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<p>Estuaries receive substantial terrestrial inputs that profoundly affect sediment organic nitrogen (SON) dynamics. However, the mechanisms by which watershed land-use patterns and fresh-seawater mixing processes jointly regulate SON transformations remain understudied. In this study, we examined SON composition, specifically acid hydrolysable nitrogen (AHN), non-hydrolysable nitrogen (NHN), and sediment dissolved organic nitrogen (SDON), and characterized the associated microbial and watershed influences in the Pearl River Estuary. The results indicated that SDON was dominated by CHON-type molecules (1N-SDON 88.09%±1.83%), with lignin (40.56%±2.23%) and polyphenols (13.25%±2.36%) serving as the major recalcitrant fractions. Along the land-to-sea continuum, watershed land-use impacts, particularly those from forestland and cropland, declined seaward, significantly reshaping SON and SDON composition. Although SON content and microbial assemblages varied significantly along this gradient, CHON-type compounds displayed a non-monotonic seaward pattern, decreasing initially and subsequently increasing in relative abundance from 88.30% to 87.00% and then to 89.23%. In estuarine mixing zones, microbial taxa including <i>Woeseia</i> (mean relative abundance: 3.69%) were associated with the degradation of lignin- and polyphenol-derived SDON, potentially enhancing aromatic compound turnover and nitrogen transformation. Further analysis revealed that forestland and cropland inputs directly shaped SDON sources and indirectly modulated SON through physicochemical properties-mediated microbial activities. These findings elucidate how land-use-driven terrestrial inputs and estuarine mixing jointly govern SON transformation, emphasizing the critical role of microbial control over refractory SDON degradation and refining the framework of nitrogen cycling across the land-to-sea continuum.</p>

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Land-use-driven terrestrial inputs and fresh-seawater mixing jointly shape sediment organic nitrogen in the Pearl River Estuary

  • 期刊论文

  • 发表日期：

    2026年7月16日

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  • Jia Yang,
  • Pengju Li,
  • Yunchao Wu,
  • Jinlong Li,
  • Feng Ye,
  • Yuanbi Yi,
  • Shicheng Lin,
  • Ling Zhang,
  • Zhijian Jiang,
  • Songlin Liu,
  • Xiaoping Huang,
  • Ding He

摘要

Estuaries receive substantial terrestrial inputs that profoundly affect sediment organic nitrogen (SON) dynamics. However, the mechanisms by which watershed land-use patterns and fresh-seawater mixing processes jointly regulate SON transformations remain understudied. In this study, we examined SON composition, specifically acid hydrolysable nitrogen (AHN), non-hydrolysable nitrogen (NHN), and sediment dissolved organic nitrogen (SDON), and characterized the associated microbial and watershed influences in the Pearl River Estuary. The results indicated that SDON was dominated by CHON-type molecules (1N-SDON 88.09%±1.83%), with lignin (40.56%±2.23%) and polyphenols (13.25%±2.36%) serving as the major recalcitrant fractions. Along the land-to-sea continuum, watershed land-use impacts, particularly those from forestland and cropland, declined seaward, significantly reshaping SON and SDON composition. Although SON content and microbial assemblages varied significantly along this gradient, CHON-type compounds displayed a non-monotonic seaward pattern, decreasing initially and subsequently increasing in relative abundance from 88.30% to 87.00% and then to 89.23%. In estuarine mixing zones, microbial taxa including Woeseia (mean relative abundance: 3.69%) were associated with the degradation of lignin- and polyphenol-derived SDON, potentially enhancing aromatic compound turnover and nitrogen transformation. Further analysis revealed that forestland and cropland inputs directly shaped SDON sources and indirectly modulated SON through physicochemical properties-mediated microbial activities. These findings elucidate how land-use-driven terrestrial inputs and estuarine mixing jointly govern SON transformation, emphasizing the critical role of microbial control over refractory SDON degradation and refining the framework of nitrogen cycling across the land-to-sea continuum.