Spatiotemporal Distribution Characteristics Of DOM And Microbial Community In Surface Water And Sediment Of Liaohe Reservation Zone

Dissolved Organic Matter(DOM)and microorganism are important components of river ecosystem,which have important influence on the transformation of environmental pollutants,and have importance significance for maintaining the function of river ecosystem.In this paper,surface water and sediment samples were collected from Liaohe Reservation Zone during dry and wet seasons to investigate the spatiotemporal distribution characteristics of ecological environment quality.On this basis,the spatiotemporal characteristics of DOM structure and microbial community structure in Liaohe Reservation Zone were studied by spectral and high throughput sequencing techniques.The correlation analysis was used to reveal the correlation between DOM composition and microbial community structure and environmental factors.The main conclusions are as follows:(1)The environmental quality of the Liaohe Reservation Zone is good but unstable.In general,the surface water of Liaohe Reservation Zone is mainly affected by the input of N,P and organic matter.Spatially,the pollutant concentration of surface water in tributaries of Liaohe Reservation Zone was higher than that of main stream in dry season.The pollution degree of the main stream is higher than tributaries,and the concentration of N and organic pollutants is higher in the lower reaches in wet seasons.Seasonally,the surface water environmental quality of Liaohe Reservation Zone was poor in wet season,and the concentration of TN,NH₃-N and COD increased significantly,while the concentration of TP decreased significantly.(2)The main components of DOM in Liaohe Reservation Zone are C1(terrestrial and marine humus),C2(fulvic acid)and C3(tryptophan).The main components were humus(C1,C2).Its source is affected by both endogenous and exogenous factors.Spatially,the concentration of DOM in the tributaries is higher than that in the main stream,and the degree of humification of DOM in the tributaries is higher.The humification degree of DOM in the surface water decreased gradually from the upstream to the downstream of the river,but the humification degree of DOM in the sediments increased gradually from the upstream to the downstream.Seasonally,the concentration of DOC and protein components increased,while the aromaticity of DOM decreased.The fluorescence components of DOM have a good correlation with TN,TP,COD and heavy metals,which has a certain environmental indication significance for Liaohe Reservation Zone.(3)Spatially,the microbial community structure between the upper and lower reaches of the Liaohe Reservation Zone is significantly different.The microbial community richness in the lower reaches is generally higher than that in the upper reaches,and the microbial diversity and species richness in sediments were higher than those in surface water.Seasonally,the microbial diversity in the surface water of the Liaohe Reservation Zone is higher in wet season than in dry season.At the level of phylum classification,during the dry season,the dominant microorganisms in the surface water of Liaohe Reservation Zone were Bacteroidota,Cyanobacteria and Proteobacteria,and Temperature and COD were the key factors affecting the composition of the community structure.During wet season,the dominant microorganisms in the surface water of Liaohe Reservation Zone were Proteobacteria,Firmicutes and Bacteroidota,and DO and Cu were the key factors affecting the composition of the community structure.The dominant microorganisms in sediment of Liaohe Reservation Zone were Proteobacteria,Firmicutes,Actinobacteriota,and most of microorganisms in sediment showed good tolerance to heavy metals.The relative abundance of Firmicutes and Actinobacteriota increased and Cyanobacteria decreased during the dry season,which indicated that the surface water in Liaohe Reservation Zone may be polluted by industrial and agricultural wastewater.The relative abundance of Chloflexi in sediments was significantly higher than that in surface water.Further study on the response of DOM to microorganisms in Liaohe Reservation Zone showed that there was a certain correlation between the components of DOM and the microbial community structure,it can provide a certain data base for revealing the factors of DOM degradation and microbial community abundance.