In abandoned aquaculture ponds, the anammox process contributes relatively more to nitrogen removal

Impact of the development of coastal aquaculture on nitrogen (N) cycle has been a central issue in wetland ecological and environmental protection project. However, the process of N removal in offshore aquaculture remains unclear. Here this study reported the rates, abundance and community structure of anaerobic ammonium oxidation (anammox) and denitrification using N-15 isotope tracing technology, quantitative polymerase chain reaction (qPCR), and high-throughput sequencing methods in different types of aquaculture ponds including the Sinonovacula constricta ponds, the Shrimp-crab polyculture ponds and the abandoned aquaculture ponds along the coast of Fujian Province. Results showed that anammox rates in the abandoned aquaculture ponds were 1.44 +/- 0.11 nmol center dot g(-1)center dot h(-1), contributing to 15.15% +/- 1.18% of the N removal, which were significantly higher than those in the S.constricta ponds and the Shrimp-crab polyculture ponds (P < 0.01). Denitrification remained the main pathway for the N removal. The abundance of AMX, nirS, and nirK genes in the Shrimpcrab polyculture ponds was higher than the other two types of aquaculture ponds, but the anammox and denitrifying microbial community structure was the simplest. In contrast, the abandoned aquaculture ponds showed the most abundant and complex microbial community structure. Aquaculture ponds abandoned significantly increased the anammox rates and community structure. The microbial diversity, species composition, and stable substrate condition such as DO, pH, NH4+, NO3-, TN, and C:N ratio were the main factors affecting the anammox process in the abandoned aquaculture ponds. The abundance of nirS and nirK gene, the human management, and aquaculture substrate environment including DO, pH, NH4+, and NO2- enhanced the denitrification process in the S.constricta ponds and the Shrimp-crab polyculture ponds. These findings indicated that aquaculture ponds abandoned improved environmentally friendly the anammox N removal process and restored biodiversity.