Study On The Spatiotemporal Correlation Between Water Quality And Microbial Community Of Typical Inflow Rivers In South Taihu Basin

During the past decades,serious water pollution issues caused by rapid industrialization and urbanization in Taihu and other major basins have been paid considerable attention.Previous studies showed that inflow rivers are the main cause of eutrophication,algae bloom and drinking water safety of downstream lakes?reservoirs?especially for Taihu Lake,and were focused on the ecological restoration of inflow rivers and algae control of lakes.However,issues such as frequently backflow of water led to the accumulation of algal bloom,poor performance of restoration,and difficulties on meeting the standard stably of monitoring sections in inflow rivers are existed,because of the continuously social and economic development,water diversion from Yangtze River to Taihu Lake,and excessive exploitation and utilization of water resources.The study on physicochemical characteristics of water quality and microbial spatiotemporal succession in different pollution types,favors the carry out of"One River,One Plan"and restoration of healthy river ecosystem,especially in the basin with developed economy,large population and complex hydrological condition.In this thesis,two typical inflow rivers located at South Taihu Basin?Changxing river and West Tiaoxi river?are as research objects,and four pollution types?Estuary of Taihu Lake,Discharge outlet of urban wastewater treatment plants,Storm water outlets and Drainage area of agricultural non-point source?in four seasons are sampled.High-throughput sequencing and multivariate statistical analysis are used to analyze the water physicochemical property,microbial community diversity and structure,and effects of pollution types on river ecosystem are discussed.The main results are as follows:?1?The water physicochemical properties of two typical inflow rivers in South Taihu Lake were analyzed.Water qualities of Changxing river were worse than those in West Tiaoxi river constantly,and the main pollution factors included ammonia?NH₄⁺-N?,total nitrogen?TN?and total phosphorus?TP?.The pollution level of rivers varied in different seasons.Thereinto,the water qualities of Changxing river in autumn and West Tiaoxi river in winter were the worst,and belonged to the heavy pollution level.The worst water quality among pollution types was at the Storm water outlets,and the concentrations of NH₄⁺-N,TN and TP were 1.02-2.19 mg/L,3.14-5.30 mg/L,0.22-0.55mg/L respectively,indicating a signification influence by combined sewage and storm discharge in Changxing river and West Tiaoxi river.Meanwhile,the Estuary of Taihu Lake had relatively high p H?7.5-8.0?,and the DO was as low as 2.20 mg/L during the algae bloom at Taihu Lake in autumn.?2?The microbial community structure of two rivers were analyzed,and results showed that seasonal variation was the main factor causing the differences on microbial community diversity.The diversities of microbial community in summer and autumn were the highest,and Chao1 index was 3278 and 1247,respectively.Samples were divided into two groups by cluster analysis:first group included Estuary of Taihu Lake,Drainage area of agricultural non-point source and Drinking water source,where Microcystis was significantly enriched?16.6%-26.0%?;the second group consisted of Discharge outlets of urban wastewater treatment plants and Storm water outlets,with higher relative abundances of Pseudomonas,Arcobacter,Acinetobacter?4.4%-9.7%,5.5%-8.2%,0.6%-4.2%?.Results demonstrated that the abundance of microbial community in different rivers was similar at the same pollution type.?3?Based on pollution type as the main factors affecting the microbial community of rivers,correlations between water quality and microbial community at different monitoring sites of inflow rivers were analyzed by RDA method.The relative abundance of Microcystis and Nostocaceae at the Estuary of Taihu Lake was correlated with DO and p H positively.At the Storm water oulets,Pseudomonas,Arcobacter,Malikia were correlated positively with TN,NO₃^--N.While Aquabacterium,Acinetobacter,Dechloromonas and Hydrogenophaga had a positive correlation with NH₄⁺-N,but negative correlation with DO.Based on the above results,it is suggested that the hydralic circulation and reoxygenation at the detention zone should be taken into account during the pollution remediation at the Estuary of Taihu Lake,so as to alleviate the cyanobacteria retention and nitrogen&phosphorus accumulation,and to realized the enrichment of nitrifiers and denitrifiers.The remediation at Storm water oulets should focus on the moderate aeration?DO should be controlled at 5-6 mg/L?and suitable carrier arrangement,so as to effectively enrich and retain the nitrifiers and realize nitrification and denitrification simultaneously.