Primary Studies On The Holocene Diatom Assemblages And Their Paleoenvironmental Significance In The Kanas Lake, Xinjiang

Global environmental problems are prominent in recent years,especially the significant issues such as climate change is too important to ignore.Holocene is closely related to human production and living,so the study of Holocene environmental change will provide a crucial scientific basis for the correct understanding of contemporary global environmental problems,reliable prediction and positive response to future global changes.As an important part of the global ecosystem,lakes collect the input of aquatic and terrestrial materials from the catchment,which can comprehensively reflect the key information of the environmental conditions within the lake area,furthermore the lake sedimentary record has good continuity and is easy to measure credible age,so it is widely used in the study of paleoenvironmental change.Diatoms are widely distributed in lakes,with a large abundance and a wide variety of species,also the specificity of habitat requirements,large inter-specific differences and short life cycle,they can quickly respond to hydrological environment changes.Besides,their valves are easy to be preserved well in lake sediments,thus diatoms play an important role in the reconstruction studies of lake ecosystem and regional environment changes.Kanas Lake is in the most northern part of Xinjiang Uygur Autonomous region,China.Diatoms of Kanas Lake sediment are well preserved,high in content and various in species,which made it an ideal carrier for the studies of hydro-ecology and paleoenvironmental reconstruction.This research is based on diatom identification and data analysis from KNS15 D core,combined with reliable chronological framework,experimental results like biogenic silica and grain size,the response of diatom assemblages in Kanas Lake since Holocene has been preliminarily discussed.The results showed that 163 taxa belonging to 48 genera fossil diatom were observed in KNS15 D core sediment.Diatom assemblages of sediment core and other proxies reflected the dynamic changes of ecological evolution and climate characteristics in different periods.Before Younger Dryas(YD),the lake primary productivity was low,so was the diatom concentration and species varieties,and the diatom assemblages showed the climate was cold;in the early Holocene,the diatom assemblages were mainly composed of small benthic diatom species,which indicated that the lake primary productivity was high,and the climate was optimum,together with the rare earth elements and pollen records in the lake area,all showed that the climate was warm and dry;in the mid Holocene,the dominant constructive species began to shift into planktonic species,and both the lake primary productivity and nutrition level were comparative high,which indicated that the climate was still generally warm,but the humidity of the lake area increased;in the late Holocene,the content of Pantocsekiella gordonensis,a very tiny planktonic specie,increased rapidly,replacing other diatom species and being the most dominant diatom specie,and the data of TOC,PCA1 value and biogenic silica percentage showed the continuous decline of lake nutrient level and primary productivity;otherwise,in the recent hundred years,with the increase of temperature,the level of lake nutrition further declined,which made the competitiveness of P.gordonensis greatly improve,resulting in diatom concentration and the values of planktonic/benthic species(P/B)significantly rising,reflecting that under the background of climate warming,the thermal stratification of the lake was more stable,and the nutrition utilization rate of smaller diatom species was higher,thus they were more competitive in Kanas Lake.In addition,the combination of cold-water planktonic specie Cyclotella ocellata and the decline of small benthic species showed that diatom in Kanas Lake responsed to the abrupt climate events in different periods,which included YD event,4.2 ka(1 ka =1000 cal yr BP)and 8.2 ka cold events.The preliminary investigation indicated that diatom assemblages in the sediments from Kanas Lake are sensitive both to hydrological variation and regional climate changes,which can have some reference significance in the future for further researches of hydro-ecology in lakes of Xinjiang Uygur Autonomous region under the background of global warming.