5. Conclusion

This study investigated NH4+ dynamics including its regeneration, potential uptake, and demand in the river-estuary continuum of Yangtze River. Higher REGs, Upots, and CBAD were found in the estuary, while relatively lower in the river sections. Moreover, compared to in the river sections, the higher regeneration and uptake rates of NH4+ as well as CBAD in the estuary are due to higher PN, COD, and SS concentrations. Faster microbial uptake of NH4+ than its regeneration result in obvious NH4+ demand in the estuary. In addition, NH4+regeneration is an important pathway of N supply in the Yangtze River, and regenerated NH4+ was estimated to be 21.81 × 108 kg N yr−1, accounting for about 25% of total N inputs in the study area. This study indicates that NH4+ recycling is critical for regulating the supply and demand of NH4+ along the river-estuary continuum of Yangtze River. Effective managements to reduce SS inputs will alleviate N pollution and blooms (i.e., red tide) in the river-estuary continuum of the Yangtze River.