Abstract The accumulation of organic carbon (OC) in the sediments of river-dominated continental margins plays a critical role in the global carbon budget and is subject to human modification. However, the relationships between human activities in drainage basins and carbon burial in modern sediments are still poorly understood. Here, a well preserved sediment core from a mud zone in the East China Sea (ECS) was analyzed for isotopes (δ13Corg and δ15N), radioisotopes (210Pb and 137Cs), bulk organic carbon and nitrogen, sediment grain size, major elements, trace metals and chemical properties (pH and Eh), in order to reveal the fate of the OC buried in the studied shelf over the last 70 years. The results showed that the input of terrestrial organic matter (TOM) from the Yangtze River into the ECS declined by 15% between 1980 and 2005, in concomitance with decreasing terrestrial-derived Ca and Zr. These changes were mainly due to alterations in the sediment load and cultivated land, induced by river damming and soil conservation practices. The amount of marine organic matter (MOM) was strongly and positively correlated with chlorophyll a concentrations and the loads of dissolved inorganic nitrogen and phosphate. The discharge of riverine nutrients from artificial fertilizers seems to be one of the key factors influencing marine productivity. OC burial fluxes varied between 33.8 and 54.7 g C m−2 yr−1 and were primarily related to changes in the mass accumulation rates (MARs) and OC%. Notably, due to the construction of the Three Gorges Dam (TGD) in 2003, the input of eroded material from the downstream and subaqueous delta of the Yangtze River increased, profoundly altering the local hydrodynamics and sedimentary redox levels. These changes may, in turn, accelerate the degradation of sedimentary OC, preventing carbon deposition and preservation.

中文翻译：

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以江为主的东海有机碳埋藏的归宿——来自过去 70 年沉积物地球化学记录的证据

摘要 以河流为主导的大陆边缘沉积物中有机碳（OC）的积累在全球碳收支中起着至关重要的作用，并且受到人类的改造。然而，流域人类活动与现代沉积物中碳埋藏之间的关系仍知之甚少。在这里，对来自东海 (ECS) 泥浆带的保存完好的沉积岩芯进行同位素（δ13Corg 和 δ15N）、放射性同位素（210Pb 和 137Cs）、大量有机碳和氮、沉积物粒度、主要元素、痕量金属和化学性质（pH 值和 Eh），以揭示过去 70 年来埋藏在研究大陆架中的 OC 的命运。结果表明，1980—2005年长江输入ECS的陆地有机质（TOM）下降了15%，伴随着来自陆地的 Ca 和 Zr 的减少。这些变化主要是由于河流筑坝和土壤保持措施引起的泥沙负荷和耕地的变化。海洋有机质 (MOM) 的数量与叶绿素 a 浓度和溶解无机氮和磷酸盐的负荷呈强正相关。人工肥料对河流养分的排放似乎是影响海洋生产力的关键因素之一。OC 埋藏通量在 33.8 和 54.7 g C m-2 yr-1 之间变化，主要与质量积累率 (MARs) 和 OC% 的变化有关。值得注意的是，由于2003年三峡大坝（TGD）的建设，长江下游和水下三角洲的侵蚀物质输入增加，深刻地改变了当地的流体动力学和沉积氧化还原水平。反过来，这些变化可能会加速沉积 OC 的降解，防止碳沉积和保存。