Studies On The Distribution Characteristics And Its Influencing Factors Of Polycyclic Aromatic Hydrocarbons In Changjiang River-estuary-sea System

River-Estuary-Sea system is an important research object of "Land-Ocean Interaction in Coastal Zone" which is the core of the International Geosphere-Biosphere Programme.This system is a very fragile ecosystem with complex physical and chemical process and is affected by both land and ocean.In addition,the development of social economy makes this region also faces enormous pressure from human activities,which resulted in a large number of pollutants are released into this area and makes the system suffered great damage to the ecology and environment.Therefore,studies on the environmental behaviors of pollutants in this system become very important and urgent.In this study,Changjiang River-Estuary-Sea system is considered as a typical study area to explore the occurrence of polycyclic aromatic hydrocarbons(PAHs).We also research the source,distribution,and composition of PAHs in this system,and delve into their environmental behaviors and possible influencing factors.The concentration of dissolve PAHs(DPAHs)in surface water of the Changjiang River Basin ranges from 17.7 ng/L to 110 ng/L,with an average of 42.6 ng/L.The highest and lowest value of DPAHs concentrations occur in the Dongting Lake station and Wujiang station,respectively.Overall,the PPAHs concentrations are relatively higher in the Upper and Lower researches than that in the Middle research,which could be influenced by the impoundment of Three Gorges reservoir.The main composition of PAHs in surface water is low molecular weight PAHs with 2-3 rings,which accounted for more than 67%of the total PAHs.The result of source apportionment shows that there are four sources of PAHs in surface water of the Changjiang River:biomass and coal combustion source,petroleum residual source,traffic source(diesel and gasoline engine),and coke source.The contribution rate of each sources are 40.1%,19.6%,17.5%,and 22.8,respectively.The concentration of particle PAHs(PPAHs)in surface water of the Changjiang River Basin ranges from 595.91 ng/g to 2473.74 ng/g,with an average of 1369.92 ng/g.The highest DPAHs concentration is found at Zhenjiang station and the lowest value occur in Jiujiang station.The concentration of PPAHs in the middle research(from Three Gorge Dam to Jiujiang station)is relatively lower than that in the upper and lower research.However,the PPAHs concentration in two lakes(Dongting Lake and Poyang Lake)are relatively high.Impoundment of Three Gorge reservoir makes the PAHs in water is diffused,which resulted the outbound PPAHs concentration in water is low.These two lakes as catchment basin can receive large amount of water and associated PAHs,and their basin belong to the rapid economic development area.Therefore,large amount of PAHs was discharged into these two lakes and resulted to high PPAHs concentration.The PPAHs concentration in the lower research shows an obvious cumulative effect especially in Zhenjiang station where occurred the highest PPAHs concentration.However,the PPAHs concentration in the Changshu station was relatively lower than that in the Zhenjiang station,which could be influenced by the tidal effect because Changshu station close to the estuary.Therefore,spring tide could influence this station and make the PPAHs concentration was diluted.The PPAHs in the middle and lower research was mainly composed by high molecular weight PAHs with 4-6 rings,which accounted for more than 84%of the total PAHs.The concentration of PAHs in surface sediment from the Changjiang River Estuary and its adjacent area ranged from 26.6 ng/g to 621.6 ng/g,with mean value of 158.2 ng/g.Spatially,PAHs concentration in the study area can be divided into two partitions:the Changjiang River Estuary region and the offshore water in the south of Hangzhou Bay.The high value of PAHs occurred in the east of Zhoushan archipelago.The concentration of PAHs in the Changjiang River Estuary ranged from 27.2 ng/g to 400.9 ng/g,with an average of 137.7 ng/g,which is relative lower than the level of PAHs in the Zhejiang Coastal water(ranged from 27.3 ng/g to 621.6 ng/g,with mean value of 175.8 ng/g).Spatially,PAHs concentration presented a wide fluctuation,and exhibited an increasing tendency from north to south,which is consistent with the distribution pattern of sediment grain-size.In addition,the PAHs concentration also tend to decrease with increasing distance between the estuary and the sea,which could be influenced by the Changjiang Dilute Water.The concentration of HMW PAHs in the study area was relatively high and ranged from 12.9 ng/g to 436.3 ng/g,which accounting for 30.3%to 89%of total PAHs,with a mean value of 69%.Liner regressions were carried out between PAHs concentration and sediment grain-size or TOC content,which showed there are no significant correction between them.This results seems to indicate that there were no relationship between PAHs concentration and sediment grain-size or TOC content.Nevertheless,we think factors that influence PAHs concentration in the study area were complicated.For example,the strong regional hydrodynamics could be made sediment resuspend and redistribute.In addition,the distribution pattern of PAHs could be controlled by both sediment grain-size and TOC content.Four factors,each explaining percentage contributions of various PAHs,were finally extracted using the PMF model.Four possible sources extracted by PMF model were coal combustion,petrogenic source,wood combustion,and traffic sources,and their contributions were 40.9%,23.9%,23.6%,and 11.5%,respectively.