Characteristics Of Typical Agricultural Non-point Source Pollutants Removal And Microbial Community In Ecological Regulation And Storage Pond Wetland System

Ecological governance technology provides sustainable solutions for controlling agricultural non-point sources with relatively low costs and operational management requirements.In the Shahe River basin,the primary tributary of the Dongjiang section of the the Pearl River basin,it is one of the current research topics in the southern region to intercept non-point source pollution from the agricultural catchment area by using the ecological regulation pond with the attribute of semi natural wetland to deal with the low dissolved oxygen problem in some downstream tidal river basins.This study focuses on the characteristics of influent water quality,pollutant reduction efficiency,and microbial communities in sediments,surface water,and plant rhizosphere of the ecological regulation and storage pond system in Chating.Evaluate the main migration and transformation processes of pollutants within the system and their reduction effectiveness in different periods through on-site research and long-term monitoring along the flow path.The 16Sr RNA gene high throughput sequencing technique was used to explore microbial community composition,functional prediction,and symbiotic networks in different habitats in the study area.In addition,through RDA and co-occurrence network analysis,environmental factors that have an important impact on microbial communities were selected,as well as the correlation between important functional bacteria and environmental factors and reduction performance.The main research conclusions are as follows:（1）The average concentration of ammonia nitrogen（NH₄⁺-N）in the influent water of the system is larger than the concentration of nitrate nitrogen（NO₃^--N）,which is 4.42mg/L and1.28mg/L,respectively,indicating that the influent water may be affected by other factors,rather than agricultural water withdrawal.（2）The organic matter and phosphorus in the ecological storage pond wetland system are mainly intercepted through physical processes such as sedimentation,filtration,and interception,while nitrogen is mainly removed through biological nitrification and denitrification.Due to the high concentration and wide distribution of dissolved oxygen,the denitrification process is inhibited to a certain extent,resulting in the accumulation of NO₃^--N.In addition,with a wetland/catchment area ratio of 0.9%,the treatment efficiency of the ecological regulation and storage pond system has achieved stable operation.The average reduction rates of chemical oxygen demand（COD）,ammonia nitrogen（NH₄⁺-N）,total phosphorus（TP）,total nitrogen（TN）,and total suspended solids（TSS）in the dry and rainy seasons are 8.4%,59.3%,66.7%,31.8%,-31.9%,and 23.2%,52.9%,51.5%,23.4%,and22.5%,respectively.The removal capacity of TN and NO₃^--N is limited,and the rainy season has a significant impact on the interception and pollutant reduction of ecological storage ponds.（3）Analysis of microbial community diversity,distribution of dominant bacteria,and functional differences in the ecological regulation and storage pond wetland system.In the entire study area,the dominant bacteria are Proteobacteria,Chloroflexi,Cyanobacterium,and Actinobacteria;From the water inlet to the water outlet section,the relative abundances of Proteobacteria and Firmicutes gradually decreased,while the relative abundances of Cyanobacterium and Acidobacter increased.However,at the generic level,there is no significant difference in community composition,which is mainly due to the occurrence of short flows in the flow path,short hydraulic stop times,and different microbial communities entering the next functional area with the flow,resulting in homogenization and variation of microbial communities during long-term operation.There are significant differences in microbial communities among different habitats（sediment,surface water,and plant rhizosphere）,indicating that different substrate and environmental choices have a significant impact on the structure of microbial communities.In addition,functional bacteria with high abundance are mainly aerobic（1.1%～7.4%）,phototrophic（1.5%～30.7%）,fermentation（1.2%～5.3%）,nitrate reduction（0.4%～4.2%）,sulfur related（～8.7%）,and iron related（～1.5%）,as well as human pathogens（0.7%～4.2%）,among which aerobic and phototrophic bacteria are mainly distributed in water and rhizosphere,and anaerobic or facultative anaerobic bacteria are mainly distributed in sediments.In addition,co occurrence network analysis shows that the composition of microbial communities in surface water is more complex than that in sediment.（4）The relationship between microbial community composition and important functional genera and the environment.Through distance based RDA analysis,the key influencing factors of microbial community abundance in sediments（NH₄⁺-N and NO₃^--N）and surface water（DO）were selected,and it was pointed out that environmental factors（land use）and parameters（pollutant concentration,nutrient composition,combination and distribution of intensification techniques）were closely related to the distribution of dominant genera.According to linear regression and co occurrence network analysis,only the desulfurization related genera in the sediment belong to the dominant bacteria in the system,and drive the pollutant reduction efficiency.Moreover,there is a significant negative correlation between desulfurization and DO and NO₃^--N（a significant positive correlation between DO and NO₃^--N）,indicating that DO concentration is one of the key factors leading to the accumulation of NO₃^--N.This study conducted relevant research on the pollutant migration and transformation process,microbial community composition changes,and key factors related to environmental change and driving reduction efficiency of the ecological regulation and storage pond wetland system.The interception characteristics,microbial community composition and distribution characteristics in the southern non-point source pollution control project were obtained,and the reduction efficiency of the engineering system for typical non-point source pollutants and its relationship with microorganisms and environmental factors were evaluated.The results of this study provide an important basis for the design,scientific maintenance and ecological restoration technology of non-point source pollution control projects in the the Pearl River Basin.