Shi Xuesong, Ye Feng, Wu Yunchao, Li Jinlong, Wei Gangjian
State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China.
Mar Environ Res. 2025 Feb;204:106911. doi: 10.1016/j.marenvres.2024.106911. Epub 2024 Dec 12.
Dissolved organic nitrogen (DON) has recently been recognized as an important nitrogen source for marine phytoplankton. However, the composition, sources, and biogeochemical cycling of DON in coastal ecosystems remain poorly understood. This study investigates the spatial distribution and seasonal variability of DON in Daya Bay, a subtropical semi-enclosed bay in the northern South China Sea. We measured DON concentrations, the DIN:DIP ratio, and the spectral characteristics of dissolved organic matter (DOM), including a(350), SUVA, and fluorescence components. Our findings reveal clear seasonal differences in the controlling factors for DON distribution: in summer, land-based sources and biological activities dominate, whereas in winter, oceanic circulation and its associated water mass mixing play a predominant role. The combined spectral indexes suggest that the transformation of DON is significantly more active in summer than in winter. Additionally, most stations exhibited low DIN:DIP ratios (<16) and relatively high chlorophyll a concentrations (>2 μg/L) during the summer months, while DIP concentrations in Daya Bay remained generally low (<1 μmol L). This suggests that phytoplankton may assimilate DON, potentially leading to algal blooms and changes in population structure. Overall, these findings highlight the potential role of DON in the coastal nitrogen budget and phytoplankton dynamics, emphasizing the need for further investigation.
溶解有机氮（DON）最近被认为是海洋浮游植物的重要氮源。然而，沿海生态系统中DON的组成、来源和生物地球化学循环仍知之甚少。本研究调查了南海北部亚热带半封闭海湾大亚湾中DON的空间分布和季节变化。我们测量了DON浓度、DIN:DIP比率以及溶解有机物（DOM）的光谱特征，包括a(350)、SUVA和荧光成分。我们的研究结果揭示了DON分布控制因素的明显季节差异：夏季，陆源和生物活动起主导作用，而冬季，海洋环流及其相关的水体混合起主要作用。综合光谱指数表明，DON的转化在夏季比冬季明显更活跃。此外，大多数站点在夏季月份表现出低DIN:DIP比率（<16）和相对较高的叶绿素a浓度（>2μg/L），而大亚湾的DIP浓度总体上仍然较低（<1μmol/L）。这表明浮游植物可能吸收DON，潜在地导致藻华和种群结构变化。总体而言，这些发现突出了DON在沿海氮收支和浮游植物动态中的潜在作用，强调了进一步研究的必要性。
