Reservoir Regulation Changed Terrestrial Particulate Organic Carbon Transport and Burial Processes off the Yellow River Mouth

Abstract The dynamic behavior of particulate organic carbon (POC) is crucial for understanding biogeochemical carbon cycling in coastal and oceanic environments. However, intense watershed human activities have significantly altered the POC transport and burial in the estuary‐coast continuum. Here, we developed a novel parameterization scheme that incorporates grain‐size constraints to investigate the dispersal and accumulation processes of POC off the Yellow River mouth during the water‐sediment regulation scheme (WSRS) using a three‐dimensional hydrodynamic model (FVCOM). The result shows that the model successfully captures the offshore transport and hydrodynamic sorting of POC, which leads to a progressive increase in POC content with offshore dispersion and significant variations in POC and sediment deposition across different isobaths. Rapid fluctuations in river discharge and sediment composition during WSRS stages result in noticeable differences in sedimentation patterns for sediment and POC. At the Water‐regulation stage, distinct differences are observed in the distribution of riverine POC and sediment across various isobaths. In contrast, during the Sediment‐regulation stage, these differences are significantly reduced due to the finer riverine sediment. Compared to the sediment‐regulation, the Water‐regulation plays a crucial role in enhancing the effective burial of POC. Coarse‐grained sediment can form an armored layer that protects OC from disturbance. Additionally, increased runoff during this stage promotes the offshore transport of POC to a less energetic environment (>10 m in depth). This study provides valuable insights into POC dynamics in high‐turbidity estuarine and coastal environments. It underscores the importance of employing comprehensive modeling approaches to elucidate these complex processes.