洞庭湖湿地景观格局变化以及三峡工程蓄水对其影响

CHANGES OF LANDSCAPE STRUCTURE IN DONGTING LAKE WETLANDS AND THE EVALUATION ON IMPACTS FROM OPERATION OF THE THREE GORGES PROJECT

通过对近20a遥感影像的解译分析,结果表明:洞庭湖湿地景观格局变化较为迅速,在几种湿地景观类型中,芦苇分布面积稳定增长,由475km2增至751km2,年均增加13.1km2,湖草的分布面积比较稳定,而水面与泥滩的分布面积则大幅减少。湿地格局演变总体上呈现芦苇挤占湖草的分布空间、湖草挤占水面泥滩的态势。分析认为泥沙淤积和湖泊水情变化改变了洲滩的淹水历时,引起植被分布的变化,是影响洞庭湖湿地景观格局的主要因素。2000年后,随着泥沙淤积减缓,湖泊水情变化对湿地景观格局影响更为重要,其中三峡水库的运行使洞庭湖中、低位洲滩提前出露,淹水历时缩短,导致湖草的分布界线明显向下延伸。

The analysis of landscape structure in the Dongting Lake region by remote sensing interpretation indicates that the wetlands structure changed significantly in the past 20 years. Among the four major types of classification （i. e. reed,grass,water and mudflat） ,the distribution area of reed increased steadily （from 475 km2 to 751 km2） ,the area of grass was relatively stable,the area of water and mudflat was substantially reduced. In this process, some grass communities were replaced with the reed communities, and the grass communities invaded the mudflat areas. Sediment and hydrological regime were two main factors affecting the change of landscape pattern in Dongting Lake wetlands,but this situation changed after 2000 with the impact of sharp reduction in sediments and prolonged low flow period. Analysis by coupled hydrological calculation and spatial analysis on landscape reveals that although the elevations for different type of vegetation covers varied in different regions, their inundation patterns were much similar. Sediment and hydrological regime changes had triggered vegetation succession by changing the wetland inundation patterns. The operation of the Three Gorges Reservior had shortened the inundation period of middle-lower wetlands,which in turn resulted in the grass invasion to water area up to 0.5 m.