Marine aquaculture regulates dissimilatory nitrate reduction processes in a typical semi-enclosed bay of southeastern China

Marine aquaculture in semi-enclosed bays can significantly influence nutrient cycling in coastal ecosystems.However,the impact of marine aquaculture on the dynamics of dissimilatory nitrate reduction processes(DNRPs)and the fate of reactive nitrogen remain poorly understood.In this study,the rates of DNRPs and the abundances of related functional genes were investigated in aquaculture and non-aquaculture areas.The results showed that marine aquaculture significantly increased the denitrification(DNF)and dissimilatory nitrate reduction to ammonium(DNRA)rates and decreased the rate of anaerobic ammonium oxidation(ANA),as compared with non-aquaculture sites.DNF was the dominant pathway contributing to the total nitrate reduction,and its contribution to the total nitrate reduction significantly increased from 66.72%at non-aquaculture sites to 78.50%at aquaculture sites.Marine aquaculture can significantly affect the physicochemical characteristics of sediment and the abundances of related functional genes,leading to variations in the nitrate reduction rates.Although nitrate removal rates increased in the marine aquaculture area,ammonification rates and the nitrogen retention index in the aquaculture areas were 2.19 and 1.24 times,respectively,higher than those at non-aquaculture sites.Net reactive nitrogen retention exceeded nitrogen removal in the aquaculture area,and the retained reactive nitrogen could diffuse with the tidal current to the entire bay,thereby aggravating N pollution in the entire study area.These results show that marine aquaculture is the dominant source of nitrogen pollution in semi-enclosed bays.This study can provide insights into nitrogen pollution control in semi-enclosed bays with well-developed marine aquaculture.

Overlooked nitrogen-cycling microorganisms in biological wastewater treatment

Nitrogen-cycling microorganisms play key roles at the intersection of microbiology and wastewater engineering.In addition to the well-studied ammonia oxidizing bacteria,nitrite oxidizing bacteria,heterotrophic denitrifiers,and anammox bacteria,there are some other N-cycling microorganisms that are less abundant but functionally important in wastewater nitrogen removal.These microbes include,but not limited to ammonia oxidizing archaea(AOA),complete ammonia oxidation(comammox)bacteria,dissimilatory nitrate reduction to ammonia(DNRA)bacteria,and nitrate/nitrite-dependent anaerobic methane oxidizing(NO_(x)-DAMO)microorganisms.In the past decade,the development of high-throughput molecular technologies has enabled the detection,quantification,and characterization of these minor populations.The aim of this review is therefore to synthesize the current knowledge on the distribution,ecological niche,and kinetic properties of these“overlooked”N-cycling microbes at wastewater treatment plants.Their potential applications in novel wastewater nitrogen removal processes are also discussed.A comprehensive understanding of these overlooked N-cycling microbes from microbiology,ecology,and engineering perspectives will facilitate the design and operation of more efficient and sustainable biological nitrogen removal processes.