Sediment diffusion is feasible to simultaneously reduce nitrate discharge from recirculating aquaculture system and ammonium release from sediments in receiving intensive aquaculture pond.

Nitrogen accumulation has become one of the greatest unresolved challenges restricting the development of aquaculture worldwide. In recirculating aquaculture system (RAS), lack of organic matter (OM) and sensitive organisms makes it difficult to apply efficient denitrifying technology, thus leading to a high nitrate‑nitrogen (NO-N) accumulation. In contrast, excess OM accumulation in intensive aquaculture pond sediments is associated with dissolved oxygen depletion and ammonium‑nitrogen (NH-N) accumulation in the sediments. Based on the opposing effects of OM on the nitrogen accumulation in RAS and intensive aquaculture ponds, this study assessed the feasibility of simultaneously reducing NO-N discharge from RAS and controlling NH-N accumulation in intensive aquaculture ponds by in situ diffusing RAS tailwater containing NO-N into intensive aquaculture pond sediments. The results showed that NO-N diffusion strategy improved the native sediment denitrification capacity, thus increasing NO-N removal efficiency from RAS tailwater and significantly decreasing the NH-N concentration in interstitial water and the total organic carbon content in intensive aquaculture pond sediments. High-throughput sequencing and quantitative real-time polymerase chain reaction (qPCR) results revealed that NO-N addition significantly increased both nitrifying bacteria and denitrifying bacteria abundance. These results implied that NO-N diffusion strategy could effectively stimulate microbial decomposition of OM, thus relieving the hypoxia limitation of sediment nitrification. Overall, this study offers a feasible method for simultaneous reduction of NO-N from RAS tailwater and NH-N in intensive aquaculture ponds with low cost and high efficiency.