Dissolved organic matter (DOM) in the coastal tidal marsh–estuary systems are complex mixtures with different source materials that vary with hydrological regimes, seasons, and environmental conditions and are modified by removal processes including photochemical and microbial degradations. Here, monthly surveys of DOM and its optical properties (i.e., absorbance and fluorescence of DOM) covering a complete semi-diurnal tidal cycle were conducted in two coastal marshes with distinct hydrological regimes (i.e., one freshwater and one brackish marsh) in the Changjiang River Estuary (CRE). Four fluorescent components were identified by excitation–emission matrix fluoresces combined with parallel factor analysis (EEMs–PARAFAC) as two terrestrial humic-like components and two autochthonous protein-like components. Results indicated that ebbing waters draining the marshes were consistently enriched with highly absorbing, more humic and highly aromatic DOM compared to the flood tidewaters. On a seasonal basis, DOM dynamics were largely modulated by the marsh productivity and the seasonal Changjiang runoff. Protein-like fluorophores, however, demonstrated a constant, less variable pattern on both the tidal and seasonal timescales. Onsite water incubation experiments with photochemical and microbial alterations revealed that photochemistry was primarily responsible for the removal of optically active components in the marsh DOM pools whereas the impact of microbes was minor. Principal component analysis (PCA) illustrated the processes regulating the DOM dynamics at the marsh–estuarine interface and allowed a clear distinction of samples between the two marshes, in addition to the samples under the influence of episodic weather events (i.e., Super Typhoon Lekima in summer 2009 and the basin-wide severe flood event occurred in summer 2020). This study underscores the importance of world large-rivers such as Changjiang on estuarine marsh DOM dynamics and also highlights the substantial heterogeneity of the marsh DOM across a river-dominated estuary.

沿海潮汐沼泽-河口系统中的溶解有机质 (DOM) 是具有不同来源物质的复杂混合物，这些物质因水文状况、季节和环境条件而异，并通过包括光化学和微生物降解在内的去除过程进行修改。在这里，在长江的两个具有不同水文状况的沿海沼泽（即一个淡水和一个半咸水沼泽）中进行了涵盖完整半日潮循环的 DOM 及其光学特性（即 DOM 的吸光度和荧光）的月度调查。河口 (CRE)。通过激发-发射矩阵荧光结合平行因子分析（EEMs-PARAFAC）将四种荧光成分鉴定为两种陆地腐殖质样成分和两种本土蛋白质样成分。结果表明，与泛滥的潮水相比，从沼泽中排出的退潮水始终富含高吸收性、更多腐殖质和高度芳香的 DOM。在季节性基础上，DOM 动态很大程度上受沼泽生产力和季节性长江径流的调节。然而，蛋白质样荧光团在潮汐和季节性时间尺度上表现出恒定的、变化较小的模式。具有光化学和微生物改变的现场水孵化实验表明，光化学主要负责去除沼泽 DOM 池中的光学活性成分，而微生物的影响很小。主成分分析 (PCA) 说明了在沼泽 - 河口界面调节 DOM 动态的过程，并允许清楚地区分两个沼泽之间的样本，除了受偶发性天气事件影响的样本（即2009年夏季的超级台风利奇马和2020年夏季发生的全流域特大洪水事件）。本研究强调了长江等世界大河对河口沼泽 DOM 动态的重要性，并强调了以河流为主的河口沼泽 DOM 的巨大异质性。