Lake Sediment Records On Environmental Changes And Organic Carbon Burial Rate In Xingyun Lake Since The Late Holocene

The Late Holocene is the closest geological period to the present,which has the closest relationship with human beings and is most affected by human beings.During this period,the earth's orbital parameters and global ice volume did not change significantly.And it was in the stage of rapid development of human society,so it was helpful to identify human influence on climate and environment.Especially since the industrial revolution,human activities and industrial production have aggravated the global warming,and then caused more ecological and environmental problems.Lakes,as information records of climate change and human activity intensity,and places where organic carbon is buried,have received extensive attention.It is necessary to understand and reconstruct the change system of environment and organic carbon burial under the influence of human activities in historical period.That can be used as an important means to evaluate future climate change and carbon sequestration potential,and provide basic data which is support for future regional and even global carbon cycle estimation.Xingyun Lake,located in the middle of Yunnan Plateau,is extremely sensitive to climate change.In recent years,due to the strong influence of human activities,lakes present a series of ecological and environmental problems,which seriously restrict people's survival and regional economic development.Therefore,this study reconstructed the age model of Xingyun Lake since 2690 cal.a BP,and analyzed the change characteristics of sediment grain size,?_lf,SR,Ca CO₃,TOC,TN,TP,OCBR and other multi-proxy indicators.In addition,combined with Morlet wavelet analysis and PCA,the climatic and environmental changes in Xingyun Lake watershed since late Holocene and the influencing factors of OCBR were further discussed.On this basis,the driving mechanism of climate change in this basin is also studied.The results are as follows:1.Environmental changes and human activities of sediments in xingyun lake since late Holocene.In 2690?1890 cal.a BP,the changes of these proxies in Xingyun Lake are relatively stable,the productivity in the basin is low,the endogenous organic matter accounts for a large proportion,and the overall climate is warm and dry.In the later period,the values of TP and md increased due to the influence of human activities;In1890?1270 cal.a BP,the climate of Xingyun Lake catchment is warm and dry,and develops towards temperature and humidity in the later period.The content of TP indicates that the environment is disturbed by human activities at this time;In1270?610 cal.a BP,the climate changes from warm humidity to cold humidity and the impact of human activities is extremely significant.But in 830?680 cal.a BP,the climate is characterized by cold and dry;610 cal.a BP to now,the climate is relatively cold and humid.And in 690?200 cal.a BP,the humidity increases slightly.The sudden increase of organic matter content in surface sediments is not only related to climate change and human activities,but also influenced by the rapid deposition rate at the top,the short burial time of TOC,and the incomplete mineralization of some TOC.2.Change trend and influencing factors of OCBR in Xingyun Lake since late Holocene.In 2690?1890 cal.a BP,the total OCBR is greatly affected by exogenous OCBR with an average of 22 g/(cm²·a);In 1890?1270 cal.a BP,compared with the previous stage,the total OCBR is obviously larger,and the maximum value can reach116 g/(cm²·a).In these two stages,human activities are relatively weak,and temperature changes have a significant impact on OCBR of sediments in Xingyun Lake.In 1270?610 cal.a BP,the source of organic matter is still mainly exogenous and the total OCBR decreases gradually from high value.It may be due to the decrease of vegetation coverage,the increase of erosion intensity and the oxidation and decomposition of organic matter;610 cal.a BP to now,the change trend of total OCBR is relatively stable,and the rapid increase of surface rate is related to the development of agriculture and animal husbandry and the use of chemical fertilizers.3.Climate Change Cycle in Xingyun Lake since late Holocene.Between 2400 cal.a BP and 1200 cal.a BP,the periodic signal of climate change in Xingyun Lake is mainly 500 a,and the periodic signal of 250 a is also obvious;Since 800 cal.a BP,the environmental changes of Xingyun Lake have appeared short-period signals on the scale of 100 years and 10 years.4.Driving Mechanism of Environmental Change in Xingyun Lake since late Holocene.Comparing the climate and environmental changes between Xingyun Lake and Dongge Cave,it is found that the multi-proxy of Xingyun Lake and the oxygen isotope of stalagmites in Dongge Cave show relatively cold and dry climate characteristics with the decrease of solar radiation intensity.Therefore,the change of solar radiation is of great significance to the change of climate and environment in monsoon region.The 500-year climate change cycle in Xingyun Lake further shows that the change of solar radiation is the main factor leading to the change of climate environment.But the short-period signal in recent thousand years reveals that human activities have a certain influence on the environmental change in Xingyun Lake.