The pollution of the Yunzhong Lake in the Jiugongshan Scenery Spot of Tongshan County,Hubei Province has been aggravating with each passing day in the recent years,which has aroused concerns from all walks of life.However,it is still unclear about trajectory and the main causes of the changes in ecological environment of this lake.The history of the environmental changes in the Yunzhong Lake during the past fifty years were reconstructed based on chronological and physic chemical analyses of the sediments in the lake for trace elements,organic carbon and particle size composition,coupled with cluster analysis and geo accumulation indexes.Results show that 14 trace elements were found in the sediment of the lake and their contents varied with depth of the sediment in similar trends with depth and correlated positively with each other,indicating that the fourteen elements come from the same material source.The trace elements in the sediment before the 1980s varied very slightly in content,indicating that the environment of the catchment did not change much during that time period,but they began to fluctuate in content after the 1980s,with two drops at the depths of 10 cm and 4 cm.The low value in the lower layer corresponded to the trend of the sedimentary becoming coarser in particle size,which could probably be attributed to climatic changes and the development of tourism,while the low value in the upper layer was concurrent with an increase in organic carbon content,reflecting the eutrophication process of the water body and dilution effect of the input of organic matter on contents of the trace elements. V/Cr ratio of the elements increased significantly and exceeded 2.0 after 1993,reflecting that the bottom layer of the water body turned to be oxygen deficient.Geo accumulation indices of all the elements are lower than 0.5,indicating that the lake is only slightly polluted with heavy metals.Comprehensive analysis of the research data reveals that the environment was relatively stable before the 1990s,and then the catchment environment underwent significant changes,particularly the water body environment,showing a trend of deterioration.Therefore,it is essential and urgent for us to strengthen water pollution control in the Jiugongshan tourist areas,in order to protect this precious alpine lake ecosystem.