关于在长江经济带布局以水质改善为目标的流域生态缓冲体系的思考

生态缓冲带能够有效减缓流域内的人类活动或自然过程对水环境和水生态系统的影响.在长江经济带构建流域生态缓冲体系，对长江生态保护修复具有十分重要的意义.讨论了构建流域生态缓冲体系涉及的生态缓冲带位置选择、缓冲体系所占最低面积比率、宽度划定等一些基本的原则要求；利用卫星遥感影像数据，提取各汇水单元的地形特征、土地利用类型特征、土壤类型、土壤侵蚀强度、水文水系等数据，对长江经济带流域生态缓冲体系进行布局.结果表明:①长江经济带内林草地是主要土地利用类型，占区域总面积的62.46%，但是分布很不均匀，主要集中在西部高地和中下游的丘陵地带，在人口密集、农田密集的区域分布偏少；城镇用地主要集中在长江中下游地区.②土壤类型空间差异显著，浙江省、江苏省、湖南省、江西省及安徽省大部分区域的土壤多是黏性比较大，污染物迁移能力较低；而污染物迁移能力较强的砂质土或者土层较薄的山地草甸土主要分布在四川省北部、西北部.水力侵蚀、风力侵蚀和冻融侵蚀均有分布，且以水力侵蚀为主，建议在中度及以上侵蚀强度区域尽量减少污染源，重点布置缓冲带，增加该区域的缓冲力度.③长江经济带范围内可以利用的中小型湿地、小型河流支浜的面积至少有1.4×104 km2，再结合林草缓冲带，就可以形成一个生态缓冲体系.④在土地利用类型分布结果基础上，叠加土壤侵蚀强度和水系分布，将污染源区、中度及以上侵蚀强度区、水体区作为缓冲对象，建立缓冲体系的重点区域，总面积约14.26×104 km2，占长江经济带总面积的6.95%.对照欧美地区的研究，6.95%的缓冲体系面积占比是偏低的，需要在长江经济带开展深入研究来确定适宜的缓冲体系面积比，推进长江经济带流域生态缓冲体系的构建. 

Layout of Watershed Ecological Buffer System Aiming at Water Quality Improvement in the Yangtze River Economic Belt

Ecological buffer zone can effectively buffer or reduce the impact of human activities or natural processes on the water environment and water ecosystems. In order to protect and restore the Yangtze River enviornment, it is of great significance to construct an ecological buffer system at the watershed level with various buffers as the main body. The concept of watershed ecological buffer system is put forward in the paper, and the principles of setting watershed ecological buffer system from the aspects of the location selection, the minimum area ratio in the whole watershed, and the delimitation of the width of ecological buffer zone, are elaborated. Based on the water environment target of the Yangtze River Economic Belt, using satellite remote sensing image data such as topography characteristics, land use type characteristics, soil type, soil erosion intensity, hydrological system, etc., to study the layout of the ecological buffer system in the Yangtze River Economic Belt. The results show that: (1) In the Yangtze River Economic Belt, forest-grassland is the main land use type, accounting for 62.46% of the total area, but forests and grasslands are distributed unevenly, mainly in the western highlands and the hilly areas of the middle and lower reaches, but in the densely populated and farmland intensive areas, they are relatively low. The urban land is mainly concentrated in the middle and lower reaches of the Yangtze River. (2) The spatial distribution of soil types is significant difference. Most soils in Zhejiang Province, Jiangsu Province, Hunan Province, Jiangxi Province and Anhui Province are relatively cohesive, with low migration ability for pollutants. Sandy soils with strong migration ability of pollutants or the mountain meadow soils with too thin soil layer are mainly distributed in the north and northwest of Sichuan. Hydraulic erosion, wind erosion and freeze-thaw erosion are all found in the Yangtze River Economic Belt, and hydraulic erosion is the dominat type. In areas with moderate and higher erosion, buffer zones should be setup to reduce pollution transfer. (3) This study shows that there are at least 14,000 km² of small and medium-sized wetlands and small rivers in the Yangtze River Economic Belt, which can form an organic combined ecological buffer system by combining these buffer elements with the forest and grass buffer zones. (4) The key area of the watershed buffer zone is about 142,600 km², accounting for 6.95% of the total area of the Yangtze River Economic Belt, which inludes the buffer zones around lakes and reservoirs, farmland and towns, erodible areas and areas where pollutants are easy to migrate. Compared with the research of European and American countries, 6.95% of the buffer system area is relatively low. It is necessary to carry out in-depth research in the Yangtze River Economic Belt to determine the appropriate buffer system area ratio, and carry out pilot demonstration, improve the coverage of the river basin ecological buffer system in the Yangtze River Economic Belt according to local conditions, and promote the construction of the river basin ecological buffer system in the Yangtze River Economic Belt.