Distribution Characteristics Of Petroleum And Its Correlation With Environmental Factors In Tianjin Coastal Waters

Based on the monitoring data of Tianjin coastal waters in Bohai Bay from 2009 to2021,the distribution,long-term variation characteristics,migration and transformation characteristics and influencing factors of petroleum in seawater,sediments and organisms in Tianjin coastal waters were studied,and the community structure and variation of phytoplankton and zooplankton were analyzed.The effect of petroleum pollution on the ecosystem was also discussed.The main results are as follows:（1）From 2009 to 2021,the variation range of petroleum in summer surface seawater in Tianjin inshore sea area was 0.00650～0.0560 mg/L,with an average of0.0337 mg/L,showing a general downward trend,and the high value areas were mainly distributed in the north and middle of the investigated sea area.From 2009 to 2012,the variation range of petroleum in sediments in Tianjin coastal waters was（73.1～297）×10^-6,with an average of 183×10^-6,showing an overall upward trend,and the high value areas were mainly located in the central and northern waters.From 2013 to 2017,the contents of petroleum hydrocarbons in Scapharca subcrenata and Sinonovacula constricta in Tianjin coastal waters generally showed a downward trend.The petroleum pollution of seawater,sediments and organisms is generally light.Petroleum in the surface seawater of Tianjin inshore in summer was significantly positively correlated with PO₄-P and DIN（p<0.01）,the correlation coefficients were 0.191 and 0.398,respectively,and was significantly positively correlated with COD（p<0.05）,the correlation coefficient was 0.168;There was a significant negative correlation（p<0.01）with salinity,and the correlation coefficient was-0.306.（2）A total of 144 species of Phytoplankton belonging to 5 phyla were found in Tianjin coastal waters from 2009 to 2018,including 100 species of Bacillariophyta,39species of Pyrrophyta and 5 species of other algae,accounting for 69.4%,27.1%and3.5%,respectively.The proportion of Pyrrophyta has increased significantly in recent years.A total of 82 species of zooplankton were found from 2009 to 2018,and the main groups were Copepods,Jellyfish and Planktonic Larvae.There were 48 red tides in Tianjin coastal waters from 2005 to 2020,and the total occurrence area was 17565.6km².After 2013,the number of algae species causing red tides increased rapidly,and the species changed significantly.There were significant negative correlations（p<0.01）between petroleum and the species number,Shannon index,evenness index and richness index of phytoplankton,and the correlation coefficients were-0.197,-0.251,-0.210 and-0.271,respectively;There was a significant negative correlation（p<0.05）with zooplankton richness index,with a correlation coefficient of-0.167.There was no significant correlation with other zooplankton diversity indices.（3）The main sources of petroleum in Tianjin coastal waters are marine pollution mainly from fishing vessels and land-based pollution mainly from industrial wastewater discharge.It is suggested that the prevention and control of petroleum pollution should be carried out by strengthening the anti-pollution facilities and equipment of fishing vessels and improving the management and control system of sewage outlets into the sea.