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Terrestrial Input and Phytoplanktonic Shifts Shaped Urea and Amino Acid Patterns in a Large River-Dominated Estuary and Adjacent Area
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PRE
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李
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DOI：10.1029/2025JC022772.png)
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Abstract
En 中文
Estuarine dissolved organic nitrogen (DON), particularly the two detectable bioactive components (urea and total dissolved amino acids/TDAA), is crucial for coastal biogeochemistry but poorly understood in estuaries influenced by high runoff and human activity. This study investigated the inter-regional transport patterns, degradability, and mixing dynamics of urea and TDAA under the influence of terrestrial inputs and fresh-seawater mixing through two cruises in the Pearl River Estuary (PRE) and its adjacent waters. Our results demonstrate that both urea and TDAA concentrations are higher in summer than in winter with highest concentrations in the fresh-seawater mixing zone (M zone; 2.38 ± 1.38 and 2.01 ± 0.91 μmol/L N, respectively) compared to the terrigenous-dominated zone (T zone; 1.67 ± 1.33 and 1.7 ± 1.18 μmol/L N, respectively) and the seawater-based zone (S zone; 1.05 ± 0.91 and 1.43 ± 0.80 μmol/L N, respectively). Terrestrial urea accumulated in the M zone due to a salinity front barrier. Increasing nitrogen-normalized yields of TDAA (TDAA-N%) and degradation index (DI) from the T to S zones, alongside shifts in amino acid compositions (decreasing glycine/alanine, accumulating glutamic acid/histidine in the M zone), indicate that TDAA sources shift from terrestrial inputs to phytoplankton release. Diminished terrestrial runoff from the T to M zones and a phytoplankton community shift from diatom to dinoflagellate drove these changes. Our findings indicate that the nonlinear spatial variations of urea and TDAA in the PRE and adjacent areas are co-regulated by terrestrial inputs and phytoplankton community dynamics.
Keywords:
dissolved organic nitrogen
total hydrolyzed amino acids
degradation states
phytoplankton production
terrestrial input
Pearl River estuary
Journal
J
IF:
3.4
Papers:
1.1W
Citations:
4.4W
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