Characterization Of Water Pollution And Self-Purification Ability In YuLong River-Li River Connected Water System

To study the pollution characteristics of water bodies in connected water systems and to analyse the microbial diversity and self-purification capacity of connected water systems This study selected 19 sampling points from streams,ditches,and ponds in the Yangshuo Yulong River-Li River connected water system,and conducted sampling analysis from August 2021 to July 2022.The pollution characteristics of conventional pollutants and antibiotics from connected water lines and their temporal and spatial variations were investigated,and the microbial community composition and diversity of the connected water lines were analyzed based on high-throughput sequencing techniques,combined with the study of the rapid biodegradation of compounds in water lines and the study of their physical,chemical and biological purification effects,and the self-purification ability of the connected water lines was evaluated.The main findings are as following:(1)The water quality of the connected water systems was evaluated using the Nemero pollution index method,and the results showed that the water quality(Class Ⅰ-Ⅱ)of the diversion and drainage channels in the rural segments was superior to Shuangyue Brook(Class Ⅲ-Ⅳ)in the urban area,and that the water quality(Class Ⅱ-Ⅲ)of the regulatory lake was superior to that of the lake ponds and reservoirs(Class Ⅲ-Ⅴ),and that the water quality was the worst in the low water period during the time and superior to that in the high water period;The lake bank eutrophication evaluation results showed that the semi-connected Baoquan lake and non-connected Lotus ponds were moderately eutrophic and severely eutrophic throughout the year,and the remaining Lake banks were moderately eutrophic during different water periods;The results of the health evaluation of connected water systems showed that,except for the ponds of Dacunmen,which was very healthy,and the Baoquan lake and Lotus ponds,which were unhealthy,the remaining water bodies were sub healthy.(2)Antibiotic monitoring results showed that a total of 14 kinds(6 kinds of Sulfonamides,4 kinds of Tetracyclines and Quinolones,respectively)were detected in 17 target antibiotics;The cumulative concentrations of antibiotics in each section were as follows:low flow period > normal level period > high flow period.Correlation analysis showed that norfloxacin was significantly correlated with total nitrogen,total phosphorus and ammonia(r= 0.611,0.590 and 0.624),while sulfamethazine and oxytetracycline were both negatively correlated with permanganate index(r =-0.735 and-0.696);Antibiotic ecological risk factors in the study area were mainly ciprofloxacin and ofloxacin,with a scenario of reaching moderate or even high risk.(3)16S rRNA sequencing results showed that the highest relative abundance of microbial composition in connected water groups was betaproteobacteria(9.78% ～ 51.24%in river and 6.86% ～ 46.80% in lake bank),the second highest relative abundance of Actinobacteria in River(1.76% ～ 30.60%),and the second highest relative abundance of chloroplast in Lake Bank(0.98% ～ 34.18%);The total amount of organisms and the diversity of bacteria are related to the degree of pollution in water bodies,and the high degree of pollution is more than the low degree of pollution,and the species of organisms have some similarity;Cod and do affect microbial communities to the greatest extent,and chloroplast can characterize the effects of environmental factors on microbial communities.(4)The results of rapid biodegradation of sodium acetate,anhydrous ethylene glycol and aniline showed that drenching River exhibited more degradation ability for the added compounds than Yulong River,the water channels in the rural section were stronger than those in the urban area,and the ponds in urban area exhibited the following: semi connected Ametrine ponds > non connected lotus ponds > fully connected flat peach lakes > fully connected migratory pools.