近33年白洋淀景观动态变化

湿地具有重要的生态功能,由于各种因素的影响改变了湿地水文条件,并且导致湿地退化。利用1974、1987、1996和2007年遥感影像,使用ERDAS 9.1、ARCGIS 9.2和FRAGSTATS 3.3,分析了白洋淀景观动态变化过程及其驱动力。研究结果表明:从1974至2007年,白洋淀湿地面积从249.4km²下降到182.6km²,农田和居民地面积分别从70.0、2.1km²增加到126.4、12.5km²;在景观水平上,斑块密度、景观形状指数和香农多样性指数增加,蔓延度减小,景观破碎化程度增加,优势景观类型湿地对整个景观的控制作用减小;在类型水平上,明水面和沼泽的斑块密度和周长-面积分维数增加,最大斑块指数、平均斑块面积和连接度减小,居民地的斑块密度、最大斑块指数、平均斑块面积、周长-面积分维数和连接度都增加,农田的斑块密度、最大斑块指数和连接度增加,平均斑块面积和周长-面积分维数减小;水位变化是影响白洋淀景观变化的主要因素,水位升高会使湿地面积增加,反之,使湿地面积减小;流域人类活动和降水量变化是白洋淀水位和景观变化的重要驱动力。引水补淀只能暂时缓解白洋淀缺水问题,从流域角度考虑,实施有效的水资源管理方式,才能从根本上解决白洋淀湿地退化的问题。

Landscape dynamics of Baiyangdian Lake from 1974 to 2007

Wetland has important ecological services including water resources regulation, quality purification, and biodiversity conservation. These services were greatly impacted by landscape patterns and their changes, which were closely linked to human activities and climate change. Thus the research on wetland dynamics and its influencing factors is of significance to ecological services of wetland. In this study, landscape changes and its drivers of Baiyangdian Lake between 1974 and 2007 were analyzed based on satellite images of 1974, 1987, 1996 and 2007, using ERDAS 9.1, ARCGIS 9.2 and FRAGSTATS 3.3. Results showed that the area of wetland decreased from 249.4 km² to 182.6 km² between 1974 and 2007, but farmland and residential area increased from 70.0 km² to 126.4 km², and from 2.1 km² to 12.5 km², respectively. At landscape level, values of patch density, landscape shape index and Shannon's diversity index increased, but that of contagion index decreased. It indicated that landscape fragmentation and landscape diversity increased, shape of patches became complicated, and the relative dominance of wetland decreased in the study area. At class level, there was great difference between different kinds of landscape components. As for water area and marsh, values of patch density and perimeter-area fractal dimension increased, but those of largest patch index, mean patch size and patch cohesion index decreased. As for residential area, values of all five indices decreased during the study period. As for farmland, values of patch density, largest patch index and patch cohesion index increased, but those of mean patch size and perimeter-area fractal dimension decreased. Among all influencing factors, water-level fluctuation was the main one for landscape changes of Baiyangdian Lake, and area of wetland was positively influenced by water level of the lake. Human activity and precipitation change of the basin were important drivers of water-level fluctuations and landscape changes of Baiyangdian Lake. As the growth of population, grain production and precipitation, values of patch density and landscape shape index decreased after increasing to a peak value, while those of Shannon's diversity index increased after decreasing to the lowest point. Value of contagion index decreased when population or grain production increasing, and it increased after decreasing to the lowest point when the precipitation increasing. The diversion of water to Baiyangdian Lake raised the water level temporarily and had significant benefits on the wetland ecosystem, but it was not sustainable. To solve the ecological degradation of the lake, effective water resources management must be implemented at the basin scale.