Seasonal and vertical variations in the characteristics of the nitrogen-related functional genes in sediments from urban eutrophic lakes

Abstract

Urban lakes play an important role in urban residents lives, but they are more vulnerable to nitrogen pollution due to the large number of pollution sources in urban areas. Analyzing the characteristic variation of nitrogen-related functional genes in sediments could improve our understanding of nitrogen removal from urban lakes. Based on field samples of lake sediments in Wuhan, China, the seasonal and vertical variations in the characteristics of seven genes were detected using metagenome sequencing and qPCR. The genes examined were the ammonia-oxidizing bacteria gene (AOB amoA), ammonia-oxidizing archaea gene (AOA amoA), anammox gene (anammox 16S rRNA), denitrification genes (narG, nirS, nosZ), and dissimilatory nitrate reduction to ammonium gene (nrfA). The sequencing results revealed that the strain types of nosZ and nrfA were more abundant than amoA, anammox 16S rRNA, narG, and nirS. The nitrogen-related genes abundances were much lower in summer than in winter. In the vertical zones of the sediments, the abundances of the seven genes mainly decreased as the sediment depth increased. The abundances of ammonium-oxidizing microorganisms had no significant difference in the vertical direction (P > 0.05), but there were significant differences in the vertical direction for the abundances of narG, nirS, nosZ, and nrfA (P < 0.05). Canonical correspondence analysis (CCA) illustrated that the main environmental factors affecting the gene abundances were NH -N in the interstitial water, dissolved oxygen (DO) and electrical conductivity (EC) in the overlying water, and total nitrogen (TN) in the sediment. The anammox 16S rRNA abundances were significantly correlated with the nrfA abundances, while the narG abundances were also significantly correlated with nirS abundances. The results extend the knowledge of spatiotemporal variations of nitrogen-cycle microorganisms characteristics in urban eutrophic lakes.