The Sporopollen And Charcoal Records Recorded The Environmental Evolution Of The Nearly 100-year-old Yangtze River

With the analysis of TE,ZZ-2,CB-1 oxbow lake sediment characteristics in hubei river,three column samples totaling 145 sporopollen,carbon dust samples.identification of sporopollen 64949 grains,the average sample statistics 447 grains,carbon dust 92483 grains and the average sample statistics 638 grains.We organized the annals record flood,fire,land use change events,and analyzed the TE,ZZ-2,CB-1 hole of sedimentary characteristics change,which recorded the vegetation around the lake,land use,such as the environment changes,and try to reveal the change of the environment and human activities in the oxbow lake on the influence mechanism in the process of evolution.We have got the following conclusions:(1)Both of the base age in TE and ZZ-2 hole is before the formation year of the lake,so it’s covered different sedimentary characteristics of rivers and lakes,however the result of CB-1 hole showed all the samples were lacustrine sediments.The grain size of fluvial sediments was significantly higher than that of lake stage,and The three boreholes can well respond to the climate change characteristics of Jingzhou in the past 100 years.With the increase of vegetation coverage around the Oxbow lake,the pollen concentration rising in the development process;the carbon chips are mainly derived from the sediments of the upper reaches of the Yangtze River before the truncation of the TE hole(before 1972),so the carbon concentration is smaller,the concentration of carbon chips become larger because of the farming around after the lake stage;The concentration of carbon in the ZZ-2 hole was significantly greater than that of the river before the truncation(before 1967),The concentration of carbon chips clearly indicates the fire events in 1946 and 1963 year;With the change of land use types around the lake area,the deposition of pollen and charcoal concentration increased gradually.(2)TE,ZZ-2 and CB-1 three column pollen and charcoal records rich environmental changes and human activities:1916 to 1954 years,in the deciduous tree pollen tree pollen,include deciduous oak,birch,Pterocarya and Alnus,the climate is slightly dry.Artemisia pollen gradually increased in herbaceous pollen,It also reflected that there were more wasteland and less vegetation coverage.The peak value of carbon content at 70 cm which corresponded 1946 wildfire event.The pollen content of crops increased in the later stage,at the same time,the percentage of companion plant rised such as pollen plants of Compositae,Rosaceae,Saxifragaceae,which is the embodiment of human agricultural activities;1955~1972,Construction of artificial flood prevention forest in Binjiang District,causing the percentage of herbaceous pollen and tree pollen increased greatly.1973~1983,the percentage of pollen and herb pollen decreased significantly after the cutting off of the tree,due to the development of the infrastructure of the area around the lake,people destructed the vegetation around the lake,the 1980 floods also resulted in a marked increase in the amount of spores of aquatic plants and ferns.1984~2012,herbaceous pollen pollen especially cruciferous(rape)pollen percentage continues to rise after the reform and opening up of agricultural technology progress in gramineous crops,at the same time,people pay more and more attention to the optimization of environment,with the increase of vegetation coverage,the content of woody pollen increased.1940~1954 in ZZ-2 hole,the lake vegetation is evergreen oak,Quercus,Betulaceae and Ulmus,480 acres of forest vegetation had been destroyed when 1946 Peach Hill fire happened.The agricultural policy had changed of in Jianli after 50 s,Increase the yield of crops,resulting in the increase of Malvaceae(cotton)and Gramineae pollen content;1955~1967,People began to dike reclamation,farms,weihuzaotian cultivated land area increased Which results in the increase of the pollen content,In the 50 cm corresponding to the 1963 Bay fire,25~50 m carbon chips and carbon chip concentrations showed a peak;1968~2012,After the reform and opening up,the change of agricultural production technology,crop pollen to rice,Cruciferae(rape)pollen percentage gradually increased,with the increase of vegetation coverage around the lake,trees and understory herbaceous content increased,which causing the total pollen concentration gradually increased.CB-1 hole is lacustrine sedimentary,at 77,47 and 25 cm corresponding to the flood events of 1954,1983 and 1998,the percentage of pollen in trees and herbs decreased,and the percentage of small and medium sized carbon chips showed a peak value,at the same time,there was an increase in the spore content of aquatic fern.A large number of planted forest in 80 s,causing the Pterocarya pollen percentage was significantly increased.(3)Palynological Assemblages of TE holes,holes and ZZ-2 hole CB-1 display,there was a negative correlation between flood events and some herbs,the flood events in 1954,1983 and 1998,respectively correspond to the low values of the percentage of pollen in trees and herbs,floods did not bring more trees and herbaceous pollen in the deposition,but the lake area of trees,herbaceous pollen to the downstream sediment.