Vegetation System Evolution And Analysis Of Key Drivers In Dali-nor Lake Region Since 2400 Cal.a BP

Lakes,as the nodes of the interaction of land system elements,are an important part of the process of regional environmental evolution.The sediments of the lakes have been suggested as a carrier for analyzing and reconstructing the evolution of regional ecological environment.Dali-nor Lake(43°13??43°23? N,116°26??116°45?E) is located in the northern edge of East Asian Summer Monsoon.Its sediments recorded the evolution process of the lake might response to the ecological environment.In this study,a core of 238 cm in length was collected at a depth of 9 m in the lake.The age at the bottom of the core is about 2355 cal.a BP by dating.Based on biogeochemical methods,the n-alkane and sterol were tested,and combined with SN and EASM data,this paper reveals the evolution of the ecological environment and the driving mechanism in the Dali-nor Lake region since 2400 cal.a BP.The carbon number distribution of n-alkanes in the sediments of Dali-nor Lake ranges from C17 to C33.There are three distribution characteristics:single peak distribution with C25 as the main peak,double peak distribution with C19 and C25 as the main peak,and double peak distribution with C25 and C27 as the main peak,accounting for 57%,30%,and 13% of the total samples respectively.It's suggested the source of biomarkers in the sediments was the common input of algae,aquatic plants,and terrestrial plants,in which mainly aquatic plants was dominated.The environmental proxy index established by the n-alkane content in the sediment was used to reconstruct the eco-environment evolution in the Dali-nor Lake region since 2400 cal.a BP.It is roughly divided into 6 stages,of which stages 1,3,and 5(75 cal.a BP-to-date,985-600 cal.a BP,2180-1550 cal.a BP) were in warm and wet climate stages,and stages 2,4,and 6(600-75 cal.a BP,1550-985 cal.a BP,2355-2180 cal.a BP) were in cold and dry climate stages.The change of the index parameters of n-alkanes shown that the evolution of ecological environment in the region has not only been consistent with the global climate events(i.e.Rome Warm Period,Dark Cold Period,Medieval Warm Period,Little Ice Age,and 20th Century Warm Period) since 2400 cal.a BP,but also affected by the changes of summer monsoon precipitation in East Asia and the cold and warm changes in the lake region.The n-alkane content in the sediment reflects the succession process of algae,aquatic plants and terrestrial plants in the Dali-nor Lake region;the sterol content reflects the succession of plankton in the lake.Among them,the content of phytoplankton is significantly higher than that of zooplankton,but there is a certain consistency between the two trends,while the trends of diatom,chlorophyceae and cyanobacteria have their own characteristics.The results of spectrum and wavelet coherence spectrum analysis shown that the evolution of eco-environment was related to the solar activity,East Asian Summer Monsoon,Atlantic Muhidecadal Oscillation,and Pacific Decadal Oscillation.Comprehensive analysis shown that the local climate change was from warm and wet to cold and dry in the Dali-nor Lake since 2400 cal.a BP.and the evolution process of plankton also reflected the basic consistency with the climate change.In the warm and wet climate stage,the effective humidity of the region was high.As a result of this,woody plants were dominant,aquatic plants grown vigorously,lake nutrition was good.In the cold and dry climate stage,the growth of algae was fast,the proportion of herbaceous plants was increased,and the primary lake was growing with a low productivity.Overall,The solar activity affects the intensity of East Asian Summer Monsoon and drives the evolution of eco-environment in Dali-nor Lake region.