Suspended solids induced
increasing microbial ammonium recycling along the river-estuary
continuum of Yangtze River
Jingya Xue a,b, Zhonghua Zhao a,
Xiaolong Yao a, Weiting Liu a,b, Lu
Zhang a11Corresponding author. Tel.: +86
2586882237; fax: +86 2557714759
E-mail:luzhang@niglas.ac.cn (L.
Zhang)
a State Key Laboratory of Lake Science and
Environment, Nanjing Institute of Geography and Limnology, Chinese
Academy of Sciences, Nanjing 210008, China
b University of Chinese Academy of Science,
Beijing 100049, China
Abstract: Many large
rivers worldwide are enriched with high levels of suspended solids (SS),
which are known to be hotspots of many nitrogen (N) transformation
processes (e.g., denitrification, nitrification). However, the influence
of SS on microbial ammonium (NH4+)
recycling remains
unclear.
Water column NH4+ regeneration rates
(REGs) and potential uptake rates (Upots) as well as
community biological NH4+ demand
(CBAD) was measured in the river-estuary continuum of the third longest
river in the world—Yangtze River, where shows
dramatic
SS gradients. We found that, REGs, Upots, and CBAD all
showed increasing trends
along
the river flow, with higher REGs, Upots, and CBAD in the
estuary than in the river sections. The regeneration and uptake of
NH4+ were nearly balanced in the river
sections, while the positive CBAD in the estuary indicated obvious
NH4+ demand of
microbes. Concentrations of SS,
which also controls the content of chemical oxygen demand and
particulate N, were the main factor influencing
NH4+ recycling rates and CBAD. SS
induced regenerated NH4+ in the
river-estuary continuum of Yangtze River was estimated to be 21.81 ×
108 kg N yr−1 and accounted for
about 25% of total N inputs, suggesting that regenerated
NH4+is
an important N source for microbes and may influence nutrient dynamics
in lower coasts. To our knowledge,
this is the first to report
NH4+ recycling in Yangtze River with
an emphasis on its influencing factors and contribution to N budgets.
Keywords: Suspended solids; Ammonium recycling; River-estuary
continuum; Community biological ammonium demand