Nitrogen removal performance, and microbial community structure of water and its association with nitrogen metabolism of an ecological engineering pond aquaculture system

The ecological engineering pond aquaculture system was promoted in China in recent years as it can save water and reduce pollution. In the present study, an ecological engineering pond aquaculture system was established, consisting of a drainage ditch, a settling pond, an aeration pond, a filter dam, eco-ponds, and fish ponds for tilapia farming. Water from different ponds were sampled and sequenced by Illumina sequencing, and then the microbial communities were analyzed. The metabolic activity of bacteria in the water samples was tested using Biolog EcoPlates. The concentrations of total nitrogen (TN), ammonia-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), and total phosphorus (TP) in water after treatment by the system were 0.71 ± 0.19, 0.48 ± 0.15, 0.51 ± 0.21, 0.03 ± 0.01, and 0.04 ± 0.01 mg/L, respectively. All the units of the system could remove TN in water. Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, and Planctomycetes were the dominant phyla in the water of the system. The genera Candidatus Aquiluna and Dechloromonas positively correlated with the microbial metabolic activity of organic nitrogen and NH4-N concentrations in water, which could be the functional bacteria for nitrogen removal. Several genera showed positive correlation with the TN and NH4-N concentrations of water and were probably involved in nitrogen cycling of the system. Our data indicated that the ecological engineering pond aquaculture system notably improves water quality and alters the microbial populations. The results supply substantial information on the functional microbiota for nitrogen removal from freshwater aquaculture ecosystems.