Sub-theme
4. Supporting Aquatic Ecosystem Health and Functions
Topic
4-8. Water quality improvement
Body
This study focuses on the nitrogen removal capability of the mangrove wetland system towards resolving the excessive inorganic nitrogen content in the marine water of Shenzhen’s Deep Bay. In situ measurement, 15N isotope tracing technique, q-PCR, and 454 high-throughput pyrosequencing were jointly applied to investigate the nitrogen distribution characteristics, biological nitrogen removal processes, nitrogen removal functional genes, and bacterial community characteristics in five wetland sites in the intertidal zone of the Deep Bay, viz. the Kandelia candel, Bruguiera gymnorrhiza, Sonneratia apetala, Aegiceras corniculatum, and mud flat sites. The results showed that ammonia and nitrate in the marine water were significantly removed in the five wetlands sites, with respective removal efficiencies of 70.9–75.5% and 89.5–94.0%. Among them, Kandelia candel and Aegiceras corniculatum most significantly promoted ammonia and nitrate removal, respectively. The concentration of ammonia and nitrate in pore water remained significantly unchanged with depth. Denitrification and anammox were each system’s main biological nitrogen removal processes, and their rates were 1.70–3.22 and 0.07–0.36 μmol/(kg·h), respectively. The denitrification rates in the plant sites were 1.1–1.9 times that in the mud flat site, while the anammox rate in the mud flat site was 1.5–2.0 times those in the plant sites. These values indicate that mangroves promote denitrification but inhibit anammox. The numbers of denitrifying functional genes nirS, nosZ, and anammox functional gene hzsB ranged from 3.5×10^7 to 10.1×10^7, 4.9×10^7 to 25.1×10^7, 0.17×10^3 to 6.54×10^3 copies.g, respectively. The numbers of each gene showed an excellent linear relationship with the relevant process rates. Bacillus and Pseudomonas were the main heterotrophic denitrifying bacteria genera identified. The autotrophic denitrifying bacteria genus Sulfurovum was also identified in the systems, while Candidatus Scalindua was the only anammox genus dentified in this study. The results of this study improve our understanding of the nitrogen removal characteristics of coastal wetlands and the role of mangrove plants in the biological nitrogen removal processes.