Characteristics Of Temporal-spatial Differentiation Of Landscape In Nansihu Lake Wetland During The Past 30 Years

Nansihu Lake is not only the largest natural water source in Shandong Province,but also an important energy base in East China,having crucial strategic significance in maintaining ecological balance and promoting economic development in regions.In recent years,increasing anthropogenic disturbance to the lake caused the shortage of water resources,the damage of natural wetland ecosystem,and the decrease of antiinterference ability and stability.In order to find out the dynamic changing progress of landscape patterns and landscape pattern vulnerability in Nansihu Lake wetland from 1985 to 2015,we chose 1985?1992?2000?2007 Lantsat5 TM and 2015 Lantsat8 OLI remote sensing images as data resources and statistics and other maps as auxiliary data.Supported by RS and GIS,we selected dynamic degree model ? centre of gravity change model ? landscape pattern indices ?landscape pattern vulnerability model and geostatistical analysis model as research methods.By analyzing the dynamic process of landscape in Nansihu Lake wetland during the past 30 years,we mastered the change of landscape types,summarized the changing rules of landscape patterns on longitudinal transect and horizontal transect,studied the temporal and spatial variation about landscape pattern vulnerability,and revealed the connection among the landscape pattern vulnerability?nature factors and human factors.We hope this study can provide scientific theory for the development and protection in Nansihu Lake wetland.The results indicated that:(1)A large number of natural wetlands transferred to artificial wetlands during the study period.The roll out of reed was the largest,and the biggest area that other landscape types transferred into was breed surface.The area of reed and lotus field decreased most rapidly in natural wetlands,while the fastest speed of increased area was breed surface.The dynamic degree of synthesis land use increased first and then decreased.The highest dynamic degree of synthesis land use occurred in 1992,which meant the sharpest rangeability.Except centre of gravity of reed migrated to the Northeast and breed surface to the Southeast,other landscape types moved to the upper lake in the Northweat.(2)The whole landscape patterns in Nansihu Lake wetland changed a lot.Landscape fragmentation and diversity increased,dominance and patch connectivity decreased,and landscape shape became gradually simple and regular.The dominant landscape types changed from lake,reed and lotus field in1985 to breed surface,rice field and lake in 2015.(3)On longitudinal transect,the most obvious changes of landscape structure showed at the junction of lakes and in the areas of intensive human activity,which had strong heterogeneity and diversity and high fragmentation.The speed of land development and utilization is accelerated by violent human interference activities.On horizontal transect,with the increase of distance from the center of lake,landscape fragmentation ? division and diversity increased,landscape shape became complicated,and connectivity and landscape dominance decreased.(4)Although middle and below landscape pattern vulnerability still occupied the main area,the high risk area of landscape pattern vulnerability expanded with time.The landscape pattern vulnerability in Nansihu Lake wetland deteriorated gradually from 1985 to 2015.(5)The spatial heterogeneity of landscape pattern vulnerability increased,and the influence of non-structural factors on landscape pattern vulnerability strengthened,while spatial variability affected by spatial autocorrelation weakened slightly.Landscape pattern vulnerability had strong global spatial positive correlation,showing the significant form of spatial agglomeration.And the phenomenon of agglomeration was becoming more and more obvious.The local autocorrelation mainly based on high-high accumulation zone and low-low accumulation zone(6)Natural factors affected water-level and landscape distribution,thus changing the landscape pattern vulnerability of Nansihu Lake wetland.The main reason of deterioration of landscape pattern vulnerability was man-made activities,including social economy activity and policy system,which lead to regional expansion of high vulnerability and higher one,and notable increase of spatial heterogeneity.