Characteristics of Nitrifying and Denitrifying Microbes in the Bioretention Cell with Submerged Zone during a Dry Period

Microbial transformation is a vital mechanism to internally treat nitrogen (N) within bioretention cells (BRCs); nitrifying and denitrifying microorganisms are the main drivers of permanent nitrogen removal. The limited research of the characteristics of nitrifying and denitrifying microbes in different layers during dry periods has prevented further understanding of nitrogen behavior in bioretention cells. In this paper, high-throughput sequencing technology and qPCR were used to analyze the microbial community and the abundance of six functional genes in soil and water samples of a layered BRC. This study found that the microbial community structure of the gravel layer was distinguished from that of the other three layers. With the extension in the dry period, the amount of microbial species shared by all four layers increased, showing a convergent succession of microorganisms. The nitrification and denitrification functional genes mainly existed in the upper layer of the bioretention cell; in addition, the abundance of the functional genes in the sand layer increased after rainfall and peaked at about 24–48 h, after which the abundance decreased and became steady. Correlation analysis indicated that the abundance of nitrification and denitrification functional genes was significantly affected by TOC, ammonia nitrogen concentration and nitrate nitrogen concentration.