Study on numerical simulation of spatiotemporal response of water environment in Pearl River Estuary under influence of human activities

Abstract

[Objective] With the continuous expansion and deepening of development in the Pearl River Estuary and the sustained rapid economic growth, 1.8 to 2 billion tons of industrial and domestic wastewater are discharged into the estuary annually, exacerbating local water pollution. At the same time, shoreline variations during engineering construction have made the process of water quality evolution more complex. The aim is to investigate the spatiotemporal distribution characteristics of typical pollutants in the Pearl River Estuary and their response patterns to shoreline variations during the development processes such as industrial development, engineering construction, and land reclamation from 1990 to 2020. [Methods] A three-dimensional hydrodynamic and water environment coupled model for the Pearl River Estuary was established to simulate the transport and transformation processes and the spatiotemporal distribution of key water quality parameters under shoreline conditions in 1990 and 2020. [Results] The simulation result showed that from 1990 to 2020, under the influence of the narrowing of Lingdingyang Bay, chlorophyll-a concentration decreased in the upper estuary but increased from the central region to the estuary mouth. The land connection project at Gaolan Island impeded water exchange and chlorophyll-a transport between Huangmaohai Sea and the open sea, leading to an increase in chlorophyll-a concentration in the upper Huangmaohai Sea. Additionally, the distribution of suspended sediment and nutrients underwent significant variations due to the alterations in residual flow structures and chlorophyll-a distribution. Compared with the 1990 shoreline condition, under the 2020 shoreline condition, the average concentrations of nitrate and ammonium in the entire estuary during summer decreased by 28.8% and 33.8%, respectively, while the average concentrations of chlorophyll-a, suspended sediment, and silicate increased by 12.6%, 15.5%, and 1.9%, respectively. [Conclusion] During the development of the Pearl River Estuary, shoreline variations have led to increased flow velocities within the estuary while decreasing residual flows at the estuary mouth, thereby altering the spatiotemporal distribution of water quality parameters throughout the estuary, especially near the engineering areas and the estuary mouth.

Keywords

Pearl River Estuary / human activities / water quality / hydrodynamics / numerical simulation