Distribution And Source Of PAHs In The Mud Deposition Along Eastern Coast Of Liaodong Peninsula,and Its Responses To Environmental Changes

Estuary and coast is transitional zones between land and ocean,and the interaction between land and ocean is strong.As a link between land and ocean,rivers are the main transport channels of land-based materials from source to sink in river basins.As a complex ecosystem,estuaries and coasts have the natural resources needed by human beings,and their ecological environment plays an important role in human survival and development.As an important inland shelf shallow sea in China,the North Yellow Sea is affected by the material input of many rivers along the coast.With the development of social economy,a large number of PAHs produced by human activities are transported to the ocean through rivers and deposited in the shelf muddy area,which greatly increases the pollution of PAHs in the ocean and seriously endangers the marine ecosystem.Composition and influencing mechanism of PAHs in estuarine and coastal areas,it is helpful to analyze the inflow flux of PAHs into the sea,to explore the process and mechanism of the impacts of human activities in the basin on the ecological environment of estuarine and coastal areas,and to analyze and predict the evolution trend of the ecological environment of estuarine and coastal areas,so as to provide theoretical basis and guidance for the environmental management and planning of the sea area.In order to study the distribution characteristics,sedimentary records and influencing factors of polycyclic aromatic hydrocarbons(PAHs)in the sediments of the northern North Yellow Sea,31 surface samples and 2 cores samples were collected in the muddy area of the eastern coast of Liaodong Peninsula and adjacent sea areas.Polycyclic aromatic hydrocarbons(PAHs),grain size,organic carbon(OC)and 210Pb in sediments were analyzed.Socio-economic data(population,energy consumption,GDP)were collected.On this basis,the distribution,composition,source and influencing factors of PAHs were studied.Based on the variation of PAHs content and source in core sediments with time and their relationship with human and natural activities,the impacts of human activities on estuarine and coastal environment were discussed.The results of surface samples show that the concentration of PAHs ranges from 3.54 to 93.07 ng/g,with an average of 34.50 ng/g in surface sediments of mud deposition along eastern coast of Liaodong Peninsula The concentration is lower than that in the muddy sediments of the Bohai Sea,the South Yellow Sea and the coastal areas of Zhejiang and Fujian,and is generally at a lower pollution level.In terms of composition,PAHs are mainly low molecular weight polycyclic aromatic hydrocarbons,mainly from coal and petroleum and other sources of fossil fuel combustion.Spatial distribution of PAHs in Changshan Islands and the eastern sea area shows a decreasing trend from coastal to offshore.There are two high-value distribution areas along the Liaodong Peninsula and the muddy area in the western North Yellow Sea.Further analysis shows that the distribution of PAHs in the study area is mainly affected by the sources of the Yalu River,the small and medium rivers along the eastern coast of Liaodong Peninsula and the Yellow River.The input of land-based materials is an important factor to control the distribution of PAHs.The complex hydrodynamic conditions and the ocean current system of the North Yellow Sea also have an important impact on the distribution of PAHs in the study area.Before 1820,the results of core samples show that the typical agricultural civilization emitted less PAHs from human activities,and the content of PAHs remained at a low level for a long time,which is mainly low molecular weight PAHs.From 1820 to 1900,the increase of population led to the increase of PAHs content due to the relaxation of the Qing government blockade policy.However,the mode of human activities was still dominated by biomass combustion,and low molecular weight PAHs were dominant in sediments.From 1901 to 1949,the content of PAHs is fluctuated and increased with the development of modern industry and the outbreak of many wars in Northeast China,reflecting the relationship between the content distribution of PAHs and economic and social stability.At the same time,high molecular weight polycyclic aromatic hydrocarbons(HMW)began to increase gradually in this period,and gradually dominated.From 1949 to 1978,the vertical and composition changes of PAHs also reflected the influence of socio-economic factors on PAHs records.For example,the economic recovery after the founding of the People's Republic led to the increase of PAHs content,and the stagnation of production during the Cultural Revolution led to the decrease of PAHs content.After 1978,China's economy has developed rapidly and energy consumption has increased.The total amount of PAHs shows an increasing trend,and high molecular weight PAHs occupy an absolute dominant position.There is a good correlation between PAHs content and socio-economic indicators(population,energy consumption and GDP).The change of energy utilization structure plays a key role in the vertical distribution of PAHs.According to the results of HMW/LMW,ratio method and principal component analysis,the energy structure of Northeast China can be divided into three stages.Before 1920,the main energy use was biomass combustion;from 1921 to 1980,biomass combustion and fossil fuel combustion were mixed;after 1980,fossil fuel combustion was dominant.Generally speaking,the sedimentary record characteristics of PAHs in the core sediments of the muddy area along the eastern coast of Liaodong Peninsula are closely related to human activities and natural activities,and human activities are the key factors controlling the vertical characteristics of PAHs.Population migration,social stability,socio-economic development and energy utilization are important factors affecting the changes of PAHs depositional records in the region.