Characteristics of N2O release from polluted creeks in the Taihu Lake Basin: sources and microbial populations

Polluted rural creek systems are a potential primary source of nitrous oxide (N₂O). However, to date, the N₂O emission pathways of rural creek systems have yet to be investigated. In particular, the correlations between N₂O emissions and ammonia-oxidizing archaea (AOA), ammoniating bacteria (AOB), and denitrifying communities remain poorly understood. In this paper, a sediment–water–environment simulation system was established to analyze the N₂O emission pathways, and the correlations between N₂O emissions and nitrogen-related functional genes for two creeks that have been polluted by domestic sewage and industrial wastewater have been studied. The results indicated that the N₂O release rate of the creek polluted by domestic sewage was higher than that of the creek polluted by industrial wastewater, and the heterotrophic denitrification and nitrification were the main N₂O emission pathways for the creek polluted by domestic sewage. On the contrary, nitrification and chemical denitrification were the primary N₂O emission pathways for the creek polluted by industrial wastewater. The quantitative PCR (qPCR) results obtained for nitrogen-cycle functional genes in creek sediments indicated that the abundances of AOA genes (AOA amoA), AOB genes (AOB amoA), and denitrification genes (nosZ) were lower in the creek polluted by industrial wastewater than that in the creek polluted by domestic sewage. For the creek polluted by domestic sewage, the N₂O emission rate exhibited a significant positive correlation with the abundances of AOA amoA and AOB amoA and a correlation with the abundances of the dominant nitrogen-cycling microorganisms (p < 0.05). However, no such correlations were found for the creek polluted by industrial wastewater. In the future, the patterns detected here will be useful as markers to distinguish whether water has been polluted by industry.