|Other Abstract||The Bohai Rim is known as the "Northern Gold Coast". At the same time, oil and gas resources are abundant. Oil-gas exploration and exploitation, oil transportation volume and frequency are increasing year by year, and the accumulation of heavy industries along the coast has caused the marine pollution in the Bohai Sea to intensify. As an important carrier of pollutants, marine sediments can indicate the pollution status of marine ecosystems. Petroleum hydrocarbons and heavy metals often coexist. Study on the spatial distribution and their influencing factors of petroleum hydrocarbons and heavy metals in sediments are helpful to understand the impact of human activities on changes in the marine environment, and can provide scientific and technological support for marine environmental protection and restoration.
In this paper, the physical and chemical propertie, petroleum hydrocarbons and heavy metals content of surface sediment samples from the three bays of Bohai Sea were analyzed. The spatial distribution and sources of n-alkanes, PAHs and heavy metals (Pb, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As and Cd) in Laizhou Bay, Bohai Bay and Liaodong Bay were studied. In addition, the comparative analysis of the pollution levels and ecological risks in the three regions were made, and the impact of coastal economic development on the marine sedimentary environment were analyzed. The correlation between sedimentary physicochemical properties, petroleum hydrocarbons, and heavy metals was explored, and the interaction of the two pollutants was discussed. Research indicates:
(1) The content range of total organic carbon (TOC) in the Bohai Sea is 0.11-1.82%, and the range of total nitrogen (TN) is 0.01-0.11%. Bohai Bay has the highest content and Laizhou Bay has the lowest content. The linear correlation analysis of C and N elements indicate that Laizhou Bay has the highest correlation, which may be caused by the input of terrestrial organic matter. The source of organic matter in Liaodong Bay is more complex, and the correlation is not obvious.
(2) The average values of total n-alkanes contents in Laizhou Bay, Bohai Bay and Liaodong Bay were 1117.81, 482.27 and 716.48 ng / g dw, respectively. None of the stations exceeded the UNEP standard, indicating that the level of n-alkanes pollution was relatively low in studied area. In three bays, the analysis of LMW / HMW, n-C16 index, NAR, CPI and other characteristic parameters show that the n-alkanes in the three bays belong to the mixed input of terrestrial, marine organic matter and petroleum pollutants. Through the correlation analysis of the characteristic parameters, we found that Liaodong Bay is greatly affected by the input of terrestrial plants, while the input proportion of petroleum pollutants in the Bohai Bay is the highest. In addition, the isoprenoid alkane parameter, Pr / Ph <0.8, can indicate reducing environment. The terpene and sterane parameters further verified the presence of petroleum hydrocarbon pollutants in the sea.
(3) The average values of total PAHs in Laizhou Bay, Bohai Bay, and Liaodong Bay were 952.15, 1000.91, and 347.89 ng / g dw, respectively. PAHs in part of the Bohai Bay and Laizhou Bay reached moderate or even severe pollution levels. The specific gravity of each ring PAHs and the isomer ratios were analyzed. The PAHs in the Laizhou Bay and Bohai Bay sediments are a mixed source of petroleum and combustion sources, while biomass and coal high-temperature combustion sources in the Liaodong Bay PAHs dominate the contribution. The pollution degree of high molecular weight PAHs in 16 kinds monomers are better than low molecular weight, the pollution degree of Liaodong Bay is better than Laizhou Bay and Bohai Bay, and its potential ecological risk level of PAHs is the lightest. TEQBaP did not exceed the SQGs concentration, indicating that PAHs are currently at a safe level.
(4) The As, Cr, Cu, and Cd in the sediments of the three major bays all exceeded the standard, and the heavy metals content in Laizhou Bay and Bohai Bay were relatively low. Except for Pb, As and Cd, the other elements are highly correlated, indicating the same or similar origin. In the Bohai Sea, Pb is at a clean level, Cr, Ni, Cu and Zn pollution levels are relatively lighter, As and Cd pollution are relatively serious. At the same time, the potential ecological risks of Cd and As are the largest, and the ecological risks of Zn are the smallest. The comprehensive potential ecological risks in most sea areas have reached a medium level.
(5) Petroleum hydrocarbons in the Liaodong Bay have the highest correlation with clay and powder particles. It is possible that the influence of land-based source input is the greatest. Most metal elements in the three bays are positively correlated with TOC, and Laizhou Bay has reached a significant level, while the correlation between heavy metals and particle size in the Bohai Bay is the lowest, which may be greatly affected by human activities. Some heavy metal elements in Laizhou Bay and Liaodong Bay are highly correlated with high molecular weight PAHs, which may be related to the large amount of heavy metals adsorbed by high molecular weight organics. The correlation between petroleum hydrocarbons and heavy metals in the Bohai Bay are not high, which may be related to the main sources of organic pollutants and heavy metals are different.
Based on previous studies of the classification of pollutants in the Bohai Sea, there are few studies on the composite pollution of various pollutants in the sediments. This study analyzes the interaction between petroleum hydrocarbons and heavy metals through Laizhou Bay, Bohai Bay and Liaodong Bay at same time, and explores the impact of different economic development activities on the marine sedimentary environment. It is hoped to provide a certain theoretical basis for the exploration of petroleum hydrocarbon-heavy metal composite pollution, and provide data and scientific and technological support for the smooth implementation of the "Bohai Comprehensive Governance Action Plan".|