Environmental Evolution Of Baiyangdian Lake In Xiong’an New Area In The Past Hundred Years

Baiyangdian Lake is the largest freshwater lake wetland in North China,which plays an irreplaceable role in maintaining the ecological environment of Beijing,Tianjin and North China.In 2017,the Central Committee of the Communist Party of China established xiong’an new area,Baiyangdian Lake as its core water system,the lake water environment is more important.However,in recent decades,due to the impact of human activities,the climate of the basin is dry and early,the amount of water entering Baiyangdian Lake is decreasing year by year,the water pollution is becoming more and more serious,and the biodiversity is damaged.Based on the 210 Pbex radionuclide dating method,this paper established the sediment chronology,combined with the environmental proxies such as nutrient elements and heavy metals,combed the variation characteristics of sedimentation rate of Baiyangdian Lake in xiong’an New Area in recent 100 years;Combined with the sediment age and nutrient pollution status,the pollution degree of different historical stages was analyzed;Based on the evaluation of heavy metals in sediments by geoaccumulation index method and Nemerow index method,this paper analyzes the historical evolution process and main sources of pollutants,which can provide scientific basis for solving the ecological and environmental problems faced by Baiyangdian Wetland,and also provide reference for the construction of ecological civilization in xiong’an new area.The results are as follows:(1)The specific activity analysis data of 137 Cs and 210 Pbex are in good condition,both of which are used for dating.The recent sedimentation rate of Baiyangdian Lake is estimated by 210 Pb excrs model,and the environmental change represented by the change trend of sedimentation rate in recent 100 years is discussed.(2)The TOC content of CPT in Baiyangdian sediment core samples of xiong’an new area is 4.607-77.173mg/g,with an average value of 36.579mg/g;TN content was 0.963-7.236mg/g,with an average value of 3.357mg/g;TP content was 0.341-0.706mg/g,and the average value was 0.534mg/g;The TOC content of QT was 13.539-81.469mg/g,with an average value of 38.883mg/g;TN content was 1.775-5.852mg/g,with an average value of3.421mg/g;TP content was 0.431-0.985mg/g,and the average value was 0.556mg/g;The results showed that the trend of rapid growth was observed since the end of 1950s(TOC increased from 40.24mg/g to 69.68mg/g,TN increased from 3.93mg/g to 7.23mg/g,TP increased from 0.55mg/g to 0.71mg/g),and the later growth rate was relatively large.Especially in recent years,the eutrophication of Baiyangdian Lake was more severe.Because of the long-term input of a large amount of nitrogen containing nutrients,the core CPT and QT were far higher than the background value.Based on the 210 Pb dating results,the multistage distribution characteristics of TOC,TN,TP and n/p elements and the reasons for the changes of environmental stages are analyzed.The deposition rate has experienced four stages from stable to fast: before 1963,the deposition rate was stable and natural deposition was dominant;From 1963 to 1986,the rate decreased,the fluctuation range was small,and the human influence was dominant;From 1986 to 2007,the deposition rate increased,and the human influence continued to strengthen,but turned into beneficial influence;From 2007 to 2018,the deposition rate increased rapidly,and the impact of human activities still dominated.(3)Based on the evaluation of heavy metals in Baiyangdian Lake by geological accumulation index method and Nemerow index method,it is found that Baiyangdian Lake has been polluted by heavy metal Pb(22.0-39.7 mg / kg,average 26.9 mg / kg)in recent 110 years,which has a trend of slowing down.By using Nemerow index method,the pollution index of Cu is the largest,reaching moderate pollution,and the rest are mild pollution.Zn has been moderately polluted since 2015,which indicates that Zn pollution has increased.(4)This paper has a positive effect on the pollution assessment and source identification of Baiyangdian Lake,and on the prevention and control of nutrients and heavy metal pollution in Baiyangdian Lake.It shows that the environmental evolution trend of Baiyangdian Lake in recent 100 years is closely related to human activities.