Variation Characteristics Of Physical,Chemical And Bacterial Community Structure Of Water In Lanzhou Section Of Yellow River In Dry And Wet Season

Ecological civilization have been written into“five in one”strategic layout by the eighteen National Congress of Communist Party of China,and have been put into the constitution by the National people's Congress,thus opening a new journey of China's ecological civilization construction.Yellow River is called Mother River in China,she is also the most important drinking and irrigation water resources in northwest and north China.Therefore,its water environment is related to the economic development of the Yellow River basin and the safety of drinking water by nearly 200 million people along the coast.According to the China's Environmental Bulletin,the water quality of Yellow River is under medium bias in the seven major rivers in China,COD and ammonia nitrogen pollution are particularly serious,this shows that human activities have seriously affected the safety of water environment in the Yellow River.Lanzhou is the only heavy industry capital city which was passed through by Yellow River in the entire valley.The water is the only source of drinking water for Lanzhou citizens.But,how is the water quality in Lanzhou section of Yellow River?There is no scientific assessment of this question.So,the water samples from different section in Lanzhou region?Liujiaxia,Xincheng bridge,Xigu district,Qilihe,Zhongshan bridge,Baolan bridge and Qingcheng bridge?during low and high water periods were collected in 2016-2017,16S rRNA and functional gene high throughput sequencing,real time fluorescence quantification and multivariate statistical analysis methods were used,then we analyzed the conventional physico-chemical properties and heavy metals,evaluated the health risk and the source of pollutants,depth analyzed the bacterial community structure,the community structure of functional organism of ammonia nitrogen elimination and there correlation with the environment.The results showed that:?1?The situation of water environment in Lanzhou section of Yellow River has obvious difference in dry and wet season,sample points from upper reaches to lower reaches.The better water quality was found in dry season and in the upper reaches,the environment around the sample points has significant impact on the Yellow River water environment.The average content of some physico-chemical indexes were out of the national standard in the two water periods,including five day biochemical oxygen demand,ammonia nitrogen,nitrite nitrogen,total nitrogen,fecal coliform and some of the heavy metals,arsenic were out of the limit in the wet season.Arsenic has more risk on the human health as carcinogen and non-carcinogen,hexavalent chromium has health risk as carcinogen.The industrial enterprise,domestic sewage treatment plant and human activities along the river may be the main reasons which caused the water quality deterioration.?2?The bacterial phyla of Proteobacteria,Bacteroidetes,Cyanobacteria and Actinobacteria were more abundance in the two water periods,the distribution of these bacteria groups has characteristic in different season and environment.Bacteroidetes and Actinobacteria have more abundance in the two water periods,Proteobacteria in wet season,nearly twice as much as in dry season,but Cyanobacteria in dry season,10 times more than in wet season.The results indicated that the change of the bacteria community structure was as an indicator of water quality,the nitrogen and phosphorus compounds can simulate the growth of the bacteria,and make the diversity of bacteria community increase.?3?There were three groups of ammonia oxidizing microorganism in the Yellow River water of Lanzhou section,including ammonia oxidizing archaea?AOA?,ammonia oxidizing bacteria?AOB?,and anaerobic ammonia oxidation bacteria?Anammox,AMX?.Relative and absolute quantitative results displayed AOA has the most community diversity and gene abundance than the other two groups.In AOA group,Nitrosopumilus and Nitrososphaera have more abundance than others.Nitrosopumilus related to the lower C/N,and Nitrososphaera correlated with the lower environment temperature.It is also found that a large number of AOA do not belong to common group,indicating that the Lanzhou section of the Yellow River is rich in AOA population resources.Nitrosospira and Nitrosomonas have more abundance in AOB group,Nitrosospira has the most abundance,Nitrosomonas was less than Nitrosospira which related to the lower water temperature.Candidatus Brocadia,Candidatus Scalindua and Candidatus Kuenenia were more abundance than the other groups in Anammox,Candidatus Brocadia dominanted in anammox process.?4?The correlation analysis between five heavy metals and ammonia oxidizing microorganism showed that AOA was most significantly affected by heavy metals,the response of AOB was not obvious.The gene abundance of AOA has significant positive relationship with heavy metals,Anammox has positive correlation with As,Cu,Pb,AOB was inhibited by Cr⁶⁺,and has no obvious relationship with most of the heavy metals.On the other hand,As,Cu and Pb have the same impact on three kinds of ammonia oxidizing microorganism,their contents have positive relation with the gene abundance of AOA and Anammox,with no obvious correlation with AOB gene abundance.Hg only has positive correlation with AOA.Cr⁶⁺was more special,it can simulated the growth of AOA,but inhibited the reproduction of AOB.?5?Bacterial community structure was more sensitive to the environmental factors,it can be used as an important auxiliary measure for water quality detection.Ammonia oxidizing microorganism can be used as an important way and means of water pollution restoration in the Yellow River.The results provided scientific and technological basis for the construction and management of ecological civilization in the Yellow River Basin.