Drivers of Phytoplankton Variability in and Near the Pearl River Estuary, South China Sea During Typhoon Hato (2017): A Numerical Study

Abstract

The Pearl River is the second largest river in China in terms of freshwater discharge, fed by three main tributaries (the West River, the North River, and the East River) and many local rivers. The Pearl River Estuary (PRE) includes three subestuaries, Lingding Bay, Modaomen, and Huangmaohai. About 50%-55% of the freshwater from the Pearl River discharges into the Lingding Bay, which is the focus area of this study. The PRE is located in the central area of the Guangdong-Hong Kong-Marco Greater Bay Area of China. In recent years, with a rapidly growing population and socioeconomic development, input of nutrients and diverse contaminants increased rapidly, which led to a wide range of environmental problems, such as eutrophication, hypoxia,

Impact of typhoons on the ecological environment of the Pearl River Estuary in the summer of 2021—a study of an algal bloom event

“…The northeast current, influenced by the summer southwest monsoon, causes the flow of the PRP toward the northeast of the estuary (Gan et al, 2010), and the passage of typhoons disrupts the flow dynamics, resulting in an amplified impact of the PRP on the western side of the estuary (Supplementary Figure S3). These findings highlight the dominance of the advection process driven by typhoons in the occurrence of algal blooms, which dissipate as the flow field changes (Zhao et al, 2009;Fang et al, 2022;Feng et al, 2022). However, unlike the findings from previous studies, the temporal fluctuations in the Chla and NO3 concentrations appeared nearly synchronous, emphasizing direct Chla transport rather than a process of nutrientinduced phytoplankton growth.…”

“…The RMSE for the Chla differences was 1.22 mg•m -3 , indicating that the simulation of the distribution of the chlorophyll concentrations in the surface layer during this period was satisfactory overall. Moreover, considering the poor observation results available from satellite remote sensing in nearshore turbid waters, the simulation discrepancy is acceptable (Ye et al, 2020;Feng et al, 2022). Based on the model results, the Chla concentrations in the estuary decreased under the influence of Typhoon Lupit, and the Chla concentrations in the algal bloom area that were caused by Typhoon Cempaka also decreased.…”

“…This runoff carries substantial amounts of nutrients, resulting in notable ecological features in the Pearl River estuary (PRE), such as eutrophication, algal blooms, and hypoxia (Harrison et al, 2008;Lai and Yin, 2014;Lu and Gan, 2015). Furthermore, the PRE is frequently impacted by typhoons with an average of about 3 typhoons passing through the PRE each year, which cause changes in the extent of the Pearl River plume (PRP) because of the change of flow field caused by wind field and the increase of Pearl River discharge (Wang and Zhang, 2021;Fang et al, 2022;Feng et al, 2022). These interactions between typhoons and the Pearl River runoff have obvious implications for the marine ecosystem in the region.…”

“…Due to the limitations of the current observation methods (Chang et al, 2008;Feng et al, 2022), the spatial and temporal characterizations of typhoon effects such as algal blooms are subject to certain constraints. Numerous studies have been conducted to investigate the mechanisms of oceanic responses to typhoons, primarily through satellite observations and limited field observations.…”

“…Numerical simulations using biogeochemical models have been an effective method for studying the responses of oceans to typhoons, especially under extreme weather conditions (Pan et al, 2017;Zhang et al, 2021), and it provide continuous time series and large-scale data for comprehensive analysis. These simulations have shown that phytoplankton growth in nearshore areas is influenced by various factors, including mixing and nutrient input (Fang et al, 2022;Feng et al, 2022;Li et al, 2022). In addition, the impacts on upwelling and plumes vary under different typhoon trajectories or intensities (Pan et al, 2012;Chen et al, 2023), and the factors that contribute to coastal algae blooms also differ, such as typhoon wind pumps and transportation of terrestrial material by precipitation, with algal blooms primarily dependent on nutrient supply (Liu et al, 2021;Chen et al, 2023;Lao et al, 2023b, Lao et al, 2023cChen et al, 2024).…”