Responses Of Microbial Communities In Coastal Effluent Receiving Area Of Hangzhou Bay To Land-sourced Wastewater Discharge

Microbial community structures are affected by both natural factors and human activities.In coastal area,a typical and conventional human activity is discharging wastewater treatment plant(WWTP)effluent to the sea,thus the water qualities turn worse and marine ecology become unhealthy.Microorganisms are important for ecosystems,as they play key roles in pollutants degradation and ecological remediation.However,by now there is little research analyzing how the WWTP effluent disposal influences the coastal microbial communities.In this study,sediment samples were collected in Jiaxing effluent receiving area(JX)and Shangyu effluent receiving area(SY)in Hangzhou Bay.A comparative study was conducted to explore the responses of microbial communities to the land-sourced pollution.Firstly,the microbial community structures in sediments were analyzed by 16 S rDNA high-throughput sequencing.The significant differences in microbial community structures between the two effluent receiving areas were analyzed by Principal Co-ordinates Analysis(PCoA);the key differential microbes were analyzed by LEfSe;and the relationship between microbes and environmental factors was analyzed by Redundancy Analysis(RDA).The results found that water temperature as natural factor,COD,labile phosphorus and ammonia nitrogen as pollution factors in sediments significantly affected microbial community structures.The correlation analysis between microbes and environmental factors found that different environmental factors led to the emergence of differential microorganisms and caused the community structure changes.Secondly,a total of 80 functions were predicted for the microbial community by FAPROTAX,including carbon metabolism,nitrogen metabolism,pathogenicity,and heavy metal resistance.Differential analysis of functional genes involved in carbon and nitrogen metabolisms was performed by Linear Discriminant Analysis(LDA).The relationship between microbial community functions and environmental factors were analyzed by RDA.The results showed that the key environmental factors,which significantly affected the community functions,were COD,water temperature,labile phosphorus and ammonia nitrogen in the sediments.Co-occurrence network was analyzed by MENA to compare the microbial networks in two effluent receiving areas.It was found that under higher environmental pressures,microorganisms tended to construct simple network structures and cooperate with each other.The microbial community assemblage mechanism was analyzed by null model,and it was found that the community compositions were mainly selective,fitting with the ecological niche theory.The important findings of this study are as follows: SY community composition was significantly positively correlated with seawater COD.Its endemic species are capable to degrade toxic and harmful organic pollutants,which might be related to the higher and mostly recalcitrant COD emitted by SY WWTP.The pollution discharge also changed the functions of the microbial communities,resulting in the differences among microbial community functions in the effluent receiving areas.The impact of human activities has strongly changed the structures,functions and evolution of the microbial communities.According to the local environmental characteristics,the treatment processes should be improved,and the WWTP discharge standards should be supplemented and modified.