Exploring water accumulation dynamics in the Pearl River estuary from a Lagrangian perspective

Abstract

Abstract. Investigating water accumulation is essential for understanding estuarine mass distribution and ecosystem management. In this study, we examined the water accumulation dynamics in the Pearl River estuary (PRE) from a Lagrangian perspective. Generally, there is a notable negative correlation between the horizontal velocity divergence (∇h⋅Vh) and the accumulation. Influenced by density fronts and velocity convergence, significant bottom-layer accumulation of particles was observed in the western part of the estuary and the Hong Kong waters during summer, whereas this accumulation moved landward in winter. Subregions with distinct accumulation patterns and interconnections were identified and combined with the trajectories. In summer, the western part of the estuary and the Macau waters exhibit significant net negative ∇h⋅Vh values, and strong density fronts are major accumulation targets, attracting particles from the entire estuary. Conversely, the eastern part of the estuary and Hong Kong waters exhibit significant westward motion, influencing the western side. In winter, particles are more likely to accumulate in their initial locations. The upper part of the estuary becomes a major accumulation area due to the obstructive density front and decreased river discharge. Tidal currents and river discharge mainly control water accumulation in the estuary by changing the mixing or current intensity. The weakening of tidal currents and river discharge induce intensified bottom intrusion and the landward movement of accumulation.