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.