Estuaries significantly affect the transport of dissolved organic matter (DOM) from land to ocean. While the transport and composition of estuarine DOM have been extensively studied, the direct link between DOM chemistry and its age remains unclear, limiting a comprehensive understanding of the dynamics and fate of estuarine DOM under severe conditions (e.g., floods). This study applied radiocarbon and ultrahigh-resolution mass spectrometry analysis to investigate the correlation between DOM chemistry and apparent radiocarbon age of 102 samples collected from the Yangtze River Estuary during both non-flood and flood periods. The results showed that young estuarine DOM are characterized by low-molecular-weight, unsaturated molecules, while aged estuarine DOM are relatively saturated with high-molecular-weight molecules. Phosphorus and nitrogen-containing compounds were key to DOM aging, potentially increasing the lability of aged DOM. Floods significantly impact DOM by introducing more labile aged DOM and young terrestrial DOM. Furthermore, floods enhanced the flux of aged DOM transported to the East China Sea by approximately 1.4 times. Our findings contribute to the study of estuarine DOM and its response during severe floods. Additionally, incorporating apparent radiocarbon age evidence improves the understanding of terrigenous DOM and its fate in large river estuaries before it contributes to the ocean carbon reservoir.

中文翻译：

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使用放射性碳和分子指纹揭示洪水期间河口溶解有机物的动员和年龄


河口显著影响溶解有机物 （DOM） 从陆地到海洋的运输。虽然河口 DOM 的运输和组成已得到广泛研究，但 DOM 化学与其年龄之间的直接联系仍不清楚，这限制了对河口 DOM 在恶劣条件（例如洪水）下的动力学和归宿的全面理解。本研究应用放射性碳和超高分辨率质谱分析，研究了 DOM 化学与长江口非洪期和汛期采集的 102 个样品的表观放射性碳年龄之间的相关性。结果表明，年轻的河口 DOM 以低分子量、不饱和分子为特征，而老化的河口 DOM 则相对饱和于高分子量分子。含磷和含氮化合物是 DOM 老化的关键，可能会增加老化 DOM 的不稳定性。洪水通过引入更不稳定的老化 DOM 和年轻的陆生 DOM 来显着影响 DOM。此外，洪水使输送到东海的老化 DOM 的通量增加了约 1.4 倍。我们的研究结果有助于研究河口 DOM 及其在严重洪水期间的响应。此外，结合表观放射性碳年龄证据可以提高对陆源 DOM 及其在大型河流河口的命运的理解，然后再将其贡献到海洋碳储层中。