Abstract
The coupling of nitrification and denitrification has attracted wide attention since it plays an important role in mitigating eutrophication in aquatic ecosystems. However, the underlying mechanism is largely unknown. In order to study the coupling relationship between nitrification and denitrification, as well as its effect on phosphorus release, nutrient levels, functional gene abundance and potential rates involved in nitrification and denitrification were analyzed in three shallow urban lakes with different nutrient status. Trophic level was found positively related to not only copy numbers of functional genes of nitrosomonas and denitrifiers, but also the potential nitrification and denitrification rates. In addition, the concentrations of different forms of phosphorus showed a positive correlation with the number of nitrosomonas and denitrifiers, as well as potential nitrification and denitrification rates. Furthermore, the number of functional genes of nitrosomonas exhibited positive linear correlations with functional genes and rate of denitrification. These facts suggested that an increase in phosphorus concentration might have promoted the coupling of nitrification and denitrification by increasing their functional genes. Strong nitrification–denitrification fueled the nitrogen removal from the system, and accelerated the phosphorus release due to the anaerobic state caused by organic matter decomposition and nitrification. Moreover, dissolved organic nitrogen was also released into the water column during this process, which was favorable for balancing the nitrogen and phosphorus ratio. In conclusion, the close coupling between nitrification and denitrification mediated by nitrifier denitrification had an important effect on the cycling mode of nitrogen and phosphorus.
Highlights
The biogeochemical cycle of nitrogen in aquatic ecosystems has consistently been a significant issue [1]
Nitrification take place in the aerobic layer while denitrification is conducted in low-oxygen or anaerobic conditions, and the production of N2 O is found to be highest at the interfaces between the two areas [7]
Our results showed a connection between nitrification and denitrification (Figure 5)
Summary
The biogeochemical cycle of nitrogen in aquatic ecosystems has consistently been a significant issue [1]. Within this cycle, nitrification and denitrification are key steps and are mainly catalyzed by microbes [2,3]. Nitrification, the microbial oxidation of ammonia to nitrite and nitrate, keeps N in the water ecosystem [4,5]. Denitrification, removes N from the water ecosystem by converting nitrate into gaseous nitrogen [6]. Nitrification take place in the aerobic layer while denitrification is conducted in low-oxygen or anaerobic conditions, and the production of N2 O is found to be highest at the interfaces between the two areas [7]. NO2 − or NO3 − produced during nitrification can be quickly transferred to the anaerobic zone and utilized by denitrifying bacteria [8]
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