Numerical simulation of tidal-driven particulate dispersion and transport in a Larimichthys crocea enclosure aquaculture zone.

Understanding the dispersion and deposition of particulate waste from marine aquaculture systems is essential for conducting environmental capacity assessments and managing ecological risks. In this study, we focused on a typical large yellow croaker (Larimichthys crocea) enclosure aquaculture zone located in the coastal area of Taohua Island, Zhoushan, China. A coupled MIKE21 hydrodynamic-lagrangian particle tracking model was established to simulate the transport dynamics of two major solid waste sources-uneaten feed and feces-under different tidal conditions. Model simulations revealed that feed particles, due to their lower density and longer suspension time, exhibited enhanced long-distance dispersion, with a maximum transport distance of 22.68 km during spring tides. In contrast, fecal particles settled rapidly, and the deposition zone remained largely confined to the near-field of the enclosure aquaculture zone, with a maximum dispersion distance of 20.9 m at peak flood tide and 34.4 m at peak ebb tide. The interaction between tidal dynamics and complex reef topography formed low-flow areas and eddies, which promoted localized sedimentation. Field measurements of TN and TP in surface sediments showed spatial patterns consistent with model predictions. The results suggest that particle properties, hydrodynamic forces, and topographic features jointly drive the spatial heterogeneity of nutrient deposition. This study provides a quantitative approach for identifying high-risk sedimentation zones and offers a technical reference for ecological zoning and environmental regulation in offshore enclosure aquaculture systems.