Nitrification and denitrification by algae-attached and free-living microorganisms during a cyanobacterial bloom in Lake Taihu, a shallow Eutrophic Lake in China

Cyanobacterial blooms may stimulate epiphytic nitrification and denitrification in the water column. To validate this hypothesis, a 4-week floating mesocosms experiment that involved a cyanobacterial decay–growth–decay period was conducted at Lake Taihu. In addition to conventional methods for detecting the physical and chemical properties, quantitative real-time PCR was used to identify the nitrification and denitrification genes (archaeal and bacterial amoA, nirS and nirK). Treatment with cyanobacteria led to removal of about 3.62 mg N L total nitrogen, 40% of which was organic nitrogen, indicating a nitrogen transformation and removal mechanism was present in the system. Variations in the biogeochemical properties suggested that remineralization and coupling nitrification and denitrification by epiphytic and pelagic microorganisms was the primary pathway through which organic nitrogen was removed. The results of this study revealed that algal blooms can accelerate nitrogen removal efficiency, which may be the primary reason that nitrogen is limited in summer in Lake Taihu.