Study On The Spatial And Temporal Distribution Of Petroleum Hydrocarbon And Bacterial Diversity In The Surface Seawater Of Laizhou Bay

The petroleum pollutants emission fluxes from main rivers and outfalls of Laizhou Bay(LZB)were estimated based on three simultaneous land-sea detailed surveys of flux of pollutants into the sea and marine pollution distribution in the LZB in October 2018(autumn),May 2019(spring)andAugust 2019(summer).The spatial and temporal distribution of petroleum hydrocarbon of LZB in different seasons and influential factors were analyzed.And the sources of petroleum hydrocarbons of LZB were discussed combined with the n-alkane component and composition of petroleum hydrocarbon.The results suggested that petroleum pollutants in LZB are significantly negative correlated with salinity(p<0.01),and the high value areas are mainly located at the estuary of Xiaoqing River at the bottom of the bay,where the influential areas of land-based emissions have the highest contribution to the flux to the sea.And the mean values of petroleum pollutant concentrations in different seasons are consistent with the changes in the flux to the sea,showing a higher trend in summer than in spring and in autumn,indicating that the spatial and temporal distribution of petroleum hydrocarbon pollutant concentrations in Laizhou Bay is determined by land-based emissions.In addition,in the surface seawater of M4,C2,C4 and C5 stations of Laizhou Bay inAugust 2019,the total petroleum hydrocarbon contents were0.1374±0.0018 mg/L,0.0719±0.0044 mg/L,0.0576±0.0026 mg/L and 0.0269±0.0020mg/L,respectively.The M4 and C2 stations significantly exceeded the water quality standard of seawater category I(II)(?0.05 mg/L).The carbon number of n-alkanes in the surface seawater of the LZB showed an obvious bimodal distribution of “low carbon number” and “high carbon number”,and the low carbon number peaks have obvious odd-even advantages,with the main peaks being n-C15 and n-C18 respectively,which indicated that petroleum in this sea area originated from aquatic organisms and terrestrial plants,but the local sea was obviously polluted by exogenous petroleum.Due to the advantages of low price,good effect and no secondary pollution,microbial degradation has been widely used in the treatment of marine oil pollution.To explore the effects of petroleum hydrocarbon content and physicochemical parameters on bacterial communities of LZB,16 S r RNA genes sequences of bacteria from surface seawater samples were performed by using the Ilumina Nova Seq sequencing platform to analyze the relative abundance of bacteria,community composition,ecological functions at different taxonomic levels in the sea water and correlation between environmental factors and hydrocarbon degrading bacteria.The results showed that the overall abundance of bacteria in the sea was high,and 18 bacterial phyla were found,such as Proteobacteria,Bacteroidetes,Actinobacteria,etc.Among them,Proteobacteria accounted for the highest abundance and were the main taxa in marine bacteria.At the genus level,the dominant hydrocarbon degradation bacteria were mainlyAlcanivorax,Vibrio,Flavobacterium,Mycobacterium and Pseudomonas,among which,Flavobacterium belonged to Bacteroidetes,Mycobacterium belongs toActinobacteria,and the others belong to Proteobacteria.The highest bacterial abundance and diversity were observed at M4 station,and the bacterial diversity in the surface seawater from nearshore to the bay estuary showed a gradually decreasing trend.Meanwhile,the M4 sample was more contaminated by petroleum,and their corresponding abundance of hydrocarbon-degrading bacteria were also higher,indicating that petroleum contamination would lead to differences in bacterial community and abundance.Additionally,Alcanivorax showed significant positive correlation with T,pH and DO,while Pseudomonas showed significant negative correlation with T,pH and DO,suggesting that environmental factors(T,pH and DO)have different effects on various hydrocarbon degrading bacteria(p<0.05).The functional taxa and species composition of microbial communities in surface seawater and the correlation between the hydrocarbon degradation functional genes and environmental factors were analysed with metagenome sequencing technology.The dominant phyla in the four stations of Laizhou Bay were Proteobacteria,Bacteroidetes,Actinobacteria and Cyanobacteria,and the common predominant phyla were Proteobacteria and Bacteroidetes,accounting for 56.28% and 21.64%,respectively,indicating the dominance of both in seawater.At the genus level,the dominant bacteria were mostly Synechococcus,Flavobacterium,Novosphingobium,Gilvibacter and Hydrogenophaga.In the M4 and C2 stations,the relative abundance of bacteria associated with petroleum hydrocarbon degradation was higher,which were mainly Flavobacterium,Pseudomonas,Sphingomonas and Vibrio,demonstrating that the increase of petroleum hydrocarbon content contributed to the growth of the abundance of dominant bacteria.In the diversity analysis of the macrogenome,four diversity indices were higher in the C2 and M4 samples than in the other samples,indicating that the richness and diversity of the communities were higher in both stations,while in the functional level of the communities,all four samples were closer to each other,revealing a high similarity in the functional abundance profile between the samples.The only gene related to alkane degradation in all seawater samples were alk B,and the genes associated with aromatic hydrocarbon degradation were bamA,xylE,pcaL,tmoA,phdF,badA and nahAb,among which the hydrocarbon degradation genes of higher abundance were bamA,alkB and xylE.The hydrocarbon degradation functional genes in the four samples were significantly correlated with petroleum hydrocarbon degrading bacteria and environmental physicochemical factors.Except for the phdF gene,other PAHs degradation genes showed significant positive correlation with TPHs content and significant negative correlation with pH and dissolved oxygen(DO)(p<0.05).