The Effect Of Lake Pan On The Bacterial Abundance And Community Structure Of Taihu Lake

Black blooms has become another serious problem in eutrophic lakes together with cyanobacterial blooms nowadays.Black blooms not only decreased water quality,but also induced bacterial community shifting in the lake.It damaged the lake ecosystem seriously,and resulting in adverse social impact in China.We carried out our study in Lake Taihu,where black blooms caused by algae-blooms happened constantly.Molecular biology techniques and multivariate statistical analysis method were used to evaluate relationships between bacterial abundance and environmental variables in the areas where black blooms happened regularly(ABBs).We also accessed the spatial bacterial community differences during black blooms happened,and effects of sediment on the black blooms as well as bacterial community in water column.Results based on daily monitoring data in situ indicated that black bloom prone to happened in late spring and early summer(June to July),late summer and early autumn(October)in Zhushan Bay,Meiliang Bay and western part of the lake.Our findings include:1?There were significant spatial bacterial abundance differences among ABBs.Positive relationships were detected between bacterial abundance and water temperature,dissolved oxygen concentrations(DOC)and chlorophyll-a.Negative relationships were found between bacterial abundance and Secchi depth(SD).Results of generalized additive models(GAM)also indicated that nutrient concentrations play a vital role in mediating bacterial abundance.2?The black blooms deteriorated water quality significantly in the field.DO,SD and pH decreased significantly,particularly,DO would decreased as low as 0.5 mg/L,which indicated an anaerobic environment in the water column.In addition,black blooms would increase nutrient concentrations(total nitrogen,total phosphorus),phytoplankton biomass and bacterial abundance.The bacterial abundance in the central of black booms exceeded 107 cells/L,which was an order of magnitude higher than other areas without black blooms.3?High-throughput sequencing technology was used to analyze differences of bacterial community structure among different areas with or without black blooms.Results indicated that,bacterial community structure were significantly different among the areas.Main species in Lake Taihu have undergone significant changes,e.g.alpha-,beta-,and gamma-Proteobacteria,Bacteriodetes,Actinobacteria,Firmicutes.Namely,along black blooms,a-.y-proteobacteria decreased from 13.16%and 4%to 0.5%and 1.9%respectively;and Actinobacteria decreased from 19.08%to 0.98%.In contrast,Bacteriodetes increased from 1.12%to 36.32%.4?Lab-experiments were designed to evaluate the effects of sediment on black blooms.Our results indicated that nutrient concentrations in the sediment from estuaries were much higher than sediment from other two areas.The extent of black blooms induced by sediment from estuaries were much heavier than black blooms induced by sediment from other two areas.In contrast,the extent of black blooms induced by the sediment from eastern part of the lake was the lightest,and the duration of the blooms was the shortest.Our experiments demonstrated that the features of sediment have an important impact on the onset and duration of black blooms.5?Trends of bacterial community succession during black blooms were general consistent both in situ and lab-experiments in our study.Bacteroidetes and Firmicutes have shown a substantial increase in the percentage,while percentage of Proteobacteria and Actinobacteria dropped after the blooms.6?After the bloom,the abundance of actinomycetes,which can decompose organic matter,increased significantly.The treatment with sediment from eastern part of the lake had the most significant increasing in Actinobacteria percentage(approximately 22 times).Proteobacteria percentage remain constant in treatment with sediment from the eastern part of the lake and control groups,while the percentage decreased in the treatments with sediments from estuaries and lake centers.Bacteroidetes and Firmicutes percentage decreased after the blooms in each treatment.Bacteroidetes percentage in the treatment with sediment from eastern of the lake turn back to the start value ultimately,and the percentage of Firmicutes in the treatment after the blooms was 6 times higher than initial ones.In the treatments with sediments from east of Taihu,recovery rate of some bacterial species's percentage was faster than the recovery rate from other treatments.