近50a来霍林河流域下游沿岸湿地景观格局演变

以干旱半干旱生态脆弱区霍林河流域下游沿岸洪泛湿地为研究对象,利用1954和1964年地形图,1986、1996和2000年的TM遥感影像作为基本信息源,在GIS支持下,建立湿地空间数据库,通过对不同时期各湿地景观类型进行景观变化过程、景观格局指数和景观转换过程分析,揭示近50 a来霍林河流域下游沿岸湿地景观格局动态及规律。研究发现,沼泽湿地是霍林河流域下游沿岸的主导湿地景观类型,次之为河流湖泊湿地,人工湿地比重小。研究区内湿地面积的减少以沼泽湿地的贡献量最大,这是由于大面积的沼泽湿地退化为盐碱地和草地,沼泽湿地景观破碎化表现突出。河流湖泊湿地在研究时期内则表现出最快的变化速度,年均动态度达到2.60%,它的这种减少变化是由数量众多的小斑块退化为盐碱地和沼泽湿地导致。水库坑塘景观变化受流域发展水利及霍林河径流量大小控制,水田湿地则主要受后者作用。共同的一点是,受霍林河1998年特大历史洪水泛滥影响,研究区内大面积盐碱地、沼泽湿地和草地转换为河流湖泊湿地,与此同时也有大面积草地和盐碱地转换为沼泽湿地,导致两种自然湿地景观类型在2000年表现出面积扩大,景观破碎化降低,整体性增强的变化,这在一定程度上体现出洪水脉冲在退化湿地景观恢复中的生态功能。

Evaluation Patterns of the Wetland Landscapes along the Lower Reaches of the Huolin River since Recent 50 Years

Taking floodplain wetlands in the lower reaches of the Huolin River Basin,an arid and semi-arid region in China,as the research objects,in this paper the wetland spatial database is developed using GIS based on the topographic maps in 1954 and 1964 and the TM images in 1986,1996 and 2000.After analyzing the change process,pattern indexes and transition process of the landscapes at different stages,the dynamic change of wetland landscapes along the lower reaches of the Huolin River since recent 50 years is revealed.The results show that the marsh wetlands are dominant in the wetland landscapes in the lower reaches of the Huolin River Basin,then the fluviatile and lacustrine wetlands,and the proportion of artificial wetlands is low.The reduction of wetland area in the study area is dominated by that of marsh wetlands because the large-area marsh wetlands are degraded into the saline or alkaline lands and grasslands,and the fragmentation of the marsh wetland landscape is significant.The change speed of the fluviatile and lacustrine wetlands is the highest,and the annual dynamic change rate is as high as 2.60%,such reduction is mainly caused by that many small plots are degraded into saline or alkaline lands and marsh wetlands.The dynamic change of reservoir and pond landscapes is affected by the construction of local irrigation works and streamflow of the Huolin River,especially the paddy fields are mainly affected by the latter.A fact is that large-area saline or alkaline lands, marsh wetlands and grasslands were shifted into fluviatile and lacustrine wetlands due to the influence of an extraordinary flood of the Huolin River in 1998,large-area grasslands and saline or alkaline lands were changed into marsh wetlands.Thus,the areas of these two kinds of natural wetlands were enlarged,their fragmentation was reduced,and their integrity was increased,these reveal that flood plays an active ecological role in regenerating the degenerated wetlands.