Ecological Responses Of Benthic Communities To Chemical Contaminants Using Sediment DNA Meta-systematics

Contaminants deposited from anthropogenic activity have been causing biodiversity loss and ecological malfunction. Sediment is not only the habitat of benthic organisms but also the "sink" and "source" of chemical pollutant mixtures in the aquatic environment. During the monitoring and evaluation of sediment quality, the microbial communities which play key roles in ecological functions are always neglected. Conventional biological monitoring focus on limited communities rather than multi-community, and cannot meet the needs of multi-community biomonitoring. Furthermore, the associations of microbial communities with both pollutant mixtures and ecotoxicological endpoints in response to sediment contamination have been poorly evaluated. Microbial communities in sediment are responsive to pollutants and could be used as alternative ecological indicators of sediment pollutants. However, there is few study on microbial bioindicators predicting specific pollutants in sediment. Overall, Ion Conductor Sequencing-based sediment DNA meta-systematics were developed to monitor multiple benthic communities, including bacterial, protist and metazoan communities. Associations of benthic communities with pollutant mixtures were assessed by the sediment DNA meta-systematics to use the in situ communities to evaluate the ecological responses of in situ communities to the effects of pollutant mixtures in aquatic ecosystems. The bio-indicators were identified for health assessment of aquatic ecosystem and quality evaluation of aquatic sediment.Therefore, one Ion Conductor Sequencing-based platform combined both sediment DNA meta-systematics and ecological statistical methods was developed to characterize the bacterial, protistan and metazoan communities. To study the ecological responses of benthic communities and their indication to major ecological risks, the "Hebei Spirit" Oil Spill and Three Gorges Reservoir (TGR) which backgroud were relatively clear were studies by the sediment meta-systematics platform:1) Assessed the long-term ecological effects of the oil spill residual, and discovered the potential bioindicators predicting the degree of oil residual pollution.2) Evaluated the ecological responses of benthic microbial communities to AhR mediated organic pollutants of sediments from TGR, and discovered the potential bioindicators predicting the degree of organic pollutants mediating aryl hydrocarbon receptor (AhR) activity.3) Characterized ecological responses of bacterial communities to pollutants mixtures in sediments from different land use type in the area of Nanfei River (Hefei, China), evaluated the associations between bacterial communities and pollutants, and found the potential key chemical stressors. The main conclusions are listed as follows.1) Developing Ion Conductor Sequencing-based sediment DNA meta-systematics and statistical methods to monitor multiple benthic communities, including bacterial, protist and metazoan communities and assess their associations with pollutant mixtures.2) Alterations in diversities and structures of micro-and macro-biomes were observed in the contaminated area with an elevated concentration of total polycyclic aromatic hydrocarbons. The presence of bacterial families (Aerococcaceae and Carnobacteriaceae) and protozoan family (Platyophryidae) might have conferred sensitivity of communities to oil pollution. Hydrocarbon-degrading bacteria families (Anaerolinaceae, Desulfobacteraceae, Helicobacteraceae, and Piscirickettsiaceae) and algal family (Araphid pennate) were resistant to adverse effects of spilled oil. Protistan family (Subulatomonas) and arthropod families (Folsomia, Sarcophagidae Opomyzoidea, and Anomurd) appeared to be positively associated with oil pollution. The relative abundance of these associated taxonomic groups could distinguish the degree of oil contamination with reasonable accuracy.3) In situ microbiomes from the TGR area of the Yangtze River were characterized by sediment DNA meta-systematics, and then, changes of in situ microbiomes were compared with the ecotoxicological endpoint, AhR mediated activity, and level of PAHs in sediments. PAHs and organic pollutant mixtures mediating AhR activity had different effects on the structures of microbiomes. Specifically, Shannon indices of protistan communities negatively correlated with the levels of AhR mediated activity and PAHs. The sediment AhR activity was positively correlated with the relative abundance of prokaryotic Acetobacteraceae but had a negative correlation with protistan Oxytrichidae. Furthermore, a quantitative classification model was built to predict the level of AhR activity based on the relative abundances of Acetobacteraceae and Oxytrichidae.4) The bacterial communities in sediments from Nanfei River were dominated by Proteobacteria, Bacteroidetes, and Chlorqflexi. Both the profiles of environmental predictors and the composition of microbial communities differed among agriculture, industrial and confluence regions. There were significant associations between bacterial community phylogenies and the measured contaminants in the sediments. Nutrients (TN and TP) and two metals (Cd and Zn) were negatively correlated with the essential "core" of the bacterial interaction network(Betaproteobacteria and Deltaproteobacteria). Metals (Fe, Ni, and Zn) and nutrients (TN and TP) had a higher impact on bacterial community compositions than PAHs, OPs and PRTs according to the correlation and network analyses. Furthermore, several sensitive candidate genera were identified as potential bioindicators to monitor key contaminants by species contaminant correlation analysis. Components and structures of in situ sediment bacterial communities can be used to track the key stressors among multiple pollutants of the freshwater river ecosystem.