Distribution And Source Of Polycyclic Aromatic Hydrocarbons Nd Their Indicative Effect On Microbial Community Assembly In Abandoned Yellow River Delta

Polycyclic Aromatic Hydrocarbons(Polycyclic Aromatic Hydrocarbons)are a class of organic pollutants with toxic,teratogenic and carcinogenic effects.Marine sediments are considered to be one of the important sinks of PAHs.PAHs can cause different effect on marine organisms,the research on microorganisms mainly focuses on the change of abundance and diversity under PAHs,without in-depth exploration on the response of interaction among microorganisms.In order to further explore the microbial community responses of different marine microorganisms under the influence of PAHs,carrying out field experiments in the Abandoned Yellow River delta in northern Jiangsu,collecting surface marine sediment samples from a total of 33 sites,and determining the concentration of 34 PAHs(18 parental PAHs and 16 alkylated PAHs)and 16s rRNA and 18s rRNA amplification and sequencing data.The main conclusions of the paper are as follows:The concentration range of PAHs in the Abandoned Yellow River delta is 32.695.3 ng/g,among which the concentration of 16 PAHs(16-PAHs)that preferentially controlled suggested by EPA is 23.4-73.5 ng/g,and the total concentration of alkylated PAHs is 6.15-20.6 ng/g;There was no significant positive correlation between the concentration of PAHs and the distance from the shore,SOC content,The distribution of PAHs did not show the law of decreasing or increasing toward the shore or other obvious distribution characteristics.There are two high-value region on the ancient estuary and the north bank of the study area.On the one hand,they may be affected by the strong hydrodynamics of the ancient estuary,and on the other hand,they are affected by the inland Yellow Sea and Bohai sea sediments with higher PAHs concentration.The source of PAHs in the Abandoned Yellow River estuary was identified by the diagnostic ratio which indicate a mixed source of diagenetic source and combustion source.Most of the sites showed combustion source characteristics,but there were some contradictions in the results of diagnostic ratio,which may be due to the background value of PAHs was relatively low and was affected by multiple sources.The PMF model was further used for source identification and further differentiate into three sources:coal combustion and automobile exhaust source(43.5%),diagenetic source and biomass combustion(38%),petroleum combustion source(18.5%),compared with characteristic ratio method,PMF model showed a more robust results.The diagnostic ratio indicated differentiation results,33 sites were divided into 6 regions according to their quantiles.The relative abundance and diversity of archaea,bacteria and fungi didn’t show obvious differences between the sub-region.However,CAP analysis showed that environmental factors,including PAHs source indicators,drove the overall construction of microbial community.Among them,archaea hold the closest relationship with the environmental factors(50.6%+7.6%),whereas,relatively weaker in bacteria and fungi;microorganisms were not affected by the concentration of PAHs,on the contrary,it showed a certain dependence on the indicators of the source of PAHs.For example,archaea were affected by PMF1 and PMF2 factors,and bacteria were related to the ratio of Fla/(Fla+Pyr).Through futher screening of representative OTUs,considerable OTUs responded to the source of PAHs,suggesting that the source of PAHs did have a certain regulatory effect on the community structure.At the level of phylum,the number of OTUs in response to PAHs source indicators was not correlated with the total amounts of representative OTUs,indicating that this correlation had an evolutionary relevance in species generation.Most of the archaea had negative correlation with the indicator factors of PAHs source,which might lead to the disappearance of some archaea with high research value,while most of the bacteria and fungi showed positive correlation.The three microorganisms showed different response modes under the influence of subcritical PAHs concentration,indicating the complexity of organisms adapting to PAHs.The node degree,node centrality,node stress and Zi value of the molecular ecological network of bacteria were all greater than fungi and archaea,suggesting that the microbial molecular ecological network in the Abandoned Yellow River delta was dominated by bacteria.Proka_OTU235 in the Proteobacteria had the largest node degree value and the eigenvector centrality,occupied a central position in the whole ecological network structure,indicating that this phylum plays a key role in maintaining the microbial community structure.Biomass combustion zone(c-c zone)has higher connectivity(total number of connections),average number of nodes,average path distance and density than petroleum combustion and biomass combustion mixing zone(c-p zone),the ecological network structures in archaea,bacteria and fungi also hold similar characteristics,which proves that the microorganisms in the c-c zone indeed had a stronger interaction relationship.In conclusion,the source of PAHs can also be used as an indicator to judge the interaction intensity between microorganisms,which may due to that PAHs from different sources can cause different levels of stress.