Numerical investigation of the transport and accumulation of conservative pollutants off Changjiang Estuary

The increasing input of terrestrial pollutants is one of the major threats to coastal marine ecosystems. However, the impacts of pollutants discharged off the Changjiang Estuary (CJE) on the coastal waters of Zhejiang Province have not been quantitatively investigated. In this study, we focus on the transport processes of conservative pollutants discharged off the CJE using Eulerian tracers and Lagrangian particles coupled with a reliable 3D hydrodynamic model. The results show significant seasonal variations in pollutant transport and dispersion, which are highly associated with river discharge variation, the East Asian monsoon, and shelf circulations. Approximately 79% and 94% of the released pollutants are transported into the Zhejiang coastal waters in autumn and winter, respectively, which are mainly controlled by the Zhe-Min Coastal Current. We further reveal that, winter pollution covers ∼68% larger area in the Zhejiang coastal region, with ∼40% higher peak concentration value and ∼9 day longer duration compared to autumn pollution. Our study suggests that the water quality in the Zhejiang coastal region is potentially more vulnerable to pollutants discharged off the CJE in autumn and winter than in the other seasons, due to the influence of the coastal currents.