HOLOCENE PALYNOLOGICAL RECORDS OF VEGETATION,CLIMATE CHANGE AND HUMAN ACTIVITIES IN THE DONGTING LAKE WATERSHED
The Dongting Lake watershed(24°38′29″～30°24′25″N,107° 16′56″～114° 14′50″E)is situated in the subtropical region of China,significantly influenced by monsoons,rendering it highly responsive to climate and vegetation changes.With a history of rice cultivation dating back to the Early Holocene,this watershed has become an ideal region for studying Holocene paleoclimatic changes,vegetation evolution,and ancient human activities.This study focuses on three research sites within the Dongting Lake watershed,namely the Shiwangutian peat(SWGT:26°05′N,110°21′E;1700 m a.s.l.)in southern Hunan,Jiulongchi wetland(JLC:27°55′N,108°41′E;2213 m a.s.l.)in Fanjing Mountain,Guizhou,and the Jiangling profile(JL:30°08′N,112°20′E;30 m a.s.l.)in Hubei.The SWGT core has a depth of 250cm,and AMS 14C dating,coupled with Bacon model for linear interpolation,establishes an age-depth model,reaching an approximate age of 11.6 cal.ka B.P.at the bottom.The JLC core,with a depth of 400 cm,undergoes AMS 14C dating,utilizing Clam model for age-depth model interpolation,reaching an approximate age of 11.9 cal.ka B.P.at the bottom.The JL profile,with a depth of 594 cm,undergoes conventional 14C dating,followed by tree-ring calibration.Linear interpolation is used for age-depth model interpolation and extrapolation,reaching an approximate age of 9.4 cal.ka B.P.at the bottom.Palynological analysis of the SWGT,combined with published results from JLC and JL,provides insights into the vegetation and climate changes in the Dongting Lake watershed during the Early to mid-Holocene.Additionally,a Human Influence Index(HII)is reconstructed using the Modern Analog Technique(MAT)to explore the impact of human activities during the Holocene.Results indicate the following:(1)Early Holocene:Dominance of subtropical plant pollen types such as Evergreen Quercus,Cyclobalanopsis,Castanopsis,Fagus,and Carpinus,suggesting a warm and humid climate with a strong East Asian summer monsoon(EASM)intensity.(2)Mid-Holocene(approx.9.0～4.0 cal.ka B.P.):Highest tree pollen content,lowest herbaceous plant pollen content,and maximum forest coverage.Increased content of subtropical evergreen broadleaf trees,primarily Evergreen Quercus and Cyclobalanopsis,indicating a warmer and wetter climate with further strengthened EASM.Notably,between 6.0～4.0 cal.ka B.P.,Evergreen Quercus and Cyclobalanopsis reach their highest content,signifying the onset of an optimum period during the Holocene.(3)Late Holocene(4.0 cal.ka B.P.onwards):Highest HII values,reflecting intensified human impact on the environment.Decreased pollen content of Evergreen Quercus,Castanopsis,and Cyclobalanopsis,coupled with a higher percentage of pine pollen,indicates extensive deforestation by human activities,leading to the expansion of secondary pine forests.Simultaneously,an increase in Poaceae pollen suggests the initiation of agricultural activities in low-altitude areas.(4)Factors such as solar radiation,Northern Hemisphere high-latitude ice volume,and meltwater flux from ice sheet melting may have exerted significant influences on Early to mid-Holocene climate changes.However,the Late Holocene record in this region appears more strongly influenced by human activities.It is emphasized that identification of signals related to human activities is crucial when utilizing pollen for quantitative reconstruction of Holocene paleoclimate in this region.
pollen recordvegetation and climate changeHuman Activity Index(HII)Dongting Lake watershedHolocene
万方数据
维普
