长江中游大型通江湖泊湿地景观格局演变特征

鄱阳湖和洞庭湖湿地是长江中游仅有的两个天然通江湖泊湿地,具有不可替代自然和人文价值。近年来,尤其是三峡工程运行以后两湖湿地景观格局发生改变,对区域生态系统平衡和社会经济发展产生重要影响。以Landsat 7为数据源,通过决策树分类及高斯回归的方法定量评估了三峡工程运行前后两湖湿地景观格局的演变特征及其差异性,旨在正确认识大型水利工程的生态效应,为湿地保护与重建提供科学依据。结果表明:2000~2014年,洞庭湖枯水期水位变化不明显。从历史演变特征来看,虽然有少部分植被挤占泥滩和水体,但总体上3种湿地景观类型面积变化不大。相比之下,三峡工程运行后鄱阳湖枯水期水位显著下降,水体面积萎缩近14%,植被面积增加约8%。与2000年相比,2014年鄱阳湖植被分布高程下降了1 m多。不同程度的干旱胁迫是形成两湖湿地景观格局差异性演变特征的主要原因。

WETLAND LANDSCAPE PATTERN EVOLUTION OF LARGE YANGTZE-CONNECTED LAKES IN THE MIDDLE REACHES OF YANGTZE RIVER

The wetlands of Poyang Lake and Dongting Lake,both of which were naturally connected to Yangtze River,are of irreplaceable natural and cultural significance.In recent years,especially after the operation of the Three Gorges Dam (TGD),wetland landscape patterns of the two lakes have changed,which has significant impacts on the regional ecological balance and social economic development.Based on the datasets derived from Landsat 7,we quantitatively assessed the changes of the wetland patterns before and after the operation of TGD and identified the differences between the two lakes,by employing the Decision Tree Classification and Gauss Regression method.This study aims to better understand the ecological effects of large water conservancy project and to provide a scientific basis for wetland protection and reconstruction.The results suggested that there was barely change of the Dongting Lake water level during the dry period between 2000 and 2014.The historical evolution patterns of Dongting Lake wetland indicated that although a small part of vegetation occupied the region of mudflat and water body,there was little change in area of these three typical wetland landscape types.By contrast,the lake level of Poyang during the dry period dropped significantly after the operation of TGD.Moreover,the water body has shrunk by nearly 14％ and vegetation coverage has increased by around 8％.Compared with the situation in 2000,the evaluation of vegetation distributed in the wetland of Poyang Lake in 2014 has decreased more than 1 m.The different evolution patterns in the wetlands of the two lakes were mainly attributed to the different extents of drought stresses.