Microbial Community Structure And Abundance Of Functional Genes Of Nitrification And Denitrification In Huixian Karst Groundwater

Karst groundwater is an important water source for people's production and life in karst areas.However,nitrogen pollution of karst groundwater caused by agricultural non-point source pollution and domestic sewage has become an important environmental geological problem in karst areas.In order to seek the possibility of in-situ treatment of nitrogen pollution in karst groundwater,it is necessary to clarify the structure of indigenous microbial community and the abundance of functional genes related to nitrogen cycle in karst groundwater.Although there are some reports on microbial community structure in karst groundwater at present,further understanding of the characteristics of unique microbial communities and functional microflora in groundwater in different karst areas is still needed.Quantitative study on functional genes related to nitrogen cycle in karst groundwater is helpful to understand the characteristics of functional microflora related to nitrogen cycle.In this paper,a groundwater vein in Huixian County of Guilin in a typical karst area was taken as the research object,and three types of karst groundwater,namely shallow underground river,shallow mechanical well and karst spring were chosen for study the characteristics of microbial community structure diversity in Huixian karst groundwater based on 16S rDNA high-throughput sequencing analysis,and the abundance of functional genes related to nitrification and denitrification in groundwater was quantitatively analyzed.Then,the relationship between community structure as well as related functional gene abundance and environmental factors was analyzed.The main results obtained in this paper are as follows.?1?Different types of karst groundwater environments had formed different microbial community structures.Proteobacteria were the dominant microflora in three types of karst groundwater.In addition,the relative abundance of Actinobacteria varied greatly in different types of karst groundwater.The relative abundance of Actinobacteria?up to 52.67%?even exceeded that of Proteobacteria in some shallow underground river samples,suggesting that Actinobacteria might be used as an indicator species to distinguish different types of karst groundwater.?2?The microbial community structure of Huixian karst groundwater was greatly affected by rainfall.Firstly,due to the large amount of precipitation leaching the soil into the groundwater in rainy season,the microbial community structure of Huixian karst groundwater was greatly affected by soil microorganisms,especially shallow underground rivers.Secondly,a large amount of rainfall promoted karstification,which further strengthened the influence of Ca²⁺and DIC?HCO₃^-?which were the significant influencing factors of microbial community structure in karst groundwater,especially karst springs.?3?The form of nitrogen pollution in Huixian karst groundwater was mainly NO₃^-,but its hydrochemical characteristics were not conducive to denitrification by denitrifiers to remove NO₃^-,and strengthening karstification might be beneficial to promoting denitrification in Huixian karst groundwater.The results of this study preliminarily revealed the features of indigenous microbial community structure and abundance of functional genes related to nitrification and denitrification of nitrogen cycle in Huixian karst groundwater,which provided a scientific basis for the development of in-situ treatment strategies for nitrogen pollution in karst groundwater.