Study On The Characteristics Of Benthos And Microbial Community Structure In Coastal Urban Rivers

With the deepening of the urbanization process,the destruction of river ecosystems has been exacerbated,especially for coastal urban rivers,which are subjected to the dual pressures of tidal and runoff.This has posed many challenges and difficulties for the restoration and protection of coastal river ecosystems.In this study,through on-site exploration and investigation,combined with the habitat conditions and urbanization level within the river sections,the study area was divided into different habitats.Sampling was carried out for three quarters to analyze the differences in water quality between different river sections,investigate the characteristics of benthic animal community structures,conduct water quality biological evaluations,and study the structure and characteristics of microbial communities.（1）Analysis of water environmental conditions in different habitatsBased on a large-scale habitat survey,differences in river bed geomorphology,vegetation coverage,and urbanization levels among different river segments were distinguished.The study area was divided into five habitats,including the tidal zone,urban river sections within the inner city and suburban areas,the Liuzi River urban river section,and rural river sections.Water quality analysis showed that the overall water quality in the study area met the Class V water standard,with TN being the main pollutant.From a time scale analysis,TN and TP were the main pollutants in summer,with average concentrations of 6.13 mg/L and 0.33 mg/L,respectively.In autumn and winter,the main pollutants were TN and NH₃-N,with concentrations of 15.06 mg/L and 1.45 mg/L in autumn,and 16.06 mg/L and 4.93 mg/L in winter,respectively.Water quality evaluation analysis showed that the overall pollution level in the river section was relatively severe,with the best water quality in summer,followed by autumn,and the worst in winter.（2）Analysis of benthic animal community structurePeriodic sampling was conducted at seven sampling points in different habitats over the summer,autumn,and winter seasons,and a total of 1639 large benthic animals were collected,including 48 species belonging to 4 phyla,9 classes,16 orders,and 29families.The proportion of arthropods was the highest,and the benthic animal habitat density was highest in winter（4104ind/m2）,followed by autumn（1984ind/m2）and summer（468ind/m2）.The richness index was highest in summer,followed by winter,and lowest in autumn.From a spatial scale analysis,the Liuzi River section was lower than the inner city river section,and the richness index showed a positive correlation with water temperature and dissolved oxygen.The Shannon diversity index was lower in autumn than in summer and winter,and the overall biological index value in summer was lower than that in autumn and winter.Each river segment was subject to varying degrees of pollution.The BI biological index showed a negative correlation with water temperature and a positive correlation with TN,NH₃-N,COD_Mn,and DO.（3）Microbial community structure analysis OTU species classification annotation was performed on samples from the study area.After sequence normalization and species filtering,a total of 63 phyla,174 classes,457 orders,827 families,2294 genera,and 6904 species were detected,with an overall OTU range of 372 to 10322.The main dominant bacterial phyla in the study area were Proteobacteria,Bacteroidetes,Actinobacteria,and Firmicutes.The main dominant bacterial genera were Flavobacterium,Pseudomonas,Micrococcus,and Chloroplast.The diversity analysis results showed that microbial diversity was mainly related to COD_Mn,DO,TN,and water temperature,and the correlation between dominant species and water environment was not significant,indicating a complex water environment.Through habitat division and water quality evaluation,analysis of benthic community structure characteristics and water quality biology evaluation,as well as analysis of microbial community structure characteristics and correlation,it was shown that the pollution level was high in the urban sections of Neijia River and Liuzi River,but the water environment in other sections was also not optimistic.