A Preliminary Study On The Paleoenvironment Of The Mid-late Holocene In The Catchment Area Of Fuxian Lake,Based On Elements And N-alkanes

The elemental geochemistry and n-alkanes of FXH-6 core in Fuxian Lake were analyzed for reconstructing the history of environmental change and human activity in the catchment of Fuxian Lake during the past 5000 years.We discussed that the Monsoon intensity changes and the driving factors of environmental changes in the catchment area since the Middle and Late Holocene,which based on the comparison of the sedimentary records between the Fuxian Lake catchment and the southwestern monsoon regions.Analysising factor analysis of XRF core scanning of the sediments in Fuxian Lake,we could get the following conclusions:(1)elements(Ti,Mn,Fe,Rb,and Zr)may come from terrigenous detrital mineralsd,and Ca and Sr elements may relate to lacustrine carbonate precipitation.The content of these elements may be affected by precipitation in the catchment.(2)elements Al and Si also come from terrigenous debris,but they may be more indicative of human activity.The n-alkanes in the sediments of Fuxian Lake may come from the endogenous biological sources of lakes and there may have post-degradation and later transform after settlement.Since the middle and late Holocene,the n-alkanes in the sediments of Fuxian Lake were mainly endogenous,while the contribution from land-sourced plants was only the change of relative proportion.The environment of the catchment in Fuxian Lake has experienced the following three stages,during the past 5000 years.(1)5000 ~ 2300 Cal yr BP stage: The environment of the catchment was relatively stable.The surface erosion of the Fuxian Lake catchment at this stage was relatively weak,which may reflect the small surface runoff,high vegetation coverage,and relatively low precipitation.And the climate may play a leading role in the environment.(2)2300 ~ 1900 Cal yr BP stage: There was a rapid climate change during this period which was affected more by environment factors than human activities.(3)1900 ~ 0 Cal yr BP stage: Human activities may be the dominant factor in the environmental change at this stage.The vegetation coverage in the research area mightbe destroyed by human activities.Therefoe,the reduction of plant interception and the increasing of precipitation have increased the surface erosion of the catchment,and the amount of land-derived debris that flows into Fuxian Lake has increased the surface runoff.