Characteristics Of Surface Soil Pollen In The Northeastern Qaidam Basin And Recent Vegetation And Environment Change Recorded By Sediment Pollen In Toson Lake

With the increasing climate warming,many attentions have been paid on global environment change.Understanding the change laws of the past environment can better predict the future.Located on the northeastern margin of the Qinghai-Tibet Plateau,the Qaidam Basin is sensitive to climate change and it is an ideal area for the climate and environment study.Analysis of 32 surface soil pollen samples in the northeastern Qaidam Basin(97°00'25.67"?100°07'8.79"E,36°37'33.36"?38°12'35.49"N)indicated that different vegetation types have unique pollen component characteristics;The relationship between pollen and plants is complex,and the representativeness of the same pollen in different vegetation types is different;Principal component analysis showed that the humidity change may be the main factor affecting the characteristics of pollen component of each vegetation type;When the sum of Artemisia and Chenopodiaceae was>20%,A/C value could be used as a good indicator of dry or wet condition.The A/C value gradually decreases from the grassland-desert steppe-desert,reflecting the tendency of the environment to gradually dry.A/Cy value can distinguish alpine meadows from other vegetation types.The Toson Lake TSLC core(37°08.185' N,96°57.387' E)was drilled at the maximum water depth,and the short core length was 35.5 cm,and 48 samples were obtained.The chronology of TSLC core was established through 210Pb and 137Cs dating.The pollen analysis in the TSLC core showed that the pollen component can be divided into three pollen zones from bottom to top.The herb pollen dominated the zones,tree pollen is extremely low,and shrub pollen is also very low.Herb pollen was_mainly composed of Artemisia,Chenopodiaceae and Poaceae,and shrub pollen was constituted by Nitraria and Ephedra.According to the characteristics,concentration,and A/C value in the pollen zone,the vegetation and environment change in Toson Lake area since 129 years were reconstructed.In the pollen zone I:1883-1932a AD(35.5-27.5cm),the pollen assemble is mainly composed of Artemisia,Chenopodiaceae and Poaceae in herb pollen.Shrub pollen is dominated by Nitraria and Ephedra.The concentration did not change much,and the A/C value was low,indicating that there was no significant change in vegetation cover.The desert vegetation,which is dominated by the Chenopodiaceae,Artemisia,and Poaceae,is widely distributed in the vast area around Toson Lake.The regional environment is relatively dry.Pollen zone II:1932-1992a AD(27.5-10cm)pollen component is still dominated by Artemisia,Chenopodiaceae and Poaceae.The A/C value increased but fluctuated greatly.The change of pollen concentration showed that the regional vegetation coverage changed,indicating the sensitive response of vegetation to environmental change.The vegetation around Toson Lake was dominated by desert grassland which was made up of Artemisia and Chenopodiaceae.During this period,the climate fluctuations were obvious,indicating that the area dry and wet conditions were replaced frequently.Pollen zone ?:1992-2011a AD(10-0.5cm)pollen assemble is mainly herb pollen,and the proportion of Artemisia,Chenopodiaceae and Poaceae is very large,and Chenopodiaceae was slightly increased.Artemisia was decreased,while Poaceae did not change much.Shrub pollen is dominated by Nitraria and Ephedra,and Nitraria rise a little.The pollen concentration showed a significant increasing trend,but the A/C value was lower compared with the previous zone.The desert was dominated by Chenopodiaceae,Artemisia and Poaceae,and widely distributed around Toson Lake.Regional humidity was reduced and the environmental condition was relatively dry.Comparing the 129-years-old sediment pollen recorded in the TSLC core with the precipitation of the tree-ring reconstruction in the northeastern Tibetan Plateau,the meteorological and the pollen record of Gahai Lake,it was found that there is a good contrast,indicating that the sediment pollen can respond positively to climate change and may be a partial response to global warming.However,since the 1970s,a large scale farmland irrigation area has been cultivated due to the influence of human activities,which has resulted in inconsistent regional effective humidity change.Thus,it indicated that the pollen A/C value in lake sediments during the intense phase of human activity can not be used to represent regional environment change,but it implies the increased human activity.It is necessary to combine many types of environment indicators to recover environment in the region,and study further to assess the impact of the intensity of human activities on the environment.