Assemblage Characteristics Of Ostracods And Environmental Changes In Xingyun Lake During The Last 200 Years

The Yunnan-Guizhou Plateau is located on the east slope of the Tibet Plateau,which is influenced by the confluence of India Southwest monsoon,North Africa Continental Southwest Monsoon and the southeast monsoon of the Pacific.Xingyun Lake is located in the eastern part of the Yunnan-Guizhou plateau,Jiangchuan-basin region,which affects the climate of the central Yunnan province significantly,and carries the economic lifeline of more than 200,000 people around.However,with the rapid progress of human civilization,pollution of the surrounding environment has been increasing,there has been a series of economic development victims,among them,Xingyun Lake bear the brunt.In this paper,we study the assemblage characteristics and the distribution of Ostracods based on XYL-01 core drill in Xingyun Lake.Combined with the grain size,carbonate,total organic carbon,total nitrogen,carbon and nitrogen isotope,and other environmental indicators.Identify the factors of climate and human activities,while comparing,verifying the archaeological data of the region,human history literatures and modern records,etc.Explore the relationships between the environmental changes of the lake and human activities,then rebuild the environmental changes in Xingyun Lake during the past 200 years:(1)1850~1890 a A.D.,Natural Evolution Stage.The assemblage characteristics of Ostracods is Cypridopsis vidua-Cetacella inermis,the abundance is high,but the diversity is low.Warm and humid climate,deep water,the gradual increase of submerged plants,very suitable for living organisms,the water environmental changes mainly affected by climatic conditions.The value of TOC and TN are low,so it should be poor nutrition.(2)1890~1985 a A.D.,Human Activity Impact Stage.The assemblage characteristics of Ostracods is Cypridopsis vidua-Cetacella inermis-Cypria kreapelini-Eucypris cf.cuneata,the abundance increased slightly and then decreased speedly,the diversity increased by step-type.This stage can be further divided into 3 sub stages: 1890~1950 a A.D.,the impact of human activities is small,and the temperatures increased slightly compared with the previous period,but still warm and cool,the drought events of 1940 s have a clear response to the lake sedimentary records;1950~1970 a A.D.,human activity gradually strengthened,the C3 plants(the majority of trees,shrubs,and grasses which adapted to grow in cold and humid environments)declined within the regions.As human productivity is still low at this stage,the level of eutrophication in the water changes little.But "Great Leap forward" lakes incident in 1950 s caused the water level and trophic status of the water body to decline obviously,the water environment has changed obviously;1970~1985 a A.D.,human activities more intense,as the explosion of stone residue was thrown into the lake,which leads to the specises of Eucypris cf.cuneata back.It shows that the species of ostracod prefer nutrient or high salinity environment.Compared with the modern records and human history literatures,the event of human activitives are related to the climate changes.(3)1985 a A.D.~present,Eutrophication Stage.The assemblage characteristics of Ostracods is Cypridopsis vidua-Cetacella inermis-Cypria kreapelini-Eucypris cf.cuneata-Candonocypris novaezelandiae-Schellencandona cf.belgica,the abundance is low,but the diversity is high.Under the influence of human activities,increased the greenhouse effect,temperatures were significantly increased,but the average annual rainfall is uneven.Agricultural,industrial and domestic sewage discharge make the lake eutrophication seriously,blue-green algae outbreak massively,new species may be more adaptable to polluting environments.If the project of “ Xingyun-Fuxian Lakes Stream Diversion” after 2003 a A.D.can imprive the environment of the lake,for now,in the short term,there is no obvious effect.