The Ostracode Assemblages Of Lacustrine Sediments And Its Environmental Implications Of Yilong Lake

As a water body,lakes are widely distributed on the surface of the land.There are many plateau lakes on the Yunnan-Guizhou Plateau.The information on environmental surrogate indicators in lake sediments is extracted.The reconstruction of past environmental changes is an important research content of global climate change.As a good indicator of paleontology,the ostracod has become a good carrier for the study of environmental change,and it has received more and more attention from researchers.The research area of this paper,Yilong Lake,is located in the low latitude plateau near the Tropic of Cancer,belonging to the subtropical monsoon climate.At present,there are few studies on the past environmental changes on the short-term scale of the Yilong Lake.Therefore,this paper uses the biological indicators of the metamorphic species in the lake sediments to recover its environmental changes.(1)A total of 11 392 petal-shaped shells were found and identified in 69 sediment samples,celebrity: Candonocypris novaezelandiae,Cypria kreapelini,Candona sp.,Yunnanicyhere cf.reticulate gen.et sp.nov,Eucypris cf.cuneate and Candona candida.Among them,the wedge-shaped true star E.cf.cuneata is a once extinct species in the strata,its re-emergence in modern lakes may be related to human activities,human activities lead to the recovery of its dormant eggs,which may prefer an eutrophic shallow water environment.Reticulated Y.cf.reticulate gen.et sp.nov belongs to the endemic genus of Yunnan,we speculate that this kind of like a warm and quiet fresh water environment.C.sp.is a shallow water species that prefers to live in freshwater and cold water environments.C.candida likes to live in the shallow waters of lakes and rivers.It is a kind of cold species;C.novaezelandiae and C.kreapelini are widely distributed in the whole lake.It shows that the eutrophication of Yilong Lake is serious and the water level has dropped significantly.(2)The relative percentage content and cluster analysis of modern ostracods indicate that the modern genus of Yilong Lake can be divided into two groups: shallow water species and broad species.The combination is: C.novaezelandiae-C.kreapelini and E.cf cuneate-C.sp.-Y.cf.reticulate gen.et sp.nov-C.candida.Most of the shallow water species are representative of the shallow water phase,and the abundance is low,indicating that the watershed area of the Yilong Lake is shrinking and the water level in the basin is decreasing.Widely distributed throughout the lake,it is highly adaptable and is mainly distributed in areas with strong sunlight and abundant aquatic plants.(3)Based on the modern ostracods cluster analysis and the relative percentage of drilling ostracods,we classify the interbeds of the Yilong Lake borehole into three combined zones,namely: 36~30cm to C.novaezelandiae-C.kreapelini-E.cf.Cuneate-Y.cf.reticulate gen.et sp.nov-C.candida is a combination;30~16cm to C.novaezelandiae-C.kreapelini-C.sp.-Y.cf.reticulate gen.et sp.nov is a combination;16~0cm is a combination of C.novaezelandiae-C.kreapelini-E.cf.Cuneate-C.sp.-Y.cf.reticulate gen.et sp.nov-C.candida.(4)According to the drilling type combination and other surrogate indicators,the past environmental changes of Yilong Lake are divided into three stages: 1880~1909a AD: This stage is the natural evolution stage,human activities have not affected it,and the lake basin has greater hydrodynamics.The precipitation increased and the lake water area expanded;due to the increase in precipitation,rainfall brought about a drop in temperature.1909~1993a A.D.: At this stage,the climate is warm and dry,rainfall is reduced,the lake water area is rapidly shrinking,and the lake is greatly affected by human activities.1993~2013a A.D.: During this period,the climate was warmed by cold,and the temperature rising trend was sharp,the precipitation increased,and human activities were relatively weak.Although there are still many shortcomings in this paper,this paper uses the ancient biological indicators of the metamorphic class to restore the past environmental changes of the Yilong Lake.This point has implications for the study of past environmental changes in other lakes in Yunnan.It also plays an important role in the environmental research of plateau lakes.