland,and further from constructed wetland to the construction land. Tidal flat has decreased 283 km^2,but reservior,aquaculture pond and paddy field in Chongming Dongtan and Qidong coasts have increased 92,355 and 319 km^2,respectively.Also,built-up has gain of 154 km^2 and shrub has decreased 147 km^2. We also analyzed and compared different environment driving factors related to wetland variations in the study site.The wetlands in Qidong coasts and Nanhui Dongtan are greatly affected by human activities due to the rapid economic development and hydraulic projects.The over-reclamation of natural wetlands contribute to the growth of constructed wetland.The changes of the middle zones are mainly affected by runoff,precipitation and sea level rise.