Hydrodynamics and water quality impacts of large-scale reclamation projects in the Pearl River Estuary

Abstract

The mechanism that underlies the evolution of the seasonal environment and the effects of reclamation projects in the Pearl River Estuary (PRE) were studied by modeling the hydrodynamics, suspended sediment, and water quality. Due to the seasonal variation of the freshwater discharge, the residual currents in the estuary are generally larger during the summer than during the winter. Reclamation projects significantly affect the residual current fields and decrease tidal prisms across the PRE, resulting in the variation of water exchange and material transport process. During the summer, waters high in chlorophyll-a move downstream, with increased seaward residual currents, and they more widely range from the middle estuary to the estuarine mouth than during the winter; moreover, the chlorophyll-a value peaks in these areas. Reclamation projects significantly promote the expansion of waters high in chlorophyll-a towards the estuarine mouth. The distribution of suspended sediment, nitrate, ammonium, and silicate also obviously varies with altered water exchange and chlorophyll-a distribution. Average chlorophyll-a, suspended sediment, and silicate concentrations in the whole computational domain increase by 12.71%, 15.19%, and 1.91%, respectively, while the growth of algae consumes a large amount of nitrate and ammonium.