The burial of organic carbon (OC) in the river-dominated margin plays an important role in global carbon cycle, but its accumulation mechanism is not well understood. Here, we examined the concentration and distribution of water-extractable organic matter (WEOM) and base-extractable organic matter (BEOM) in surface sediments from the lower Yangtze River, estuary, and the East China Sea. Chemical characteristics of the WEOM and BEOM were described by multiple ultraviolet-visible and fluorescence spectral indicators. Concentrations of both WEOM and BEOM showed significant correlations with sediment grain size, suggesting that mineral surface area is a key factor for OC loadings on sediments. Three components (C1, C2, and C3) extracted from fluorescence excitation emission matrices-parallel factor analysis were assigned as terrigenous humic-like substance, mixed terrigenous/aquatic humic-like substance, and microbial protein-like substance, respectively. From the lower Yangtze River to the East China Sea, the C1%, specific UV absorbance at 254 nm (SUVA₂₅₄), and humification index (HIX) of the WEOM decreased, while the C3%, fluorescence index (FI), and biological index (BIX) of the WEOM increased. This suggested the loss of terrigenous OC and addition of microbial OC in the WEOM. While for BEOM, the overall increase of C1% and HIX and the decrease of C3% and FI suggested selective removal of microbial OC and preferential preservation of terrigenous OC. Our study demonstrates complex behaviors of sediment organic matter (OM) during the land-to-sea transport that is largely controlled by the binding strength of OM–sediment association, and that the formation of BEOM is an important pathway for accumulation of terrigenous OM in the river-dominated margin.

在以河为主导的边缘埋葬有机碳（OC）在全球碳循环中起着重要作用，但其积累机理尚未得到很好的理解。在这里，我们研究了长江下游，河口和东海的表层沉积物中水可萃取有机物（WEOM）和碱可萃取有机物（BEOM）的浓度和分布。WEOM和BEOM的化学特性由多个紫外可见和荧光光谱指示剂描述。WEOM和BEOM的浓度均与沉积物粒度显着相关，这表明矿物表面积是沉积物中OC含量的关键因素。三个组件（C1，C2，将从荧光激发发射矩阵-平行因子分析中提取的C3和C3）分别指定为陆源腐殖质样物质，混合陆源/水生腐殖质样物质和微生物蛋白样物质。从长江下游到东海，C1％，在254 nm处的比紫外线吸收率（SUVA₂₅₄），且WEOM的增湿指数（HIX）降低，而WEOM的C3％，荧光指数（FI）和生物学指数（BIX）升高。这表明WEOM中源性OC的损失和微生物OC的添加。而对于BEOM，C1％和HIX的总体上升以及C3％和FI的下降表明选择性去除微生物OC和优先保护陆源性OC。我们的研究表明，陆上-海洋运输过程中沉积物有机质（OM）的复杂行为主要受OM-沉积物结合力的控制，BEOM的形成是陆源性OM积累的重要途径。河流为主的边缘。