The impact of algal blooms on promoting in-situ N2O emissions: A case in Zhanjiang bay, China

• Published in: Journal of environmental management 2024-05, Vol.358, p.120935, Article 120935
• Main Authors: Cai, Shangjun, Lao, Qibin, Chen, Chunqing, Zhu, Qingmei, Chen, Fajin
• Format: Article
• Language: English
• Subjects: 15N isotope; Algal bloom; Nitrification-denitrification; Nitrous oxide emission; Zhanjiang bay
• ISSN: 0301-4797; 1095-8630; 1095-8630
• DOI: 10.1016/j.jenvman.2024.120935

Under the influence of many factors, such as climate change, anthropogenic eutrophication, and the development of aquaculture, the area and frequency of algal blooms have showed an increasing trend worldwide, which has become a challenging issue at present. However, the coupled relationship between nitrous oxide (N2O) and algal blooms and the underlying mechanisms remain unclear. To address this issue, 15N isotope cultures and quantitative polymerase chain reaction (qPCR) experiments were conducted in Zhanjiang Bay during algal and non-algal bloom periods. The results showed that denitrification and nitrification-denitrification were the two processes responsible for the in-situ production of N2O during algal and non-algal bloom periods. Stable isotope rate cultivation experiments indicated that denitrification and nitrification-denitrification were promoted in the water during the algal bloom period. The in-situ production of N2O during the algal bloom period was three-fold that during the non-algal bloom period. This may be because fresh particulate organic matter (POM) from the organisms responsible for the algal bloom provides the necessary anaerobic and hypoxic environment for denitrification and nitrification-denitrification in the degradation environment. Additionally, a positive linear correlation between N2O concentrations and ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (nirK and nirS) also supported the significant denitrification and nitrification-denitrification occurring in the water during the algal bloom period. However, the algal bloom changed the main process for the in-situ production of N2O, wherein it shifted from denitrification during the non-algal bloom period to nitrification-denitrification during the algal bloom period. The results of our study will improve our understanding of the processes responsible for the in-situ production of N2O during the algal bloom period, and can help formulate effective policies to mitigate N2O emissions in the bay. [Display omitted] •Algal blooms caused a threefold increase in the in-situ production of N2O.•Algal blooms differentially boosted nitrification-denitrification and denitrification.•Algal blooms evidently changed the main process for the in-situ production of N2O.•During the non-algal bloom period, denitrification prevailed as the main process.•Nitrification-denitrification became dominated during the algal bloom period.