Deposition Characteristic,Source Analysis And Trend Prediction Of Heavy Metals In Typical Lakes In Northern China

Lake is an important part of terrestrial hydrosphere,which has many functions,such as adjusting regional climate,improving regional environment,maintaining river runoff,maintaining regional balance,providing water for production,living and agricultural irrigation,and breeding aquatic organisms.In recent decades,with the rapid development of Chinese industry,agriculture and other social economy,the invrease intensity of human activities intensifies,and harmful substances flow into lakes through various channels,resulting in the rapid deterioration of lake ecological environment and frequent pollution,among which heavy metal pollution is one of the most important types of Lake ecological pollution.Because heavy metals have the characteristics of extensive sources,long residual period,non biodegradation,and can be transferred and enriched through the food chain,causing damage to the biological central nervous system and circulatory system,it is particularly important to study the source and pollution history of heavy metals in lake sediments.Bosten Lake in arid area,Wuliangsu Lake in semi-arid area and Chagan Lake in semi hu n this paper,Bosten Lake in arid area,Wuliangsuhai Lake in semi-arid area and Chagan Lake in semi humid area of northern China are selected as research objects.On the basis of ²¹⁰Pb and ¹³⁷Cs accurate dating,ten heavy metal elements(Cr,Mn,Fe,Co,Ni,Cu,Zn,As,Cd and Pb)were analyzed to evaluate the pollution degree,pollution characteristics and ecological risk of heavy metals in the lakes in the study area,and to determine the sources of heavy metals The influence of the concentration and intensity on heavy metals in lake sediments.The statistical regression analysis model was established to predict the development trend of heavy metal content in lake sediments in the future,and to provide scientific basis for the effective control of heavy metal pollution and environmental governance.The main results are as follows risk of heavy metals in the lakes in the study area,and to determine the sources of heavy metals.The influence of the concentration and intensity on heavy metals in lake sediments.The statistical regression analysis model was established to predict the development trend of heavy metal content in lake sediments in the future,and to provide scientific basis for the effective control of heavy metal pollution and environmental governance.The main results are as follows:(1)The contents of heavy metals in the sediments of the three lakes all increased with time,but the contents of heavy metals in different lakes were different,and the contents of heavy metals were Chagan Lake,Wuliangsu Lake and Bosten Lake in turn.The content of heavy metals in the sediments of Chagan Lake was relatively stable before 1982,and began to fluctuate from 1982 to 2003.After 2003,the content of heavy metals gradually increased,especially Cd and Pb.The content of heavy metals in Wuliangsu sediment was relatively stable before 1997,and began to fluctuate from1997 to 2009,in which the content of Cr and Mn even began to decrease.After 2009,the content of heavy metals began to increase significantly,in which the content of Cr,Mn,Ni,Cu and Zn increased significantly.The content of heavy metals in the sediments of Bosten Lake remained relatively stable before 1996.From 1996 to 2009,the content of heavy metals began to rise on a large scale.The content of Co,Cu,Zn,Cd and Pb increased significantly.After 2009,the content of Mn and Pb increased again.(2)Three evaluation methods were used to evaluate the pollution degree of heavy metals in the sediments of three lakes.Among them,the heavy metals Ni,Cu and Zn in the sediments of Chagan Lake are mild pollution risk,while the pollution level of Cd and as has reached moderate or even severe pollution risk.The comprehensive results of the risk assessment of sediment pollution in Wuliangsu Lake show that the four heavy metals Fe,Cu,Cd and Pb have mild pollution risk.According to the comprehensive results of pollution risk assessment of Bosten Lake sediments,except for Cd and Pb,there is no pollution risk of other heavy metals.(3)The comprehensive risk assessment index of Chagan Lake is on the rise,from medium ecological hazard to high ecological hazard,and gradually to high ecological hazard in recent years.Wuliangsu Lake comprehensive risk assessment index has been hovering between medium and high ecological hazards.The comprehensive risk assessment index of Bosten Lake was in the range of low ecological hazard before,and now it has gradually developed into medium ecological hazard.(4)According to the sources,heavy metals can be roughly divided into three categories by multivariate statistical method:firstly,Co,Cu,Zn,Cd,As and Pb have homology,including wastewater,waste residue and waste gas from industrial activities,pesticide residues from agricultural activities and pollution of domestic sewage,which are all factors greatly affected by human activities;secondly,the sources of Cr and Ni are relatively complex and self-contained;Thirdly,Mn and Fe are relatively stable,which are basically natural sources and less affected by human activities.(5)The intensity of the impact of human activities is directly proportional to the economy,population density,industrialization level,content of mineral resources,mineral mining and agricultural activities in the area.The impact of human activities on the content of heavy metals in lake sediments is in order from strong to weak as Chagan Lake,Wuliangsu Lake and Bosten Lake.(6)Statistical regression analysis model was used to predict the future development trend of heavy metal content in lake sediments.The results show that the heavy metal elements in Chagan Lake show a downward trend,but all the heavy metal elements are in the high value.The contents of Fe and As in Wuliangsuhai showed an upward trend,while the contents of other heavy metals began to show a downward trend.In Bosten Lake,Cr,Mn,Ni and Cu showed an increasing trend,while the contents of other heavy metal elements showed a decreasing trend.In general,industrial activities,agricultural activities,household emissions and atmospheric pollutants in the northern lake area had a continuous effect on the heavy metal pollution in the lake sediments.