Estuaries and bays provide favorable conditions for mariculture, which in turn influences regional carbon cycling. However, a key challenge lies in comprehending the role of mariculture in sedimentary organic matter (SOM) dynamics during the transport of organic carbon (OC) along river-estuary-bay continuums. To address this knowledge gap, surface sediments were collected from a typical oyster farming area, i.e. the lower reaches of Dafeng River (LDR) to Dafeng River Estuary (DRE) and adjacent Qinzhou Bay (QZB). The sediments were analyzed for total OC (TOC) and nitrogen (TN), as well as stable isotopic composition (δ13C and δ15N) to determine the source and fate of SOM. The results revealed higher TOC and TN contents in DRE than LDR and QZB due to an increased proportion of fine-grained components, which was caused by weak hydrodynamic sorting in the estuary. Bayesian mixing model based on δ13C and TOC/TN ratio indicated that shellfish biodeposition was an important source of SOM, with an annual mean contribution of 36.6 ± 8.0 %. Notably, despite the small scale of oyster farming in QZB, shellfish biodeposition contributed 39.3 ± 6.2 % to SOM, suggesting that intensive oyster farming in the estuary reshaped the composition of SOM in the bay. Furthermore, terrestrial input made a significant contribution to SOM during summer in QZB compared to DRE due to remineralization of labile shellfish-derived OC during transport from the estuary to bay. Overall, this study highlighted the substantial impact of oyster farming and hydrodynamics conditions on SOM dynamics in coastal waters.

中文翻译：

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牡蛎养殖和水动力条件调节着典型的河流-河口-海湾连续体中沉积有机物的组成和来源

河口和海湾为海水养殖提供了有利条件，这反过来又影响了区域碳循环。然而，一个关键的挑战在于理解海水养殖在沿河流-河口-海湾连续体输送有机碳 （OC） 过程中沉积有机物 （SOM） 动力学中的作用。为了解决这一知识差距，从典型的牡蛎养殖区收集了表层沉积物，即大丰河下游 （LDR） 至大丰河口 （DRE） 和邻近的钦州湾 （QZB）。分析沉积物的总 OC （TOC） 和氮 （TN） 以及稳定的同位素组成 （δ13C 和 δ15N），以确定 SOM 的来源和归宿。结果显示，DRE 中的 TOC 和 TN 含量高于 LDR 和 QZB，这是由于河口水动力分选较弱导致细粒成分比例增加。基于 δ13C 和 TOC/TN 比值的贝叶斯混合模型表明，贝类生物沉积是 SOM 的重要来源，年平均贡献率为 36.6 ± 8.0 %。值得注意的是，尽管 QZB 的牡蛎养殖规模较小，但贝类生物沉积对 SOM 的贡献为 39.3 ± 6.2%，这表明河口的集约化牡蛎养殖重塑了海湾 SOM 的组成。此外，与 DRE 相比，陆地输入对 QZB 夏季的 SOM 做出了重大贡献，因为不稳定的贝类衍生的 OC 在从河口运输到海湾的过程中会再矿化。总体而言，本研究强调了牡蛎养殖和水动力学条件对沿海水域 SOM 动力学的重大影响。