## 5 Conclusions  
Green tides have been a cosmopolitan issue in recent decades that deteriorate the ecological environment and have caused tremendous economic loss. In this study, the migration process of a green tide event that happened in August 2021, in Jimmeng Bay, Qinhuangdao, China, was investigated using a particle-tracking model based on a hydrodynamic model. The hydrodynamic model applies three meshes with different refinements and scales for the domains of Bohai, Qinhuangdao, and Jinmeng Bay, respectively, and pro  
Figure 11: Trajectories of green macroalgae under the wind magnitudes of (**a**,**d**,**g**,**j**) 2 m/s, (**b**,**e**,**h**,**k**) 4 m/s, and (**c**,**f**,**i**,**l**) 6 m/s with the wind directions of ENE, ESE, SSE, and SSW, respectively. The areas surrounded by dotted red lines represent the coverage of the green macroalgae trajectories.  
vides the results of currents for the particle-tracking model. The performance of these two models fits well with the field observation data, and thus is reliable for the hydrodynamic modeling and particle-tracking modeling of the green macroalgae in Jinmeng Bay.  
From the hydrodynamic results of the model, it is concluded that amphidromic point M2 near the coastal waters of Jinmeng Bay causes this to be an area with low tidal energy, and the current field in the study area indicates that the semi-enclosed waters surrounded by multiple artificial structures are a low-energy hydrodynamic environment, which is not helpful for water exchange, and thus the dispersion of nutrients. From the results of the spatiotemporal distribution of the green tide, the macroalgae are distributed substantially within the semi-enclosed waters, and few are transported out with low biomass concentration due to the enhanced currents in the channels on the southwest and northeast sides of Hailuo Island. The effect of wind and the existence of artificial structures both increase the coverage of the green macroalgae trajectories, and the effect of wind plays the more important role. It is worth noting that, despite the increased coverage caused by artificial structures, the biomass concentration out of the semi-enclosed waters is very low, and the low-energy area within the semi-enclosed waters provides a favorable environment for nutrient deposition and macroalgae growth. The sensitivity analysis of the effect of wind concluded that the coverage of the green macroalgae trajectories reaches a maximum of 30.73 km\({}^{2}\) under winds of 6 m/s in ENE. Lastly, the expected improvements of the model were discussed, considering the involvement of water quality and growth mechanisms of the green macroalgae. This research can provide useful reference information for the early warning and mitigation measures of green tides in Jinmeng Bay, in addition to other places suffering from green tides.  
Conceptualization, X.H. and C.K.; methodology, X.H. and C.K.; software, X.H., R.Q. and D.W.; validation, X.H., R.Q. and D.W.; investigation, Y.L. and W.S.; data curation, Y.L. and W.S.; writing--original draft preparation, X.H. and C.K.; writing--review and editing, C.K.; supervision, C.K.; funding acquisition, Y.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Key Research and Development Project of China, under contract no. 2019 YFC1407902, and the National Natural Science Foundation of China, under contract no. 41976159.  
Not applicable.  
We are sincerely grateful to the Eighth Geological Brigade of the Hebei Geological Prospecting Bureau for supporting the fieldwork and measured data for the model validation, and three anonymous reviewers who provide constructive comments and suggestions to improve the quality of this manuscript. The authors declare no conflict of interest.