The Relationship Between Human Actitivies And Environmental Records Of Typical Plateau Lake: Dianchi Lake And Fuxian Lake

In recent years,with the rapid development of socio-economy and urbanization,lake environmental problems are becoming increasingly serious.Many lake systems in the world are increasingly disturbed by human activities.The impact of human activities on environmental change has become the focus of global research.Lake sediments faithfully record the information of lake environmental evolution and human activities in the basin,which is a good carrier of lake evolution.Due to the special geographical location of plateau lakes,with the strengthening of human activities,lake environmental problems are becoming increasingly prominent.Understanding the changes of lake environment in the past is of great significance to the governance and management of lake environment in the future.This paper selected typical plateau lakes Dianchi and Fuxian.Based on the dating results of radionuclides ²¹⁰Pb and ¹³⁷Cs,a chronological model was established.On this basis,the changes of biogenic elements（TOC,TN,TP and phosphorus forms）and heavy metals（Cr,Ni,Zn,As,Cd,Pb,Hg）contents,sedimentary fluxes,isotopic compositions(δ¹³C,δ¹⁵N)and C/N ratios in the sediment cores were analyzed.Based on human activities（socio-economic conditions such as population and industrial development）and natural changes（meteorological conditions such as rainfall）,Discuss the relationship between the sedimentation process and natural evolution and human activities in Dianchi and Fuxian in recent 100 years,and reveal the degree and key period of the impact of human activities on the lake environment.The main conclusions are as follows:（1）The variation of ²¹⁰Pb and ¹³⁷Cs indicates that the sedimentary ages of Dianchi and Fuxian core（about 40 cm）are 120 and 280 years,respectively.In the past 100 years,the accumulation rate of Fuxian has increased significantly,which is closely related to the human activities around the lake.（2）The meteorological data show that there is no significant change of natural environment in Dianchi and Fuxian Basin in recent 100 years.However,human activities have had a significant impact on the sedimentary environment of Dianchi and Fuxian,and the impact period and extent of the biogenic elements and heavy metal deposition in the two watersheds are significantly different.The key period for human activities to influence Dianchi and Fuxian is after 1960s and 1980s,respectively,and the degree of human disturbance in Dianchi is far greater than that in Fuxian.After the21st century,with the implementation of sustainable development and environmental protection policies,man-made pollution emissions have been greatly reduced,and the water environment of Dianchi has been significantly improved.In the 21st century,with the continuous strengthening of environmental protection control,the pollution of Dianchi and Fuxian has improved significantly.Human activities have significantly affected the material cycle and lake water environment.In recent decades,changes in the sedimentary environment of Dianchi and Fuxian are closely related to human activities.（3）The analysis of sediment C/N,δ¹³C andδ¹⁵N showed that the source of organic matter in the sediments of Dianchi and Fuxian gradually shifted from internal sources to external pollution inputs.The contents of TOC,TN,TP and fluxes in the sediments of Dianchi and Fuxian increased with the time of deposition.After 1960s,TOC and TN in Dianchi increased most obviously.TP content increased rapidly in 1960s-1990s,and then decreased.During the 1960s-1990s,soil erosion intensified,which promoted the accumulation of Ca-P in sediments.After the reform and opening up,the rapid development of urbanization and industrialization in Dianchi Basin,during this period,the input of industrial wastewater and domestic sewage increased sharply,resulting in the increase of Fe/Al-P.After the 1990s,the phosphorus content in Dianchi decreased due to the government’s increasing efforts to control it.Through the analysis of phosphorus forms,it is found that the phosphorus forms increase with the increase of sedimentary age.After 1980s,the TOC,TN contents and sediment fluxes of Fuxian increased rapidly.Industrial and agricultural activities（sewage discharge and fertilizer application,etc.）are the main human factors causing the changes of carbon and nitrogen in Dianchi and sediment.（4）Human activities have caused a significant increase in the input flux of heavy metals.The Cr,Ni,Zn,As,and Pb elements in the sediments of Dianchi and Fuxian belonged to low pollution in the sedimentary history.Since the 1960s,Cd and Hg have become the main heavy metal pollution elements in the sediments of Dianchi and Fuxian,at moderate-severe pollution and moderate pollution levels,respectively.Heavy metal pollution in Dianchi and Fuxian is controlled by the industrial economic development of the basin,and Cd and Hg pollution mainly comes from non-ferrous metal smelting and ore mining in the basin.