【摘要】 河口是陆海界面碳循环的关键场所，厘清有机碳的来源、组成和分布特征对于深入了解其在边缘海的归宿具有重要意义。本研究于2022年8月采集黄河及黄河口的颗粒物和沉积物，通过分析总有机碳参数(POC%、TOC%、C/N比和δ¹³C)、矿物特征参数（平均粒径和比表面积）并结合环境参数，探讨夏季黄河口有机碳的来源特征及影响因素。结果显示，颗粒有机碳（POC）浓度范围为0.33～36.95 mg/L,受到河流输入、絮凝沉降及再悬浮的影响，总体上呈现近岸高远岸低的趋势。POC%平均值为（1.25±1.40）%,中低盐度海域POC%和δ¹³C_POC较低，表明有机碳主要受黄河陆源输入影响，高盐度海域POC%和δ¹³C_POC升高，河流径流影响减弱，浮游植物来源的海源有机碳贡献增加，因此黄河口颗粒有机碳的分布主要受到来源控制。沉积有机碳（TOC）含量平均值为（0.33±0.21）%,与中低盐度POC%接近，这是由于调水调沙时期和夏季黄河输入的大量颗粒物沉积在河口区域，沉积物和颗粒物有机碳性质的差异减小。沉积有机碳在河口的分布受粒径效应控制，TOC%与平均粒径（MGS）呈负相关关系，随盐度增加粒径减小而TOC%升高；TOC%较低的粗颗粒主要在近岸沉积，TOC%较高的细颗粒可以被输送到远岸沉积。进一步基于C/N比和δ¹³C的三端元模型量化了不同来源有机碳的贡献及其在河口的分布，结果显示POC中土壤和海源有机碳占主导，土壤有机碳贡献占比从近海51%降至远岸19%,海源有机碳贡献从24%增加至68%;沉积物中土壤有机碳贡献占比约为40%。本研究结果将为深入研究不同来源有机碳在黄河口的迁移和保存提供重要基础，对于厘清河口有机碳循环过程和机制具有重要意义。更多还原

【Abstract】 Estuary is the key site of carbon cycling at the land-sea interface, thus clarifying the source, composition and spatial distribution of organic carbon is important for a deeper understanding of its fate in the marginal seas. In this study, surface particulate matter and sediments from the Yellow River estuary（YRE） were collected in August, 2022（after water-sediment regulation scheme）, and we analyzed total organic carbon parameters(POC%, TOC%, C/N ratio and δ¹³C), mineral characterization parameters and environmental parameters in order to explore the source composition, distribution characteristics and influencing factors of organic carbon in the YRE in summer. The results show that the concentration of particulate organic carbon（POC） ranged from 0.33 to 36.95 mg/L, with high values nearshore and low values offshore because of riverine inputs, flocculation sedimentation and resuspension. The mean value of POC% is（1.25±1.40） %, and POC% and δ¹³C_POC are lower in the low-middle salinity area, suggesting the organic carbon is mainly derived from the terrestrial input of the Yellow River. POC% and δ¹³C_POC increased in the high salinity area, because the influence of river runoff weakened and phytoplankton blooms would lead to an increase of marine OC contribution, thus, the distribution of POC was mainly controlled by OC sources. The mean value of sedimentary organic carbon（TOC） content is（0.33±0.21） %, which is close to POC% in the low-middle salinity area. A large amount of particulate matter input from the Yellow River during the period of water-sediment regulation scheme and summer is deposited in the estuary region, which minimized the difference of the properties between sedimentary OC and POC. The spatial distribution of TOC in the estuary is controlled by the particle size effect. TOC% is negatively correlated with mean grain size（MGS）, with decreasing grain size and increasing TOC% along the increase of salinity, indicating that coarser particles with low TOC% are deposited in the nearshore and the particles with high TOC% are transported to the offshore. The three-end member model by using C/N ratio and δ¹³C is applied to quantify the contribution of different OC sources of organic carbon and its distribution. The results show that soil and marine OC were dominant in POC, with contribution of soil OC decreasing from 51% to 19% offshore, and contribution of marine OC increasing from 24% to 68%. The contribution of soil OC accounted for about 40% in sedimentary OC. This study will provide support for further research on the transfer and preservation of OC from different sources in the YRE, which is of great significance for understanding the OC cycles in estuaries.更多还原