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.