| The vast northwest region of China has a dry and arid climate with scarce precipitation.The lack of surface water and groundwater resources makes life extremely inconvenient for the people,and some economically underdeveloped villages and towns still use rainwater collected in cisterns as a source of drinking water for humans and livestock.However,due to factors such as the method of collecting rainwater through the catchment area and the environmental conditions of the cistern,indicators such as nitrogen and phosphorus in the cistern water often exceed the standards.TN and TP have exceeded the Class III water quality standards in the Surface Water Environmental Quality Standards(GB3828-2002),and some indicators even exceed the Class V water quality standards.Long-term use of cistern water contaminated by such pollutants as a source of drinking water poses a great threat to human health.Currently,water resources have become the main factor restricting further economic development and improvement of people’s living standards in some villages and towns.In the comprehensive solution and technical system for water purification to achieve the water quality standards in stages for cellars,enhancing in-situ biological restoration of cellar water is a key step.Previous studies have shown that cistern water contains a rich and diverse range of microbial species,and the nitrogen transformation process during the self-purification of cistern water is closely related to the microbial community in the cistern water.These microorganisms form a complex nitrogen cycling system in the cistern water,which plays an important role in water quality purification and maintaining the ecological balance of cistern water.Although there have been many studies on nitrogen cycling in aquatic ecosystems,most of these studies have focused on large watersheds such as oceans and estuaries,and there are relatively few studies on the microbial community structure related to nitrogen transformation in relatively closed systems such as cistern water.In this study,the key nitrogen transformation processes in cistern water,namely,the ammonia oxidation process and the denitrification process,were selected.The amo A and nir K genes were used as marker genes,and high-throughput sequencing technology was used in combination with PCA,PCo A,RDA,LEf Se,and other analysis methods to study the microbial community structure and diversity related to the key nitrogen transformation processes in cistern water.Furthermore,the study explored the relationships between nitrogen transformation-related microorganisms and different environmental factors in cistern water.The results are as follows:(1)The microbial communities associated with the amo A gene in cellar water are relatively simple and have low resistance to shock and instability.Microbial community diversity is greatly affected by seasonal changes,with Proteobacteria being the dominant bacterial phyla and the Betaproteobacteria being the dominant class that contains most of the microbial communities responsible for ammonia oxidation.At the order level,Nitrosomondales and norank＿c＿Betaprotcobacteria alternately become dominant in different samples over time.The dominant bacterial species at the family level include Nitrosomonadaceae and norank＿c＿Betaprotcobacteria,and the dominant bacterial species at the genus level are mainly found in norank＿f＿＿Nitrosomonadaceae and norank＿c＿＿Betaprotebacteria,with Nitrosomonas and Nitrosospira being the main ammonia-oxidizing bacteria and the abundance of Nitrosospira being several times higher than that of Nitrosomonas.(2)The microbial communities associated with the nir K gene in cellar water are more diverse than those associated with the amo A gene.Furthermore,microbial community diversity and richness are less affected by external factors such as seasonality.The dominant bacterial phyla are unclassified＿k＿＿norank＿d＿＿Bacteria(35.09%～83.52%),Proteobacteria(2.94%～40.12%),and norank＿d＿＿Bacteria(1.41%～57.44%).Most of the bacteria responsible for denitrification are found in Alpha Proteobacteria at the genus level.The denitrifying bacterial community in cellar water show more species diversity and a greater proportion of rare species,with only a few high-abundance species forming the basic structure of the microbial community at different taxonomic levels.Increasing the concentration of organic matter in cellar water can enhance denitrification,and the functions of rare species in the nitrogen cycle need further investigation in future research.(3)In the microbial communities associated with nitrogen transformation in cellar water,the dynamic changes in the microbial communities at different taxonomic levels show varying degrees of regularity over time.However,this regularity is a complex process subject to multiple factors.In addition to cellar water environmental factors and the connections between different links in the nitrogen cycle,external factors such as seasonal changes and precipitation events also play a role.Furthermore,the cellar water ecosystem is not an independent aquatic ecosystem.The external input of surface runoff connects the microbial communities in cellar water with those in terrestrial soil,and together they participate in the conversion of matter and the flow of energy in the ecosystem,ultimately completing the key processes of nitrogen cycling in cellar water.Through this study,a deeper understanding of the key nitrogen transformation processes and microbial mechanisms in collected rainwater cisterns has been gained.The community structure and diversity of ammonia oxidizing microorganisms and denitrifying microorganisms in collected rainwater cisterns,as well as the interrelationships between microbial communities and different environmental factors,have been preliminarily explained.The results of this study are important for controlling and reducing nitrogen pollution in collected rainwater cisterns,strengthening the biological purification function and effectiveness of cistern water,and improving the safety of drinking collected rainwater cistern water. |
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