Investigation On Sediment Microbial Community Response To Water Eutrophication In Estuary System

Estuary is a bridge connecting the land and the sea,and is a hot spot for element biogeochemical cycle.Charactering of organic matter in the estuary and its fate are of vital importance for assessing the efficiency of "carbon burial" at regional and global scales.In particular,high primary productivity caused by eutrophication can significantly change the source and structure of organic matter,affect microbial degradation and transformation processes of organic matter in river-estuary transport system,and carbon burial efficiency,which is hotspots and knowledge gap in our understanding of global carbon cycle.In this thesis,the Xiaoqing river-Laizhou Bay is choosed as the research target.Molecular composition of organic matter in surface sediments are analyzed.The spatial and seasonal distribution characteristics of sedimentary organic matter in Xiaoqing estuary are discussed.Using the combination of physi chemical indicators,microbial community diversity and Q-PCR of functional gene to explore the mechanism of the rapid turnover of organic matter under the high primary productivity condition;finally,an in-situ experiment was designed to simulate the process of organic carbon input under periodic oil input by tidal action,and verified organic matter input had effect on the structure and function of microbial community.The main understandings are as follows:1.The total organic carbon(TOC)content in the water and sediments in Xiaoqing rive was significantly higher than that in the Yangtze,Yellow,and Pearl Rivers.The TN concentration is seriously exceeded the national standard for surface water.Dectection of sterane,terpane and polycyclic aromatic hydrocarbons(PAHs)in surface sediments shows typicalfossil fuel combustion input;Fecal sterols indicates the livestock wastewater and the untreated industrial runoff direct discharge.2.The distribution of sedimentary organic matter in Xiaoqing river-Laizhou Bay shows significant spatial and seasonal differences.The spatial variation is mainly controlled by salinity,the contribution of terrestrial source is decreased while the conribution of algae sources is elevated along the river to estuary,the mean value of the organic carbon isotope(?13Corg)is enriched from-26.1‰ to-23‰,which is dominated by higher plant input from the;Seasonally:there is a stronger input of algae-derived organic carbon in summer the proportion of n-alkanes from plankton is increased from about 30%.The distribution patterns of chromatographically indistinguishable compounds(UCM)reflecting biodegradation are significantly different.Spring samples UCM was result from petroleum hydrocarbon input and terrestrial high-grade plant degradation;while summer samples not only have,UCMis present in the high carbon fraction,but also have UCM in the low carbon fraction,indicating that degradation algae-derived OM.3.The microbial community structure of sediment samples in Xiaoqing river-Laizhou Bay has obvious spatial heterogeneity.The river station is dominated by Betaproteobacteria,Clostridia and Actinobacteria,while Flavobacteria and Cyanobacteria are obviously enriched in the estuary.The relative abundance of the spring archaea Crenarchaeota,Thermosolasatain and other groups belonging to the MBGB and MCG groups increased rapidly in summer sediments,which became the main contributor to the differences in microbial diversity between spring and summer.Multivariate statistical analysis showed that the source,abundance and physical and chemical parameters of organic carbon dominated the microbial distribution.Among them,TOC content is the most important constraint factor of spring microbial community structure,and the influence factors restricting summer distribution are differentiated.The inner station of estuary is mainly subject to acceptance parameters,while the outer station of estuary is mainly affected by the source of organic carbon.4.The overall potential capacity for organic carbon degradation in summer samples is higher than spring samples.The aerobic genes for alkanes and aromatics were enriched in summer samples.Significantly positive relationship was observed between the absolute and the relative contents of gene expression and labile organic carbon,which may indicate the "priming effect".5.In situ experiments were performed at an oligotrophic gravel beach sediment that received period of oil input by tidal action,results showed that microbial community degradation efficiency was coupled with the dynamic of functional gene abundance,indicating the OM input could induce the typical succession characteristics of the dominant degrading microbial community.OM-degrading bacteria were successed from the Oceanospirillales and the Actinomycetes to Alternomonadales,Rhizobias and Chromatiales,which also verified the existence of the "priming effect" in the natural environment.